improving the solar hot water system in the duke smart home · 2009-01-15 · 2 abstract the goal...

Pratt School of Engineering

Duke University

Department of Mechanical Engineering and Materials Science

Improving the Solar Hot Water

System in the Duke Smart Home

ME 160

Dr. Robert Kielb

Spring 2008

4/27/2008

Advisor: Milan Simonivic

Holly Hackman, Tiffany Hui, Jeff Schwane, Scott Strickland

2

ABSTRACT

The goal of this project was to improve the overall heat transfer rate of the solar hot water system

in the Duke Smart Home, thereby increasing both energy and cost savings. The design team spent a

semester investigating ways to improve the system’s efficiency through implementation of variable

speed pumps. Preliminary design work was performed and is summarized in this report. The variable

speed pumps were installed in the Smart Home and the programming and experimentation processes

are outlined herein as well. The experiment resulted in a marked efficiency improvement by running

the pumps at variable speed rather than constant speed. Results of this project are presented in detail

and suggestions for further improvements are presented in the conclusion.

Problem Definition

Purpose

The intent of this design project was to increase the heat transfer of the current solar water

heating system installed in the Home Depot Smart Home.

retrofitted to rely on variable speed circulators instead of the standard constant

constantly adjusting the flow of water, the new system would hopefully be able to take far greater

advantage of changes in external temperature and thus

Current Solar Water Heating System

The water heating system currently installed in the Smart Home relies on two constant

Taco 009 pumps to circulate water in a closed

system.

Figure 1 -

The water begins at the heat exchanger near the hot water storage tank in the basement of the

building, and it is pushed to the roof where a solar collector is used to heat the water.

flows back down, and its thermal energy is used to heat the water in the storage tank

3


heating system installed in the Home Depot Smart Home. To accomplish this task, the system was

retrofitted to rely on variable speed circulators instead of the standard constant-speed pumps.


external temperature and thus achieve greater efficiency.

Current Solar Water Heating System

The water heating system currently installed in the Smart Home relies on two constant

Taco 009 pumps to circulate water in a closed-loop system. Figure 1 provides a simplistic model of this

- Schematic of Current Solar Hot Water Heating System


is pushed to the roof where a solar collector is used to heat the water.

flows back down, and its thermal energy is used to heat the water in the storage tank via a heat


To accomplish this task, the system was

speed pumps. By


The water heating system currently installed in the Smart Home relies on two constant-speed

Figure 1 provides a simplistic model of this


The heated water

via a heat

exchanger. To regulate this process, a

thermocouples attached to both the roof

of a sixteen degree Fahrenheit or greater temperature difference between the collector and the tank,

power is sent from the Steca control unit to the pumps to turn them on,

pumps will continue to operate until

apparatus provides adequate heating, but it can be

Proposed Modifications to Solar Hot Water Heating System

By modifying the previous system, it may be possible to extract an even greater amount of

energy from the solar radiation. Figure 2 shows the retrofitted system.

Figure 2

The most obvious change to the standard system is the substitution of the variable speed circulators

for the constant speed ones. These new pumps can be controlled by an external

from 0 to 10V—a 0V signal will not move the pump, 5V is half speed, and 10V is maximum speed.

method by which these pumps are controlled is also altered.

before, there are now two. The Steca system still controls

however, once the pumps are on, flow control is regulated by the installed Siemens

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To regulate this process, a Steca 0301U Temperature Difference Controller

thermocouples attached to both the roof-top solar panel and the storage tank are installed. In the case

degree Fahrenheit or greater temperature difference between the collector and the tank,

control unit to the pumps to turn them on, and water begins to flow.

pumps will continue to operate until the temperature differential drops to five degrees

apparatus provides adequate heating, but it can be improved.

Modifications to Solar Hot Water Heating System


Figure 2 shows the retrofitted system.

- Schematic of Retrofitted Solar Water Heating System


These new pumps can be controlled by an external signal varying linearl

a 0V signal will not move the pump, 5V is half speed, and 10V is maximum speed.

method by which these pumps are controlled is also altered. Where there was one control system

The Steca system still controls whether the pumps will turn on or not;

however, once the pumps are on, flow control is regulated by the installed Siemens APOGEE

ference Controller and

top solar panel and the storage tank are installed. In the case

degree Fahrenheit or greater temperature difference between the collector and the tank,

and water begins to flow. The

s. The current



signal varying linearly

a 0V signal will not move the pump, 5V is half speed, and 10V is maximum speed. The

Where there was one control system

whether the pumps will turn on or not;

APOGEE Modular

5

Equipment Controller (MEC). This controller is capable of accepting inputs from varying sources and

generating various kinds of outputs (current, voltage, etc.) that are regulated by a written program.

Additional temperature sensors were installed on the water pipe leading to the solar collector and the

water pipe heading away from it. Finally, a program to command the water flow by varying output

voltages to the pumps was generated and uploaded into the APOGEE MEC.

Intended Customer/Market

The most immediate and readily-available market for the activities of this project is the Home

Depot Smart Home, the end result of the Duke University Smart Home Project. The building was

constructed in 2007 to function as a living laboratory that combines the residential needs of college

students with the latest technologies in home design. One intended result of these technologies is to

create a more environmentally-friendly lifestyle for its inhabitants. Reclaimed water from the roof is

used to fill the toilets and wash clothes, high efficiency windows adorn the walls, and a solar hot water

heating system provides hot water to the showers and dishwasher. Improvements to this hot water

system would appropriately align with the goals of the Smart Home as an eco-friendly dorm.

Additionally, with oil prices approaching $115 a barrel at the time of this writing, and emitted

greenhouse gases leading to global warming, “green” living has become a global imperative. In 2006,

industry experts expected the green market to grow by 10-20 billion dollars in the next five years.

Additionally, 60 percent of all architects, designers, etc. responded that they incorporate

environmentally-friendly techniques into their new projects. By 2010, green building is expected to

account for 5-10 percent of all new construction (up from 2 percent in 2004).

Furthermore, the United States government and other organizations have realized the necessity of

preserving the environment. The United States Green Building Council (USGBC) is an organization

dedicated to sustainable building and construction. They have a green building rating system called

Leadership in Environmental and Energy Design

Platinum rating at the time of this writing, which is the highest rating a building can achieve.

United States offers tax incentives to those attempting to lead a more sustainable lifestyle. The green

market is growing rapidly, and its expansion opens an enormous market for the modifications presented

in this report. The techniques presented within can be used by bo

construction of new buildings and the renovations of old ones in the years to come.

INFORMATION GATHERED

Existing Products

The solar hot water system initially installed in the Smart Home is a fairly effective system used

for extracting the sun’s energy. The original system utilized Taco constant speed pumps, shown in

Figure 3, which would run at 10 volts when the system was activated. The system, made by Sundance

Power Systems, was programmed to turn on when the solar c

sixteen degrees hotter than the hot water tank. The system would then run until the temperature

difference decreased to five degrees, at which point the system would shut off.

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Leadership in Environmental and Energy Design (LEED). The Smart Home is expected achieve a LEED

Platinum rating at the time of this writing, which is the highest rating a building can achieve.

ffers tax incentives to those attempting to lead a more sustainable lifestyle. The green


in this report. The techniques presented within can be used by both builder and consumer in the

construction of new buildings and the renovations of old ones in the years to come.



, which would run at 10 volts when the system was activated. The system, made by Sundance

Power Systems, was programmed to turn on when the solar collector reached a temperature at least

degrees hotter than the hot water tank. The system would then run until the temperature

difference decreased to five degrees, at which point the system would shut off.

Figure 3 - TACO 009 Constant Speed Pump

(LEED). The Smart Home is expected achieve a LEED

Platinum rating at the time of this writing, which is the highest rating a building can achieve. Finally, the

ffers tax incentives to those attempting to lead a more sustainable lifestyle. The green


th builder and consumer in the



, which would run at 10 volts when the system was activated. The system, made by Sundance

ollector reached a temperature at least

degrees hotter than the hot water tank. The system would then run until the temperature

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This design certainly saves energy and money since hot water from the solar system minimizes the

use of the natural gas boiler. The overall current Sundance Power Systems design is professionally

installed and proven effective. There are temperature sensors on both the incoming and outgoing pipes

which send signals to a Siemens APOGEE system. Additionally, there are temperature sensors on the

solar collector and the hot water tank. These sensors send signals to the Sundance System, which

controls when the system turns on and off.

While this system is effective, there are potential energy losses since the system runs at a constant

speed regardless of temperature difference. It was noticed that the system sometimes runs too fast or

too slow to maintain an optimal temperature difference between the incoming and outgoing pipes. If

the constant speed pumps were replaced with variable speed pumps, there would be great potential to

increase heat transfer. The increased cost of the variable speed pumps over the constant speed pumps

could likely be made up through cost and energy savings from decreased use of natural gas.

Expert Consultation

A number of experts were consulted for the project. First, multiple Duke engineering professors

were contacted regarding theory and application. Dr. Jon Protz provided insight concerning the heat

transfer analysis of the system. He helped establish a quantitative model that would determine both

mass flow rate and overall heat transfer rate. Throughout the semester, the model was adjusted with

his assistance. Dr. Edward Shaughnessy was helpful in fluid dynamics modeling as well.

Next, Dr. Rhett George provided some insight into electrical drives and motors. He determined that

it would be very difficult to control the existing system variably. It would involve accessing the two

internal windings, generating a signal whose frequency determines revolutions per minute, and

installing a separate amplifier for each winding. This would be an extremely complicated procedure,

particularly for mechanical engineers with little electrical circuit experience. Additionally, the pulsing

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that would arise from this procedure would create a great loss in efficiency. There would be electrical

losses from restarting the motor and the restoring of momentum takes a lot of additional power. This is

hence counter-productive and would not be a viable way to alter the system.

Dr. Michael Gustafson’s expert advice was sought concerning electrical controls. He suggested two

main methods for controlling variable speed pumps if they were installed. One method would be to use

a Parallax Basic Stamp. This converts the measured temperature difference to a voltage between zero

and ten volts. This would require a DC chip conversion to produce an analog signal. Another potential

way to control the pump was to use the Siemens APOGEE system which is currently installed in the Duke

Smart Home. There is a computer installed in the Smart Home which contains the program Insight. This

is a Siemens program which is used to control the APOGEE system. In order to control this system,

additional help from someone familiar with Siemens systems was necessary.

Woody Cheek, a Duke energy control specialist, was consulted regarding controlling the Sundance

system by means of the Siemens system. He specializes in Siemens systems control across Duke’s

campus, and was very knowledgeable about the practicality of controlling a system of this type.

Installation of the system would not be very difficult; it was essential to determine how to control the

system numerically through quantitative analysis. He recommended reevaluating the model and

coming up with a table statement to deterministically control the system.

Mark Wilkinson, another Duke energy control specialist, was also consulted regarding splitting

signals to send to the Siemens system. Because the sensors measuring the temperature of the solar

collector and the hot water tank send signals to the Sundance system, an additional signal needed to be

sent to the Siemens system. It was not possible to splice the wires and duplicate the signal as was

originally proposed. One possible solution was to add an additionally sensor on the hot water tank and

the solar collector. It was determined that this would add unnecessary additional costs. Rather, the

model was reevaluated using the temperatures of the incoming and outgoing pipes from the tank to the

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collector. High accuracy thermistors were added to the pipes to measure the temperatures. Signals

were then sent from these thermistors to the Siemens APOGEE system and the control code was based

on the temperature difference between these two sensors.

PRELIMINARY DESIGN WORK

Product Design Specification (PDS)

When designing a product, it is necessary to address customer and market needs. Therefore,

some overall goals were determined from analyzing these needs. A detailed PDS is included in Appendix

I.

Customer Needs:

The most important aspects of this system for a customer are energy efficiency, effective water

heating, and reliability. The energy payback should ideally be less than 5 years; this is a reasonable

energy payback for a homeowner.

Demand:

There are a number of reasons why a variable speed pump system would be desirable over a

constant speed pump system. Ideally, to market this product, the pumps should provide smoother

water flow, more accurate temperature control, energy and cost savings, a longer lifespan, and quieter

operation.

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Performance Goals:

This system should be self-sustaining and fully operable without user control necessary. The

Siemens system allows for the system to run based on a program, which an operator can change at any

time if it becomes necessary. However, the system should not require user input to operate.

Quality Function Development (QFD)

QFD is a design tool used to analyze a design idea and generate possible improvements during

the planning process. It compares customer needs and requirements with engineering parameters of

the design.

Four different design ideas were compared to various customer needs. These included two possible

ways to reduce shower-warm-up waste, which was an originally proposed idea, a plan to alter the

temperature threshold of the current system, and to exchange the standard pumps for variable speed

pumps. Each design idea was ranked according to its ability to meet each customer need (1 = weak

correlation, 5 = strong correlation). The significant custom requirements included water conservation,

energy conservation, operating safety, cost effectiveness, reliability, water heating effectiveness, ease of

installation, and ease of use. The QFD can be seen in Appendix II.

Each of the four ideas was assigned correlations to the customer needs according to our best

judgments. A total score was determined for each idea. The QFD returned results that the variable

speed pumps would best meet the relevant customer needs. For example, simply altering the

temperature threshold of the current system would probably not be very beneficial. Because the

system is already installed, it would certainly be safe to operate, easy to install and use, and reliable.

There’s a possibility for increased energy and cost savings, but it would be relatively low. The

mechanical and electromechanical shower warm-up waste reduction devices could potentially save a

significant amount of water. They would not save much in terms of energy. There could be potential

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safety issues, particularly with the electromechanical device. As mechanical engineers, we have limited

experience with electrical circuitry, so this would not be the ideal project. Furthermore, competitors

already have an existing product to achieve this, known as Shower Start. It is unlikely a much better

product could be produced given the knowledge base for this type of project.

Replacing the existing pumps with variable speed pumps could potentially save a lot of energy, and

hence money. It would be cost-effective, easy to operate and install, reliable, and safe. It is most likely

more effective than the current system and is therefore the method chosen to improve the solar hot

water system in the Duke Smart Home.

Theory of Inventive Problem Solving (TRIZ)

Engineering design problems generally face contradictions between numerous parameters. TRIZ

is an engineering problem solving method invented by Genrich Altschuller in 1946 to specifically combat

this problem of contradicting parameters. TRIZ has 39 engineering characteristics and 40 inventive

principles which are used to solve these contradictions. The main function of TRIZ is to eliminate the

disadvantages of these contradictions rather than compromise the product.

For this particular problem, there were three main design contradictions which needed to be

addressed. The first of these was to increase the speed of the device without significantly increasing the

complexity of the device. The main resolution to this contradiction was to replace a mechanical means

with a sensory means or to disregard a portion of the system which has served its function. In this case,

the control of the new speed pumps would in fact be controlled by a sensory control, the SIEMENS

system, which is the basis of the project.

The second contradiction encountered was between decreasing the amount of energy wasted

without increasing device complexity. Once again, this is the main basis of our project and hence was

very important to consider. The TRIZ principle to consider was to introduce some form of feedback

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action to improve the process. This is precisely the type of control for which the Siemens APOGEE

system is designed.

The third and final contradiction faced in the design of this project was improving accuracy of

measurement without compromising the reliability of the device. There were two main inventive

principles that could be utilized to minimize this contradiction. The first was to increase the degree of

device segmentation. This would ensure that if one component of the device fails, it would be more

easily replaceable and hopefully would not jeopardize the entire device. This was utilized in the project

by keeping the Steca control system in place along with the Siemens APOGEE system; this will be

discussed later in more detail. The second inventive principle pertaining to this problem was to

introduce feedback to improve the process. Again, this was similar to the second problem and will be

discussed further.

The following figure shows the TRIZ method and how it can be used to solve engineering

contradictions.

Worsening →

Improving ↓

Device

Complexity

Reliability

Speed -Mechanics substitution

-Discard Function

X

Energy Efficiency -Feedback X

Accuracy of

Measurement

X -Feedback

-Segmentation Table 1 - TRIZ Contradictions

Design Decision

The results obtained from the QFD and TRIZ led towards adapting parameters for the final

design decisions. Most importantly, the QFD led to the decision to implement a variable speed pump to

improve the solar hot water system in the Duke Smart Home. Additionally, the TRIZ method confirmed

use of the Siemens APOGEE system as a reliable way to control the system.

In order to further ensure system reliability, it was determined that the Steca system would

continue to control when the system turns on and off.

new system, the Steca system would ensure the system ran as it did previously.

The Siemens system utilizes a feedback PID controller. This ensures the device will run base

external conditions. This should increase energy savings and hence cost savings, which are in

customer requirements.

Higher-accuracy thermistors were installed on the incoming and outgoing pipes as well. This was to

ensure accurate, reliable control and measurement of the system. Because the temperature differential

determines the speed of the operating system, it was essential to have accurate temperature

measurements.

The following figure shows the prototype design:

13


l when the system turns on and off. If something went wrong in installation of the

new system, the Steca system would ensure the system ran as it did previously.

The Siemens system utilizes a feedback PID controller. This ensures the device will run base

external conditions. This should increase energy savings and hence cost savings, which are in

were installed on the incoming and outgoing pipes as well. This was to

able control and measurement of the system. Because the temperature differential


gure shows the prototype design:

Figure 4 - Prototype Design System Layout


something went wrong in installation of the

The Siemens system utilizes a feedback PID controller. This ensures the device will run based on

external conditions. This should increase energy savings and hence cost savings, which are in-line with

were installed on the incoming and outgoing pipes as well. This was to

able control and measurement of the system. Because the temperature differential


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QUANTITATIVE ANALYSIS

Summary of Overall Approach

The process of determining the equation to use in the SIEMENS APOGEE system for controlling

the variable speed pump can be broken down into two parts. First, an analytical approach was used to

model the solar hot water heat exchanger system, utilizing Maple to solve for heat transfer in terms of

specific temperatures and differentiate with respect to mass flow. Then, a numerical approach was used

to solve for the mass flow value that maximizes heat transfer and plot a linear fit for corresponding

voltage and temperature difference values.

Variables and Assumptions

As the figure 5 illustrates, the Q1 heat flows from the solar panel to the water coming up from the

water tank, and the Q2 heat flows from the heat exchanger in the tank to the water. Q3 can be defined as

the overall heat flow in the system. The heat exchanger equations below model these three heat flows.

Because the water pipes are well insulated, it can be assumed that there is negligible heat loss along the

pipes. In addition, constant specific heat was assumed for the relevant temperatures.

Equation 1 - Modeling Heat Flows

)(

)1()(

)1()(

343

242

311

2

1

TTcmQ

eTTcmQ

eTTcmQ

p

cm

UA

p

cm

UA

p

p

p

−⋅⋅=

−⋅−⋅⋅=

−⋅−⋅⋅=

⋅

−

⋅

−

15

Figure 5 - Diagram of Heat Flows and Temperatures

Approximating Overall Heat Transfer Coefficient

The overall heat transfer coefficients UA of heat exchangers are constant for ideal heat

exchangers. However, because the solar hot water system does not have ideal heat exchangers, Excel was

used to find a way to approximate UA1 (for the solar panel) and UA2 (for the water tank heat exchanger).

The equations for Q1 and Q2 were set equal to each other and were solved for UA1, yielding the equation

below. Similarly, the equations Q2 and Q3 were set equal to each other and solved for UA2. Using these

equations, UA1 and UA2 were calculated for all the preliminary collected temperature data. Then, the UA

values were plotted against their corresponding temperature differences on Excel. As shown in the graphs

in figure 6, a linear fit equation was determined to approximate UA1 and UA2. The linear fits had R2

values of 0.888 and 0.943 respectively.

T1

T2

T3 T4

Q1

Q2

pcmTT

TTUA ⋅⋅

−

−−=

31

411 ln

Figure 6 – Overall heat transfer coefficients times area vs. temperature difference of pipes for

0.0

1000.0

2000.0

3000.0

4000.0

5000.0

6000.0

7000.0

8000.0

0

UA

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

0

UA

16

Equation 2 - UA Values

Overall heat transfer coefficients times area vs. temperature difference of pipes for solar collector (UA

tank heat exchanger (UA2)

y = 375.2x

R² = 0.888

5 10 15 20

∆T

UA1 vs. ∆T (pipes)

y = 40.05x

R² = 0.943

5 10 15 20

∆T

UA1 vs. ∆T (pipes)

pcmTT

TTUA ⋅⋅

−

−−=

24

232 ln

solar collector (UA1) and

y = 375.2x

R² = 0.888

25

y = 40.05x

R² = 0.943

25

17

Analytical Quantitative Analysis with Maple

The Q1, Q2, and Q3 equations (equation 1) were manipulated in Maple, shown in equation 3. First,

Q was written in terms of T1 and T2. This was done by setting Q1 and Q2 equal and solving for T3. Then,

Q2 and Q3 were set equal and solved for T4. Finally, the expression for T4 was plugged into the Q2

equation and the resulting equation was solved in terms of T1 and T2. This resulting equation is shown

below.

Equation 3 – Q2 in terms of T1 and T2, the temperatures of the collector and tank

Then Maple was used to differentiate this equation with respect to mass flow. The very complicated

equation is shown below and further simplified and factored with Maple.

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Equation 4 - ��

�� with respect to constants and T1 and T2

Using the analytical approach, the above equation must be set equal to zero and solved for the optimal

mass flow.

Numerical Quantitative Analysis with Excel

Equation 4 cannot be solved explicitly for �� , the mass flow rate. Thus, Excel’s “goal seek”

function was used to numerically solve this equation and find the optimal mass flow through iteration.

With each temperate data set collected, an optimal mass value was determined. Then, using the equation

below, mass values were normalized to give output voltages. 0.37 kg/s is the maximum pump speed and

10V is the maximum voltage.

Equation 5 - Normalized Voltage

Finally, the output voltages were plotted with respect to their corresponding temperature differences

in Excel. A linear fit equation was determined by Excel, as shown in figure 7 and equation 6, and was

used for the voltage control programmed into the SIEMENS APOGEE system.

Vskg

mVoltage 10

/37.0⋅

=

&

Figure 7

Equation 6

Prototype Construction

Materials and Devices Used

When discussing the materials and devices used in this experiment, one must begin with the

pumps themselves. The two Taco 009

pumps.

0.00000

20.00000

40.00000

60.00000

80.00000

100.00000

120.00000

0

Vo

lta

ge

19

Figure 7 – Optimal voltage for given temperature differences

Equation 6 – Control voltage given temperature difference


pumps themselves. The two Taco 009-VV Cartridge Circulators are relatively small, variable speed

Figure 8 - Taco 009-VV Circulators

y = 5.493x

R² = 0.904

5 10 15 20

∆T

Voltage vs. ∆T (pipes)


VV Cartridge Circulators are relatively small, variable speed

y = 5.493x

R² = 0.904

25

They were chosen because they are identical (except for the voltage

previously installed, which makes for easy integration with the previous system. Like the old pumps, the

new ones are constructed from bronze as opposed to cast iron. This deci

oxidation effects that plague cast iron in a non

pumps possess a head range of 0 to 34 ft. and are capable of flow ranging from of 0 to 8 gallons per

minute (GPM). Finally, their speed can be controlled linearly by varying the input

to 10 V.

The next installation components to consider are the pipe temperature sensors.

Figure

The two installed Mamac TE-704

their 6 foot plenum rated cables and 2 inch 304 SS probes, they are capable of detecting temperature

differences as minute as ± 0.2˚C. The final primary component to consider is the S

Modular Equipment Controller (MEC). While one may consider the pumps to be the heart of this project,

the MEC is without doubt the brain.

20

because they are identical (except for the voltage-varying components) to those


new ones are constructed from bronze as opposed to cast iron. This decision was made to minimize the

oxidation effects that plague cast iron in a non-isolated system: bronze is immune to these effects. The


y, their speed can be controlled linearly by varying the input control


Figure 9 - Mamac TE-704-A-3 Pipe Temperature Sensors

704-A-3 Pipe Temperature Sensors are highly accurate instruments. Via


˚C. The final primary component to consider is the Siemens APOGEE


the MEC is without doubt the brain.

Figure 10 - Siemens APOGEE MEC

varying components) to those


sion was made to minimize the

isolated system: bronze is immune to these effects. The


control voltage from 0


3 Pipe Temperature Sensors are highly accurate instruments. Via


iemens APOGEE


The APOGEE system, by accepting a wide assortment of inputs and genera

analog outputs, is capable of controlling numerous devices

programming it through the Powers Process Control Logic, it is capable of varying the voltage sent to

these circulators in a controlled and prede

Fabrication

The fabrication of this product required

pumps, connect the pumps to the APOGEE system, integrate the high accuracy pipe sensors, and write

the system code. Obtaining project approval was no small matter, for the Duke

Administrators take students tampering with the school’s property very seriously.

Meetings, request letters, and an on

stages.

The next necessary task was the actual replacement of t

all the water running through the pumps b

Once the water was stopped, the old constant

bolts attaching them to the pipe.

21

The APOGEE system, by accepting a wide assortment of inputs and generating both digital and

analog outputs, is capable of controlling numerous devices—including the Taco pumps. By


these circulators in a controlled and predetermined manner.

ication of this product required five main steps: obtain project approval, replace the


btaining project approval was no small matter, for the Duke Faculty

dministrators take students tampering with the school’s property very seriously.

Figure 11 - Obtaining Project Approval

Meetings, request letters, and an on-site inspection were all required to get past this most crucial of

the actual replacement of the circulators. The first step was

all the water running through the pumps by turning two shut-off valves above and below their positions.

stopped, the old constant-speed circulators were removed by loosening several

ting both digital and

including the Taco pumps. By


steps: obtain project approval, replace the


Faculty and

site inspection were all required to get past this most crucial of

he circulators. The first step was to shut off

off valves above and below their positions.

removed by loosening several

The Taco 009-VV pumps were chos

installing them into the current system

the two new pumps where the previous ones were, tightening the

that was needed. Once the new circulators

Controller. Wires were run from the MEC’s outputs to the input connections on the Taco pumps.

Figure 13 - Connections on Taco Pump (left)

Once the pumps were installed and connected,

These sensors measure the temperature of a pipe’s outer wall. In doing this, a

of the inside water’s temperature may be obtained. The first step

the pipe, for this coating may interfere with heat transfer.

22

Figure 12 - Replacing Pumps

VV pumps were chosen because of their similarity to the preexisting ones. To this end,

installing them into the current system was quite easy. Simply reversing the previous process by placing

the two new pumps where the previous ones were, tightening the bolts, and opening the valves

circulators were installed, they had to be connected to the APOGEE

run from the MEC’s outputs to the input connections on the Taco pumps.

Connections on Taco Pump (left), Output Connection on APOGEE Controller (right)

were installed and connected, the pipe temperature sensors had to

These sensors measure the temperature of a pipe’s outer wall. In doing this, an accurate approximation

of the inside water’s temperature may be obtained. The first step was to sand away the outer coating of

y interfere with heat transfer.

en because of their similarity to the preexisting ones. To this end,

the previous process by placing

the valves was all

be connected to the APOGEE

run from the MEC’s outputs to the input connections on the Taco pumps.

Connection on APOGEE Controller (right)

had to be installed.

n accurate approximation

s to sand away the outer coating of

Next, to increase heat transfer, thermal compound

resided. Finally, the sensors were strapped to the pipe and connected to the Siemens APOGEE system.

The final step in the fabrication of this project wa

within the system.

Results and Analysis

Experimental Setup

After the installation of new circulators into the solar hot water system, it was necessary to setup

the system for testing. A successful system tests was accomplished by comparing the

the new variable speed solar hot water system to the constant speed one. The setup of the old system

could essentially be emulated by driving the pumps at 10V, or their full sp

system setup before and after the addition of the

Siemens APOGEE controller included in the layout. T

of the solar collectors, T2 is the temperature in the solar hot water tank, and T

temperatures of the outgoing and incoming pipe, respectively, from the collector.

23

Figure 14 - Installing Temperature Sensors

at transfer, thermal compound had to be placed on the spots where the sensors

strapped to the pipe and connected to the Siemens APOGEE system.

he fabrication of this project was to create the code that will govern the f


A successful system tests was accomplished by comparing the heat transfer of

new variable speed solar hot water system to the constant speed one. The setup of the old system

could essentially be emulated by driving the pumps at 10V, or their full speed. Figure 1

system setup before and after the addition of the new temperature sensors on the pipes, with the

controller included in the layout. T1 represents the temperature in the

is the temperature in the solar hot water tank, and T3 and T4 are the

temperatures of the outgoing and incoming pipe, respectively, from the collector.

be placed on the spots where the sensors

strapped to the pipe and connected to the Siemens APOGEE system.

will govern the flow of water


heat transfer of

new variable speed solar hot water system to the constant speed one. The setup of the old system

15 shows the

new temperature sensors on the pipes, with the

represents the temperature in the absorber plate

are the

24

Figure 15 – Schematic of changes to solar hot water system

The experimental process consisted of recording data via the Siemens APOGEE System. Table 2

shows the variables that were collected, and the description for each one.

Variables Description

VC39Test Test Status - Outputs a “1” if 10V constant mode is enabled, outputs a “0” for variable

“program” control

C39P01 Pump Status - Outputs a “1” if pumps are turned on, outputs a “0” if pumps are off

VC39DT01 Temperature Difference between pipes (T4-T3)

C39PZ01 Voltage speed signal sent to the pumps (4.3-10VDC)

VC39PZ01 Voltage desired by the program to run pumps at optimal speed (can exceed pump limits) Table 2 – Collected Experimental Variables and Descriptions

The primary concern with testing was to figure out a method for keeping as many conditions

constant as possible. Since it would be necessary to run the pumps for a period of time at constant

speed, and a period of time at variable speed, it was of the upmost importance to control for any

variations in weather or outside conditions that would vary the heat transfer rates. It was speculated

that since every half-hour interval of time throughout the day has relatively constant condition (in terms

of temperatures and light intensities), the pumps could be run by alternating between the constant 10V

mode, and variable “program” control every fifteen minutes. A separate variable, VC39Test, kept track

of which mode the pumps were being run in.

T4

T3

Output

s

Input

s

Pump

Output

sInput

s

T2

T1

Steca Controller

Siemens

Controller

Pump

Output

s

Input

s

T2

T1

Steca Controller

Programming the Pumps

The program for controlling the pumps was coded onto the Siemens

Siemens program, Insight. It was written in the

BASIC. A computer in the Smart Home clean lab was connected via Ethernet to the

and allowed full access to the system.

Figure 16

The first section of the code set

clock. This timer was used for testing purposes to alternate every 15 minutes between program control

and constant speed. The second section of code calculated the

two pipe temperature sensor inputs.

The third section of code was added to

been off for a while. This was instituted because the solar hot water system is a drain

it therefore takes a minute or two for water to flow continuously throughout the system when the

25

The program for controlling the pumps was coded onto the Siemens APOGEE Controller using the

Siemens program, Insight. It was written in the Powers Process Control Language, which is similar to

A computer in the Smart Home clean lab was connected via Ethernet to the APOGEE

and allowed full access to the system. Figure 16 shows the code of the program.

– Siemens APOGEE program code for controlling pumps

first section of the code set up a timer that counted in seconds, and was synchronized to a real

used for testing purposes to alternate every 15 minutes between program control

The second section of code calculated the ∆T variable between the pipes from the

two pipe temperature sensor inputs.

The third section of code was added to allow the pumps to come on at full speed after they have

stituted because the solar hot water system is a drain-


Controller using the

, which is similar to

APOGEE controller,

s synchronized to a real

used for testing purposes to alternate every 15 minutes between program control

∆T variable between the pipes from the

allow the pumps to come on at full speed after they have

-back system, and


26

pumps have been off for a period of time. It was desired to have full head when the system was initially

turned on, and because pump head is a function of rotor speed, the maximum speed was set on startup.

The fourth section of code alternates the pump control between a constant 10 V and variable speed

every fifteen minutes. The optimal voltage, as found earlier from the quantitative analysis (equation 6)

was governed by the following linear equation:

�� 5.49 � ∆�

Because the calculated optimal voltage can be higher than 10V, the upper limit for the pump speed

signal, and lower than 4.3V, the lower limit for which there is enough pressure to pump the water

through the system, additional code had to be written to prevent the pump speed signal from going out

of bounds. The last statement of the code sends the program back to the top, thereby allowing the

code to run in a continuous loop.

Results

The pertinent variables for the experiment were logged in Siemens APOGEE system. The computer

recorded values every minute in the APOGEE controller, and the data was logged to the Siemens

computer in the clean lab every three hours. The Insight program has a plotter module, which allows

collected data to be plotted vs. time. The results for the first four days are shown in figure 17, and

additional days are shown in Appendix V.

27

Figure 17 – Graphs of data collected for the first four days of testing (4/17 – 4/20). The blue line is the optimal voltage,

the red line is the actual voltage sent to the pump, the green line is ∆T, the purple line is the pump status, and the yellow line

is the test status.

The first two days of testing were very sunny days, as noted by the large parabolic shaped curves of

the blue and green lines. Since the green line represents ∆T, and ∆T is a function of Q, the heat transfer,

the height of the green line reflects the amount of heat transferred throughout the day. The second

two days of testing were partly cloudy. As seen in the data, during various portions of the day, the heat

transfer dropped substantially when the sun was behind the clouds.

MATLAB Analysis

From graphs of the data, it seems that our variable pumping method was much more valuable

during cloudy days. Throughout these days, the optimal voltage often dipped below the upper limit of

10V, and the pumps were able to run variably. For the sunny days, the only gains obtained from a

variable system are at the beginning and end of the days, when the sun intensity is lower. It can be seen

28

from the sunny days, however, that the solar hot water system would have benefitted from having

pumps with a maximum speed about two or three times faster than the pumps installed in the system.

The data was then exported into Microsoft Excel, where it was formatted properly for input into

programs for analysis. The first attempt to analyze the data was via MATLAB. Because the data in the

two different time intervals (constant and variable speed) needed to be compared against each other

directly, a program had to be written to perform the proper integration. To find the total heat transfer

for each day, the time intervals had to be separated for constant and variable speed, and then

integrated over time throughout the day. Dividing by the amount of time that each is active, the

average heat transfer rate for each method can be analyzed. Figure 18 shows the initial attempt at

coding in MATLAB.

Figure 18 – Initial MATLAB code written to analyze test data

29

JMP Analysis

While writing the MATLAB code, however, it was decided that a different program would be more

useful for analyzing the collected data. JMP, a statistical analysis program, was designed to organize and

analyze large amounts of easily. All 9,320 useable data points obtained over the course of a week were

tabulated in JMP. The results were quite encouraging. In general, the modified system performed

significantly better than the one originally installed. The average heat transfer for both standard and

modified systems for each of the days included in the study is presented below.

Date Standard

System (W)

Modified

System (W)

Difference (W)

4/19/2008 1345.46 1449.05 103.58

4/20/2008 1529.08 1879.10 350.02

4/21/2008 -672.22 -1141.89 -469.67

4/22/2008 -487.39 1103.58 1590.98

4/23/2008 911.95 1437.78 525.83

4/24/2008 2269.75 2563.35 293.60

2/25/2008 1226.01 1550.01 324.01 Table 3 - Heat Transfer Values for Given Date

As can be readily seen from the last column, in only one out of the 7 days tested did the original

system outperform our modifications. Looking at the values for April 21st brings an interesting point. In

order for the system to run properly, the program is set to run the pumps at 10 volts for approximately 3

minutes. This is necessary to allow the stagnant water in the outgoing pipe to move through the

system. Additionally, since the incoming pipe feeds water into a drainback tank, there will be a lower

temperature in this pipe while the system is off. When the system first starts, it takes a while for the

temperature sensor in the outgoing pipe to return to the temperature of the water. This explains why

there are negative values of ∆T, and therefore heat transfer. Weather conditions which would run the

system at short, intermittent periods throughout the day could lead to an overall heat transfer value

that is negative.

30

Looking at the individual days is beneficial, but taking the total values for the week provides a much

more adequate evaluation. Over the course of a week, the system is tested much more thoroughly, for

it is subjected to a wider assortment of environmental conditions. Furthermore, a larger amount of data

points leads to better statistical results. The averaged results over the entire week are presented below.

Date Standard

System (W)

Modified

System (W)

Difference (W)

Week 1164.29 1625.45 461.16

Table 4 - Averaged Weekly Heat Transfer

For the entire week, the modified variable speed system averaged an additional 461.16 W of heat

transfer when compared to the original. After running a significance test on the data, it is determined

that these results are statistically significant and not merely the results of random chance. The following

figures further analyze the data. Figure 19 provides a histogram showing the number of data points

falling within a given heat transfer distribution range.

Figure 19 - Histograms of Modified System (left), Original System (right)

Figure 20 plots heat transfer as a function of time and include a second degree polynomial fit to the

data. While the fit may be a poor predictor of heat transfer given the changing environmental

conditions, it does provide considerable insight into heat transfer trends.

31

Figure 20 - Plots of Heat Transfer vs. Time for Modified (left), Original (right)

Upon investigating the polynomial fits and their respective units, one can easily determine that the

heat transfer for the modified fit is greater at all points in time than that for the original fit.

Cost and Energy Savings

The final task in evaluating the effectiveness of the system modifications was to determine the

energy and money saved in a typical year. Using the new system, it was projected that 928.04 kilowatt

hours of electricity or natural gas will be saved during a typical year. The cost benefits of this increase in

efficiency are presented in table 5.

Energy Source Energy Saving

(KWh/yr)

Cost of Heating

Source* ($/KWh)

Heating Efficiency Cost Savings

($/yr)

Natural Gas 928.04 $0.04 80% $46.40

Electricity 928.04 $0.10 90% $103.12 Table 5 - Savings on Water Heating Costs for Gas and Electric Resistance Heaters (*Source: Colorado Renewable Energy

Society)

The modifications to the Home Depot Smart Home’s solar water heating system do indeed produce

tangible results. On a natural gas system such as that employed by the Smart Home, a homeowner

would save $46.40 per year. An electric customer would save $103.12 per year. The final question to

answer is whether these modifications are worth the cost involved. The additional costs involved in

switching to variable speed pumps and adding temperature sensors amounted to

This means the payback period for the natural

payback period for an electric customer is under five.

Energy Source Cost ($)

Natural Gas $445

Electricity $445

These payback periods are not unreasonable considering the expected life of the system is over 30

years. The variable speed modification to the Smart Home

valuable, tangible results.

Figure 21 – Payback of system modifications for life of system for different heating methods

-1000

-500

0

500

1000

1500

2000

2500

3000

0 5

Inv

est

me

nt

($)

Payback for Life of System

Eletric Resistance Heating

32

switching to variable speed pumps and adding temperature sensors amounted to approximately

This means the payback period for the natural gas-using Smart Home is just under ten years.

payback period for an electric customer is under five. This information is summarized in

Cost Savings

($/yr)

Cost of Heating

Source ($/KWh)

Payback

Period (yr)

$46.40 $0.04 9.59

$103.12 $0.10 4.32Table 6 - Payback Periods


years. The variable speed modification to the Smart Home solar hot water system does indeed prod

Payback of system modifications for life of system for different heating methods

10 15 20 25 30

Time (years)

Payback for Life of System

Eletric Resistance Heating Natural Gas Boiler

approximately $445.

using Smart Home is just under ten years. The

This information is summarized in table 6.

Payback

Period (yr)

9.59

4.32


solar hot water system does indeed produce

Payback of system modifications for life of system for different heating methods

30 35

Monte Carlo Simulation

As a part of designing for Six Sigma, Monte Carlo simulations

deterministic model is found, it can be run using randomly distributed input values. The corresponding

output yields a probabilistic analysis.

In the payback analysis above, it

during a typical year. This number was obtained from our experimental results. It can be assumed that

this value in actuality has a gaussian distribution. The standard deviation of this distribution was

estimated to be about 150 kilowatt hours.

cost savings per year can be calculated based on the distribution, and is displayed in the histogram in

figure 22.

Figure 22 – Histogram for cost savings per year for Monte Carlo

0

5

10

15

20

25

30

50 60 70

Fre

qu

en

cy

Histogram for Savings Per Year

33

As a part of designing for Six Sigma, Monte Carlo simulations can be extremely valuable. After a


output yields a probabilistic analysis.

it was projected that 928.04 kilowatt hours of energy

. This number was obtained from our experimental results. It can be assumed that


ilowatt hours. Using the deterministic model calculated above, the actual


Histogram for cost savings per year for Monte Carlo Simulation

80 90 100 110 120 130 140 150

Dollars Saved / Year

Histogram for Savings Per Year

can be extremely valuable. After a


energy will be saved

. This number was obtained from our experimental results. It can be assumed that


Using the deterministic model calculated above, the actual


150 More

34

CONCLUSIONS

Project Takeaways

The variable speed control program successfully increased the overall heat transfer of the solar

hot water system in the Duke Smart Home. Yearly payback was lower than expected, but nonetheless

did result in cost and energy savings. This system is particularly worthwhile if the back-up heating

system is an electrical resistance one. The payback for a system of this type is around four years. The

payback for a system with a natural gas backup system is around 10 years.

The system proved reliable and effective. The variable system is particularly advantageous on

cloudy days, where the program frequently runs the pumps at a lower speed. There is no energy loss to

using this system rather than the previous system. Therefore, given the additional savings that can be

achieved during cloudy weather, it is advantageous to choose a variable speed system over a constant

one.

Future Project Directions

The main way to improve the effectiveness of this system is to install pumps which are capable

of operating at a mass flow rate greater than the current pumps. There were many instances where the

program calculated the ideal voltage to be much higher than ten volts. If pumps allowing greater flow

rates were installed, much larger savings would be possible.

The main restriction for this application was that it required rearranging the pipes in the system for

the appropriate pumps to be installed. Therefore, this method is only feasible when installing a new

system rather than improving a previously-installed system.

35

A second improvement would be to control the system entirely with the Siemens APOGEE system

rather than with the Steca control as well. Since the Steca program was already programmed to turn

the pumps on and off, those signals remained as they were. However, if the system were built from

scratch, the signals from the temperature sensors could be sent to the Siemens system for overall

control. This would be ideal since the Siemens system is proven very reliable, and it is desirable to have

only one control for the system.

A third suggestion would be to analyze the power requirements of the pumps. Since pumps running

at a slower speed consume less electric power, there may also be energy savings in this area. For our

analysis, it was assumed that this energy savings would be negligible compared to heat energy gains

from running at variable speeds. However, a test to determine how much energy could be saved by

running the pumps at a lower speed could be valuable.

36

References

Cengel, Y. A. (2007). Heat and Mass Transfer: A Practical Approach (3rd Edition ed.). New York:

McGraw-Hill.

http://ezinearticles.com/?Booming-Green-Building-Market-Continues-to-Grow&id=179435

http://www.cres-energy.org/blogs/blogs_roedern06Jan.html

37

APPENDIX I

Product Design Specification

1.0 Product Title

1.1 Smart Home Variable Speed Water Pump for the Solar Hot Water System

2.0 Mission Statement

2.1 To retrofit and improve the Home Depot Smart Home’s Solar Water Heating system by

focusing on heating capability and efficiency

3.0 Customer Needs

3.1 Energy Conservation

3.2 Effective Water Heating

3.3 Reliability

4.0 New or Special Features

4.1 Variable speed water pump

4.2 Reprogramming of temperature thresholds

4.3 Additional sensors to accurately measure temperature change

4.4 Additional sensors to effectively measure power consumption

5.0 Competition

Competition is comprised of other hydronic system companies including:

5.1 MetLund D’MAND Systems – pumpless system

5.2 Laing Instant Hot Water Pumps – recirculation pumps

6.0 Intended Market

6.1 TACO – Hydronic Systems and Components company sells a variety of pumps and pump

accessories. TACO pump currently installed on solar hot water heater in the Smart Home.

6.2 Other hydronic systems companies

7.0 Relationship to Existing Product Line

Currently, TACO sells a variety of multi-purpose valves to ensure more reliable pump flow.

Products include:

7.1 shut-off valves

7.2 flow control valves

7.3 non-slam check valves

7.4 flow-metering valves

New products to be introduced applying specifically to solar hot water heating systems include:

7.5 Solar X-Pump Block – combines stainless steel flat plate heat exchanger, variable speed

mixing control, 2 bronze circulators, and solar differential temperature control

7.6 New circulators with integral temperature differential controls

38

Variable speed mixing control can be added to systems already in place that simply have single-

speed temperature differential control. Must be easily installed in current TACO system, be

consistent with sizing and materials for standard operation.

8.0 Market Demand

Variable speeds pumps offer a variety of components desirable for consumers:

8.1 Smoother water flow

8.2 More accurate temperature control

8.3 Uses less power – energy and cost savings

8.4 Less wear and tear on pump – longer lifespan

8.5 Quieter operation

9.0 Price

9.1 Current TACO circulator pumps range from $75 - $275

10.0 Functional Performance

10.1 Easily controllable

10.2 Easy to wire

10.3 Variable speed control

10.4 Voltage range of controller

10.5 Ability to analyze outside conditions for optimal heat transfer

10.6 Low power requirements

10.7 Pump can withstand temperatures up to 180F

11.0 Physical Requirements

11.1 Because the controller will probably be hidden, the physical requirements are not strict.

The controller must be UL approved, and fit into a compact box. Any outdoor sensors must also

be UL listed and waterproof.

12.0 Service Environment

12.1 Outdoor sensors will be exposed to the elements (corrosive environment, dirt and dust,

humidity)

12.2 Pump and controller will perform in a controlled environment with temperature

fluctuations between 50 and 80 F. Humidity will be controlled. Pump will need to handle fluid

temperatures up to about 180F.

13.0 Life-Cycle Issues

13.1 Should have a working life as long as the entire solar hot water product system, or be easily

replaceable or fixable during the life of the system

13.2 Eco-friendly materials should be recyclable and contain minimal heavy metals

14.0 Human Factors

14.1 One-time installation will be required.

14.2 The modified factors will require no additional maintenance compared to the fixed speed

pump.

14.3 Monitoring system will be required to ensure system is running at optimal conditions.

14.4 Aesthetics considerations are not relevant because the system will be installed in the

basement of the Smart Home.

39

15.0 Corporate Constraints

15.1 Convincing Residential Life and Housing Services that the Smart Home Variable Speed

Water Pump saves a significant amount of energy and therefore should be installed in the Smart

Home.

15.2 The Pratt School of Engineering must also approve the installation of the Variable Speed

Water Pump in the Smart Home.

16.0 Legal Requirements

16.1 Making sure the name “Smart Home” does not infringe on trademark rights

16.2 Verifying that the product does not violate patent laws on similar inventions

16.3 Investigate list of related patents

16.4 Making sure the product is UL listed for safety considerations

40

APPENDIX II

QFD

41

APPENDIX III

Gantt ChartSmart Home Variable Speed Water Pump

1/10/2008 1/17/2008 1/24/2008 1/31/2008 2/7/2008 2/14/2008 2/21/2008 2/28/2008 3/6/2008 3/13/2008 3/20/2008 3/27/2008 4/3/2008 4/10/2008 4/17/2008 4/24/2008

Conceptual Design

Preliminary Design

Product Design Specification

Schedule

Expert Meeting

Budget

Prototype Description

Order Parts

Detailed Design

Build Prototype

Obtain Approval for Installation

Test Prototype

Final Report

42

APPENDIX IV

Budget

Items Purchased Quantity Price Total

Price

TACO MODEL 009-VVBF5 VARIABLE SPEED SETPOINT CIRCULATOR

PUMPS

2 $ 476.00 $ 952.00

Mamac Systems TE-704-A-3 Pipe Temperature Sensors 2 $ 15.00 $ 30.00

Subtotal $ 982.00

Items Replaced

TACO MODEL 009-BF5 BRONZE CIRCULATOR PUMPS 2 $ 268.50 $ 537.00

Net Cost $ 445.00

43

Appendix V

Additional Charts

Figure 23 – Graphs of data collected for the last five days of testing (4/21 – 4/25). The blue line is the optimal voltage,

the red line is the actual voltage sent to the pump, the green line is ∆T, the purple line is the pump status, and the yellow line

is the test status.

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