Contents lists available at SciVerse ScienceDirect
Energy and Buildings
j ourna l ho me p age: www.elsev ier .com/ locate /enbui ld
conomic and environmental life cycle analysis of solar hot water systems in thenited States
in Hang1, Ming Qu ∗, Fu Zhao2
urdue University, United States
r t i c l e i n f o
rticle history:eceived 28 June 2011eceived in revised form 19 October 2011ccepted 31 October 2011
eywords:ife cycle analysisolar water heating
a b s t r a c t
This paper evaluates the solar water heating systems for the U.S. typical residential buildings, from theenergetic, economic and environmental perspectives, and includes two different types of solar collectors(i.e. flat-plate and evacuated-tube solar collectors), two types of auxiliary systems (i.e. natural gas andelectricity), and three different locations (i.e. Los Angeles, Atlanta, and Chicago). The performance of solarwater heating systems is also compared with conventional systems that use either natural gas or electric-ity. The results showed that the flat-plate solar water heating systems using natural gas auxiliary heaterhas the best performance among all the types and at all locations. The energetic and environmental pay-
back periods for solar water heating systems are less than half of a year, and the life cycle cost payback forsolar water heating systems vary from 4 to 13 years for different cities and different configurations whenusing the conventional electrical water heating system in each city as the benchmark. For a representa-tive case, i.e. flat-plate solar water heating system with natural gas auxiliary heater in Atlanta, sensitivityanalysis shows that the daily hot water use has the most significant effects on energetic, environmental
ce.
vacuated tube and economic performan
. Introduction
According to the 2010 DOE Building Energy Data Book, residen-ial buildings in the United States are responsible for 2.27 × 1010 GJrimary energy use and 6.4 × 109 tons carbon dioxide emissions.hese correspond to 22% of total primary energy consumptionsnd 21% of total carbon dioxide emissions in the United States,espectively [1]. A breakdown of primary energy use in the resi-ential sector indicates that 18% of the primary energy is used forater heating, which is second only to space heating (45%) [1]. Solarater heating systems (SWHS) are attracting increasing interest as
solution to reduce fossil fuel consumption and greenhouse gasmissions of residential buildings [2].
A SWHS typically includes solar collectors mounted on the tiltedoof and a separate hot storage tank beside the conventional watereater (usually referred to as an auxiliary heater). The solar col-
ectors convert solar radiation into thermal energy, which provides
omestic hot water to the house. Residential buildings often requireot water temperature around 50–60 ◦C, which SWHS can meetasily [3]. SWHS has been studied for almost 70 years and is the
most widely used solar energy application in the world. In 2008,the global SWHS capacity had reached 145 GW [4]. In the UnitedStates, the installed capacity for SWHS has increased each year since2004. In 2010, it is estimated that over 2.4 × 105 m2 of SWHS capac-ity was installed in the U.S., which equals to 158 MW-thermal, andmore than 80% of them are installed for residential buildings [5].To date, more than 1.5 million homes currently use SWH systemsin the United States [6], which represents 1.3% of the total numberof households in the U.S.
A SWHS saves energy and reduces greenhouse emissions rela-tive to conventional fossil fuel water heating system (WHS) in theuse phase. However, a complete examination should include everystage of the life cycle of a SWHS, i.e. from raw material extraction toend of life disposal while considering energetic, economic and envi-ronmental performance comprehensively. Life cycle assessment(LCA) is to date the most widely used tool for generating the envi-ronmental profile (including energy consumption and greenhousegas emissions) of a product or process. For the study of the SWHS,it is a common approach to combine LCA with life cycle cost (LCC)analysis.
A literature search on LCA studies of SWHS suggests that mostof the research reported is for European scenarios, and the casesfor United States are rare. These studies included the whole life
cycle of the system, but different life span has been used, rangingfrom 10 to 25 years [7–12]. The functional unit selected is eitherhot water supplied to a typical household [7,10–12] or a certainamount of conventional energy replaced [8]. Aside from analyses
will be on to provide 60 ◦C hot water to the demand use, and theauxiliary heater will be off when the output temperature (T5) ishigher than 60 ◦C. In the cities (e.g. Chicago) where there existsa freezing issue, glycol will be added to the solar collection loop;
Solarcollec
tors
Hotstorage
Auxiliaryheater
T4
T1
T3
T5
82 Y. Hang et al. / Energy an
or greenhouse gas emissions and cost, some studies also includedhe primary energy consumption [9]. For SWHS considered, theuxiliary heater uses either natural gas or electricity as the energyource and comparison is usually made against conventional WHSshat use electricity, natural gas or oil [7–11]. The results of thesetudies showed that the life cycle emissions of SWHSs are domi-ated by the use phase, while the capital cost of SWHSs accounts
or the majority of LCC [7]. The environmental impact of the SWHystems with natural gas heater backups is smaller than the impactf the systems with electrical heater backups [10,11], and the pureatural gas heaters have lower environmental impact compared tohe SWH systems with electrical backups [10].
Although most of the studies included more than one type ofvailable SWHSs and conventional WHSs, usually only one type ofolar collectors and one location are considered, the only exceptions Crawford et al. [7], which included two locations, i.e. Melbournend Brisbane in Australia. In addition, flat-plate solar collectorsFPC) are used for most studies, except in Kalogirou [11], wherevacuated tube solar collectors (ETC) were considered. For practi-al applications, there is a need for comparative studies of all theajor commercially available SWHS configurations and types of
olar collectors to aid potential installers and end users in assessinghich device best suits their needs [12]. Moreover, when calculat-
ng the energy required by operating SWHSs, a simple calculationethod by using monthly or even annual solar fraction to estimate
he energy required by the SWHSs is adopted by most of the papers.or example, Crawford et al. [7] used annual solar fraction in thewo cities to calculate the energy consumed by SWHSs; Tsilingiridist al. [10] adopted a f-chart method to calculate the monthly solarraction; Rey-Martinez et al. [8] use simulation tool named CalSolaro procure the monthly solar fraction. A more detailed model, whichan provide an hourly energy profile, is not adopted by most ofhe papers, except Kalogirou [11], who developed detailed energy
odel of SWHSs in a TRNSYS simulation tool to estimate the hourlynergy consumption required by SWHSs.
In this paper, an environmental and economic LCA study isonducted for several representative SWHSs to compare theirerformance against conventional water heating systems for UScenarios. SWHSs driven by electricity and natural gas are con-idered, the same as for conventional WHSs. Three locationsre considered in this study, including Los Angeles, Atlanta, andhicago. In addition, detailed energy model developed in TRN-YS is used to estimate the energy consumption required by solarystems.
. Methodology
.1. Goal, scope and system boundaries
The goal of the study is to compare the life-cycle energetic, eco-omic and environmental impacts of six types of water heatingystems, including both SWHSs and conventional WHSs, as shownn Table 1. Two types of solar collectors, i.e. FPC and ETC, are con-idered. For the auxiliary heater and conventional heater, eitherlectricity or natural gas is used as the energy source. The perfor-ance of all the systems is assessed for Los Angeles (LA), Atlanta
AT), and Chicago (CH), which represent different climate zones andolar radiation intensities in the United States. The LCA boundary isrom cradle to grave, including raw material acquisition, manufac-uring, usage, disposal, and transpiration among all the stages. Theife span for all the water heating systems is 20 years. Based on the
SHRAE handbook [13], the overall US family domestic hot waterse is 236 l/day. Therefore, the functional unit for the LCA is to meethe daily heating energy for a typical US family (2.53 persons [14])hich requires 236 l of hot water at 60 ◦C. The area of FPC is sized
6 Natural gas WHSwith tank
NGWHS – 236
to be 4 m2, with which the SWHS will meet 60%, 69% and 76% ofthe HW demand in CH, AT, and LA, respectively. In order to makethe capital cost of all the SWHSs similar, 2.4 m2 ETC are selected.The volume of the hot storage tank is assumed to be 236 l, whichequals the daily hot water demand for a typical American family.
In this study, cumulate energy demand (CED) per person isused as the indicator of energetic performance, while carbon foot-print (determined using IPCC Global Warming Potential in 100year time horizon) per person as the indicator for environmen-tal performance. Life cycle cost (LCC) study is also conducted, andequivalent uniform annual cost (EUAC), i.e. LCC converted into thecost in an annual basis equivalently per person is used to representthe economic performance. Besides, the payback times of energy,economic and environmental aspects are calculated as well.
2.2. Description of SHWS
Fig. 1 shows the schematic diagram of a typical SWHS. There arethree major components in a SWHS: solar collectors, a hot storagetank and an auxiliary heater driven by electricity or natural gas.
When the outlet temperature of solar collectors (T1) is 10 ◦C(adjustable) higher than the water temperature in the hot storagetank (T2), the pump in the solar collection loop will be on; andwhen the temperature difference between T1 and T2 is less than2 ◦C (adjustable), the pump will be off. The three-way automaticvalve is modulated to maintain the outlet temperature (T4) at 60 ◦C(adjustable). If T4 is less than 55 ◦C (adjustable), the auxiliary heater
herefore, an extra heat exchanger inside the hot storage tank isequired to separate the glycol and pure water loops.
To date, the most commonly used solar collectors in SWHSsre FPC and ETC which use water as the energy carrier [15]. FPCnd ETC can use both beam and diffuse solar radiation, and theyo not require tracking of the sun. Typical FPC consists of anbsorber, glazing, heat transfer medium, thermal insulation, andeaders. The maximum efficiency of a well-designed FPC ranges
rom 40% to 60% with heat normally delivered between 50 and5 ◦C. ETCs have lower thermal losses due to an internal vacuum,nd less dependence on solar angle due to cylindrical geometry.herefore, ETC can reach temperature up to 120 ◦C, with a normalfficiency around 40–50%. However, the price for evacuated-ube collectors is almost twice of the flat-plate collectors. In thistudy, two typical FPC and ETC with market average performancere selected. Table 2 shows the characteristics of the two solarollectors.
. Life cycle inventory analysis
The life cycle inventory analysis was completed using SimaPro.1 and Ecoinvent 2.0, and includes manufacturing, use, disposaltages, and transportation among these stages.
.1. Manufacturing stage
The bills of materials for the major equipments are listedn Table 3 [16]. In this stage, all the processes used are from
able 3ill of materials.
Equipment Components Material
FPC
Trim Aluminum
Absorber Copper
Frame Steel
Insulation Rock wool
Insulation Corrugated board
Glazing Glass
Transfer fluid Propylene glycol
Transfer fluid Water
Sheet Copper
Coating Copper sheet
Production Electricity
Production Water
ETC
Absorber Copper
Frame Steel
Insulation Rock wool
Insulation Corrugated board
Glass tube Glass
Transfer fluid Propylene glycol
Transfer fluid Water
Sheet Copper
Coating Copper sheetProduction Electricity
Production Natural gas
Production Water
HST HST Steel
EAH EAH EAH
GAH GAH GAH
ote: HST, hot storage tank; EAH, electrical auxiliary heater; GAH, gas fired auxiliary heat
ings 45 (2012) 181–188 183
Ecoinvent 2.0 database, assuming the materials are produced andmanufactured in the similar way as in the United States. Table 3also includes the energy associated with the collector manufac-turing and transportation. Although the materials used to produceboth FPC and ETC are similar, the energy used to produce anETC is much higher than the energy used for FPC. The energyused for transportation of the materials to produce the collectorsis assumed the same for both types of collectors. It is assumedthat the energy used for transportation includes two parts: roadtransportation of 16.8 tkm, and rail transportation of 16.8 tkm. Theinventories of the hot storage tank, the tankless electrical heaterand the natural gas heater use data from the Ecoinvent databasedirectly.
3.2. Use phase
3.2.1. Fuels for auxiliary heaterAccording to the Building Energy Data book 2010 [1], for the
WHS in the residential sector, 68% of the energy is provided bynatural gas, 22% of it is provided by electricity, and rest of the9% is provided by oil and LPG. Therefore, natural gas and elec-tricity are considered as two major conventional fuel types in thisstudy. When considering the use of electricity, different genera-tion mixes should be considered for different regions according toEnvironmental Protection Agency (EPA) [17]. The percent of eachpower generation type (including coal, gas, oil, nuclear, hydro, andother renewable energy), and the conversion factor of CED andGWP based on different power generation mixes [18], are listedin Table 4. The conversion ratios are calculated by using the CEDand GWP required by each type of power generation fuel multiply-ing its percentage. The EPA website lists “Non-Hydro Renewable”
as the final category, which is assumed to be wind and solar PVpower by half/half in this study. In addition, the price of natural gasand electricity for each representative city [19] is shown in Table 4as well.
Mass/area EcoInvent process
1.8 kg Al, production mix, wrought alloy2.82 kg Copper, at regional storage/RER4.14 kg Chromium steel 18/8, at plant/RER2.43 kg Rock wool, packed, at plant/CH3.68 kg Corrugated board, mixed fiber, single wall9.12 kg Solar glass, low-iron, at regional storage1.01 kg Propylene glycol, liquid, at plant/RER1.38 kg Water, completely softened, at plant/RER2.82 kg Sheet rolling, copper/RER1 m2 Selective coating, copper sheet, black chrome1.16 kWh Electricity, medium voltage, at grid9.4 kg Tap water, at user/RER
2.8 kg Copper, at regional storage/RER4 kg Chromium steel 18/8, at plant/RER2.03 kg Rock wool, packed, at plant/CH3.33 kg Corrugated board, mixed fiber, single wall14.2 kg Glass tube, borosilicate, at plant/DE0.654 kg Propylene glycol, liquid, at plant/RER0.9 kg Water, completely softened, at plant/RER2.8 kg Sheet rolling, copper/RER1 m2 Selective coating, copper sheet, black chrome17 kWh Electricity, medium voltage, at grid16.5 MJ Natural gas, burned in industrial furnace53.6 kg Tap water, at user/RER
236 l Hot storage tank, 600 l, at plant/CH/I
23 kW Auxiliary heating, electric, 5 kW, at plant/CH/I
23 kW Gas boiler, 10 kW/RER/I
er.
184 Y. Hang et al. / Energy and Buildings 45 (2012) 181–188
Table 4Generation mix for representative cities.
City Coal (%) Gas (%) Oil (%) Nuclear (%) Hydro (%) Renewable (%) CED(kWh equiv./kWh)
control system cost is assumed 50% of the initial cost of the SWHS[25], and the installation cost of the conventional water heatingsystems is assumed 30% of the investment cost [24].
Fraction of da ily ho
Fig. 2. Daily hot w
.2.2. Residential hot water demandThe water withdrawal profile is shown in Fig. 2, as suggested by
he ASHRAE Standard 90.2 [20], which is shown in Fig. 2. Based onhe daily water usage (236 l/day) and water withdrawal profile, theourly domestic hot water usage can be calculated. The hot wateret point is assumed as 60 ◦C in this study.
.2.3. Energy system simulation model developmentThe energy model is developed in TRNSYS, which is a flexible
ool designed to simulate the transient performance of thermalnergy systems. The model is used to estimate the conventionalnergy required for SWH systems during the operation stage in annnual basis. The time step is 15 min. The following are the majorssumptions of the energy model:
1) The system layout is based on Fig. 1.2) The solar collectors are installed in the tilted roof of the house
with a pitch of the same degree as the latitude of the city, facingthe south direction.
3) The hot water systems are used for the typical American family,with 2.53 persons. The hot water energy can be calculated basedon Eq. (1). In this equation, Cp,w is the specific heat of water, thehot water demand (VHW) is 236 l/day, f is the fraction of dailyhot water draw based on Fig. 2, �w is the density of the water,Th,o is the hot water set point as 60 ◦C, and the cold city waterinlet temperature (Tc,i) varies with locations based on Table 5.
QHW = Cp,w × VHW × f × �w × (Th,o − Tc,i) (1)
4) The daily water draw profile follows Fig. 2.5) The FPC and ETC area is 4 m2 and 2.4 m2, respectively for each
city.
able 5limate conditions for the representative cities [21].
City Latitude Ground water temperature (◦C)
LA 34◦N 16.7AT 33◦N 15.6CH 41◦N 8.3 (lake temperature)
r dra w Flow rate
ithdrawal profile.
(6) The hot storage tank volume is equal to the daily hot waterdemand (236 l) for each city.
(7) The auxiliary heater in the SWHS is sized based on 1:1 backup,which equals the peak domestic hot water load of the city. Theelectrical auxiliary heater efficiency is assumed as 90%, and thenatural gas auxiliary heater efficiency is assumed as 80%.
(8) The control sequence of the SWHS is described in Section 2.2.
3.3. Disposal stage
It is assumed that all the materials will be sent to the land fillafter the life span of 20 years. Although some metals, such as copper,can be recycled, this end-of-life treatment is not considered in thisstudy.
3.4. LCC analysis
Table 6 shows the cost for the equipment. The unit price for theFPC and ETC includes the panel and the structure system [22]. Thetankless electrical and natural gas water heaters are assumed to beauxiliary heaters used in SWHSs. Normally, the water heater withstorage tank in the United States is sized based on the tank vol-ume, which is equal to the daily hot water usage of the family [23].And the tankless water heater is sized based on the peak flow raterequirement of the family [23]. The installation cost and integration
Table 6Unit price of major equipment.
Equipment Unit price
FPC $498/m2
ETC $830/m2
Hot storage tank $1000/m3
EWH with storage tank (236 l) $800GWH with storage tank (236 l) $500Tankless EWH (7.57 l/min) $350Tankless GWH (7.57 l/min) $460
Y. Hang et al. / Energy and Buildings 45 (2012) 181–188 185
Solar collector outlet temp. Hot storage tank to solar collector temp.Hot storage tank outlet temp. Temp. after the mixingCold water inlet temp. Solar radiationUseful solar energy Hot water demandHot water demand provided by solar
Fig. 3. PFC SWHS performance in CH during two days of May.
nd co
4
4
tdcd6hDcte
Fig. 4. Monthly solar fraction a
. Results and discussion
.1. Energy analysis
Fig. 3 shows the profiles of solar irradiation during a two dayime period in May for the FPC SWHS in CH. One is a partially cloudyay, and the other is a sunny day. The outlet temperature of the solarollection loop follows the trend of solar radiation. During the firstay, when the cloud covers the sun, the solar side cannot provide0 ◦C hot water, hence the auxiliary heater is on. And the auxiliaryeater is also triggered when there is no solar energy available.
uring the second day, due to the rich sunshine, the solar systeman provide the hot water demand for a long period, and even storehe extra energy in the storage tank for night use. This detailednergy profile makes it possible to consider control sequences close
llector efficiency for each city.
to the reality and calculate annual performance of the SWHSs withimproved accuracy.
The annual solar fraction and collector efficiency for each city(shown in Fig. 4) are calculated based on simulation over a oneyear period. Due to the high initial cost of the ETC, systems withETC have a much smaller collector area. The higher thermal effi-ciency seems unable to compensate for the smaller collector area,which makes the energy performance of systems with ETC muchlower when compared with systems with FPC. The overall trend ofmonthly solar fraction is higher in the summer and lower in thewinter where the largest difference was seen for CH. CH and AT
have higher collector efficiency in summer, and lower ones in win-ter, while the trend is opposite in LA. The reason is that the highcold water temperature in LA makes the heat loss in the summermuch larger than rest of the cities.
186 Y. Hang et al. / Energy and Buildings 45 (2012) 181–188
Fig. 5. Comparative study for energetic performance.
Fig. 6. Comparative study for economic performance.
y for
4
ncpnt
(
Fig. 7. Comparative stud
.2. Comparative LCA and LCC
The comparative results for each system in the energetic, eco-omic and environmental aspects as well as the payback periodompared with electrical water heating systems in each city areresented in Figs. 5–7. The CED, EUAC and carbon footprint areormalized to per person. Some observations can be found from
he comparative studies:
1) Fig. 5 shows the life cycle CED consumed per person in anannual basis, and the CED payback for each system. The CED
economic performance.
consumed per person of the SWHSs varies in a large range,from 600 kWh to 5000 kWh, while the CED payback periodsfor the SWHSs do not change a lot, varying from 1 monthto 2 months. All the systems in CH have the highest CEDconsumptions, followed by the ones in AT and LA, while theCED payback periods of the cities have the opposite trend,mainly because the power generation mix in LA is dominated
by natural gas, which has a lower conversion ratio of electricityto CED. Among all the WHSs, FPC&NGSWHSs have the bestenergy performance. In addition, the NGWHS is better thanthe ESWHS. Furthermore, the NGWHS has much better energy
d Buildings 45 (2012) 181–188 187
(
(
Y. Hang et al. / Energy an
performance compared with EWHS, and can be paid backalmost immediately. They have similar initial cost, while theNGWHS consumed much less primary energy than EWHS.
2) Fig. 6 shows the annual LCC per person for each WHSs, andthe life cycle cost payback periods. The annual LCC per personof the SWHSs varies from $150 to $300, and the LLC paybackperiods of the SWHSs vary from 4 to 13 years. SWHSs can savelots of energy in the operating stage, however, due to the highinitial and installation cost, their economic performance isnot as good as the NGWHSs. Although the SWHSs used in LArequire less operating energy, the annual LCC does not have asignificant difference compared with the SWHSs in CH and AT,due to the high initial cost as well. In addition, due to the lowNG price in LA, systems using NG in LA is favorable. Similarly,due to low electricity prices in AT, systems using electricity inAT has a better economic performance than other cities. ThisLCC study did not consider government incentives or subsidies.In the economic analysis, location is important besides theamount of exposed sun available for the SWHS. If locatedin a state with generous incentives to install solar systems,the scenario might have shorter payback periods. Federalgrants and tax credits may also be available for the SWHSs.Sometimes builders and utility companies also offer incentivesfor solar systems. A new federal law provides a 30% tax credit,maximum $2000 for SWHSs. Also, different states will havedifferent incentives. For example, Illinois offers a 30% rebateup to $10,000 for solar-thermal systems designed to produceat least 50,000 BTUs per day or contain at least 60 square feetof collectors. California offer $12.5 per therm for the SWHSdisplaced NGWHS (maximum $1875), and $0.37/kWh forthe SWHS displaced EWHS (maximum $1250) for residentialbuildings. And California also has other rebates for different
type of buildings. Georgia offers $1.8/sq. ft. incentives for thebuildings using SWHSs, up to 35% of the system cost.
3) Fig. 7 shows the carbon footprint per person and the carbonfootprint payback periods for the three cities. It has the similar
Fig. 9. Sensitivity ana
Fig. 10. Sensitivity analysis on l
Fig. 8. Sensitivity analysis on CED.
trend as the energetic performance. The personal carbon foot-print by using SWHS varies from 150 kg to 1100 kg by usingdifferent systems, and the carbon footprint payback periodsvary from 1 to 4 months. The WHSs in LA emit the fewestgreenhouse gas, while they have the longest payback periods.The major reason is because LA has a much cleaner generationmix than the other two cities. And the FPC&NGSWHSs havethe best environmental performance.
Based on these observations, some general conclusions can bedraw. The best choice for a SWHS is a FPC&NGSWHS.
4.3. Sensitivity analysis
According to the results from a comparative study,FPC&NGSWHS is the promising solution. A sensitivity analy-sis is conducted considering using the FPC&NGSWHS in AT. Thesensitivity analysis is conducted for energetic, economic andenvironmental performance by changing parameter values fromthe base case plus and minus 20%. The CED, EUAC and carbon
footprint are normalized to per person. Figs. 8–10 present theresults for the sensitivity analysis.
The sensitivity analyses on CED and GWP per person pro-vide similar results: the daily hot water use is the most sensitive
lysis on EUAC.
ife cycle carbon footprint.
1 d Build
paalartn
5
fcitebnass
hiibpdsma
btspoefltwe
A
(
[
[
[
[[
[
[
[
[[
[[
[
[
88 Y. Hang et al. / Energy an
arameter, followed by the collector area, cold water inlet temper-ture, life span and unit CED/GWP of FPCs. For the LCC sensitivitynalysis, the most sensitive parameter is the collector price, fol-owed by daily hot water demand, life span, discount rate, collectorrea, cold water temperature, and the FIR. In addition, although theesults show that the life cycle energy, economic and environmen-al performances improve when the solar fraction increases, it mayot always be the case.
. Conclusions
SWH systems are capable of providing 60 ◦C domestic hot wateror most of the climates in the United States with a reasonable solarollector area. With the same capital cost, the affordable FPC areas much larger than that of the ETC, due to the low initial cost ofhe FPC. The small ETC collector area is not capable of providingnough thermal energy to the houses, therefore, the solar fractiony using ETC is lower than systems with FPC. Therefore, the ETC isot suitable for water heating systems in its current price. Gener-lly, in cities with warmer climates and better solar insulation, amaller SWHS will produce the same amount of energy as a largerystem in a city with a colder climate.
From the study, it can be concluded that the FPC&NGSWHSsave the best energetic, economic and environmental performance
n all of the three representative cities. The performance of NGWHSs better than that of ESWHS. The energetic and environmental pay-ack periods for SWHSs are less than half of a year, and the LCCayback for SWHSs vary from 4 to 13 years for different cities andifferent types by using EWHS in each city as the base case. The sen-itivity analysis results showed that the daily hot water use is theost significant parameter for all the three indicators: CED, EUAC
nd carbon footprint.It is expected that the domestic SWHS market continues to grow,
ut the actual growth rate is largely dependent on many other fac-ors, such as the costs of conventional heating methods, the cost ofolar collectors, the local power generation structure and energyrices, as well as government subsidies. For example, if the pricef natural gas rises, and the cost of solar collector decreases, accel-rated growth in the SWHS market is expected. However, if theseactors turn to the opposite directions, the growth rate will be muchower. This study provides a method for homeowners to evaluatehe effects of these factors and make investment decisions on solarater heating systems while considering tradeoffs among energy,
nvironmental and economic performance.
cknowledgements
This study was supported by the National Science FoundationNSF) of the United States (Award No. 1034348). Any opinions,
[
[
ings 45 (2012) 181–188
findings, and conclusions or recommendations expressed in thismaterial are those of the authors and do not necessarily reflect theviews of the National Science Foundation.
References
[1] DOE Building Energy Data Book, Residential Sector, 2010.[2] X.Q. Zhai, R.Z. Wang, Y.J. Dai, J.Y. Wu, Y.X. Xu, Q. Ma, Solar integrated energy
system for a green building, Energy and Buildings 39 (8) (2007) 985–993.[3] F. Cuadros, F. López-Rodríguez, C. Segador, A. Marcos, A simple procedure to
size active solar heating schemes for low-energy building design, Energy andBuildings 39 (1) (2007) 96–104.
[4] J. Byrne, L. Kurdgelashvili, M.V. Mathai, A. Kumar, J. Yu, X. Zhang, J. Tian, W.Rickerson, World Solar Energy Review: Technology, Markets and Policies, Uni-versity of Delaware, 2010.
[5] Solar Energy Industry Association (SEIA), U.S. Solar Market Insight, 2010 Yearin Review (Exclusive Summary), 2010.
[6] Environment and Energy Study Institute, Solar Energy, 2010.http://www.eesi.org/solar.
[7] R.H. Crawford, G.J. Treloar, B.D. Llozor, P.E.D. Love, Comparative greenhouseemissions analysis of domestic solar hot water systems, Building Research &Information 31 (1) (2003) 34–47.
[8] F.J. Rey-Martinez, E. Velasco-Gomez, J. Martin-Gil, L.M. Navas Gracia, S. Her-nandez Navarro, Life cycle analysis of a thermal solar installation at a ruralhouse in Valladolid (Spain), Environmental Engineering Science 25 (5) (2008)713–723.
[9] F. Ardente, G. Beccali, M. Cellura, V.L. Brano, Life cycle assessment of a solarthermal collector, Renewable Energy 30 (2005) 1031–1054.
10] G. Tsilingiridis, G. Martinopoulos, N. Kyriakis, Life cycle environmental impactof a thermosyphonic domestic solar hot water system in comparison withelectrical and gas water heating, Renewable Energy 29 (2004) 1277–1288.
11] S. Kalogirou, Thermal performance, economic and environmental life cycleanalysis of thermosiphon solar water heaters, Solar Energy 83 (2009)39–48.
12] C. Dharuman, J.H. Arakeri, K. Srinivasan, Performance evaluation of an inte-grated solar water heater as an option for building energy conservation, Energyand Buildings 38 (3) (2006) 214–219.
fam/cps2003/tabAVG1.pdf.15] W. Weiss, I. Bergmann, R. Stelzer, Solar Heat Worldwide, Markets and Con-
tribution to the Energy Supply 2007, IEA Solar Heating and Cooling Program,2009.
16] SolarRoofs.com. SolarRoofs Skyline 10-01 and 20-01 Solar Collectors, 2010.http://solarroofs.com/documents/collectordiagram.pdf.
17] EPA, eGRID Subregion and GHG Emissions Finder Tool, Version 3.1, 2010,http://www.epa.gov/cleanenergy/energy-and-you/how-clean.html.
18] EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2006, 2007.19] EIA, Electricity Price. http://www.eia.doe.gov/cneaf/electricity/epm/table5 6 b.
html; Natural Gas Price. http://www.eia.doe.gov/dnav/ng/ng pri sum dcu nusm.htm, 2011.
20] ASHRAE, ASHRAE Standard 90.2, 2004.21] Eno Scientific, Ground Water Temperature, 2010. http://www.enoscientific.
com/groundwater-temp-map.htm.22] Solar Water Heater Price, 2010. http://www.alpinehomeair.com/viewproduct.
cfm?productID=453062564&linkfrom=froogle.23] Local Lowe’s Cost Consulting, West Lafayette.
24] J. Armstroing, W. Barry, R. Cox, R. Gilley, K. Humphreys, P. Jackson, M. Joyce,
RSMeans Mechanical Cost Data, 31st Annual ed., 2008.25] U. Eicker, D. Pietruschka, Design and performance of solar powered absorp-
tion cooling systems in office buildings, Energy and Buildings 41 (2009)981–991.
