Air Conditioning Laboratory

Project 99.10

Design Team Members:

Sean Gallagher Prathana Vannarath 260 Elkton Rd, Apt D-9 211-8 Thorne Lane Newark, DE 19711 Newark, DE 19711 (302) 369-2820 (302) 738-8765 seangall@udel.edu 91719@udel.edu

Brian Davison Pamela McDowell 64 Willow Creek Lane 135 E Cleveland Ave

Newark, DE 19711 Newark, DE 19711 (302) 239-1340 (302) 366-7473

davison@me.udel.edu pamela@udel.edu

Sponsors:Dr. Tony Wexler226 Spencer Lab

Mechanical Engineering DepartmentUniversity of Delaware

Newark, DE 19716(302) 831-8743

wexler@me.udel.edu

Dr. Suresh Advani205 Spencer Lab

Mechanical Engineering DepartmentUniversity of Delaware

Newark, DE 19716(302) 831-8975

advani@me.udel.edu

Executive Summary:

The University of Delaware, Department of Mechanical Engineering, is

drastically changing the curriculum for the class of 2000 in order to keep up with ABET

standards. As a result, a new joint Thermodynamics and Heat Transfer laboratory has

been created. Our mission is to design a set of experiments for this joint lab class. These

experiments are to be based on an air conditioning cycle.

After interviewing our customers to identify their wants, we made use of the SSD

process to weight them. System benchmarking was used to identify our major

competitors, and again SSD helped us compare them to a window air conditioner. None

of the alternatives had nearly as many as the window air conditioner. Functional

benchmarking was used to investigate specific types of window air conditioners and

sensors.

This project consists of two integrated parts, the lab apparatus and the lab

experiments. When analyzing our project, we first considered the lab apparatus. As

mentioned above, we decided that a window air conditioner was the best apparatus. From

here, we generated concepts about the actual written experiments. Through evaluating

our metrics, we decided on a set of labs that will have between four and seven

experiments, each examining a component of the air conditioning unit. The students will

be asked to write a short report following each lab, and after every experiment has been

completed, a technical paper will be written bringing together all the concepts learned.

Sensors were then chosen based on the needs of each experiment, and on our metrics.

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After fabrication of the apparatus was completed and lab experiments were

written, we began the testing phase. From the results of the testing, we made

modifications and repeated the testing. Upon comparing our results with our wants and

metrics, we concluded that we had successfully completed the project.

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Table of Contents:

Executive Summary…………………………………………………..3

Table of Contents……………………………………………………..4

Introduction…………………………………………………………...5

Background……………………………………………………5

Customers…………………………………………………….6

Wants…………………………………………………………7

Constraints……………………………………………………8

Metrics & Target Values……………………………………..8

Concept Generation………………………………………………….12

System Benchmarking……………………………………….13

Functional Benchmarking……………………………………15

Lab Experiment Benchmarking……………………………...17

Concept Generation………………………………………….18

Concept Selection……………………………………………………24

Fabrication…………………………………………………………...26

Assembly…………………………………………………………….31

Testing/Re-Design…………………………………………………...34

Hardware…………………………………………………….34

Labs………………………………………………………….37

Suggested Modifications…………………………………………….39

Conclusion…………………………………………………………..41

Appendix

A – file – Appendix A_Team10.xls………………………….43B – file – Appendix B_Team10.xls………………………….43C – file – Appendix C_Team10.xls……….…………………43D…………………………………………...………………...44E……………………………………………………………...45F……………………………………………………………...47G……………………………………..………………………69

H……………………………………………………………..77J – file – Team10.vi………………….………………………80K – file – Appendix K_Team10.xls…………………………81

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Introduction:

Background:

The University of Delaware, Department of Mechanical Engineering, is

drastically changing the curriculum for the class of 2000 in order to keep up with ABET

standards. Part of this new curriculum includes a joint laboratory class; this lab is for

Thermodynamics and Heat Transfer. The professors of these courses, Dr. Wexler and Dr.

Advani, have proposed a project to the New Castle Design Associates to design a set of

experiments for this joint lab. The problem is to design a set of thermodynamic and heat

transfer experiments using a window air conditioner unit for the Undergraduate

Laboratory. Experiments will be based on lessons designed by our senior design group.

Our mission is to design a set of thermodynamic and heat transfer experiments for

the University of Delaware, Mechanical Engineering Undergraduate Laboratory, using an

apparatus that will be completed by April 1999 for no more than four thousand dollars.

In evaluating our concepts, we compared them in terms of their correlation to the

wants and constraints set forth by our customers. In order to determine how exactly the

concepts correspond to the wants we used metrics and target values derived from

benchmarking.

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Customers:

Our customer list encompasses our sponsors as well as experts in the fields of

HVAC, education, and scholarly work. Our customers are as follows:

1. Dr. Wexler, Professor

1. Dr. Advani, Professor

2. Undergraduate students

3. Graduate student TA’s

4. Judy Greene, Educational Expert

5. Dr. Sun, Professor, Lab Expert

6. William Davison, HVAC Engineer

7. Manufacturers: Hampden, Armfield Ltd.

8. Other schools (Georgia Institute of Technology, Pennsylvania State

University)

The list can be seen on our SSD chart, which is attached in Appendix A. The list is

ranked by order of importance, which is set by the team. We determined that Dr. Wexler

and Dr. Advani were of the utmost importance as sponsors. The project is not only their

idea, but they are jointly funding it. Undergraduate students are directly effected by each

and every aspect of our project. The primary purpose of any laboratory experiment is to

effectively teach ideas in a hands-on manner. The graduate students are also directly

effected in that they will be actively in charge of the hands-on learning process. Judy

Greene, an educational expert, helped us evaluate the level of effectiveness of our

laboratory experiments. Dr. Sun is an expert in the field of laboratory experiments,

perhaps one day he will use our experiments and our apparatus to teach his classes.

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William Davison is an expert in determining which hardware will function effectively

under our given conditions. Manufacturers and other schools help in benchmarking, and

are of concern in the case that our apparatus be manufactured for more widespread use.

Wants:

Our list of wants encompasses the top eleven most important wants set forth by

our customers. It is as follows:

1. Educational Effectiveness

1. Portable

2. Easy to use

3. Self Evident

4. Easy to Set-Up

5. Cost Effectiveness

6. Multiple Purposes

7. LabVIEW Compatible Data Acquisition

8. Forgiving of Incompetence

9. Quiet

10. Quick

These wants appear in their order of importance according to our SpreadSheet Design

Chart, in Appendix A. This ranking comes about from assigning values to the wants

according to their location on the customer list, and then weighting those numbers by

multiplying them by the inverse of customer rank. For example, if Mr. Davison’s first

want is cost effectiveness, then cost effectiveness is assigned a value of .45 because it

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appears in the first column and then it gets multiplied by 1/6 because he has a rank of 6th

on our list of customers.

Constraints:

The constraints for this project include a number of issues. The most important is

the size. It must be small enough to be portable because it may be moved often. Also, we

are on a strict schedule which states that this project be finished by April 1999, and the

format of our presentations and written reports are given, which is all dictated by New

Castle Design Associates. Lastly, our budget is four thousand dollars (see Appendix C).

Our mission is to be fulfilled in such a way as to include as many customer wants

and constraints as possible. We are going to measure whether we have satisfied this by

using metrics and set target values.

Metrics & Target Values:

Although our project integrates two parts, lab experiments and the hardware,

some of the wants pertain to the experiments and some to the lab apparatus. Considering

the aspect of our lab experiments, each needs to be a self-evident, easy to use, effective

learning tool. The most important benefit is that the undergraduate students here at the

University of Delaware will learn about heat transfer and thermodynamics and the

realities of measured versus theoretical quantities.

To measure how well we have achieved each want, we will use metrics and the

target values associated with them. As described previously, our wants are prioritized by

their relative importance. Each want has at least one metric associated with it, and some

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have multiple metrics. As for priority among the metrics, we used the association of the

want as a determining factor. For example, if the want is ranked number one the metric

corresponding with it is also ranked number one. If a want has multiple metrics, then we

considered each to have the same rank. For instance, if the number two want has three

metrics, then all three metrics have a rank of two. To see an all–encompassing table of

prioritized wants, metrics and target values, see Appendix B. Below we discuss each

metric according to whether it pertains to the lab experiments or the hardware.

Several of the wants correspond to the lab experiments; they are educational

effectiveness, self evident, and quick. Educational effectiveness is going to be measured

by the evaluation chart found in Appendix C, for now, but ultimately by survey during

the testing. Whether it is self-evident is going to be determined by survey. The questions

on the survey are the basis for Appendix C. At this point in time, Judy Greene has

evaluated our lab experiments and commented on them. She used her expertise based on

her professional experience to perform the evaluation. When the apparatus is complete,

we will persuade some undergraduates to perform the experiments and fill out surveys,

commenting on how clear the lessons and objectives are and if the procedure is in a

logical order. These surveys will have rankings on them from one to five, with five being

the best. We have a target value of 4 because we want it to be self evident to everyone,

but we realize that nothing will please everyone. For now we have evaluated these things

based on our own experience, as we consider ourselves as experts in the field of

laboratories for undergraduate students. Lastly, we want the experiments to be quick.

From our personal experiences, those of other undergraduates, those of present teaching

assistants, and those of Dr. Advani and Dr. Wexler: if the lab is too long very little is

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retained. We are going to measure this with time. We have a constraint of two hours,

which is the scheduled amount of time for the laboratory. However, we are aiming for no

longer than an hour because based on our experience and under the advisement of Judy

Greene, students attention deteriorates rapidly at this point.

The rest of the wants pertain to the hardware aspect of the project. The most

important according to our SSD chart, as described above, is that it be portable. We are

going to measure this by size. The apparatus should fit on a cart that has wheels and is

able to pass through a regular doorway, so we have set our target values to be 36 inches

in width and 60 inches in height. We are also going to measure this by weight; we have

designated 100lbs to be the target value in order to ensure that any one could push the

cart.

The next want is easy to use. We are going to measure this by physically looking

at the apparatus and determining whether the components are visible and how accessible

they are. By accessible, we mean that the students should be able to touch all the parts,

not take them apart. In other words, we want to not only see the components in the

apparatus, but we want to be able to touch them. We could physically count all the visible

parts and the number of touchable parts; however, each apparatus may have a different

number of parts so these numbers may not be comparable. Instead, as we consider each

apparatus, we will visually examine them and determine whether the components are in

fact visible and touchable. Each will receive either a ‘yes’, if they are, or a ‘no’, if they

are not, for each category, visible components and accessible components. Our target

value is of course yes, because we want everyone to be able to use the apparatus.

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We also want the apparatus to be easy to set up. Time is the key method to

measure this; we have a target value of 15 minutes, as this is the amount of time between

classes and the TA should not need more time than this to set up the lab. We are also

going to measure this by the number of separate parts. The idea is to be able to get the

entire apparatus onto one moveable cart, because this would greatly minimize the time it

would require to set up therefore increasing the ease of setting up the apparatus. Either it

fits onto one cart or it does not. Our target value for this is that it does.

The next want regarding the hardware is cost effectiveness. The apparatus should

have a low initial cost, a low operating cost, be long lasting, and the parts should be

easily available from a store or catalogue. Our target value for a low initial cost is the

$4000 budget that we were given. For low operating cost we are aiming for $22, this

comes from estimating that the apparatus runs for 12 hours a day, 5 days a week, for four

weeks at a rate of 9 cents per kilowatt /hour (This is the rate charges by the City of

Newark). For long lasting, we are targeting 10 years because of changes in technology

and EPA standards. Currently R-22, the refrigerant in the window air conditioner, is

banned from use in car air conditioners and central ac units in homes because of the

environmental effects. Right now it is still being used for window air conditioners

because of cost considerations, but in a few years it may be illegal to use R-22.

Another want is that the apparatus have multiple purposes. It must contain both

thermodynamic and heat transfer principles. This is a yes or no question asked of every

concept. Our target value is going to be yes because this is a lab for both heat transfer and

thermodynamics so both topics should be included.

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This system should also have a LabVIEW compatible data acquisition system so

that the existing acquisition board can be used to read the data. This is either present or it

is not. Our target value is present. We are investigating other software packages besides

LabVIEW; however, LabVIEW is what the ME department currently uses and would be

the most convenient. LabVIEW satisfies all metrics associated with the acquisition

program required, as it is compatible with itself and it is free.

The apparatus should also be forgiving of incompetence. What this means is that

the apparatus should give relatively good data even if the operator makes a few mistakes.

This will be measured by physically trying the limits of the apparatus when it is finally

assembled, but for now we are taking this into consideration when purchasing parts. We

are consulting our customers, such as Dr. Sun, Dr. Advani, Dr. Wexler (who has written a

book on sensors and can be considered an expert in this area) and other manufactures of

sensors, such as Omega and Optrand. When we are able to test the apparatus, we will

compare the data collected, and we have set a target value of 10%. By this, we mean that

as long as the error in the data is less than 10%, it is acceptable.

Lastly, we want the apparatus to be quiet. This will be measured by a target value

we have set at 60 decibels, which is a conversation level of noise. OSHA laws are not

important here, the noise level limitation is for the convenience of the users.

Concept Generation:

Although the project consists of two integrated parts, the hardware and the lab

experiments were benchmarked separately. The following sections, system and

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functional benchmarking, pertain to the hardware, and the benchmarking for the lab

experiments follows below that.

System Benchmarking:

System level benchmarking began with a search for existing thermodynamics and

heat transfer labs. We started by looking at what is being offered and what has been

offered previously here at the University of Delaware. We found that the MEEG 391,

Engineering Science Lab, taught by Dr. Sun, was the closest match, but none of the

apparatuses displayed the Heat Transfer and Thermodynamics principles we had in mind.

Investigations into various other universities’ engineering departments revealed

information of little use. The same result applies to research into HVAC programs in

technical schools. Through inquiries to professors and searches on the Internet,

manufacturers in this area were found to be Armfield Limited and Hampden Engineering

Corporation. Dr. Prasad provided some literature on both the Armfield and Hampden

labs. A further check into the companies’ respective Internet pages provided updated

information on the old labs and listings of new laboratory offerings.

Armfield Limited offers a large selection of engineering teaching research

equipment. The laboratory equipment most applicable to this project can be found in

Armfield’s Heat Transfer line of laboratory equipment. Of primary interest is the HT10X

line of heat transfer teaching equipment. This line is comprised of single bench top

Service Unit, and seven individual laboratory accessories, each illustrating a single heat

transfer fundamental. Each of the individual laboratory setups can be purchased with a

Data Logging Accessory package. Additionally, in Armfield’s Fluid Mechanics line, the

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FM23 Plunger Pump Demonstration Unit can be used to partially simulate the

compressor found within an air conditioning unit. The air conditioning unit compressor

is typically a piston type compressor and the FM23 uses a positive displacement pump.

However, this is not a true match. This can also be said for the rest of Armfield labs.

Some of Armfield’s products display heat transfer and thermodynamic principles, but

none of them do everything a window air conditioner can do.

Hampden differs from Armfield by offering laboratory equipment related to

specific industry equipment such as cooling towers, heat exchangers, heat pumps, and

refrigeration cycles. Of interest is Hampden’s H-ACD-2 Basic refrigeration Cycle

Trainer. According to Hampden’s product literature, this equipment “has been designed

to demonstrate the principles of … R-134 a refrigeration system … including heating,

cooling, humidification, de-humidification, recirculation, and mixing.” The inclusion of

humidification, de-humidification, recirculation, and mixing is beyond the original scope

of our project, as this equipment is more oriented to larger, building HVAC systems

rather than the small, window unit style air conditioning unit we are interested in. This is

also evident in the size of the H-ACD-2. The unit measures 88” x 70” and 31” deep.

Total weight for the unit is 1170 lbs. The H-ACD-2 requires 208V, three phase power

and a water supply. Hampden offers an option data logging package including 13 type-T

thermocouples, a single air velocity meter, three pressure transducers, two differential

pressure transducers, and two wattmeters.

Hampden also manufactures a Refrigeration Cycle Trainer, H-RST-2, that covers

the complete refrigeration cycle. This does not take the form of a recognizable piece of

machinery. All of the equipment, such as the coils, are specially fabricated for this lab

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apparatus and are not industry standard equipment. The unit is also similar in size and

weight as the H-ACD-2. There remains a number of Hampden labs such as the H-RST-

3B Basic Refrigeration Cycle and Heat Pump Trainer, the H-6710-CDL Refrigeration

Demonstrator, and the H-6830 Heat Pump Trainer that each satisfy a few of our

requirements, but are inferior to the H-RST-2 and H-ACD-2 as a competitor.

Overall, we did not learn very much from the system benchmarking. What we did

learn was that the window air conditioner appears to be our best choice.

Functional Benchmarking:

For functional level benchmarking, we researched the major manufacturers of

laboratory equipment and scientific sensors. Omega Engineering, Incorporated was

found to supply an extensive line of sensors. Additionally, their catalogs and web site

offered plenty of technical information about each sensor. The sensors in Omega’s

product line that we were interested in included thermocouples, pressure transducers, a

mass flow sensor, and a relative humidity sensor. This was beneficial as a source to help

determine specific types of sensors need for the purpose of this project.

In terms of thermocouples, we found that type K are the best choice for our needs,

the type K range from –100 oC to 400 0C. As for the other sensors we are investigating,

all of them have outputs of volts, so they will not require modules to convert their signals.

Pressure sensors come in a wide variety with fairly large ranges, so we will not have any

problems choosing one that will be compatible with the air conditioner. The air

conditioner, while off has a pressure of approximately 150psi, and while operating at full

capacity, a low pressure of about 75psi and a high of about 250psi. Considering this, we

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are investigating pressure sensors that have a range of 0 to 500psi. Relative humidity

sensors are fairly standard. They all measure 0% to 100% relative humidity. These

sensors also determine the temperature of the air, but the velocity will have to be

determined with a separate sensor. The mass flow sensors are very delicate. It is difficult

to find ones that are compatible with refrigerant. Therefore, the engineering department

of Omega is guiding us. We trust their advisement because if it doesn’t work, they’ll

replace it.

Another company, Optrand, produces fiber-optic pressure transducers. This

provides an alternative method of pressure measurements for the lab as well as allowing a

thorough study of a compressor. Optrand’s AutoPSI-TC Dynamic Pressure Sensor would

allow continuous measurements of the pressure inside the compressor. This is a new

discovery and its feasibility for this particular lab will be further evaluated.

Window air conditioner manufacturers were also researched. A large number of

air conditioners in the range of products we are interested in were found in Carrier’s

room Air Conditioners series, Airtemp’s Room Air Conditioner series, and Port-a-Cool’s

product line to name just a few. The University of Delaware’s HVAC department

donated an older air conditioning system. Unfortunately, this system uses R-22 for a

refrigerant. We desire a newer system with an environmentally safe refrigerant. It does

not do any good for the students to study a system using an obsolete refrigerant. Our

customer, Dr. Wexler, agrees with the importance of using an environmentally safe

refrigerant for the lab. This air conditioner did, however, provide an excellent

opportunity to study the air conditioning system hardware in order to get a better picture

of what the eventual lab setup will require.

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The LabVIEW software and data acquisition board and computer are already

available in the department. Therefore, the selection and purchasing of the data

acquisition card and the software does not need to be considered. The number of

channels and type of inputs that the board can handle has been determined to aid in the

selection of the individual sensors.

Finally, the actual mounting of the sensors needs to be determined. The fittings

required in mating the sensors to the air conditioning unit refrigerant lines and coils is

dependent on the sensor and its location on the air conditioner. Various tee fittings can

be purchased with the required thread to match any threaded sensor and thermowells can

be used for temperature measurements. The tee fittings can be soldered to the refrigerant

lines, but the sensors should be removable for replacement or maintenance. The wiring

and wire connectors required will also be determined later by sensor type and location.

Lab Experiments Benchmarking:

Benchmarking of thermodynamics and heat transfer labs from other schools

turned out to be not that beneficial. Of all the schools we researched, none of them use a

window air conditioner as a lab apparatus. The most helpful site was that of Michigan

State. We got ideas for lab experiment styles and how to prove specific principles from

labs with similar heat transfer and thermodynamic principles.

The educational benchmarking we did was primarily through Judy Greene, an

educational expert. As a way of measuring the teaching effectiveness of our labs, she

recommended we evaluate the lab apparatus and lab reports. She provided us with

pamphlets on teaching techniques and writing clear lesson plans. The pamphlets she

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provided were “Evaluate Your Instructional Effectiveness”, ”Develop a Unit of

Instruction”, and “Establish Student Performance Criteria”; we used these to help write

the lab manual. She said we would have to evaluate the manual and apparatus for

teaching effectiveness with actual students, and the best way to do this would be to

conduct a survey and make modifications. We also researched a couple of web sites and

books concerning educational effectiveness, however they were not nearly as beneficial

as Judy Greene.

Concept Generation:

As previously stated, our project consists of two parts that must be integrated.

One aspect is to design the experiments, and the other is to investigate the hardware

needed to execute the experiments.

The lab experiments section can also be examined in three different ways. The

first being the number of experiments performed during the semester, the second being

the basis of the experiments, either by component or by heat transfer/thermodynamic

principle, and the third being the way in which the students write their lab reports. The

three wants mentioned above for lab experiment concepts are educational effectiveness,

self evident, and quick. The key method used to evaluate these concepts is through

metrics for educational effectiveness.

For number of experiments preformed during the semester, there are three

possible concepts. The first is to do one experiment repeatedly, the only change being

that different sensors will be used each time. For instance, we may only be able to

evaluate conservation of energy in our apparatus. Conservation would be measured

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repeatedly, every week, using a different type of sensor each week. This rated very

poorly with undergraduates, graduate students, and professors. It rated poorly in terms of

educational effectiveness because it would be monotonous since the objectives will be the

same every time. Talking with Dr. Greene revealed that as a result, this monotony will

cause the students to lose interest. It rated poorly in terms of the number of concepts

covered because only a small number of objectives can be achieved, so this set of lab

experiments will only cover the principles present. Although, seeing the different answers

from different sensors can be an effective learning tool, it is not in our case because the

main point demonstrated is experimental error, and these students, being in their third

year and having performed numerous labs before, already know what experimental error

is.

The second possibility for number of experiments performed during the semester

is to do four to seven laboratory experiments. Each experiment would differ in that they

would present different fundamentals. This set of experiments would generate more

interest because the experiments would vary from lab to lab.

The last possibility is to do 13 experiments. This comes down to one lab per

week. Within the apparatus there are a limited number of fundamentals. In order to

stretch the fundamentals over 13 labs, the experiments would be short. From our own

personal experience, we thought that this would not keep the students interest because the

labs would seem pointless.

When considering the basis of experiments, as mentioned above, we considered

two options. One is to divide the experiments by fundamentals. Here each lab would deal

with a different thermodynamic or heat transfer principle. For example, if the topic is

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convection, the students would analyze the apparatus everywhere convection is taking

place. The overview of how this set of experiments would flow is as follows:

I Conservation of Energy

II Convection

III Conduction

IV Psychometric Chart

V Thermodynamic Diagrams (T-s & P-v)

VI Cross Flow Heat Exchanger

VII Overall Efficiency

This concept contains the fundamentals covered in the classes. With each topic, there

would be numerous components and data to analyze.

The other way to divide the experiments is by component within the apparatus.

Each lab would deal with a specific part, analyzing every thermodynamic and heat

transfer aspects. For example, if the part is a throttle, the students would measure

temperature and pressure and show that enthalpy remains constant throughout. Also, the

fluid is going through a phase change as it passes through the throttle, so another

objective would be to find the quality of the fluid. Another objective would be to

determine whether the engineering assumption of approximating the fluid as saturated is

appropriate. The overview of how this set of experiments would flow is as follows:

I Heat Exchanger

- Heat Transfer

- Efficiency

II Compressor

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- Conservation of Energy

III Throttle

- Constant Enthalpy

- Quality

IV Overall Efficiency

- Coefficient of Performance

This category contains the fundamentals covered in the class. The student is able to see

what is going on with each component in every aspect.

In the third examination of the lab experiments, we looked at the way in which the

students write their lab reports. Two options were examined. One is to write standard lab

reports after each experiment. By standard we mean they would have all the section

including an objective, a procedure, a list of equipment, a theory, a background, results,

data analysis, and a conclusion. These reports are typically 5-8 pages. The students

would be writing a thorough report on the experiment.

The other option is to write short weekly lab reports; then, in the end, write a

technical paper on how the apparatus works. The short weekly lab reports would consist

of a short background, results, data analysis, and a conclusion. The technical paper would

tie all the labs together and the student would have to support all their conclusions with

data that they collected from the labs. One constraint that goes along with this concept is

time. The students would need time to write the technical paper after all the labs had been

completed and all the short lab reports were written. Our target value is to allow the

students four weeks to write the technical paper. The technical paper allows the student

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to physically understand what is happening inside the apparatus, which gives a complete

real world connection.

The hardware section can be examined in two ways: apparatus and sensors.

Through conversations with our sponsors, Dr. Wexler and Dr. Advani, as well as a

thorough evaluation of our metrics, (see Appendix C) the window air conditioner was

selected as the lab apparatus. Most importantly, a window air conditioner is a real world

machine that students have seen. This is a point of major concern to our sponsors. The

cost of creating a special built apparatus will be well over the cost of purchasing a

commercially available air conditioning unit. Finally, the time constraint imposed on us

by the senior design process prevent the thorough design of a specialized apparatus in

conjunction with the thorough development of the educational values and laboratory

procedures. Therefore, the option of creating our own lab apparatus is not feasible. The

air conditioner chosen should use the newer, environmentally friendly refrigerant. The

older refrigerants are obsolete, so there is no reason to have the students studying an

already obsolete system.

Purchasing and instrumenting a window air conditioner is also superior to

purchasing a commercially available lab apparatus from our competitors. Again, through

discussion with our sponsors and a thorough evaluation of the wants that appear on the

evaluation chart, found in Appendix C, the window air conditioner is found to be superior

to any commercially available lab apparatus.

The sensor package requirements are partially determined by the lab experiments.

The number of sensors required is determined by the data required to complete the labs.

Eliminating overlapping or redundant sensors can optimize the cost of the sensor

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package. The specific sensor concepts related to each individual lab concept can be

summarized as follows; instrumented with redundancy, fully instrumented, and

economically instrumented.

In the case of the fully instrumented with redundancy, there are redundant sensors

for the measurements required, allowing the comparison for different types of sensors.

This concept requires the largest and most expensive sensor package. The second case,

fully instrumented without redundancy, allows the complete measurement of all points in

the air conditioning unit required to complete the labs without the redundancy in the

previous case. This does not require a sensor package as large as in the previous case;

therefore, it is not as expensive. The trade off is the redundancy factor, which is not a

want; therefore, it is not nearly as important according to our wants as cost effectiveness.

The last option is to economically instrument the air conditioner. In this case, we would

cut the number of sensors to a bare minimum, including just enough to demonstrate a few

heat transfer and thermodynamic principles. This would limit the capability of the air

conditioner to perform all the requirements necessary to satisfy the want of educational

effectiveness. The number of principles will not score well enough on our survey to meet

the target value of four. This sensor package is the smallest and least expensive of all the

cases, but it trades educational effectiveness for cost effectiveness.

Concept Selection:

In order to propose a complete solution, we need to choose a sensor package, the

number of experiments to be preformed during the semester, the basis of the experiments,

and the way that the students will write their lab reports. We have already justified using

23

a window air conditioner for the lab apparatus. To completely analyze all of our choices

as they compare to our wants, we have created a table that correlate all of our wants with

our metrics for each possibility. The metrics are answered with a ‘yes’ or ‘no’, either the

metric is met or it is not. This table can be found in Appendix C, the evaluation chart.

Once the table is filled out, the percentage of ‘yes’s’ is multiplied by that particular

want’s Rate of Importance, determined by the SSD process, Appendix A. Each

competing option with the highest number in the end is our best choice. When this is

complete, we will have a complete solution.

Upon detailed and careful observation of our metrics on the evaluation chart, we

will compare the three cases possible for the number of experiments preformed during

the semester. Educational effectiveness is the key want as mentioned above. The second

case, four to seven experiments, keeps the students interest better than the other two

concepts because it has variety and is complex enough to hold their attention. The first

case, one experiment, is too monotonous. It lacks a number of fundamentals and doesn’t

keep the students interest. The last case, 13 experiments, is too simple. It doesn’t keep the

students interests either because the labs will be too short for the objective to seem clear,

as the students would have to come several times to collect the necessary data to perform

the analysis. Case two, four to seven experiments, contains more fundamentals than case

one, and integrates the fundamentals better than case three. It is apparent using our

metrics as they apply to our choices that four to seven labs is the best option for

educational effectiveness.

Comparing the two ways to base the experiments, by component or by principle,

using educational effectiveness, we see that the basis of component has more real world

24

connections because they are analyzing components. These are things that the students

can understand and relate to. The basis of heat transfer/thermodynamic principle

analyzes the apparatus by topic; however this does not make real world connections to

the students because they are not grasping how each individual component works. The

students are only studying fundamentals, and not how they relate to the real world.

Knowing that a real world connection is a metric for educational effectiveness, this

comparison leads us to the conclusion that basing the experiments on components is the

better choice.

Evaluating the choices for the way the students could write their lab reports, leads

us to choose the short lab reports followed by a technical paper. By examining Appendix

C, it is apparent that this option scored twice as well as the option to write standard

weekly reports. The technical paper brings all the fundamentals from the experiments

together, forces the students to prove the heat transfer and thermodynamic principles

through theory and experimental data, and goes that extra distance to make the real world

connection.

Regarding the sensors, the fully instrumented without redundancy was selected.

While the fully instrumented with redundancy is more detailed, the additional cost of the

sensors prevents its use. The economically instrumented package was not selected due to

its hindering effect on the educational effectiveness of our labs. We have estimated the

numbers of sensors needed to run our best lab experiments based on components. The

specifics are outlined in our Drawing Package, Appendix G. The properties of the sensor

are detailed in the fabrication section, as they depend on the specific operation conditions

of the chosen window air conditioner.

25

From the above analysis, it is obvious that our current complete solution is to use

a window air conditioner as the apparatus. Approximately four experiments will be

written, each in reference to a specific component within the air conditioner. The lab

reports will be short and followed by a technical paper, which will summarize the

complete function of a window air conditioner, using experimental data to support all

statements and analyses.

Fabrication:

Top Cover:

The original air conditioner cover needed to be removed to make the internal

components visible during lab. The removal of this cover also exposed the main

electrical wiring for the control panel and the easily damaged styrofoam ducts. Finally,

the original top cover provided the structural restraint for the cooling coil and fan. A new

cover needed to be fabricated that would protect the foam and wiring, retain the original

structural integrity, and keep the major components visible and accessible. A new top

cover was designed and galvanized steel selected for its durability and ease of fabrication.

(See Figure 1, Appendix G)

Fabrication of the top cover began with the initial laying out of the pattern onto a

sheet of galvanized steel. Next, 0.125” diameter holes were drilled at all internal

corners. These holes provided a point to cut to as well as allowed clean bends to the

corners. The pattern was then sheared from the sheet with a jump shear and finished

with aviation snips. All bends were made on a brake. The cover is installed with self-

26

tapping sheet metal screws, therefore no mounting holes are provided. The cover was

left unfinished, bare galvanized steel.

Safety Guards:

Three Safety Guards are required for the apparatus. (See Figures 2, 6, & 5, in

Appendix G) The air conditioner uses two fans, which were exposed by the removal of

the original cover. A guard must be placed over the opening between these fans to

prevent injury due to the exposed fan blades. Additionally, the fragile coil fins were

exposed with the removal of the original cover. These fins need to be protected from

damage. The fins are also sharp and therefore cannot be left exposed. A galvanized

steel frame with galvanized steel screen was selected for ease of fabrication and

availability. The screen is ¼” mesh to provide sufficient protection and maintain

visibility of the protected components.

The first step in fabricating the guards was the laying out of the frame onto the

sheet steel. The steel guards were cut on a shear and bent on a brake. The screen was

cut with aviation snips. The frame was installed on the screen using 1/8” pop rivets.

The guards were finished with black wrinkle-finish paint. The guards are installed with

self-tapping sheet metal screws, therefore no mounting holes are provided. Heavier gage

steel is recommended for future guards. The heavier steel would allow for cleaner bends

and a stronger guard.

27

Thermocouple and Pressure Transducer Connector Panels:

One of the wants for the lab apparatus was portability. To increase the ease in

which the apparatus can be connected to the computer and to clean up the wiring, panels

were created to mount connectors for all of the thermocouples and pressure transducers.

Two panels were designed, one for thermocouples and one for the pressure transducers.

Each panel is similar in design, varying only through the dimensions of the connector

holes. Two separate panels were selected rather than a single panel to accommodate

future changes or upgrades in either the thermocouples or pressure transducers. (See

Figure 4 in Appendix 4)

The panels were cut from .080” aluminum sheet on a band saw. 0.125” holes

were drilled at all internal corners before cutting. The connector mounting holes were

fabricated by drilling holes for each corner then cutting and filing the rectangular hole.

For future production, the purchase and use of a square or rectangular punch would

dramatically decrease the time required for fabrication as well as result in a much cleaner

and accurate panel. All holes were drilled on a drill press after laying out the hole

locations with a prick punch and center punch. The additional accuracy of the milling

machine was deemed unnecessary for these panels and the drill press was chosen for

speed. After all holes were made, the panels were bent on a brake. The guards are

installed with self-tapping sheet metal screws, therefore no mounting holes are provided.

RH Sensor Hangers:

To minimize the expense of the sensor package, one RH sensor will be used to

measure three points of interest. This will require a quick and convenient method of

28

mounting the RH sensor in each of these locations. ¾” PVC clips were used for the RH

mounts. The clips are mounted to the air conditioner with angle brackets. The front and

middle brackets are mounted with self-tapping sheet metal screws while the rear is

mounted to a plastic shroud with double sided automotive trim tape. The clips are

installed on the bracket using two 6-32 machine screws. Therefore, the only holes to be

drilled are for the machine screws. The angle brackets were fabricated from .080”

aluminum sheet. The brackets were cut on a shear, the holes drilled on a drill press, and

the bend made in a vice. (See Figure 7, in Appendix G)

Pressure sensors:

The pressure sensors mount with a 1/8”NPT male connections. Bullet piercing

valves were used to tap the pressure transducers to the refrigerant lines for two important

reasons. First, using the piercing valves eliminates the need to cut the lines and sweat in

fittings. Secondly, in the event of a pressure transducer failure or the need to change

transducers, the valve can be shut off and the transducer removed without the need for

evacuating the system of refrigerant. The valves use a ¼” male flare fitting. A

1/8”NPT to flare adapter was used in conjunction with a swivel nut flare fitting to mate

the parts properly. The swivel nut flare adapter was used to allow rotation of the

transducer with relation to the valve in order to guarantee proper alignment before

tightening the seal. The No. 1 pressure transducer location required a clearance cut in the

air conditioner chassis. This cut can be made properly with a die grinder. (See Figure 3,

Appendix G)

29

Wiring of the transducers was done after installation. The transducers share a

power source with the relative humidity sensor. All of the transducers’ power and ground

leads are tied into a single two-pin connector on the pressure transducer connector panel.

A power lead was made with a mating two-pin connector. The outputs of each of the

pressure transducers are connected to two-pin connectors, even though the output only

uses a single wire. Some pressure transducers and transmitters use a two-wire output.

Using a two-pin connector allows the future modification to a different style of pressure

transducer without changing the connector arrangement.

Mass flow sensors:

The mass flow sensor is supplied with two compression fittings. The sensor is

heavy enough to require support other than a simple hanging from the copper lines. The

bottom of the sensor has two tapped holes for 4-40 machine screws. The top cover was

removed and the machine screws threaded in from the bottom. University of Delaware

HVAC spliced additional copper tubing into the lines to route the refrigerant through the

mass flow sensor.

Thermocouples:

The thermocouples are supplied with 36” leads. The leads were cut 10” from the

thermocouple, creating a thermocouple with 10” leads to be mounted on the air

conditioner and a 26” long lead to run from the air conditioner to the data acquisition

board. A female miniature thermocouple connector was installed on the thermocouple

leads while a male miniature thermocouple connector was installed on the data

30

acquisition leads. These connectors are installed by unscrewing the connector halves,

carefully stripping the insulation off the leads, installing the leads at the connector’s

screw terminals using the soft nylon washers, and reassembling the connector halves.

Additionally, the panel mount brackets were installed on the female connectors.

RH sensor:

The relative humidity sensor requires an external power source. The sensor uses

a four pin connector. The female end of the connector is wired to the sensor, the male

end is supplied with the sensor. The power source and output leads need to be soldered

to the male connector. The connector is disassembled by removing the two screws

holding the tail piece on and the single screw holding the halves together. The wires are

soldered to the sockets in the connector and the halves reassembled.

Assembly

Before assembly can be started, a few items need to be removed from the air

conditioner. The outer casing of the air conditioner needs to be removed first. This

requires the removal of the mounting screws as well as the air conditioner control knobs

and face-plate. The knobs and controls face-plate need to be retained for reinstallation.

Next, a damper control pull tab can be removed from the front duct.

The air conditioner should now be sent to an HVAC shop to have the refrigerant

recovered from the system. This needs to be done before the mass flow can be installed

and doing this first has the added safety of eliminating the possibility of puncturing a

31

high pressure line during assembly. With these items removed and the refrigerant

evacuated, the assembly process can begin.

The first item to be installed is the top cover. The first step in installing the top

cover is screwing the mass flow sensor to the cover. Next, the cover is fit over the front

coil and control box. Once the cover is in complete alignment, self-tapping sheet metal

screws are used to fasten the cover to the air conditioner.

The connector panels can now be installed. These panels are fastened by driving

self-tapping screws through the mounting flanges and into the air conditioner chassis.

The power cable for the air conditioner passes through the air conditioner body near the

location of the screws. This cable must be held out of the way of the screws to prevent

damage. Once the screws are in place, the cable needs to be held away from the

protruding screw points with a zip ties.

The guards can be installed with self-tapping screws. The location of the screws

needs to be examined to avoid piercing a tube in the coil.

The relative humidity sensor clips and brackets can be mounted after the guards

are in place. The bracket for the rear coil is adhered to the plastic coil shroud with

double-sided automotive trim tape. The remaining two are fastened with self-tapping

sheet metal screws.

As stated in the fabrication procedure for the transducers, a clearance cut needs to

be made on the air conditioner chassis before the pressure transducers can be installed.

This cut is best made with a die grinder. Installation of the pressure transducers is

simple. The valves can be installed on a variety of tubing diameters by using the shims

included with the valves. First, the transducer, adapter fittings, and valve assemblies are

32

made. Teflon tape needs to be used to ensure a good seal on the pressure transducer’s

pipe thread. The location of the valves is cleaned using a Scotch-Brite pad. The

required shim is then placed in the valve and the valve attached to the tube using the three

cap screws included with the valve. Any required adjustments to the rotational

orientation of the transducers in order to make them fit can be done by loosening one of

the flare fittings and rotating the assembly. The final step in installing the valve is to

thread the needle into the valve body, piercing the tube, and then back it out a full turn,

opening the valve. The nylon connectors are then fastened to the connector panel with 4-

40 machine screws.

The air conditioner is now ready to return to the HVAC shop to have additional

copper tubing routed to the mass flow and to have the refrigerant recharged. The

installation of the thermocouples must wait until after this process due to the relative

fragility of the thermocouples.

The thermocouples are supplied on adhesive backed pads. Installation of the

thermocouples involves cleaning the area of the tubing to which the thermocouple will be

installed with a Scotch-Brite pad and rinsing with acetone. Once the thermocouples are

adhered to the air conditioner, the female connectors can be mounted to the thermocouple

panel using the machine screws supplied with the panel mount brackets.

The final details of the installation can now be completed. The control panel

face-plate is attached with double-sided automotive trim tape. The face plate needs a

small clearance notch in the bottom right to clear a wire. With the plate installed, the

control knobs can be reattached by pressing them back onto the studs. This completes

the hardware installation. (See Figure 8, in Appendix 8)

33

Testing/Re-Design

Hardware (calibration):

The hardware consists of four components: the AC unit, the sensors, the

acquisition boards and the LabVIEW program. Part of the Testing of the air conditioning

unit was necessary before testing of the other hardware could be accomplished. First we

needed to determine that the unit was portable. Since the air conditioner easily fit on the

cart that we had purchased, it was concluded that the constraint of ‘portable’ was

satisfied. Secondly, it was necessary to determine how much noise was produced during

operation of the air conditioner. Using a decimeter we determined that the air conditioner

produced approximately 50dB during operation. This easily meets our target value of

60dB. Then we had University of Delaware HVAC evacuate the refrigerant so that the

pressure sensors could be installed; after we did that, we had UD HVAC recharge unit

with refrigerant. Again we had to make sure that the AC unit turned-on, and that the

refrigerant was not leaking in order for us to test the rest of the hardware.

Once we determined that the AC unit was functioning properly we were able to

proceed with the testing of the other three components of the hardware. First a sample

LabVIEW program was written. It is possible to test a program in LabVIEW by using its

capability to read-in sample data. Usually it would be difficult to test the sensors and the

acquisition board independently of each other. Fortunately the UD Mechanical

Engineering department has a number of sensors that have already been determined to

operate properly. With functional sensors we were able to determine the correlation

34

between LabVIEW channels and inputs on the acquisition board. In LabVIEW a

different ‘channel’ must be used for each input to the program from the acquisition board.

By specifying a ‘channel’ the user is telling LabVIEW where on the acquisition board to

‘look’ for a certain input.

With the acquisition board and the LabVIEW program being operational we were

able to turn our attention toward the sensors determining if they were operational and, if

so, how to calibrate them. The pressure sensors were not an issue since the manufacturer

calibrated them. They have a linear output of 1-5Volts with 1V being 0psi and 5V being

500psi.

The thermocouples, however, presented a bit more of a roadblock. The only

metric/restriction on thermocouples was that they be the economical and function over

the entire temperature range of the air conditioner. Therefore, we originally had

purchased ‘Type-T’ thermocouples since they best fit our temperature range and were

quite inexpensive. In trying to test them we immediately noticed that, although we had

‘Type-T’ thermocouples, the university’s acquisition board is equipped with ‘Type-K’

modules. The problem being that, since different ‘Type’s of thermocouples are specified

for different temperature ranges, the very same temperature is converted to different

voltages depending on the ‘Type’ of thermocouple. Since the manufacturer was not

aware of a correction factor between ‘Type-T’ and ‘Type-K’ products, a purchase was

required. We determined that buying ‘Type-K’ thermocouples was a more cost and time

effective option than re-quipping the acquisition board with ‘Type-T’ modules.

If only life were so simple. We come to find out that the range on ‘Type-K’

modules is 0-5Volts and 0-500degrees Celsius. The problem here is that there are points

35

in the air conditioning cycle that the temperature of the refrigerant drops below 0degrees

C. It is interesting to note that if in the LabVIEW program it is specified that the

expected voltage is –1-4V instead of 0-5V then the module is ‘tricked’ into accepting

different voltages than usual. And no error occurs since the module is still being asked to

accept voltages within a 5Volt range. Now the temperature range on the ‘Type-K’

thermocouples is effectively –100-400degrees C, as opposed to 0-500degrees C.

With this problem solved it became possible to calibrate the thermocouples. This

is necessary since the correlation between temperature and voltage is not precisely linear.

Calibration is done by placing the thermocouples in a medium of a known temperature;

namely ice water at 0degrees C and boiling water at 100degrees C. The voltage is read at

these two temperatures. With two points it is now possible to make a new linear

correlation between voltage and temperature. This correlation is approximately 93%

accurate and is thus acceptable given our target of 90%. However it is considerably more

reliable than simply taking –1V to be -100degrees C and 4V to be 400degrees C, and it

is accurate certainly enough for the purposes of our labs.

The mass flow sensor has it’s own read-out and thus does not need to be run

through LabVIEW. And although it is calibrated for the mass flow of Nitrogen a

correction factor for refrigerant was readily attainable. It was important, though, to have

the mass-flow sensor placed in a location where no phase is homogenous, since phase

change introduces error into the readings. Such a location is readily determined from an

understanding of the air conditioning cycle.

The relative humidity (rh) sensor has two outputs, temperature and relative

humidity. The temperature was calibrated using ice water and boiling water, the same as

36

for the thermocouples. And stream was used as the calibration medium for the relative

humidity. Actually, since this sensor uses temperature as one of its tools to calculate the

rh, the steam was used to check the accuracy. And with a rh near 97% was obtained

using steam, it was assumed that the relative humidity sensor was now properly

calibrated.

The velocity sensor is hand held with its own digital indicator and does not need

to be run through LabVIEW. It also has a temperature reading. It can be placed at the

inlet or exit of the condenser or evaporator and give a reading of the maximum velocity

of the airflow if held perpendicular to the flow.

The wattmeter is clamped to the end of the power cord and there is a digital read-

out, revealing the power drawn by the air conditioning unit.

Labs:

In order to test the labs we determined that it would be most effective to actually

have undergraduate students come-in to perform and evaluate them. The reason that this

is the most effective method is that our metrics for evaluating the labs are very subjective

and extremely difficult to evaluate using typical engineering methods. So, by talking to

experts in the educational field, out judgement to have student surveys was reinforced

and we proceeded thusly.

We had students from the ME undergraduate thermodynamics class come to our

lab in groups of 4 to perform any one of 4 labs that we had written. While they

performed the labs we, as instructors, made notes regarding the duration of the

37

experiment, how much time was spent waiting, and the nature of the questions that the

students asked.

After the students performed the lab we had them fill-out a survey. (See Appendix

H) On this survey we asked them to evaluate our lab in several key areas, we asked:

1) Did you learn/see a number of fundamentals?

2) Were the lessons/objectives clear?

3) Did you feel ‘real world’ connections?

4) Did the lab keep your interest?

5) Was the lab hands-on/interactive?

6) Was the procedure logical?

7) Was the lab fun?

With regard to these questions, the students rated the lab from 1 to 5 (1=poor,

5=excellent). We also asked them to write specifically which fundamentals they saw

demonstrated in the lab; this was to ensure that the students truly understood the point of

the lab. Most importantly, though, we asked the students to write down any suggestions

for making the experiment better.

After evaluating this first round of surveys we were rated with a high percentage

of 4’s and 5’s and no 1’s or 2’s (for complete results see appendix E). We received a

number of comments about what we had done well; but we also received a number of

suggestions. The suggestions included: better labeling the sensors and components of the

air conditioner; more clearly identifying the relation between the location of each sensor

and where its output was reading in LabVIEW. Also, we took note of the fact that the

38

students seemed to learn the most about the air conditioner when they were discussing its

functions among themselves.

Using their suggestions and our own observations we determined that it would be

beneficial to put all the experiments into a lab manual and include an introduction

explaining some important aspects of the labs. We also included a complete description

of all the hardware aspects of the lab (for a complete copy of our lab manual see

appendix F). Upon completion of the lab manual we brought all the students into the lab

for a second round of testing. Again we asked them to read the lab manual as well as run

an experiment after which they were to fill out a survey. The second round survey was

identical to the first round survey except that was asked for an additional evaluation: “If

you participated in the previous round of experiments, please comment on whether or not

you found the changes beneficial.”

The second round of surveys yielded extremely positive results. The percentages

of 4’s and 5’s rose significantly and all comments were positive. And every single

person who participated in the first round of experiments found our changes to be

beneficial (for complete results see appendix E).

Suggested Modifications:

We feel that, at this point, the lab manual that we have put together is truly an

optimization given the input that we have received from lab experts, educational experts,

and especially undergraduate students. However we also realize that we have never

participated a lab course in which we didn’t have suggestions for improvement.

Therefore we propose that, after each semester, the students should be asked for their

39

input and the lab manual should be modified accordingly. It will be known that he

modifications have been beneficial as long as the same criticisms do not continue to be

voiced.

Also, we feel that it would be beneficial to have a larger pool of experiments to

choose from. For instance, out of eleven total experiments, every semester four or five

will be chosen. Not only will this provide an option for the professor to choose labs

based on the specific needs of the class; but also it will help prevent the passing down of

experiments from older engineers. We realize that it is not uncommon for students to

obtain lab reports from older students and use them to aid in their own reports. By

simply re-using old reports the student will lose the benefits of putting their own

independent thought into the writing of the lab reports and especially the technical paper.

As for hardware modifications we suggest that the mechanical engineering

department purchase an entirely new apparatus. This includes: a new air conditioner,

specifically a different brand; and new sensors, specifically different types of the same

kind of sensor. By having an entirely new apparatus the students will be able to

investigate how different air conditioners look and operate, as well as differences in

accuracy’s between different types of sensors. Both of these are important real-life skills

for an engineer. This should not be a monetary problem given the fact that we completed

the entire design project for approximately half of our expected budget, although this

could possibly turn out to be a problem in terms of actually finding someone to spend the

time doing this.

40

Conclusion:

In conclusion it can be seen that through our surveys we have satisfied our wants

of ‘educational effectiveness’ and ‘self evident’. Since the components of the air

conditioner are both visible and accessible the want of ‘easy to use’ is satisfied. Our

experiments can be set-up in less than 15 minutes and all of the parts fit on our cart, thus

we conclude that our experiment is ‘easy to set-up’. Our experiments successfully

demonstrate the desired thermodynamic and heat-transfer concepts (as set-forth) by Dr.

Advani and Dr. Wexler, therefore we have demonstrated ‘multiple purposes’. Our

apparatus is LabVIEW compatible, and is thus ‘compatible with a data acquisition

program’. The air conditioner operates under 60dB and can thusly be considered ‘quiet’.

And finally the experiments were completed in 20min, well under the desired 2 hours,

and are therefore ‘quick’.

It needs to be made clear, if not already done so, that the wants of ‘educational

effectiveness’ and ‘self evident’ truly drove our project. While ‘easy to use’ was the

second most important want that, along with most of the other wants were both very

easily measurable and easily obtainable using our metrics and target values.

Consequently, nearly all of our time was spent meeting the two aforementioned wants.

41

Wants Metrics Target Values Obtained Values

1Educational

Effectiveness Survey 4 4.6Judy Green approval approval

3 Self Evident Survey 4 4.6

This table includes the metrics we feel drove our project. A table including the rest of

wants can be found in Appendix K.

Through benchmarking and evaluation of our customers’ wants and constraints,

we determined our metrics as well as target values for each metric. Benchmarking and

input from our customer provided the necessary information for brainstorming concepts

and determining the optimal solution. We tested our prototype, including a lab-manual

and apparatus, and made modifications where necessary. The final product consists of a

window air conditioning unit, fully instrumented and labeled without redundancy, a lab

manual consisting of four component-based labs, and a recommendation for short lab

reports with a technical paper. We completed our project within the given time constraint

and well under budget. Our customers are thoroughly satisfied with the final product.

We have successfully completed the project.

42

Appendix A:

The SSD Chart.

See file Appendix A_Team 10.xls

Appendix B:

Table: Wants – Metrics – Target Values (Prioritized)

See file Appendix B_Team 10.xls

Appendix C:

The evaluation chart.

See file Appendix C_Team 10.xls

43

Appendix D:

The budget

44

Appendix E:Test Results

45

46

Appendix F:

Lab Manual for

Air Conditioning Experiments

For Heat Transfer and ThermodynamicsJoint Laboratory

47

Mission Statement:

Our mission is to teach the students the Thermodynamic and Heat Transfer principles of a window air conditioner with as little guidance as possible. This lab manual consists of what we hope is the only necessary information needed for the student to independently investigate these principles. We envision the lab time spent as a brainstorming session for the student to discuss the air conditioner with minimal time spent collecting data.

WARNING: Be careful when examining the air conditioner, as some of the parts get

very hot!

48

Table of Contents

Introduction………………………………………………..50

Schematic of Refrigeration Cycle…………………………51

Description of Parts………………………………………..52

Sensors……………………………….……………………53

LabVIEW Controller……………………………………...54

Lab Reports………………………………………………..56-66

Compressor……………………...…..56

Throttling Valve………………....…..59

Air Flow Across the Coil……….……62

The Ideal Air-Conditioning Cycle…...65

References…………………………………………………68

49

Introduction:

The basic objective of an air conditioner (or window AC as it would be) is to

remove heat from the air of a room that is being cooled. The heat is discharged to the

environment outside the room. It should be noted that the same air conditioner could be

used as a heat pump as well by simply turning it around. In this case the air conditioner

would be absorbing heat from the outside environment and rejecting it into the room.

The ideal vapor-compression refrigeration cycle is the most widely used for

refrigerators, air conditioning systems, and heat pumps. It is composed of four processes.

Starting form the compressor, refrigerant is isentropically compressed. Then, it is sent

through the condenser, where pressure remains constant. From the condenser, warm air

is rejected into the outside environment. From there, the refrigerant flows through the

throttling valve, which is an expansion device. Next, the refrigerant is sent through the

evaporator, where pressure is again constant (as in the condenser). Finally, the

refrigerant reaches the compressor where the cycle begins all over again.

It is important to recognize that the refrigerant does not simply flow through the

devices mentioned above. The refrigerant is experiencing phase changes throughout the

cycle. As the refrigerant enters the compressor, it is a saturated vapor. During the

compression process, the temperature of the refrigerant increases to well above that of the

surroundings. As it enters the condenser it is a super-heated vapor, and it leaves as a

saturated liquid. This phase change results from the refrigerant losing heat while flowing

through the condenser. It should be noted that the temperature of the refrigerant at this

phase is still well above that of the environment.

Upon entering the throttling valve, the refrigerant experiences a pressure-drop,

which in turn results in a decrease in temperature. It is at this point that the temperature

of the refrigerant finally falls below that of the surroundings. As it enters the evaporator

the refrigerant is a low quality saturated mixture. The refrigerant uses the heat from the

room to provide the necessary energy to complete the evaporation process. At this point

it is again a saturated vapor and ready to re-enter the compressor and start the cycle over.

50

It is often helpful to use graphs to interpret the process, which is the air-

conditioning cycle. One such graph is the ‘T-s diagram’. The heat transfer for internally

reversible processes is represented as the area under the process curve ‘4-1’ (as shown in

figure 2).

Another commonly used graph is the ‘P-h’ diagram. As can be seen from figure

3, three of the four processes appear as straight lines. The heat transfer in the condenser

and the evaporator is proportional to the lengths of the corresponding process lines.

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Description of Parts:

Condenser/Evaporator:

In the window air conditioner, the condenser and the evaporator are actually heat

exchangers. All that can be seen of either one are the ‘U’ shaped coils attached to the

sides on the front and the back of the unit. One set of coils gets hot and the other gets

cold, so be careful when touching them.

Throttling Valve:

A throttling valve, in this case, reduces the pressure of the refrigerant. To achieve

this, the refrigerant should flow from a smaller diameter tube to a larger diameter tube. If

you still are unsure where the throttle is, ask the TA.

Compressor:

The compressor is the tall black cylinder that sits between the heat exchangers. It

gets very hot when the air conditioner has been running after several minutes.

Other:

The little black cylinder behind the compressor is a collector that has no effect on

the Thermodynamic/Heat Transfer processes of the unit, so it is ignored. Fans are needed

to move the air over the coils of the heat exchangers. There are two of them. They are

both attached to the same motor, which is located next to the collector, between the heat

exchangers. A shield covers them for your safety.

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Sensors:

Numbering of the Sensors:

The sensors are labeled with numbers. These numbers are made to correspond

with the LabVIEW program. They have no significance to any other numbering scheme

mentioned in this laboratory manual or any of the written lab instructions.

Pressure Sensors:

There are four pressure sensors placed throughout the air conditioner. Basically

one between each device (between the condenser and the compressor, etc.) They are

black with the OMEGA label on them. They measure the pressure in volts (1-5V, 1

being 0 psi and 5 being 500 psi). They are connected to the data acquisition board

through the blue wires.

Thermocouples:

There are also four thermocouples, placed the same as the pressure sensors. They

are attached to the outside wall of the tubing. They are connected to the data acquisition

board through the copper wires. Their output (in volts) is converted by LabView, and is

displayed in degrees Celsius.

Relative Humidity Sensor:

This sensor is long and cylindrical in shape, and silver in color. It mounts to the

air conditioner in three places, the outside of the evaporator, the outside of the condenser,

and in between the two. It has two functions, measuring the relative humidity of the air

and the temperature of the air. It output is also in volts, and converted by LabView to %

relative humidity and degrees Celsius, respectively.

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Mass flow sensor:

The box mounted on top of the casing is the mass flow sensor. It has a digital

display of it’s own. The number shown must be multiplied by a conversion factor of

0.4956, for refrigerant-22.

Velocity Sensor –

A hand held device use to measure the velocity and temperature of the air exiting

the condenser and the evaporator. This device is used by simply holding it in front of

desired air flow. NOTE: The fan should be perpendicular to the direction of the flow to

maximize accuracy. This device also had a digital indicator of it’s own. The output of the

temperature is in degrees Celsius, and the velocity is in meters per second.

Watt Meter:

This clamps to the power cord of the air conditioner, which is connected to the

outlet. A digital read-out shows how much power the air conditioner is using.

LabVIEW Program:

The LabVIEW program (see Appendix H) is interfaced with the data acquisition

boards. The two acquisition boards are 1) a green box, and 2) a green board with blue

boxes. The green box is connected to the pressure sensors and the mass flow sensor. The

green board with the blue boxes is connected to it; it reads the thermocouple outputs and

the relative humidity sensor outputs. Our LabVIEW program (see Appendix H) reads

and converts the signals from each of the sensors to their respective units of measure, for

example pressure is converted from volts to psi and temperature in Kelvin. LabVIEW

has the capability to read up to sixteen channels. The green board with the blue boxes is

read into the first eight channels (0-7), and the green box reads into the upper eight

channels (8-15).

The pressure sensors are labeled 1-4 and their respective channels are 8-11. The

thermocouples are also labeled 1-4, and their respective channels are 0-3. The mass flow

54

is read through channel 12, and the relative humidity is read through channel 4. Be sure

the check the channel numbers BEFORE collecting any data.

55

Compressor

Objectives:To understand the thermodynamic principles involved in the function of a

compressor. To use conservation of energy to find heat loss to the environment.

Background:The purpose of a compressor is to increase the pressure of a fluid. Work is done

on the fluid therefore the work term is negative when dealing with a compressor. Certain engineering assumptions are made when dealing with a compressor:

(figure 1)

56

In the case of a compressor there is intentional cooling, therefore the heat transfer term cannot normally be neglected

A compressor involves a rotating shaft crossing its boundaries, therefore the work term is important.

The change in potential energy is normally quite small and thus neglected.

In a compressor the velocities involved are usually not high enoughto effect the kinetic energy at all, especially compared to the change in enthalpy.

1.

2.

3.

4.

0

0

0

0

ke

pe

W

Q

P1,T1

P2,T2

q

A compressor can be modeled as a steady flow system.

Relevant Equations:

Conservation of Energy:

q – w = h + pe + ke (eq. 1)

By making the assumptions presented previously, eq. 1 can be reduced to

q – w = h (eq. 2)

Power:

Power = (mass flow rate)*(work per unit mass w) (eq. 3)

Procedure:

1. Measure the temperature and pressure at the inlet (1) and exit (2) of the compressor.Note: The numbers (1) and (2) do not correspond to the sensor numbers only the figure 1 numbers.

2. Measure the mass flow rate of refrigerant (read from indicator on sensor).3. Determine the power input to the compressor by reading the current and voltage off the motor to the fan. OPTIONAL: Read the power from the Power Clamp on the cord, which is connected to the electrical outlet.

Analysis:

1. Do the measured values of temperature and pressure correspond to what you know is happening in the compressor? Explain in terms of thermodynamic principles.

2. Using the measured temperature and pressure values, determine the specific enthalpy h at the inlet and exit using the refrigerant tables in the back of your thermodynamics text.

3. Solve for the work done on the fluid using the power input (read from the fan motor) to the compressor and eq. 3.

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4. Solve for the heat loss to the environment using the values from parts 1 and 2 of the analysis and eq. 2.

5. Calculate the power input to the compressor using eq. 3, assuming heat loss can be neglected. Could this be a reasonable engineering assumption? Explain.

6. OPTIONAL: Compare the power calculated from reading the voltage and current off the fan motor to the power reading from the Power Clamp. Explain differences.

58

Throttling Valve

Objectives:To understand the thermodynamic principles involved in the function of a

throttling valve. To determine whether approximating the fluid as saturated at the inlet of the valve is a good engineering approximation. To determine the relationship between the quality of the mixture at the exit and the temperature.

Background:The purpose of a throttling valve is to cause a significant drop in the pressure of

the fluid. A good example of this is any adjustable valve such as a sink faucet. Along with the drop in pressure comes a drop in temperature. In an air conditioner, it is this temperature drop that is the primary purpose of a throttling valve. As with any device, several engineering assumptions are made in order to simplify the analysis:

(figure 2)

A throttling valve can be modeled as a steady flow system.

59

The fluid is usually moving rather quickly and throttling valves are usually small. Thus it is assumed that there is neither sufficient time nor area for significant heat transfer to occur.

A throttling valve involves no moving boundaries and therefore no work is done by or on the fluid.

The change in potential energy is normally quite small and thus neglected.

Even though the change in velocity can be quite large, the change in kinetic energy is considered insignificant.

1.

2.

3.

4. 0

0

0

0

ke

pe

w

q

fluid

Throttling Valve

Relevant Equations:

Conservation of Energy:

q – w = h + pe + ke (eq. 1)

By making the assumptions presented previously, eq. 1 can be reduced to

h = 0 or h1 = h2 (eq. 2)

It is more useful to expand eq. 2:

u1 + P1v1 = u2 + P2v2 (eq. 3)whereP is the pressureu is the internal energy, andv is the specific volume.

Qualityx = mvapor (eq. 4)

mtotal

where mvapor is the mass of the vapor, andmtotal is the total mass of the liquid and the vapor

It can be derived that:x = (hav – hf)/hfg (eq. 5a)x(exit) = (h(e) – hf(e) )/hfg(e) (eq. 5b)where hf is the specific enthalpy of the liquidhfg is the difference between the specific enthalpy of the fluid and the gas, andhav is defined as hf + xhfg.the subscript e is for the exit pressure

Procedure:

1. Measure the temperature and pressure at the inlet (1) and exit (2) of the throttling valve. NOTE: The numbers (1) and (2) do not correspond to the sensor numbers, but they do correspond to the numbers in figure 1.2. Measure the mass flow rate of refrigerant (read from indicator on the sensor).

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3. Repeat step 1 for at least 2 more settings on the air conditioner (e.g. low, med, high).

Analysis:

Questions 1 through 3 need only be evaluated at 1 air conditioner setting.7. Using only the inlet pressure reading and assuming that the refrigerant is a saturated

liquid as it flows through the throttling valve, find the specific enthalpy.8. Assuming that the enthalpy across a throttling valve does not change, use the enthalpy

from question 1 and the reading of the exit pressure, determine what state the mixture at the exit is.

9. If the refrigerant is a saturated mixture at the exit, find the quality using equation 5b.10. Using the temperature and the pressure form the inlet reading, does the previous

assumption that the inlet and of the throttling valve is a saturated refrigerant? Explain why or why not.

11. What is the temperature change for this process? A) Using the saturation temperatures from the given pressures. B) Using the data read off of the air conditioner. Is there a difference and if so, explain.

61

Air Flow Across the Coil

Objective:To understand the heat transfer principles by determining the convection heat

transfer rate involved with cross flow over the coils (tubes).

Background:There is a coolant flowing inside the coils and as the air flows over the coils, heat

is transferred between the flowing coolant in the coil and the air around it. The rate at which the heat is transferred is dependent upon the heat transfer coefficient. The coil rows are either arranged in an aligned or staggered bank.

geometry of the coils

V, T (Tinlet)

ST

SL

Relevant Equations:

Maximum Velocity of the fluid around the tube

(eq. 1)

V is the measured velocity

Reynolds number for the air

(eq. 2)

D is the diameter of the tube is for the inlet of the air

Air-side Nusselt number

(eq. 3)

C2, C, and m values come from tables 7.7 and 7.8 from the Heat Transfer book

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The other properties are evaluated at the average of the inlet and outlet temperature of the fluid and the subscript s is for the surface temperature.

The average heat transfer coefficient

(eq. 4)

the k value is from the inlet of the air

Knowing only the inlet temperature of the fluid in the coil

(eq. 5)

N is the number of coils NT is the number of coils that are first hit by the air flow and cp are properties from the inlet of the air

Log mean temperature difference

(eq. 6)

Ts is the temperature of the coil surface

Heat transfer rate per unit length of the tube

(eq. 7)

Procedures:1. Measure the diameter of the coil.2. Count the number of coils that are first hit by the air and the total number of coils for

each exchanger (for every U shape seen, there are two coils running through).3. Find the coil surface temperature.4. Find velocity of the air entering the coils.5. Find the temperature of the air entering the flow over the coils. 6. With the humidity sensor, take relative humidity and temperature readings of the air

near the cool side of the air conditioner.7. Repeat step 6 at the other locations on the air conditioner.

Analysis:

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1. Using the tables in the back of the Heat Transfer book find the relevant properties of the air using table A4. Air properties using temperatures of the inlet and the coil surface.

2. Using the given equations, find the convection heat transfer rate.3. Looking at the temperature and the relative humidity data, is this a comfortable

atmosphere?

64

The Ideal Air-Conditioning Cycle

Objectives:To determine the coefficient of performance (COP) of a window air-conditioner

using the assumptions of an ideal vapor-compression refrigeration cycle. To determine the rate of heat removal from the refrigerated space and heat rejected from the refrigerant to the environment. To determine the power into the compressor.

Background:The ideal vapor-compression refrigeration cycle is the most commonly

used/assumed cycle for air-conditioning. This cycle in made-up of four processes:

1-2 Isentropic compression in a compressor.2-3 Heat rejection in a condenser coil, P = constant.3-4 Expansion in the throttling valve.4-1 Heat absorption in an evaporator coil, P = constant.

(Figure 1)

For an ideal cycle the refrigerant enters the compressor as a saturated vapor and is compressed isentropically. The temperature increases during the compression. The refrigerant enters the condenser as a superheated vapor and leaves as a saturated liquid.

65

Win

3

4

2

1

Evaporator

Condenser

Compressor

Throttling Valve

The pressure and temperature both drop as it passes through the throttling valve. The refrigerant then enters the evaporator as a low quality mixture and evaporates completely as it absorbs heat from the surroundings.

All four parts can be modeled as steady-flow devices. The change in kinetic and potential energy are usually small compared to the work and potential energy terms. The conservation of energy equation reduces to:

q – w = he - hi (eq. 1)

The condenser and evaporator do not involve any work. The compressor can be approximated as adiabatic. The COP of an air conditioner can be expressed as:

(eq. 2)

(eq. 3)In the ideal case h1 = hg@P1 and h3 = hf@P3.

Relevant Equations:

Rate of Heat removal

(eq. 4)

Power input

(eq. 5)

Procedure:

1. Measure the temperature and pressure each of the four states described in the background.2. Measure the mass flow rate of refrigerant (read from the indicator on the sensor).

66

3. OPTIONAL: Read the voltage and current from the fan motor and the power given by the Power Clamp.

Analysis:

12. Determine the specific enthalpy h at each of the four states using the refrigerant tables in the back of your thermodynamics text.

13. Using the answers from (1):(a) Use eq. 4 to determine the rate of heat removal from the refrigerated space.(b) Use eq. 5 to determine the power input to the compressor.(c) Use eq. 4 to determine the rate of heat rejection from the refrigerant to the

environment.14. Determine the coefficient of performance of the refrigerator and the heat pump using

equations 2 and 3 respectively.15. OPTIONAL: Compare the power calculated in 2b to the power obtained by reading

voltage and current from the motor of the fan and to the power read from the Power Clamp.

67

References:

Boles, Dr. Michael A., and Dr. Yunus A. Cengel, Thermodynamics, An Engineering

Approach, McGraw-Hill Inc., New York, 1994.

Dewitt, David P., and Frank P. Incropera, Introduction to Heat Transfer, Third Edition,

John Wiley & Sons, New York, 1985, pp. 351-360, 757.

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Appendix G:

The drawing package

Figure 1

69

Figure 2

70

Figure 3

71

Figure 4

72

Figure 5

73

Figure 6

Brian Davison’s Responsibility

74

Figure 7

Brian Davison’s Responsibility

75

Figure 8

Brian Davison’s Responsibility

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Appendix H:

The surveys

Instructor Survey

Name of Lab Preformed __________________________________________

Start time _______ End time __________

Number of students in the group _____________

What questions did the students ask?________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

How many of the above questions pertain to each of the following?

Procedure ____________Data Analysis ____________Other _____________

How much of the time was spent waiting, “down time”? _____________________

77

Student Survey (1st Round)

Name: _________________________________

Name of Lab: ____________________________ Date: _____________

Please answer the following questions on the basis of your personal experience during the lab. Please choose a number rating between one and five, with one being the lowest and five being the highest.

Did you learn/see a number of fundamentals? 1 2 3 4 5

Were the lessons/objectives clear? 1 2 3 4 5

Did you feel “real world” connections? 1 2 3 4 5

Did the lab keep your interest? 1 2 3 4 5

Was the lab hands-on/interactive? 1 2 3 4 5

Was the procedure logical? 1 2 3 4 5

Was the lab fun? 1 2 3 4 5

What fundamentals did you see demonstrated in this experiment:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Thank you for your time and patience, your participation is greatly appreciated.Please list any comments or suggestions you may have below; they would be extremely beneficial to us.

Comments/Suggestions:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

78

Student Survey (2nd Round)

Name: _________________________________

Name of Lab: ____________________________ Date: _____________

Please answer the following questions on the basis of your personal experience during the lab. Please choose a number rating between one and five, with one being the lowest and five being the highest.

Did you learn/see a number of fundamentals? 1 2 3 4 5

Were the lessons/objectives clear? 1 2 3 4 5

Did you feel “real world” connections? 1 2 3 4 5

Did the lab keep your interest? 1 2 3 4 5

Was the lab hands-on/interactive? 1 2 3 4 5

Was the procedure logical? 1 2 3 4 5

Was the lab fun? 1 2 3 4 5

If you participated with Dr. Wexler’s class, please comment on whether or not you found the changes beneficial.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Thank you for your time and patience, your participation is greatly appreciated.Please list any comments or suggestions you may have below; they would be extremely beneficial to us.

Comments/Suggestions:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

79

Appendix J:LabVIEW ProgramSee file Team10.vi

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Appendix K:

Table: Metrics: Target values versus Obtained Values

See file Appendix K_Team 10.xls

81