Energy demands and potential savings in European office buildings: Case studies based on EnergyPlus simulations

Energy and Buildings 65 (2013) 19–28

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Energy demands and potential savings in European office buildings: Case studies based on EnergyPlus simulations A. Boyano a,c,∗ , P. Hernandez b , O. Wolf a a European Commission, Joint Research Center (JRC), Institute for Technological Prospective Studies (IPTS), Edificio EXPO, Inca Garcilaso 3, E-41092 Seville, Spain1 b Tecnalia, Parque Científico y Tecnológico de Bizkaia, C/Geldo, Edificio 700, E-48160 Derio (Vizcaya), Spain c UCL Australia, International Energy Policy Institute, 220 Victoria Square, Adelaide, SA 5000, Australia

a r t i c l e

i n f o

Article history: Received 15 March 2013 Received in revised form 20 May 2013 Accepted 27 May 2013 Keywords: Energy consumption Energy savings Office buildings

a b s t r a c t This article presents key energy use figures and explores the energy saving potentials in office buildings across Europe by simulating several currently available scenarios. The information provided in this research work is based on a review of relevant literature and the results of EnergyPlus simulations of a reference office building that can be considered as a representative office building across Europe. Three locations were selected to represent the three climate zones in which Europe was divided. Lighting has been pointed out as an area with significant improvement potentials. These improvements have been investigated by using two scenarios with different lighting control systems. In both cases and regardless of the location of the office building, the energy savings were achieved with already existing technology and will bring important reductions in the overall energy bill. Two further aspects were investigated in this work: the first one is an improvement of the insulation of the windows and the external walls (U-value) and the second one the orientation of the building. Unlikely to the lighting improvements, the location of the buildings highly influences the amount of energy required by HVAC systems. It is observed that higher insulation factors are recommended in cold and medium climate zones while they should be carefully chosen in the warmer climate zones. Office buildings constructed in warm climate zones are subjected to higher heat gains that cannot be easily released from buildings within a well-insulated envelope. Consequently, the energy demand for cooling purposes is increased, affecting the overall energy consumption and the economic performance of the building. © 2013 Elsevier B.V. All rights reserved.

1. Introduction European energy consumption presents the following energy distribution for end-user sectors in 2007 [1]: 34.6% in transport, 24.6% household, 27.9% industry and 14.9% commercial and others. Buildings, commercial and residential, account for 38.7% of the

Abbreviations: BREEAM, BRE Environmental Assessment Method; DHW, domestic hot water; DGNB, Deutsche Gesellschaft fuer Nachhaltiges Bauen; ECP, Energy Performance Certificate; EPBD, Energy Performance Building Directive; HQE, Haute Qualité Environnementale; HVAC, heating, ventilation and air conditioning; NR, non-residential. ∗ Corresponding author at: UCL Australia, International Energy Policy Institute, 220 Victoria Square, Adelaide, SA 5000, Australia. Tel.: +61 881109991; fax: +61 882123039. E-mail address: [email protected] (A. Boyano). 1 The views expressed in this study are purely those of the authors and may not in any circumstances be regarded as stating an official position of the European Commission. 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.05.039

total energy consumption in Europe, which justifies a variety of initiatives for energy consumption reduction [1]. For example, the European Parliament and the council launched in 2002 the Energy Performance Building Directive (EPBD) 2002/91/EC and its recast 36/EC/2010 that obliges Member States to set up the minimum energy performance in each Member State, and to develop and implement an Energy Performance Certificate (EPC) to rate the energy performance of the buildings. In addition, there are voluntary schemes across Europe, e.g. BREEAM [3] in UK, HQE [4] in France or DGNB [5] in Germany that promote the design, construction and operation of high performance green buildings. Among the total final energy consumption of Europe, it is estimated that around 26% was consumed in residential buildings and 13% in non-residential buildings [2]. The tertiary sector (nonresidential building and agriculture) is among the fastest growing energy demand sectors and is projected to be 26% higher in 2030 than it was in 2005, compared to only 12% higher for residential buildings [6]. This fact points out the importance of investigating the use of energy in this sector.

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As reported by Spyroupoulos et al. [7] the breakdown of the final energy consumption by end use in European non-residential buildings (NR-buildings) is dominated by space heating and other heat uses, electric equipment, cooling and lighting. Electrical energy consumption in NR-buildings has exhibited a constant increase over the last years due to the extensive use of HVAC and office equipment (especially electronic devices and computers) and is expected, particularly in this sector, to increase from 42% in 2005 to almost 50% of the total energy consumption by 2030. Most of the available knowledge and data on energy consumption and the assessment of energy conservation measures are for residential buildings, while data for NR-building stock is quite limited. Office buildings are classified among the NR-buildings with the highest energy consumption. Their annual energy consumption in Europe varies from 100 to 1000 kWh/m2 a of conditioned floor space [8], depending on location, construction, HVAC and lighting installations, use and type of office equipment, operating schedules, etc. This paper has two objectives. First, it aims to provide new data about the energy consumption and energy demand profile of European office buildings. The energy consumption simulation software for the analysis of office buildings requires considering interactions among the building, HVAC systems and surroundings (climate conditions, orientation, etc.). Secondly, it aims at identifying and quantifying possible energy saving measures that can be easily implemented and will significantly reduce the energy bills from the sector. This information will facilitate the implementation of future actions to reduce the overall energy consumption and operational costs [9,10]. 2. Methodology The methodology proposed in this paper is based on building computer simulations using EnergyPlus. With regard to office building simulations, EnergyPlus is a well-recognized and accepted building energy analysis software tool [11,12] since it freely models heating, cooling, lighting, ventilating and other energy flows as well as water in buildings. EnergyPlus has been used previously in other studies to estimate building energy performance. For example, Griffith and Crawley [13] used EnergyPlus to propose a methodology for evaluating the energy performance for the US commercial building sector to estimate the technical potential of zero-energy buildings. Fumo et al. [11] presented a simple methodology to estimate the electricity and fuel consumption of a building by applying correction factors from the electricity and fuel bills. 2.1. Building description and building system A total of three weather scenarios are selected for this study. These three weather scenarios have been considered as representative of the three main climate zones in which Europe is divided. Further information can be found in [14]. Tallinn has been chosen to represent cold climate weather conditions representative, London corresponds to medium climate conditions and Madrid was chosen for the warmer climate conditions. The model building is supposed to have been constructed in 2010, and is comprised of a basement with three aboveground stories. The sample building chosen is an air-conditioned, rectangular plan that is the type of office building that best represents the typical office building found across Europe, especially in the main capital cities or major regional centers where the concentration of office buildings is higher (see Fig. 1). The gross heated area of the building is 4620 m2 . The gross heated volume is 13,860 m3 including offices, meeting rooms and auxiliary rooms. Office and primary work areas are heated or cooled

Fig. 1. Office building design selected as base case.

to 21 ◦ C in winter and 25 ◦ C in summer while secondary rooms are heated by neighboring areas and internal loads. Room heating is provided by a natural gas fueled conventional heating system with an energy efficiency of 80% and cooling is provided by a system with a seasonal COP = 3. Further data on the design of the base case are provided in Table 1 and in [14] Domestic hot water (DHW) is provided by natural gas water heaters. The estimated consumption is 0.2 l/m2 /day. 2.2. Simulation details Energy consumption for space heating and cooling, ventilation, DHW, electricity, lighting and office equipment is calculated separately but considers the influence of the internal heat loads. EnergyPlus is able to consider all outdoor and indoor parameters (outdoor temperature, position and global irradiance, wind speed and direction, shading and radiation characteristics of the glazing, energy gains through internal loads, air change rate, temperatures of surfaces surrounding the areas, etc.) for running a complete simulation of the energy consumption. The simulations were validated by comparing them with published measurements of similar office buildings and general buildings devoted to other uses. The main characteristics of the building envelope are presented in Table 2. The U-values of the external walls and the flat roof for the base cases correspond to national legislation requirements and these levels of insulation were increased in the different simulations of the alternative options under study. Table 2 also includes the main specifications of other building components under study. The occupancy schedule for the building was assumed to be between 7 h and19 h, Monday to Friday. The information concerning the work patterns and what appliances were in use was assumed as summarized in Table 3. This table shows an example of the equipment energy load in the office as well. The lighting zones correspond to the office rooms, existing corridors and other auxiliary rooms. The required workplace illumination during the occupancy was simulated using 500 Lux, which Table 1 Constructive characteristics of the base case office building. Size Geometry Walls Roof Glazing Floor

4620 m2 Lay-out 3 floors Rectangular shape Orientation East–west Insulated cavity wall, outer layer brickwork and concrete block as indoor layer Plasterboard, insulation and asphalt flat roof Wooden frame and double layer Insulated concrete, screed and timber flooring

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Table 2 Main characteristics of the building envelope (U-values in W/m2 K). Location

Case study

External walls

Windows

Floor

Roof

Glazinga

Ref.

Tallinn

Base case Variation 1 Variation 2

0.20 0.14 0.10

3.16 1.78

0.2

0.15

1.2

[15]

Madrid

Base case Variation 1 Variation 2

0.66 0.29 0.15

3.16 1.78

0.49

0.38

2.9

[18]

London

Base case Variation 1 Variation 2

0.30 0.18 0.12

3.16 1.78

0.25

0.2

2.0

[16,17]

a

Two levels of glazing have been considered: 30 and 50%. All base case simulations were performed considering 30% of glazing.

Table 3 Main operating conditions of the base case. Occupancy hours

7–19 h

Hours Monday to Friday

Density of occupation Metabolic rate Set point cooling Set point heating Hot water Ventilation Equipment

0.11 120 25 21 0.2 10 12

person/m2 W/person Celsius degrees Celsius degrees l/m2 day l/person second W/m2

is the minimum recommended value following the specifications in EN 12464-1.2009 [19]. 2.3. Presentation of the results 2.3.1. Energy consumption simulation Hourly energy consumption data for all sources were simulated. The energy consumption tends to be zero outside the working time but steadily increases due to the turning on of office equipment, lighting and HVAC, when the work day commences. 2.3.2. Comparison between simulations and literature and statistical data The investigated buildings, together with the HVAC systems and lighting were recreated in the EnergyPlus software. The total energy consumption was simulated based on the source and specific consumption. Table 4 provides the maximum, minimum and average energy consumption figures for office buildings in the three climatic zones, represented by the three cities, under study. The values shown are ranked in accordance with the total energy demand of the building during the use stage. Therefore some specific energy demands of the simulations classified as minimum energy demand can be higher than those of the buildings classified as maximum energy demand. This is the case of the cooling energy demand of the building within the minimum overall energy consumption in Madrid which value is higher than the cooling energy demand of the building classified as maximum overall energy demand. The average energy consumption was calculated as the arithmetical average of all the simulations carried out for each city, regardless of the construction parameters considered. The changes in the building design include three levels of insulation of the external walls and two of the windows, two levels of percentage of glazing (30 and 50%), the installation of renewable energy sources as solar thermal or PV panels or the installation of two levels of lighting control systems (partial and total). All in all, 42 simulations for each location were performed. The statistic analysis shows standard deviations of 6.73, 14.89 and 11.68 and median values of 106.93, 79.19 and 73.46 for Tallinn, Madrid and London, respectively. These values indicate the higher dispersion in the overall energy demand of the buildings located in Madrid in comparison to

Fig. 2. Breakdown average energy consumption depending on the locations.

the other locations which can be attributed to the higher influence of the energy saving measures investigated in this work. In addition, Fig. 2 provides the breakdown of the energy consumption for several specific base cases. Although the office equipment accounts for the highest energy consumption, mainly as electricity in all the cases, it has not been included in the chart. Office equipment energy demand was considered not to be part of energy demand of the office building itself and was presumed to be highly dependent on the office building function and end user’s behavior. In addition, it seems to have little room for improvement as reported by Spyropoulos et al. [7]. According to these authors, in most of the cases, the new energy efficient electric and electronic devices are the most common ones. Additionally, they reported that it is difficult to reduce their standby energy consumption for practical reasons: staff revealed that under heavy work pressure it is not practical to turn on/off the equipment during the working hours. For these reasons, no investigations were carried out regarding the office equipment energy use in this work. In all cases, HVAC and lighting energy demands present the highest values. Both energy demands have been selected in this study to investigate their potential energy savings. The values shown in Fig. 2 are in agreement with those reported in the literature [19] where the breakdown of the energy consumption of an office building during the use phase is approximately 40% for HVAC and 30% for lighting. 2.3.3. Energy use and costs The analysis of the energy saving potentials was carried out by comparing several scenarios. As a starting point, simulations were carried out considering the worst conditions: no lighting control, lower external wall insulation, single glazed windows, etc. and subsequently, simulations regarding possible improvements were carried out. These simulations were performed changing the aspect under study while all other aspects remained constant.

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Table 4 Maximum, minimum and average energy consumption of office buildings for the three climatic zones under study (kWh/m2 a). Final energy consumption (kWh/m2 a) Lighting

Heating

Cooling

HVAC

DHW

Auxiliary energy

Total

Tallinn

Base casea Maximumb Average Minimumc

39.02 39.02 35.03 17.00

53.10 55.37 55.30 49.19

7.66 9.49 7.56 7.23

60.76 64.85 62.86 56.43

3.89 3.89 3.98 3.89

3.26 3.26 3.34 3.26

106.93 111.03 105.21 80.57

Madrid

Base casea Maximumd Average Minimume

39.02 39.02 33.10 11.16

12.97 17.49 13.26 7.75

20.05 20.43 20.58 21.29

33.02 37.92 33.85 29.04

3.89 3.89 3.98 3.89

3.26 3.26 3.34 3.26

79.19 84.10 74.27 47.36

London

Base casea Maximumf Average Minimumg

39.02 39.02 34.66 15.16

17.18 17.11 17.83 13.04

10.10 16.61 10.21 9.54

27.29 33.71 28.04 22.59

3.89 3.89 3.98 3.89

3.26 3.26 3.34 3.26

73.46 79.89 70.02 44.90

a b c d e f g

Building characteristics corresponding to those specified in Table 2, no lighting control and 30% glazing area and no renewable energy installed. Uwalls = 0.20 W/m2 K, Uwindow = 3.157 W/m2 K, 50% glazing, no lighting control and no renewable energy installed. Uwalls = 0.10 W/m2 K, Uwindow = 1.776 W/m2 K, 30% glazing, total lighting control and PV panels as renewable energy sources installed. Uwalls = 0.29 W/m2 K, Uwindow = 3.157 W/m2 K, 30% glazing, no lighting control and no renewable energy sources installed. Uwalls = 0.15 W/m2 K, Uwindow = 1.776 W/m2 K, 30% glazing, total lighting control and PV panels as renewable energy sources installed. Uwalls = 0.18 W/m2 K, Uwindow = 3.157 W/m2 K, 50% glazing, no lighting control and no renewable energy sources installed. Uwalls = 0.12 W/m2 K, Uwindow = 1.776 W/m2 K, 30% glazing, total lighting control and PV panels as renewable energy sources installed.

Results are reported in absolute and relative values on an annual basis during the operation of the building. Energy consumption differences were calculated regarding the energy demand for the specific use under analysis as well as the overall energy consumption of the office building. Annual costs were calculated based on the average prices of natural gas and electricity during May 2012 as reported by http://www.energy.eu. Different prices were considered for each location. Annual cost saving potentials is reported solely in relative values to avoid the influence of possible energy price fluctuations. The cost saving values shown in this study should not be considered as exact values but they are provided to give a relative idea of cost-effectiveness of the measure under study.

3. Energy consumption and energy saving potentials 3.1. Energy consumption of the base cases Table 4 shows the overall energy consumption and its breakdown for several base cases. For the cold zone (Tallinn), the average final energy consumption amounts to 105.21 kWh/m2 a, while maximum and minimum values were 111.03 and 80.57 kWh/m2 a, respectively. Following an in-depth analysis of the data from the energy consumption, the estimated annual energy consumption for HVAC ranged between 64.85 and 56.43 kWh/m2 a. In the average values, HVAC accounts for 60% of the total final energy consumption (of which 12% is for cooling and 88% for heating), lighting follows with 33% and other factors comprise 6%. The analysis revealed that artificial lighting contributes significantly to the total energy consumption mainly due to the long operating time and the impossibility of controlling it (simulation done assuming no lighting control and 12 operating hours). For the medium climate zone (London), the average final energy consumption was 70.02 kWh/m2 a where the minimum and maximum values were 44.90 and 89.85 kWh/m2 , respectively. The energy consumption breakdown for the different end-uses in the office building of the medium climate zone shows the HVAC contribution to the total final energy consumption is around 40% (of which 36% is for cooling and 64% for heating). Lighting, in contrast to the other cases, is the highest contributor to energy consumption at 50% of the total and other uses amount to 10%. The estimated annual energy consumption for HVAC ranged between 22.59 and 33.71 kWh/m2 a. The percentage for cooling in the total final energy

consumption ranged between 12 and 21% and for heating from 17 to 44%. The estimated annual consumption for lighting ranged between 27 and 57%. Similarly, the average energy consumption was 74.27 kWh/m2 a for the warm climate zone (Madrid), with maximum and minimum values being 84.10 and 47.36 kWh/m2 a respectively. On average, lighting contributes to the total energy consumption at 45% of the total. The HVAC contribution to the total final energy consumption is 45% and other energy uses comprise 9%. Based on the simulations and the data obtained for the almost 200 base cases investigated, the average energy consumption in European office buildings is slightly over 40% of the final total energy consumption for lighting and 50% for HVAC. These figures point out the importance of developing feasible and cost-effective strategies across Europe to reduce both energy end demands. 3.2. Energy saving potentials An analysis of the obtained data shows that significant energy savings can be achieved in the European offices by the adoption of various energy conservation measures for lighting and HVAC. 3.2.1. Energy savings potential for lighting Lighting was identified as one of the major sources of energy consumption with high energy saving potentials. This information has recently been highlighted in numerous side events that took place during the United Nation Climate Change Conference [20]. Indeed, this is one of the aspects where the literature is more abundant. Several different measures were examined in this work. A typical first option, not relevant to this work, would be replacing the conventional incandescent lamps with more energy efficiency CFL lamps having the same output (lm/W). The energy savings of this approach has been largely reported by several authors. Among them, the study carried out by Bertoloni and Atanasiu [21] summarized the energy saving potentials of lighting in the residential sector in Europe. This study quantifies the savings potential and also identifies the barriers, introducing recommendations about the energy policy tools to be applied in the future. A second option, investigated in this work, includes the installation of lighting controls. Two possible scenarios were proposed: the first scenario considers the existence of partial lighting control (50% of the office facilities) reducing the operating hours that the

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Table 5 Potential energy consumptions and savings related to lighting depending on the building location. Location

% glazing

30 Tallinn 50

30 Madrid 50

30 London 50

Lighting control %

Elighting (kWh/m2 a)

Etotal (kWh/m2 a)

0 50 100 0 50 100

39.02 29.52 20.01 39.02 28.01 17.00

105.72 97.38 88.89 110.13 100.61 91.09

0 50 100 0 50 100

39.02 25.09 11.18 39.02 24.10 9.18

80.10 63.91 49.90 81.60 66.55 51.50

0 50 100 0 50 100

39.02 28.92 18.81 39.02 27.09 15.16

74.18 62.88 53.18 75.74 64.55 53.36

Esaving vs. Elighting (%)

Esaving vs. Etotal (%)

24.36 48.71

8.99 17.98

28.22 56.44

10.00 20.00

35.70 71.36

17.39 34.76

38.24 76.48

18.29 36.57

25.89 51.78

13.62 27.24

30.58 61.15

15.75 31.50

Energy cost Euro/year 39,989.05 34,443.20 28,817.53 41,563.37 35,157.83 28,752.43 61,988.58 47,118.63 32,917.18 64,290.39 49,074.76 33,859.35 36,067.67 28,625.11 22,114.98 37,061.45 28,943.62 21,345.53

% cost savingsa , b 13.87 27.94 15.41 30.82 23.99 46.90 23.67 47.33 20.63 38.68 21.90 42.41

a

Cost savings are estimated on the basis of the energy consumption, it does not take into account the investment costs, maintenance costs or end-of-life costs. % costs savings is calculated on the basis of the energy consumption, investment costs of the lighting control system of 69300 euros in 2010 and a lifespan of 20 years. In both cases energy cost are according to natural gas and electricity prices in May 2012 and reported in http://www.energy.eu. b

lamps are turned on while the second scenario includes the total lighting control (100% of the office facilities).

3.2.1.1. Scenario 1: Installation of partial lighting control (50% of the office building facilities). The use of lighting control allows for progressive reduction of artificial lighting depending on the availability of natural daylight, adjusting to the needs of the employees and visitors. The lighting studied under the base case is assumed to be working for 12 h non-stop. The detailed simulation carried out revealed that using lighting control for 50% of the facilities of the office building significantly reduces the number of hours that the installed lights are working (8.6 h on average) and consequently the lighting energy demand of the building decreases. In our case study, a representative sample of lighting control in the office rooms and service facilitates including stair cases, restrooms, etc. was considered. Table 5 shows the potential energy consumption and savings that can be achieved with partial lighting control, which vary depending on the building location due to different availability of daylight. Partial lighting control has the potential of saving between 9 and 37% of the total energy consumed, which amounts to 14–47% of the annual energy costs. This fact points out the importance of this measure from the economic viewpoint. The previous figures do not include the cost of installing the lighting control system as the simulations assumed that the energy saving measures are alternative designs of new office building. This means, that the differences between the total investment costs of the base cases and the alternatives under study are not significant, even in the alternatives were external walls have higher insulation. Further details can be found in [14]. Moreover, the possible difference in the investment costs can become negligible if the long lifespan of the building (50 years) and a discount rate of 3–5% are considered. On the other hand, if the implementation of the energy saving measures are considered in existing buildings, the investment costs required can make a difference in the values presented in Table 5 and some options can become less profitable. The use of manual or automatic dimming and occupancy sensors related to the possible energy savings was also reviewed by Dubois et al. [22]. Several studies have generated promising results showing that electrical energy use can be substantially reduced by using lighting control systems such as manual dimming and occupancy sensors. For manual dimming, the electric

lighting energy savings obtained range between 7–25% [23–25] while for switch-off occupancy sensors, lighting electricity savings range from 20-35% [23,26,27]. Both ranges of energy savings are in agreement with the results of this study.

3.2.1.2. Scenario 2: Installation of total lighting control (for 100% of the office building facilities). The use of total lighting control contributes significantly to the reduction in lighting energy as it decreases the operating hours to 4.6 h, depending on the presence of employees and visitors as well as the weather conditions and luminance. In the base case located in London, reduction between 52 and 62% for the lighting energy demand, or 27 to 32% of the total final energy consumption can be achieved. Similarly, reductions of total final energy of between 18 and 20% for the building located in Tallinn and 35–37% of total final energy in the building located in Madrid resulted from our simulations. As seen in Table 5, the use of total lighting control allows larger energy savings than partial lighting control. The estimated energy savings vary from 18 to 37%, with an average value of 28%, which represents a total annual energy cost savings between 28 and 47% with an average value close to 40%. This significant saving potential in annual energy costs, in comparison to other energy saving measures proposed in this study, is mainly due to the higher costs of electricity in comparison to natural gas in all the locations. It ranks this approach high on the list of options. The values obtained by the energy simulations are in line with those published by Dubois et al. [22], who carried out a literature review of the energy saving potential for lighting in the North European countries, including a recent inventory of Swedish office buildings revealing an average energy intensity of 21 kWh/m2 a for office lighting, with a variability according to the room type. In these studies, the reduction of the energy consumed in lighting is estimated to be cost-effectively reduced by 50% using the existing technology [28,29]. These authors suggested that, based on the European EN-15193 standard [30] which prescribes normal illuminance levels of 8–10 W/m2 for individual office rooms, a reference annual time of use of 2500 h and various lighting control strategies, the calculated annual energy use ranges from 20 to 7 kWh/m2 a, which still shows large potential for energy savings through control strategies (up to 65% reduction). Especially in the case of lighting control systems, further investigations carried out by the authors

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Table 6 Potential energy consumptions and savings related to window improvements depending on the building location. U-value (W/m2 a)

Lighting control (%)

Lighting demand (kWh/m2 a)

Heating demand (kWh/m2 a)

Tallinn

3.16 3.16 1.78 3.16

0.00 1.00 0.00 1.00

39.02 18.50 39.02 17.00

53.08 59.16 51.23 49.19

8.68 5.18 7.90 7.23

107.93 89.99 105.31 80.57

40,776.21 28,784.98 39,942.18 26,902.31

Madrid

3.16 3.16 1.78 1.78

0.00 1.00 0.00 1.00

39.02 10.18 39.02 11.16

12.78 16.87 8.69 7.75

21.90 16.50 22.79 21.29

80.85 50.70 77.66 47.36

63,139.48 33,388.26 62,708.20 35,854.53

London

3.16 3.16 1.78 1.78

0.00 1.00 0.00 1.00

39.02 16.99 39.02 15.16

15.95 21.87 14.02 13.04

12.83 7.26 10.17 9.54

74.96 53.27 70.37 44.90

36,564.56 21,730.26 34,587.88 20,059.17

Cooling demand (kWh/m2 a)

Total demand (kWh/m2 a)

Energy cost (Euro/year)

Ereduction vs. EHVAC (%)

Ereduction vs. Eheating (kWh/m2 a)

Ereduction vs. Ecooling (kWh/m2 a)

2.05 6.54

4.24 12.29

1.84 9.96

0.77 −2.06

3.95 6.59

0.68 −7.39

9.21 12.98

4.09 9.12

−0.89 −4.79

6.12 15.71

5.41 7.69

15.94 22.46

1.93 8.82

2.66 −2.28

Lighting control (%)

Energy saving (%)

Tallinn

0.00 1.00

2.43 10.46

Madrid

0.00 1.00

London

0.00 1.00

Cost saving (%)

and reported in [14] indicate that the additional investment costs (even in the cases of major renovations) are recovered in all the locations in much shorter periods than 20 years. Therefore, according to the data obtained in this work and those data reported by authors, the installation of lighting control systems seems to be a cost-effective measure to save both energy and total costs in all the locations. The influence of increasing the glazing in the building fac¸ade was also investigated. An increase in the glazing area allows larger daylight harvest and can bring a reduction of the energy lighting demand. Simulations were performed with fac¸ade areas reaching 30 or 50% of the total surface and results are shown in Table 5. As seen, an increase in the glazing area offers the possibility of reducing energy lighting demand in all the cases under study. These reductions range from 0.5 to 4.2% depending on the location and the lighting control considered. Generally speaking, in terms of cost, the increase of the glazing area during the design phase of a new office building can be beneficial as annual cost savings can go up to 4.2%. However, there are several cases in which cost savings may not be achieved. This is due to the increase of the HVAC energy demand either from higher solar heat gains during summer seasons or an increase of the heat losses during the winter seasons. Another possibility is that the costs of erecting the building with a larger glazing surface exceed the possible energy cost savings that can be achieved during its lifespan. Therefore, it is recommended that an overall energy performance analysis together with an economic analysis of the building be carried out before increasing its glazing area.

3.2.2. Energy savings potential for HVAC Although the energy consumption for HVAC is one of the most important factors in all the base cases under study, it is difficult to set up general rules or recommendations for its reduction as it strongly depends on the location, climate conditions, construction techniques and technologies used. Regardless of the characteristics of each building, the most straightforward measure would be to increase or decrease the indoor set point temperature during the heating or cooling seasons respectively. This measure is, not considered in this study since it is a decision of the end users.

For studying the energy saving potential in HVAC energy demand, two scenarios were considered. These scenarios examine the potential reduction of the cooling and heating loads in two ways: by improving the thermal envelope and by replacing double pane windows with triple glazing. 3.2.2.1. Scenario 3: Installing new insulated double or triple glazing. Data collected from national databases and national standards of different Member States about the minimum quality of the glazing required showed that a large number of office buildings are equipped with non-insulated single glazing or just double glazing facades and windows. This section investigates the potential of energy savings associated with an improvement in glazing. Keeping this goal in mind, two types of glazing were simulated for two different glazing areas (accounting for 30 or 50% of the total external area of the building) in each of the three locations under study. The U-value for the double glazing is considered at 3.16 W/m2 K while for a triple glazing the U-value was estimated at 1.78 W/m2 K. The calculations were again performed using EnergyPlus. Based on the results, by replacing double glazing with triple glazing the average annual reduction in HVAC demand can be up to 12, 13 or 23% or average savings on the total energy consumption of 10, 7 or 16% for Tallinn, Madrid and London, respectively, as reported in Table 6. The effect of the window characteristics is one of the main concerns in most of the energy saving potential studies related to sustainable construction. The size, shape, position, orientation and number of windows influence the daylight indoors, as does the framing and transmittance of glazing. Moreover, the energy requirements for HVAC also depend on the window design (in this case glazing areas) and possible heat gains. As shown in Table 6, although an improvement of the U-value of the window brings energy savings in the overall HVAC energy consumption, it is only in some locations that these energy savings are reflected in the annual energy cost. According to this study, those office buildings located in cold climate zones (e.g. Tallinn) are likely to see greater energy savings and energy cost savings than the office buildings located in warm climate zones, such as Madrid. Improving window insulation has a double effect. On one hand, the improved insulation avoids heat losses, reducing the energy

A. Boyano et al. / Energy and Buildings 65 (2013) 19–28

demand for heating during the cold season. On the other hand, this improvement does not allow the release of possible heat gains during the warm season, increasing the energy demand for cooling. The heat gains in office buildings are mainly due to the office equipment, lighting, and especially in the warm climate zone during the hot seasons, to the solar gains (solar radiation). These heat gains are compensated for by a higher cooling energy demand. This fact is reflected in the office building located in Madrid. As reported in Table 6, the energy demand for heating is reduced between 4 and 9 kWh/m2 a depending on the lighting control scenario but the cooling demand is increased 1 and 5 kWh/m2 a respectively. Although it seems that the energy reduction is larger in the heating demand it is not larger in the overall annual energy cost of the building. There are two main reasons for this result: 1) the office building is assumed to use electricity for cooling and natural gas for heating and 2) electricity is more expensive than natural gas in terms of thermal control performance. Therefore, the implementation of appropriate measures to reduce the HVAC energy demand in those locations with high electricity prices and higher cooling loads cannot just rely on an improvement of the insulation conditions, as in the case of Madrid which experiences up to −8% cost savings regarding the annual energy expenses. This study considers the influence of a single thermal parameter of the window in the overall energy performance of the office building, showing that higher insulation of windows or glazing is not always the best option. In this sense, when choosing a window or glazing it is highly recommended that the total energy balance be considered along with the specifics of the office building in which it is to be installed instead of focusing on just one of the thermal parameters individually. This conclusion has been pointed out by the authors in other works [31] where it was recommended to assess the replacement of the windows and external doors based on their energy balance and not just on singular thermal parameters such as U-value, g-value or L-50. 3.2.2.2. Scenario 4: Improving the thermal insulation of the walls. The thermal insulation of the external walls is examined in this section. Because of the large surface of the walls according to the design of the reference base case compared to the transparent area (windows) energy savings can be expected. The thermal insulation of the base case was first calculated assuming little improvements regarding the minimum thermal insulation of the walls required by the national legislation and standards where the office buildings were located. In the base case located in London (see Table 7), the thermal insulation of the external walls was increased from U-values of 0.30 W/m2 K up to 0.18 W/m2 K or 0.12 W/m2 K. The results show that by increasing the thermal insulation of the external walls energy savings can reach up to 20% of annual HVAC energy demand. However, if any lighting control system is installed, these energy savings are only slightly reflected in the annual energy costs savings due to an increase in the cooling demand. The improvement of the wall insulation leads to savings between 0.5 and 1.8% of the annual energy cost depending on the scenario. In the case of the office building located in Madrid (see Table 7), the thermal insulation of the external walls was considered from U-values of 0.66 W/m2 K up to 0.29 W/m2 K or 0.15 W/m2 K. The results show that even if the improvement of the thermal insulation of the walls can lead to energy savings (up to total energy savings of 8% and HVAC savings of 12%), the annual energy costs do not significantly improve. This fact is in accordance with the above mentioned effect and confirms that an excess of insulation in warm climate zones leads to higher cooling energy demands and consequently does not bring significant overall energy cost savings.

25

However, in the case of the office building located in Tallinn (see Table 7), representative of the office buildings located in cold climate zones, the improvement of the thermal insulation of the external walls does offer energy and energy cost savings. As seen in Table 7, there is a clear correlation between the improvement of the insulation and the savings in the energy demand (both HVAC and total energy demand) and the energy cost. This correlation between the energy savings and the energy cost savings is because the increased thermal insulation of the external walls leads to a decrease in heating energy demand, whereas the cooling energy demand remains approximately constant, leading to reductions in the overall energy consumption and costs. 3.2.3. Energy savings due to the office building orientation The orientation of the office building influences several aspects related to the energy performance, in particular daylighting and solar gains. A comparison of the energy demands of an office building located in London and oriented toward east–west or toward north–south was carried out in this study. Table 8 shows the results of this comparison. As seen, the total energy demand of the building decreases when the orientation is changed from east–west toward south–north due to the lower HVAC demand. In these simulations, lighting demand has been assumed to remain constant. However, lower lighting energy demand can be also expected due to the change in the orientation as the southern fac¸ade will harvest much more daylight. This fact is pointed out in the literature as reported in one of the most recent and interesting studies carried out by Susorova et al. [32]. These authors investigated the roles of several factors, such as the orientation and the window to wall ratio in several scenarios across more than six climate zones. The simulations were performed by using a model of a room in a typical office building created in Design Builder and EnergyPlus to evaluate the total annual energy consumption. The study showed that the energy consumption is significantly increased in hot climates and cold climates but only marginally in mild/medium climates. Energy savings for the optimized combinations were found to be on average 3% and 6% with a maximum of 10–14%. Although the overall energy consumption of the south–north oriented building is lower, an increase in the cooling demand can be expected. This increase is not significant in buildings located in medium climate zones but could be significant in those located in warm ones, leading to an increase in the overall energy consumption of the building and especially in the annual energy bill. Concerning this aspect, other studies reported that north oriented room consumption was always higher than for other orientations but they did not use solar shading devices in their research [33]. So the savings obtained for the south, east and west orientations may be lower in reality when solar shadings are used. The study of the influence of the orientation of the building is interesting since it is usually a measure that has negligible investment costs while being able to bring large energy savings. However, the building orientation can only be decided in certain cases, since the vast majority of office buildings are constructed following the requirements of the local authorities without the possibility of choosing the best conditions to decrease the final energy consumption of the building. When freedom is provided the analysis showed that a proper building orientation can significantly reduce the needs for HVAC and possibly lighting since the daylighting harvest is increased and the solar gains can be optimized. 3.2.4. Summary of the energy saving potentials According to the simulations and the literature reviewed in this study, the energy saving potential of the office buildings in Europe depends, to a certain extent, on the zone where they are located. Summing up the results of the different aspects investigated and

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Table 7 Potential energy demands and energy and energy cost savings related to external wall improvements depending on the building location. Lighting control (%)

U-wall (W/m2 a)

U-window (W/m2 a)

Heating (kWh/m2 a)

Cooling (kWh/m2 a)

TOTAL (kWh/m2 a)

3.16 1.78 3.16 1.78 3.16 1.78 1.78 1.78

54.23 52.41 52.94 51.09 52.06 50.21 58.62 49.19

8.58 7.81 8.69 7.91 8.76 7.99 4.42 7.23

108.98 106.39 107.80 105.17 107.00 104.36 90.20 80.57

3.16 1.78 3.16 1.78 3.16 1.78 1.78 1.78

13.06 10.02 14.60 8.36 10.69 7.71 18.30 7.75

21.58 22.38 21.97 22.88 22.14 23.10 14.95 21.29

80.81 78.57 82.74 77.41 79.00 76.98 51.57 47.36

3.16 1.78 3.16 1.78 3.16 1.78 1.78 1.78

17.64 15.01 16.47 13.83 13.76 13.23 21.95 13.04

11.10 9.95 15.89 10.21 11.50 10.35 6.37 9.54

74.91 71.14 78.53 70.22 71.43 69.75 54.29 44.74

Esavings vs. Etotal (%)

Cost Euro/year

Cost savings (%)

EHVAC vs. Etotal (%)

(a) Tallinn 0.20 0.14 0.10 100.00

0.20 0.10

1.08 1.14 1.82 4.23 10.67

0.54 0.57 0.91 0.96

1.88 2.01 3.15 7.35

7.50

10.49

62,932.99 62,739.24 63,757.46 62,690.55 62,728.01 62,694.80 33,316.62 35,854.53

−1.31 0.08 0.33 0.07

−5.59 3.57 5.21 11.04

−7.62

12.67

35,921.38 34,675.76 38,465.79 34,570.14 35,306.52 34,517.73 22,296.70 19,966.82

−7.08 0.30 1.71 0.46

−12.60 3.67 12.10 17.95

10.45

20.26

(b) Madrid 0.66 0

0.29 0.15

100

0.66 0.15

−2.40 1.47 2.23 4.73 8.17

(c) London 0.30 0

0.18 0.12

100

0.30 0.12

−4.83 1.29 4.64 6.89 17.59

A. Boyano et al. / Energy and Buildings 65 (2013) 19–28

0

40,973.73 40,146.87 40,752.38 39,916.37 40,602.51 39,763.29 29,082.96 26,902.31

A. Boyano et al. / Energy and Buildings 65 (2013) 19–28

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Table 8 Energy consumption of the building located in London associated to its orientation. Energy demand

East–west (kWh/m2 year)

North–south (kWh/m2 year)

Esaving vs. Etotal (%)

Lighting Auxiliary energy Heating Cooling Hot water

38.52 3.22 16.96 9.97 3.84

38.52 3.22 15.42 9.63 3.84

0.00 0.00 2.13 0.48 0.00

discussed in this work, and considering the estimations of the office building stock in Europe reported in [14] in 2010, an annual energy saving of approximately 400 TWh/y could have been achieved. These energy savings are estimated by using currently available technology and construction techniques for each location. Taking into account that the office stock is expected to be increased and refurbished at an annual rate of 2%, and the current energy saving technologies are expected to improve, even higher energy savings can be forecast in the medium and long-term. Even if these improvements in the technology are not considered in the analysis, an overall energy performance improvement of 4% in 2020 and 10% in 2050 can be expected. Moreover, there are several aspects of the office buildings that have not been investigated in this work where further energy saving potentials could be expected, e.g. energy savings due to water consumption reduction, the installation of passive constructive elements or the recovery of heating exhaust gases. As a consequence of the limited aspects investigated in this study, these results are rather conservative, reporting an overall annual energy saving potential in the new and refurbished European office buildings of approximately 30%, with energy savings of approximately 10% in 2020 and 23% in 2050 in the European office building scenario with respect to a business as usual scenario. Indeed, there are other studies that reported higher energy saving potentials for the European building sector. For example, the Action Plan for Energy Efficiency [34] reported an estimated savings potential in the building sector of 28% in 2020 and the World Business Council for Sustainable Development recently published a study [35] that asserts that a 60% reduction in energy use in buildings is possible by 2050. Finally, the Energy Performance of Building Directive 36/EC/2010 claims for public buildings to be constructed with nearly zero energy consumption by 2018 and beyond would probably exceed the values estimated in this study. From the environmental point of view, the above mentioned energy saving potentials will bring benefits to our society regardless the location or measure undertaken. There is no doubt that any energy saving measure will contribute to the preservation of the environment and avoidance of the depletion of the resources. However, the quantification of the environmental benefits strongly depends on the location of the building as well as the energy source used to satisfy its energy demand. Generally speaking, the environmental impacts attributed to electricity consumption, even depending on the local or national electricity mix, are higher than those attributed to other energy sources such as natural gas, being those energy saving measures focused on electricity saving of higher priority. Further information can be found in [14].

4. Conclusions One of the most significant barriers for achieving substantial building energy efficiency improvements is the lack of knowledge about the factors determining energy use. Therefore, one of the main objectives of this work is to investigate the methodologies and techniques for simulating the total energy use in office buildings across Europe and to demonstrate how the resulting information can be used to provide meaningful advice for better building energy performance.

Energy consumption data from new office buildings across Europe were obtained through EnergyPlus simulations. Although the results obtained in these simulations are in accordance with other authors, their extrapolation should be carefully done as the models were built on additional assumptions briefly reported in Sections 2.1 and 2.2 of this work. Electricity is the main energy source for all the base cases under study used for lighting, office equipment and cooling. Natural gas was assumed to be used for heating and domestic hot water. Electricity is considered to be a more expensive and higher polluting energy source than natural gas and, therefore, although the overall energy demand is desired to be reduced, the electrical energy savings are highly recommended. In this context and based on the results of our simulations, the contribution of the final energy consumption end-uses to the overall final energy consumption amounts on average to 46% for lighting, 23%, for heating and 20% for cooling. It was revealed that lighting plays a significant role in the total energy demand mainly because of its large operating time. Reducing the equivalent operating time by installing partial or total lighting control can result in total energy savings of up to 18% (for partial lighting control) or 36% (for total lighting control). The evaluation of energy saving measures for HVAC was focused on the insulation improvement, although the literature review revealed that regulation of the indoor set point temperature is the easiest and most straightforward measure. Improvement of the envelope was studied by decreasing the U-values of windows as well as those of the external walls. Because of variations in the location of the building and the possible heat gains (mainly due to the office equipment and the solar gains) an improvement of the thermal insulation of the envelope may not be the best recommendation, especially in those locations where solar gains are significant, such as the Mediterranean climates. This fact points out the responsibility of the designers to choose the best design and materials in accordance with the site. Finally, the energy savings potential due to the orientation of the building were also investigated resulting in average energy savings between 3 and 6%. Energy saving potentials can be enhanced by applying a combination of these factors and other aspects not investigated in this study which may have a significant impact on the energy bill of the building, especially if the electricity demand of the building is reduced (e.g. in the case of lighting). However, a reduction of the overall energy demand may not be reflected in the annual energy bill if an increase of the electricity demand occurs. This fact has been observed in the office buildings located in warmer climate zones and suggests the need of carefully implementing the optimal measures (optimal insulation conditions) to reduce the air conditioning energy demand in those locations with high electricity prices and high cooling loads.

Acknowledgments Results presented in this paper are part of a research project for the development of the Ecolabel and GPP criteria for office buildings, which JRC-IPTS acquired the commitment to lead, and

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A. Boyano et al. / Energy and Buildings 65 (2013) 19–28

involved CIRCE (Universidad de Zaragoza), GiGa (Universidad Pompeu Fabra) and TECNALIA Research & Innovation. The authors would like to acknowledge the fruitful discussions within the project and to thank the European Commission for funding this research. A. Boyano is debt to the European Commission for her GH30 contract. References [1] Europe’s Energy Position: Markets and Supply. Market Observatory for Energy, Directorate General for Energy, REPORT 2009. [2] European Union Energy and Transport in Figures – 2009 Edition, Office for the Official Publications of the European Communities, Luxembourg, 2009, 228 pp. [3] BREEAM, BRE Environmental Assessment Method, available at: http://www. breeam.org/ [4] HQE, Haute Qualité Environnementale, available at: http://www.certivea.com/ assets/download/certification HQE/en/a8a2d-Brochure-INTL-EN-V7.pdf and http://assohqe.org/hqe/ [5] DGNB, Deutsche Gesellschaft fuer Nachhaltiges Bauen, available at: http://www.dgnb.de/ [6] P. Capros, L. Mantzos, V. Papandreou, N. Tasios, EU Energy and Transport Trends 2030 – Update 2007, Office for Official Publications of the EU Communities, Luxemburg, 2008, 158 pp. [7] G.N. Spyroupoulos, C.A. Balaras, Energy consumption and potential of energy savings in Hellenic office buildings used as bank branches: a case study, Energy and Buildings 43 (2011) 770–778. [8] D. Caccaveli, H. Gugerli, TOBUS – a EU diagnosis and decision making tool for office building upgrading, Energy and Buildings 34 (2002) 113–119. [9] A. Hernandez, F.A. Sanzovo, Use of Simulation Tools for Managing Energy Demand, available from: http://simualtionresearch.lbl.gov/EPO/ep main.html [10] S. Gamou, R. Yokoyama, K. Ito, Optimal unit sizing of cogeneration systems in consideration of uncertain energy demands as continuous random variables, Energy Conversion and Management 43 (2002) 1349–1361. [11] N. Fumo, P. Magro, R. Luck, Methodology to estimate building energy consumption using EnergyPlus benchmark models, Energy and Buildings 42 (2010) 2331–2337. [12] U.S. Department of Energy, Energy Efficiency and Renewable Energy Office, Building Technology Program, Building Energy Software Tools Directory, available from: http://apps1.eere.energygov/buildings/tools directory [13] B. Griffith, D. Crawley, Methodology for Analyzing the Technical Potential for Energy Performance in the US Commercial Building Sector with Detailed Energy Modeling, available from: http://simulationresearch.lbl.gov/EP/ep main.html [14] EU Ecolabel and Green Public Procurement for Buildings, JRC-IPTS, available from: http://susproc.jrc.ec.europa.eu/buildings/stakeholders.html [15] NORTHPASS Project, available from: http://northernpass.us/project-overview [16] National Calculation Methodology (NCM 2008), available from: http://www.ncm.bre.co.uk/ [17] UK Building Regulation (Part L, 2010), Conservation of Fuel and Power, New Dwellings 2010 Edition, available from: http://www.planningportal. gov.uk/buildingregulations/approveddocuments/partl/approved#Approved DocumentL1A

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