- Email: [email protected]
Energy performance of a solar mixed-use community
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
Sustainable Cities and Society xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Sustainable Cities and Society journal homepage: www.elsevier.com/locate/scs
Energy performance of a solar mixed-use community C. Hachem-Vermette a,∗ , E. Cubi b , J. Bergerson c a
Faculty of Environmental Design, University of Calgary, 2500 University Drive NW, Calgary AB T2N 1N4, Canada Schulich School of Engineering, University of Calgary, Canada c Department of Chemical and Petroleum Engineering. University of Calgary, Canada b
a r t i c l e
i n f o
Article history: Received 7 May 2015 Received in revised form 4 July 2015 Accepted 12 August 2015 Available online xxx Keywords: Mixed-use neighbourhood Net zero energy Carbon emissions Energy consumption Energy generation potential
a b s t r a c t This paper explores a solar mixed-use community that combines residential and commercial buildings. The pilot location of this study is Calgary, Canada (52◦ N), representing northern, cold climate. Energy performance of the neighbourhood is estimated in terms of energy consumption and generation potential by means of building integrated PV systems. In addition, the analysis takes in to account the overall primary energy demand and greenhouse gas emissions. EnergyPlus is employed to simulate the overall energy consumption of the neighbourhood. Investigation of different options of mechanical systems is carried out using TRNSYS. Designing and analysing energy performance of a mixed-use community as an integrated system presents an opportunity to explore sharing of energy resources and interaction with the utility grid. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Net zero energy buildings have the potential to alleviate the negative environmental impact of the built environment including the reduction of greenhouse gas (GHG) emissions. The principle of net zero energy has been extensively applied to buildings. These are buildings that generate annually as much energy from renewable energy sources as they consume (Torcellini & Crawley, 2006). The design of net zero energy solar buildings involves a twofold approach of enhancing energy efficiency while optimizing active solar energy production using photovoltaic technologies and thermal collectors. Reduction of energy consumption can be achieved through several measures, including enhanced HVAC efficiency measures. In addition, use of energy for heating can be significantly reduced by means of solar heat gains. A well-designed passivesolar building may provide 45–100% of daily heating requirements (ASHRAE, 2007). Applying the net zero energy concept at urban scale can provide opportunities for seasonal storage, implementation of smart grids for power sharing between housing units, controlling peak electricity production timing and reducing utility peak demand. Additional advantages of net zero energy neighbourhoods include enabling design flexibility and increasing available surface areas for the integration of photovoltaic systems.
∗ Corresponding author. E-mail address: [email protected] (C. Hachem-Vermette).
A small-scale, low-density residential neighbourhood of singlefamily houses can reach net-zero energy status assuming a careful design of building shapes and orientation (Hachem, Athienitis, & Fazio, 2012a). A mixed-use neighbourhood, which combines residential and commercial buildings (retail, office, residential, hotel, recreation or other functions (Niemira, 2007)) is significantly less amenable to achieving such status. Mixed-use communities have several economic and environmental advantages that lead to reduced levels of greenhouse gas emissions (Coupland, 1997; Grant, 2007; Rabianski, Gibler, Tidwell, & Clements, 2009). Such neighbourhoods are considered as part of a strategy to achieve sustainable developments (Grant, 2007; Hoppenbrouwer & Louw, 2005). Despite this fact, quantification of the performance of mixed-use neighbourhoods is not currently available. Moreover, comprehensive design guidelines for achieving high-energy performance mixed-use neighbourhoods are sorely lacking. A systematic design and analysis of energy and GHG emissions of these neighbourhood designs has yet to be completed. This paper presents a concise summary of the design of an energy efficient solar mixed-use community, and its performance estimated in terms of energy consumption and generation potential assuming building integrated PV systems. In addition the paper examines the impact of various mechanical systems on the overall neighbourhood energy performance and on its carbon emissions. The effect of neighbourhood is taken into account both in the simulations and the analysis of the results. The study forms part of a large scope research programme aimed at assessing the effects of multiple design parameters on energy performance of such
http://dx.doi.org/10.1016/j.scs.2015.08.002 2210-6707/© 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
2
communities, and the development of guidelines for their design. This base case design is intended as a reference against which the effects of modifications to selected design parameters are to be assessed. This complex research programme includes different categories of parameters that will be investigated in order to develop guidelines for the design of archetypes of high performance multifunctional communities. These categories include: overall design; energy options and additional categories such as environmental impact, sustainability and “resilience” parameters. The design category will encompass parameters such as pattern of the communities (circular, linear, hexagonal, etc.), density (on per capita basis and number of buildings), and design of the centre and its effect on transport (e.g. number of vehicle trips per day). Energy related parameters would include shift of load and generation, district energy, storage, cogeneration, and energy use for transport under different design parameters.
2. Design of the base case The neighbourhood design developed and analysed in this paper represents the first stage towards proposing a design procedure for high performance solar mixed-use communities. In view of the absence of general guidelines for the design of multifunctional high-energy performance, the design presented in this paper is based on various assumptions of design guidelines for shaping a sustainable neighbourhood. The main criteria for the selected guidelines relate to reducing dependency on cars (i.e. walkability), determining the minimal required density for a viable community, and maintaining a balance between the built area and green public land and street area. These assumptions are briefly described below. The base case development illustrating the design procedure reflects a Northern cold climate and is assumed to be located in Calgary, Canada (52◦ N). The general design of the community layout relies on traditional neighbourhood developments guidelines (TND) (TND, 2014), combined with the fused grid street system of the Canadian Mortgage and Housing Corporation (CMHC) (CMHC, 2011). A TND, known as a village-style development, includes a variety of housing types, a mixed land use, an active centre, a walkable design and often a public transit option within a compact neighbourhood (TND, 2014). The TND guidelines are used to define the approximate relative land areas for each of the functions, as summarized below. CMHC fused grid system is designed to allow mixed-use, densification, and efficient public transport (CMHC, 2011), and therefore can constitute a basis for the design of a new sustainable neighbourhood. Employing the guidelines aforementioned, a land area of 16 ha is determined with a geometry based on the assumption of a ½ km maximum walking distance from the centre of the development (Kemp & Stephani, 2011). The land partition employs a mixture of fused grid and TND designs: the built area constitutes 64% of the land, streets use about 24% of the land, and the remaining 12% represents the green public area. Residential areas form about 80% of the total built area (including surrounding land), with the remainder (approximately 20%) as a mixture of viable commercial space and civic functions. The residential buildings include single detached houses, attached houses, and mid-rise apartment buildings (3–5 stories). The main commercial amenities included in the neighbourhood are: office building, retail area and grocery store, in addition to a primary school. The commercial and civic functions are concentrated in the core of the development (Rowley, 1996). The density is based on the assumption of a minimal number of 4000 residents, to achieve a viable mixed-use neighbourhood (Barton et al., 2010). The total number of residents is employed to
Fig. 1. Neighbourhood design.
determine the number of residential units, assuming an average of 4 persons per unit. A total of 1003 residential units are designed, including 180 houses and 27 apartment buildings with varying number of apartments. A variable residential density is adopted in the design of this neighbourhood. The dense area (125 units/ha) is designed around the centre of the development, while the low-density areas (25–50 units/ha) are located towards the outskirts. 2.1. Buildings design 2.1.1. Residential Residential units are designed as two-story detached and attached houses (180 m2 and 120 m2 respectively) and apartments in low-rise buildings (3–5 floors). The houses are designed to optimize passive solar design (Hachem, Fazio, & Athienitis, 2013) with south-facing windows occupying about 35% of the south fac¸ade. Other thermal characteristics are presented in Table 1. The apartments have a floor area of 110 m2 (average apartment size in Canada (Armstrong, Swintona, Ribberink, BeausoleilMorrison, & Millette, 2009)) (Fig. 1). 2.1.2. Commercial buildings Below is a summary of the main design considerations for each of the commercial buildings employed in the design of this neighbourhood. Fig. 2 illustrates a schematic of each of these buildings. 2.1.2.1. Office building. Guidelines that assist in determining office areas in a neighbourhood with a given population are lacking. This is due to the large number of factors that should be considered in planning such areas in an urban development (e.g. type of business, area required for a business, local employees, etc. (Kyle, Baird, & Spodek, 2000)). For this hypothetic neighbourhood a mid-size 3-story office building of 3600 m2 (i.e. 1200 m2 per floor) is assumed. The building envelope is designed as specified in Table 1. Assumptions for electrical loads are specified based on ASHRAE recommendations (ANSI et al., 2007). 2.1.2.2. Primary school. The single story 4500 m2 school building is designed to specifications for a primary school for a population of 4000 persons. This is based on an estimated number of pupils
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
3
Table 1 Main characteristics and electric loads. Residential units Thermal resistance values:
Thermal mass
Window type
Area of south glazing
Houses Apartment buildings
Shading Strategy Shading control Occupants Set point temperatures Infiltration rate Ventilation rate Lighting (houses and front apartments) Equipment
Exterior wall: 7 RSI Roof: 10 RSI Slab on grade (for ground floor): 1.2 RSI Slab perimeter: 7 RSI 20 cm concrete slab on grade (ground floor) 15 cm concrete slabs (in all apartments except ground floor) Triple glazed, low-e argon filled (SHGC = 0.57), 1.08 RSI 35% of south fac¸ades 30% of south fac¸ades Interior blinds Blinds shut at indoor air temperature of 22 ◦ C 2 adults and 2 children, occupied from 17:00 to 8:00 Heating set point 21 ◦ C, cooling set point 25 ◦ C 0.8ACH @50 Pa 0.35ACH 3.8 W/m2 (ASHRAE 90.1) (ANSI et al., 2007) 5.38 W/m2 (ASHRAE 90.1) (ANSI et al., 2007)
Commercial buildings Thermal resistance values Window type Electrical Loads School Office Retail Supermarket
Similar to residential units Similar to residential units Lights Depending on zone activity (ANSI et al., 2007)
(Barton et al., 2010) and an average area of 11 m2 per pupil (Benson et al., 2010).
Electric Equipment Depending on zone activity (ANSI et al., 2007)
land is used equally between the office area, supermarket and retail, after considering the land needed for the school. 2.2. Thermal characteristics and electrical loads
2.1.2.3. Supermarket and retail. The supermarket and the retail buildings are designed as single storey buildings of 1200 m2 floor area, each. There is no documentation on an acceptable size of a supermarket or retail area for a specific population, especially on a neighbourhood scale. In this study, a 20% of the built area is dedicated to commercial buildings (based on the TND principles). This
All buildings are designed to be energy efficient (wall and roof insulation of 7 m2 K/W and 10 m2 K/W, respectively; triple glaze, low-e argon fill windows, and airtight construction). The basic design of residential units conforms to passive solar design principles (Hachem et al., 2013). Building envelope characteristics are
Fig. 2. Commercial buildings designed in the neighbourhood.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
4
Table 2 Annual electricity consumption and electricity generation, per building type and per neighbourhood, for each scenario. Buildings
School Retail Office Supermarket Apartment building Attached house Detached house Neighbourhood
Total annual energy consumption (kWh)
Annual electricity generation (kWh)
Sc1
Sc2
Sc3
Sc4
Electricity
Electricity
Electricity
NG (DHW)
Electricity
NG (DHW and heating)
5.36E + 05 1.52E + 05 3.76E + 05 4.39E + 05 2.70E + 05 7.39E + 03 9.42E + 03 1.01E + 07
5.33E + 05 1.76E + 05 4.10E + 05 4.38E + 05 3.05E + 05 8.56E + 03 1.13E + 04 1.13E + 07
4.89E + 05 1.67E + 05 4.01E + 05 4.19E + 05 2.23E + 05 4.98E + 03 7.75E + 03 8.41E + 06
4.41E + 04 8.54E + 03 8.48E + 03 1.85E + 04 8.23E + 04 3.58E + 03 3.58E + 03 2.89E + 06
4.60E + 05 1.23E + 05 3.45E + 05 4.11E + 05 1.71E + 05 3.20E + 03 4.64E + 03 6.50E + 06
9.62E + 04 9.36E + 04 1.07E + 05 3.69E + 04 1.65E + 05 5.27E + 03 9.39E + 03 5.86E + 06
detailed in Table 1. Lighting and electrical loads in residential and commercial buildings are determined in terms of average load per m2 (ANSI et al., 2007). 2.3. Roof design The roof design of all residential buildings consists of a gable roof, with 45◦ tilt angle. A BIPV system is assumed to cover the complete south facing roof surface. The tilt angle of 45 is selected for being within the optimal range for the studied location (Calgary, latitude 52◦ N) corresponding to latitude ±10◦ (Hachem et al., 2012b). In buildings of large plan area, including multistorey and commercial buildings, the roof is designed as saw tooth, where PV is integrated on the south areas, at a tilt angle of 45◦ . The saw tooth design is adopted to reduce the overall height of the roof (and consequently of the building). The tilt angle of the north facing side of a roof unit is estimated to avoid shading on the next south PV integrated surface. 3. Parametric investigation The paper examines the impact of various mechanical systems on the overall neighbourhood energy performance and its associated carbon emissions. Four scenarios are investigated, incorporating some options of mechanical and domestic hot water systems. These systems are summarized in the following. The base case assumes a heat pump and chiller to supplement the heating and cooling for all buildings. For this base case two variations are studied and compared: Scenario 1, adopts heat pumps with a fixed COP of 4, aiming at simplifying the simulations, while an electric resistor is assumed for DHW; Scenario 2 calculates the performance of the same systems (heat pumps and chillers) with models that account for the variation of performance with outdoor air temperature and partial load. Details of the simulations are presented below. Scenarios 3 and 4 explore options of DHW and heating fuels. In Scenario 3, the same assumptions as in Scenario 2 are implemented, however natural gas is assumed for domestic hot water. Scenario 4 adopts natural gas for both domestic hot water and heating. All scenarios are compared to Scenario 2, which presents more realistic assessment, as compared to scenario 1, of energy consumption by heat pump and chillers for heating and cooling, of an all-electric neighbourhood. 3.1. Simulations Two energy simulation programs are employed in this study, EnergyPlus in conjunction with ScketchUp/openstudio plugin, and TRNSYS.
5.92E + 05 1.51E + 05 1.39E + 05 1.22E + 05 1.26E + 05 9.01E + 03 1.36E + 04 6.22E + 06
The neighbourhood is simulated using EnergyPlus (Energy Plus, 2012), to determine heating and cooling load, and energy consumption for DHW, lighting and equipment. SketchUp/OpenStudio (Legacy OpenStudio, 2014) is employed to generate geometric data of the building designs for EnergyPlus. EnergyPlus is employed to perform the neighbourhood simulations for its capacity to account for mutual shading, and microclimate effect caused by buildings’ adjacency (e.g. wind, shade, exterior surface temperature), on various buildings ‘loads. To simplify the overall modelling of the neighbourhood, each residential unit is modelled as a single conditioned zone. The simulations of commercial/civic buildings assume several thermal zones for each building, to accommodate various zone characteristics (e.g. occupation, activities, location, etc.). For instance, the office building requires 18 thermal zones, while the supermarket is divided into two zones. The Equivalent One-Diode Model (or“TRNSYS PV” model (Eckstein, 1990)) employed in EnergyPlus is selected to perform electricity generation simulations of the BIPV/T systems. The TRNSYS PV model employs a four-parameter empirical model to predict the electrical performance of PV modules (Duffie & Beckman, 2006). For this study, the PV array is selected from the EnergyPlus database to provide approximately 15% electrical efficiency. TRNSYS (University of Wisconsin, 2014) is used to perform the analysis of the mechanical systems for heating, cooling and domestic hot water systems. The hourly heating and cooling load of each building determined by EnergyPlus is used as input for the analysis performed in TRNSYS. Heating and cooling loads estimated in EnergyPlus take into account the design of the buildings (e.g. attached or detached houses) as well as mutual shading. The TRNSYS models for the air-source heating and cooling systems (heat pumps and chillers, respectively) account for the variations of system performance as a function of outdoor air conditions and load. The heat pump model is based on the performance map (i.e. heat pump capacity and efficiency under a variety of load and outdoor air and water temperature conditions) of a cold climate heat pump, which is the only heat pump type capable of handling the outdoor air temperatures of a Canadian winter (albeit with a high efficiency penalty, with a COP dropping from a nominal 3–4 to 1, for outdoor air temperatures below −15 ◦ C). The weather files of EnergyPlus are used for the simulations (EnergyPlus: Weather files (Energy Plus, in press)). The weather data file, which is based on the Canadian Weather for Energy Calculations (CWEC), provides hourly weather observations. Hourly weather data for Calgary is used to estimate the annual electricity generation of the BIPV systems installed, as well as the total energy demand, including heating, cooling and DHW. The hourly data is used to calculate the amount of primary energy required (and associated GHG emissions) to satisfy these demands throughout the year.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
5
Fig. 3. (a) Comparison of electrical energy consumption of each scenario to Sc2, (b) comparison between energy generation and electrical energy consumption for each scenario.
3.2. Simulations of the scenarios
calculate the GHG intensity of a natural gas based grid (0.47 kg CO2 eq/kWhfe ).
For Scenario 1, a simplified HVAC system (ideal load) is assumed. TRNSYS (University of Wisconsin, 2014) is used to perform an indepth analysis of the mechanical systems for heating, cooling and domestic hot water systems. In Scenarios 2, 3 and 4, the TRNSYS models for the air-source heating and cooling systems (heat pumps and chillers, respectively) account for the variations of system performance as a function of outdoor air conditions and load. The heat pump model is based on the performance map of a cold climate heat pump, which is the only heat pump type capable of handling the outdoor air temperatures of a Canadian winter (at a high efficiency penalty).
4. Results and discussion Total energy use (electricity and natural gas (NG)) is determined for each building type, and then for the neighbourhood as a whole, taking into account the effect of mutual shading among buildings. These results are compared with the overall potential of the neighbourhood to generate its own electricity using integrated PV systems on available roof surfaces. The energy performance is established for each of the four scenarios detailed above. In addition, carbon emissions and total primary energy use associated with each of these scenarios are estimated.
3.3. GHG emissions and primary energy use calculations
4.1. Energy generation and energy use
Primary energy, representing the energy consumed at the source, can indicate the environmental impact of the community in terms of resource depletion. On the other hand, estimation of GHG emissions illustrates the impact on climate change. Primary energy and GHG calculations are based on the annual net electricity balance (electricity use vs. generation) and natural gas use of the buildings. The primary energy and GHG conversion factors for the Alberta electricity grid (assumed in this study) and for natural gas are calculated based on the total electricity production by utilities in the province, total fossil fuel use for electricity generation by utilities, and energy and carbon content of the fossil fuels combusted (Statistics Canada, 2013a, 2013b; US EPA, 2004). Currently, the electricity generation system in Alberta is principally reliant on fossil fuels (coal and natural gas). The GHG intensity of average electricity generated in Alberta (in the year 2013) and natural gas are 0.71 and 0.19 kg CO2 eq/kWhfe , respectively. The ratios of primary to final energy of electricity and natural gas are 3.2 and 1.0 kWhpe /kWhfe , respectively. Performance data for the natural gas fired power plants in Canada (Statistics Canada, 2013a, 2013b; US EPA, 2004) is used to
Results of the simulations of each type of building, in terms of total electrical energy consumption, the natural gas (NG) consumption (Sc 3 and 4), and potential energy generation for each of the 4 scenarios are summarized in Table 2. Fig. 3 presents the comparison between the total annual electricity consumption of each of the scenarios and Scenario 2 (Fig. 3a). Fig. 3b presents for all the studied scenarios the comparison between their total annual electrical energy consumption and potential annual energy generation employing BIPV systems. The results indicate that houses and some other single-story buildings with large roofs, such as the school, can achieve energy positive status, for all scenarios. Multi-storey buildings generate only a fraction of their energy use. The use of a heat pump with fixed COP in Sc1 underestimate the energy use for heating, and therefore the overall electrical energy use of the neighbourhood in this scenario is reduced as compared to Sc2, which reflects a more realistic situation (by about 14%, Fig. 3a). The electricity consumption in Sc3 and Sc4 is significantly less than in Sc2, as expected, due to the significant effect of heating and domestic hot water. The comparison of the potential of electricity generation of each scenario to its energy use indicates that Sc2
Table 3 Annual total primary energy use, per building type and per neighbourhood, for each scenario. Total primary energy use (kWh)
School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc1
Sc2
Sc3
Sc4
−1.82E + 05 1.97E + 03 7.72E + 05 1.03E + 06 4.68E + 05 −5.25E + 03 −1.36E + 04 1.25E + 07
−1.94E + 05 8.07E + 04 8.81E + 05 1.03E + 06 5.82E + 05 −1.45E + 03 −7.34E + 03 1.65E + 07
−2.93E + 05 6.15E + 04 8.62E + 05 9.85E + 05 3.97E + 05 −9.50E + 03 −1.54E + 04 9.99E + 06
−3.34E + 05 2.43E + 03 7.76E + 05 9.79E + 05 3.11E + 05 −1.36E + 04 −1.97E + 04 6.78E + 06
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
6
Table 4 Annual total GHG emissions, per building type and per neighbourhood, for each scenario. Total GHG emissions (kg CO2 )
Monthly average energy use (kWh)
School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc1
Sc2
Sc3
Sc4
−4.01E + 04 4.34E + 02 1.70E + 05 2.27E + 05 1.03E + 05 −1.16E + 03 −2.98E + 03 2.75E + 06
−4.27E + 04 1.78E + 04 1.94E + 05 2.26E + 05 1.28E + 05 −3.18E + 02 −1.62E + 03 3.63E + 06
−6.57E + 04 1.33E + 04 1.90E + 05 2.16E + 05 8.50E + 04 −2.19E + 03 −3.49E + 03 2.12E + 06
−7.61E + 04 −2.09E + 03 1.68E + 05 2.14E + 05 6.37E + 04 −3.14E + 03 −4.59E + 03 1.33E + 06
2000 1800 1600 1400 1200 1000 800 600 400 200 0
Sc1 Sc2 Sc3 Sc4
Fig. 4. Monthly average electricity use of all scenarios.
Table 5 Annual total GHG emissions, per building type and per neighborhood, for each scenario. Total GHG emissions (kg × 103 CO2 ) Sc1 School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc2
−40.1 −42.7 0.434 17.8 170 194 227 226 103 128 −1.16 −0.32 −2.98 −1.62 2.75E + 06 3.63E + 06
Sc3 −65.7 13.3 190 216 85 −2.19 −3.49 2.12E + 06
Sc4 −76.1 −2.09 168 214 63.7 −3.14 −4.59 1.33E + 06
covers about 56% of its total annual energy use, while Sc4 around 95% (Fig. 3b). Fig. 4 presents the monthly average electrical energy consumption of each scenario. The graph implies that Sc2 during the winter months is higher than Sc1; while for the summer months the performance of the two scenarios is comparable. This is, as mentioned above, due mainly to the fact that the assumption of a fixed COP of 4 for the heat pump in Sc1 undervalues the energy use for heating. The high performance envelope and solar gains in the studied community contribute to reducing significantly the heating load during mild periods, which means that the mechanical heating systems are only required during very cold periods. Therefore, the assumption of a constant heat pump performance (COP) that equals the nominal performance is particularly inaccurate in high performance buildings, as these only require mechanical heating during periods of extreme cold (i.e. when the heat pump performance is the worst) (Table 3).
Fig. 5. Energy use and energy generation of the neighbourhood (a) in a week in December, (b) in a week in June
the net energy balance of the buildings (i.e. electricity production is accounted for as a negative energy use). Schools, attached houses and detached houses result in overall primary energy and GHG emissions savings (i.e. negative annual contributions) on an annual basis. This is due to net surplus of electricity production through PV vs. energy use. The remaining building types are net primary energy users and GHG emitters on an annual basis. The supermarket is the building type with the worst energy balance and environmental impact. The neighbourhood as a whole is a net primary energy user and GHG emitter. The surplus PV production in the school and houses partially offsets the negative energy balance of the most energy intense building types, but not to the point of reaching a net zero primary energy use balance on a community scale. Relative to Scenario 2, Scenario 1 underestimates the total neighbourhood primary energy use and GHG emissions by approximately 24%. Scenario 3 and Scenario 4 result in an approximately 40% and 60% reductions, respectively, in terms of both primary energy use and GHG emissions relatively to the base case (Scenario 2). The environmental benefits of Scenarios 3 and 4 relative to the base case can be explained by the high fossil fuel intensity of the Alberta electricity grid. These two scenarios partially shift electricity use to natural gas, which is a relatively cleaner source compared to the Alberta grid. 4.3. Peak use versus generation
4.2. Primary energy use and GHG emissions Tables 4 and 5 complement the final energy results above by summarizing the total primary energy use and the total GHG emissions, respectively, per building type and for the whole neighbourhood. Both primary energy and GHG calculations are based on
An important issue in the design of PV integrated neighbourhoods is the timing of electricity generation and its correspondence to the energy use. The graphs of Fig. 5 present plots of electrical energy use versus generation during the winter and summer solstice weeks. The plots show the mismatch between use and
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
generation in these weeks. The winter illustration shows that although in some days it is possible to cover the electricity use at noon, a large portion of the consumption in the morning and afternoon is not covered by the electricity generated. The plot depicting the summer week performance shows high peak generation at noon, that which exceeds significantly the energy need. Similar to winter performance, morning and evening consumption are not met by the energy generation, though to a lesser extent.
7
controlling peak electricity production timing and reducing utility peak demand. Future stages of this research aim at assessing the effect of modification of design parameters on mixed-use community performance. Additional studies will explore various control strategies of peak loads, variation of energy generation profiles, thermal storage, and variations in neighbourhood design including commercial area design and their size and density. References
5. Concluding remarks and follow-on investigations This paper presents a base case design of a mixed-use neighbourhood located in Calgary, AB, Canada. The neighbourhood comprises 1000+ residential units, and ca. 8000 m2 ground area of commercial, office and educational buildings. The design is based on various guidelines for sustainable mixed-use communities. Primary functions, such as dwellings, services, offices and institutional building, are defined. Different solutions are proposed for the supply of energy, according to four different scenarios, with reference to the kind of energy supplied (all-electrical or by natural gas), for the various energy uses (heating, cooling, domestic hot water, lighting, plug appliances). PV systems are assumed to cover all south facing roof areas, to generate electricity to neighbourhood. Analysis of the study takes into account both overall primary energy demand and greenhouse gas emissions. Energy simulations of different types of buildings indicate that detached and attached houses can achieve an energy positive status, under the given climatic conditions. Other types of buildings studied in the scenarios, such as apartment buildings, office and supermarket, are capable of generating only a small portion of their energy consumption. This is partly due to reduced surface area of roof for the implementation of PV technologies. In commercial buildings, this reduced electricity generation potential is coupled with increased energy demand. The comparison of various mechanical systems indicates that assuming a fixed COP for a heat pump underestimates the total electricity consumption for heating. This results in an underestimate by approximately 14% of the actual energy consumption as simulated by TRNSYS. Environmental performance is assessed in terms of total primary energy use and GHG emissions. Both indicators show the best results for schools and houses, which achieve a net positive impact on the environment on an annual basis. PV generation in the remaining building types (and in the neighbourhood as a whole) is not sufficient to totally offset the environmental impacts of energy use. The parametric analysis shows that a move towards natural gas systems for heating and DHW result in some environmental benefits for the studied location. This is mainly due to the very high fossil fuel content of the electricity grid in Alberta. This work is intended to serve as a model for the design and analysis of energy efficient mixed-use neighbourhoods and as a reference against which the effects of design modifications are assessed in future research. Due to the universal principles employed in the design of this community, the study can be easily replicated in other locations, under different climatic conditions. The broader impact of this research is to act as first stage to develop guidelines for the design of mixed-use high performance solar communities. Design guidelines are sorely lacking and systematic analysis of the energy and emissions performance of such neighbourhoods is required to move cities into sustainable future. Moreover, designing and analysing energy performance of a mixeduse community as an integrated system represents a prospect to share energy resources (e.g. between energy positive buildings and others), and to explore opportunities for seasonal storage,
ANSI/ASHRAE/IESNA. (2007). ANSI/ASHRAE/IESNA Standard 90.1-2007, Energy Standard for Buildings Except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia. Armstrong, M., Swintona, M. C., Ribberink, H., Beausoleil-Morrison, I., & Millette, J. (2009). Synthetically derived profiles for representing occupant-driven electric loads in Canadian housing. Journal of Building Performance Simulation. ASHRAE. (2007). Chapter 33. Solar energy use. In ASHRAE handbook HVAC applications. Atlanta, GA: ASHRAE. Barton, H., Grant, M., & Guise, R. (2010). Shaping neighbourhoods: For local health and global sustainability (2nd edition). Routledge. Benson et al. (2010). Building our schools, Building our future, A Report from the Expert Panel on Capital Standards. CMHC. (2011). The fused grid. http://www.cmhc.ca/en/inpr/su/sucopl/fugr/index. cfm. Accessed 12.01.14. Coupland, A. (1997). Reclaiming the city: Mixed-use development. London: E & FN Spon. Duffie, J. A., & Beckman, W. A. (2006). Solar engineering of thermal processes. Wiley. Eckstein, J. H. (1990). Detailed modeling of photovoltaic components, M.S. Thesis. Madison: Solar Energy Laboratory, University of Wisconsin. EnergyPlus. (2012). Lawrence Berkeley National Laboratory, Berkely, CA. Energy Plus, Weather Data http://apps1.eere.energy.gov/buildings/energyplus/ cfm/weather data3.cfm/region=4 north and central america wmo region 4/ country=3 canada/cname=CANADA Grant, J. (2007). Chapter 3. Encouraging mixed-use in practice. In G. J. Knaap, H. A. Haccou, & J. W. Frece (Eds.), Incentives, regulations and plans: The role of states and nation-states in smart growth planning (pp. 57–76). UK: Edwin Elgar Publishers. Hachem, C., Athienitis, A., & Fazio, P. (2012). Evaluation of energy supply and demand in solar neighbourhoods. Journal of Energy and Buildings, 49, 335–347. Hachem, C., Athienitis, A., Fazio, P. (2012). Design of roofs for increased solar potential of BIPV/T systems and their applications to housing units. ASHRAE Transactions RNS-00226-2011.R1. Hachem, C., Fazio, P., & Athienitis, A. (2013). Solar optimized residential neighbourhoods: Evaluation and design methodology. Journal of Solar Energy, 95, 42–64. Hoppenbrouwer, E., & Louw, E. (2005). Mixed-use development: Theory and practice in Amsterdam’s Eastern Docklands. European Planning Studies, 13(7), 967–983. Kemp, R., & Stephani, C. (2011). Cities going green: A handbook of best practices. McFarland & Co Inc Pub. Kyle, R., Baird, F. M., & Spodek, M. (2000). Property management Kaplan financial series Dearborn real estate. Legacy OpenStudio Plug-in for SketchUp. (2014). http://apps1.eere.energy.gov/ buildings/energyplus/openstudio.cfm Niemira, M. P. (2007). The concept and drivers of mixed-use development: Insights from a cross-organizational membership survey. Research Review, 4(1), 53–56. Rabianski, J., Gibler, K., Tidwell, O. A., & Clements, J. S. (2009). Mixed-use development: A call for research. Journal of Real Estate Literature, 17(2), 205–230. Rowley, A. (1996). Mixed-use development: Ambiguous concept, simplistic analysis and wishful thinking. Planning Practice & Research, 11(1), 85–98. Statistics Canada. CANSIM Table 127-0004: Fuel consumed for electric power generation, by electric utility thermal plants. (2013). http://www5.statcan.gc. ca/cansim/ a26?lang=eng&retrLang=eng&id=1270004&tabMode=dataTable&srchLan=1&p1=-1&p2=9 Statistics Canada. CANSIM Table 127-0006: Electricity generated from fuels, by electric utility thermal plants, annual. (2013) http://www5.statcan.gc.ca/ cansim/ a26?lang=eng&retrLang=eng&id=1270006&tabMode=dataTable&srchLan=1&p1=-1&p2=35 Traditional Neighborhood Development (TND) http://www. sustainablecitiesinstitute.org/topics/land-use-and-planning/traditionalneighborhood-development-%28tnd%29 Accessed 07.09.14. Torcellini, P. A., & Crawley, D. B. (2006). Understanding zero-energy buildings. ASHRAE Journal, 48(9), 62–64. University of Wisconsin. (2014). TRNSYS 17 http://sel.me.wisc.edu/trnsys/index. html US EPA. Unit Conversions, Emissions Factors, and Other Reference Data (2004). http://www.epa.gov/appdstar/pdf/brochure.pdf
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
ARTICLE IN PRESS
SCS-316; No. of Pages 7
Sustainable Cities and Society xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Sustainable Cities and Society journal homepage: www.elsevier.com/locate/scs
Energy performance of a solar mixed-use community C. Hachem-Vermette a,∗ , E. Cubi b , J. Bergerson c a
Faculty of Environmental Design, University of Calgary, 2500 University Drive NW, Calgary AB T2N 1N4, Canada Schulich School of Engineering, University of Calgary, Canada c Department of Chemical and Petroleum Engineering. University of Calgary, Canada b
a r t i c l e
i n f o
Article history: Received 7 May 2015 Received in revised form 4 July 2015 Accepted 12 August 2015 Available online xxx Keywords: Mixed-use neighbourhood Net zero energy Carbon emissions Energy consumption Energy generation potential
a b s t r a c t This paper explores a solar mixed-use community that combines residential and commercial buildings. The pilot location of this study is Calgary, Canada (52◦ N), representing northern, cold climate. Energy performance of the neighbourhood is estimated in terms of energy consumption and generation potential by means of building integrated PV systems. In addition, the analysis takes in to account the overall primary energy demand and greenhouse gas emissions. EnergyPlus is employed to simulate the overall energy consumption of the neighbourhood. Investigation of different options of mechanical systems is carried out using TRNSYS. Designing and analysing energy performance of a mixed-use community as an integrated system presents an opportunity to explore sharing of energy resources and interaction with the utility grid. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Net zero energy buildings have the potential to alleviate the negative environmental impact of the built environment including the reduction of greenhouse gas (GHG) emissions. The principle of net zero energy has been extensively applied to buildings. These are buildings that generate annually as much energy from renewable energy sources as they consume (Torcellini & Crawley, 2006). The design of net zero energy solar buildings involves a twofold approach of enhancing energy efficiency while optimizing active solar energy production using photovoltaic technologies and thermal collectors. Reduction of energy consumption can be achieved through several measures, including enhanced HVAC efficiency measures. In addition, use of energy for heating can be significantly reduced by means of solar heat gains. A well-designed passivesolar building may provide 45–100% of daily heating requirements (ASHRAE, 2007). Applying the net zero energy concept at urban scale can provide opportunities for seasonal storage, implementation of smart grids for power sharing between housing units, controlling peak electricity production timing and reducing utility peak demand. Additional advantages of net zero energy neighbourhoods include enabling design flexibility and increasing available surface areas for the integration of photovoltaic systems.
∗ Corresponding author. E-mail address: [email protected] (C. Hachem-Vermette).
A small-scale, low-density residential neighbourhood of singlefamily houses can reach net-zero energy status assuming a careful design of building shapes and orientation (Hachem, Athienitis, & Fazio, 2012a). A mixed-use neighbourhood, which combines residential and commercial buildings (retail, office, residential, hotel, recreation or other functions (Niemira, 2007)) is significantly less amenable to achieving such status. Mixed-use communities have several economic and environmental advantages that lead to reduced levels of greenhouse gas emissions (Coupland, 1997; Grant, 2007; Rabianski, Gibler, Tidwell, & Clements, 2009). Such neighbourhoods are considered as part of a strategy to achieve sustainable developments (Grant, 2007; Hoppenbrouwer & Louw, 2005). Despite this fact, quantification of the performance of mixed-use neighbourhoods is not currently available. Moreover, comprehensive design guidelines for achieving high-energy performance mixed-use neighbourhoods are sorely lacking. A systematic design and analysis of energy and GHG emissions of these neighbourhood designs has yet to be completed. This paper presents a concise summary of the design of an energy efficient solar mixed-use community, and its performance estimated in terms of energy consumption and generation potential assuming building integrated PV systems. In addition the paper examines the impact of various mechanical systems on the overall neighbourhood energy performance and on its carbon emissions. The effect of neighbourhood is taken into account both in the simulations and the analysis of the results. The study forms part of a large scope research programme aimed at assessing the effects of multiple design parameters on energy performance of such
http://dx.doi.org/10.1016/j.scs.2015.08.002 2210-6707/© 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
2
communities, and the development of guidelines for their design. This base case design is intended as a reference against which the effects of modifications to selected design parameters are to be assessed. This complex research programme includes different categories of parameters that will be investigated in order to develop guidelines for the design of archetypes of high performance multifunctional communities. These categories include: overall design; energy options and additional categories such as environmental impact, sustainability and “resilience” parameters. The design category will encompass parameters such as pattern of the communities (circular, linear, hexagonal, etc.), density (on per capita basis and number of buildings), and design of the centre and its effect on transport (e.g. number of vehicle trips per day). Energy related parameters would include shift of load and generation, district energy, storage, cogeneration, and energy use for transport under different design parameters.
2. Design of the base case The neighbourhood design developed and analysed in this paper represents the first stage towards proposing a design procedure for high performance solar mixed-use communities. In view of the absence of general guidelines for the design of multifunctional high-energy performance, the design presented in this paper is based on various assumptions of design guidelines for shaping a sustainable neighbourhood. The main criteria for the selected guidelines relate to reducing dependency on cars (i.e. walkability), determining the minimal required density for a viable community, and maintaining a balance between the built area and green public land and street area. These assumptions are briefly described below. The base case development illustrating the design procedure reflects a Northern cold climate and is assumed to be located in Calgary, Canada (52◦ N). The general design of the community layout relies on traditional neighbourhood developments guidelines (TND) (TND, 2014), combined with the fused grid street system of the Canadian Mortgage and Housing Corporation (CMHC) (CMHC, 2011). A TND, known as a village-style development, includes a variety of housing types, a mixed land use, an active centre, a walkable design and often a public transit option within a compact neighbourhood (TND, 2014). The TND guidelines are used to define the approximate relative land areas for each of the functions, as summarized below. CMHC fused grid system is designed to allow mixed-use, densification, and efficient public transport (CMHC, 2011), and therefore can constitute a basis for the design of a new sustainable neighbourhood. Employing the guidelines aforementioned, a land area of 16 ha is determined with a geometry based on the assumption of a ½ km maximum walking distance from the centre of the development (Kemp & Stephani, 2011). The land partition employs a mixture of fused grid and TND designs: the built area constitutes 64% of the land, streets use about 24% of the land, and the remaining 12% represents the green public area. Residential areas form about 80% of the total built area (including surrounding land), with the remainder (approximately 20%) as a mixture of viable commercial space and civic functions. The residential buildings include single detached houses, attached houses, and mid-rise apartment buildings (3–5 stories). The main commercial amenities included in the neighbourhood are: office building, retail area and grocery store, in addition to a primary school. The commercial and civic functions are concentrated in the core of the development (Rowley, 1996). The density is based on the assumption of a minimal number of 4000 residents, to achieve a viable mixed-use neighbourhood (Barton et al., 2010). The total number of residents is employed to
Fig. 1. Neighbourhood design.
determine the number of residential units, assuming an average of 4 persons per unit. A total of 1003 residential units are designed, including 180 houses and 27 apartment buildings with varying number of apartments. A variable residential density is adopted in the design of this neighbourhood. The dense area (125 units/ha) is designed around the centre of the development, while the low-density areas (25–50 units/ha) are located towards the outskirts. 2.1. Buildings design 2.1.1. Residential Residential units are designed as two-story detached and attached houses (180 m2 and 120 m2 respectively) and apartments in low-rise buildings (3–5 floors). The houses are designed to optimize passive solar design (Hachem, Fazio, & Athienitis, 2013) with south-facing windows occupying about 35% of the south fac¸ade. Other thermal characteristics are presented in Table 1. The apartments have a floor area of 110 m2 (average apartment size in Canada (Armstrong, Swintona, Ribberink, BeausoleilMorrison, & Millette, 2009)) (Fig. 1). 2.1.2. Commercial buildings Below is a summary of the main design considerations for each of the commercial buildings employed in the design of this neighbourhood. Fig. 2 illustrates a schematic of each of these buildings. 2.1.2.1. Office building. Guidelines that assist in determining office areas in a neighbourhood with a given population are lacking. This is due to the large number of factors that should be considered in planning such areas in an urban development (e.g. type of business, area required for a business, local employees, etc. (Kyle, Baird, & Spodek, 2000)). For this hypothetic neighbourhood a mid-size 3-story office building of 3600 m2 (i.e. 1200 m2 per floor) is assumed. The building envelope is designed as specified in Table 1. Assumptions for electrical loads are specified based on ASHRAE recommendations (ANSI et al., 2007). 2.1.2.2. Primary school. The single story 4500 m2 school building is designed to specifications for a primary school for a population of 4000 persons. This is based on an estimated number of pupils
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
3
Table 1 Main characteristics and electric loads. Residential units Thermal resistance values:
Thermal mass
Window type
Area of south glazing
Houses Apartment buildings
Shading Strategy Shading control Occupants Set point temperatures Infiltration rate Ventilation rate Lighting (houses and front apartments) Equipment
Exterior wall: 7 RSI Roof: 10 RSI Slab on grade (for ground floor): 1.2 RSI Slab perimeter: 7 RSI 20 cm concrete slab on grade (ground floor) 15 cm concrete slabs (in all apartments except ground floor) Triple glazed, low-e argon filled (SHGC = 0.57), 1.08 RSI 35% of south fac¸ades 30% of south fac¸ades Interior blinds Blinds shut at indoor air temperature of 22 ◦ C 2 adults and 2 children, occupied from 17:00 to 8:00 Heating set point 21 ◦ C, cooling set point 25 ◦ C 0.8ACH @50 Pa 0.35ACH 3.8 W/m2 (ASHRAE 90.1) (ANSI et al., 2007) 5.38 W/m2 (ASHRAE 90.1) (ANSI et al., 2007)
Commercial buildings Thermal resistance values Window type Electrical Loads School Office Retail Supermarket
Similar to residential units Similar to residential units Lights Depending on zone activity (ANSI et al., 2007)
(Barton et al., 2010) and an average area of 11 m2 per pupil (Benson et al., 2010).
Electric Equipment Depending on zone activity (ANSI et al., 2007)
land is used equally between the office area, supermarket and retail, after considering the land needed for the school. 2.2. Thermal characteristics and electrical loads
2.1.2.3. Supermarket and retail. The supermarket and the retail buildings are designed as single storey buildings of 1200 m2 floor area, each. There is no documentation on an acceptable size of a supermarket or retail area for a specific population, especially on a neighbourhood scale. In this study, a 20% of the built area is dedicated to commercial buildings (based on the TND principles). This
All buildings are designed to be energy efficient (wall and roof insulation of 7 m2 K/W and 10 m2 K/W, respectively; triple glaze, low-e argon fill windows, and airtight construction). The basic design of residential units conforms to passive solar design principles (Hachem et al., 2013). Building envelope characteristics are
Fig. 2. Commercial buildings designed in the neighbourhood.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
4
Table 2 Annual electricity consumption and electricity generation, per building type and per neighbourhood, for each scenario. Buildings
School Retail Office Supermarket Apartment building Attached house Detached house Neighbourhood
Total annual energy consumption (kWh)
Annual electricity generation (kWh)
Sc1
Sc2
Sc3
Sc4
Electricity
Electricity
Electricity
NG (DHW)
Electricity
NG (DHW and heating)
5.36E + 05 1.52E + 05 3.76E + 05 4.39E + 05 2.70E + 05 7.39E + 03 9.42E + 03 1.01E + 07
5.33E + 05 1.76E + 05 4.10E + 05 4.38E + 05 3.05E + 05 8.56E + 03 1.13E + 04 1.13E + 07
4.89E + 05 1.67E + 05 4.01E + 05 4.19E + 05 2.23E + 05 4.98E + 03 7.75E + 03 8.41E + 06
4.41E + 04 8.54E + 03 8.48E + 03 1.85E + 04 8.23E + 04 3.58E + 03 3.58E + 03 2.89E + 06
4.60E + 05 1.23E + 05 3.45E + 05 4.11E + 05 1.71E + 05 3.20E + 03 4.64E + 03 6.50E + 06
9.62E + 04 9.36E + 04 1.07E + 05 3.69E + 04 1.65E + 05 5.27E + 03 9.39E + 03 5.86E + 06
detailed in Table 1. Lighting and electrical loads in residential and commercial buildings are determined in terms of average load per m2 (ANSI et al., 2007). 2.3. Roof design The roof design of all residential buildings consists of a gable roof, with 45◦ tilt angle. A BIPV system is assumed to cover the complete south facing roof surface. The tilt angle of 45 is selected for being within the optimal range for the studied location (Calgary, latitude 52◦ N) corresponding to latitude ±10◦ (Hachem et al., 2012b). In buildings of large plan area, including multistorey and commercial buildings, the roof is designed as saw tooth, where PV is integrated on the south areas, at a tilt angle of 45◦ . The saw tooth design is adopted to reduce the overall height of the roof (and consequently of the building). The tilt angle of the north facing side of a roof unit is estimated to avoid shading on the next south PV integrated surface. 3. Parametric investigation The paper examines the impact of various mechanical systems on the overall neighbourhood energy performance and its associated carbon emissions. Four scenarios are investigated, incorporating some options of mechanical and domestic hot water systems. These systems are summarized in the following. The base case assumes a heat pump and chiller to supplement the heating and cooling for all buildings. For this base case two variations are studied and compared: Scenario 1, adopts heat pumps with a fixed COP of 4, aiming at simplifying the simulations, while an electric resistor is assumed for DHW; Scenario 2 calculates the performance of the same systems (heat pumps and chillers) with models that account for the variation of performance with outdoor air temperature and partial load. Details of the simulations are presented below. Scenarios 3 and 4 explore options of DHW and heating fuels. In Scenario 3, the same assumptions as in Scenario 2 are implemented, however natural gas is assumed for domestic hot water. Scenario 4 adopts natural gas for both domestic hot water and heating. All scenarios are compared to Scenario 2, which presents more realistic assessment, as compared to scenario 1, of energy consumption by heat pump and chillers for heating and cooling, of an all-electric neighbourhood. 3.1. Simulations Two energy simulation programs are employed in this study, EnergyPlus in conjunction with ScketchUp/openstudio plugin, and TRNSYS.
5.92E + 05 1.51E + 05 1.39E + 05 1.22E + 05 1.26E + 05 9.01E + 03 1.36E + 04 6.22E + 06
The neighbourhood is simulated using EnergyPlus (Energy Plus, 2012), to determine heating and cooling load, and energy consumption for DHW, lighting and equipment. SketchUp/OpenStudio (Legacy OpenStudio, 2014) is employed to generate geometric data of the building designs for EnergyPlus. EnergyPlus is employed to perform the neighbourhood simulations for its capacity to account for mutual shading, and microclimate effect caused by buildings’ adjacency (e.g. wind, shade, exterior surface temperature), on various buildings ‘loads. To simplify the overall modelling of the neighbourhood, each residential unit is modelled as a single conditioned zone. The simulations of commercial/civic buildings assume several thermal zones for each building, to accommodate various zone characteristics (e.g. occupation, activities, location, etc.). For instance, the office building requires 18 thermal zones, while the supermarket is divided into two zones. The Equivalent One-Diode Model (or“TRNSYS PV” model (Eckstein, 1990)) employed in EnergyPlus is selected to perform electricity generation simulations of the BIPV/T systems. The TRNSYS PV model employs a four-parameter empirical model to predict the electrical performance of PV modules (Duffie & Beckman, 2006). For this study, the PV array is selected from the EnergyPlus database to provide approximately 15% electrical efficiency. TRNSYS (University of Wisconsin, 2014) is used to perform the analysis of the mechanical systems for heating, cooling and domestic hot water systems. The hourly heating and cooling load of each building determined by EnergyPlus is used as input for the analysis performed in TRNSYS. Heating and cooling loads estimated in EnergyPlus take into account the design of the buildings (e.g. attached or detached houses) as well as mutual shading. The TRNSYS models for the air-source heating and cooling systems (heat pumps and chillers, respectively) account for the variations of system performance as a function of outdoor air conditions and load. The heat pump model is based on the performance map (i.e. heat pump capacity and efficiency under a variety of load and outdoor air and water temperature conditions) of a cold climate heat pump, which is the only heat pump type capable of handling the outdoor air temperatures of a Canadian winter (albeit with a high efficiency penalty, with a COP dropping from a nominal 3–4 to 1, for outdoor air temperatures below −15 ◦ C). The weather files of EnergyPlus are used for the simulations (EnergyPlus: Weather files (Energy Plus, in press)). The weather data file, which is based on the Canadian Weather for Energy Calculations (CWEC), provides hourly weather observations. Hourly weather data for Calgary is used to estimate the annual electricity generation of the BIPV systems installed, as well as the total energy demand, including heating, cooling and DHW. The hourly data is used to calculate the amount of primary energy required (and associated GHG emissions) to satisfy these demands throughout the year.
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
5
Fig. 3. (a) Comparison of electrical energy consumption of each scenario to Sc2, (b) comparison between energy generation and electrical energy consumption for each scenario.
3.2. Simulations of the scenarios
calculate the GHG intensity of a natural gas based grid (0.47 kg CO2 eq/kWhfe ).
For Scenario 1, a simplified HVAC system (ideal load) is assumed. TRNSYS (University of Wisconsin, 2014) is used to perform an indepth analysis of the mechanical systems for heating, cooling and domestic hot water systems. In Scenarios 2, 3 and 4, the TRNSYS models for the air-source heating and cooling systems (heat pumps and chillers, respectively) account for the variations of system performance as a function of outdoor air conditions and load. The heat pump model is based on the performance map of a cold climate heat pump, which is the only heat pump type capable of handling the outdoor air temperatures of a Canadian winter (at a high efficiency penalty).
4. Results and discussion Total energy use (electricity and natural gas (NG)) is determined for each building type, and then for the neighbourhood as a whole, taking into account the effect of mutual shading among buildings. These results are compared with the overall potential of the neighbourhood to generate its own electricity using integrated PV systems on available roof surfaces. The energy performance is established for each of the four scenarios detailed above. In addition, carbon emissions and total primary energy use associated with each of these scenarios are estimated.
3.3. GHG emissions and primary energy use calculations
4.1. Energy generation and energy use
Primary energy, representing the energy consumed at the source, can indicate the environmental impact of the community in terms of resource depletion. On the other hand, estimation of GHG emissions illustrates the impact on climate change. Primary energy and GHG calculations are based on the annual net electricity balance (electricity use vs. generation) and natural gas use of the buildings. The primary energy and GHG conversion factors for the Alberta electricity grid (assumed in this study) and for natural gas are calculated based on the total electricity production by utilities in the province, total fossil fuel use for electricity generation by utilities, and energy and carbon content of the fossil fuels combusted (Statistics Canada, 2013a, 2013b; US EPA, 2004). Currently, the electricity generation system in Alberta is principally reliant on fossil fuels (coal and natural gas). The GHG intensity of average electricity generated in Alberta (in the year 2013) and natural gas are 0.71 and 0.19 kg CO2 eq/kWhfe , respectively. The ratios of primary to final energy of electricity and natural gas are 3.2 and 1.0 kWhpe /kWhfe , respectively. Performance data for the natural gas fired power plants in Canada (Statistics Canada, 2013a, 2013b; US EPA, 2004) is used to
Results of the simulations of each type of building, in terms of total electrical energy consumption, the natural gas (NG) consumption (Sc 3 and 4), and potential energy generation for each of the 4 scenarios are summarized in Table 2. Fig. 3 presents the comparison between the total annual electricity consumption of each of the scenarios and Scenario 2 (Fig. 3a). Fig. 3b presents for all the studied scenarios the comparison between their total annual electrical energy consumption and potential annual energy generation employing BIPV systems. The results indicate that houses and some other single-story buildings with large roofs, such as the school, can achieve energy positive status, for all scenarios. Multi-storey buildings generate only a fraction of their energy use. The use of a heat pump with fixed COP in Sc1 underestimate the energy use for heating, and therefore the overall electrical energy use of the neighbourhood in this scenario is reduced as compared to Sc2, which reflects a more realistic situation (by about 14%, Fig. 3a). The electricity consumption in Sc3 and Sc4 is significantly less than in Sc2, as expected, due to the significant effect of heating and domestic hot water. The comparison of the potential of electricity generation of each scenario to its energy use indicates that Sc2
Table 3 Annual total primary energy use, per building type and per neighbourhood, for each scenario. Total primary energy use (kWh)
School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc1
Sc2
Sc3
Sc4
−1.82E + 05 1.97E + 03 7.72E + 05 1.03E + 06 4.68E + 05 −5.25E + 03 −1.36E + 04 1.25E + 07
−1.94E + 05 8.07E + 04 8.81E + 05 1.03E + 06 5.82E + 05 −1.45E + 03 −7.34E + 03 1.65E + 07
−2.93E + 05 6.15E + 04 8.62E + 05 9.85E + 05 3.97E + 05 −9.50E + 03 −1.54E + 04 9.99E + 06
−3.34E + 05 2.43E + 03 7.76E + 05 9.79E + 05 3.11E + 05 −1.36E + 04 −1.97E + 04 6.78E + 06
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model
ARTICLE IN PRESS
SCS-316; No. of Pages 7
C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
6
Table 4 Annual total GHG emissions, per building type and per neighbourhood, for each scenario. Total GHG emissions (kg CO2 )
Monthly average energy use (kWh)
School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc1
Sc2
Sc3
Sc4
−4.01E + 04 4.34E + 02 1.70E + 05 2.27E + 05 1.03E + 05 −1.16E + 03 −2.98E + 03 2.75E + 06
−4.27E + 04 1.78E + 04 1.94E + 05 2.26E + 05 1.28E + 05 −3.18E + 02 −1.62E + 03 3.63E + 06
−6.57E + 04 1.33E + 04 1.90E + 05 2.16E + 05 8.50E + 04 −2.19E + 03 −3.49E + 03 2.12E + 06
−7.61E + 04 −2.09E + 03 1.68E + 05 2.14E + 05 6.37E + 04 −3.14E + 03 −4.59E + 03 1.33E + 06
2000 1800 1600 1400 1200 1000 800 600 400 200 0
Sc1 Sc2 Sc3 Sc4
Fig. 4. Monthly average electricity use of all scenarios.
Table 5 Annual total GHG emissions, per building type and per neighborhood, for each scenario. Total GHG emissions (kg × 103 CO2 ) Sc1 School Retail Office Supermarket Apartment Attached Detached Neighbourhood
Sc2
−40.1 −42.7 0.434 17.8 170 194 227 226 103 128 −1.16 −0.32 −2.98 −1.62 2.75E + 06 3.63E + 06
Sc3 −65.7 13.3 190 216 85 −2.19 −3.49 2.12E + 06
Sc4 −76.1 −2.09 168 214 63.7 −3.14 −4.59 1.33E + 06
covers about 56% of its total annual energy use, while Sc4 around 95% (Fig. 3b). Fig. 4 presents the monthly average electrical energy consumption of each scenario. The graph implies that Sc2 during the winter months is higher than Sc1; while for the summer months the performance of the two scenarios is comparable. This is, as mentioned above, due mainly to the fact that the assumption of a fixed COP of 4 for the heat pump in Sc1 undervalues the energy use for heating. The high performance envelope and solar gains in the studied community contribute to reducing significantly the heating load during mild periods, which means that the mechanical heating systems are only required during very cold periods. Therefore, the assumption of a constant heat pump performance (COP) that equals the nominal performance is particularly inaccurate in high performance buildings, as these only require mechanical heating during periods of extreme cold (i.e. when the heat pump performance is the worst) (Table 3).
Fig. 5. Energy use and energy generation of the neighbourhood (a) in a week in December, (b) in a week in June
the net energy balance of the buildings (i.e. electricity production is accounted for as a negative energy use). Schools, attached houses and detached houses result in overall primary energy and GHG emissions savings (i.e. negative annual contributions) on an annual basis. This is due to net surplus of electricity production through PV vs. energy use. The remaining building types are net primary energy users and GHG emitters on an annual basis. The supermarket is the building type with the worst energy balance and environmental impact. The neighbourhood as a whole is a net primary energy user and GHG emitter. The surplus PV production in the school and houses partially offsets the negative energy balance of the most energy intense building types, but not to the point of reaching a net zero primary energy use balance on a community scale. Relative to Scenario 2, Scenario 1 underestimates the total neighbourhood primary energy use and GHG emissions by approximately 24%. Scenario 3 and Scenario 4 result in an approximately 40% and 60% reductions, respectively, in terms of both primary energy use and GHG emissions relatively to the base case (Scenario 2). The environmental benefits of Scenarios 3 and 4 relative to the base case can be explained by the high fossil fuel intensity of the Alberta electricity grid. These two scenarios partially shift electricity use to natural gas, which is a relatively cleaner source compared to the Alberta grid. 4.3. Peak use versus generation
4.2. Primary energy use and GHG emissions Tables 4 and 5 complement the final energy results above by summarizing the total primary energy use and the total GHG emissions, respectively, per building type and for the whole neighbourhood. Both primary energy and GHG calculations are based on
An important issue in the design of PV integrated neighbourhoods is the timing of electricity generation and its correspondence to the energy use. The graphs of Fig. 5 present plots of electrical energy use versus generation during the winter and summer solstice weeks. The plots show the mismatch between use and
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002
G Model SCS-316; No. of Pages 7
ARTICLE IN PRESS C. Hachem-Vermette et al. / Sustainable Cities and Society xxx (2015) xxx–xxx
generation in these weeks. The winter illustration shows that although in some days it is possible to cover the electricity use at noon, a large portion of the consumption in the morning and afternoon is not covered by the electricity generated. The plot depicting the summer week performance shows high peak generation at noon, that which exceeds significantly the energy need. Similar to winter performance, morning and evening consumption are not met by the energy generation, though to a lesser extent.
7
controlling peak electricity production timing and reducing utility peak demand. Future stages of this research aim at assessing the effect of modification of design parameters on mixed-use community performance. Additional studies will explore various control strategies of peak loads, variation of energy generation profiles, thermal storage, and variations in neighbourhood design including commercial area design and their size and density. References
5. Concluding remarks and follow-on investigations This paper presents a base case design of a mixed-use neighbourhood located in Calgary, AB, Canada. The neighbourhood comprises 1000+ residential units, and ca. 8000 m2 ground area of commercial, office and educational buildings. The design is based on various guidelines for sustainable mixed-use communities. Primary functions, such as dwellings, services, offices and institutional building, are defined. Different solutions are proposed for the supply of energy, according to four different scenarios, with reference to the kind of energy supplied (all-electrical or by natural gas), for the various energy uses (heating, cooling, domestic hot water, lighting, plug appliances). PV systems are assumed to cover all south facing roof areas, to generate electricity to neighbourhood. Analysis of the study takes into account both overall primary energy demand and greenhouse gas emissions. Energy simulations of different types of buildings indicate that detached and attached houses can achieve an energy positive status, under the given climatic conditions. Other types of buildings studied in the scenarios, such as apartment buildings, office and supermarket, are capable of generating only a small portion of their energy consumption. This is partly due to reduced surface area of roof for the implementation of PV technologies. In commercial buildings, this reduced electricity generation potential is coupled with increased energy demand. The comparison of various mechanical systems indicates that assuming a fixed COP for a heat pump underestimates the total electricity consumption for heating. This results in an underestimate by approximately 14% of the actual energy consumption as simulated by TRNSYS. Environmental performance is assessed in terms of total primary energy use and GHG emissions. Both indicators show the best results for schools and houses, which achieve a net positive impact on the environment on an annual basis. PV generation in the remaining building types (and in the neighbourhood as a whole) is not sufficient to totally offset the environmental impacts of energy use. The parametric analysis shows that a move towards natural gas systems for heating and DHW result in some environmental benefits for the studied location. This is mainly due to the very high fossil fuel content of the electricity grid in Alberta. This work is intended to serve as a model for the design and analysis of energy efficient mixed-use neighbourhoods and as a reference against which the effects of design modifications are assessed in future research. Due to the universal principles employed in the design of this community, the study can be easily replicated in other locations, under different climatic conditions. The broader impact of this research is to act as first stage to develop guidelines for the design of mixed-use high performance solar communities. Design guidelines are sorely lacking and systematic analysis of the energy and emissions performance of such neighbourhoods is required to move cities into sustainable future. Moreover, designing and analysing energy performance of a mixeduse community as an integrated system represents a prospect to share energy resources (e.g. between energy positive buildings and others), and to explore opportunities for seasonal storage,
ANSI/ASHRAE/IESNA. (2007). ANSI/ASHRAE/IESNA Standard 90.1-2007, Energy Standard for Buildings Except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia. Armstrong, M., Swintona, M. C., Ribberink, H., Beausoleil-Morrison, I., & Millette, J. (2009). Synthetically derived profiles for representing occupant-driven electric loads in Canadian housing. Journal of Building Performance Simulation. ASHRAE. (2007). Chapter 33. Solar energy use. In ASHRAE handbook HVAC applications. Atlanta, GA: ASHRAE. Barton, H., Grant, M., & Guise, R. (2010). Shaping neighbourhoods: For local health and global sustainability (2nd edition). Routledge. Benson et al. (2010). Building our schools, Building our future, A Report from the Expert Panel on Capital Standards. CMHC. (2011). The fused grid. http://www.cmhc.ca/en/inpr/su/sucopl/fugr/index. cfm. Accessed 12.01.14. Coupland, A. (1997). Reclaiming the city: Mixed-use development. London: E & FN Spon. Duffie, J. A., & Beckman, W. A. (2006). Solar engineering of thermal processes. Wiley. Eckstein, J. H. (1990). Detailed modeling of photovoltaic components, M.S. Thesis. Madison: Solar Energy Laboratory, University of Wisconsin. EnergyPlus. (2012). Lawrence Berkeley National Laboratory, Berkely, CA. Energy Plus, Weather Data http://apps1.eere.energy.gov/buildings/energyplus/ cfm/weather data3.cfm/region=4 north and central america wmo region 4/ country=3 canada/cname=CANADA Grant, J. (2007). Chapter 3. Encouraging mixed-use in practice. In G. J. Knaap, H. A. Haccou, & J. W. Frece (Eds.), Incentives, regulations and plans: The role of states and nation-states in smart growth planning (pp. 57–76). UK: Edwin Elgar Publishers. Hachem, C., Athienitis, A., & Fazio, P. (2012). Evaluation of energy supply and demand in solar neighbourhoods. Journal of Energy and Buildings, 49, 335–347. Hachem, C., Athienitis, A., Fazio, P. (2012). Design of roofs for increased solar potential of BIPV/T systems and their applications to housing units. ASHRAE Transactions RNS-00226-2011.R1. Hachem, C., Fazio, P., & Athienitis, A. (2013). Solar optimized residential neighbourhoods: Evaluation and design methodology. Journal of Solar Energy, 95, 42–64. Hoppenbrouwer, E., & Louw, E. (2005). Mixed-use development: Theory and practice in Amsterdam’s Eastern Docklands. European Planning Studies, 13(7), 967–983. Kemp, R., & Stephani, C. (2011). Cities going green: A handbook of best practices. McFarland & Co Inc Pub. Kyle, R., Baird, F. M., & Spodek, M. (2000). Property management Kaplan financial series Dearborn real estate. Legacy OpenStudio Plug-in for SketchUp. (2014). http://apps1.eere.energy.gov/ buildings/energyplus/openstudio.cfm Niemira, M. P. (2007). The concept and drivers of mixed-use development: Insights from a cross-organizational membership survey. Research Review, 4(1), 53–56. Rabianski, J., Gibler, K., Tidwell, O. A., & Clements, J. S. (2009). Mixed-use development: A call for research. Journal of Real Estate Literature, 17(2), 205–230. Rowley, A. (1996). Mixed-use development: Ambiguous concept, simplistic analysis and wishful thinking. Planning Practice & Research, 11(1), 85–98. Statistics Canada. CANSIM Table 127-0004: Fuel consumed for electric power generation, by electric utility thermal plants. (2013). http://www5.statcan.gc. ca/cansim/ a26?lang=eng&retrLang=eng&id=1270004&tabMode=dataTable&srchLan=1&p1=-1&p2=9 Statistics Canada. CANSIM Table 127-0006: Electricity generated from fuels, by electric utility thermal plants, annual. (2013) http://www5.statcan.gc.ca/ cansim/ a26?lang=eng&retrLang=eng&id=1270006&tabMode=dataTable&srchLan=1&p1=-1&p2=35 Traditional Neighborhood Development (TND) http://www. sustainablecitiesinstitute.org/topics/land-use-and-planning/traditionalneighborhood-development-%28tnd%29 Accessed 07.09.14. Torcellini, P. A., & Crawley, D. B. (2006). Understanding zero-energy buildings. ASHRAE Journal, 48(9), 62–64. University of Wisconsin. (2014). TRNSYS 17 http://sel.me.wisc.edu/trnsys/index. html US EPA. Unit Conversions, Emissions Factors, and Other Reference Data (2004). http://www.epa.gov/appdstar/pdf/brochure.pdf
Please cite this article in press as: Hachem-Vermette, C., et al. Energy performance of a solar mixed-use community. Sustainable Cities and Society (2015), http://dx.doi.org/10.1016/j.scs.2015.08.002