79248311 Thermo Economic Analysis of Solar Powered Adsoption Heat Pump

7/31/2019 79248311 Thermo Economic Analysis of Solar Powered Adsoption Heat Pump

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Thermo-economic analysis of solar powered adsorption heat pump

Michael A. Lambert *, Asfaw Beyene

Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1323, United States

Received 19 January 2006; accepted 31 March 2006Available online 6 December 2006

Abstract

The economic feasibility of the residential solar thermal (ST) cooling system designed in the companion article [1] is ascertained bycomparing it with a solar electric (SE) cooling system, and also with the baseline (i.e., control case), a grid dependent, highest efficiencyCOPC = 5.66 heat pump. The economic scenario is analyzed for 24 cities across the southern USA, south of the 37N. The SE coolingsystem provides lifecycle (20 year) savings to the homeowner only where electric rates are high and it is heavily subsidized. The overallsocietal effect (sum of taxpayer funded rebate and homeowner savings) is actually an increased cost everywhere except the CaliforniaCentral Valley, where the net savings is $1500. In the same valley, The ST cooling system provides greater lifecycle savings to the home-owner with more modest subsidies, and the overall societal effect is a benefit, a savings of $3600. The far and away best location for a STsystem is Hawaii, where it affords homeowner savings of $9900 and societal savings of $7600. 2006 Elsevier Ltd. All rights reserved.

Keywords: Adsorption heat pump; Solar cooling; Thermo-economic analysis

1. Thermal modeling

The economic feasibility of the residential solar thermalcooling system [evacuated flat panel (EFP) solar thermalcollectors, adsorption heat pump with COPC = 1.5, andice thermal reservoir] described in the companion article[1] is ascertained by comparing it with a solar electric cool-ing system [grid-connected photovoltaic array with batterystorage connected to an electrically driven, mechanicalvapor compression heat pump with COPC = 5.66 (SEER =19.3)] and also with a grid dependent SEER 19.3 heat

pump. The economic scenario is analyzed for 24 citiesacross the southern Sunbelt of the USA, south of the37th parallel.

1.1. Model house

In order to enhance the realism of the economic analy-sis, a mathematical model house is constructed based

on information about houses which have been convertedto total reliance upon solar energy. Over 85% of annualinstallations, in terms of MW, of solar photovoltaic sys-tems are in California, and another 3% are in Arizona,due to generous rebates and tax credits in those two states.The typical homeowner choosing to convert to solar energyis in the middle to upper middle income bracket, not livingin a small or starter house. Consequently, it is assumedherein that the house being converted is larger than aver-age: 279 m2 (3000 ft2).

The conversion to reliance upon solar energy is more

often than not part of an overall strategy of maximizingenergy efficiency. Thus, it is assumed that the house is builtor retro-fit with extra insulation in the walls and attic, awn-ings over all windows and doors, and double-glazed, lowemittance, tinted windows. It is further assumed that allseams have been caulked and that all windows and doorshave been weather stripped to reduce air leakage. It isassumed photovoltaic panels of 3 kW peak output (annualaverage) are installed to handle non-HVAC demand.

The house is modeled using standard ASHRAEmethods applicable for a commercial, single-zone building

1359-4311/$ - see front matter 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.applthermaleng.2006.09.005

* Corresponding author. Tel.: +1 619 594 5791; fax: +1 619 594 3599.E-mail address: [email protected] (M.A. Lambert).

www.elsevier.com/locate/apthermeng

Applied Thermal Engineering 27 (2007) 15931611
mailto:[email protected]:[email protected]


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Nomenclature

Acoll surface area of thermal collector sheet for flatpanel or inner tube for concentrators (m2)

Aaper aperture area of thermal collector (m2)

B cost of building modifications necessary to sup-port the cooling systemcp specific heatC federal, state, and utility credits in the form of

tax credits, rebates, sales tax exemptionsCDD cooling degree days (K)CLF cooling load factorCLTD cooling load temperature difference (K)CPC compound parabolic concentrating solar collec-

torCR concentration ratio for solar concentratorCOPC coefficient of performance for coolinge escalation rate in electric rates

EFP evacuated flat panel solar thermal collectorEHP electric heat pumpF fuel cost, the residential electric rate during

the cooling season ($/kW h)Fslab conductance of foundation slab (W/m K)G assessed value of cooling system for determining

property taxh enthalpy (kJ/kg)HEX heat exchangerHTF heat transfer fluid, 50/50 mixture of ethylene

glycol and wateri interest rate on investments

H total solar irradiance (insolation) on a horizon-tal plane at the earths surface (W/m2)H0 solar irradiance (insolation) on a horizontal sur-

face at the top of the atmosphere (W/m2)Hb beam solar irradiance (insolation) on a horizon-

tal plane at the earths surface (W/m2)Hd diffuse solar irradiance (insolation) on a hori-

zontal plane at the earths surface (W/m2)I initial cost for search, purchase, and installation

of cooling systemIb beam solar flux (W/m

2)Kcond conductance of house envelope before adding

air leakage (W/K)

Ktotal total conductance of house envelope with airleakage (W/K)

L loan amount for cooling system financed on a2nd mortgage

m mortgage interest rateM maintenance costN number of years for determining net value (20

years) or payoff (120 years)O cost of space occupied by the cooling systemP perimeter of foundation slab (m)PV photovoltaic solar cellsq heat flux (W/m2)

Q heat (kW h or Btu)_Q heat rate (kW or Btu/h)

R repair and replacement cost

S salvage costSC shading coefficient for windows, solar transmit-tance with respect to standard plate glass

SEER seasonal energy efficiency ratio, =3.412 (Btu/h/kW) COPC

SHGF solar heat gain factor (W/m2)tprop property tax ratetincome income tax rate, both state and federalTa ambient temperature (C)Tbal balance point temperature (C)Tdb outdoor dry bulb temperature, = Ta (C)Ti indoor dry bulb temperature (C)Twb outdoor wet bulb temperature (C)

DT temperature difference (K)U area normalized, overall heat transfer coefficient

(W/m2 K)U A overall heat transfer coefficient (W/K)V0 present (year 0) net value of solar electric or

solar thermal cooling systemV volume (m3)_Vleak volumetric flow rate of leakage (m

3/s)aS solar absorptivityb tilt angle from horizontal of PV or thermal col-

lectorcc azimuth angle of PV or thermal collector, mea-

sured from direction toward equatorcS solar azimuth angle, measured from direction

toward equatord solar declination angleD change in a quantityeIR infrared emissivity (@ 300600 K)g efficiencyh solar incidence angle on photovoltaic panel or

solar thermal collectorq density (kg/m3)qS solar reflectivity of cover glass for thermal col-

lectorsqsurr solar reflectivity of surroundingssS solar transmittance of cover glass for thermal

collectorsu latitudexSS sunset hour angle (0 at noon, 15h), sunrise

angle is equal magnitude and negativeX acceptance half-angle for CPC thermal collector

Superscripts and subscripts

averagecool coolingEHP electric heat pump without photovoltaic arrays,

i.e., dependent on the electric grid

1594 M.A. Lambert, A. Beyene / Applied Thermal Engineering 27 (2007) 15931611


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since it provides greater accuracy than the simplifiedmethod for modeling houses [2]. Relevant parametersfor the model house are in Tables 1 and 2 for the exam-ple location of Raleigh-Durham, NC, #1 of 24 cities acrossthe southern Sunbelt states analyzed herein.

The model described above is used to predictannual cooling load for 24 cities across the southern

Sunbelt states (below 37N). Four basic climates areencountered

Southeast and South Central: hot, muggy summers andmild to moderately cool winters.

Southwest Desert: very hot, dry summers and short,cool winters.

free free heat gaini indoorint internal source of heat gain: lights, appliances,

and occupantsj year number from 1 to 20

o outdoor

out outletrad radiationS solarSE solar electricST solar thermal

Table 1

Parameters of cooling load analysis for a 279 m2 (3000 ft2) single-storey house, built or retro-fit to achieve high energy efficiency by adding awnings, extrainsulation in attic and walls, and double-glazed, low e, tinted windows, and minimizing leaks

Indoor conditions Solar gain parameters, July Internal heat gain

Ti (C) 23.9 Opaque surfaces Gas and Elec. appliances andlights (W)

1500

Relative humidity 50% CLTD, avg., N wall (K) 4.5 Occupants (W) 293hi (kJ/kg) 65.6 CLTD, avg., S wall (K) 3.5 Avg. total internal, Qint (W) 1793qi (kg/m

3) 1.173 CLTD, avg., E wall (K) 7.11CLTD, avg., W wall (K) 7.14 Free heat gain

Outdoor conditions CLTD, avg., roof (K) 17.2 Internal (W) 1793Tdb (C) on 0.4% design day 33.9 CLTD, avg., windows and doors

(K)3.08 Solar thru windows/doors (W) 828

DTdb (K) on 0.4% design day 10.4 Color factor for roof 1 Solar absorbed by walls (W) 38Tdb (C) on 0.4% design day 28.7 Color factor for walls 0.5 Solar absorbed by roof (W) 980

Twb (C) on 0.4% design day 24.4 Leakage, sensible (W) 237ho (kJ/kg) on 0.4% design day 91.7 Fenestrations Avg. free heat gain, _Qfree (W) 3876

SHGF, N (W/m2), w/awnings 126.2 Tbal (C) 11.5

Envelope conductive parameters SHGF, S (W/m2), w/awnings 126.2 CDD = (Tdb Tbal), 0.4% designday (K)

17.2

Floor area (m2) 279 SHGF, E (W/m2), w/awnings 126.2# of stories 1 SHGF, W (W/m2), w/awnings 126.2 Total heat gainRoof and slab area, Aroof (m

2) 279 CLF, N, avg. 0.483 Internal (W) 1793Slab perimeter, Pslab (m) 47.2 CLF, S, avg. 0.268 Solar thru windows/doors (W) 828Wall height per storey (m) 2.59 CLF, E, avg. 0.229 Conduction thru windows/doors

(W)300

Conditioned volume, V (m3) 722 CLF, W, avg. 0.228 Solar and Conduction thru walls(W)

268

Gross wall area (m2) 173 SC, double glazed, low e, bronzetinted

0.42 Solar and Conduction thru roof(W)

1359

Net wall area, Awall (m2) 121 Conduction thru slab (W) 183Windows and doors as % of walls 30% Leakage Leakage, sensible + latent (W) 1285

Window and door area, Awindow/door (m2) 52 Cumulative leakage area (cm2) 968 Avg. total heat gain, _Qtot (W) 6016

Uroof (W/m2 K) 0.284 Stack coeff., as (l/s)

2/(cm4 K) 0.000145 Avg. total heat gain, _Qtot (Btu/h) 20,526

Uwall (W/m2 K) 0.397 Wind coeff., aw (l/s)/(cm

4 (m/s)2) 0.000104 Heat gain, 0.4% design day (kW h) 144.4Uwindow/door (W/m

2 K) 1.87 Wind velocity, v (m/s), typicalsummer

3.35 Heat gain, 0.4% design day (Btu) 492,600

Fslab (W/m-K) 0.814 DT Tdb Ti (K) 4.78 Peak cooling load, _Qmax (W) 9673

Kcond = R(U A)+Fslab Pslab (W/K) 263 Leakage rate, Vleak (m3/h) 152 Peak cooling load, _Qmax (Btu/h) 33,003

Air changes per hour, ACH 0.21 CDD (C day), cooling season @Tbal

2131

qi _Vleak cp Tdb Ti (W) 237 Annual cooling load (kW h) 17,905Ktotal Kcond qi _Vleak cp(W/K)

312.6 Annual cooling load (MMBtu) 61.1

Weather and annual CDD is for Raleigh-Durham, NC, one of 24 cities across US Sunbelt considered.

M.A. Lambert, A. Beyene / Applied Thermal Engineering 27 (2007) 15931611 1595


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Table 2Design conditions and cooling load for example house in 24 US cities across the sunbelt (below 37th parallel)

City Latitudeu

Elevation(m)

0.4% Design day Annual CDD at

Tbal (C day)Tdb(C)

DTdbdaily (C)

Tdb(C)

Twb(C)

h0 (kJ/kg)

_Qfreeb

(W)

_Qtotb

(W)Tbal(C)

1 Raleigh-Durham, NCa

35.87 134 33.9 10.4 28.7 24.4 91.7 3876 6016 11.5 2131

2 Charleston,

SCa

32.90 15 34.4 9.0 29.9 26.1 96.3 3954 6070 11.3 3120

3 Atlanta, GAa 33.65 315 33.9 9.6 29.1 23.9 89.3 3901 6030 11.4 2344 4 Miami, FLb 25.82 4 32.8 6.3 29.6 25.0 94.0 4044 6581 11.0 4799 5 Tampa, FLb 27.97 3 33.3 8.3 29.2 25.0 94.0 4017 6441 11.1 4169

6 Montgomery,ALa

32.30 62 35.0 10.4 29.8 24.4 89.3 3945 6252 11.3 2944

7 Jackson, MSa 32.32 101 35.0 10.7 29.7 25.0 94.0 3937 6448 11.4 2992 8 Nashville, TNa 36.13 180 34.4 10.6 29.2 24.4 91.7 3904 6164 11.4 2330

9 Little Rock,ARa

34.92 95 36.1 10.8 30.7 25.0 94.2 4003 6785 11.2 2547

10 New Orleans,LAa

29.98 9 33.9 8.6 29.6 26.1 98.6 3931 6659 11.4 3431

11 OklahomaCity, OKa

35.40 397 37.2 11.7 31.4 23.3 87.0 4049 6610 11.2 2495

12 Austin, TXa 30.30 189 36.7 11.2 31.1 23.3 84.9 4028 6406 11.2 3508

13 Brownsville,TXb

25.90 6 35.0 9.2 30.4 25.6 96.3 4095 6958 10.9 4543

14 El Paso, TXc 31.80 1194 38.3 15.6 30.6 17.8 67.5 3994 5326 11.3 2751 15 Albuquerque,

NMc35.05 1620 35.6 14.1 28.5 15.6 60.9 3866 4459 11.5 1934

16 Phoenix, AZc 33.43 337 43.3 12.8 36.9 21.1 78.4 4472 7720 10.2 4157

17 Las Vegas,NVc

36.08 664 42.2 13.8 35.3 18.9 71.0 4341 6810 10.5 3446

18 Fresno, CAd 36.77 100 39.4 17.2 30.9 21.7 80.5 4014 6103 11.2 2450 19 Los Angeles,

CAd33.93 32 29.4 6.1 26.4 17.8 67.7 3753 4233 11.7 2447

20 Burbank/Glendale, CAd

34.20 236 36.7 13.0 30.2 20.6 76.8 3968 5708 11.3 3480

21 Ontario, CAd 34.05 287 38.9 15.4 31.2 21.7 81.0 4036 6225 11.2 3864

22 San

Bernardino,CAd

34.10 353 39.4 17.5 30.7 21.1 78.6 4003 5956 11.2 3664

23 San Diego,CAd

32.85 128 33.3 9.7 28.5 20.6 76.8 3865 5226 11.5 2136

24 Honolulu, HIb 21.35 5 31.7 6.8 28.3 22.8 84.9 3964 5717 11.2 4959

a Southeastern/south central location; hot, humid summers and mild to moderate winters.b Tropical or subtropical climate, balmy year round or most of the year.c Southwest Desert, very hot, dry summers and short, cool winters.d Southern California Coast, similar to Mediterranean climate.


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Southern California Coast (Mediterranean): warm tohot, dry summers and mild winters.

Tropical or subtropical: balmy year round or most ofthe year.

1.2. Solar radiation

1.2.1. Monthly average daily and hourly insolation: total,

beam (direct), and diffuse

Methods for computing hourly (instantaneous) andmonthly average daily (long-term) insolation are takenfrom the literature. The un-attenuated daily insolationH0 on a horizontal unit area at the top of the atmosphereis a function of latitude u and declination angle d.Monthly average daily (long-term) values of total H, beam(direct) Hb, and diffuse Hd insolation on the earths sur-face (horizontal) are computed from monthly averagedaily H0 and monthly average clearness index KT (left col-umn below) The correlation for Hd (below) is one of the

simplest, yet one of satisfactory accuracy, and is due toPage [3]. Liu and Jordan [4] demonstrated that theserelationships hold for hourly (instantaneous) values (rightcolumn)

MonthlyAverageDailyValues HourlyInstantaneousValues

KT H=H0 KT H=H0

Hd=H 1:00 1:13KT Hd=H 1:00 1:13KT

Hb HHd Hb HHd

Liu and Jordan [4] provide an expression for insolationqS on a tilted surface, a solar thermal collector or photovol-taic panel.

qS Ib cos h Hd cos2b=2 Hqsurr sin

2b=2

Boes et al. [5] developed a very simple correlationbetween KT and Ib for the United States based upon mea-surements from about 30 stations:

Ib 520 1800KT for 0:85 > KT P 0:30

Ib 0 for 0:30 > KT

1.2.2. Orientation and net insolation on solar collector panels

It is assumed that there are no trees or structures toblock the sun and the panels are south-facing, that is, col-lector azimuth angle cc = 0, although 15 6 cc 6 15 hasminimal effect on the amount of insolation on the collec-tors [6]. The PV modules have fixed tilt angle equal tothe latitude, b = u, which usually affords the greatestcumulative annual insolation. Flat panel thermal collectorsare fixed at b that minimizes the number of collectorsneeded during the month with greatest cooling load. Con-centrating thermal collectors have automatic tilt control.

Hour angle xSS converts the earths rotation rate into anangle: xSS 0 at solar noon, dxSS/dt = 360 24 h =

15/h. Hour angle is used in determining solar elevation

angle aS and solar azimuth angle cS, both needed for com-puting h, the solar incidence angle with respect to the nor-mal to the collector aperture. During spring and summerwhen declination d > 0, the effective sunrise time fortilted panels comes after actual sunrise at the horizon andeffective sunset comes before sunset. The corresponding

hour angle x0

SS for relative sunrise (negative) or sunset(positive) on the panels is the lesser of:

x0SS cos1 tanu tan d

x0SS cos1 tanu b tan d

1.3. Performance of solar collecting panels

1.3.1. Solar photovoltaic modules

In computing the required area of PV panels for a par-ticular location and cooling load, it is assumed that PVmodules use either single crystal or multi-crystalline silicon

cells with 15% efficiency at operating temperature, the max-imum commercially achievable. PV modules can convertboth beam and diffuse insolation to electricity and operatefrom sunrise to sunset.

1.3.2. Solar thermal collectors

Thermal performance of various configurations is pre-sented in the companion article [1]. Thermal efficiency gcolland cost ($/m2) is listed in Table 3 for standard flat panel,evacuated flat panel (EFP), and compound parabolic con-centrator (CPC) collectors.

1.3.3. Comparison of various types of solar collectorsThe efficiency of photovoltaic modules and various con-

figurations of solar thermal collectors [6,7] discussed aboveand in the companion article [1] are compared in Table 3for average climatic conditions across the southern Sun-belt. Average daytime ambient temperature during thecooling season is approximately Ta 32:5

C. KT for themonth with the highest cooling load, either July orAugust depending upon location, ranges from 0.47 to0.74 with average 0.605, so a round figure of 0.60 is usedin Table 3.

The price per kW peak for additional PV modules abovethe 3 kW capacity needed for non-HVAC usage is $6500/kW if adding 1 kW (total = 3 + 1 = 4 kW), $6000/kW ifadding 2 kW (total = 3 + 2 = 5 kW), and $5500/kW ifadding 3 kW (total = 3 + 3 = 6 kW).

The installed cost per kW for evacuated flat panels(EFP) is only about 1/3 that of standard (non-evacuated)flat panels with solar selective coating. For the mean valueof clearness index KT 0:60, EFP are 63% of the installedcost of CPC, $524/kW versus $831/kW. At the lowest sum-mertime KT 0:47; gEFP 0:486 and gCPC = 0.400, andEFP are 55% (=$825/kW $1504/kW) of the cost ofCPC. At the highest summertime KT 0:74; gEFP 0:627and gCPC = 0.680, and EFP are 72% (=$407/kW $563/

kW) of the cost of CPC.



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1.4. Sizing of solar photovoltaic and solar thermal arrays

The required output of photovoltaic modules and ther-mal collectors (kW electric or thermal) and correspondingareas are determined from a model incorporating the:

House thermal model. Summer weather (0.4% design day). Solar radiation expressions. Efficiency (COPC) of both electro-mechanical and

adsorption heat pumps. Performance of solar photovoltaic modules and thermal

collectors.

Results are computed on a monthly basis, and areshown in Table 4 for Honolulu, Hawaii, #24 of the 24 citiesconsidered across the southern Sunbelt states (below37 N).

The top rows ofTable 4 provide optimal tilt angle b for

fixed, evacuated flat panel (EFP) thermal collectors. CPCcollectors have automatically adjusted tilt to track the riseand fall of the suns arc across the sky from summer sol-stice to winter solstice. PV modules are fixed at tilt equalto latitude, b = u. It is assumed collectors face due south,collector azimuth cc = 0.

Following are the monthly CDD at base 18.3 C (65 F),monthly CDD at the computed Tbal, and monthly averagedaily cooling load Qcool. Annual sums are in the rightmostcolumn.

These are followed by noontime solar incidence angle hon the fixed EFP collectors, sunset angles, both actual xSS

(at the horizon) and effective x0SS (for the panel), and

monthly average daily values for insolation on tiltedEFP: Qbeam, Qdiffuse, Qreflected, and net amount QS, whichis the daily integral of instantaneous insolation qS in Sec-tion 1.2.1.

Net daily heat gain per m2 and required areas forCPC and EFP thermal collectors are next. These arebased on predicted COPC = 1.50 for the adsorption heatpump from in the companion article [1]. The maximumrequired area for both types is carried over to the rightmostcolumn.

The last three rows show noontime h and daily QPV onthe fixed PV modules, and monthly average daily consump-tion to operate an EHP with highest available COPC =5.66 (SEER = 19.3). The rightmost column contains therequired annual average daily peak (noontime) generatingcapacity of the PV array on which system pricing is based.This assumes an annual average of 5.5 sun hours perday, the typical value assumed for sunny climates as perwww.solarbuzz.com [8] (downloaded 12/19/05).

It is further assumed that the homeowner has a netmetering agreement with the utility. This allows the home-owner to sell excess electricity generated in winter by theportion of the PV array installed to offset summer cooling.The homeowner banks electricity in winter to draw upon

for summer cooling. The utility bills the homeowner annu-Table3

E

fficiencyandnetsolarconversion(W/m2)forphotovoltaicmodulesandthermalcollectors:flatpanel,evacuatedflatpanel(EFP),andcompoundparabolicconcentrator(CPC)

T

ypeofsolarcollector

Efficiencyexpression

Efficiencyg

at

specifiedconditionsa

Netconversion(W/m2)at

specifi

edconditionsa

Costperm

2c

I

nstalledcostperNet

k

W

elec.orthermal

Photovoltaic(PV),singlecrystalorpoly-crystalline,notthinfilm

0.15

0.15

123

$616$740

$

5500$6500b

7F

latPanel:single-glazed(sS=0.86),blackp

aint(aS/eIR

=0.96/

0.96)

0:838

:6Tcoll

Ta

=qS

0@

max.

Tcoll=111C

0

$175

C

annotreachTcoll

7F

latPanel:double-glazed(sS=0.79),black

paint

(aS/eIR

=0.96/0.96)

0:764

:9Tcoll

Ta

=qS

0@

max.

Tcoll=160C

0

$200

C

annotreachTcoll

7F

latPanel:single-glazed(sS=0.89),solar-selective

(aS/eIR

=0.90/0.20)

0:803

:8Tcoll

Ta

=qS

0.162

133

$200

$

1500

6F

latPanel:double-glazed(sS=0.79),solar-selective

(aS/eIR

=0.95/0.15)

0:753

:4Tcoll

Ta

=qS

0.179

147

$225

$

1530

E

vacuatedFlatPanel(EFP):etchedsingle-glazed(sS=0.95),

solar-selective(aS/eIR

=0.92/0.10)

0:8741

:754TcollT

a=qS

0.580

477

$250

$

524

C

ompoundParabolicConcentrator(CPC):C

R=10,etched

single-glazed(sS=0.95),solar-selective(aS/eIR

=0.92/0.10)

0:6130

:381TcollT

a=qS

0.549

451

$375

$

831

a

Tcoll

170C

;

Ta

32C

;

KT

0:60;h

%

0

;

b

20

;

qsurr

0:2;qS

822W=m2.

b

CostofadditionalPVneededforHVAC

addedonto3kW

arrayfornon-HVACus

age.

c

Equalsretailpriceplusestimatedinstallationcostof$50/m2.

http://www.solarbuzz.com/http://www.solarbuzz.com/


7/19


8/19

ally for net consumption from the grid, but does not paythe homeowner for net excess generation, then zeroes anycredits to begin a new annual billing cycle. So, systemsare usually sized to very nearly satisfy, but not exceed,annual consumption. Net metering allows the homeownerto sell excess electricity to the utility at the seasonal residen-

tial (retail) rate. If net metering is not in effect, then a sec-ond meter is needed for tabulating excess generation andthe utility credits the homeowner at only the wholesalerate, roughly 2/kW h, as compared with the retail rateof 8 to 20/kW h.

Net metering is currently available in 39 states, including10 of the 15 southern Sunbelt States considered herein.However, more and more states are legislating or utilitiesare allowing net metering, so it is assumed herein that netmetering is applicable in all 24 cities considered.

The annual average daily peak PV output (rightmostcolumn) needed to offset annual cooling for the 24 citiesranges from 39% (Southern California Coastal Mediterra-

nean climate) to 74% (Hawaii, tropical) of the peak valuefor the sunniest month. This means that much less energycan be banked in wintertime in tropical climates sincethe weather remains balmy year round. The upshot is thatsignificantly larger PV arrays are needed in tropical cli-mates to offset cooling.

2. Economic analysis

2.1. Installed cost of cooling systems

2.1.1. Installed cost of grid dependent electric heat pump

(EHP)In this study the homeowner has already decided to

install a 3 kW peak output PV array to offset annualnon-HVAC consumption. He is content to wait for thelong-term payoff when the initial and upkeep cost of thePV is exceeded by the value of foregone consumption fromthe electric grid. Therefore, it is assumed the homeownerwill opt for an EHP with the highest availableCOPC = 5.66 (SEER = 19.3), despite its higher initial cost,to replace the existing unit with performance in the rangeof SEER 10-12 (COPC = 2.93.5) if it is around 1015years old.

The initial cost, IEHP, of an EHP includes capital cost,installation, and search cost for the outdoor unit (compres-sor, condenser, and cooling fan) of a central air condition-ing system. The preexisting indoor evaporator, blower, andductwork are retained. Installed cost is computed as $2500for 7.0 kW (24,000 Btu/h), plus $250 more for each 1.8 kW(6000 Btu/h) increment in capacity, e.g., $3000 for 10.6 kW(36,000 Btu/h) capacity. This is based on a survey of majormanufacturers: Lennox, Ruud, Trane, Carrier, Frigidaire,and Goodman. The installed cost of an EHP, properlysized for the model house in all 24 cities considered, is listedin Table 5.

For this scenario the homeowner has decided not to

install additional PV capacity to offset electricity consump-

tion for summer cooling. This serves as the baseline againstwhich to compare the economic viability of the solar elec-tric (SE) and solar thermal (ST) cooling systems.

2.1.2. Installed cost of solar electric (SE) cooling system

In this scenario, the homeowner has already selected

an electric heat pump with highest available efficiency(COPC = 5.66, SEER 19.3) described above for the base-line scenario.

The initial cost of the solar electric cooling system, ISE,is for purchase and installation of the portion of the PVsystem needed to totally offset electricity consumption forcooling in year 1, before subtracting any rebates or taxcredits, plus IEHP for a new electric heat pump with highestavailable SEER = 19.3 (COPC = 5.66). IEHP and IPV arelisted separately in Table 5.

It is assumed the homeowner has decided to convertcompletely to solar energy on a net annual basis, requir-

ing 3 kW of PV capacity to offset non-HVAC relatedconsumption. This equates to 3 kW 5.5 sun hours/day 365 days = 6023 kW h/year = 502 kW h/month =16.8 kW h/day, a modest amount for a 279 m2 (3000 ft2)house with energy efficient appliances. The additionalPV capacity for HVAC is added to the baseline 3 kWcapacity and ranges from 1.06 kW in Albuquerque to3.58 kW in Miami (Table 5).

Installed cost of additional PV capacity (above 3 kW)for HVAC is computed as follows: Grid-connected, residential 2 kW (annual avg. peak)

PV system is $17,865, or $8933/kW, as quoted

on www.solarbuzz.com [8] (downloaded 10/22/06),which includes 20% added to the purchase price forinstallation. This website maintains a regularlyupdated tracking of all worldwide price points fromall PV vendors and installers.

The DOE National Renewable Energy Laboratory(NREL) website [9] lists a typical installed cost of$16,000$20,000 for a 2 kW system ($8000/kW$10,000/kW) and $30,000$40,000 for a 5 kW system($6000/kW$8000/kW) as of Dec. 2003.

This analysis uses a sliding scale of $18,000 for a2 kW system (or $9000/kW, rounded from the cur-rent price $17,865 [8]), to $37,500 for a 5 kW system($7500/kW) from the average on the DOE website [9]for a 5 kW system ($7000/kW) adjusted for inflationat 2.5% per annum from Dec. 2003 to Oct. 2006._WPV is in kW.

IPV _WPV$10; 000 $500 _WPV

The baseline (non-HVAC usage) 3 kW system hasinstalled cost $25,500 ($8500/kW).

The following example illustrates how the cost ofadditional PV capacity is computed. Assume 3 kWis needed to offset electricity consumption for summercooling. Total system output is 6 kW (3 kW non-

HVAC + 3 kW HVAC) and costs $42,000. Thus,



9/19

Table 5Solar array area and installed cost of solar electric and solar thermal cooling systems for 24 cities across US Sunbelt (south of 37N)

City Solar electric cooling system Solar thermal cooling system

PVarea(m2)

PV peakoutput_WPV (kW)

PVinstalledcost IPV

Peak coolingload, 0.4% designday _Qcool;max (W)

Installed cost ofelectrical heat pumpSEER = 19.3COPC = 5.66

CPCarea(m2)

CPCInstalledCost ICPC

EFParea(m2)

EFPinstalledcost IEFP

Tlodd

1 Raleigh-Durham, NCa

13.5 1.57 $9731 9673 $3000 84.1 $31,521 56.1 $14,024 5

2 Charleston,SCa 19.8 2.34 $13,660 9875 $3000 115.8 $43,416 77.7 $19,424 5

3 Atlanta, GAa 14.2 1.68 $10,335 9314 $3000 77.6 $29,113 52.4 $13,102 54 Miami, FLb 27.7 3.58 $18,657 8824 $3000 104.1 $39,044 73.0 $18,253 55 Tampa, FLb 23.5 3.13 $16,996 9408 $3000 96.6 $36,207 64.4 $16,092 56 Montgomery,

ALa17.1 2.10 $12,475 9772 $3000 77.4 $29,010 52.9 $13,235 5

7 Jackson, MSa 17.9 2.22 $13,053 10,207 $3000 74.3 $27,845 52.4 $13,107 58 Nashville,

TNa15.8 1.70 $10,466 9858 $3000 69.1 $25,913 48.2 $12,047 5

9 Little Rock,ARa

14.9 1.86 $11,309 10,562 $3250 62.2 $23,336 46.4 $11,611 5

10 New Orleans,LAa

20.9 2.64 $14,990 9809 $3000 87.2 $32,705 60.1 $15,014 5


12.7 1.71 $10,500 10,419 $3000 50.4 $18,901 39.8 $9962 5

12 Austin, TXa 18.1 2.37 $13,792 10,000 $3000 61.3 $22,980 51.2 $12,797 513 Brownsville,

TXb25.6 3.41 $18,073 10,230 $3000 60.8 $22,816 51.4 $12,842 6

14 El Paso, TXc 9.1 1.59 $9888 9618 $3000 29.3 $10,993 27.9 $6972 4

15 Albuquerque,NMc

6.2 1.06 $6883 8161 $2750 23.8 $8922 23.1 $5779 3

16 Phoenix, AZc 14.7 2.52 $14,468 11,408 $3250 40.3 $15,127 39.2 $9797 617 Las Vegas,

NVc11.3 1.98 $11,920 10,589 $3250 31.7 $11,880 32.8 $8201 5

18 Fresno, CAd 10.5 1.60 $9903 11,436 $3250 25.0 $9362 27.0 $6747 519 Los Angeles,

CAd10.0 1.48 $9259 5974 $2500 36.2 $13,569 33.7 $8423 3

20 Burbank/

Glendale,CAd

15.0 2.21 $13,042 9642 $3000 54.1 $20,305 50.5 $12,628 4

21 Ontario, CAd

16.4 2.52 $14,483 11,008 $3250 58.7 $22,024 55.9 $13,981 522 San

Bernardino,CAd

14.8 2.36 $13,722 11,313 $3250 52.2 $19,590 50.4 $12,593 5

23 San Diego,CAd

9.3 1.38 $8711 8221 $2750 37.7 $14,150 33.8 $8450 4

24 Honolulu,

HIb24.7 3.50 $18,361 7983 $2750 48.2 $18,071 44.2 $11,050 4

a Southeastern/south central location; hot, humid summers and mild to moderate winters.b Tropical or subtropical climate, balmy year round or most of the year.c Southwest Desert; very hot, dry summers and short, cool winters.d Southern California Coast, similar to Mediterranean climate.


10/19

the cost of the portion of the PV array for offsettingsummer cooling is $42,000 $25,500 = $16,500(equates to $5500/kW for the additional 3 kW).

Installed cost of the SEER 19.3 electric heat pump,IEHP, is given in Section 2.1.1.

2.1.3. Installed cost of solar thermal (ST) cooling system

In this scenario the homeowner has chosen a solar ther-mal cooling system comprised of an adsorption heat pumpwith COPC = 1.50, ice thermal reservoir, and either CPC orEFP solar collectors. The initial cost of the ST cooling sys-tem, IST, includes search cost, purchase, and installation,before subtracting any rebates or tax credits. The initialcost of the CPC and EFP collectors is listed separatelyfrom the cost of adsorption heat pump and ice reservoirin Table 5.

2.1.3.1. Installed cost of CPC and EFP solar collectors.

Installed cost of CPC collectors is taken to be $375/m2,the sum of $300/m2 retail for the collectors, plus $25/m2

for the automatic tilt mechanism, plus $50/m2 forinstallation. The retail price is the average of quotes from the very

few vendors. The installation cost is deduced from an estimate of 4

hours labor per panel (or 2 h/m2) at an overall laborrate of $25/h, including overhead.

Installed cost of EFP collectors is taken to be $250/m 2,the sum of $200/m2 retail for the panels plus $50/m2 for

installation (same as CPC), or $100 to install a2 m 1 m panel. The retail price is deduced from a current retail price

of $150/m2 for flat panel collectors, single-glazed,with solar selective coating. $50/m2 is added to cover:

* Etching low-iron, alkali-borosilicate glass to mini-mize solar reflectivity ($$15/m2).

* Internal posts to support cover glass and fiberglassshell against vacuum ($$15/m2).

* Proportionate share of vacuum tubing connectingpanel to vacuum pump ($$5/m2).

* Vacuum pump capable of attaining soft vacuumof 0.001 atm to eliminate convection ($$15/m2

equates to a pump price of $600 for a 40 m2 array).

2.1.3.2. Installed cost (List Price) of adsorption heat pump

and ice thermal reservoir. Table 6 lists the cost of materialsand components for an adsorption heat pump and ice ther-mal reservoir with ice making capacity of 633 MJ/day(600,000 Btu/day), averaging 17.6 kW (60,000 Btu/h) over10 useful sun hours, with a maximum rate of 29.3 kW(100,000 Btu/h).

Nearly all materials and components are readily avail-able, stock sizes and shapes sold in mass quantities: e.g.,

steel, aluminum, and PVC piping, tubing, and fittings, sol-

der, rubber hose, wood, structural shapes, fasteners, acti-vated carbon, valves, controllers, etc. The few customparts such as the end caps, tube sheets, and internal tubefins for the adsorber vessels, and the HTF distributionmanifold, can be machined or extruded from billet. Pricesare from quotes and catalogs. The cost of materials and

components for a 633 MJ/day heat pump is $4237.Table 7 lays out the labor ($2118) and overhead ($775)costs for manufacturing the 633 MJ/day heat pump andice thermal reservoir, which requires 82 h labor per unit.This is based on a start-up small business that builds andinstalls 1000 heat pumps per year in a viable market, suchas central and southern California or Hawaii. The labor forinstalling the EFP collectors is already included in the retailcost of $250/m2. The salaries and wages listed in Table 7are average or above for states with high costs of living,such as California and Hawaii.

Personnel (95 total: owner/inventor plus 94 employees):

The inventor/owner/chief engineer and four employeeengineers handle design, manufacture, and sales. The37 manufacturing staff is a mix of highly skilled mastermachinists and CNC operators with foreman duties($5), skilled journeyman machinists ($12) and elec-tronic technicians, and a number of semi-skilled fabrica-tors ($20). The 48 installers are in 8 teams of 6, and eachteam completes an installation in two days. There arethree clerical staff.

Factory: The factory is either leased or purchased at$100,000 per year.

Tools and equipment: $1,000,000 of tooling is financed at

$100,000 per year. Optional components: A gas-fired heater can allow the

heat pump to operate in case of a fault in the EFP arrayor the ice reservoir. It adds $534 to the cost of produc-tion, and is excluded, assuming the manufacturer pro-vides rapid service in repairing any faults.

2.1.3.3. Profitability. The cost of producing and installingthe adsorption heat pump and ice reservoir is the sum ofmaterials, labor, and overhead. Production costs andinstalled (list) prices are given in Table 7 for three capaci-ties: 633, 506, and 380 MJ/day. The before tax profit on1000 heat pumps and ice reservoirs (for an equal mix of633, 506, and 380 MJ/day units) is $885,000/year.

A typical 40 m2 EFP array has installed cost of $10,000($250/m2 retail). The adsorption heat pump manufacturerwould purchase 40,000 m2 of EFP per year, and negotiatea wholesale price 6 200/m2 (680% retail). Twenty percentprofit on 1000 arrays adds $2,000,000 to gross profit fora total of $2,885,000 minus 20% corporate tax rate for anet profit of about $2,300,000. One-thousand complete sys-tems would result in gross annual sales of $17,500,000($7500 for the heat pump and ice reservoir, $10,000 forthe EFP array). So, net profit is about 13% of gross annual

sales.



11/19

2.1.4. Comparison of installed costs

Table 5 lists the installed cost of SE and ST cooling sys-tems. It includes areas and prices of PV, CPC, and EFP

arrays for all 24 cities considered, as well as prices for a

properly sized EHP (SEER 19.3) and a correct capacityadsorption heat pump (COPC = 1.50) with associated icereservoir. CPC collectors cannot compete with EFP collec-

tors and are eliminated from consideration.

Table 6Material costs for 633 MJ/day (600,000 Btu/day) adsorption heat pump

Cost for adsorbers: shell and tube with helical annular fins on tubes

Adsorber shell (1): 4 in. nominal, schedule 40 aluminum alloy pipe (4.50 in. O.D., 0.120 in. wall), $100 for 21 0, cut to 36 in. lengths $14.30Adsorber end caps (2): aluminum alloy, 4.5 in. diameter, 0.50 in. thick, 3/4 in. holes (7) drilled for HTF tubes, 0.6 lb 2 at $1.50/lb $1.80HTF tubes (7): aluminum alloy (0.75 in. O.D, 0.040 in. wall, 36 in. long), with aluminum annular helical fins (1.5 in. O.D., 0.010 in. thick, 10

fins per inch), $2.00/ft$42.00

Extruded, six-pointed asterisk internal fins for HTF tubes (7): aluminum alloy, 36 in. lengths, 0.040 in. thick spokes, at $0.50/ft $11.00Extra Coarse (grade #4, %100 lm fiber dia.) aluminum wool, loosely packed b/w annular fins, 6% by volume, 1.7 lb at $2.00/lb $3.403/4 in. tube elbows for HTF tubes (14): aluminum alloy, in quantity $3.00HTF manifolds (2), aluminum alloy cylinders, 1.5 in. O.D. by 1.25 in. long, with 7 3/4 in. holes, 0.4 lb at $1.50/lb $0.60Higher melting temperature tinsilver solder, 0.1 lb at $5.00/lb $0.50Adsorbent: activated carbon, 19 lb at $0.50/lb in quantity $9.502 in. fiberglass insulation with aluminum backing, 6 ft2 @ $0.25/ft2 $1.50Subtotal per adsorber $87.60Subtotal for 20 adsorbers $1752.00Ammonia condenser and HTF cooler: cooled by natural convection, max. heat rejection rate = 167,000 Btu/h = 100,000 Btu/h

max. ice-making rate (1+1/COPC)Tubes (96 = 57 for NH3 and 39 for HTF), aluminum alloy (1.00 in. O.D., 0.060 in. wall, 8

0 long) with alum. annular helical fins (3.0 in.O.D., 0.015 in. thick, 3.54 fins per inch), clear anodized for low solar absorptivity and corrosion protection, $2.00/ft

$1536.00

Manifold tubing and fittings, anodized aluminum, tees (32) and 180 elbows (80), $0.25 each; tube (1.00 in. O.D., 0.060 in. wall, 10 0) $5.00 $33.00Subtotal for HTF cooler: $1569.00

Pumps and valvesHTF gear pump: 10 l/min, 50 psig differential $30.00R-134a gear pump: 5 l/min, 5 psig differential $15.00Ball check valves for ammonia (40): 20 to condenser and 20 to evaporator, 1/2 in.NPT 1/2 in. comp., $5.00 each in quantity $200.00Thermostatic expansion valve (TEV) for ammonia $50.00On/off solenoid valve for ammonia; $3.00 in quantity $3.00HTF circuit: anodized aluminum; tubing (0.50 in. 100 0 annealed coil) $0.25/ft, compression fittings (80) $0.50 each $65.00HTF distribution manifold, anodized aluminum, milled from billet ($25.00) on CNC; O-rings ($5.00); stepper motor ($20.00) $50.00NH3 circuit: anodized aluminum; 1/2 in. fittings = nipples (40) + tees (40) @ $0.50 ea, tubing (0.50 in. 20

0 annealed coil) $0.25/ft $45.00

Subtotal for pumps and valves: $458.00Frame: Unistrut channel, 80 lengths (8) @ $10.00 each $80.00Unistrut connector tees (4 $1.00), corners braces (8 $2.00) $20.00Unistrut 1/2 in. 1 in. bolts (64 @ $0.20) and additional fasteners $32.80Stainless sheet cover panels to protect adsorbers from weather $25.00Subtotal for frame: $157.80

Ice making HEX (ammonia evaporator): max. ice-making rate = 100,000 Btu/h [29.3 kW]1600 0 of elastomeric tubing (1 in. O.D., 0.040 in. wall), in 24 660 sections, each coiled around 8 0 lengths of 3 in. PVC pipe (3.5 in. O.D.), 60

turns per coil, $0.05/ft$80.00

Anodized aluminum crimped hose nipples (48), $0.25 each $12.00Anodized aluminum tubing for NH3 evaporator manifolds (2), 0.75 in. O.D., 0.060 in. wall, 10

0, $5.00 each $10.00Anodized aluminum fittings: 3/4 in. tees and elbows (50), $0.25 each $12.50PVC: 24 10 lengths of 3 pipe, 48 fittings, and cement $300.00Subtotal for ice making HEX (NH3 evaporator): $263.00Ice thawing HEX (R-134a condenser): 50,000 Btu/h capacity [14.7 kW]Tubes (10), aluminum alloy (0.75 in. O.D., 0.060 in. wall, 7.5 0 long), with aluminum annular helical fins (2.0 in. O.D., 0.010 in. thick, 6.0 fins

per inch), anodized, $2.00/ft$150.00

Anodized aluminum tubing, R-134a condenser manifolds (2), 10 0 0.75 in. tubing (1), $10.00 each $10.00Anodized aluminum fittings: 3/4 in. tees and elbows (25), $0.25 each $6.25Subtotal for ice thawing HEX (R-134a condenser): $166.25Deck to cover ice reservoir and support heat pump

Plywood (2), 4 0 8 0 3/4 in., pressure treated, $15.00 each $30.00Lumber: 2 in. 6 in. 10 0 (6), $6.00 each $36.00Wood screws, anti-corrosion coated, 1 lb box (2), $2.00 $4.00OSB sheets, 4 0 8 0 (4), for foam in place insulation, $7.50 each $30.00Foam-in-place poly-isocyanurate, 100 ft3 @ $1.00/ft3 $100.00Spray-on waterproof liner, 250 ft2 $50.00Subtotal for ice reservoir and cover deck: $250.00Controller: weatherized, programmable, with thermocouples $30.00Total for materials $4797.50



12/19

2.2. Lifecycle cost of cooling systems

The economic viability of the solar electric and solarthermal cooling systems versus the baseline, a grid-con-nected electric heat pump, and each other is determined

below.

2.2.1. Lifetime monetary benefit and payback period

2.2.1.1. Present value of solar electric cooling system versus

grid dependent heat pump. The present net value V0,SE ofthe complete SE cooling system [photovoltaic modules,inverter, batteries, and charge controller, paired with a

SEER 19.3 (COPC = 5.66) electric heat pump] as compared

Table 7Labor and Overhead for Fabricating and Installing 633 MJ/day (600,000 Btu/day) Adsorption Heat Pump

LABOR: Effort per heat pump:

Highly skilled (5): $50,000 annual gross = $25.00/h 40 h/wk 50 wk/yr; Skilled (12): $40,000 annual gross = $20.00/h 40 h/wk 50 wk/yr; Semi-skilled (20): $30,000 annual gross = $15.00/h 40 h/wk 50 wk/yr; Average labor rate = $25.00/h ($18.00/h avg. wage + fringe (20%) + payroll tax($8%) + workmens compensation (10%))

Set up and machine/drill/cut apart end caps on CNC mill in batch (20 2) for entire heat pump (2 h 20) $2.50

Swaging internal fins into HTF tubes (20 7 = 140) (6 h) $150.00Wrapping aluminum wool between helical annular fins on HTF tubes (20 7 = 140) (8 h) $200.00Cleaning, assembling, heating, and soldering HTF shells, tubes, elbows, and manifolds (20 7) (8 h) $200.00Filling adsorbers with activated carbon and simultaneous vibratory compaction (20) (2 h) $50.00Assembling Unistrut frame (2 h) $50.00Installing adsorbers (20) in frame (2 h) $50.00Cutting refrigerant (NH3) tubing, and connecting ball check valves (40), solenoid valve, and TEV (8 h) $200.00Cutting HTF (glycol-water) tubing and connecting adsorber inlets/outlets (20 2) to distribution manifold (4 h) $100.00Installing HTF and R-134a pump, pressure testing HTF circuit (1 h) $25.00

Subtotal for building and installing 20 adsorbers (40 h) $1027.50Cutting manifold tubing for NH3 Condenser and HTF cooler (1 h) $25.00Assembling finned tubes for NH3 Condenser (57 tubes) and HTF cooler (39 tubes) with manifold tubes and fittings, then soldering (8 h) $200.00Pressure testing and installing condenser and HTF cooler (2 h) $50.00

Subtotal for assembling NH3condenser and HTF coolers (11 h) $275.00Cutting PVC pipe, assembling with fittings, and cementing (3 h) $75.00

Cutting NH3 hosing (24 660

) and crimping hose nipples (48) (3 h) $75.00Cutting manifold tubing, assembling w/fittings, and soldering (3 h) $75.00Coiling NH3 hoses (24) on PVC frame, connecting nipples to manifolds (48), and pressure testing (3 h) $75.00Subtotal for ice making HEX (NH3evaporator) (12 h) $300.00Cutting manifold tubing for R-134a Evaporator, assembling with fittings, and soldering (3 h) $75.00Assemble R-134a finned tubes (10) and manifolds and soldering (2 h) $50.00Subtotal for ice thawing HEX (R-134a condenser) (5 h) $125.00Subtotal: Installing controller and thermocouples (1 h) $25.00HTF distribution manifold: set-up, milling, drilling on CNC (1 h) $25.00Assembly, installing inlet/outlet fittings, and pressure testing (4 h) $100.00Subtotal: fabricating HTF distribution manifold (5 h) $125.00Total for entire heat pump and ice reservoir components (74 h)

On-Site Installation: Excavation of pit: 9 0L 50W 5 0D with backhoe in 3 hours (1/2 day per job, one in morning, one in afternoon) $75.00Leased backhoe: $500/month = $12.50 per 1/2 day (for 20 work days per month), $12.50 per 1/2 day for diesel (5 gal $2.50/gal), lube, oil,

and maintenance $200/month = $10.00 per 1/2 day$40.00

Install oriented strand board (OSB) forms in excavated hole, add poly-isocyanurate foam and spray-on waterproof liner (3 h) $75.00Install ice making HEX and ice thawing HEX (1 h) $25.00Build, foam fill, waterproof, and install plywood deck (1 h) $25.00Subtotal for on-site installation (8 h) $240.00TOTAL for LABOR (82 h) $2117.50OVERHEAD: Small business producing and installing 1,000 heat pumps per year so that costs are distributed over 1,000 units

Personnel 92 employees: 37 manufacturing, 4 engineering and sales, 3 accounting and clerical, 48 installation (8 crews of 6)Factory: 20,000 ft2 lot in industrial park ($750 k valuation) with 15,000 ft 2 steel bldg. ($500 k valuation); lease = $100 k/year ($75 k for

principal and interest, $25 k for profit to property owner)$100.00

Tooling: ($1 M) depreciated and/or replaced over 10 years @ $100 k/year, distributed over 1,000 heat pumps per year $100.00Utilities: Gas: 1,000 MMBtu/yr @ $10.00/MMBtu = $10,000/yr; Electricity: 125,000 kW h/yr @ $0.12/kW h = $15,000/yr; $40.00

Water: 1000 HCF (HCF = 100 ft3) @ $5.00/HCF = $5000/yr;Sewer $5000/yr and waste $4000/yr

Accounting/Clerical: 3 $35,000/yr (w/fringe/payroll tax/comp.) $105.00Engineering and Sales: 4 $70,000/yr (w/fringe/payroll tax/comp.) $280.00

Advertising: $100,000/yr $100.00Insurance and Licenses: $50,000/yr $50.00

TOTAL for OVERHEAD $775.00TOTAL for MATERIALS, LABOR, and OVERHEAD $7690.00List price for 633 MJ/day unit, production cost $7690.00 $8500.00List price for 506 MJ/day unit, production cost $6615.00 $7500.00List price for 380 MJ/day unit, production cost $5541.00 $6500.00



13/19

with the same electric heat pump (EHP) fully dependentupon the power grid is:

V0;SE ISE CSE BSE OSE IEHP CEHP BEHP OEHP

XNj1

F0 1 0:01 j 1 1 e

1 i

j"

RSE;j MSE;j SSE;j

1 ij

1 tincometpropGSE;j

1 ij

tincomemLSE;j

1 ij#

2.2.1.2. Present value of solar thermal cooling system versus

grid dependent heat pump. The present net value V0,ST of theST cooling system [evacuated flat panel (EFP) collectors,adsorption heat pump (COPC = 1.5), and ice thermal reser-voir] versus a SEER 19.3 (COPC = 5.66) electric heat pump(EHP) fully dependent upon the power grid (EHP) is:

V0;ST IST CST BST OST IEHP CEHP BEHP OEHP

XN

j1

F01 e

1 i j

RST;j MST;j SST;j

1 ij"

1 tincometpropGST;j

1 ij

tincomemLST;j

1 ij

#

The net monetary benefit afforded by the solar thermalcooling system as compared with the solar electric coolingsystem over its lifetime is:

V0;STSE V0;ST V0;SE

2.2.1.3. Definition of terms and assignment of input

parameters.

BEHP, BSE, BST = Cost of building modifications neces-sary to support the EHP, SE, or ST cooling systems. Allare minimal and already included in (installed) costs:IEHP, ISE, IST.CEHP = $250 typically for a higher efficiency heat pump(SEER > 16).CSE = credits to homeowners for installing the portionof the PV system dedicated to cooling (i.e., >3 kW) aslisted in Table 8, plus CEHP = $250 for the SEER 19.3electric heat pump.CST = credits to homeowners for installing the solarthermal cooling system. Utilities typically pay a rebate for installing new

equipment that reduces peak grid load, called peakshedding, as compared with existing equipment.The rebate is taken to be $250/kW reduction in peakgrid load. It is assumed that the solar thermal coolingsystem replaces an older (10+ years) electricheat pump with typical SEER 12; CST $250 _Qcool;max=COPC _Qcool;max 3:412=SEER. This credit

is assumed to be awarded in $125 increments byrounding to the nearest 0.5 kW of peak reduction.

North Carolina grants a rebate of 35% of installedcost up to a maximum of $10,500.

Hawaii allows a tax credit of 35% of installed cost up

to a maximum of $1750. Table8

SubsidiesforphotovoltaicpanelsintheSouthernUSASunbelt

F

ederal

Taxcredit=30%

ofinstalledcost,uptoamaximumof$200

0,minusstatetaxcreditsorrebates

N

orthCarolina

Rebateof35%of

installedcostuptoamaximumof$10,500

G

eorgia

$500taxcrediton

installedcost

F

lorida

Salestaxexemptio

n

T

exas,Austinonly

Rebateof$4.00/W

upto$12,000,allappliedtothebaseline

3kW

arrayfornon-HVACusage,meaning

zerorebatefortheHVACportionofthePVarray

A

rizona

Taxcreditof25%

ofinstalledcostupto$1000,plus$4.00/W

or50%ofinstalledcost,whicheverisless

N

evada

Rebateof$3.00/W

upto$15,000,$9000ofwhichwouldbeappliedtowardthebaseline3kW

arrayfor

non-HVACusage

H

awaii

Taxcreditof35%

ofinstalledcostuptoamaximumof$175

0

C

alifornia

Rebateof$2.80/W

inthefirsthalfof2006,decreasing$0.20/W

everysixmonthsthereafter.AnumberofCaliforniacitiesandcountieshavemoreattractiverebateswhich

maybeclaimedin

lieuofthestaterebate



14/19

e = annual escalation rate in fuel (electricity and gas).This is assumed to be 6%, since an ever greater propor-tion of electricity is generated by gas turbines, and theprice of gas has been climbing for several years as aresult of the dash to gas because it is cleaner burningthan coal and does not entail the enormous capital cost

and waste disposal problem of nuclear.F0 = fuel (electricity) cost in the present year to operatea SEER 19.3 electric heat pump ( 0 for year 1 for boththe SE and ST system, i.e., totally independent of thegrid). F0 is assumed to remain zero over the 20 year use-ful life of the ST cooling system. But for the SE coolingsystem, F0 rises at 1% per annum after year 1 to 19% ofconsumption in year 20 due to degradation of the PVmodules. See the definition of RSE,j + MSE,j SSE,jbelow.GEHP,j, GSE,j, GST,j = Assessed value of the new SEER19.3 electric heat pump, SE cooling system, or ST cool-ing system in year j.

i= interest rate on earnings from investing in fiduciariesrather than on a SE or ST system. It is assumed to be 6%for a 50/50 mix of bonds (3% return) and large cap secu-rities (9% return) typical of the portfolio for a middle-aged person with a managed retirement account.IEHP = initial cost of grid dependent electric heat pump,described and valued in Section 2.1.1.ISE = initial cost of SE cooling system, which includesIEHP, valued in Section 2.1.2.IST = initial cost of ST cooling system, described andvalued in Section 2.1.3.LSE,j = Additional outstanding mortgage loan attrib-

uted to the portion of the solar photovoltaic system usedfor cooling in year j, as compared with a grid dependentEHP, since the SE cooling system is probably entirelyfinanced on a 2nd or 3rd mortgage so LSE,j V0,SE.LST,j = analogous to SE system, so LST,j V0,ST.m = mortgage interest rate expressed as a decimal.Assume 8% for a 2nd (or 3rd) mortgage, which is prob-ably what would be used to finance a solar PV or ther-mal system.N= number of years from the present. N can be eitherthe useful lifetime of the system Nuseful 20 years, orthe number of years necessary to achieve payback (whenVSE = 0 or VST = 0).OEHP, OSE, OST = Cost of space occupied by EHP, SEor ST cooling system. All are assumed 0.RSE,j + MSE,j SSE,j = present value of replacementand repair costs RSE,j in year j, plus maintenance costsMSE,j in year j, less the salvage value SSE,j of those partsreplaced in yearjforall Nyears for the portionof the solarPV system used for cooling. This is estimated at anaverage per annum expense of 1.3% of installed cost forfour-season climates or 2.5% of installed cost for tropicalor subtropical climates over the 20 year design lifetime. Most PV module manufacturers guarantee no more

than 20% reduction in output over a typical 20 year

warranty according to www.solarbuzz.com [8]. Utili-

ties do not pay homeowners for excess generationsupplied to the grid. Therefore, it is assumed the PVarray is sized to match demand at the time of instal-lation, and that output decreases 1% per annum to80% of consumption (assumed steady) at the end of20 years.

DC/AC inverter is solid state and assumed to last theentire 20 year design lifetime. Batteries are assumed used to provide not only back-

up power, but also to permit more substantial peakshedding of residential demand at sufficient marketpenetration. They comprise about 15% of totalinstalled cost [8]. Solar systems employ lead-acidbatteries that require replacement every % 1000cycles when nearly fully discharged each cycle,occurring daily during the peak of the cooling sea-son. The number of approximately full cycles canrange from $100 per year for four-season climates,to $200 for subtropical, to 300+ for tropical. So,

batteries are assumed to be replaced at 10 year inter-vals in four-season climates at an average annualexpense of 1.5% of ISE, and at 5 year intervals insubtropical and tropical climates at an averageannual expense of 3% of ISE. Salvage price of thelead is assumed to reduce these to 1.3% and 2.5%,respectively.

Charge controller (solid state) is $10% of installedcost [7], and lasts the entire 20 years.

RST,j + MST,j SST,j = present value of replacementand repair costs RST,j in year j, plus maintenance costsMST,j in year j, less the salvage value SST,j of those parts

replaced in year j for all N years for the solar thermalHVAC system. This is projected at an average perannum expense of 0.7% of installed cost over the 20design lifetime of the system. Etched glass cover, aluminum absorber sheet and

tubing with black nickel solar selective coating, andfiberglass box (with UV protective paint) are not sub-ject to significant degradation over 20 years.

Silicone sealants, for making a vacuum-tight sealbetween the cover glass and fiberglass box, are oftenwarranted for well over 20 years, even when exposedto direct sunlight.

Low iron cover glass and aluminum absorber sheetand tubing are salvageable for new solar collectors,but their value is likely offset by the cost of removaland transportation.

Mechanical vacuum pumps can be very reliable, sothe pump is assumed to last the entire 20 year designlifetime. The oil is changed every few years at negligi-ble cost.

Heat transfer fluid (HTF) is 50/50 ethylene glycoland water. Newer liquid corrosion inhibitors can pro-tect for several years, so the HTF is assumed to bechanged every 5 years, with a negligible annualizedcost of less than 0.1% of total installed system

cost.



15/19

Adsorbent canisters have no moving parts, and theadsorbent can be cycled essentially indefinitely. TheHTF gear pump and motor can easily last 20 years.The solenoid valves comprising the HTF manifoldare very reliable, often lasting millions of cycles. Itis assumed that replacing faulty parts would

cost < 0.1% of IST per annum over 20 years. Expandable rubber tubing in the ice thermal reser-

voir, which serves as the ammonia evaporator, willbecome dry-rot every several years, requiring periodicinspection and replacement at an annual average costof 0.5% of total installed system cost.

tincome = income tax rate in the highest bracket paid.Federal income tax is 25% or 31.6% for middle or uppermiddle income brackets. State income taxes in the south-ern Sunbelt range from 0% (FL, TN, TX, and NV) to9.3% (CA), and are deductible from federal income tax.tprop = property tax rate, although a number of statesallow renewable energy systems to be excluded from

property value assessments. Property tax is also deduct-ible from federal income tax. In many states, assessed(taxable) value is not necessarily equal to fair marketvalue, making the effective rate difficult to determine.Local millage rates (1/1000th of a percent) addedonto the state property tax rate further complicate thematter. For cities in which the exact rate proved hardto ascertain, an estimate of 1% is used.

2.2.2. Interpretation of lifecycle economic model

Tables 9A and 9B present the lifecycle (20 year) costs

of SE and ST cooling systems, respectively, as comparedwith a grid dependent EHP with highest availableCOPC = 5.66 (SEER = 19.3). The economic equations forthe SE and ST cooling systems are given in Sections2.2.1.1 and 2.2.1.2, respectively, while input parametersare defined and assigned values in Section 2.2.1.3 The lastcolumn in each table lists the present net value of the cool-ing systems, V0,SE (in Table 9A) or V0,ST (in Table 9B);positive values are net costs and negative values are netsavings.

2.2.2.1. Solar electric cooling system. For the conditions ofthe present analysis, the SE system cannot provide sav-ings compared with the relatively low or middling resi-dential electric rates in the Southeast, South Central,and part of the Desert Southwest (El Paso, TX andAlbuquerque, NM). Even in NC, the one state in theseregions offering a substantial rebate ($4456), the SE cool-ing system costs more to the homeowner than a griddependent COPC = 5.66 (SEER 19.3) heat pump. InAZ and Central and Southern CA, generous subsidiesdo provide a savings to the homeowner, with payoff in912 years, as indicated by bold numbers in parenthesesin the last column following negative V0,SE (net savings)over 20 years. The generous subsidy in NV yields payoff

at 17 years.

However, the net societal economic effect in all but onelocation is a cost rather than a savings, determined by add-ing state and federal subsidies CSE and the V0,SE, rangingfrom $$200 to $$5600. The only location affording a netsocietal savings, approx. $1500, is Fresno, CA, represent-ing the average for the huge Central Valley with a popula-

tion of several million. This is largely due to very highelectric rates charged by Pacific Gas & Electric Co.These predictions are sensitive to the electric rate or

fuel cost F0,j. An increase in the escalation rate e of elec-tricity, as compared with the interest rate ion investments,would hasten payoff, whereas a decrease in the ratio ofe toi would extend payoff. Long term i has changed little overthe past 80 years, whereas e has been much more volatile,especially recently since an ever greater proportion of elec-tricity is generated from gas, which is a highly volatilemarket.

It is assumed in Section 2.2.1.3 that e = 6%, about twicethe average inflation rate over the past two decades. At

e = 6%, electric rates would increase to 321% of presentrates over the 20 year projected useful lifetime of the SEcooling system. A nominal inflation rate of 3% would raisethe price of everything else to 181% of present prices. So,electricity would be 77% (=321%/181%) relatively moreexpensive in 20 years than it is now. Unless a very pessimis-tic outlook is taken regarding electric rates, a value ofe = 6% seems sufficiently large. For a 1% reduction of efrom 6% to 5%, with isteady at 6%, the net societal savingsin the CA Central Valley, the only region affording suchsavings, is reduced from $1500 to a mere $400.

2.2.2.2. Solar thermal cooling system. The solar thermalcooling system (Table 9B) would pay for itself within 14years in Fresno, CA (Central Valley), with savings to thehomeowner of about $4000. The net societal benefit(CST + V0,ST) is about $3200. The ST cooling system alsoaffords a net savings to the homeowner in the eastern LosAngeles basin (e.g., Ontario, San Bernardino, and River-side). But the payoff is 1819 years. And the net societalvalue is about $0 (nil) to about $600 (a savings).

The far and away most advantageous location for a STcooling system is Hawaii, where the net savings to thehomeowner is nearly $9500, which is 52% of the installedcost of about IST = $18,100. The societal savings (CST +V0,ST) is about $7100, about 39% of IST. The payoff is11 years. This significant savings is due in part to the highelectric rate, but also because the climate is tropical, balmyyear round, resulting in a large annual cooling load. If edrops from 6% to 5%, while i is constant at 6%, the home-owners savings are reduced to $7400 (41% of IST) andthe societal savings are $5000 (28% of IST). The payoffis 12 years.

2.2.3. Economic projections

2.2.3.1. Solar electric cooling system. Photovoltaic modulesrepresent $50% of total installed system cost and thus are

the principal driver in cost [8]. The remainder of cost is for



16/19

Table 9ANet cost over 20 years of solar electric cooling system in comparison with grid dependent electric heat pump for 24 cities across US Sunbelt (south of 37N); negativ

dependent heat pump

City Residential

electric

rate

($/kW h)

Annual electric

usage for cooling

by SEER 19

H.P. (kW h)

Installed

cost of

same

SEER 19H.P.

Installed cost of grid-

tied PV system for

cooling and same

SEER 19 H.P.

State

credit,

rebate,

etc.

Federal

credit,

rebate,

etc.

Differential

loan

amount and

assessedvalue

Annual avg.

maintenance,

repair, and

salvage

Net state and

federal income

tax rate (assume

25% fed. rate)

P

ta

1 Raleigh-Durham,

NCa

0.0904 3142 3000 12,731 4456 0 5275 166 0.3119 0

2 Charleston,SCa

0.0863 4705 3000 16,660 0 2000 11,660 217 0.3025 0.

3 Atlanta, GAa 0.0986 3375 3000 13,355 500 1500 8355 174 0.2950 0.

4 Miami, FLb 0.0907 7190 3000 21,657 0 2000 16,657 541 0.2500 0.

5 Tampa, FLb 0.0833 6275 3000 19,996 0 2000 14,996 500 0.2500 0.

6 Montgomery,

ALa0.0584 4208 3000 15,475 0 2000 10,475 201 0.2875 0.

7 Jackson, MSa 0.0720 4447 3000 16,053 500 1500 11,053 209 0.2875 0.

8 Nashville,

TNa0.0709 3417 3000 13,466 500 1500 8466 175 0.2500 0.

9 Little Rock,ARa

0.0738 3741 3250 14,559 0 2000 9309 189 0.3025 0.

10 New Orleans,

LAa0.0982 5298 3000 17,990 0 2000 12,990 234 0.2950 0


0.0826 3430 3000 13,500 0 2000 8500 176 0.2999 0.

12 Austin, TXa 0.1062 4762 3000 16,792 0 2000 11,792 218 0.2500 013 Brownsville,

TXb0.1054 6855 3000 21,073 0 2000 16,073 527 0.2500 0

14 El Paso, TXc 0.1113 3200 3000 12,888 0 2000 7888 168 0.2500 0

15 Albuquerque,NMc

0.1144 2136 2750 9633 0 2000 4883 125 0.3010 0.

16 Phoenix, AZc 0.1231 5061 3250 17,718 9859 0 4609 230 0.2878 0.

17 Las Vegas,NVc

0.1190 3983 3250 15,170 5952 0 5968 197 0.2500 0

18 Fresno, CAd 0.2160 3206 3250 13,153 3832 0 6071 171 0.3198 0

19 Los Angeles,

CAd0.1718 2969 2500 11,759 5176 0 4083 153 0.3198 0

20 Burbank/

Glendale,

CAd

0.1718 4442 3000 16,042 5311 0 7731 209 0.3198 0

21 Ontario, CA

d

0.1718 5067 3250 17,733 6058 0 8425 231 0.3198 022 San

Bernardino,

CAd

0.1718 4732 3250 16,972 5657 0 8065 221 0.3198 0

23 San Diego,

CAd0.1840 2772 2750 11,461 3313 0 5398 149 0.3198 0

24 Honolulu,

HIb0.1569 7018 2750 21,111 1750 250 16,361 528 0.3119 0



17/19

Table 9BNet cost over 20 years of solar thermal cooling system in comparison with grid dependent electric heat pump for 24 cities across US Sunbelt (south of 37N); negativ

dependent heat pump

City Residential

electric rate

($/kW h)

Annual

electric usage

for cooling bySEER 19

H.P. (kW h)

Installed

cost of

electricH.P.

SEER 19

Installed cost of

EFP solar

collectors,adsorption

H.P. , and ice

reservoir

State

credit,

rebate,etc.

Federal

credit,

rebate,etc.

Differential

loan

amount andassessed

value

Annual

avg.

mainten-ance,

repair, and

salvage

Net state and

federal

income taxrate (assume

25% fed. rate)

1 Raleigh-

Durham, NCa

0.0904 3142 3000 21,524 8283 0 10,490 151 0.3119

2 Charleston,

SCa0.0863 4705 3000 27,424 750 0 23,924 192 0.3025

3 Atlanta, GAa 0.0986 3375 3000 20,602 625 0 17,227 144 0.2950

4 Miami, FLb 0.0907 7190 3000 26,253 625 0 22,878 184 0.2500

5 Tampa, FLb 0.0833 6275 3000 24,092 625 0 20,717 169 0.2500

6 Montgomery,

ALa0.0584 4208 3000 21,235 750 0 17,735 149 0.2875

7 Jackson, MSa 0.0720 4447 3000 21,107 750 0 17,607 148 0.2875

8 Nashville,

TNa0.0709 3417 3000 19,547 750 0 16,047 137 0.2500

9 Little Rock,ARa

0.0738 3741 3250 19,611 750 0 15,861 137 0.3025

10 New Orleans,

LAa0.0982 5298 3000 23,014 750 0 19,514 161 0.2950

11 Oklahoma

City, OKa0.0826 3430 3000 17,962 750 0 14,462 126 0.2999

12 Austin, TXa 0.1062 4762 3000 20,297 750 0 16,797 142 0.2500

13 Brownsville,

TXb0.1054 6855 3000 20,842 750 0 17,342 146 0.2500

14 El Paso, TXc 0.1113 3200 3000 13,972 625 0 10,597 98 0.2500

15 Albuquerque,

NMc0.1144 2136 2750 12,279 625 0 9154 86 0.3010

16 Phoenix, AZc 0.1231 5061 3250 18,797 750 0 15,047 132 0.2878

17 Las Vegas,NVc

0.1190 3983 3250 16,201 750 0 12,451 113 0.2500

18 Fresno, CAd 0.2160 3206 3250 14,247 875 0 10,372 100 0.3198

19 Los Angeles,CAd

0.1718 2969 2500 14,423 375 0 11,798 101 0.3198

20 Burbank/

Glendale,

CA

d

0.1718 4442 3000 19,628 625 0 16,253 137 0.3198

21 Ontario, CAd 0.1718 5067 3250 21,481 750 0 17,731 150 0.3198

22 SanBernardino,

CAd

0.1718 4732 3250 19,593 750 0 15,843 137 0.3198

23 San Diego,

CAd0.1840 2772 2750 14,950 625 0 11,825 105 0.3198

24 Honolulu,

HIb0.1569 7018 2750 18,050 2375 0 13,175 126 0.3119



18/19

inverter ($5%), batteries ($15%), charge controller($10%), and installation ($20%). From October 2000through May 2004, the cost of PV modules decreased inreal terms (constant dollars) from $5.87/W to a low of$4.94/W. But since then the price has risen to $5.46/W inOct. 2006, which has been attributed to increased demand

for silicon feedstock by the electronics industry that dwarfsthe PV industry [8]. The net price change since October2000 is $0.41/W (7.0%), or 1.2% per annum overthe past 6 years. Batteries, inverters, and charge controllersare all mature technologies with nearly static real cost. So,the net price change for complete PV systems with batter-ies, inverters, and charge controllers has been 0.6% perannum. Extrapolation suggests the economic prospects ofPV systems will improve gradually over the next severalyears, dependent of course on the actual escalation rate e.

The price of electric heat pumps in real terms has beenfairly constant over several years.

The PV industry has lobbied for continued incentives

(rebates, tax credits, etc.) on the premise that these willspeed market penetration, eventually resulting in substan-tial price decreases afforded by mass production. World-wide production has increased 2030% per annum forthe past several years, with most of installed capacity($70%) in energy poor Japan and Germany [8]. Despitesteadily increasing production, prices have decreased byonly the aforementioned 1% in real terms over the past5 years. At this pace, the PV industry may become self-supporting in more advantageous US markets, those withhigh electric rates (e.g., Central & Southern CA), in per-haps 20 years, well beyond original optimistic projec-

tions.

2.2.3.2. Solar thermal cooling system. The installed cost ofevacuated flat panel (EFP) thermal collectors comprises4670% of installed cost of a solar thermal cooling system.The installed cost is assumed herein to be a conservativelyhigh $250/m2. But, mass production on the order of tens ofthousands of panels per year for sales of 1000+ adsorptionheat pumps per year, would justify full automation andassociated cost savings. Such savings could readily exceed10% ($25/m2). So, economic prospects for solar thermalcooling systems would be expected to improve overcomputations.

3. International applications

Interest in the use of solar adsorption chillers for indoorspace cooling is still in its formative years, but growing allover the world, driven by the fact that this technology isenvironmentally friendly and economically advantageousin regions with expensive and perhaps unreliable electricity.Conventional electro-mechanical air conditioning con-sumes large amounts of electricity, thereby exacerbatingutility peaking during summer months, and employs refrig-erants that have negative environment effects. Adsorption

cooling is also attractive because it can be used year round,

for heating in the winter and for cooling in the summer. Asthese benefits of solar thermal energy become recognizedmore and more globally, the role of adsorption chillers willbecome more and more prominent.

The German Federal Ministry of Economics and Tech-nology (http://www.german-renewable-energy.com) esti-

mates that by the end of 2005 about 70 systems wereinstalled in Europe that use solar heat for summer air-con-ditioning. This low figure suggests that this promising tech-nology is yet to emerge as a viable alternative. Thechallenges seem to be standardization, cost, reliability,and efficiency. The COPC has been improved with theintroduction of high efficiency heat exchangers. Totalefficiency ratings can be further improved by includingadsorption chillers in co-generation or tri-generationapplications.

European research has also reduced the footprint by40% by simplifying the internal design, a factor than canprove to be crucial in crowded inner cities. A sensitive tem-

perature sensor in the high efficiency evaporator allows theproduction of chilled water temperatures as low as almost3 C (37 F).

Miller [10] developed the first commercial adsorptiondevice, which was used for refrigerated box cars in theUSA in the 1920s and 1930s. It fell into disuse after theinvention of CFCs in 1931 and national electrification.Adsorption technology started being resurrected in the late1970s after the oil shocks of 197374. The first moderncommercial device was developed in Japan by the Nishi-yodo Kuchoki Corp. of Kyoto in the mid-1980s. Adsorp-tion chillers have started to be recently marketed in Hous-

ton, Texas, USA. There are two other USA dealers, both inCalifornia. To date, only about five systems have beeninstalled in the USA.

Adsorption chillers were introduced to Europe in theearly 1990s, and reportedly scores of successful applica-tions have followed. The first solar-driven adsorption chil-ler was engineered and installed at the University ofFreiburg. Results were later published by the institutesHans-Martin Henning and by Hendrik Glaser of Univer-sitatsklinikum Freiburg Geschaftsbereich Technik(Sustainable Habitat Design Advisor, http://www.sustain-able-buildings.org/files/).

The technology is also setting foot in parts of Asia. InNovember 2003 the National University of Singaporeannounced that it is signing licensing agreements foradsorption chillers with five small and medium-sized enter-prises to bring technologies developed within research labsat the University to the market.

Limited research has also been initiated in Brazil at theFederal University of Ceara [11]. Ambient data collecteddaily over 18 years were then divided into hourly valuesto simulate reactor temperature during adsorption/desorp-tion. The adsorbent was salt impregnated with graphiteand the refrigerant was ammonia. The refrigerator oper-ated well in Fortaleza and better results are expected in

the countryside of the state of Ceara.

http://www.german-renewable-energy.com/http://www.sustainable-buildings.org/files/http://www.sustainable-buildings.org/files/http://www.sustainable-buildings.org/files/http://www.sustainable-buildings.org/files/http://www.german-renewable-energy.com/


19/19

As testimony to the growing role of the adsorption cool-ing, the International Energy Agencys Solar Heating &Cooling Program included solar driven adsorption chillersin its 2001 Annual Report [12] of research activities. Sub-tasks B and C of the report mention design tools and sim-ulations, market aspects, and environmental benefits for

solar assisted air conditioning including adsorption chill-ers. Because of the global availability of solar energy atleast for parts of the year, the environmental benefits,and the growing pressure on grid-supplied electricity,adsorption cooling technology has a bright global future.

4. Conclusions

Solar electric (SE) and solar thermal (ST) cooling sys-tems afford savings to the homeowner only in states withmoderately high and greater electricity prices (NV, AZ,CA, and HI). The net societal cost, the sum of taxpayer

funded credits, rebates, etc. (CSE or CST) and the net valuefor the homeowner (V0,SE or V0,ST), makes such systemsself-supporting in an even smaller number of locations.SE cooling system is self-supporting only in the CA CentralValley with CSE + V0,SE % $1500, (negative means sav-ings) over 20 years, largely due to exorbitant electric pric-ing of $0.216/kW h. ST cooling system is also selfsupporting in this region of CA, with CSE + V0,SE %$3200 over 20 years.

In four-season climates, where cooling is needed duringonly part of the year, SE cooling systems can bankenergy generated during the rest of the year with the utilitycompany, to be drawn upon for cooling when needed. Thisallows for a smaller PV array. This also assumes a netmetering agreement is in effect, already in 39 states andincreasing. In such regions, SE cooling systems are eco-nomically superior to ST cooling systems, the latter ofwhich cannot bank energy for more than a day in theice thermal reservoir.

However, in tropical and subtropical climates, withcooling required year round, or nearly year round, SE cool-ing systems cannot bank much energy in the cooler seasonto be used in the warmer season. On the other hand STcooling systems are used year round, at or near capacityin the warmer season, and at partial capacity in the cooler

season instead of lying idle as in a four-season climate. Insuch locales, the ST system is vastly economically superiorto the SE system.

Four such tropical or subtropical regions are included inthe present study, Florida (Miami and Tampa), SouthTexas (Brownsville), and Hawaii. Miami, Tampa, andBrownsville are subtropical with minimum winter cool-ing loads of only 11-22% of maximum summer coolingload, meaning the ST system is not used very much in win-ter. Monthly average usage is 53-61% of peak capacity.

Moreover, electricity prices in these three cities are rela-tively low. But in Hawaii, minimum cooling load in thecooler season is 47% of maximum cooling load, andmonthly average usage is 72% of peak capacity. This highusage percentage, coupled with a high electricity price(approaching prices in CA) results in substantial savings.

With current subsidies, the saving to the homeowner,V0,ST, is 52% of installed cost IST over the 20 year lifecycle.Without subsidies the net savings to the homeowner is still39% of IST.

Hawaii has a population of 1.2 million, about 3/4 ofwhom live on Oahu and pay an electricity price of about$0.157/kW h. The other 1/4 of the population pays about$0.224/kW h. Hawaii represents a modest market withinthe US. But there are a number of tropical countries withhigh electric prices, and less reliable electric grids thanthe US, representing a very large market. Examples includeBrazil, Equatorial Africa, India, Southeast Asia, Indonesia,and the Pacific Islands. Moreover, ST collectors can be fab-

ricated with common machine tools, not in clean roomswith multi-million dollar semiconductor manufacturingequipment, accessible only in the US, Japan, Western Eur-ope, Singapore, Taiwan, South Korea, and Indonesia.

References

[1] M.A. Lambert, Design of solar powered adsorption heat pump withice storage, Journal of Applied Thermal Engineering, in press,doi:10.1016/j.applthermaleng.2006.09.016 .

[2] J.F. Kreider, P.S. Curtiss, A. Rabl, Heating and Cooling of Buildings:Design for Efficiency, second ed., McGraw-Hill, Boston, Massachu-setts, USA, 2002.

[3] J.K. Page, The estimate of monthly mean values of daily total short-wave radiation on vertical and inclined surfaces from sunshinerecords for latitudes 40N to 40S, Paper No. 35/5/98, in: Proceedingsof United Nations Conference on New Sources of Energy, Rome,1961.

[4] B.Y.H. Liu, R.C. Jordan, The interrelationship and characteristicdistribution of direct, diffuse, and total solar radiation, Solar Energy 4(3) (1960) 119.

[5] E.C. Boes, I.J. Hall, R.R. Prairie, R.P. Stromberg, H.E. Anderson,Distribution of direct and total radiation available for the USA, in:Proceedings of the 1976 Annual Meeting of the American Society ofISES, Sharing the Sun, vol. 1, Winnipeg, August 1520, 1976, pp.238263.

[6] J.R. Howell, R.B. Bannerot, G.C. Vliet, in: Solar-Thermal EnergySystems: Analysis and Design, McGraw-Hill, New York, 1982, ISBN

0-07-030603-6, p. 100.[7] D. Rapp, in: Solar Energy, Prentice-Hall, Englewood Cliffs, NJ, 1981,

ISBN 0-13-822213-4, pp. 326329.[8] www.solarbuzz.com, downloaded 12/18/05 to 10/22/06.[9] www.doe.gov, downloaded 12/20/05.

[10] E.B. Miller, The development of silica gel refrigeration, AmericanSociety of Refrigeration Engineers 17 (4) (1929).

[11] M.E. Vieira, H.B.C. Moreira, Solar refrigerating unit with anadsorption reactor and evacuated tube collectors, Brazilian Journalof Chemical Engineering 14 (3) (1997).

[12] P. Murphy (Ed.), Morse Associates, Inc., 1808 Corcoran Street, NW,Washington, DC 20009, USA, March 2002, IEA/SHC/AR01.

http://dx.doi.org/10.1016/j.applthermaleng.2006.09.016http://www.solarbuzz.com/http://www.doe.gov/http://www.doe.gov/http://www.solarbuzz.com/http://dx.doi.org/10.1016/j.applthermaleng.2006.09.016

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79248311 Thermo Economic Analysis of Solar Powered Adsoption Heat Pump