Effectiveness and viability of residential building energy retrofits in Dubai

Journal of Building Engineering 13 (2017) 116–126

Contents lists available at ScienceDirect

Journal of Building Engineering journal homepage: www.elsevier.com/locate/jobe

Effectiveness and viability of residential building energy retrofits in Dubai a,⁎

Kambiz Rakhshan , Wilhelm A. Friess a b

MARK

b

Rochester Institute of Technology Dubai, PO Box 341055, Dubai, United Arab Emirates University of Maine, Mechanical Engineering Department, 5711 Boardman Hall, Orono, ME 04469, USA

A R T I C L E I N F O

A B S T R A C T

Keywords: Energy efficiency Retrofit Insulation CO2 equivalent emission

The rapid economic growth of Dubai over the past three decades has triggered the construction of a large number of residential villas. Most of these were built before the first energy efficiency regulation came into effect in 2003 and, while new energy efficiency regulations are applied in buildings of new construction, the existing building stock remains energetically inefficient. The viability of different retrofit measures is examined here using two calibrated energy models of villas typical of different urban development periods. The retrofit measures considered focus on both envelope and air conditioning system, with energy targets selected at two efficiency levels: first, the level required by the current Dubai Green Building Regulations, and second, required efficiency levels to the stricter demands of the German Building Regulation. Results indicate that improving wall insulation to a U value of 0.3 W/m2 K, and upgrading the Air Conditioning system to a COP of 2.78, is financially viable and has a significant effect on energy consumption and CO2 equivalent emissions. Considering the existing building stock, the effect of applying these measures at an Emirate-wide scale can reduce summer peak demand by 40% and CO2 emissions for the villas by nearly 32%.

1. Introduction Buildings consume 40% of global energy and 60% of the world's electricity [1,2]. In addition, buildings are accountable for 25% of the global water consumption and are responsible for up to 33% of the world's GHG Emissions [1]. Global population growth and economic development, with ever increasing demands on indoor comfort, will continue to augment the demand buildings exert on energetic resources and the associated negative impact on the environment. While technology exists to drastically mitigate these demands and emissions, the implementation of this technology is typically contingent on enforcement by codes and regulations. As these codes and regulations have only been widely adopted over the past two decades (triggered by the increased cost of fossil fuels and a growing worldwide awareness of the environmental consequences of fossil fuel consumption), a large proportion of the existing building stock does not incorporate adequate energy efficiency considerations. Retrofitting these older buildings to higher energy standards can generate significant energetic savings and

reduce CO2 equivalent emissions. The study presented here examines the idealized attainable energy savings and financial viability of a range of retrofit measures for residential villas. Two different villa styles that reflect Dubai's existing built environment are examined: a Traditional Villa with little to no insulation, and a more Modern Villa that conforms to early Dubai energy codes. The energy demand of both villas is simulated using a calibrated computational model, and then retrofit measures following two standards are computationally applied and examined: first, the Dubai Green Building Regulations standard followed by, as a comparative, the German Building Energy standard, which is one of the most stringent energy standards worldwide. The retrofit measures (i.e. wall insulation, fenestration improvements, etc.) of the two different standards are simulated individually to evaluate the cost and energy efficiency of each measure, and finally, a cost-effective combination of these retrofit measures for Dubai's specific conditions is proposed. A building's GHG emission is caused by two principal mechanisms; the on-site emissions caused by the burning of fossil fuels (cooking,

Abbreviations: ASHRAE, American Society for Heating, Refrigeration and Air Conditioning Engineers; CCGT, Combined Cycle Gas Turbine; CEI, Carbon Emission index, defined as kg of CO2 produced per square meter per year; CV, Coefficients of Variation; DB, Dry Bulb Temperature; DGBR, Dubai Green Building Regulation; DEWA, Dubai Electricity and Water Authority; EPS, Expanded Polystyrene; EPBD, Energy Performance in Buildings Directive; ERR, Error; EUI, Energy utilization Intensity (kW h/m2 a); FEMP, Federal Energy Management Program; GBR, German Building Regulation; GHG, Greenhouse Gas; GWh, Gigawatt hour; HVAC, Heating, Ventilation, and Air Conditioning; IPMPV, International Performance Measurement and Verification Protocol; LCCA, Life Cycle Cost Analysis; Mt, Million tons; MV, Modern Villa; NPV, Net Present Value; RH, Relative Humidity; RMSE, Root Mean Squared Error; TV, Traditional Villa; TWh, Terawatt hours; UAE, United Arab Emirates; U-value, Measure of heat loss through a given thickness of particular material, including conduction, convection and radiation losses (W/m2 K); XPS, Extruded Polystyrene ⁎ Corresponding author. E-mail addresses: [email protected] (K. Rakhshan), [email protected] (W.A. Friess). http://dx.doi.org/10.1016/j.jobe.2017.07.010 Received 23 November 2016; Received in revised form 9 July 2017; Accepted 26 July 2017 Available online 27 July 2017 2352-7102/ © 2017 Elsevier Ltd. All rights reserved.

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

7% due to electricity transmission to the building sites [15], resulting in an average primary (or source) to site efficiency of 47%. The overall CO2 equivalent emissions for the UAE from the burning of fossil fuels in 2014 have been reported to be 175.4 Mt [15]. Based on an emission rate of 694 g/kW h [16] of CO2 for combined cycle power plants, the CO2 equivalent emission from the overall electricity generation is 73.1 Mt, the emission from the residential build environment is 27 Mt, and the cooling of residential buildings directly generates 12.7 Mt of CO2 equivalent emissions annually. The very high emissions and energetic expenditures of residential buildings in the UAE, in combination with a large building stock that was built prior to the introduction of any energetic code, warrant the investigation of the effectiveness of the retrofit measures presented here.

heating, etc.), as well as the emissions associated with the generation of the electricity consumed by the building. While the latter is directly related to the specific energy mix of the location, each is proportional to its respective demand in the building. In the case of the UAE, where electricity is the principal energy form used in buildings, GHG are produced primarily in the electricity generation process, and not at the site. The UAE's extreme climate places heavy demands on space conditioning systems. HVAC dry bulb design temperatures of 45.0 °C and 80% humidity in winter and 70% in summer [3] result in HVAC systems accounting for an average of 40% and a summer peak of 60% of the total electric demand of the Emirate [4]. The increase in population and thermal comfort expectations has triggered a continued increase in electricity generation, increasing by 5.4 TW h each year from 2000 until 2013 (13.5% average annual growth). Production in 2013 was at 110 TW h, with demand following suit at 105.4 TW h [5]. Dubai's earliest energy code, Administrative Resolution No. (66) of 2003 [6], recommends an indoor DB of 24 °C and a RH of 50 ± 5% for residential buildings and 25 °C DB and 55 ± 5% for RH in commercial buildings. The more recent Dubai Green Building Regulation recommends a DB range between 22.5 °C and 25.5 °C with RH values ranging between 30% and 60% [7]. While there is limited research data available on actual indoor thermal conditions in Dubai, in a survey conducted in Abu Dhabi [8] around 80% of the people were feeling too cold in their buildings. This survey [8] revealed that temperature setpoints for many public buildings like shopping Malls, banks, and government buildings are lower than the recommended values, leading to the reported uncomfortable indoor conditions and resulting in higher energy consumption. Despite these perceived low indoor temperatures, the author reports that measured temperatures vary from 17 °C to 31 °C depending on the building type and location inside the building. This is indicative of the strong effect solar heating has on the building envelope, in particular, the windows, and the often inadequate cooling strategies that create significant temperature gradients inside the building. A similar effect is observed by M.O. Fadeyi et al. [9] who studied the indoor environmental quality of 16 classrooms in Dubai and Fujairah. While the average temperature of 24.5 °C was recorded for all the studied classrooms, the classroom specific DB varied between 20.5 °C and 27.5 °C with RH between 31% and 52%. One classroom had temperature value lower than the recommendations of Dubai Green Building Regulations, and five classrooms had temperature values higher than the recommended values. This limited data available for indoor comfort in public buildings indicates that low indoor set-points (lower than the recommendations of the building energy codes) are often chosen to compensate for uneven heating of the building, resulting in higher energy consumption and poor thermal comfort. No data was available reporting on specific indoor comfort conditions for residential buildings in the UAE. Electric consumption reported in the literature and attributed to residential buildings ranges from 37% to 45.6% of the gross electricity consumption [10,11], and results in a lower bound of 39 TWh of total electricity consumed by residential buildings in 2013. In the United Arab Emirates, the cooling electricity load accounts for 47% of the total electricity demand by the residential building which can increase to above 60% during summer peak [12]. Considering the reported 47% average cooling energy fraction of the total residential electric energy consumption [12], residential building in the UAE consume 18.3 TWh electric energy for cooling. At the estimated unsubsidized cost of energy of $0.104 per kW h [13], this cooling related annual consumption would represent a real cost of 1.9 Billion USD. In addition to this very high financial cost, the associated GHG emissions have to be considered. In the UAE, the electricity generation process takes on the form of combined cycle cogeneration, with further waste heat utilized for desalination (primarily Multistage Flash Desalination) [12]. This process yields a conversion efficiency reported between 50% and 58% [14], which is further reduced by approximately

1.1. Literature review Energy efficiency measures were introduced in industrialized nations in the wake of the 1970's oil crisis, and have intensified over the past two decades due to the increased awareness of global warming as reflected in the Kyoto Protocol, as well as further increases in fossil fuel prices. In the US, building codes are adopted at the state and local level, and are typically based on the evolving International Energy Conservation Code [17] or the ASHRAE Code model, both prescriptive in nature [2] and applicable to new construction and major retrofits. Japan relies on voluntary building efficiency standards, which have been estimated to reduce heating and air conditioning by 20% [18]. In Europe, building energy efficiency regulations are driven by EU directives (Energy Performance in Buildings Directive, EPBD), which are implemented by the member states in accordance with their individualized models [2]. The initial EPBD (2002/91/EU) originated from the targets set by the Kyoto Protocol's agreement of the EU states to reduce their GHG emissions by 8%, and came into effect in 2003 for implementation in the member states. Following the development of yet stricter targets, the Directive 2010/31/EU was adopted by the EU countries in 2010 [19]. Under these Directives, each country develops and implements a building energy framework to meet the Directive's requirements, including both new construction and the retrofit of existing building stock undergoing significant renovation. In addition, most Western European countries have provided financial stimulus in the form of tax incentives or grants to support the implementation of the energy efficiency measures. The specific instruments and incentives for the implementation of the prescriptive measures to comply with the EPBD differs from country to country, such as a new Chapter 5 in the Netherland's Building Code, the Code for Sustainable Homes and Part L of the Building Regulations in the UK, the Spanish “Codigo Técnico de la Edificacion” subpart HE [20], or the German Energy Savings Ordinance (“Energie Einspar Verordnung”, or EnEV) [21]. In the study presented here, Germany was selected as comparative European benchmark due to its longstanding commitment to energy efficiency, which began after the oil crisis of the 70's, and the current high level of achieved savings; results show a reduction of heating energy per unit floor area from 1978 to 1993 of about 30% [17]. In contrast, no significant retrofit of existing building stock has been conducted in the UAE. In the 1970's, as an oil exporting country that was just in the early years of its formation and characterized by a relatively low population compared to today's numbers, the UAE had remained insensitive to the oil crisis, and thus none of the economically driven efficiency measures introduced in the western countries were necessary and/or implemented. This explains to a certain extent the lack of awareness and the very late introduction of energetic codes, which were in turn primarily triggered by the wave of energy codes in the western world rooted in an increased awareness regarding the need to reduce CO2 emissions to slow global warming. The primary driver in both occupant behavior and constructive heat 117

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

discusses the viability of aerated concrete block as a building material from the perspective of thermal efficiency and financial viability [25]. The blocks satisfied UAE code requirements at the time of the study without the need to supplement with additional insulation, and are cost effective in some emirates that do not have very high electrical subsidies. In addition to code compliance, using the blocks can save energy use of the residential sector by up to 7% [25]. Radhi [28] also discusses the effectiveness of façade integrated PV systems in UAE residential built environment, concluding that to be financially viable, the price of electricity should reflect the actual cost, and not be subsidized extensively as is the current practice. In that scenario, the deployment of PV panels can significantly reduce CO2 equivalent emissions when compared to electricity generated by conventional power plants and distributed via a centralized grid. Another study by Radhi analyzes the impact of improved building energy efficiency under various global warming scenarios [11], and their effectiveness in mitigating CO2 emissions now and in the future. Results indicate that global warming scenarios can raise cooling energy demand by up to 23%, and increase CO2 equivalent emissions by about 5.4% over the next few decades. Insulation, thermal mass, and conductive fenestration measures are sensitive to global warming, whereas shading measures are insensitive [11]. The building used for this study is utilized here as an example of a traditional building typically built without any efficiency code requirements. Fang et al. [29] conducted an experimental study to analyze the effect of thermal insulation on walls in a hot climatic region of China. They constructed two experimental chambers: one with construction typology of the 1980-90's that uses solid brick and single glazed windows, and another that uses hollow brick, external insulation (30 mm XPS), and double glazed windows. In addition to a more stable indoor thermal environment, results indicate energy savings of over 23.5% by using the insulated construction method. AlFaris et al. [30] confirm the effectiveness of energetic retrofit measures in arid climates, reporting savings ranging from 14.4% to 47.6% depending on the combination of conservation measures chosen. However, the authors do not present quantitative data on the individual measures and of the costing model applied. Their conclusions confirm the necessity to improve the building envelope and the air conditioning, and the importance of occupant behavior on the overall energy consumption. However, adding thermal insulation is not always beneficial. Buildings with high internal heat gains such as office buildings may react negatively to the increased thermal resistance of the walls and roof. This anti-insulation effect has the potential to trap the excess heat inside the building and create the need for higher capacity active systems to remove the additional thermal load as the studies presented below show. However, this effect is only observed in high internal gain buildings and under specific constructive and climatic circumstances, and does not apply to residential villas presented in this work. Guan [31] studied the effect of increased wall insulation on the energy performance of a typical office building in eight Australian cities. According to this study, if the internal set-point of a building with high internal heat gains is above the dominant ambient temperature, the external walls will act as a heat sink which helps in removing the heat generated inside the building. This study shows that increased thermal resistance of the outer walls has the potential to change the behavior of the external walls to a heat source by trapping the heat inside the building which yields in higher energy consumption (cooling) and less thermal comfort. Masoso [32] studied the anti-insulation behavior of a three-story office building in Botswana using a DesignBuilder simulation. In this study, the insulation level is increased from no insulation to 160 mm for six different internal set-points. The results of the energy simulation reveal that for interior set-points higher than 25.7 °C, increasing the wall insulation will increase the cooling load of the building. Friess et al. [33] conducted a sensitivity analysis of increased wall

and humidity control measures is the achievement of adequate interior thermal comfort, which is directly affected by the heat loss or gain through the building's envelope. Adequate indoor thermal comfort parameters (indoor set-points and RH ranges) are typically defined a priori and based on either standardized psychometric values or, in a more modern development, taking into account the specific cultural context, activity, and environment of the building and its occupants [22]. A building's passive and active systems are subsequently designed or redesigned to achieve these parameters. The Dubai Municipality recommendations for interior temperature comfort limits range from 22.5 °C to 25.5 °C, and RH from 30% to 60% [7]. While no studies of actual interior thermal conditions of residential villas exist, Behzadi and Olawale [23] have measured indoor thermal conditions at six Dubai elementary schools, with results of RH ranging from 27% to 43%, and interior temperature between 17 °C and 26 °C. Thus while the definition of thermal comfort varies from site to site and from person to person, the technology driving thermal comfort is rooted in the building's thermal insulation, which then dictates the size of the HVAC system, and has a direct impact on the energy signature of a building. In the UAE, and in order to maintain locally acceptable indoor thermal comfort levels, the heat loss in low-rise villas and multiunit residential buildings can account for over 30% of the total cooling load of the building [24,25] and thus, increasing wall and roof insulation is critical to limit the energy consumption of the building. A number of studies have examined the quality of the thermal envelope of buildings in the UAE. Afshari et al. [3] studied the effect of thermal insulation over the perimeter of a fifteen-story building in Abu Dhabi. The authors increased the thermal resistance of the external walls from U-value of 1.71 W/m2 K to a U-value of 0.324 W/m2 K by adding 80 mm of EPS. However, due to 70% window-to-wall ratio of the building, the decrease in the cooling load was limited to 2.6%. Al Masri et al. [26] integrated traditional courtyard housing design into midrise buildings and evaluated the environmental impacts of the new concept. The authors analyzed the effect of the number of floors, type of glazing, wall thickness and insulation type and thickness on the energy performance of the new design. The results show that by changing the traditional building to a courtyard design and keeping all other elements the same, a saving of 6.9% in annual energy consumption is achievable. In this paper, the authors compared the effect of 10 cm cellular polyurethane, 7.5 cm phenolic foam, 5 cm EPS (Styrofoam), and 2.5 cm Glass-Fiber Quilt. With reference to the base model, the results indicate that cellular polyurethane decreases the energy use by 3.6% and Glass-Fiber Quilt increases the energy consumption by 5.44%. Friess et al. [6] analyzed the effectiveness of full perimeter insulation in the Modern Villa used in this study. The results indicate that, although the villa was built to an early form of energy regulation (Dubai Municipality Decree 66, which required the concrete block to have a maximum U-value of 0.57 W/m2 K), these concrete blocks were ineffective, as only 24% of the perimeter consisted of this prescribed block. The work showed that the extensive thermal bridging of the reinforced concrete structure decreases the effectiveness of the insulation of the walls far below the limits intended by the regulation. However, retrofit measures consisting of full perimeter insulation were able to lower the energy consumption by up to 29%. A variety of constructive elements and their effect on building energy efficiency in the UAE have been discussed by Radhi. In a study utilizing a similar villa to the Traditional Villa utilized here, Radhi et al. [11] discuss building envelope measures and their effect in indoor comfort conditions. Their results indicate a high effectiveness of thermal mass and fenestration and a moderate effectiveness of increased insulation on indoor comfort levels. In particular, the importance of appropriate solar control to reduce the radiative heating through the windows is discussed. This includes appropriate glass treatments, as well as shading alternatives [27]. In another study, Radhi 118

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

insulation thickness on a typical 10-story rectangular office building at a global scale. The purpose of this research was to study the heattrapping effect of increased wall insulation in internal gain dominated buildings and its correlation to climatic, constructive, and use factors. Results indicate that buildings in a mixed climate condition (both heating loads and cooling loads) with more heating degree days will display this behavior. In other climate zones, the increased wall insulation will either have no effect (i.e. with very few to no HDD's) or be beneficial. This study was performed in 132 locations representing major Köppen climate zones. The results of Friess et al. [33] work are confirmed by Boyano [34] in his study addressing the energy performance of office buildings in Europe. The study addressed the thermal quality of building envelope elements and was conducted for a typical office building in three major European climate zones: Tallinn (cold), London (moderate) and Madrid (warm). By decreasing the thermal conductance of the external wall from 0.30 W/m2 K to 0.12 W/m2 K, a 20% reduction in energy consumption of the HVAC system was achieved in London and Tallin. However, in the case of Madrid, the increase in building wall insulation had no significant improvement in annual energy consumption. The authors concluded that using insulation in cold and medium climate zones is beneficial; however, in climate zones with higher cooling needs, the thickness of the insulation should be carefully selected because a well-insulated building can increase the chance of heat-trapping inside the building, which may result in increased energy demand for cooling. While the results reported in the literature illustrate individual shortcomings of constructive elements, the effect of explicit upgrades to existing standards and beyond on the overall energy consumption of the Emirate (given the distribution of villas of a different age that exhibit the efficiency characteristics intrinsic to that age) has not been quantitatively analyzed. Further, there is limited information on the financial viability of such changes.

Table 2 Traditional Villa characteristics and modeling options. Parameters

Villa

No. of floor Total Area Floor Height External walls (U-Value: 2.32 W/m2 K)

2 370 m2 3.7 m 24 mm plaster (outer surface) 150 mm reinforced concrete with 1% steel 24 mm plaster 50 mm cement mortar 35 mm polyurethane foam 150 mm cast concrete 30 mm timber flooring 70 mm floor screed 100 mm cast concrete 132.7 mm urea formaldehyde foam 0.30 Single pane clear 6 mm, (SHGC 0.86, U-Value 6.0 W/ m2 K) 5 m3/h/m2 (1.35 ac/h) First floor: Bedroom activity and nighttime occupation Ground floor: Family lounge activity and daytime occupation Split + separate mechanical ventilation (7.5 l/sperson) COP:2.00 22.5 °C

Roof (U-Value: 0.6 W/m2 K) Floor (U-Value: 0.25 W/m2 K)

Window to wall ratio Glazing Infiltration rate Model thermal zones

HVAC Set point temperature

2. Method The research presented here utilizes two different base models of UAE typical residential units, and that correspond to different constructive eras, to investigate the overall effect of a matrix of retrofit measures. In addition, a cost analysis of each retrofit measure is conducted to ascertain the viability of the different alternatives.

2.1. Home model 1.2. Evolution of construction and energy codes in Dubai

In order to reflect the evolution of the villa construction style and technology over the past four decades, the study utilizes two different models. First, a more traditional villa, that reflects typical pre-2003 characteristics, and that incorporates little to no insulation [11], and second, a villa of more modern construction (2008) that incorporates AD 66 energy criteria [6]. The villas were selected to leverage actual consumption data reported in the literature, allowing the calibration of the computational energy simulation.

The rapid growth of the Emirate of Dubai since the creation of the UAE has triggered a sustained building boom over the past decades. Dubai's urban area has exhibited an average annual growth rate of over 10% from 1972 until 2011 [35]. The resulting increase in the area of residential units is reported by AlNaqbi [4] and shown in Table 1. For the purpose of this study, the constructive practices are grouped into three periods:

• Pre-2003, represented by the absence of energetic building code • 2003–2011, represented by the requirements imposed by the AD66 based energy code • Post-2011, represented by buildings aligned with the current Green

2.1.1. Pre-2003 construction (Traditional Villa) This villa reflects the standard pre-2003 construction method in the UAE and has been utilized by Radhi [11] to evaluate the impact of global warming on the emirate's energy consumption.

Building Regulations

2.1.2. 2003–2011 construction (Modern Villa) This villa was built as part of a large complex of villas around 2008 and incorporates AD66 energy saving measures, which primarily dictate maximum U-Values for the non-structural wall elements and windows. Villas from this development have been used by Friess et al. [6] and Rakhshan et al. [37] to ascertain the effect of improved thermal bridge insulation on the energetic efficiency of the villa, as well as the sustainability effect of this improved insulation. In addition, Taleb [38,39] utilized a villa in the same development to analyze the effect of a range of retrofit measures and urbanistic options. As such it provides a well-tested baseline. The constructive details of the villa are shown in Table 3: The villa incorporates the typically used composite insulated block, however also reflects extensive thermal bridging that has a strong adverse effect on the overall energy consumption [6].

Two calibrated simulation models are constructed, one that represents the pre-2003 period, and a second that represents the 2003–2011 period. The constructive characteristics of UAE villas built before the introduction of energy codes were obtained from information presented in the literature [4,11].

Table 1 Newly constructed residential area in Dubai by period [4]. Period

Villa (m2)

Buildings (m2)

1980–1989 1990–1999 2000–2002 2003–2011

779,438 1,566,506 2,924,036 14,228,703

1,987,383 5,705,821 3,687,755 30,839,414

119

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

Table 3 Characteristics of the 2003–2011 villa base model [6]. Parameters

Villa

No. of floor Total area Floor height External walls (U-Value: 0.523 W/m2 K)

2 231 m2 3.5 m 15 mm mortar (outer surface) 200 mm Composite insulated block (mid-plane 60 mm EPS) 20 mm gypsum plastering 15 mm mortar (outer surface) 200 mm reinforced concrete 20 mm gypsum plastering 140 mm gravel (outer surface) 2 mm bitumen, felt/sheet 50 mm EPS expanded polystyrene 80 mm aerated concrete 200 mm reinforced concrete slab 150 mm cast concrete 30 mm XPS Extruded Polystyrene 0.21 Double coated 6/12/6 (SHGC 0.37, U-Value: 1.8 W/m2 K) 1.71 ac/h @ 50pa (measured) or 6.02 m3/h/ m2 Occupant defined – 0.35 ac/h applied for model First floor: Bedroom activity and nighttime occupation Ground floor: Family lounge activity and daytime occupation Split no fresh air. Fresh air supply considered with natural ventilation COP: 1.80 21 °C bedrooms 22 °C living areas

RC structure (U-Value: 2.398 W/m2 K) Roof (U-Value: 0.422 W/m2 K)

Floor (U-Value: 0.778 W/m2 K) Window to wall ratio Glazing Infiltration rate Natural ventilation Model thermal zones

HVAC Set point temperature

Fig. 1. Traditional Villa [36].

Transfer Function (CTF) which ignores moisture storage or diffusion in the construction elements [44]. The Thermal Analysis Research Program (TRAP) algorithm [44] based on variable natural convection based on temperature difference from ASHRAE algorithms is followed for inside convection heat transfer calculations. For outside convection calculations, the DOE-2 [44] convection model was used, which is a combination of the MoWiTT [44] and BLAST Detailed convection. The simulation process follows a minimum number of 6 warm-up days and is limited to 25 warm-up days for the annual hourly energy simulation. (Figs. 1 and 2) 2.3. Calibration of simulation 2.3.1. Traditional Villa The model used here was used previously to study the impact of improved building energy efficiency under various global warming scenarios [11]. Fig. 3 shows the output of the energy simulation superimposed onto the metered data available in [11]. The model represents the actual consumption with high fidelity (Table 4).

2.2. Energy simulation The energy simulation is conducted using EnergyPlus (version 8.3) via the commercial DesignBuilder interface (version 4.7.0.027). EnergyPlus has been developed by the US Department of Energy and has been validated by numerous studies published in the literature [34,40,41]. The model reproduces the constructive details of the dwellings and carries out an hourly energy simulation over a one-year period. The weather data input into the model originates from ASHRAE's International Weather for Energy Calculation (IWEC) files and reflects the weather at Dubai International Airport for the Modern Villa and (for calibration) Al Ain airport data for the Traditional Villa (which is located in Al Ain). The Traditional Villa reflects typical constructive data for the region, and for the purpose of the retrofit options presented here will be analyzed in Dubai, however as the only metered consumption data available for this type of villa stems from Al Ain, the model is calibrated using that climate. After the calibration case, and to analyze the effectiveness of the retrofit cases within the constructive and regulatory framework of the Emirate of Dubai, computations of both calibrated villa models are conducted using Dubai weather data. The models are calibrated with metered consumption and checked to lie within the acceptable tolerances as recommended by Alspector [42]. The calibration of the model for the Modern Villa was carried out by the authors in a previous study using metered data [6], and the Traditional Villa simulation was calibrated using metered data collected and presented by Radhi in [11] The details of the calibration process is introduced in 2.3. Each villa is composed of two thermal zones (one zone per floor) for the simulation, and a zone time-step of 2 was used per hour. The zone time-step of 2, as used in this study, indicates that the model performs heat transfer and load calculations for the building two times per hour, i.e. every 30 min [43]. The temperature control is performed through each zone's mean air temperature control governed by the heating and cooling set-points. The surface heat balance follows the Conduction

2.3.2. Modern Villa The model used here was used previously to study the thermal bridging effect [6], and has been shown to align with the metered data. The comparison between the metered data [6] and the model is shown in Fig. 4. The energy model reproduces the metered data with high fidelity, except for the month of January. The nature of this discrepancy is unknown but could be caused by a special event for the occupants during that month (the consumption data represents only one year of data collection, and thus will reflect anomalies in occupant behavior). However, even with this anomaly, the model lies on or within the acceptable tolerances and becomes highly accurate for the remaining months (Table 4). Also, the effect of the January anomaly remains

Fig. 2. Modern Villa [36].

120

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess 12000

small, as relatively little energy is consumed during the winter months. To calculate the primary energy consumption per unit area, first, a conversion factor of 1.07 is employed to account for the transmission losses [45]. Most of the power plants in the UAE are of co-generation type (Combined Cycle Gas Turbine based power and desalination plant, CCGT) and burn natural gas [14,37]. The approximate efficiency range for such power plants is between 50% and 58% [14]. Considering the above listed transmission losses and assuming a conservative generation efficiency of 55% for the CCGT power and desalination plants, the primary (or source) to site energy conversion efficiency is then 47%. An analysis of the adequacy of the model calibration with metered data was conducted using the approach and acceptable tolerances reported by Alspector [42], which applies the guidelines of ASHRAE 14–2002, FEMP guidelines, and IPMVP. The following calibration results and tolerances were achieved: The energy models reflect the constructive details of the villas and were fine-tuned to align to the metered data by adjusting occupancy schedules, as recommended by Radhi [42,46]. (Table 5)

11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

Bill (kWh)

Simulation

Fig. 3. Comparison between computed and metered data for traditional style villa [11].

Table 4 Monthly and annual electricity bills per unit area [6,11]. Month

January February March April May June July August September October November December Annual (kW h/ yr)

Traditional Villa (kW h/ m2) [11]

Traditional Villa (kW h primary/ m2) [11]

Modern Villa (kW h/m2) [6]

Modern Villa (kW h primary/m2) [6]

19.6 18 17.4 21.2 25.1 26.4 30.2 29.2 24.5 22.9 16.3 20.6 271.4

41.7 38.3 37 45.1 53.4 56.2 64.3 62.1 52.1 48.7 34.7 43.8 577.4

8 4.3 9.5 17.2 24.3 27.6 27.6 29.6 27.4 16.9 7.7 4 204.1

17 9.1 20.2 36.6 51.7 58.7 58.7 63 58.3 36 16.4 8.5 434.2

2.4. Retrofit options studied The columns in the below table show what measures would be required for the buildings studied here to reach the Dubai Green Building Regulation Requirements (DGBR) and German Building Requirements (GBR), respectively. The following commonly executed retrofit measures have been examined here (Table 6): Reducing the infiltration rate is an important criterion and often represents a major driver in energy efficiency. In this study, both the Modern and Traditional Villas have been reported to already exceed the minimum standards of both the GBR and the DGBR, and thus no further retrofit simulations of improved infiltration are conducted here. The sources for both buildings indicate direct measurement using a blower door test for the Modern Villa [6], and data from working drawings, utility bills, and municipality and utility reports [11] for the Traditional Villa. Both buildings with their respective infiltration rates have been used in prior calibrated studies, and thus are considered adequate for the parametric study presented here. The energy efficiency targets listed above are based on Dubai Green Building Regulations, German Building Regulations, and the more extreme Passivhaus requirements as an option for the windows. The retrofit targets were selected to:

8000 7000 6000

• Assess the overall effect of improving the energy efficiency of both

5000 4000 3000 2000

•

1000 0

Bill (kWh)

the older generation of homes (Traditional Villa) as well as the type of villa constructed under early energy efficiency regulations (Modern Villa) to the current Dubai Green Building standard and second, To assess the effect of the retrofits to one of the arguably strictest energy efficiency standards currently in use (the German Building Requirements) augmented to Passivhaus regulations for fenestration.

Thus the targets were selected to reflect current practices and standards at two levels of efficiency. The different measures have been applied individually to the base building while keeping all other factors constant (Table 7). This process is intended to analyze the effectiveness of each measure individually on the overall energy consumption.

Simulation

Fig. 4. Comparative of metered vs. computed monthly energy use for the Modern Villa [6].

Table 5 Acceptable tolerances as reported by Alspector [42] and results from both model villas studied here. Index

ASHRAE 14 tolerance

IPMVP tolerance

FEMP tolerance

Traditional Villa

Modern Villa

ERRmonth ERRyear CV (RMSEmonth)

± 5%

± 20%

± 15%

± 5%

± 15% ± 10% ± 10%

+ 1% to −5% < 1% 5%

65% to −3.6% (12 month)2.9% to −3.6% (excluding January) 2.2% (including January) 15.7% (12 month) or 6.4% (excluding January)

121

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

Table 6 Retrofit target matrix and necessary building retrofit measures. Building component

Walls Roof Windows

Dubai Green Building Regulation Requirements (DGBR)

German Building Requirements (GBR)

0.57 W/m2 K 0.3 W/m2 K U = 2.1 W/m2 K

Modern Villa DGBR

GBR

DGBR

GBR

0.3 W/m2 K 0.2 W/m2 K Maximum U-Value to be limited to 0.8 W/m2 K

Add40 mm EPS Add40 mm EPS Building meets criterion

COP: 2.78

Replace AC to COP: 2.78 Building meets criterion

Add 100 mm EPS Add 105 mm EPS Replace windows with Triple Glazing: U = 0.78 W/m2 K SC = 0.4 (max) LT = 0.25 (min) Replace AC to COP: 2.78

Add 55 mm EPS Add 65 mm EPS Replace windows with Double Glazing: U = 2.1 W/m2 K SC = 0.4 (max) LT = 0.25 (min) Replace AC to COP: 2.78 Building meets criterion

Add 120 mm EPS Add 135 mm EPS Replace windows with Triple Glazing: U = 0.78 W/m2 K SC = 0.4 (max) LT = 0.25 (min) Replace AC to COP: 2.78 Building meets criterion

SC = 0.4 (max) LT = 0.25 (min) HVAC Infiltration

COP: 2.78 2

10 m³/h/m

2

3.9 m³/h/m (regulation with mech vent.)

B – Reduce Wall U-Value to less than 0.57 W/m2 K C – Reduce Wall U-Value to less than 0.3 W/m2 K D – Reduce Roof U-Value to less than 0.3 W/m2 K E – Reduce Roof U-Value to less than 0.2 W/m2 K F –Replace windows with DGBR Window G – Replace windows with Passivhaus Window H – Replace HVAC to better than COP: 2.78

Building meets criterion

base case, yielding an overall EUI of 204 kW h/m2 a. The above results indicate that the benefit of the constructive measures on EUI does not exceed 14%, however replacing the AC unit from a COP of 1.80 to one of a COP of 2.78 has a significantly higher impact of up to a 31.2% lower EUI.

Table 7 Individual retrofit measures studied (MV = Modern Villa, TV = Traditional Villa). Retrofit case

Traditional Villa

Constructive measure taken (all other factors unaltered) Original wall + 40 mm EPS • MV: Original wall + 55 mm EPS • TV: Original wall + 100 mm EPS • MV: Original wall + 120 mm EPS • TV: Original roof + 40 mm EPS • MV: Original roof + 65 mm EPS • TV: Original roof + 105 mm EPS • MV: TV: Original roof + 135 mm EPS • MV and TV: Replace windows with Double

3.1.2. Traditional Villa Table 2 shows the as-built characteristics of the Traditional Villa studied here. The U-Value of the walls in the original as-built configuration is equal to 2.32 W/m2 K, which is significantly higher than the value required by the DGBR. Table 9 lists the various individual retrofit measures studied to optimize the performance of this building. Due to this energetically inefficient building envelope, the simulations show that a full perimeter insulation to a maximum U-value of 0.3 W/m2 K yields EUI savings of up to 13.3% over the base case, while the control of heat gains through the roof has an impact of less than 1%. In contrast to the Modern Villa, the replacement of the AC unit does not play such a dominant role (17.1% EUI savings).

glazing: U = 2.1 W/m2 K, SHGC = 0.348, LT = 0.25 MV and TV: Replace windows with triple glazing: U = 0.78 W/m2 K, SHGC = 0.348, LT = 0.25 MV and TV: replace AC unit

3.2. Cost of retrofit measures

The individual retrofit cases analyzed for both buildings are shown below (case A is the unmodified original building):

The cost of each retrofit measure has been computed using the NREL retrofit measure database [47]. The data presented in this reference refers to the US construction environment; however, due to the lack of similar reliable data for the region the US data is used here. While the absolute values of the retrofit measures may vary, the relative cost of each one will be reflected in the US data, and thus can be used here for comparative analysis. Using a lifetime of a UAE villa of 30 years [48,49], a lifetime of the AC system of 15 years, and a conservative yearly increase in electricity price of 2%, the lifetime energy savings can be computed for each measure.

3. Results and discussion The analysis follows a two-step process; first, the energetic effect of each of the individual measures is computed using the energy simulation. Then the cost of each retrofit measure is computed using the reference values of NREL [47], and the simple payback and NPV of each measure computed. From these results, a viable combination of retrofit options is obtained, and a new simulation of the villas with the applied measures is conducted. The financial viability is discussed, and the sustainability benefits of the optimized retrofit measures are addressed, both at individual villa scale, as well as at Emirate-wide scale considering the age distribution of the existing villa stock.

3.2.1. Simple payback and NPV To choose the optimum retrofit measures, a simple payback method for an operational year and a NPV analysis over 30 years is followed. The unit cost of electricity is selected based on Dubai Electricity & Water Authority (DEWA) tariffs for the years 2016 [13]. Then, the average energy consumption for both villas according to each retrofit measure is evaluated, and the annual energy saving of each measure is calculated and used to estimate the simple payback period. Payback period is simply the cost of each retrofit measure divided by the savings achieved for the same retrofit in a year. Further, a NPV calculation is carried out to analyze the effect of the measures over a 30-year period utilizing a conservative 2% annual energy price increase and a discount rate of 6%. All measures with the exception of the Air Conditioning replacement have a lifetime of 30 years. The investment cost in the NPV calculation reflects a replacement of the AC unit to one of the same

3.1. Energy savings 3.1.1. Modern Villa Seven different permutations of individual retrofit measures that reflect the different options of the retrofit matrix have been computed for the Modern Villa (Table 8). It is important to note that in the case of the Modern Villa, and due to the large area of reinforced concrete structure, an area-average for the U value was found to realistically reflect matching the requirements of the individual codes. While the building's wall U-Value generally satisfies the requirements of Dubai green building regulation (0.57 W/ m2 K), the average U-Value of the walls due to the presence of reinforced concrete frame is equal to 1.31 W/m2 K, which is utilized as 122

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

Table 8 Site energy efficiency impact of retrofit alternatives studied for Modern Villa. Retrofit option

EUI (kW h/m2 a)

Change with as built (%)

A – Original building B – Reduce Wall U-Value to less than 0.57 W/m2 K C – Reduce Wall U-Value to less than 0.3 W/m2 K D – Reduce Roof U-Value to less than 0.3 W/m2 K E – Reduce Roof U-Value to less than 0.2 W/m2 K F –Replace windows with DGBR Window G – Replace windows with Passivhaus Window H – Replace HVAC to better than COP: 2.78

204 182 177 204 203 176 176 140

0 10.6 13.2 0.2 0.4 13.5 13.8 31.2

standard after 15 years of operation. (Tables 10, 11)

Table 10 Cost of retrofit measures [47].

3.2.2. Optimum combination of measures The simple payback period and the NPV of the individual measures computed above indicate that both window replacement and roof insulation retrofit are not financially viable, as these measures exhibit a negative NPV and payback periods in excess of the lifetime of the building. Among the two wall-insulation options, the reduction to 0.3 W/m2 K (addition of 100 mm and 120 mm of EPS) displays a slightly longer simple payback, however also exhibits a higher NPV over the reduction to only 0.57 W/m2 K, and thus the former is chosen for the analysis of the combined measures. Based on these results, the following retrofit measure combinations were selected for the optimized building:

Building component

Walls Roof Windows HVAC

Traditional Villa

DGBR minimums

GBR minimums

DGBR minimums

GBR minimums

$ 2730 $ 1959 MEETS standard $ 4367

$ 4611 $ 3421 $ 70,095

$ 7861 $ 4829 $ 20,570

$ 12,869 $ 7845 $ 46,414

$ 8735

site energy. Due to the electric power transmission and distribution losses, the site energy is always lower than the delivered energy to the grid. In the case of the UAE, the average value of these losses is around 7.2% [45] which means that for each kW h electricity consumed at the site (by the end user), 1.07 kW h electricity is generated at the power plant. According to IEA [16], each kW h of electricity generated in the UAE will produce 0.694 kg CO2. Table 13 shows the total CO2 savings resulting from the considered retrofit combinations for each of the buildings. Considering the CO2 savings presented in Table 13, and applying the same combined retrofit measures for the total stock of villas in the UAE as per Table 1 (assuming that all pre-2003 villas reflect a similar EUI that the Traditional Villa and all villas constructed from 2003 to 2011 reflect the EUI of the Modern Villa), a total decrease of 1.15 million tons of CO2 emission can be achieved annually which improves the CO2 footprint of the villas by around 32%.

• Addition of 100 mm and 120 mm of expanded polystyrene external •

Modern Villa

insulation to the Modern and Traditional Villas respectively, to decrease the wall U value below the targeted 0.3 Wm2 K Replace the Air Conditioning unit to one with a COP of 2.78 or better.

Considering an estimated lifetime of the buildings in the UAE of 30 years, the combination of these measures is deemed a viable retrofit strategy and has been applied to both villas. Simulation results of the combined measures and simple payback periods are shown in Table 12: The combination of these retrofit measures generates an EUI reduction of almost 40% in the Modern Villa, and of over 27% in the Traditional Villa. The changes will save the villa owner money over the long term, but will also significantly decrease the energetic demand of the Dubai residential villa sector, in particular, reduce the peak summer loads. Fig. 5 shows the original and retrofitted seasonal energy curves for the Dubai's existing building stock as listed in Table 1, under the assumption that the pre-2003 building stock reflects the characteristics of the Traditional Villa, and the 2003–2011 building stock reflects the constructive characteristics of the Modern Villa. Fig. 5 indicates that under these assumptions the peak summer energy consumption of the pre-2011 residential villa sector can be reduced by up to 40%.

3.2.4. The rebound effect and its impact on attainable savings The direct rebound effect considers changes in usage patterns attributable to lower discounted lifetime cost of a commodity, as well as the necessary behavioral changes caused by altered indoor comfort conditions due to the energy efficiency measure [50]. The literature presents multiple paths to estimating the rebound effect, including quasi-experimental studies, as well as economic studies analyzing the price elasticity of energy [50] and, while no studies report on the rebound effect on increased energy efficiency in a cooling environment, there is limited data on the rebound effect linked to energy efficiency improvements in a heating environment [50–52]. Milne and Boardman

3.2.3. Sustainability of combined measures for each villa The annual electric energy reduction listed in Table 12 represents Table 9 Site energy efficiency impact of retrofit alternatives studied for Traditional Villa. Retrofit option

EUI (kW h/m2 a)

Change with as built (%)

A – Original building B – Reduce Wall U-Value to less than 0.57 W/m2 K C – Reduce Wall U-Value to less than 0.3 W/m2 K D – Reduce Roof U-Value to less than 0.3 W/m2 K E – Reduce Roof U-Value to less than 0.2 W/m2 K F –Replace windows with DGBR Window G – Replace windows with Passivhaus Window H – Replace HVAC to better than COP: 2.78

272 241 235 270 269 257 255 225

0 11.3 13.3 0.6 0.9 5.4 6.1 17.1

123

Journal of Building Engineering 13 (2017) 116–126

$ 31,138

NA $ −51,772

$ −2953

$ 12,898 $ −1692

$ 11,361

Table 12 Combined retrofit measures for Modern Villa & Traditional Villa. Optimized retrofit measure combination

EUI (kW h/m2 a)

Change with as built (%)

Cost of Retrofit (USD)

Payback period (years)

Retrofitted Modern Villa Retrofitted Traditional Villa

123

39.8

$8978

6.5

197

27.7

$21,603

7.8

$ 48,087

$ 369 $ −23,157

$ −4327

$ 38,320 $ −2497

700

$ 35,415

NPV (USD) Traditional Villa

NPV (USD) Modern Villa

K. Rakhshan, W.A. Friess

600

GWh / year

400

300

100

3.9

0 137.4

262.5

9.5 26.9

200

7

Discounted payback Modern Villa (Years)

500

0 Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Total villas retrofitted

Fig. 5. Comparative seasonal energy demand for original vs. retrofitted residential villa building stock in Dubai.

4.0 5.1

4.8

NA 146.1 37.5 76.2

35.3 71.7

279.2 85.2

80.1

10.1 280.6 9.6 79.1

9.1 74.4

7.4 6.9

B – Decrease Wall U-Value 0.57 W/ m2 K C – Decrease Wall U-Value 0.3 W/m2 K D – Decrease Roof U-Value to 0.3 W/ m2 K E – Decrease roof U-Value to 0.2 W/ m2 K F – Replace windows to DGBR standard G – Replace windows to Passivhaus standard H – Replace AC with a COP: 2.78

6.6

Table 13 Total CO2 savings for retrofitted Villa.

Simple payback Traditional Villa (years)

Simple payback Modern Villa (Years)

Feb

Total villas base case

Retrofit option

Table 11 Simple payback, discounted payback, and NPV of retrofit alternatives for both villas.

Discounted payback Traditional Villa (years)

Jan

Scenario

CEI (kg CO2/m2 a)

CO2 emission tons per year

Reduction in CO2 equivalent emission % (Compared to as built)

Retrofitted modern villa Retrofitted traditional villa

91

21

39.8

146

54

27.6

report that in the UK heating environment, 30% of the energy savings are taken back as an increase in interior temperature (increased comfort). They also report that the rebound is most noticeable in low-income housing, where indoor temperatures can be as low as 14 °C, and that it is minimized once the indoor temperature reaches 20 °C. In contrast to this reported 30% take back attributable occupant selected increased internal comfort (higher interior temperature), in the case of the UAE it is questionable whether the same level of rebound would be attained, as normal indoor temperatures are already on the low end of the comfort zone, and interior comfort already often overrides energetic and cost considerations [8]. While the reported effects of the rebound effect can be substantial, due to the lack of cooling environment specific data, the results presented here do not include an estimate of the rebound effect, and as such represent idealized savings. 4. Conclusion Due to the large number of residential villas in Dubai that do not conform to the modern DGBR standards, it becomes of interest to analyze the energetic and financial feasibility of proposed retrofit measures, as well as the environmental impact of these. A number of retrofit measures were investigated here on two buildings of different 124

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess

age and efficiency standards typical of the Dubai built environment. Results indicate that adding relatively low-cost wall insulation, combined with a replacement of the air conditioning unit to one of higher efficiency present the highest savings potential. Replacing windows, on the other hand, offers lower financial viability. The windows installed in buildings from 2003 to 2011 already incorporate the standards of the DGBR, and increasing this standard to the very costly PassivHaus standard, with its triple glazing, selective coatings, and the inert gas filling does not offer realistic payback timeframes. Older buildings, such as the one studied here for pre-2003, typically do not have a high window to wall ratio, and thus windows, albeit offering poor insulation, play a limited role in the energy balance. Infiltration can generate significant energy losses; however, the two buildings presented here were reported to be of adequate air-tightness in their present condition, and thus retrofit options were not considered. However, since infiltration is strongly related to the quality of construction, this conclusion cannot be generalized, and individual measurements should be conducted in a building before selecting an appropriate retrofit package. Wall insulation is beneficial at all levels. A full perimeter enclosure of the building in EPS insulation eliminates thermal bridges and constitutes a cost-effective way to reduce up to 13% of the buildings’ energy consumption. This measure represents the most attractive retrofit option to the building envelope. The second most effective measure is the replacement of the air conditioning unit to one that conforms to modern efficiency standards (COP 2.78). This measure offers up to a 31% improvement over the original building. Combining the retrofit of the envelope with the replacement of the air conditioning unit provides a synergistic effect that further increments efficiency of the combination; resizing the air conditioner to the new (lower) building demand, and at the same time increasing its efficiency, can lead to energy savings of up to 40%. The above idealized results do not include the rebound effect attributable to changed behavioral patterns of occupants of retrofitted homes. These rebound effect changes have been shown to reduce attainable idealized savings by up to 30% in heating environments and, while no UAE cooling environment specific estimates exist, have the potential to adversely affect the actual savings attained from the retrofit efforts. Retrofitting older residential villas to the DGBR standard (with improved wall U-Value) has the potential to reduce emissions by 0.66% thereby saving 1.15 million tons of CO2, and decrease the summer energy demand peak caused by pre-2003 residential villas by up to 40%, thereby presenting an opportunity to positively affect the sustainability balance sheet of the Emirate of Dubai.

[11]

[12]

[13] [14]

[15]

[16]

[17]

[18] [19]

[20]

[21] [22]

[23] [24] [25] [26]

[27]

[28] [29] [30] [31]

[32] [33]

References [34] [1] U. N. E. Programme-SBCI. Available: 〈http://www.unep.org/sbci/AboutSBCI/ Background.asp〉. (Accessed 17July 2016). [2] J. Laustsen, Energy efficiency requirements in building codes, energy efficiency policies for new buildings, Int. Energy Agency IEA (2008) 477–488. [3] A. Afshari, C. Nikolopoulou, M. Martin, Life-cycle analysis of building Retrofits at the urban scale-A case study in United Arab Emirates, Sustainability 6 (2014) 483–503. [4] A. AlNaqbi, W. AlAwadhi, A. Manneh, A. Kazim, B. Abu-Hijleh, Survey of the existing residential buildings stock in the UAE, Int. J. Environ. Sci. Dev. 3 (2012) 491. [5] A. Juaidi, F.G. Montoya, J.A. Gázquez, F. Manzano-Agugliaro, An overview of energy balance compared to sustainable energy in United Arab Emirates, Renew. Sustain. Energy Rev. 55 (2016) 1195–1209. [6] W.A. Friess, K. Rakhshan, T.A. Hendawi, S. Tajerzadeh, Wall insulation measures for residential villas in Dubai: a case study in energy efficiency, Energy Build. 44 (2012) 26–32. [7] D. Municipality, Green Building Regulations and Specifications, First ed., Dubai Municipality, Dubai, UAE, 2011. [8] V. Todorova, Study finds Abu Dhabi is too cold for comfort, in: The National UAE, ed. UAE, 2012. [9] M.O. Fadeyi, K. Alkhaja, M.B. Sulayem, B. Abu-Hijleh, Evaluation of indoor environmental quality conditions in elementary schools‫ ׳‬classrooms in the United Arab Emirates, Front. Archit. Res. 3 (2014) 166–177. [10] P.-O. Karlsson, C. Decker, J. Moussalli. Energy efficiency in the UAE - Aiming for

[35]

[36] [37]

[38]

[39] [40]

[41]

[42]

125

sustainability (2015 ed.). Available: 〈http://www.strategyand.pwc.com/reports/ energy-efficiency-in-uae〉. (Accessed: 13 November 2016). H. Radhi, Evaluating the potential impact of global warming on the UAE residential buildings - a contribution to reduce the CO2 emissions, Build. Environ. 44 (2009) 2451–2462. IRENA. Renewable Energy Prospects: United Arab Emirates (April 2015 ed.). Available: 〈http://www.irena.org/remap/irena_remap_uae_report_2015.pdf〉. (Accessed 13 November 2016). DEWA. Tariff calculator. Available: 〈https://www.dewa.gov.ae/en/customer/ services/consumption-services/calculator〉. (Accessed 13 November 2016). M. Vermaut, Improving generation efficiency of power plants in Arab Countries, Energy and Arab Cooperation, Abu Dhabi, United Arab Emirates, Technical Paper, 2014. IEA. CO2 emissions from fuel combustion highlights, 2016. Available: 〈http:// www.iea.org/publications/freepublications/publication/co2-emissions-from-fuelcombustion-highlights-2016.html〉. (Accessed 13 November 2016). . IEA - Publication:- CO2 emissions from fuel combustion 2011 - Highlights, 2012. Available: 〈http://www.iea.org/publications/freepublications/publication/name, 4010,en.html〉. H. Geller, P. Harrington, A.H. Rosenfeld, S. Tanishima, F. Unander, Polices for increasing energy efficiency: Thirty years of experience in OECD countries, Energy Policy 34 (2006) 556–573. (November 2016). Energy efficiency building standards in Japan Available: 〈http:// www.asiabusinesscouncil.org/docs/BEE/papers/BEE_Policy_Japan.pdf〉. O. Brilhante, J. Skinner, European Experiences of Building Codes for Promoting Sustainable Housing 2014 Institute for Housing and Urban Development Studies (IHS), Rotterdam, the Netherlands, 2014. G.d.E. Ministerio de Fomento. Codigo Técnico de la Edificacion (The Technical Building Code), (30/06/2017). Available: 〈https://www.codigotecnico.org/index. php/menu-que-cte/estructura-contenidos.html〉. EnEV-online, Energie Einspar Verordnung, (30/06/2017). Available: 〈http://www. enev-online.de/〉. J. Raish, J.M. Ferguson. Thermal comfort: designing for people. Available: 〈https:// soa.utexas.edu/sites/default/disk/urban_ecosystems/urban_ecosystems/09_03_fa_ ferguson_raish_ml.pdf〉. N. Behzadi, M.O. Fadeyi, A preliminary study of indoor air quality conditions in Dubai public elementary schools, Archit. Eng. Des. Manag. 8 (2012) 192–213. K.A. Al-Sallal, L. Al-Rais, M.B. Dalmouk, Designing a sustainable house in the desert of Abu Dhabi, Renew. Energy 49 (2013) 80–84. H. Radhi, Viability of autoclaved aerated concrete walls for the residential sector in the United Arab Emirates, Energy Build. 43 (2011) 2086–2092. N. Al-Masri, B. Abu-Hijleh, Courtyard housing in midrise buildings: an environmental assessment in hot-arid climate, Renew. Sustain. Energy Rev. 16 (2012) 1892–1898. H. Radhi, A. Eltrapolsi, S. Sharples, Will energy regulations in the Gulf States make buildings more comfortable – a scoping study of residential buildings, Appl. Energy 86 (2009) 2531–2539. H. Radhi, Energy analysis of facade-integrated photovoltaic systems applied to UAE commercial buildings, Sol. Energy 84 (2010) 2009–2021. Z. Fang, N. Li, B. Li, G. Luo, Y. Huang, The effect of building envelope insulation on cooling energy consumption in summer, Energy Build. 77 (2014) 197–205. F. AlFaris, A. Juaidi, F. Manzano-Agugliaro, Energy retrofit strategies for housing sector in the arid climate, Energy Build. 131 (2016) 158–171. L.-.S. Guan, Will insulation always bring benefits in energy saving and thermal comfort? | QUT ePrints, presented at Proceedings of the First International Conference on Sustainable Urbanization ICSU 2010, The Hong Kong Polytechnic University, 2010. O.T. Masoso, L.J. Grobler, A new and innovative look at anti-insulation behaviour in building energy consumption, Energy Build. 40 (2008) 1889–1894. W.A. Friess, K. Rakhshan, M.P. Davis, A global survey of adverse energetic effects of increased wall insulation in office buildings: degree day and climate zone indicators, Energy Effic. 10 (2017) 97–116. A. Boyano, P. Hernandez, O. Wolf, Energy demands and potential savings in European office buildings: case studies based on EnergyPlus simulations, Energy Build. 65 (2013) 19–28. A.K. Nassar, G. Alan Blackburn, J. Duncan Whyatt, Developing the desert: the pace and process of urban growth in Dubai (5//), Comput., Environ. Urban Syst. 45 (2014) 50–62 (5//). DesignBuilder, "DesignBuilder," 4.7.0.027 ed. K. Rakhshan, W.A. Friess, S. Tajerzadeh, Evaluating the sustainability impact of improved building insulation: a case study in the Dubai residential built environment, Build. Environ. (2013). H.M. Taleb, Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings, Front. Archit. Res. 3 (2014) 154–165. H. Taleb, M.A. Musleh, Applying urban parametric design optimisation processes to a hot climate: case study of the UAE, Sustain. Cities Soc. 14 (2015) 236–253. D.B. Crawley, L.K. Lawrie, F.C. Winkelmann, W.F. Buhl, Y.J. Huang, C.O. Pedersen, et al., EnergyPlus: creating a new-generation building energy simulation program, Energy Build. 33 (2001) 319–331. R.H. Henninger, M.J. Witte, D.B. Crawley, Analytical and comparative testing of EnergyPlus using IEA HVAC BESTEST E100–E200 test suite, Energy Build. 36 (2004) 855–863. D.E. Alspector, Automatic Calibration of Baseline Models for Energy Conservation Measure Analysis, B.S, Department of Civil, Environmental and Architectural Engineering, Duke University, 2008.

Journal of Building Engineering 13 (2017) 116–126

K. Rakhshan, W.A. Friess [43] DesignBuilder. Calculation Options (05/07/2017). Available: 〈https://www. designbuilder.co.uk/helpv4.2/Content/Calculation_Options.htm〉. [44] EnergyPlus. (16/06/. Surface heat balance manager / processes (16/06/2017). Available: 〈https://www.energyplus.net/sites/default/files/docs/site_v8.3.0/ EngineeringReference/03-SurfaceHeatBalance/index.html〉. [45] World Bank Group (Electric power transmission and distribution losses (% of output)), 2017. Available: 〈http://data.worldbank.org/indicator/EG.ELC.LOSS. ZS〉. (Accessed 07 July 2017). [46] H. Radhi, Can envelope codes reduce electricity and CO2 emissions in different types of buildings in the hot climate of Bahrain? Energy 34 (2009) 205–215. [47] NREL. NREL: National Residential Efficiency Measures Database - Retrofit Measures. Available: 〈http://www.nrel.gov/ap/retrofits/group_listing.cfm〉.

(Accessed 11 October 2016). [48] E. Abdullah, Experts discuss life span of buildings, in: Gulf News, ed. UAE, 2001. [49] A.U.o. Sharjah, Life Expectancy of Buildings in the UAE, in: The Newsletter of the American University of Sharjah, ed, 2002. [50] S. Sorrell, J. Dimitropoulos, M. Sommerville, Empirical estimates of the direct rebound effect: a review, Energy Policy 37 (2009) 1356–1371. [51] G. Milne, B. Boardman, Making cold homes warmer: the effect of energy efficiency improvements in low-income homes. A report to the energy action grants agency charitable trust, Energy Policy 28 (2000) 411–424. [52] L. Schipper, On the rebound: the interaction of energy efficiency, energy use and economic activity. An introduction, Energy Policy 28 (2000) 351–353.

126