comparative investigation of thermoelectric

Applied Thermal Engineering 24 (2004) 1979–1993www.elsevier.com/locate/apthermeng

Comparative investigation of thermoelectricair-conditioners versus vapour compression

and absorption air-conditioners

S.B. Riffat *, Guoquan Qiu

Institute of Sustainable Energy and Technology, School of the Built Environment,

The University of Nottingham, University Park, Nottingham NG7 2RD, UK

Received 23 November 2003; accepted 15 February 2004

Available online 13 May 2004

Abstract

This paper compares the performance of three types of domestic air-conditioners, namely the vapour

compression air-conditioner (VCAC), the absorption air-conditioner (AAC) and the thermoelectric air-conditioner (TEAC). The basic cycles of the three types of air-conditioning systems are described and

methods to calculate their coefficients of performance are presented. General specification data for each

type of air-conditioner are given, and performance characteristics are presented. The comparison shows

that although VCACs have the advantages of high COP and low purchase price, use of these systems will be

phased out due to their contribution to the greenhouse effect and depletion of the ozone layer. AACs are

generally bulky, complex and expensive but operate on thermal energy, so their operational consumption is

low. TEACs are environmental friendly, simple and reliable but still very expensive at present. Their low

COP is an additional factor limiting their application for domestic cooling. TEACs however, have a largepotential market as air-conditioners for small enclosures, such as cars and submarine cabins, where the

power consumption would be low, or safety and reliability would be important.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Air-conditioner; Vapour compression; Absorption; Thermoelectric; Coefficient of performance; Thermo-

dynamic cycle; Depreciation

* Corresponding author. Tel.: +44-0115-951-3158; fax: +44-0115-951-3159.

E-mail address: [email protected] (S.B. Riffat).

1359-4311/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.applthermaleng.2004.02.010

mail to: [email protected]

Nomenclature

COPir;c coefficient of performance of vapour compression in an actual irreversible coolingcycle

COPir;h coefficient of performance of vapour compression heat pump in an actual heatingcycle

COPR coefficient of performance of absorption refrigeration systemCOPR;rev coefficient of performance of absorption refrigeration system in a reversible cycleCOPc coefficient of performance of thermoelectric cooling systemCOPc;id coefficient of performance of ideal thermoelectric cooling systemCOPc;opt maximum coefficient of performance of ideal thermoelectric cooling systemCOPh;id coefficient of performance of ideal thermoelectric heating systemCOPh;opt maximum coefficient of performance of ideal thermoelectric heating systemCr thermal capacity ratio of hot/cold fluid through two heat sinks in a thermoelectric

systemK total thermal conductance of thermoelectric componentsQc cooling capacity in a thermoelectric cooling systemQh heating capacity in a thermoelectric heating systemQgen heat energy given to the generator in absorption refrigeration systemQL heat energy that evaporator absorbs from the cooled space, e.g., cooling capacityR total electrical resistance of thermoelectric componentsTa ambient temperature outside the condenser in cooling modeT 0a ambient temperature outside the evaporator in heating mode

Tc cold side temperature at ceramic plate location in a thermoelectric moduleTh hot side temperature at ceramic plate location in a thermoelectric moduleTm arithmetical average temperature of a thermocoupleTL temperature of the cooled spaceTs temperature of heat source that supplies heat to generatorTcin fluid inlet temperature in a cold-side heat sink of a thermoelectric systemTcout fluid outlet temperature in a cold-side heat sink of a thermoelectric systemThin fluid inlet temperature in a hot-side heat sink of a thermoelectric systemThout fluid outlet temperature in a hot-side heat sink of a thermoelectric systemTroom room air temperature outside the evaporatorT 0room room air temperature outside the condenser in heating mode

V electric voltage exerted on a thermoelectric cooling/heating deviceVn value of an air-conditioner after n years of operationW input electric energy in a thermoelectric cooling/heating systemWpump electric energy expended by liquid pump in absorption refrigeration systemZ figure of merit of thermocoupleapn Seebeck coefficientDT temperature difference of cold and hot side of thermoelectric componentsDTcond temperature difference between refrigerant in condenser and ambient temperature

1980 S.B. Riffat, G. Qiu / Applied Thermal Engineering 24 (2004) 1979–1993

DT 0cond temperature difference between refrigerant in condenser and indoor air temperature in

heating modeDTevap temperature difference between refrigerant in evaporator and indoor air temperatureDT 0

evap temperature difference between refrigerant in evaporator and outdoor ambient tem-perature in heating mode

S.B. Riffat, G. Qiu / Applied Thermal Engineering 24 (2004) 1979–1993 1981

1. Introduction

There are three main types of air-conditioning systems, each with their specific merits anddisadvantages. Vapour compression air-conditioners have a high COP and large cooling/heatingcapacities but their use of ozone-depleting CFCs and noisy operation, especially in the case of awindow-type air-conditioner, are significant disadvantages. A split-system central air-conditioner,which has an outdoor metal cabinet containing the condenser and compressor and an indoorcabinet containing the evaporator, may mitigate system noise, and use of new refrigerants, such asR134a to replace CFCs, may reduce damage to the ozone layer, but the COP of the system is alsoreduced when alternative refrigerants are used. Absorption air-conditioners have intermediatevalues of COP and the advantage of utilising waste heat or recovered heat, but these systems aregenerally bulky and heavy. Thermoelectric air-conditioners are portable and low noise, but haverelatively low COPs and are expensive. Furthermore, these systems operate using DC power, andso would need a DC power converter if powered by AC mains. However they could be powereddirectly by PV or fuel cells.

Bansal and Martin compared the three main types of refrigerators, i.e., vapour compression,absorption and thermoelectric [1], and provided test results for these. Air-conditioners, however,should have better performance than refrigerators as they require a smaller temperature differencethan refrigerators.

2. Thermodynamic cycles and principles of the three types of air-conditioners

Air conditioners employ the same operating principles and basic components as domesticrefrigerators but the temperature required in the evaporator for air-conditioners is higher thanthat needed for refrigerators. As a result, air conditioners should have higher COPs thanrefrigerators. The three main types of thermodynamic cycle for air-conditioning systems arediscussed in the following sections.

2.1. Vapour compression (VC) cycle

Vapour compression air-conditioners without a reversing valve work only as a cooler insummer, but most VC air-conditioners can work as a cooler and a heater all year round, as shownin Figs. 1 and 2, respectively. In the cooling cycle, the high-temperature and high-pressurerefrigerant (R134a) vapour comes from the compressor, then enters the condenser to reject heat tothe ambient environment, thus refrigerant vapour turns into liquid that is throttled in the

Compressor

Expansion valve

fan fan

Reversing valve

1

2

Indoor coilEvaporator

Outdoor coil Condenser

3

4

41

1 High-pressure vapour2 High-pressure liquid3 Low-pressure liquid-vapor4 Low-pressure vapor

AIR-CONDITIONER IN COOLING MODE

Fig. 1. Schematic of VC cooling cycle.

Compressor

Expansion valve

fan fan

Reversing valve

4

3

Indoor coilCondenser

Outdoor coil Evaporator

2

1

41

1 High-pressure vapour2 High-pressure liquid3 Low-pressure liquid-vapor4 Low-pressure vapor

AIR-CONDITIONER IN HEATING MODE

Fig. 2. Schematic of VC heating cycle.


expansion valve (capillary tube), reducing its temperature and pressure in the evaporator. Thelow-temperature and low-pressure liquid–vapour mixture in the evaporator absorbs the heat fromcooling the indoor air, then the outgoing low-pressure refrigerant is superheated to ensure noliquid remains before entering the compressor.

The actual irreversible Carnot cycle COPir;c for the VC device can be given as:

COPir;c ¼Troom � DTevap

ðTa � TroomÞ þ ðDTcond þ DTevapÞð1Þ

Obviously, the real irreversible COPir is always less than the ideal Carnot cycle COPcarnot for thesame thermal source temperatures, and decreases with increasing DTevap and DTcond. From Eq. (1),the impact on COPir of DTevap is greater than that of DTcond, so the decrease of DTevap is significant.For normal operation of air-conditioners, the outlet air temperature is generally required to belower than the inlet air temperature in the evaporator by at least 8 �C, i.e., the DTevap will be largerthan 8 �C or more. With regard to the condenser, the ambient temperature is generally requiredto be less than 43 �C, so the cooling device operates efficiently.

In the heating mode, as shown in Fig. 2, the indoor evaporator shown in Fig. 1 is converted intoa condenser, and the outdoor condenser into an evaporator, by means of a reversing valve. Thedevice becomes a heat pump which transfers heat from the outdoor ambient air to the indoor air.


In order to make the heat pump work efficiently, the ambient temperature is generally required tobe higher than )5 �C. The COPir;h of the heat pump may be given as:

COPir;h ¼ 1þT 0a � DT 0

evap

ðT 0room � T 0

aÞ þ ðDT 0cond þ DT 0

evapÞð2Þ

2.2. Absorption refrigeration cycle

The vapour-compression cycle is described as a work-operated cycle because the elevation ofpressure of the vapour refrigerant is accomplished by a compressor that requires work. However,the absorption cycle is referred to as a heat-operated cycle because most of the operating cost isassociated with providing the heat that drives off the refrigerant vapour from the high-pressureliquid in the generator. The heat input may come from the combustion of oil, gas, natural gas,geothermal energy, solar energy or industrial waste heat. Indeed, there is a requirement for somework in the absorption cycle to drive the pump, but the amount of work required for a givenquantity of refrigeration is minor compared with that needed in the vapour-compression cycle.

The basic absorption cycle is shown in Fig. 3. The dotted-frame assembly with absorber andgenerator can be regarded as a thermal compressor, so the absorption cycle is similar to thevapour-compression cycle. For air-conditioning, the working pair is usually LiBr–water solution

Fig. 3. Absorption system with heat exchanger.


(water as the refrigerant, LiBr as the absorbent). The thermal compressor elevates the pressureof water vapour from the evaporator and provides the high-pressure water vapour to thecondenser by means of absorber and generator (one major advantage of the absorption cyclecompared to the vapour-compression cycle is the much lower work required to compress liquidrather than compress vapour). Low-pressure water vapour from the evaporator is absorbed bythe concentrated LiBr–water solution in the absorber. If this absorption process were executedadiabatically, the temperature of the solution would rise and eventually the absorption ofwater vapour would cease. To perpetuate the absorption process, the absorber is cooled by wateror air and ultimately rejects this heat to the atmosphere. The pump receives the diluted low-pressure solution from the absorber, elevates its pressure, and delivers it to the generator. In thegenerator, heat from a high-temperature source drives off the water vapour that has been ab-sorbed by the solution. The concentrated solution returns to the absorber through a throttlingvalve whose purpose is to provide a pressure drop to maintain the pressure difference between thegenerator and absorber. The heat-exchanger between the absorber and generator improves theperformance of the cycle. To summarise, the pattern of heat flow to and from the four compo-nents in the absorption cycle is: High-temperature heat enters the generator while low-tempera-ture heat from the air being cooled enters the evaporator; heat rejection from the cycle occursat the absorber and condenser through the circuited water or air and this is released to theatmosphere.

The COP of absorption refrigeration systems is defined as:

COPR ¼ Desired output

Required input¼ QL

Qgen þWpump

� QL

Qgen

ðWpump � QgenÞ ð3Þ

The maximum COP of an absorption refrigeration system is determined by assuming that theentire cycle is totally reversible, i.e., the heat from the source ðQgenÞ were transferred to a Carnotheat engine and the work output of this heat engine ðW ¼ gth;CQgenÞ is supplied to a Carnotrefrigerator to remove heat from the cooled space. Note that QL ¼ W COPR;C ¼ gth;CQgen COPR;C. Thus the overall COP of an absorption refrigeration system under reversible conditionsbecomes:

COPR;rev ¼QL

Qgen

¼ gth;C COPR;C ¼ 1

�� Ta

Ts

�TL

Ta � TL

� �¼ TLðTs � TaÞ

TsðTa � TLÞð4Þ

where Ta, TL and Ts are the temperatures of the atmosphere, cooled space and heat source,respectively. Several trends are detectable from Eq. (4), namely, as Ta increases, the COP de-creases; as TL increases, the COP increases; as Ts increases, the COP increases. Actual absorptionCOP is generally less than half that of an ideal reversible refrigeration cycle.

In certain respects, applying the term COP to the absorption system is unfortunate because thevalue is appreciably lower than that of the vapour-compression cycle (e.g., 0.7 versus 2.8). Thecomparatively low value of COP of absorption cycles should not be prejudice judgement ofthe absorption system, due to the different definitions of COP in the two cycles. Energy in theform of work is normally much more expensive than energy in the form of heat. In addition, useof coal gas in the summer can trade-off the peak of electricity consumption due to the use ofVCACs. Solar energy and industrial waste heat are abundantly available source of energy that


would otherwise be wasted. However, absorption refrigeration systems are generally bulky,complex and, of course, expensive in terms of initial investment. Their refrigeration capacity isgenerally tens of hundreds, even thousands of kilowatts, so they are commonly used in industrialapplications and recently in domestic central air-conditioners.

The absorption cycle is not used in heating mode. The heat supplying to the generator can beapplied directly for heating.

2.3. Thermoelectric (TE) cycle

When two dissimilar metals or semiconductors are connected and the two junctions held atdifferent temperatures, there are five phenomena taking place simultaneously [2]. These are theJoule effect, the Fourier effect, the Seebeck effect, the Peltier effect and the Thomson effect. All ofthese are irreversible phenomena. The Peltier effect is of greatest interest for air-conditioning. In acircuit containing two junctions between dissimilar conductors or semiconductors, heat may betransferred from one junction to the other by applying a DC source. Semiconductors, such asBi2Te3, are better than metals for producing the Peltier effect. Thermoelectric coolers (Peltierdevices) utilize semiconductor Peltier effects, and Fig. 4 shows the principle of thermoelectriccooling. The heat from the cooled space is transferred through n- and p-type semiconductorthermoelements to the hot-side heat sink which rejects the heat to the environment. If thedirection of the electric current is reversed, the direction of the heat flow through the semicon-ductor materials is also reversed. The cooled space is turned into a heated space, i.e., the air-conditioning system operates in the heating mode.

Fig. 4. Schematic of the thermoelectric air-conditioner.


In the cooling mode, the cooling capacity Qc ¼ ðmcpÞcðTcout � TcinÞ, the dissipated heat in thehot-side heat sink Qh ¼ ðmcpÞhðThout � ThinÞ, the input electric power W ¼ Qh � Qc, and thecooling COPc and the heating COPh may be expressed by Eqs. (5) and (6).

COPc ¼Qc

W¼ 1

Thout�ThinTcout�Tcin

Cr � 1ð5Þ

where

Cr ¼ðmcpÞhðmcpÞc

is heat capacity ratio: In the heating mode; COPh ¼Qh

W¼ 1þ COPc ð6Þ

A conventional thermoelectric air-conditioner (heat pump) usually consists of a large numberof n- and p-type bulk semiconductor thermoelements connected electrically in series by copperstrips and sandwiched between two electrically insulating, but thermally conducting ceramicplates, as shown in Fig. 4. If some parameters of thermoelectric thermoelements are available,the ideal COPc may be expressed as:

COPc;id ¼Qc

W¼

apnTc � KRDTV � 1

2V

V þ apnDTð7Þ

In the heating (heat pump) mode, the COPh can be expressed as:

COPh;id ¼Qh

W¼

apnTh � KRDTVR

þ 12V

V þ apnDTð8Þ

where apn is the Seebeck coefficient, V/K; R is the electrical resistance, X; K is thermal conduc-tance, W/K; V is electrical voltage as shown in Fig. 4; DT ¼ Th � Tc is temperature difference ofcold and hot side of thermoelements, K; Th and Tc is hot side and cold side temperature at theceramic plate locations, respectively.

By solvingoðCOPc;idÞ

oV ¼ 0, we can obtain the maximum COPc;id, i.e., COPc;opt, its correspondingwork voltage VR;opt or work current Iopt are as follows, respectively [3],

Vopt ¼apnDTffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1þ ZTmp

� 1ðVÞ ð9Þ

Iopt ¼VoptR

¼ apnDT=Rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ ZTm

p� 1

ðAÞ ð10Þ

COPc;opt ¼Tc

ðTh � TcÞ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ ZTm

p� Th

Tc

� �ð


pþ 1Þ

ð11Þ

where the arithmetical average temperature of the thermocouple is:

Tm ¼ 1

2ðTh þ TcÞ ðKÞ ð12Þ


The figure of merit of thermocouple Z

Z ¼ ðap � anÞ2

ðKRÞmin

¼a2pn

ðKRÞmin

ð1=KÞ ð13Þ

Z is a comprehensive parameter which describes the thermoelectric characteristics; its value relatesonly to the physical properties of thermocouple material. The greater the figure of merit Z, thebetter the thermoelectric material.

Using the same approach as previously, the optimum coefficient of performance of heatingCOPh;opt can be expressed as:

COPh;opt ¼Th

Th � Tc1

�� 2


p� 1

ZTm

�ð14Þ

For example 1, if Z ¼ 3 10�3 (1/K), Tc ¼ 290 K(17 �C), Th ¼ 310 K(37 �C), from Eq. (11), thenCOPc;opt � 1:89, from Eq. (14), COPh;opt ¼ 2.47. However, under the same temperature condition,the COP of Carnot circulation COPc;carnot ¼ 14:5, COPh;carnot ¼ 15:5. The efficiency of optimumthermoelectric cooling is COPc;opt/COPc;carnot ¼ 13%, COPh;opt/COPh;carnot ¼ 16%.

Thermoelectric air-conditioners have many advantages, such as being completely CFC free,simplicity, being convenient to use, lightweight, high reliability, silent operation, fast start-up andeasy control. Furthermore, their operating temperature range is very wide ()40 to 70 �C) and theycan be powered directly by a PV or fuel cell source. Their main drawbacks are low COPs and highcapital cost.

3. Performance contrast

On the basis of performance and cost, the vapour-compression type of air conditioner is the best.However, these units are not environmental friendly if conventional refrigerants are employed andfuture legislation will restrict their use. Absorption units employ low-level thermal energy andcontribute to energy-saving but are bulky and expensive. Thermoelectric systems are simpleand convenient but have low COPs and are also expensive. Table 1 presents a general contrast ofthe three types of air-conditioners. Table 2 shows specific data for the three types of air-condi-tioners. The compression-based split-system air-conditioner is familiar to us all. An absorption-based, domestic gas air-conditioner, BCT16, has a large cooling/heating capacity of 16 kW butsimultaneously a large volume and weight, as shown in Fig. 5. A typical thermoelectric air-cooledair-conditioner, MAA1200E-115 has a small cooling/heating capacity and simultaneously a smallvolume and is lightweight, as shown in Fig. 6. Its COP may be calculated from Fig. 7.

4. Economic analysis

An economic analysis is a vital part of any comparison, and can strongly influence final choice.All appliances will have a limited life expectancy. Depreciation can be caused by wear and tear,

technical or commercial obsolescence. Depreciation is commonly calculated by one of two

Table 1

General contrast of the three types of domestic air-conditioners

Type VCAC AAC (single effect) TEAC

Cooling Cooling capacity, W 2500–4500 15–2· 104 KW 15–560a

Input electric power, W 750–1670 1.8–54 KW 36–1495

COPc 2.6–3.0 0.6–0.7b 0.38–0.45c

Work permit temperature

range, �C18–45 N/A 0–70

Heating Heating capacity, kW 2–8 58–4.4· 103 KW N/A

Input electric power, W 750–2900 N/A N/A

COPh 2.6–3.0 0.86–0.92b N/A


range, �C)5 to 18 Any environmental

temperature

Any environmental

temperature

Noise, Db 35–48 Indoor N/A N/A

Size Medium Big Small

Life expectancy, years 10–12 �15 �23

Price Low High Higha Theoretically speaking, the cooling/heating capacity of a thermoelectric air-conditioner can be designed for an

arbitrary range, but the current commercial products have only 15–560 W of cooling capacities [6–8].b For a double-effect LiBr absorption system, cooling COPs range from 0.9 to 1.2 [4]. For gas-fired absorption air-

conditioner system, cooling COPs range from 1.02 to 1.21, heating COPs range from 0.86 to 0.92 [5].c The calculations of cooling COPs depend on an 8 �C temperature difference of fluid through the cold sink.


methods, i.e., the prime cost or the diminishing value (DV) method. The prime cost methodallocates an equal amount of depreciation to each full accounting period over the effective life ofthe appliance. The DV method allocates a decreasing amount of depreciation in each fullaccounting period over the effective life of the asset. Accordingly, higher deductions are availablein the early part of the asset’s life based on the rationale that an asset delivers better services in theearlier rather than later years of its life. Depreciation rates based on the DV method are 1.5 timesthat of the prime cost method. Air-conditioning systems are in frequent operation and need to bewell maintained. The DV method is therefore more appropriate to the economic analysis of airconditioning systems. Annual depreciation is modelled to apply a DV method where the value ofthe air-conditioner (Vn) after n years of operation is evaluated as:

Vn ¼ Initial cost ð1�DV factorÞn ð15Þ

where n is the year of operation and the DV factor is dependent on the life expectancy of the air-conditioner. With regard to the life expectancy of an air-conditioner, of 10, 15 and 20 years, theDV factor was chosen to be 15%, 10% and 7.5%, respectively.

Operating costs include only power consumption, as maintenance costs are not considered inthis paper. The electricity price was adopted from UK Npower (2003) to be 11.27 pence/unit, andgas price was assumed to be 2.28 pence/unit (one unit is 1 kW of electricity or gas used for 1 h,kWh). As:

Annual operation cost ¼ Annual power consumption electricity price ð16Þ

Table 2

Data for the three types of domestic air-conditioners

Type VCAC Hitachi

KFR-26 GWa

AAC BCT16 TEAC

MAA1200E-115

Cooling Cooling capacity, W 2600 2667 (one room)b 320

Input electric power, W 880 1000 840

COPc 2.95 1.01 0.38c


range, �C18–45 650 670

Heating Heating capacity, W 3000 4100 (one room)b 1159

Input electric power, W 1000 400 840

COPh 3.0 0.88 1.38


range, �C)5 to 18 Any environmental

temperature

Any environmental

Temperature

Noise (indoor/outdoor), Db 39/49 (23)35)/62 30

Size (mm3) 815 · 298 · 194(indoor)

950 · 510 · 256(indoor)

470 · 302· 216

820 · 520 · 220(outdoor)

1818 · 1100 · 550(outdoor)

1818 · 660 · 550(outdoor)

Weight (indoor/outdoor), kg 8/33 22/420 19.5

Life expec-

tancy, years

�11 �15 �23

Equipment cost, £ 318 ($500) 424 ($667)

(one room)

880 ($1385)

aA vapour compression split-system air-conditioner is considered, a window-type air-conditioner has greater noise

but lower cost.b Total cooling capacity 16 kW and heating capacity 16 kW for BCT16 [5], required natural gas 1.5 m3/h for

cooling and 1.8 m3/h for heating. It is assumed to cool/heat 6 rooms. Natural gas combustion value is

8500 Kcal/m3.c The determination of cooling COP depends on an 8 �C temperature difference of fluid through the cold sink.


The annual total cost can be expressed as:

Annual total cost ¼ Annual depreciationþ annual operation cost

þ annual maintenance cost ð17Þ
For the convenience of comparison, several assumptions were made in calculating the costs
as follows:

(1) Salvage value is zero.(2) Life expectancy came from the manufacturer’s estimate.(3) Air-conditioner operated every year for 100 days cooling in summer and 100 days heating

in winter, with 12 h operation per day.(4) For the absorption air-conditioner, take one room for comparison.

Fig. 5. A typical absorption-based domestic gas air-conditioner.


Table 3 and Fig. 8 show that the VCAC system is the cheapest purchase option and TEAC isthe most expensive, but the VCAC has the disadvantages of being non-environmental friendly if

Fig. 6. A typical Melcor thermoelectric air-cooled air-conditioner.

Fig. 7. MAA1200E-115 performance curves.


CFCs or HCFCs are employed and also high consumption of electricity. Although the AACsystem is expensive in terms of its equipment due to its bulk and complexity, it can operate mainlyon low-level energy sources, such as gas, oil, or LNG, all of which are much cheaper than elec-tricity. The TEAC system is expensive due to its low COP and production initialization, but it iscompletely environmental friendly, reliable and has a long operational life.

5. Conclusions

(1) The cooling/heating capacity of a domestic VCAC is much lower than that of a domesticcentral AAC, but much more than that of TEAC.

(2) AAC is a heat-operated cycle and consumes only a small amount of electricity to drive pumpsand fans. VCAC and TEAC system, however, use a larger amount of electricity, so the oper-ation cost of an AAC is lower than that of VCAC and TEAC.

Table 3

Economic analysis of the three types of air-conditioners

Comparative items AC types

VCAC Hitachi

KFR-26 GW

AAC BCT16 TEAC

MAA1200E-115

Cooling electric input (W) 880 1000 840

Cooling electric energy consumption (kWh)/year 1056 1200 1008

Heating electric input (W) 1000 400 840

Heating electric energy consumption (kWh)/year 1200 480 1008

Total electric energy consumption every year (kWh) 2256 1680 2016

Total heat consumption every year No 3960 m3 gas, e.g.,

39,083 kWha

No

Total energy consumption for 11 years (kWh) 24,816 18,480 (electric)

429,913 kWh

(gas)b

22,176

Total operation costs (£) for 11 years 2797 2083+ 891¼ 2974 2499

496 (one room)c

Value of air-conditioner after 11 years of operation £ 53 140d (one room) 373aCooling: 1.5· 12· 100¼ 1800 m3/year, heating: 1.8· 12 · 100¼ 2160 m3/year, total heat energy is (1800+ 2160) ·

8500· 4.18/3600¼ 39,083 kWh/year. Gas cost each year is 891£.b The absorption air-conditioner expended electric energy and gas within 11 years.cWhole absorption air-conditioner expended electric cost £2083 and gas cost £891 within 11 years. On an average for

one room, its cost is £496.d For one room, V11 ¼ 445 ð1� 0:10Þ11 ¼ 140 (£).

VCAC

1000

1500

2000

2500

3000

£ 318 445880

496

AAC TEAC

Total operation cost for 11yearsPurchase price

3500

2499

2797

Fig. 8. Comparison of purchase price and 11 years operation costs of the three air-conditioners.


(3) VCAC is the most efficient with an actual COP of 2.6–3.0. This is followed by AAC with aCOP of 0.6–0.7 (single effect absorption) and TEAC with a COP of 0.38–0.45.


(4) Indoor noise levels are approximately the same (except the window-type VCAC) because ofsole indoor noise produced by fan or blower, but outdoor noises are different. The compressorof a VCAC or liquid pumps of an AAC are large noise sources, but TEAC has only fan orblower unless a water-cooled heat sink is used with a pump.

(5) With regard to the sum of the purchasing and operating costs over a same period, AAC hasthe lowest cost and TEAC is the highest cost.

(6) The three types of air-conditioning systems have their respective merits and disadvantages.Thermoelectric air-conditioners have been widely applied in low cooling capacity cases andhave the advantage of being powered directly by DC electric sources, such as PV cells, fuelcells and car DC electric sources.

References

[1] P.K. Bansal, A. Martin, Comparative study of vapour compression, thermoelectric and absorption refrigerators,

Int. J. Energy Res. 24 (2000) 93–107.

[2] M.W. Zemansky, R.H. Dittman, Heat and Thermodynamics, sixth ed., McGraw-Hill Book Company, 1981, pp.

431–442.

[3] D.M. Rowe, CRC Handbook of Thermoelectrics, CRC Press, Inc, London, 1995, p. 23.

[4] C.B. Dorgan, S.P. Leight, C.E. Dorgan, Application Guide for Absorption Cooling/Refrigeration Using Recovered

Heat, ASHRAE, Inc, 1995.

[5] Available from <http://www.broad.com/index-eng.htm>.

[6] Available from <http://www.melcor.com>.

[7] Available from <http://www.electrografics.com>.

[8] Available from <http://www.thermoelectric.com>.

http://www.broad.com/index-eng.htm

http://www.melcor.com

http://www.electrografics.com

http://www.thermoelectric.com

comparative investigation of thermoelectric

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