energy options for residential buildings assessment

Energy Conversion and Management 65 (2013) 637–646

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Energy Conversion and Management

journal homepage: www.elsevier .com/ locate /enconman

Energy options for residential buildings assessment

Behnaz Rezaie, Ibrahim Dincer ⇑, Ebrahim EsmailzadehFaculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, Canada L1H 7K4

a r t i c l e i n f o a b s t r a c t

Article history:Received 16 October 2011Received in revised form 31 August 2012Accepted 4 September 2012Available online 8 November 2012

Keywords:ExergyRenewable energyEnergy managementResidential buildingEnvironmental impact

0196-8904/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.enconman.2012.09.008

⇑ Corresponding author. Tel.: +1 905 721 8668; faxE-mail addresses: [email protected] (B. Rezai

Dincer), [email protected] (E. Esmailzadeh).

The building sector, as one of the major energy consumers, demands most of the energy research toassess different energy options from various aspects. In this paper, two similar residential buildings, witheither low or high energy consumption patterns, are chosen as case studies. For these case studies, threedifferent renewable energy technology and three different hybrid systems are designed for a specifiedsize. Then, the environmental impact indices, renewable energy indices, and the renewable exergy indi-ces have been estimated for every energy options. Results obtained show that the hybrid systems (with-out considering the economics factors) are superior and having top indices. The importance of the energyconsumption patterns in buildings are proven by the indices. By cutting the energy consumption to about40% the environment index would increase by more than twice (2.1). Utilization of the non-fossil fuels isone part of the solution to environmental problems while energy conservation being the other. It hasbeen shown that the re-design of the energy consumption model is less complex but more achievablefor buildings.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The definition of modern world is not just limited to the use ofnew technologies, but having the knowledge as ‘‘how’’ to supplythe energy in a caring manner. One could say that the environmentis essential parts of the world; despite the last century that energyand environment were scientific subjects limited to researchers. Itis interesting to note that the awareness and the usage manners ofenergy have been modified, during the past 60 years.

Rezaie et al. [1] have described the outlook of humankind to-ward energy since the industrial revolution and the outlook evolu-tion ever since. They also highlighted the supply of the renewableenergy to reduce the emission of the greenhouse gases (GHGs)while to promote the smart use of energy. Hodder et al. [2], Heidariand Sharples [3] and Yannas [4] have reported that 50% of the car-bon dioxide emissions come from the building sector in the indus-trialized countries.

The solar energy counts for 13% of the energy consumption inbuildings, and it is planned to increase rapidly [5]. It presents agood motivation to study buildings and a challenge to find meth-ods of increasing the efficiency of buildings. Markis and Paravanits[6] have explained that the energy-efficient buildings may lowerthe carbon emission by even more than 60%, which correspondsto 1.35 billion tons of carbon, being the amount of savings pro-posed by the Environment Conferences in Rio and Berlin. Huang

ll rights reserved.

: +1 905 721 3370.e), [email protected] (I.

et al. [7] have suggested a trigeneration system with the goal ofimproving energy utilization efficiency of buildings. Sustainableoperations as well as efficient design are important strategies forbuildings [8]. Zaki et al. [9] have stated three factors to have theenvironmental friendly buildings, including energy efficiency, en-ergy conservation, and renewable energy.

A research is performed to show an ancient energy technologyused for energy efficient buildings and the results were reportedin literature [10]. Energy efficient buildings also make use of theconventional energy sources and rely mainly on oil. Over andabove the major savings in the energy usage and cutting downon the GHG one can say that much attention has been drawn re-cently on the measurement of the energy consumption of build-ings. In this regard, Balaras et al. [11] have stated that the energyconsumption of a building is a function of many variables suchas the building type, construction materials, occupancy behavior,climatologic conditions, heating and cooling equipment, domestichot water, and the lighting. As for buildings, Vivancos et al. [12]have presented the research results for the thermal characteriza-tion of brick, and Sozer [13] has illustrated the role of design forthe building envelope to enhance energy efficiency. Also, Wanet al. [14] have shown the trends of energy consumption for futurebuildings under different climates. Balta et al. [15] have stated thatexergy analysis is essential for energy system improvement andshould be used as a potential tool for sustainable buildings design.The flows of energy in the building systems are more tangible ifexergy analysis is used [16,17]. Thus, exergy analysis shows possi-bility of more efficient design by dropping inefficiencies in the sys-tem [18]. Environmental advantages and economics of energy can

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Nomenclature

CEC California Energy CommissionCOP coefficient of performanceE energyIE environmental impact indicesRCO2 reduced CO2

ECO2 emitted CO2

Ex exergy

R energy grade functionRE renewable energyIER renewable energy indexREx renewable exergyIREx renewable exergy indexTE total energyTEx total exergy demand

638 B. Rezaie et al. / Energy Conversion and Management 65 (2013) 637–646

be detected easier by exergy analysis [15]. Furthermore, energyand exergy ratios are defined and applied in building sectors forrecognizing buildings energy options benefits [19–23].

The present study is the extension of previous work [1], whichsizing various energy options for different buildings. The focus isplaced on the residential buildings while the thermodynamic anal-ysis expands to the exergy investigation. Moreover, the energyconsiderations and the exergy aspects with various energy optionsfor several case studies will be analyzed beyond the efficiencyanalysis. The study covers the environmental aspects of differentpossibilities of energy.

Two similar residential buildings are selected, one with the highand the other with low energy consumers. For every case study theenergy, exergy and the environmental impacts of these renewableenergy options have been assessed. Some indices are proposed inthis work as a tool for comparing several energy options from dif-ferent aspects including energy, exergy, and environmental impactin a peek. Application of these indices in this study illustrates thedifference between the low and high energy consumption in twosimilar buildings.

2. Methodology

Different methods of sizing various energy options, environ-mental impact, energy, and exergy aspects will be defined in thissection. Furthermore, these methods will be applied to the previ-ously mentioned case studies.

2.1. Sizing technologies

The sizing technologies were discussed in detail in the previousstudy performed by Rezaie et al. [1]. Here, the proposed methodol-ogies for sizing the solar electricity, solar thermal and geothermalsystem are used.

2.2. Environmental Impact

One of the major reasons to use the non-fossil fuel energy sup-plier is to protect the environment against the greenhouse gases(GHGs). To show the performance of each technology, initially,the emitted CO2 by the conventional fuel for each case study hasbeen estimated. Then the ‘‘environmental impact index’’ is calcu-lated for each design. The environmental impact index expresses as

IE ¼ 100ðRCO2Þ=ECO2 ð1Þ

where IE represents the environmental impact index, RCO2 stands forthe reduced CO2 by the design, and ECO2 is the emitted CO2 by theconventional design, respectively. Note that IE is a dimensionlessfactor.

It is worth mentioning that the method of estimation of CO2 forelectricity generation should be explained prior to the calculationof the environmental impact index. Electricity is generated in dif-ferent plants through using different fuels. In Canada, these re-

sources are namely, the hydro, thermal, nuclear, combustionengines, and very limited renewable energies. The resulting pollu-tion due to the electricity generation varies depending on the fuelresources. In a report entitled ‘‘Power Generation in Canada’’, pub-lished by the Canadian Electricity Association, the electricity gen-eration configuration in the Province of Ontario for the year 2004was [16]:

� 37 TW h from the hydro;� 45 TW h from the thermal (mainly coal-based power plants);� 63 TW h from the nuclear; and� 6.7 TW h from the combustion engines sources.

When visiting the website ‘‘Plug into Green Canada’’ [26] it of-fers a calculator, which considers the combination of the above-mentioned sources and presents the total generated amount ofCO2. Alternatively, this calculator can be utilized to estimate theamount of CO2 from the electricity generation.

To obtain the amount of CO2 from the burning of natural gas,one has to refer to the report published by the Natural Gas Associ-ation, [27]. It clearly states that to obtain 1 GJ of energy by burningthe natural gas one would generate the unwanted amount of50.3 kg of CO2.

2.3. Energy aspect

The energy demand for each case is important enough to bemeasured by having the index of the estimated renewable energy.The index of renewable energy is defines as:

IRE ¼ 100ðREÞ=TE ð2Þ

where IRE represents the renewable energy index, RE refers to therenewable energy, and TE stands for the total energy demand. Itis understandable that IRE is a dimensionless parameter.

2.4. Exergy aspect

Exergy is defined by Rosen et al. [28] as a tool to appraise anddevelop energy systems, by giving more meaningful and valuableinformation than the more conventional energy analysis. Exergyanalysis particularly recognizes the actual thermodynamic lossesand efficiencies. Hence, exergy analysis can help in reducing thethermodynamic losses in thermal systems. Exergy with the defini-tion of the available energy can be computed for the two Case Stud-ies #1 and #2. The exergy for Case Studies #1 and #2 consists ofthe exergy from the natural gas and the exergy form the electricity.Hence, the exergy for electricity determines as [29]:

Ex ¼ E� R ð3Þ

where Ex stands for the exergy, E is for the energy, and R stands forthe energy grade function. It can be said that R has different valuesfor various kinds of energy, e.g., for the electricity R = 1.0, and forthe natural gas R = 0.913.

B. Rezaie et al. / Energy Conversion and Management 65 (2013) 637–646 639

Then, the renewable exergy index can be calculated and the in-dex of the renewable exergy can be defines as

IREx ¼ 100ðRExÞ=TEx ð4Þ

where IREx represents the renewable exergy index. REx is therenewable exergy. TEx stands for the total exergy demand. Also, IRex

is dimensionless factor.

3. Alternative energy options

In this section various energy options for residential buildingsare listed in Table 2. These options will be applied to the respectivecase studies in the following.

3.1. Case Study #1

A 2-story residential detached house in Brampton, Ontario, Can-ada, has been chosen as Case Study #1, which has the latitude43.536 and longitude �79.556. Case Study #1 is a 4 + 1 bedroom,with five residents. In this house, furnace works with natural gasand electricity; the heating system is of the forced air type. The liv-ing area of the house is about 214 m2. The energy consumption inthis house is kept under control and the save of energy is well re-spected by the residents.

The electricity consumption of this household for the past yearwas 5506 kW h, having the average daily consumption of 15 kW h,with the highest daily rate being 18 kW h and the lowest daily rateis 12 kW h. Fig. 1 shows the distribution of the electricity con-sumption for Case Study #1

The total consumption of the natural gas for this house is2760 m3. The gas consumption for Case Study #1 is illustrated inFig. 2. Note that natural gas usages in June, July, and August arehigher than May and September because of the extra people thanusual as visitors during summer in house of Case Study #1. The en-ergy consumption distribution for Case Study #1 is also importantto know and it is depicted in Fig. 3.

3.1.1. Option 1The conventional solar water heaters are very popular for the

heating of the domestic water. In this section, the solar water heat-ers are customized for Case Study #1 to heat up the domestic

Table 1Ground source energy system for Case Study #1.

Geothermal system specifications

System capacity 51633 kJ/hNumber of pipes 2 U shapeLength of pipes 440 mCirculating liquid R-410ACooling COP 5.1Heating COP 4.1Cooling capacity 15 kWHeating capacity 11 kW

Table 2Summary of various design options for Case Studies #1 and #2.

Renewable technology Case Study #1

Renewable equipment IE

Option 1 Solar heater panels 4 WSE58 5Option 2 PV panels 22 � 215 W 6Option 3 Geothermal system GT049 13Option 4 Hybrid system #1 GT049 + 8 � 210 W 26Option 5 Hybrid system #2 4 WSE58 + 22 � 215 W 11Option 6 Hybrid system #3 4 WSE58 + GT049 17

water, and analysis is done from the point of energy generationthe pollution reduction. By using the solar water heaters, the nat-ural gas consumption has been reduced. The detail reduction of theenergy consumption is presented in the energy Section 4. Then en-ergy suppliers for Case Study #1 in this situation are the solarwater heaters (solar thermal) and also other regular sources of en-ergy, which are the grid electricity and natural gas. Heat collectorpanel has been chosen from one of the Canadian manufacturer,WSE Technology [24]. The WSE58 model generates 2741.3 kJ(2600 Btu/h).

The house considered as Case Study #1 requires four solar pan-els, WSE58 [24], to provide sufficient energy to heat water for thehousehold domestic hot water. The energy generated by four pan-els is: 2741310.00 � 4 = 11 MJ/h.

By considering seven hours of sunshine per day as an averageperiod for all days in a year, the total energy produced by these so-lar panels would be:

11� 7 ¼ 77 MJ=day

An assumption is made that there are 300 days of sunshine peryear in Canada. Hence, the energy produced by the solar collectorsis equal to 23.1 GJ per year.

Furthermore, according to the Natural Gas Factsheet website[27], the gas volume of 1 m3 releases energy at an amount of37234.00 kJ (35314.60 Btu).

This energy is released from 620.4 m3 of natural gas (23.10 GJ/37233.00 kJ = 620.40), in other words, the gas consumption is re-duced by 620.4 m3 every year. In a life period of 25 years for the so-lar panels, this saving is 15,510 m3 of the natural gas.

3.1.2. Option 2The PV panels are an appropriate technology to generate elec-

tricity for households. In this section, the PV panels are sized forCase Study #1, thereby reducing the requirement of electricity.Section 4 shows the detailed calculations and the amount of elec-tricity, which the PV panels would generate. Therefore, the energysuppliers in Case Study #1 are the PV panels (solar electricity) inaddition to the conventional energy sources, being the grid elec-tricity and natural gas.

The PV panel is chosen from the REC Group [30] from the SCMseries 210, which is the most popular PV panel in Scandinavia, andare available in larger panel wattage. The panels used in the calcu-lations are the 210 W and the 215 W ones.

The sun hour or the insulation coefficient for the Pearson Inter-national Airport varies from a minimum of 1.08 kW h/m2/d to amaximum of 5.98 kW h/m2/d based on the NASA database givenin the RETScreen software [22], and hence, the average coefficienton the insulation is 3.53 kW h/m2/d.

It is found that the average electricity consumption in CaseStudy #1 is 15 kW, and the average insulation coefficient in theToronto area is 3.53 kW h/m2/d. Therefore, the electricity con-sumption by the sun hours per day would be 15/3.53 = 4.25 kW = 4250 W (AC).

Case Study #2

IRE IREx Renewable equipment IE IRE IREx

19 21 4 WSE58 2 12 1814 15 56 � 210 W 7 21 3053 57 GT049 6 33 4855 62 GT049 + 8 � 210 W 12 34 5233 35 4 WSE58 + 56 � 210 W 9 27 4872 77 4 WSE58 + GT049 8 45 65

Fig. 1. Electricity consumption for the household as given in Case Study #1.

Fig. 2. Natural gas consumption in Case Study #1.

Fig. 3. Electricity usage distributions for Case Study #1.


According to the manufacturer REC Group, the coefficients bythe California Energy Commission (CEC) are taken as 194 for the in-verter and 0.94 for the solar modules series SCM 210. Using these,4250/(CEC = 194) = 22 W for the inverter, and 22 W / (CEC = 0.94) =24, hence, the number of panels is 24. For having a better arrayconfiguration, 215 W is replaced for the 210 W panel and 22 panelswould be chosen. The proposed configuration is having two rows ofstrings with 11 panels of module 215 W positioned in each string.

� (Inverter: Xantrax GT 2.8 208/240 V grid tie, CEC 94%)� The angles of the PV modules are given as follows:� Fall/Spring: Angle = Latitude = 43.5�.� Summer: Angle = Latitude – 15 = 43.5–15 = 28.5�.� Winter: Angle = Latitude + 15 = 43.5 + 15 = 58.5�.

With the changes of the seasons, it is strongly recommendedthat the PV modules be changed accordingly. This would ensurethe harnessing of the maximum energy from the sun.

3.1.3. Option 3The ‘‘ground source energy’’ system is an interesting source of

renewable energy since it is ‘‘reliable’’, i.e., always available with-out any interruption from the Mother Nature. Moreover, theground source heat pump provides cost effective energy for bothheating and cooling of buildings. The average coefficient of perfor-

mance (COP) of a ground source energy system is roughly 4, whichmeans that a geothermal system generates 4 units of energy(either heating or cooling) by consuming 1 unit of energy (e.g.,electricity). Particularly in Canada having such long and harsh win-ters, the use of the ground source energy systems is a very intelli-gent and logical decision.

The geothermal energy, as a renewable source of energy, to-gether with a conventional source of energy such as the grid elec-tricity and natural gas have been utilized as the energy supplier forCase Study #1. The electricity consumption for the heating andcooling of the residential building has been reduced to one/fourthby using the geothermal energy.

For sizing the geothermal system in Case Study #1, the RET-Screen software [30] is employed. There are few constant parame-ters involved in the equations, namely, the specific heats, density,and the thermal conductivity. The RETScreen software chooses itsown data in order to replace these constants. Ultimately, RET-Screen calculates all the energy losses (i.e., the conductive and con-vective), and includes all the gains (solar and internal gains) andfresh air load. Finally, it adds up the heat loads for the heating orcooling of the space and produces the power of the geothermal sys-tem, which can generate the heat load. For Case Study #1, all thedata is entered into RETScreen and the outcome from RETScreenshows that a heat pump with the capacity of 51,633 kJ/h is neededto run the heating and cooling systems in Case Study #1, while theheat loss is 4428.2 kJ/h. This is almost matched with the modelGT049 from Geosmart Energy. The GT049 model has COP 4.1 forthe heating mode and COP 5.4 for the cooling mode.

This unit is replaced in the utility room with a furnace, whichruns on natural gas. The pipe loop for Case Study #1 is a closed-loop arrangement with the cycling ethanol, R-410A refrigerant.The pipes are 3.1 cm in diameter and 440 m long. These 220 mpipes are placed into two holes with a length of 110 m each andthe diameter of holes is 12.5 cm. In the backyard and close to theutility room, these two holes are bored through the earth with spe-cial machines. In each 110 m hole there is a U-shaped pipe with atotal length of 220 m; for the two holes, a 440 m pipe is availablefor circulation of the R-410A refrigerant. The R-410A refrigerantexchanges heat with the soil through this path of 440 m, and eitherdumps the heat into the ground or extract the heat from the soil.Table 1 illustrates a summary of the ground source energy systemfor Case Study #1.

3.1.4. Option 4As previously cited, the geothermal system is a reliable source

of energy, which generates both the heating and cooling energies.The ground source heat pump obtains four units of energy from theground by spending one unit of energy (e.g., electricity), therebyproviding exactly five units of energy for cooling or heating pur-poses. This means that the geothermal system is an ideal candidatefor alternative energy option from the point of view of reliability

Fig. 4. Average daily electricity consumption in Case Study #2.


and efficiency. Furthermore, this superior energy technology re-quires only one-fifth of its energy to run an entire system.

The electricity required by the ground source heat pump is sup-plied from another source of renewable energy. The entire heatingand cooling systems would therefore, run with natural energy. Thissource of energy could be photovoltaic panels, which convert thesolar energy into electricity and can easily be built to meet theelectricity demand level. In this design, the geothermal energyand the PV panels (solar electricity) are the source of renewableenergy, and the grid electricity plus the natural gas are the conven-tional sources of energy for Case Study #1.

Subsequently, the proposed hybrid system for Case Study #1,which is an urban area, is to combine the PV panels with the geo-thermal system. This innovative system remains the same for ruralareas by including a number of batteries as the electricity sourcefor the geothermal system and the PV panels. Also, another alter-native hybrid system for country-wide areas is to couple theground source heat pump and the wind turbines with a set ofbatteries.

The cooling capacity for the ground source heat pump GT049 is15 kW and the heating capacity is 11 kW, and hence, the highestcapacity of this machine is 15 kW. It has been previously men-tioned that one-fifth of this energy supplies to the heat pump,and therefore, 15/5 = 3 kW of energy, in the form of electricity, isrequired to run the pump. Subsequently, one can say that the PVpanels should generate 3 kW/day.

The sunshine hours or the insulation coefficient for the PearsonInternational Airport is reported to be from a minimum value of1.08 kW h/m2/d to a maximum value of 5.98 kW h/m2/d, [31] andhence, the average coefficient of the insulation is 3.53 kW h/m2/d.

Since the average electricity consumption for the hybrid designof Case Study #1 is found to be 5 kW, therefore, the average insu-lation coefficient in the Toronto area requires 3.53 kW h/m2/d.Hence, the electricity consumption hours per day, by the sun, is:

5=3:53 ¼ 1:4 kW ¼ 1400 W ðACÞ

According to the REC Group manufacturer, the CEC informationfor the inverter is 194 and that for the solar modules SCM 210 ser-ies found to be 0.94.

1400 W=ðCEC ¼ 194Þ ¼ 7:2 W; and 7:2 W=ðCEC ¼ 0:94Þ ¼ 7:7

A close approximate value of 7.7 would be ffi 8 being the num-ber of panels. Then, 8 panels of 210w would deliver the requiredelectricity for the ground source heat pump.

By coupling the ground source heat pump GT049 from Geo-smart Energy with a set of eight photovoltaic panels, the 210wcooling and heating needed for Case Study #1 will be totally ob-tained from the natural energy using the REC Group series 210.

3.1.5. Option 5The second hybrid system is further developed through solar

technologies by combining the PV panels for generating the elec-tricity and solar water heaters to heat the water. In the hybrid sys-tem #2, the electricity and the natural gas consumptions arereduced and this reduction is calculated in the following para-graphs. This hybrid system is directly dependent on the solar en-ergy. In the hybrid system #2, the grid electricity and the naturalgas are present as a backup system for the time whenever thereis not sufficient sunlight. However, for longer sunny days, the extraenergy would overflow to the grid.

Hybrid system #2 consists of the solar water heaters (solar ther-mal) and the PV panels (solar electricity). The solar water heatersconsist of PV modules as already been computed. Based on the pre-vious assessment, the hybrid system #2 would include four panelsof WSE58 as the solar thermal energy to convert the solar energy to

11 MJ/h, plus 22 panels of PV modules 215 W to generate 15 kW/day. The configuration of the PV modules and the angle of panelshave been previously described.

3.1.6. Option 6The third combination of the hybrid system for Case Study #1

with the available technologies is the geothermal system and thesolar thermal energy. The ground source energy is a superior tech-nology for the heating and cooling only with one-fifth of the energyneeded. The solar water heaters are designed for Case Study #1 toprovide the domestic hot water for household everyday use. In thissystem, the energy consumption is drastically reduced because themain portion of the energy consumption, based on Fig. 3, is usedfor the space heating/cooling (57%) and to heat the water (17%).Therefore, a total of 74% energy usage is targeted to be reduced sig-nificantly in Case Study #1. The grid electricity and the natural gasis still considered as the main sources of energy in Case Study #1,however, the amount of usage has greatly been reduced.

Hybrid system #3 consists of the solar water heaters (solar ther-mal) and the ground source heat pump (geothermal system). Thesolar water heaters and geothermal system have already beencomputed. Based on the previous assessments, the hybrid system#2 includes four panels of WSE58 as the solar thermal energy forconverting the solar energy to 11 MJ/h together with a GT049 togenerate either 15 kW/day cooling energy or 11 kW/day heatingenergy.

3.2. Case Study #2

Case Study #2 is for another detached house in Oshawa, Ontar-io, Canada, with the latitude 43.696 and the longitude �78.871.The specification of this house is almost the same as for Case Study#1, having four bedrooms with five residents. The furnace in thishouse runs on natural gas, and the electricity and heating systemare also the forced air type. The living areas in this house areapproximately 215 m2. The first floor consists of the kitchen, theliving/dining room, the family room, and a bathroom; the secondfloor is made up of four bedrooms, and two bathrooms, and thebasement is considered as a full basement.

The main difference between Case Study #1 and Case Study #2is the energy consumption pattern. The energy usage in Case Study#2 is significantly higher than that of Case Study #1. The naturalgas and electricity consumptions are both noticeably higher thanthose of Case Study #1.

The last year electricity consumption of this household was13,303 kW h, which makes the average daily consumption as36.4 kW h, with the highest daily rate as 44 kW h. Fig. 4 displaysthe average daily electricity consumption for Case Study #2 inthe last year.

Fig. 6. Environmental impact Index for Case Study #1.

Fig. 7. Environmental impact index for Case Study #2.


The distribution of energy consumption for Case Study #2, as aregular household, is almost the same as Case Study #1. Fig. 4shows the electricity distribution for Case Study #2.

The natural gas consumption is reported as 3980 m3; therefore,the average daily natural gas consumption for the household ofCase Study #2 is 10.9 m3. Fig. 5 depicts the average natural gasconsumption for the household of Case Study #2.

3.2.1. Option 1Solar water heaters are used for heating the domestic water. In

this section, the solar water heaters are customized for Case Study#2 and an analysis is done from the point of energy generation,cost and pollution reduction. Note, since the numbers of peoplein the household are the same in both cases, the number of solarcollector panels in both cases is the same, as well. Thus, the calcu-lation for energy, emissions and cost is also the same. Figs. 5–7 dis-play these results for Case Study #2.

Energy resources for Case Study #2 are the solar thermal as therenewable source of energy in addition two other conventionalsources of energy – the grid electricity and natural gas. The solarthermal energy reduces the natural gas consumption by 620 m3/year as already been calculated.

3.2.2. Option 2The PV panels are desirable technology to generate electricity

for the household. The sizing of the PV panels is exactly the sameas for Case Study #1. The resources of energy for Case Study #2are the solar electricity through PV panels, grid electricity, andthe natural gas.

Based on the average electricity consumption of 36.4 kW forCase Study #2, and the average insulation coefficient of3.53 kW h/m2/d for the Toronto area, the electricity consumptionby the sun hours per day is found to be 36.4/3.53 = 10.3 kW = 10,311.6 W (AC).

10311.6/(CEC = 194) = 53 W, and 53/(CEC = 0.94) = 56, where 56is the number of PV panels; PV panels are 210 W each. Then fourrows of strings with 14 panels of module 210 W in each stringare configured. The angles of the PV panels in the four seasons are:

� Fall/Spring: Angle = Latitude = 43.7�.� Summer: Angle = Latitude – 15 = 43.7–15 = 28.7�.� Winter: Angle = Latitude + 15 = 43.7 + 15 = 58.7�.

It is strongly recommended that the PV modules be changedwhen the seasons change.

3.2.3. Option 3As mentioned the ground source energy system is a remarkable

source of renewable energy, over the reliability. In this section, thegeothermal system is customized for Case Study #2 with the anal-ysis from the point of energy generation and pollution reduction.Both houses in Case Studies #1 and # 2 are very similar, and the

Fig. 5. Natural gas consumption in household Case Study #2.

geothermal systems in both cases are also the same. Hence, the en-ergy resources for Case Study #2 are the geothermal energy as arenewable source of energy, together with the conventionalsources of energy – the grid electricity and natural gas. The elec-tricity consumption for the heating and cooling purposes is re-duced to one-fourth by using the geothermal energy.

3.2.4. Option 4As previously stated, the geothermal energy is a reliable source

of energy, which provides the heating and cooling energy. Theground source heat pump extracts four units of energy from theground by spending one unit of energy (i.e., electricity), to generateexactly five units of energy for the cooling or heating purposes.Thus, the geothermal system is an ideal candidate for an alterna-tive energy source from the point of reliability and efficiency. Fur-thermore, this supreme technology requires only one-fifth of itsenergy to run the entire system.

The electricity required by the ground source heat pump can besupplied by another source of renewable energy. Then, the wholeheating and cooling system would run with the natural energy.This source of energy could be photovoltaic panels, which convertsthe solar energy to electricity and can easily be developed to theelectricity demand level. Therefore, in this design the geothermalenergy and the PV panels (solar electricity) of the hybrid system#2 are the source of renewable energy for Case Study #2, andthe grid electricity plus the natural gas are the conventionalsources of energy. Since the geothermal system is exactly the sameas that of Case Study #1, the hybrid system #1 for Case Study #2 isexactly the same as that of Case Study #1. Therefore, the energyutilization calculation, cost analysis and the emission reduction ef-fect are the same in both cases.

3.2.5. Option 5The second hybrid system is defined through the solar technol-

ogies by combining the PV panels to generate the electricity andthe solar water heaters are to heat the domestic water. In hybrid


system #2, the consumptions of the electricity and natural gas arereduced. The reduction is calculated in the following paragraphs.This hybrid system is directly dependent on the solar energy. In hy-brid system #2, the grid electricity and the natural gas are still uti-lized in the system as a backup when there is not sufficientsunlight available. However, the extra energy overflows to the gridfor long sunny days.

The hybrid system #2 consists of the solar water heaters (solarthermal) and the PV panels (solar electricity). The solar water heat-ers and the PV modules have already been computed. Based on theprevious assessment, the hybrid system #2 includes four panels ofWSE58 to convert the solar energy to 11 MJ/h, and also 56 panels ofPV modules 210 W to generate 36.4 kW per day. The configurationof the PV modules and the angles of the panels have been describedbefore.

3.2.6. Option 6The third combination of the hybrid system for Case Study #2

with the available technologies is the geothermal system and thesolar thermal energy. Ground source energy is a superior technol-ogy for the heating and cooling purposes and the solar water heat-ers are designed for Case Study #2 to provide the domestic hotwater for the household. In this system, the energy consumptionhas been drastically reduced because the main portion of the en-ergy consumption, based on Fig. 6 for Case Study #2, is used forthe heating and cooling (57%) and hot water (17%). A total of 74%of the energy usage in Case Study #2 is targeted to be reducedsignificantly.

The grid electricity and natural gas is still the reliable sources ofenergy for Case Study #2, but the amount of usage is greatly re-duced. Since Case Study #2 is very similar to Case Study #1, andthe solar thermal system (4 panels of solar water heater WSE58)and the geothermal system (ground source heat pump GT049)are the same, hence, the hybrid system #3 for Case Study #2 isthe same as hybrid system #3 for Case Study #1. Therefore, the en-ergy utilization, emission reduction, and the cost analysis for hy-brid system #3 of Case Study #2 is exactly the same as those forthe hybrid system #3 of Case Study #1, though results are applica-ble solely for Case Study #2.

4. Analysis

The energy options are sized technologically in the last section.Different aspects of each option have been assessed in this section.When considering the importance of environment, one major as-pect of the analysis is the environmental impact of energy as themain purpose of the options. Different design proposals will bemeasured individually for each option within every case study.Also, energy analysis for each technology options will be per-formed to show the share of the renewable energy in the proposeddesign. Following that exergy, as the quality of energy for each en-ergy technology will be examined. It can be another tool to mea-sure capability of different design proposals. The overall analysisof energy options provides insight for designers and researchers.

4.1. Environmental impact

It has been explained in the introduction that environment is-sues are very serious matters for human being. The main aspectof any design should be the environmental effects of the new de-sign/product/system on the society. To quantify the environmentimpact, two case studies as explained in Section 3, with varietiesof technology options are chosen. As mentioned one case study isa single house with low energy consumption and other case studyis similar house with high energy usage. The impacts of the envi-

ronmental issues in every single energy technology, proposed inprevious section, for both case studies are examined in the follow-ing paragraphs.

4.1.1. Case Study #1When the residential building of Case Study #1 is running with

the conventional energy, say the natural gas and electricity, thevolume of the emitted CO2 is the sum of the emitted CO2 to gener-ate 5506 kW h of electricity and the burning of 2760 m3 of naturalgas. By using the calculator given in reference [12], one could findthat 19332.17 kg of CO2 has been emitted to the environmentwhen 5506 kW h of electricity has been generated. According tothe report published in Ref. [27], the energy contained in every cu-bic meter of natural gas is 36116.7 kJ. Therefore, the total energyresulted from the natural gas for Case Study #1 is:

2760 ðm3=yearÞ � 36116:7 ðkJÞ ¼ 99;682;000 kJ=year

¼ 99:7 GJ=year:

It has been mentioned before that the energy of 1 GJ from burn-ing of the natural gas is equivalent of generating 50.3 kg of CO2,hence:

99:7 ðGJ=yearÞ � 50:3 ðkg of CO2Þ ¼ 5014:91 kg of CO2 per year:

Therefore, the total amount of CO2 emitted to the environmentwhen for Case Study #1 the conventional fuel was used is:

19332:17 ðkg of CO2=yearÞ þ 5014:91 ðkg of CO2=yearÞ¼ 24347:08 kg of CO2 per year:

4.1.1.1. Option 1. The conventional solar heaters designed to gener-ate 23.1 GJ for Case Study #1. The equivalent energy for burningthe natural gas will emit 1161 kg of CO2 into the atmosphere.

4.1.1.2. Option 2. It has been previously mentioned that the PV pan-els would generate roughly about [22 � 215 � 90% � 3.53= 15 kW h] of electricity per day. By considering 300 sunny daysfor Canada the electricity generated by the PV panels is:

15 ðkW hÞ�300¼4500 kW h=year4500 ðkW h=yearÞ�3:6 ðMJ=kW hÞ¼16;200 MJ=year¼16:20 GJ=year

Then by using the calculator given in the ‘‘Plug into Green Canada’’[26], the amount of 1581 kg of CO2 per year comes out to the envi-ronment as a result of generating 16.20 GJ of electricity per year.

4.1.1.3. Option 3. Before installing the ground source heat pump,the furnace is taken out. This means that one main user of the nat-ural gas has been eliminated from the system. Therefore, the con-sumption of the gas is drastically reduced. Along with Fig. 3, onecan say that 61% of the household energy is used either for heatingor cooling the space. The natural gas consumption in Case Study #1is found to be 2760 m3 per year. The usage of natural gas has nowbeen reduced by 1683 m3.

1683 ðm3=yearÞ�36116:7 ðkJÞ¼60;784;406 kJ=year¼60:78 GJ=year60:78 ðGJ=yearÞ�50:3 ðkg of CO2Þ¼3057 kg of CO2 per year

Hence, by not burning 1683 m3 of the natural gas annually, then3057 kg of CO2 will not be released into the atmosphere every year.

4.1.1.4. Option 4. Since the system is referred as hybrid, then theemission reduction is combined from two categories: one categorybeing the elimination of the burning of the natural gas, and theother is to reduce the electricity consumption. The first category,which is resulted from reducing the natural gas consumption,


has been calculated earlier. It is estimated that by not burning1683 m3 of the natural gas per year, this will correspond in elimi-nating the amount of 3057 kg of CO2 annually.

The second part of the emission reduction is through cutbacksin the electricity. According to the calculator of ‘‘Plug into GreenCanada’’ [26], in order to generate an average amount of3 kW h � 300 = 900 kW h of electricity per year, one has to emit3,160 kg of CO2 per year into the atmosphere in the Canadian Prov-ince of Ontario.

The hybrid system, as a combination of the ground source heatpump and the photovoltaic panels, will collectively protect theenvironment by eliminating the amount of:

3150 ðkg of CO2=yearÞ þ 3160 ðkg of CO2=yearÞ¼ 6217 kg of CO2 per year:

4.1.1.5. Option 5. Along with the same logic, the emission reductionfor the hybrid system #2 is equivalent of the emission reduction byfour panels of WSE58, as calculated already along with the emis-sion reduction by 22 PV modules computed in earlier sections.Then, the quantity of emission reduction by hybrid system #2 is:


4.1.1.6. Option 6. Following the same argument, the emissionreduction for the hybrid system #3 is equal to the emission reduc-tion by four panels of WSE58 plus the emission reduction by theground source heat pump GT049. Hence, the quantity of the emis-sion reduction by hybrid system #3 can be found as:


Finally, the environmental impact index for every proposed de-sign option is tabulated in Fig. 6.

4.1.2. Case Study #2For every day running of the house for Case Study #2 with the

conventional energy system being the natural gas and electricity,the volume of the emitted CO2 can be estimated as the total emit-ted CO2 for generating 13,303 kW h of electricity plus the burningof 3980 m3 of the natural gas. The generation of 5506 kW h of elec-tricity would produce 46708.31 kg of CO2 annually according tothe reports published in reference [26].

Therefore, the consumed natural gas would contain [27]:

3980 ðm3=yearÞ�36116:7 ðkJÞ¼143;744;466 kJ=year¼143:74 GJ per year143:74 ðGJ=yearÞ�50:3 ðkg of CO2Þ¼7230:12 kg of CO2 per year

And the total amount of CO2 emitted for Case Study #2 with theconventional fuel is:

46708:31 ðkg of CO2=yearÞ þ 7230:12 ðkg of CO2=yearÞ¼ 53938:43 kg of CO2 per year:

Fig. 8. Renewable energy and renewable energy index for Case Study #1.

4.1.2.1. Option 1. The environmental impact of the solar waterheaters for Case Study #2 is exactly the same as that of Case Study#1, which has been explained earlier.

4.1.2.2. Option 2. The PV panels roughly generate56 � 210 � 90% � 3.53 = 37 kW of electricity per day. Considering300 sunny days in a Canadian year one could write:

37 ðkWÞ�300¼11;100 kW h=year11;100 ðkW h=yearÞ�3:6 ðMJ=kW hÞ¼39;960 MJ=year¼39:96 GJ per year

By using the ‘‘Plug into Green Canada’’ [25], in order to generatethe average amount of 39.96 GJ per year, then 3,892 kg of CO2 peryear was emitted into the atmosphere in Ontario. In other words,the designed PV system saves 3892 kg of CO2 per year.

4.1.2.3. Option 3. As the sizing of the ground source heat pump forthe Case Study #2 is the same as that of the Case Study #1, thenthat is also applicable here.

4.1.2.4. Option 4. Since the sizing of the hybrid system #1 for theCase Study #2 is the same as that of the Case Study #1 then theirresult would also be valid at this point.

4.1.2.5. Option 5. With similar arguments, the emission reductionfor the hybrid system #2 is equal to the emission reduction by 4panels of WSE58, calculated along with the emission reductionby 56 PV modules as computed earlier on. The quantity of theemission reduction by the hybrid system #2 is therefore:


4.1.2.6. Option 6. The results obtained for Case Study #1 – Option 6,are also valid for Case Study #2, since the design of the hybrid sys-tem #3 for Case Studies #1 and #2 are identical.

In the above paragraphs, the environmental impact of every en-ergy options for every case study has been determined in the formof the environmental impact indices (IE) to the effect of each tech-nology design. The calculated values of IE have been summarized inFig. 7.

4.2. Energy aspect

4.2.1. Case Study #1 – energy demandThe annual energy requirement of Case Study #1 is the sum of

the natural gas and the electricity consumptions. The energy valueof the natural gas used by Case Study #1 (2760 m3) was calculatedfor 99.70 GJ per year. Also, the energy value of 5475 kW h per yearcan be estimated as:

5475 ðkW h=yearÞ � 3:6 ðMJ=kW hÞ ¼ 19;710 MJ=year

¼ 19:71 GJ per year

Then the total energy demand for Case Study #1 is:

99:70 ðGJ=yearÞ þ 19:71 ðGJ=yearÞ ¼ 119:41 GJ per year

The energy value of each technology is already defined in thedesign Section 5. The summary of the energy and energy indexfor every design is illustrated in Fig. 8.

Fig. 11. Renewable exergy and renewable exergy impact for Case Study #2.


4.2.2. Case Study #2 – energy demandThe energy demand for the Case Study #2 is the total sum of the

natural gas and the electricity consumptions. The energy value ofthe natural gas used by Case Study #2 (3980 m3) was determinedin Section 4 as 143.74 GJ per year. The energy value of 13,286 kW hper year can be computed from:

13;286 ðkW h=yearÞ � 3:6ðMJ=kW hÞ ¼ 47829:6 MJ per year


Then the total energy demand for Case Study #2 would be:

143:74 ðGJ=yearÞ þ 47:83 ðGJ=yearÞ ¼ 191:57 GJ per year

Initially different technology options were examined and thenthe energy value of every technology has been adapted. Renewableenergy index of every design option is calculated accordingly. Theenergy results for Case Study #2 are summarized in Fig. 9 as de-scribed in the following.

4.3. Exergy aspect

4.3.1. Case Study #1The exergy for Case Study#1 can be estimated by using equa-

tion (3). Hence, the exergy for electricity can be determined as:

Exergy of electricity ¼ 19:71 ðGJÞ � 1 ¼ 19:71 GJ per year

and the exergy of the natural gas can be calculated as:

Exergy of natural gas ¼ 99:7 ðGJÞ � 0:913 ¼ 91 GJ per year

Then the total exergy for Case Study #1 would be:

19:71 ðGJÞ þ 91 ðGJÞ ¼ 110:71 GJ per year

The renewable exergy index for various technology options con-sidered for Case Study #1 can be calculated by using Eq. (4). Thecalculated results are presented in Fig. 10.

4.3.2. Case Study #2The exergy for Case Study #2 can be estimated using Eq. (3).

Hence, the exergy for the electricity can be evaluated as:

Fig. 9. Renewable energy and renewable energy index for Case Study #2.

Fig. 10. Renewable exergy and renewable exergy index for Case Study #1.

Exergy of electricity ¼ 47:83 ðGJÞ � 1 ¼ 47:83 GJ per year

and the exergy of the natural gas can be calculated as:

Exergy of natural gas ¼ 143:74 ðGJÞ � 0:913


Then the total exergy for Case Study #2 would be the sum ofthem as:

47:84 ðGJÞ þ 143:74 ðGJÞ ¼ 131:24 GJ per year

Eq. (4) is the renewable exergy index for different technologyoptions which has been used to compute for Case Study #2. Thecomputed results of exergy calculations for Case Study #2 havebeen summarized in Fig. 11.

5. Results and discussion

In comparing different renewable energy design options forCase Studies #1 and #2, the environmental impact, energy, andthe exergy, as well as the environmental impact indices, renewableenergy and the exergy indices have been computed. Results ofthose calculations are presented in Figs. 8 and 9 for Case Studies#1 and #2, respectively. Comparisons of various options in thisstudy are based on the environmental impact, energy and the exer-gy approaches. For the final choice decision, these various optionsmust be considered depending on the management priority costfactor.

In analyzing Case Study #1, the hybrid system #1 has the high-est environmental index while the hybrid system #3 provides thebest renewable energy and exergy indices as illustrated in Table 2.Since the hybrid systems are formed as the combination of tworenewable technologies, the ranking of the hybrid systems as thetop priority is a logical choice. For assessing Case Study #2, the hy-brid system #1 has the highest environmental index, while the hy-brid system #3 has the best renewable energy and the exergyindices as listed in Table 2.

On the overall view to the environmental index, the geothermalsystem technology design by itself and part of a hybrid systemwould present a higher index of the environmental, renewable en-ergy and the exergy in comparison with other renewabletechnologies.

Taking into consideration that Case Studies #1 and #2 are for al-most two similar houses, from the point of the space area andnumber of residents, the major distinction between them is the en-ergy consumption. Case Study #1 consumes energy 0.6 times lessthan Case Study #2 (119.41 GJ)/(191.57 GJ)) = 0.6). The rate of en-ergy consumption affects in opposite direction to the environmen-tal impact index. For the energy Options 1, 3, 4, and 6 (refer toTable 2) in which the technology is identically of the same sizefor both Case Studies #1 and #2, the environmental index (IE) is2.1. This means achieving 40% reduction of energy consumptionin a household will increase the environmental protection more


than twice (e.g. for Option 6, the hybrid system #3 would give 17/8 = 2.1). This thought comes from the result of comparing the envi-ronmental impact indices of Case Studies #1 and #2. The environ-mental impact indices for Case Study #1 is more than double ofthat for Case Study #2 in the identical renewable technology de-signs, which includes the solar heater panels, geothermal system,and the hybrid systems #1 and #2.

For the renewable technology design, including the PV panels,the proportion of environmental impact indices of Case Study #1to that of Case Study #2 is different for the reasons that size andnumber of applied PVs are different. For the renewable energyand the exergy index, the proportion of Case Study #1 to that ofCase Study #2 is about 1.5 for the identical designs, since the en-ergy consumption in Case Study #1 is lower than Case Study #2.

The study of proportions shows the importance of energy con-sumption patterns in buildings. Using the non-fossil fuels is onepart of the solution to the environmental issues and the energyconservation is another part of resolution. Re-design of energy con-sumption model is less expensive and more achievable for build-ings. When equipment is not available to use the non-fossil fuelin a building, then change of the energy consumption behaviorwould tremendously help in reducing the environmental impactof the building.

6. Conclusions

Two similar residential buildings were chosen to consider dif-ferent energy options. Each house was treated as an independentCase Study, and then various renewable energy and hybrids sys-tems are designed and sized for every one of theme. The environ-mental impact and the energy and exergy aspects of each designwere fully assessed through the analysis of the environmental im-pact index, the renewable energy index and the exergy index. Theimportant following results are obtained from the computer simu-lation runs and evaluating the results for both cases:

� The highest environmental impact index belongs to hybrid sys-tem #1, being 26 for Case Study #1 and 12 for Case Study #2.Therefore, it indicates that the hybrid system #1 is a betteroption.� The renewable energy indices demonstrate that the hybrid sys-

tem #3 has a superior technology by achieving the highestindex of 72 for Case Study #1 and 45 for Case Study #2.� The upmost renewable exergy index fits well in hybrid system #3,

being 77 for Case Study #1 and 65 for Case Study #2. This reiter-ates that hybrid system #3 is an outstanding design choice.� Hybrid systems are ranked as top choices with higher indices

since they are made with the combination of two technologiesand exhibit the advantages of both technologies.� When comparing the indices of Case Studies #1 and #2 then

one by one reveals that:� The renewable technology is identical for Case Studies #1 and

#2. Case Study #1 (the house having lower energy consump-tion) demonstrates to achieve higher values of the environmen-tal impact index, the renewable energy index, and therenewable exergy index when compared with the correspond-ing indices for Case Study #2.� When changing the energy consumption pattern towards the

goal of having a lowering energy usage, the environmentalimpact index, the renewable energy index, and the renewableexergy index will all increase.

The results presented are only based on the environmental, en-ergy and the exergy aspects without considering any economic fac-

tors. For having a thorough prioritization, it is recommended thatone should also consider the initial capital costs, the annual main-tenance cost, and other financial aspects of every design carefullyin order to arrive at an optimum decision. However, if the financialfactors take into considerations then may be the hybrid systemswould be the most expensive technologies since they are madeof the combination of two renewable technologies.

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