final report project a

A Study on The Predictability of an Air Conditioner

ME 406 – Experimental Design

Section 1

Austin Bonnes

November 18, 2016

Kenmore Model 580.72056 Air Conditioner

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Executive Summary:

This study looked to experimentally determine if it was viable to be able to use this air

conditioner, a Kenmore model 580.72056, for testing purposes with engineering students. The

goal was to determine if the performance could be predicted at measurable and not measurable

conditions. After gathering data and calculating the Coefficient of Performance (COP) and

Energy Efficient Ratio (EER) of the air conditioner, could be determined. If the results

predictable, concise, and accurate then this air conditioner can be used to test and train

engineering students

To determine the performance of the air conditioner for this study, the air conditioner was

mounted into a wall. The exhaust of the unit went into what is referred to as the controlled room

– that was filled with heaters. This room was to act as the outside heat sink for the air

conditioner, where the temperature could be controlled via the heaters. Thermocouples were used

to measure the temperature of the room, and were attached on every major component of the air

conditioner, as well as the unit’s air inlet and outlet. Additional data taken was the inlet and

outlet air flow velocities, areas, and temperatures, the barometric pressure in the room, and the

kilowatt hours consumed by the air conditioner. In order to determine the predictability of this air

conditioner, the air conditioner needed to be tested at different external heat sink temperatures.

Using the controlled room allowed the air conditioner to be tested at 3 varying temperature

ranges. Those rangers were between about 22°C and 50°C. The rangers were to look at the

effects of the outside temperature on the air conditioner when the outside (the controlled room)

was at around room temperature, in a transition temperature range above room temperature, and

in a hot temperature range that was above 40°C.

Using thermocouples attached to the components of the air conditioner, the temperatures of each

stage of the air conditioner were gathered. Next, using thermodynamics and the temperature of

the R-22 coolant in the air conditioner, the enthalpies were calculated across the condenser and

the evaporator. The differences in these enthalpies led to the cooling power (output) of the air

conditioner, and factoring the amount of energy the air conditioner consumed overall allowed us

to calculate the COP and EER.

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After comparing data from multiple trials, we concluded that - with the provided Kenmore air

conditioner - a general trend of the performance can be predicted, but predicting accurate and

precise data is unreliable. Thus, the use of the air conditioner for engineering students comes

down to if the students need to predict and calculate accurate and precise data for the

performance of the air conditioner. Ignoring the few outliers seen in the charts generated and

shown below, predictable results can be determined, though discretion is advised.

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Table of Contents:

Executive Summary: 1

Introduction 4

Background Literature 5

Theory 6

Experiment 8

Uncertainties 9

Results 10

Conclusion 12

Works Cited 13

Appendix A - Experimental Layout 14

Appendix B - Additional Data 16

Appendix C - Sample Calculations 18

Appendix D - Uncertainty Calculations 20

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Introduction Air conditioners, the most common consumer heat exchanger, are in approximately two-thirds of all

homes in the United States.1 All of these air conditioners cost American homeowners nearly $11 billion

each year, and account for approximately 5.2% of the nation's total power consumption in the process.

These units also release 100 million tons of carbon dioxide into the atmosphere each year.2 New research

must be done to maximize their efficiency to lower the power consumption and the emissions, especially

as the world shifts to a greener economy.

Prior research studies that have been done on air conditioners, and heat exchangers in general,

have focused on decreasing the volume and weight of the air conditioner itself. However, most

of this research does not factor in the external heat sink temperature, which can greatly determine

the transfer of heat between the hot and cold working fluids of the air conditioner. For future

reference, external temperature, external heat sink temperature, and outdoor temperature all refer

to the temperature of the controlled room being heated by the six small heaters. The larger lab

space was cooled by the air conditioner and averaged a steady 72°F.

The purpose behind this study was to determine how the external temperature of a building

affects the working capacity of the air conditioner. Understanding how air conditioners perform

under normal varying temperatures aid in current research, as well as contribute to increasing

future performance for both consumer and industrial purposes.

Dr. Sarma Pisupati, a professor working for the Department of Energy and Mineral Engineering,

says “Energy Efficient Ratio (EER) measures how efficiently a room air conditioner will operate

at a specific outdoor temperature,” and this will be the metric to compare and determine the use

of this air conditioner.3 Higher EER correlates to a more efficient system, with the accuracy of

the EER providing the ability to predict the performance of an air conditioner at varying

1 "Air Conditioning." Department of Energy. Accessed September 10, 2016. http://energy.go v/energysaver/air-conditioning.2 "U.S. Energy Information Administration - EIA - Independent Statistics and Analysis." How Much of U.S. Carbon Dioxide Emissions Are Associated with Electricity Generation? Accessed September 10, 2016. http://www.eia.gov/tools/faqs/faq.cfm?id=77.3 Dr. Pisupati, S. Air Conditioner Efficiency. EGEE 102: Energy Conservation and Environmental Protection. (n.d.). Retrieved from https://www.e-education.psu.edu/egee102/node/2106. September 12, 2016.

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temperatures. The information gathered was used to determine the heat load, the power required

to operate the air conditioner, and the coefficient of performance of the tested air conditioner as

the simulated environment increased in temperature. The experimental EER will be compared

with the EER provide by the manufacturer, which is calculated by exclusively looking at an

external temperature of 95°F. Depending on the outcome of the study, it will also be determined

if future mechanical engineering students should carry out similar experiments.

Background Literature For air conditioners, it is the industry standard to determine the EER in order to meet the

Department of Energy’s efficiency requirements.4 The EER value manufacturers put on their air

conditioners are based on one outside temperature, which is generally 95°F. Therefore, there is a

benefit to experimentally determine the EER at varying external temperatures to confirm what is

provided by the manufacturer. In doing so, the ability to predict the performance of the air

conditioner at different external temperature becomes possible. Experiments and reviews

covering air conditioners look at determining performance and efficiencies. The air conditioners

these research papers review varied in their applications, from use in manufacturing to steam

engines, with none found to cover the external heat sink temperature.

This experiment looked at an air conditioner for residential use and its performance at varying

external temperatures. Standards were used throughout this experiment to ensure accuracy,

precision, and repeatability. Temperature measurements were a critical part of this experiment,

and the standards for thermocouples explained the need to verify the relative accuracy of the

thermocouples. To test this accuracy, we validated the temperature of the thermocouples by

using another standalone temperature measuring source.

In the ASME Standards for Air Cooled Heat Exchangers, the standard said to measure air cooled

heat exchangers is by collecting temperature data every thirty seconds to account for

fluctuations.5 The standard also stated that air conditioners need be turned on and running for a

4 Arlan Burdick IBACOS, Inc. Strategy Guideline: Accurate Heating and Cooling Load Calculations. The United States Department of Energy. Building Technology Program. June 2011.5 ASME. PTC 30 - 1991 Air Cooled Heat Exchangers. (1991).

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period of three to five minute prior to collecting data, allowing the unit to reach a steady state

and avoid any temperature or power fluctuation. The last thing the standard required for properly

running an experiment on an air conditioner was to measure the air conditioner for at least one

hour to get steady data.

Much of the research performed on air conditioners look at determining the efficiencies dealing

with the type of heat exchanger and the type of fins the heat exchanger uses. Recent research

papers, like “A Novel “Partial Bypass” Concept to Augment the Performance of Air-Cooled

Heat Exchangers,” headed by Chi-Chung Wang, are good examples of how much of the recent

research has been around specific and important improvements.6 These different studies used

heat transfer theory and thermodynamics to analyze the changing of fins and other components

to the heat exchanger. Other research looks at new additions to the heat exchangers like new

compressors and new thermal conductive material and liquids. The purpose of our research was

to not look at improvements like many of the recent works on heat exchangers, but to understand

the performance of an air conditioner as the external temperature increased.

Theory

Air conditioners use two working fluids, in various flow and pass combinations, to transfer heat

from one fluid to the other. This experiment looked at the efficiency of the air conditioner by

measuring the inlet and outlet temperatures of the condenser and evaporator. In doing so, we

were able to determine the enthalpies at each stage of the heat transfer cycle and the

corresponding COP and EER.

6 Wang, C., Chen K., Liaw J. A Novel “Partial Bypass” Concept to Augment the Performance of Air-Cooled Heat Exchangers. Retrieved from International Journal of Heat and Mass Transfer website: http://www.elsevier.com/locat/ijhmt.(2012).

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Figure 1: Air conditioner cycle and T-s diagram7

We found the enthalpies at each stage of the heat transfer cycle by following the diagram

depicted in figure 1 above. The enthalpies were calculated by using the temperatures gathered

from thermocouples on the condenser and evaporator, and from the assumption that the R-22

refrigerant was a liquid during the entire process. Using the enthalpies, the work in (W in) and

heat in (Qin) could be determined with the COP of the air conditioner calculated by dividing Q in

by Win. The EER of this air conditioner could be determined by multiplying the COP by 3.41.

As the temperature in the controlled room changed, thermodynamics suggest that the coefficient

of performance would also change. As the controlled room increased in temperature, the air

conditioner would become less efficient in generating cool air to dump into the lab space. Since

the controlled room temperature, and therefore the enthalpy, was higher, the difference between

the enthalpy of the controlled room and the enthalpy supplied was smaller. This relationship, as

noted by Penoncello, should be linear and noticeable.8

7 Penoncello, S. G. (2015). Thermal energy systems: Design and analysis (1st ed.). Moscow, ID: CRC Press.8 Penoncello, S. G. (2015).

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Experiment

This experiment looked at determining the coefficient of performance for a horizontal room air

conditioner. We took the provided air conditioner, Kenmore 580.72056, and mounted it into the

wall of a small confined room. The air conditioner was positioned so that the exhaust would be

directed into the room with heating six small heaters. In the room were 20 thermocouples which

measured the temperature of the air in the room as well as the air conditioner’s condenser and

evaporator. Appendix A shows the setup of the room simulating the external environment, with

the location of each thermocouple and heater described in more detail.

Altering the total time, the experiment ran with different initial temperatures, temperature

measurements were taken every thirty seconds via an Agilent 34972A LXI Data Acquisition

/Switch Unit. The air conditioner was also allowed to warm up for five minutes before data

collection, removing any initial power fluctuations from the system and reaching a steady

operating state. Once the initial warm up was complete, the experiment was conducted in three

different ways, due to limited time available to run the experiment, with a total of 4 experimental

trials successfully carried out.

One way of collecting the data was with just the air conditioner running and the heaters turned

off inside the room simulating the external temperature. This was to see the performance of the

air conditioner when external temperature was similar to the set air conditioner temperature. For

the second method of data collection, the room simulating the external temperature was heated to

approximately 39°C before data collection began, with the heaters continuously running and the

air conditioner turned on. The third and final method consisted of allowing the air conditioner to

run for at least thirty minutes before turning on the heaters. For all of these methods, a fan was

used to circulate the air inside of the controlled room, with data collected for at least one hour.

As the air conditioner was running, the data logger collected the temperature readings from the

thermocouples arranged in the room. The kilowatt hours (kWh) used by the air conditioner were

measured by a P3 Kill A Watt, with measurements manually recorded every two minutes. This

data collection was done to see if any drastic changes in temperature would correlate to the rate

of power consumption.

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To meet standards and to determine the reliability, a HT-L13 dual temperature meter was used to

measure various thermocouple temperatures, determining the accuracy of each thermocouple and

its uncertainty.

Uncertainties

As the equipment used to collect data in this experiment was not perfect, each had uncertainties that

needed to be calculated. With these, more accurate results could be attained. The calculations for these

uncertainties are provided in Appendix D.

Device Error Bias (B) Random (P)

Thermocouples ± 0.5155ºC

P3 Kill A Watt Resolution 0.004417 kWh

Tektronix Resolution .002°C ± .912908 ºC

TotalsTemperature Uncertainty 1.05°C

Power Uncertainty 0.004417 kWh

Table 1: measurement uncertainties

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Results

After analyzing several days of data collection, we saw similar trends to those seen below in

figure 2. This trend was for each component of the air conditioner to gradually increase in

temperature until the heaters in the controlled room were turned on, at which point the

temperature increased more rapidly. Some of the data from these days were omitted due to

inconsistencies in this trend, such as the component temperatures oscillating back and forth.

Additional data can be found in appendix B.

Figure 3 below shows the temperatures of the R-22 refrigerant, which performed the cooling

work of the air conditioner. These temperatures described the internal cycle of the air

conditioner, and, in addition to the total work done in the system, were used to calculate the COP

and the EER. Appendix C gives a step by step process for each of these at given temperatures.

Figure 2: data compiled to determine enthalpies and work of cycle from September 15

Figures 3 and 4 show the relationship between EER and the room temperature. A trend can be

seen in figure 4, with an extreme outlier at 39°C. Likewise, figure 5 shows an upward trend with

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outliers at 26.6°C and 27.35°C. These figures indicate that the EER can - to an extent - be

predicted with respect to the external temperature, though additional information should be

gathered to make definite conclusions. Even with these fluctuations, the predicted EER can be

used to model the performance of the air conditioner.

Figure 3: Relationship of EER with respect to room temperature

Figure 4: Relationship of EER with respect to room temperature over smaller temperature range

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Conclusion

After analyzing our data, we found that you can predict the EER of an air conditioner based on

the external heat sink temperature. With the outliers seen in figures 3 and 4, however, caution

should be used when using this external temperature to predict the performance of the air

conditioner. As the EER increased from 11 to 14 BTU/W*h between 27.5 and 30°C, the

expected trend was for the EER to fluctuate around 14 BTU/W*h for hotter temperatures.

Instead, it plummeted to the lowest calculated value of 8.4 BTU/W*h at 39°C, before again

returning to 14 BTU/W*h. As the external temperature continued to increase past 45°C, the EER

began to follow a predictable downward trend.

Though we were able to determine the performance of the air conditioner, we do not recommend

this experiment to be carried out by future mechanical engineering students. There was a general

trend, but due to uncertainties and fluctuations in the data, the results are hard to accurately

predict. The method and process used in this study can be applied to experiments for students,

but they may require an air conditioner that is newer for the experiment to avoid fluctuations and

flawed data.

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Works Cited

[1] "Air Conditioning." Department of Energy. Accessed September 10, 2016. http://energy.go v/energysaver/air-conditioning.

[2] Arlan Burdick IBACOS, Inc. Strategy Guideline: Accurate Heating and Cooling Load Calculations. The United States Department of Energy. Building Technology Program. June 2011.

[3] ASME. PTC 30 - 1991 Air Cooled Heat Exchangers. (1991).

[4] Dr. Pisupati, S. Air Conditioner Efficiency. EGEE 102: Energy Conservation and Environmental Protection. (n.d.). Retrieved from https://www.e-education.psu.edu/egee102/node/2106. September 12, 2016.

[5] Khaled, M., Harambat, F., Peerhossaini, H. Analytical and empirical determination of thermal performance of louvered heat exchanger - Effects of air flow statistics (54). Retrieved from International Journal of Heat and Mass Transfer website: http://www.elsevier.com/loca t/ijhmt. (2010).

[6] Kim, A. Performance of an Air-to-Air Heat Exchanger and an Exhaust Air Heat Recovery Heat Pump. National Research Council Canada. Retrieved from http://web.mit.edu/par mstr/Public/NRCan/brn235.pdf 1). November 1, 1985.

[7] Penoncello, S. G. (2015). Thermal energy systems: Design and analysis (1st ed.). Moscow, ID: CRC Press.

[8] Sears, Roebuck and Co. Owner's Manual: Room Air Conditioner Model 58072056.

[9] Stinnes W.H., von Backstrom T.W. Effect of Cross-flow on the performance of air-cooled heat exchanger fans. Department of Mechanical Engineering, University of Stellenbosch, Private Bag X1, 7602 Matieland, South Africa. Pergamon. Applied Thermal Engineering 22. (2002).

[10] "U.S. Energy Information Administration - EIA - Independent Statistics and Analysis." How Much of U.S. Carbon Dioxide Emissions Are Associated with Electricity Generation? Accessed September 10, 2016. http://www.eia.gov/tools/faqs/faq.cfm?id=77.

[11] Wang, C., Chen K., Liaw J. A Novel “Partial Bypass” Concept to Augment the Performance of Air-Cooled Heat Exchangers. Retrieved from International Journal of Heat and Mass Transfer website: http://www.elsevier.com/locat/ijhmt.(2012).

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Appendix A - Experimental Layout

Figure 5: layout of the experiment

In this layout, the triangles represent thermocouples, the small boxes represent heaters, and the

largest box represents the air conditioner. While not to scale, this layout describes the

approximate location of each piece of equipment to the rest. Each numbered thermocouple is

defined in the table below.

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Thermocouple Thermocouple Location Data Logger Units

1 Evaporator R-22 Refrigerant Inlet Temperature T-Type

2 Evaporator R-22 Refrigerant Midpoint Temperature T-Type

3 Evaporator R-22 Refrigerant Outlet Temperature T-Type

4 Condenser R-22 Refrigerant Inlet Temperature T-Type

5 Condenser R-22 Refrigerant Midpoint Temperature T-Type

6 Condenser R-22 Refrigerant Outlet Temperature T-Type

7 Evaporator Air Inlet Temperature #1 T-Type

8 Evaporator Air Inlet Temperature #2 T-Type

9 Evaporator Air Outlet Temperature #1 T-Type




13 Condenser Air Inlet Temperature #1 T-Type

14 Condenser Air Inlet Temperature #2 T-Type

15 Condenser Air Outlet Temperature #1 T-Type




19 Control Room Air Temperature - North T-Type

20 Control Room Air Temperature - South T-Type

Table 2: numbered thermocouples

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Appendix B - Additional Data

The following data was not included in the results section as it did not show any new

information. This data was used in analysis, but for the sake of reducing redundancy it was put in

this appendix.



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Figure 8: T-s diagram of the R22 refrigerant

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Appendix C - Sample Calculations

Using temperatures of

we found the enthalpies of the air conditioner’s cycle by using Engineering Equation Solver,

which gave us values of

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Figure 9: air conditioner cycle showing enthalpy subscript locations

With these enthalpies, the work required for the compressor can be found from the difference

between points 1 and 2 on the diagram.

Similarly, heat load going into the cycle can be found

After determining the work and heat load of the system, the COP can be calculated

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Finally, once the COP is calculated, the EER is calculated by multiplying the COP by a constant

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Appendix D - Uncertainty Calculations

The expected error for a thermocouple is found by taking the difference of a reference

temperature and a thermocouple temperature, then dividing that quantity by two,

Averaging ten of these instances, the average temperature can be found

Comparing this average temperature to a reference temperature, the error for the thermocouple

can be calculated

The standard deviation for the Tektronix data logger is found by averaging the temperatures,

then squaring the difference between this average from each individual value. This summation is

dividing by the total number of samples before finally taking the square root of the entire

quantity.

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The total uncertainties for each unit of error is found by squaring both the bias and precision

errors, adding them together, and finally taking the square root.

Temperature was the only unit of error that had both bias and precision errors, and its calculation

is as follows.

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