performance improvement in air conditioning by using heat pipe

Performance Improvement In Air Conditioning By Using Heat Pipe PARAG SINGHAL

Assistant Professor Department of Mechanical Engineering, ABES Engineering College, Ghaziabad, Uttar Pradesh, India

Abstract — Heat pipe was developed by NASA for The Apollo Space program. The main factor for development of heat pipes is excellent thermal conductivity and no requirement of power for their operation. Using copper-based heat pipes, effective thermal conductivity of 1000 to 10,000 W/m-K have been achieved. This work aims to incorporate heat pipe into modern day air conditioning system in order to improve the performance parameters like humidity removal, cooling, tonnage required and hence, provide a better air conditioning system solution for both household and industrial applications. This report consists of design, calculations and comparison between a conventional air conditioning system and a system with heat pipe on the basis of humidity removal capacity at colder temperatures, along with an insight to the analysis of refrigerants which can possibly be used in such systems. A study has also been done in order to determine the compatibility of incorporation of heat pipes into existing systems.

Keywords-Heat Pipe, Air Conditioning, Heat Recovery, Humidification

1. INTRODUCTION 1.1 Heat Pipe- A heat pipe is used to transfer heat at faster rate from one location to another without using an external power supply. It is a closed tube, filled with working fluid referred as refrigerant. The refrigerant boils by absorbing heat tha from the warm return air such as in an air-conditioning system and gets vaporized inside the tube. The vapor then travels to the other end of the heat pipe, which is placed in the current of cold air that is produced by the air conditioner. The heat that was absorbed from the warm air at the low end is now transferred from the refrigerant's vapor through the pipe's wall into the cool supply air. This loss of heat causes the vapor inside the tube to condense back into a fluid. The condensed refrigerant the travels by gravity to the low end of the heat pipe where it begins the cycle all over again.

Fig.1.1A heat pipe structure

2. LITERATURE REVIEW

Nethaji (2017) showed the effect of Heat Pipe on performance Air Conditioning system. This experimental work clearly established that COP of the system improves by 20% and lower ADP also achieved , dehumidification capability increased by 30%. Latent heat recovered around 480 W.

Wei-Han Chen(2018) studied performance of air conditioning system incorporated by energy saving device. In optimum working condition system with energy saving device showed shell temperature of compressor lower by 150C , high side pressure and power consumption lower by 2.7% and 9.2%. Dehumidification capability and energy efficiency higher by 25% and 7%.

Yu.F. Maydanik studied the effect of ammonia heat pipe on flat disk shaped evaporator. Maximum heat load of 300 W at 800C evaporator temperature achieved in both favourable and horizontal position of heat pipe. Heat source temperature around 850C achieved in all testing condition.

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Vishal M. Bachhav1 reviewed the performance and characteristics of air conditioning system with Heat pipe. Clearly established improvement in COP and reduction in ADP of the system with heat pipe. Reduce energy requirement and improvement in dehumidification capability.

He Song(2016) investigated about using ammonia heat pipe with evaporator. Showed system could start successfully and work without oscillation in temperature under normal working condition. Thermal resistance and evaporator load capacity analyzed.

3. DESIGN 3.1 Theory

Heat pipes builds the proficiency of cooling framework by expanding dampness expulsion rate. In this air is pre-cooled by methods heat exchange from the warm approaching air to the cool gracefully air. This "bypassing" can be cultivated by putting the low finish of a heat pipe in the arrival air and the top of the line in the gracefully air. Heat is expelled from the warm upstream air and rerouted to the cool downstream air. This warmth, as a result, sidesteps the evaporator - despite the fact that the air that contained the warmth does for sure go through the A-C curl.

The aggregate sum of cooling required is somewhat diminished and a portion of the forced air system's reasonable

limit is hence traded for extra idle limit. Presently the unit can adapt to high-dampness air all the more effectively.

To achieve a heat move around a cooling curl through use of warmth pipe innovation, various setups might be utilized. One strategy is to organize a few warmth pipes in equal manages an account with the evaporator curl isolating the channels' evaporator finishes and condenser closes. Fins can also be used for the purpose of air cooling.

After a warmth pipe framework has been introduced, most sellers will utilize a vacuum siphon, empty the warmth channels to under 50 microns of air, at that point in part fill them with a working liquid, generally HCFC22. The channels at that point will be hermetically fixed and fastened to your cooling unit. It is significant that no administration valves be left on the channels.

A profoundly compelling aerial warmth exchanger has now been made. The outcome is that the climate control system's idle cooling limit has now been expanded. The air provided to the structure is drier than that gave by the climate control system alone. 3.2 Energy Saving Aspects of Dehumidifying Heat Pipes

The Cooling curl of a forced air system expels dampness from the air similarly that a cold glass "sweats". The colder the cooling curl, the more dampness it expels.

The present high effectiveness machines have a lot hotter curls as the loop is commonly bigger, and less vitality is

utilized to cool it, however they spare vitality to the detriment of not expelling as much dampness. The issue, as of not long ago, has been the means by which to run a cooling loop sufficiently cold to expel a lot of dampness, while not utilizing additional vitality to do as such.

The arrangement is found in dehumidifier heat pipes which "fold over" the cooling loop. One area of the warmth

pipe is situated in the arrival air and the other segment in the flexibly air. The cool gracefully air chills one area while the warm return air warms the other. Warmth is moved from the warm return air to the cool gracefully air. The warm as it is called, taken from the arrival air, is free. The impact of precooling the air heading off to the cooling curl brings it extremely near the dew point and dampness starts to gather from the get-go in the cooling loop. Since the loop doesn't need to play out the precooling capacity, a greater amount of its thickness is utilized to gather dampness and condensate stream is expanded by a factor of 1 ½ to 2. The outcome is lower relative mugginess. We additionally feel similarly good at a higher indoor regulator setting when the mugginess is decreased. One-degree higher setting speaks to around 8% energy saving in vitality. Ordinarily, 20% to 30% is possible..

Indoor air quality is improved, making a circumstance of upgraded comfort, more prominent wellbeing, end of shape and mold, and decrease of building crumbling .Energy savings through the use of heat pipes are achieved in the following ways:

By the elimination of reheat and the additional air conditioning load imposed by the reheat.

By setting the thermostat a few degrees higher to achieve the same comfort level due to lower relative humidity.

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3.3 Beneficial Effects Of Heat Pipe Exchangers In HVAC Systems • Removal of more moisture- Heat pipe exchanger removes moisture from air by means of passive precooling. Almost double moisture is removed in comparison to the case of system without heat pipe. • Control of mold growth in air ducts- Due to lower relative humidity in ducts, growth of mod is inhibited.

• Takes into account higher indoor regulator settings-By keeping up the correct moistness level, indoor regulators can be acclimated to a higher setting while at the same time looking after solace. This outcomes in energy saving of 10-30%.

• Allows for increment in chilled water temperature-By expanding dampness expulsion at the cooling loop,

chilled water temperature can be raised a few degrees while keeping up legitimate indoor states of temperature and mugginess. This builds the vitality effectiveness of the HVAC framework by decreasing chiller run time and additionally expanding the chiller dissipating temperature.

• Replaces heat framework- Heat-pipe heat-exchanger are used as an immediate substitution of electric, high temp water, steam or hot-gas sidestep warm frameworks. Since HPHX warm is latent, there is no working expense to deliver it. Since the warm is evacuated in the HPHX precooling step, there is no extra burden put on the blowers as there would be with some other type of warm. This results in capital cost savings and operating cost savings. Comfortable healthy indoor environment- By controlling humidity in the air ducts and conditioned space, heat-

pipe heat exchangers provide the following: 1. Longevity of books, records, building materials, and furniture. 2. Better operation of copy machines, computer printers, and other office equipment. 3. Economical addition of fresh air into buildings. 4. Assurance that the HVAC system can easily and economically adapt to higher latent loads. For example: increasing fresh air flow rate to meet the new ASHRAE standards for fresh air per person. 3.4 Schematic Representation

Fig.3.4.1 Schematic representation Fig.3.4.2 Temperature Profile of Air in Evaporator

3.5 Design Model

a) Condenser- Dimensions: 250x50x210cms, Pipe outer diameter: 7.2cms, Inner diameter: 6.4cms

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Fig.3.5.1 Condenser Model (AutoCAD)

b) Evaporator-

Fig.3.5.2Evaporator Model (Solidworks)

3.6 Design Calculations Most of the modern day air conditioning systems rely heavily on temperature reduction to increase their energy efficiency ratings[1]. The moisture removal is not paid enough attention and so, the latent heat removal capacities of such systems are compromised in colder temperatures. Humidity, though not being of primary importance in household systems, play a vital role in cold storage and food preservation industries, libraries and hospitals. The cooler regions are therefore in need of better humidity control systems. Researches were carried out extensively to solve this problem [3][1]. Application of heat pipes [4]showed promising results in the research conducted worldwide, doing the intended job in an efficient way [1]. So, an evaporator unit upgraded with a heat pipe assembly can solve this problem, since heat pipes need no external power source to operate. The objective of this project is to come up with a design of a heat pipe- incorporated evaporator, which could be used even in the existing systems. The moisture removal capacity and latent heat loads of both an existing conventional air conditioning system and the designed heat pipe incorporated system were calculated and compared, with a series of the settings. In order to show that heat pipe-based evaporator can solve the problem of low moisture removal, two ambient conditions were considered with different temperatures and humidity content of air and the performance of both the systems were determined using calculations. A study on the refrigerants that can be used in the evaporator was done to determine the best refrigerants on the basis of the work required for compression .Some of the most commonly used freons, as well as newer ones like ammonia and carbon dioxide were being compared to show contrast in operations. Measured values were compared with actual values in order to show that heat pipes could be infused with the already existing systems.

Calculations a) Conventional Air Conditioners without heat pipes

To determine the performance of conventional system, a 1-ton unit, with 100% outside air was studied. The bypass factor was kept zero for an ideal case comparison between the two systems. Unit mass flow rate of air was taken. Two cases of ambient were:

1. Th,i=32℃, ωi=20g/ kg of dry air (Colder and drier condition) 2. Th,i=38℃, ωi=28g/ kg of dry air (Hotter and humid condition) The air conditioning settings were taken from 18℃ to 25℃. The specific heat of moist air was calculated using:

Cp,m=1.005+1.82ωi

Temparature (℃) Humidity ratio (ωi)

16.5 0.0116

17.5 0.0124

18 0.013

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18.5 0.0132

19 0.0138

19.5 0.0143

20 0.0147

20.5 0.0154

21 0.0156

21.5 0.016

22 0.0166

22.5 0.0172

23 0.0179

23.5 0.0184

24 0.019

24.5 0.0195

25 0.02

Table 3.6: Humidity ratio at different temparatures Using this, the sensible load was calculated as follows:

SHL=maCp,m(Th,i- Th,o) The humidity of cooled air, ω0, was taken from the psychometric chart[i], and using that, the latent load was calculated: LHL=hT,ω(ωi- ω0) Total load came out as:

THL=SHL+LHL As a performance parameter, Room Sensible Heat Factor was calculated as:

RSHF=SHL/(SHL+LHL) (b) Using evaporator unit with heat pipes The value of SHL remained same as the temperature drop required was kept the same as before. The value of ambient humidity is not the humidity entering the evaporator and is denoted by ωi1. However, the air was precooled using heat pipes before entering the evaporator. 1kW of heat was made to be removed by heat pipes, and the temperature before entering evaporator was calculated as:

1kW=maCp,m(Th,i1- Th,i2) The value of SHL on evaporator remained same as the temperature drop required was kept the same as before. So, temperature at the other side of evaporator, Th,02, will be:

Th,i2- Th,02=Th,i- Th,o Hence, using these temperatures, humidity was evaluated using psychometric chart as ωi2 at temperature Th,i2and ω02 at temperature Th,02. The values of LHL and RSHF were calculated in the same previous way at the five settings and both the ambient conditions.

Graph.3.6: Representation of both processes on psychometric chart

Process AB: Conventional System, Process AA’B’C: System with Heat Pipes 3.7 Result The data obtained from both the cases were collected and tabulated to obtain a graphical representation of the

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results. Setting(℃) Moisture Removal RSHF R.E.

increase (kJ/kg) with

heat pipe without HP with HP without HP with

HP

18 0.007 0.0084 0.48 0.43 3.16 19 0.0062 0.0076 0.49 0.44 3.17

20 0.0052 0.0068 0.51 0.45 3.39

21 0.0044 0.0057 0.53 0.47 2.94

22 0.0034 0.0046 0.57 0.5 2.7 23 0.0021 0.004 0.66 0.51 4.2 24 0.001 0.0028 0.78 0.56 4.06 25 0 0.0016 1 0.67 3.6

Table 3.7.1: Results at 32℃, 0.020ωi

Setting (℃ ) Moisture Removal RSHF R.E. increase

(kJ/kg) with

heat pipe

without HP with HP without

HP

with HP

18 0.015 0.016 0.38 0.36 3.16 19 0.014 0.016 0.38 0.36 3.17 20 0.013 0.015 0.39 0.36 3.39

21 0.012 0.014 0.39 0.37 2.94 22 0.011 0.013 0.4 0.37 2.7 23 0.01 0.012 0.41 0.37 4.2 24 0.009 0.0108 0.42 0.37 4.06 25 0.008 0.0096 0.43 0.38 3.6

Table 3.7.2: Results at 38℃, 0.028ωi 3.8 Conclusion The increase in latent heat removal capacity of the two systems was calculated by subtracting the latent heat loads of the two systems. Hence, a graph was plotted showing the increase in refrigeration effect of the two systems at various setting temperatures.

Setting(℃) R.E. increase with heat pipe

18 3.16 19 3.17 20 3.39 21 2.94 22 2.7 23 4.2 24 4.06 25 3.6

Table 3.8: Increase in refrigeration effect with temperature

Ref

rige

rati

on

Eff

ect

Incr

ease

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Graph 3.8: Relationship between the increase in refrigeration effect and the setting temperature These charts gave the following results: 1) The moisture removal capacity of heat pipe-based evaporators is not only more than their conventional counterparts, but also, this difference is significant at lower ambient temperatures. 2) The increase in moisture removal capacity and the refrigeration increase was most significant at the setting of 200C. Hence, the comparison of the refrigerants was done at this optimal setting. 3) Discovered an abrupt peaking nature of refrigeration effectgraph at 22-23℃. Mathematically, this was due to the non-linearity of the psychometric chart. Further studies are required for determining this nature.

4. REFRIGERANT ANALYSIS

4.1 Work calculation Several refrigerants were compared on the basis of the work required to compress them. The setting temperature was 200C. The enthalpy was calculated from Mollierchart[7] of that refrigerant at the recommended suction and discharge pressures. The refrigeration effects were compared in both conventional and heat pipe incorporated systems, and hence, the variation in the compressor work was tabulated for each refrigerant. Taking mass flow rate of refrigerant as 0.8kg/s, refrigerant enthalpy change in both cases was determined by:

THL=mr(∆h)

Refrigerant Work required (kJ) Suction Pressure (bar) R-22 8 4.08 R-134a 6.8 2.58 R 717(Ammonia) 32 2.37 R 744(CO2) 7.4 26.18 R 507 5 2.5 R 410a 16 1.632 R407c 9 3.4 R 404a 5 1.632

Table 4.1: Work required to achieve the same refrigeration effect by different refrigerants

Graph 4.1: Comparison between refrigerants 4.2 P-h Diagram of Refrigerants

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Graph.4.2.1: R-22

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Graph.4.2.2: R134a

Graph.4.2.3: R507

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Graph.4.2.4: R507

5. INCORPORATION INTO CURRENT SYSTEMS AND COST ESTIMATION

5.1 Verification of evaporator surface areas In order test for the compatibility with current systems, the surface area of heat exchange in evaporator tubes were compared for a 1-ton AC. Measured value of the surface area was compared to the calculated surface required in case of heat pipe-based evaporator. LG L Prima was measured for the dimensions of the evaporator. Dimensions D, L and H was noted. Number of passes in evaporator was calculated as:

N=(H/D) Hence, the area of heat exchange came out to be:

A=πDLN This came out to be 0.51 sq. meters. To estimate the surface area required, LMTD method [ii] was used for an ambient of 32℃ and temperature setting of 20℃ for counter flow HX. A correction factor [11] was used for cross flow case. The temperature differences at the two ends were:

∆T1= Th,i2- Tc,o , ∆T2= Th,02- Tc,I

LMTD=(∆T1-∆T2)/ln(∆T1/∆T2) For 1-Ton, Q=3.51685kW. Using overall heat transfer equation:

Q=AU(LMTD)Cf Hence, the area came out to be 0.47 sq. meters. This result is close to the measured area. 22222211

223333

44

3R

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Fig.5.1.2: Bent Copper Pipes 5.2 Cost Analysis

Commodity Units Cost (INR)

Copper Pipes 10 (0.75m each) 2000

Evaporator,Condensor 1 Ton x1 7000

Pipe Bending 500

Sensors, Controllers, Display 2 each 800

Refrigerant R22, R134a 200-350/kg Misc. 500-1000

TOTAL 12000-13000

6. CONCLUSION

6.1 Inferred Conclusions- The project laid emphasis on the functioning benefits of heat pipe incorporation in evaporator and showed that the both the moisture removal and hence the refrigeration effect increased even when the ambient conditions were colder and drier. Increase of an average of 2 grams per kg of dry air per second of humidity removal and 3 kJ of Refrigeration Effect increase were noted. The heat pipe- based system showed better functioning at lower ambient. Also, since the heat pipes require no external power source, the effect can be achieved at lower power and tonnage than the conventional systems. Though this setup requires an initial capital, cost estimations and performance reviews worldwide [12] proved that the capital recovery duration is not only rather short (1-1.5 years) but also in long term saves energy and maintenance costs. Refrigerant analysis shows carbon dioxide as a viable refrigerant for ACs as freons are facing environmental regulations. The study of area calculation proved that not only is this system more efficient, but also that the already existing systems can be upgraded to work like this. 6.2 Current uses and future scopes- The kinds of businesses that can benefit the most from heat-pipe technology include libraries, restaurants, storage facilities and supermarkets -- any type of business that needs moisture-controlled air to preserve goods and products kept inside, to prevent the increased wear and tear associated with high humidity, or to increase occupant comfort. Any air-conditioning system that uses reheat, desiccants, or mechanical dehumidification is a good candidate for heat-pipe assistance. When reheat is used, the energy savings that can be accomplished through heat- pipe dehumidification assistance can be substantial. The percentage of energy savings may vary greatly from customer to customer due to a number of variables. Hence, to summarize:

Use of heat pipes in HVAC applications is very useful, especially in High Latent Load region This system is very useful for energy saving in buildings with low sensible load Below is the listing of some commercial applications for HPT Dehumidifier and heat recovery heat pipe system:

1. Office buildings 2. Museums 3. Supermarkets 4. Textile Manufacturers 5. Hospitals, etc.

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7. REFERENCES

[1] N. Nethaji, S. Tharves Mohideen, Energy conservation studies on a split airconditioner using loopheat pipes (2017). [2] Wei-Han Chen, Huai-En Mo, Tun-Ping Teng Performance improvement of a split air conditioner by using an energy Saving device (2018) [3] He Song, Liu Zhi-chun, Zhao Jing, Jiang Chi, Yang Jin-guo, Liu Wei Experimental study of an ammonia loop heat Pipe with a flat plate evaporator (2016). [4] Vishal M Bachhav , N.C. Ghuge A review on performance improvement of split air conditioning system using loop Heat pipe (2018) [5] “Thermodynamic and Transport Properties of Moist Air”-Z. K. Morvay, D. D. Gvozdenac, Applied Industrial Energy and Environmental Management Zoran K. Morvay and Dusan D. Gvozdenac © John Wiley & Sons, Ltd. [6] “Characteristics of Heat Transfer for Heat Pipe and Its Correlation”- AlokeMazumdar,MohammedChaudhary, Abul

Akon, Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh, March 2011. [7] P-h diagram, Refrigerant Handbook Appendix B, Swep International. [8] Properties of Ammonia, Ammonia Data Book, May 2008. [9] ” Commercial Carbon Dioxide Refrigeration Systems”-Emerson Climate Technologies. [10] “Correction factor for cross flow in LMTD”-Prof. Anandaroop Bhattacharya, IIT Kharagpur, Energy Conservation

and Waste Heat Recovery, September 2017 [11] “Optimizing 100% Outside Air Systems with Heat Pipes”- Dr. Michael West, Dr. Richard S. Combes, Melbourne Books: [12] “Efficient Humidity Control with Heat Pipes”- Roy Johannesen, Michael West, University Of Florida, December 1991. [13] “A Review on Heat Pipe for Air Conditioning Applications”- Nikhil S. Chougule, TusharS. Jadhav, Mandar M.Lele National Institute of Construction, Management and Research, Pune, India, March 2016. [14] “Recent Developments in Heat Pipes Technology”- SaffaRiffat ,Xiaoli Ma, University of Nottingham, UK. [15] “Research on Heat Recovery for Reducing the Energy Consumption of Dedicated Ventilation Systems”- LianZhang,YuFeng Zhang, Tiajin University, China, January 2016.

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performance improvement in air conditioning by using heat pipe

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