Energy options for residential buildings assessment

Energy options for residential buildings assessment

Energy Conversion and Management 65 (2013) 637–646 Contents lists available at SciVerse ScienceDirect Energy Conversion and Management journal homep...

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Energy Conversion and Management 65 (2013) 637–646

Contents lists available at SciVerse ScienceDirect

Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

Energy options for residential buildings assessment Behnaz Rezaie, Ibrahim Dincer ⇑, Ebrahim Esmailzadeh Faculty 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

Article history: Received 16 October 2011 Received in revised form 31 August 2012 Accepted 4 September 2012 Available online 8 November 2012 Keywords: Exergy Renewable energy Energy management Residential building Environmental impact

a b s t r a c t The building sector, as one of the major energy consumers, demands most of the energy research to assess different energy options from various aspects. In this paper, two similar residential buildings, with either low or high energy consumption patterns, are chosen as case studies. For these case studies, three different renewable energy technology and three different hybrid systems are designed for a specified size. Then, the environmental impact indices, renewable energy indices, and the renewable exergy indices have been estimated for every energy options. Results obtained show that the hybrid systems (without considering the economics factors) are superior and having top indices. The importance of the energy consumption patterns in buildings are proven by the indices. By cutting the energy consumption to about 40% the environment index would increase by more than twice (2.1). Utilization of the non-fossil fuels is one part of the solution to environmental problems while energy conservation being the other. It has been shown that the re-design of the energy consumption model is less complex but more achievable for buildings. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction The definition of modern world is not just limited to the use of new technologies, but having the knowledge as ‘‘how’’ to supply the energy in a caring manner. One could say that the environment is essential parts of the world; despite the last century that energy and environment were scientific subjects limited to researchers. It is interesting to note that the awareness and the usage manners of energy have been modified, during the past 60 years. Rezaie et al. [1] have described the outlook of humankind toward energy since the industrial revolution and the outlook evolution ever since. They also highlighted the supply of the renewable energy to reduce the emission of the greenhouse gases (GHGs) while to promote the smart use of energy. Hodder et al. [2], Heidari and Sharples [3] and Yannas [4] have reported that 50% of the carbon dioxide emissions come from the building sector in the industrialized countries. The solar energy counts for 13% of the energy consumption in buildings, and it is planned to increase rapidly [5]. It presents a good motivation to study buildings and a challenge to find methods of increasing the efficiency of buildings. Markis and Paravanits [6] have explained that the energy-efficient buildings may lower the carbon emission by even more than 60%, which corresponds to 1.35 billion tons of carbon, being the amount of savings proposed by the Environment Conferences in Rio and Berlin. Huang ⇑ Corresponding author. Tel.: +1 905 721 8668; fax: +1 905 721 3370. E-mail addresses: [email protected] (B. Rezaie), [email protected] (I. Dincer), [email protected] (E. Esmailzadeh). 0196-8904/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enconman.2012.09.008

et al. [7] have suggested a trigeneration system with the goal of improving energy utilization efficiency of buildings. Sustainable operations as well as efficient design are important strategies for buildings [8]. Zaki et al. [9] have stated three factors to have the environmental friendly buildings, including energy efficiency, energy conservation, and renewable energy. A research is performed to show an ancient energy technology used for energy efficient buildings and the results were reported in literature [10]. Energy efficient buildings also make use of the conventional energy sources and rely mainly on oil. Over and above the major savings in the energy usage and cutting down on the GHG one can say that much attention has been drawn recently on the measurement of the energy consumption of buildings. In this regard, Balaras et al. [11] have stated that the energy consumption of a building is a function of many variables such as the building type, construction materials, occupancy behavior, climatologic conditions, heating and cooling equipment, domestic hot water, and the lighting. As for buildings, Vivancos et al. [12] have presented the research results for the thermal characterization of brick, and Sozer [13] has illustrated the role of design for the building envelope to enhance energy efficiency. Also, Wan et al. [14] have shown the trends of energy consumption for future buildings under different climates. Balta et al. [15] have stated that exergy analysis is essential for energy system improvement and should be used as a potential tool for sustainable buildings design. The flows of energy in the building systems are more tangible if exergy analysis is used [16,17]. Thus, exergy analysis shows possibility of more efficient design by dropping inefficiencies in the system [18]. Environmental advantages and economics of energy can

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Nomenclature CEC COP E IE RCO2 ECO2 Ex

California Energy Commission coefficient of performance energy environmental impact indices reduced CO2 emitted CO2 exergy

R RE IER REx IREx TE TEx

be detected easier by exergy analysis [15]. Furthermore, energy and exergy ratios are defined and applied in building sectors for recognizing buildings energy options benefits [19–23]. The present study is the extension of previous work [1], which sizing various energy options for different buildings. The focus is placed on the residential buildings while the thermodynamic analysis expands to the exergy investigation. Moreover, the energy considerations and the exergy aspects with various energy options for several case studies will be analyzed beyond the efficiency analysis. The study covers the environmental aspects of different possibilities of energy. Two similar residential buildings are selected, one with the high and the other with low energy consumers. For every case study the energy, exergy and the environmental impacts of these renewable energy options have been assessed. Some indices are proposed in this work as a tool for comparing several energy options from different aspects including energy, exergy, and environmental impact in a peek. Application of these indices in this study illustrates the difference between the low and high energy consumption in two similar buildings. 2. Methodology Different methods of sizing various energy options, environmental impact, energy, and exergy aspects will be defined in this section. Furthermore, these methods will be applied to the previously mentioned case studies. 2.1. Sizing technologies The sizing technologies were discussed in detail in the previous study performed by Rezaie et al. [1]. Here, the proposed methodologies for sizing the solar electricity, solar thermal and geothermal system are used.

energy grade function renewable energy renewable energy index renewable exergy renewable exergy index total energy total exergy demand

sources are namely, the hydro, thermal, nuclear, combustion engines, and very limited renewable energies. The resulting pollution due to the electricity generation varies depending on the fuel resources. In a report entitled ‘‘Power Generation in Canada’’, published by the Canadian Electricity Association, the electricity generation configuration in the Province of Ontario for the year 2004 was [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 offers a calculator, which considers the combination of the abovementioned sources and presents the total generated amount of CO2. Alternatively, this calculator can be utilized to estimate the amount 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 Association, [27]. It clearly states that to obtain 1 GJ of energy by burning the natural gas one would generate the unwanted amount of 50.3 kg of CO2. 2.3. Energy aspect The energy demand for each case is important enough to be measured 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 the renewable energy, and TE stands for the total energy demand. It is understandable that IRE is a dimensionless parameter.

2.2. Environmental Impact

2.4. Exergy aspect

One of the major reasons to use the non-fossil fuel energy supplier 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 has been estimated. Then the ‘‘environmental impact index’’ is calculated for each design. The environmental impact index expresses as

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

IE ¼ 100ðRCO2 Þ=ECO2

ð1Þ

where IE represents the environmental impact index, RCO2 stands for the reduced CO2 by the design, and ECO2 is the emitted CO2 by the conventional design, respectively. Note that IE is a dimensionless factor. It is worth mentioning that the method of estimation of CO2 for electricity generation should be explained prior to the calculation of the environmental impact index. Electricity is generated in different plants through using different fuels. In Canada, these re-

Ex ¼ E  R

ð3Þ

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

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

IREx ¼ 100ðRExÞ=TEx

ð4Þ

where IREx represents the renewable exergy index. REx is the renewable 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 buildings are listed in Table 2. These options will be applied to the respective case studies in the following. 3.1. Case Study #1 A 2-story residential detached house in Brampton, Ontario, Canada, has been chosen as Case Study #1, which has the latitude 43.536 and longitude 79.556. Case Study #1 is a 4 + 1 bedroom, with five residents. In this house, furnace works with natural gas and electricity; the heating system is of the forced air type. The living area of the house is about 214 m2. The energy consumption in this house is kept under control and the save of energy is well respected by the residents. The electricity consumption of this household for the past year was 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 rate is 12 kW h. Fig. 1 shows the distribution of the electricity consumption for Case Study #1 The total consumption of the natural gas for this house is 2760 m3. The gas consumption for Case Study #1 is illustrated in Fig. 2. Note that natural gas usages in June, July, and August are higher than May and September because of the extra people than usual as visitors during summer in house of Case Study #1. The energy consumption distribution for Case Study #1 is also important to know and it is depicted in Fig. 3. 3.1.1. Option 1 The conventional solar water heaters are very popular for the heating of the domestic water. In this section, the solar water heaters are customized for Case Study #1 to heat up the domestic

Table 1 Ground source energy system for Case Study #1. Geothermal system specifications System capacity Number of pipes Length of pipes Circulating liquid Cooling COP Heating COP Cooling capacity Heating capacity

51633 kJ/h 2 U shape 440 m R-410A 5.1 4.1 15 kW 11 kW

water, and analysis is done from the point of energy generation the pollution reduction. By using the solar water heaters, the natural gas consumption has been reduced. The detail reduction of the energy consumption is presented in the energy Section 4. Then energy suppliers for Case Study #1 in this situation are the solar water heaters (solar thermal) and also other regular sources of energy, which are the grid electricity and natural gas. Heat collector panel 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 panels, WSE58 [24], to provide sufficient energy to heat water for the household domestic hot water. The energy generated by four panels is: 2741310.00  4 = 11 MJ/h. By considering seven hours of sunshine per day as an average period for all days in a year, the total energy produced by these solar panels would be:

11  7 ¼ 77 MJ=day An assumption is made that there are 300 days of sunshine per year in Canada. Hence, the energy produced by the solar collectors is 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 of 37234.00 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 reduced by 620.4 m3 every year. In a life period of 25 years for the solar panels, this saving is 15,510 m3 of the natural gas.

3.1.2. Option 2 The PV panels are an appropriate technology to generate electricity for households. In this section, the PV panels are sized for Case Study #1, thereby reducing the requirement of electricity. Section 4 shows the detailed calculations and the amount of electricity, which the PV panels would generate. Therefore, the energy suppliers in Case Study #1 are the PV panels (solar electricity) in addition to the conventional energy sources, being the grid electricity and natural gas. The PV panel is chosen from the REC Group [30] from the SCM series 210, which is the most popular PV panel in Scandinavia, and are available in larger panel wattage. The panels used in the calculations are the 210 W and the 215 W ones. The sun hour or the insulation coefficient for the Pearson International Airport varies from a minimum of 1.08 kW h/m2/d to a maximum of 5.98 kW h/m2/d based on the NASA database given in the RETScreen software [22], and hence, the average coefficient on the insulation is 3.53 kW h/m2/d. It is found that the average electricity consumption in Case Study #1 is 15 kW, and the average insulation coefficient in the Toronto area is 3.53 kW h/m2/d. Therefore, the electricity consumption by the sun hours per day would be 15/ 3.53 = 4.25 kW = 4250 W (AC).

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

Option Option Option Option Option Option

1 2 3 4 5 6

Solar heater panels PV panels Geothermal system Hybrid system #1 Hybrid system #2 Hybrid system #3

Case Study #1

Case Study #2

Renewable equipment

IE

IRE

IREx

Renewable equipment

IE

IRE

IREx

4 WSE58 22  215 W GT049 GT049 + 8  210 W 4 WSE58 + 22  215 W 4 WSE58 + GT049

5 6 13 26 11 17

19 14 53 55 33 72

21 15 57 62 35 77

4 WSE58 56  210 W GT049 GT049 + 8  210 W 4 WSE58 + 56  210 W 4 WSE58 + GT049

2 7 6 12 9 8

12 21 33 34 27 45

18 30 48 52 48 65

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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 by the California Energy Commission (CEC) are taken as 194 for the inverter 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 array configuration, 215 W is replaced for the 210 W panel and 22 panels would be chosen. The proposed configuration is having two rows of strings 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 recommended that the PV modules be changed accordingly. This would ensure the harnessing of the maximum energy from the sun. 3.1.3. Option 3 The ‘‘ground source energy’’ system is an interesting source of renewable energy since it is ‘‘reliable’’, i.e., always available without any interruption from the Mother Nature. Moreover, the ground source heat pump provides cost effective energy for both heating and cooling of buildings. The average coefficient of perfor-

mance (COP) of a ground source energy system is roughly 4, which means 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 winters, the use of the ground source energy systems is a very intelligent and logical decision. The geothermal energy, as a renewable source of energy, together with a conventional source of energy such as the grid electricity and natural gas have been utilized as the energy supplier for Case Study #1. The electricity consumption for the heating and cooling of the residential building has been reduced to one/fourth by using the geothermal energy. For sizing the geothermal system in Case Study #1, the RETScreen software [30] is employed. There are few constant parameters involved in the equations, namely, the specific heats, density, and the thermal conductivity. The RETScreen software chooses its own data in order to replace these constants. Ultimately, RETScreen calculates all the energy losses (i.e., the conductive and convective), and includes all the gains (solar and internal gains) and fresh air load. Finally, it adds up the heat loads for the heating or cooling of the space and produces the power of the geothermal system, which can generate the heat load. For Case Study #1, all the data is entered into RETScreen and the outcome from RETScreen shows that a heat pump with the capacity of 51,633 kJ/h is needed to run the heating and cooling systems in Case Study #1, while the heat loss is 4428.2 kJ/h. This is almost matched with the model GT049 from Geosmart Energy. The GT049 model has COP 4.1 for the heating mode and COP 5.4 for the cooling mode. This unit is replaced in the utility room with a furnace, which runs on natural gas. The pipe loop for Case Study #1 is a closedloop arrangement with the cycling ethanol, R-410A refrigerant. The pipes are 3.1 cm in diameter and 440 m long. These 220 m pipes are placed into two holes with a length of 110 m each and the diameter of holes is 12.5 cm. In the backyard and close to the utility room, these two holes are bored through the earth with special machines. In each 110 m hole there is a U-shaped pipe with a total length of 220 m; for the two holes, a 440 m pipe is available for circulation of the R-410A refrigerant. The R-410A refrigerant exchanges heat with the soil through this path of 440 m, and either dumps the heat into the ground or extract the heat from the soil. Table 1 illustrates a summary of the ground source energy system for Case Study #1.

3.1.4. Option 4 As 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 the ground by spending one unit of energy (e.g., electricity), thereby providing exactly five units of energy for cooling or heating purposes. This means that the geothermal system is an ideal candidate for alternative energy option from the point of view of reliability

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and efficiency. Furthermore, this superior energy technology requires only one-fifth of its energy to run an entire system. The electricity required by the ground source heat pump is supplied from another source of renewable energy. The entire heating and cooling systems would therefore, run with natural energy. This source of energy could be photovoltaic panels, which convert the solar energy into electricity and can easily be built to meet the electricity demand level. In this design, the geothermal energy and the PV panels (solar electricity) are the source of renewable energy, and the grid electricity plus the natural gas are the conventional 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 geothermal system. This innovative system remains the same for rural areas by including a number of batteries as the electricity source for the geothermal system and the PV panels. Also, another alternative hybrid system for country-wide areas is to couple the ground source heat pump and the wind turbines with a set of batteries. The cooling capacity for the ground source heat pump GT049 is 15 kW and the heating capacity is 11 kW, and hence, the highest capacity of this machine is 15 kW. It has been previously mentioned that one-fifth of this energy supplies to the heat pump, and therefore, 15/5 = 3 kW of energy, in the form of electricity, is required to run the pump. Subsequently, one can say that the PV panels should generate 3 kW/day. The sunshine hours or the insulation coefficient for the Pearson International Airport is reported to be from a minimum value of 1.08 kW h/m2/d to a maximum value of 5.98 kW h/m2/d, [31] and hence, the average coefficient of the insulation is 3.53 kW h/m2/d. Since the average electricity consumption for the hybrid design of Case Study #1 is found to be 5 kW, therefore, the average insulation 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 information for the inverter is 194 and that for the solar modules SCM 210 series 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 number of panels. Then, 8 panels of 210w would deliver the required electricity for the ground source heat pump. By coupling the ground source heat pump GT049 from Geosmart Energy with a set of eight photovoltaic panels, the 210w cooling and heating needed for Case Study #1 will be totally obtained from the natural energy using the REC Group series 210. 3.1.5. Option 5 The second hybrid system is further developed through solar technologies by combining the PV panels for generating the electricity and solar water heaters to heat the water. In the hybrid system #2, the electricity and the natural gas consumptions are reduced and this reduction is calculated in the following paragraphs. This hybrid system is directly dependent on the solar energy. In the hybrid system #2, the grid electricity and the natural gas are present as a backup system for the time whenever there is not sufficient sunlight. However, for longer sunny days, the extra energy would overflow to the grid. Hybrid system #2 consists of the solar water heaters (solar thermal) and the PV panels (solar electricity). The solar water heaters consist of PV modules as already been computed. Based on the previous assessment, the hybrid system #2 would include four panels of WSE58 as the solar thermal energy to convert the solar energy to

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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 panels have been previously described.

3.1.6. Option 6 The third combination of the hybrid system for Case Study #1 with the available technologies is the geothermal system and the solar thermal energy. The ground source energy is a superior technology for the heating and cooling only with one-fifth of the energy needed. The solar water heaters are designed for Case Study #1 to provide the domestic hot water for household everyday use. In this system, the energy consumption is drastically reduced because the main portion of the energy consumption, based on Fig. 3, is used for the space heating/cooling (57%) and to heat the water (17%). Therefore, a total of 74% energy usage is targeted to be reduced significantly in Case Study #1. The grid electricity and the natural gas is 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 thermal) and the ground source heat pump (geothermal system). The solar water heaters and geothermal system have already been computed. Based on the previous assessments, the hybrid system #2 includes four panels of WSE58 as the solar thermal energy for converting the solar energy to 11 MJ/h together with a GT049 to generate either 15 kW/day cooling energy or 11 kW/day heating energy.

3.2. Case Study #2 Case Study #2 is for another detached house in Oshawa, Ontario, 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 this house runs on natural gas, and the electricity and heating system are also the forced air type. The living areas in this house are approximately 215 m2. The first floor consists of the kitchen, the living/dining room, the family room, and a bathroom; the second floor is made up of four bedrooms, and two bathrooms, and the basement is considered as a full basement. The main difference between Case Study #1 and Case Study #2 is the energy consumption pattern. The energy usage in Case Study #2 is significantly higher than that of Case Study #1. The natural gas and electricity consumptions are both noticeably higher than those of Case Study #1. The last year electricity consumption of this household was 13,303 kW h, which makes the average daily consumption as 36.4 kW h, with the highest daily rate as 44 kW h. Fig. 4 displays the average daily electricity consumption for Case Study #2 in the last year.

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

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The distribution of energy consumption for Case Study #2, as a regular household, is almost the same as Case Study #1. Fig. 4 shows 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 of Case Study #2 is 10.9 m3. Fig. 5 depicts the average natural gas consumption for the household of Case Study #2. 3.2.1. Option 1 Solar 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 people in the household are the same in both cases, the number of solar collector panels in both cases is the same, as well. Thus, the calculation for energy, emissions and cost is also the same. Figs. 5–7 display these results for Case Study #2. Energy resources for Case Study #2 are the solar thermal as the renewable source of energy in addition two other conventional sources of energy – the grid electricity and natural gas. The solar thermal energy reduces the natural gas consumption by 620 m3/ year as already been calculated. 3.2.2. Option 2 The PV panels are desirable technology to generate electricity for the household. The sizing of the PV panels is exactly the same as for Case Study #1. The resources of energy for Case Study #2 are the solar electricity through PV panels, grid electricity, and the natural gas. Based on the average electricity consumption of 36.4 kW for Case Study #2, and the average insulation coefficient of 3.53 kW h/m2/d for the Toronto area, the electricity consumption by 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 56 is the number of PV panels; PV panels are 210 W each. Then four rows of strings with 14 panels of module 210 W in each string are 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 changed when the seasons change. 3.2.3. Option 3 As mentioned the ground source energy system is a remarkable source of renewable energy, over the reliability. In this section, the geothermal system is customized for Case Study #2 with the analysis 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.

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

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

geothermal systems in both cases are also the same. Hence, the energy resources for Case Study #2 are the geothermal energy as a renewable source of energy, together with the conventional sources of energy – the grid electricity and natural gas. The electricity consumption for the heating and cooling purposes is reduced to one-fourth by using the geothermal energy. 3.2.4. Option 4 As previously stated, the geothermal energy is a reliable source of energy, which provides the heating and cooling energy. The ground source heat pump extracts four units of energy from the ground by spending one unit of energy (i.e., electricity), to generate exactly five units of energy for the cooling or heating purposes. Thus, the geothermal system is an ideal candidate for an alternative energy source from the point of reliability and efficiency. Furthermore, this supreme technology requires only one-fifth of its energy to run the entire system. The electricity required by the ground source heat pump can be supplied by another source of renewable energy. Then, the whole heating and cooling system would run with the natural energy. This source of energy could be photovoltaic panels, which converts the solar energy to electricity and can easily be developed to the electricity demand level. Therefore, in this design the geothermal energy and the PV panels (solar electricity) of the hybrid system #2 are the source of renewable energy for Case Study #2, and the grid electricity plus the natural gas are the conventional sources of energy. Since the geothermal system is exactly the same as that of Case Study #1, the hybrid system #1 for Case Study #2 is exactly the same as that of Case Study #1. Therefore, the energy utilization calculation, cost analysis and the emission reduction effect are the same in both cases. 3.2.5. Option 5 The second hybrid system is defined through the solar technologies by combining the PV panels to generate the electricity and the solar water heaters are to heat the domestic water. In hybrid

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system #2, the consumptions of the electricity and natural gas are reduced. The reduction is calculated in the following paragraphs. This hybrid system is directly dependent on the solar energy. In hybrid system #2, the grid electricity and the natural gas are still utilized in the system as a backup when there is not sufficient sunlight available. However, the extra energy overflows to the grid for long sunny days. The hybrid system #2 consists of the solar water heaters (solar thermal) and the PV panels (solar electricity). The solar water heaters and the PV modules have already been computed. Based on the previous assessment, the hybrid system #2 includes four panels of WSE58 to convert the solar energy to 11 MJ/h, and also 56 panels of PV modules 210 W to generate 36.4 kW per day. The configuration of the PV modules and the angles of the panels have been described before. 3.2.6. Option 6 The third combination of the hybrid system for Case Study #2 with the available technologies is the geothermal system and the solar thermal energy. Ground source energy is a superior technology for the heating and cooling purposes and the solar water heaters are designed for Case Study #2 to provide the domestic hot water for the household. In this system, the energy consumption has been drastically reduced because the main portion of the energy consumption, based on Fig. 6 for Case Study #2, is used for the heating and cooling (57%) and hot water (17%). A total of 74% of the energy usage in Case Study #2 is targeted to be reduced significantly. The grid electricity and natural gas is still the reliable sources of energy for Case Study #2, but the amount of usage is greatly reduced. Since Case Study #2 is very similar to Case Study #1, and the 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 is the same as hybrid system #3 for Case Study #1. Therefore, the energy utilization, emission reduction, and the cost analysis for hybrid system #3 of Case Study #2 is exactly the same as those for the hybrid system #3 of Case Study #1, though results are applicable solely for Case Study #2.

ronmental issues in every single energy technology, proposed in previous section, for both case studies are examined in the following paragraphs. 4.1.1. Case Study #1 When the residential building of Case Study #1 is running with the conventional energy, say the natural gas and electricity, the volume of the emitted CO2 is the sum of the emitted CO2 to generate 5506 kW h of electricity and the burning of 2760 m3 of natural gas. By using the calculator given in reference [12], one could find that 19332.17 kg of CO2 has been emitted to the environment when 5506 kW h of electricity has been generated. According to the report published in Ref. [27], the energy contained in every cubic meter of natural gas is 36116.7 kJ. Therefore, the total energy resulted 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 burning of the natural gas is equivalent of generating 50.3 kg of CO2, hence:

99:7 ðGJ=yearÞ  50:3 ðkg of CO2 Þ ¼ 5014:91 kg of CO2 per year: Therefore, the total amount of CO2 emitted to the environment when for Case Study #1 the conventional fuel was used is:

19332:17 ðkg of CO2 =yearÞ þ 5014:91 ðkg of CO2 =yearÞ ¼ 24347:08 kg of CO2 per year: 4.1.1.1. Option 1. The conventional solar heaters designed to generate 23.1 GJ for Case Study #1. The equivalent energy for burning the 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 panels would generate roughly about [22  215  90%  3.53 = 15 kW h] of electricity per day. By considering 300 sunny days for Canada the electricity generated by the PV panels is: 15 ðkW hÞ  300 ¼ 4500 kW h=year

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 aspect of the analysis is the environmental impact of energy as the main purpose of the options. Different design proposals will be measured individually for each option within every case study. Also, energy analysis for each technology options will be performed to show the share of the renewable energy in the proposed design. Following that exergy, as the quality of energy for each energy technology will be examined. It can be another tool to measure capability of different design proposals. The overall analysis of energy options provides insight for designers and researchers.

4500 ðkW h=yearÞ  3:6 ðMJ=kW hÞ ¼ 16;200 MJ=year ¼ 16:20 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 environment 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 natural gas has been eliminated from the system. Therefore, the consumption of the gas is drastically reduced. Along with Fig. 3, one can say that 61% of the household energy is used either for heating or cooling the space. The natural gas consumption in Case Study #1 is found to be 2760 m3 per year. The usage of natural gas has now been reduced by 1683 m3. 1683 ðm3 =yearÞ  36116:7 ðkJÞ ¼ 60; 784;406 kJ=year ¼ 60:78 GJ=year

4.1. Environmental impact

60:78 ðGJ=yearÞ  50:3 ðkg of CO2 Þ ¼ 3057 kg of CO2 per year

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

Hence, by not burning 1683 m3 of the natural gas annually, then 3057 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 the emission reduction is combined from two categories: one category being the elimination of the burning of the natural gas, and the other is to reduce the electricity consumption. The first category, which is resulted from reducing the natural gas consumption,

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has been calculated earlier. It is estimated that by not burning 1683 m3 of the natural gas per year, this will correspond in eliminating the amount of 3057 kg of CO2 annually. The second part of the emission reduction is through cutbacks in the electricity. According to the calculator of ‘‘Plug into Green Canada’’ [26], in order to generate an average amount of 3 kW h  300 = 900 kW h of electricity per year, one has to emit 3,160 kg of CO2 per year into the atmosphere in the Canadian Province of Ontario. The hybrid system, as a combination of the ground source heat pump and the photovoltaic panels, will collectively protect the environment by eliminating the amount of:

3150 ðkg of CO2 =yearÞ þ 3160 ðkg of CO2 =yearÞ ¼ 6217 kg of CO2 per year: 4.1.1.5. Option 5. Along with the same logic, the emission reduction for the hybrid system #2 is equivalent of the emission reduction by four panels of WSE58, as calculated already along with the emission reduction by 22 PV modules computed in earlier sections. Then, the quantity of emission reduction by hybrid system #2 is:

1161 ðkg of CO2 =yearÞ þ 1580 ðkg of CO2 =yearÞ

By using the ‘‘Plug into Green Canada’’ [25], in order to generate the average amount of 39.96 GJ per year, then 3,892 kg of CO2 per year 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 for the Case Study #2 is the same as that of the Case Study #1, then that is also applicable here. 4.1.2.4. Option 4. Since the sizing of the hybrid system #1 for the Case Study #2 is the same as that of the Case Study #1 then their result would also be valid at this point. 4.1.2.5. Option 5. With similar arguments, the emission reduction for the hybrid system #2 is equal to the emission reduction by 4 panels of WSE58, calculated along with the emission reduction by 56 PV modules as computed earlier on. The quantity of the emission reduction by the hybrid system #2 is therefore:

1161 ðkg of CO2 =yearÞ þ 3892 ðkg of CO2 =yearÞ ¼ 5053 kg of CO2 per year:

¼ 2741 kg of CO2 per year: 4.1.1.6. Option 6. Following the same argument, the emission reduction for the hybrid system #3 is equal to the emission reduction by four panels of WSE58 plus the emission reduction by the ground source heat pump GT049. Hence, the quantity of the emission reduction by hybrid system #3 can be found as:

1161 ðkg of CO2 =yearÞ þ 3057 ðkg of CO2 =yearÞ ¼ 4218 kg of CO2 per year: Finally, the environmental impact index for every proposed design option is tabulated in Fig. 6. 4.1.2. Case Study #2 For 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 emitted CO2 for generating 13,303 kW h of electricity plus the burning of 3980 m3 of the natural gas. The generation of 5506 kW h of electricity would produce 46708.31 kg of CO2 annually according to the reports published in reference [26]. Therefore, the consumed natural gas would contain [27]: 3980 ðm3 =yearÞ  36116:7 ðkJÞ ¼ 143; 744;466 kJ=year ¼ 143:74 GJ per year 143:74 ðGJ=yearÞ  50:3 ðkg of CO2 Þ ¼ 7230:12 kg of CO2 per year

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

46708:31 ðkg of CO2 =yearÞ þ 7230:12 ðkg of CO2 =yearÞ

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 system #3 for Case Studies #1 and #2 are identical. In the above paragraphs, the environmental impact of every energy options for every case study has been determined in the form of the environmental impact indices (IE) to the effect of each technology design. The calculated values of IE have been summarized in Fig. 7. 4.2. Energy aspect 4.2.1. Case Study #1 – energy demand The annual energy requirement of Case Study #1 is the sum of the natural gas and the electricity consumptions. The energy value of the natural gas used by Case Study #1 (2760 m3) was calculated for 99.70 GJ per year. Also, the energy value of 5475 kW h per year can 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 the design Section 5. The summary of the energy and energy index for every design is illustrated in Fig. 8.

¼ 53938:43 kg of CO2 per year: 4.1.2.1. Option 1. The environmental impact of the solar water heaters 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 generate 56  210  90%  3.53 = 37 kW of electricity per day. Considering 300 sunny days in a Canadian year one could write: 37 ðkWÞ  300 ¼ 11; 100 kW h=year 11; 100 ðkW h=yearÞ  3:6 ðMJ=kW hÞ ¼ 39; 960 MJ=year ¼ 39:96 GJ per year Fig. 8. Renewable energy and renewable energy index for Case Study #1.

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4.2.2. Case Study #2 – energy demand The energy demand for the Case Study #2 is the total sum of the natural gas and the electricity consumptions. The energy value of the natural gas used by Case Study #2 (3980 m3) was determined in Section 4 as 143.74 GJ per year. The energy value of 13,286 kW h per year can be computed from:

13; 286 ðkW h=yearÞ  3:6ðMJ=kW hÞ ¼ 47829:6 MJ per year ¼ 47:83 GJ 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 then the energy value of every technology has been adapted. Renewable energy index of every design option is calculated accordingly. The energy results for Case Study #2 are summarized in Fig. 9 as described in the following. 4.3. Exergy aspect 4.3.1. Case Study #1 The exergy for Case Study#1 can be estimated by using equation (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:

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

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 ¼ 143:74 GJ per year Then the total exergy for Case Study #2 would be the sum of them as:

47:84 ðGJÞ þ 143:74 ðGJÞ ¼ 131:24 GJ per year Eq. (4) is the renewable exergy index for different technology options which has been used to compute for Case Study #2. The computed results of exergy calculations for Case Study #2 have been summarized in Fig. 11. 5. Results and discussion

19:71 ðGJÞ þ 91 ðGJÞ ¼ 110:71 GJ per year The renewable exergy index for various technology options considered for Case Study #1 can be calculated by using Eq. (4). The calculated results are presented in Fig. 10. 4.3.2. Case Study #2 The 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.

In comparing different renewable energy design options for Case Studies #1 and #2, the environmental impact, energy, and the exergy, as well as the environmental impact indices, renewable energy and the exergy indices have been computed. Results of those calculations are presented in Figs. 8 and 9 for Case Studies #1 and #2, respectively. Comparisons of various options in this study are based on the environmental impact, energy and the exergy approaches. For the final choice decision, these various options must be considered depending on the management priority cost factor. In analyzing Case Study #1, the hybrid system #1 has the highest environmental index while the hybrid system #3 provides the best renewable energy and exergy indices as illustrated in Table 2. Since the hybrid systems are formed as the combination of two renewable technologies, the ranking of the hybrid systems as the top priority is a logical choice. For assessing Case Study #2, the hybrid system #1 has the highest environmental index, while the hybrid system #3 has the best renewable energy and the exergy indices as listed in Table 2. On the overall view to the environmental index, the geothermal system technology design by itself and part of a hybrid system would present a higher index of the environmental, renewable energy and the exergy in comparison with other renewable technologies. Taking into consideration that Case Studies #1 and #2 are for almost two similar houses, from the point of the space area and number of residents, the major distinction between them is the energy consumption. Case Study #1 consumes energy 0.6 times less than Case Study #2 (119.41 GJ)/(191.57 GJ)) = 0.6). The rate of energy consumption affects in opposite direction to the environmental impact index. For the energy Options 1, 3, 4, and 6 (refer to Table 2) in which the technology is identically of the same size for both Case Studies #1 and #2, the environmental index (IE) is 2.1. This means achieving 40% reduction of energy consumption in a household will increase the environmental protection more

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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 environmental impact indices of Case Studies #1 and #2. The environmental impact indices for Case Study #1 is more than double of that for Case Study #2 in the identical renewable technology designs, 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 #1 to that of Case Study #2 is different for the reasons that size and number of applied PVs are different. For the renewable energy and the exergy index, the proportion of Case Study #1 to that of Case Study #2 is about 1.5 for the identical designs, since the energy consumption in Case Study #1 is lower than Case Study #2. The study of proportions shows the importance of energy consumption patterns in buildings. Using the non-fossil fuels is one part of the solution to the environmental issues and the energy conservation is another part of resolution. Re-design of energy consumption model is less expensive and more achievable for buildings. When equipment is not available to use the non-fossil fuel in a building, then change of the energy consumption behavior would tremendously help in reducing the environmental impact of the building. 6. Conclusions Two similar residential buildings were chosen to consider different energy options. Each house was treated as an independent Case Study, and then various renewable energy and hybrids systems are designed and sized for every one of theme. The environmental impact and the energy and exergy aspects of each design were fully assessed through the analysis of the environmental impact index, the renewable energy index and the exergy index. The important following results are obtained from the computer simulation runs and evaluating the results for both cases:  The highest environmental impact index belongs to hybrid system #1, being 26 for Case Study #1 and 12 for Case Study #2. Therefore, it indicates that the hybrid system #1 is a better option.  The renewable energy indices demonstrate that the hybrid system #3 has a superior technology by achieving the highest index 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 reiterates 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 technologies and 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 consumption) demonstrates to achieve higher values of the environmental impact index, the renewable energy index, and the renewable exergy index when compared with the corresponding indices for Case Study #2.  When changing the energy consumption pattern towards the goal of having a lowering energy usage, the environmental impact index, the renewable energy index, and the renewable exergy index will all increase. The results presented are only based on the environmental, energy and the exergy aspects without considering any economic fac-

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