Analysis of different shading strategies on energy demand and operating cost of office building

Analysis of different shading strategies on energy demand and operating cost of office building Kwiatkowski, J 1,2 ; Rucińska, J 1,2 ; Panek, A 1,2 1 Warsaw University of Technology, Faculty of Environmental Engineering, 20 Nowowiejska Street, 00-653 Warsaw, Poland 2 National Energy Conservation Agency S.A., 20 Swietokrzyska Street, 00-002 Warsaw, Poland European regulatory efforts towards increasing energy efficiency of buildings are focusing on building requirements. One of the main issues in office buildings is area of glazing and connected with that energy gains from solar radiation. The shadings systems can be used in order to decrease solar gains. Thus, in the paper, using DesignBuilder software different shading devices to secure proper indoor quality and energy efficiency are examined. The six shading strategies for five European climatic data were applied in the building. It was showed that using shading devices energy demand for cooling can be decreased but in the same time energy demand for heating or lighting is increased. It was also presented that some shading strategies will cause even higher operational cost in comparison to the building without any shading devices. Finally the global cost has been calculated in order to verify if any shading strategy is economically viable. Key words: office building; shadings, energy needs, global cost. 1. Introduction The Recast of the Directive on the Energy Performance of Buildings (the EPB Directive) [1] came into force on 9 June 2010. EU member states should until 9 June 2012, publish the relevant laws and administrative regulations necessary to implement its provisions. European regulatory efforts towards increasing energy efficiency of buildings are focusing on building requirements. All new public building after 31.12.2018 must be nearly zero energy buildings. Such requirement can be very hard to implement in office buildings as the energy needs for heating, cooling and lighting to provide internal comfort are typically very high. One of the main issues in office buildings is area of glazing and connected with that energy gains from solar radiation. In winter season it is required to use as much free sun energy as possible and in such way to decrease heating needs of building. In summer period solar gains can cause needs of cooling in order to provide comfortable environment. Thus shadings 1

systems are used to decrease solar gains. However using shading devices not only solar gains are limited but also light transmittance is decreased. In order to keep required light comfort more electricity for artificial light is used, what can generate higher cooling needs. This shows that energy balance of the building is very complex and none of the system can be treated separately. The aim of this paper is to examine different shading devices to secure proper indoor quality and energy efficiency. The calculation of energy demand for heating, cooling and artificial lighting were provided for office building. In such buildings most of the façade is made from glass and influence of solar irradiation can be high. The calculation were done for five weather data for different climates across the Europe taking into account potential of increase of temperature and changes in solar irradiation caused by climate changes. For each shading strategy and climate the operational cost of the energy needs of the building were estimated. Finally using Life Cycle Cost methodology for the variants where shading devices allow for energy cost decrease the global cost was calculated. In such way the decision criteria about choosing shading strategy can be set. The analysis of shading devices use in the building are a part of the Integrated Energy Design process. Such calculation provided at the concept/design stage of the building process helps the design team to choose the best solution for the building. 2. Methodology of calculation In this analysis the calculation of energy demand for heating, cooling and artificial lighting is carried out. In order to verify economic effectiveness of different shading strategy the calculation of global cost also is given. Energy simulations are carried out in the program for the comprehensive thermal analysis of buildings DesignBuilder [2]. The software is compatible with the guidelines CIBSE AM11 "Building energy and environmental modelling". DesignBuilder uses the latest Energy Plus simulation engine for energy calculation. Energy Plus is the U.S. DOE building energy simulation program for modelling building heating, cooling, lighting, ventilating, and other energy flows. In the program a numerical 3D model of the building can be created. Next each envelope is described by heat transfer coefficient and for windows also total solar transmission and light transmission. For defined zones following data can be set: occupancy, internal loads, light quality, ventilation rates, HVAC systems and usage schedules of each parameter. In the last stage the weather data are set. This detailed building model allows the calculation of the energy consumption for heating, cooling and artificial lighting. The cost calculation were provided according to methodology framework for calculating costoptimal levels of minimum energy performance requirements for buildings and building elements which is presented in Annex 1 to the Regulation No 244/2012 [3]. 2

In the Regulation two methodology are given: for financial and for macroeconomic calculation. In this analysis a methodology for a financial calculation is used. When determining the global cost of a measure/package/variant for the financial calculation, the relevant prices to be taken into account are the prices paid by the customer including all applicable taxes including VAT and charges. Global costs for buildings and building elements shall be calculated by summing the different types of costs and applying to these the discount rate by means of a discount factor so as to express them in terms of value in the starting year. 3. Climate description The climate in the Europe vary from place to place and even the change of the climate at one localization can be notice. In order to verify the influence of shading strategy at different European climates five weather data sets were used in calculations. The chosen data represent cold (Helsinki), medium (Warsaw, London and Milano) and warm (Barcelona) climates. In Table 1 the main parameters of each climate is presented. Table 1. Characteristic parameters of climatic data for chosen localizations Climate Temperature [ C] Wind [m/s] Horizontal Solar Radiation [kwh/m 2 ] Min. Max. Average Average Direct Diffuse Total Warsaw -15.35 31.75 8.37 4.45 376.22 618.28 994.50 Milano -9.35 33.50 12.41 1.16 472.29 596.94 1069.23 London -5.78 31.11 10.24 3.24 413.59 591.23 1004.82 Barcelona -1.00 30.48 15.72 3.36 1349.46 678.77 2028.23 Helsinki -21.44 28.62 5.18 3.84 377.32 566.12 943.44 It can be noticed that the highest average temperature and horizontal solar radiation are for the Barcelona and the lowest for the Helsinki. The temperature amplitude is the highest for the Helsinki and the lowest for the Barcelona. The horizontal solar radiation for Barcelona is two times higher than for the other localizations. In the medium climates the highest temperature is for the Milano and the lowest for the Warsaw. It can be noticed that the horizontal solar radiation for medium climates do not vary a lot. Such chosen climates cover a wide range of European regions, from cold north, by medium central up to warm south. The variety of localizations allow to examine the same shading devices under different weather condition. 3. Test building In the most of the office building the façade is made from glass. In order to decrease solar gains a shading devices are applied. This can influence on higher energy demand for artificial 3

light if a proper light quality must be assured. Therefore an office building has been chosen as the test building for this study. Test building has the shape of a parallelepiped with a length of 64.9 m, width of 30.0 m and height of 29.6 m. It has eight above ground and two underground floors. The total area of the building is 15 231 m 2. In the Figure 1 the building shape and typical above ground floor is showed. Figure 1. Test building model (on the left) and typical aboveground floor (on the right) (source DesignBuilder model) At the ground floor a commercial spaces were located and at the upper floors open space office was established. It is typical for office buildings to have a commercial and restaurant part at the ground level. The entrance to the building is on the north west side. It was designed that on each elevation the ratio of windows to wall is the same and is equal to 80%. The building was designed according to Polish building law. In Table 2 the most important parameters are presented. Table 2. Table with characteristic building parameters Parameter Unit Value Heat transfer coefficient of external walls W/m 2 K 0.27 0.29 Heat transfer coefficient of roof W/m 2 K 0.15 0.20 Heat transfer coefficient of ceiling over an unheated garage W/m 2 K 0.35 Heat transfer coefficient of windows W/m 2 K 1.50 Total solar transmission - 0.35 Light transmission - 0.60 Office lighting (>500 lux) W/m 2 12.5 Internal loads W/m 2 40 4

Efficiency of the heat recovery % 70 Infiltration 1/h 0.7 In the building HVAC system has been designed. The ventilation rates is provided by mechanical ventilation with 70% of heat recovery. The heating and cooling is realized by fancoil units. The heat source in the building is gas boiler and the cool source is air chiller. A total efficiency of heating system is 0.8 and cooling 3.8. In order to minimalize energy demand for lighting three step control has been set. 4. Shading strategy The shading devices and reduce the solar gains but at the same time the daylight ration is also decreased. In order to achieve good visible comfort artificial light must be turn on. Hence the shading devices can cause higher energy demand for lighting and in some cases even higher energy demand for cooling. Therefore, in order to examine this phenomena the six different shading strategies has been applied in the analysis: two with internal movable devices, two with external movable devices and two with external stationary devices. In Table 3 each of strategy is described. Table 3. Description of shading strategy variants Shading variant Basic S1 S2 S3 S4 S5 S6 Description Without shading devices External shading with blind with high reflectivity slats External shading with blind with low reflectivity slats Internal shading with blind with high reflectivity slats Internal shading with blind with low reflectivity slats Overhang with depth of 1 meter Louvre with 3 blades of depth of 1 meter with vertical spacing of 0.5 m The control system of movable shading was controlled by solar set point of 220 W/m 2. Shading is active if beam plus diffuse solar radiation incident on the window exceeds the solar set point. It was also set that the shading was not active from 1 st of November until 30 th of March. Such assumption was establish in order to maximize solar gains and daylighting in the heating season and to minimize solar gains in cooling season. Although the used climates are different the same assumptions of shading devices were set. The aim of the paper is to examine the same shading strategies and not to optimize it for each weather data. 5

5. Results of energy calculation The calculation of the energy demand for heating, cooling and artificial lighting were provided for office building with six different shading strategies and building without and shading devices. Also five different climatic data has been used. In the Table 4 the result of the calculation is given. Table 4. Results of energy calculation for different shading strategy and climates Localization System Final energy demand for different shading strategy [kwh/a] Basic S1 S2 S3 S4 S5 S6 Warsaw Heating 295 286 297 442 297 783 295 851 295 299 309 345 317 322 Cooling 247 613 213 332 213 022 240 392 266 429 220 859 208 376 Lighting 189 026 215 313 258 676 207 547 256 720 192 397 206 873 Milano Heating 137 795 137 968 137 995 137 848 137 790 143 328 145 360 Cooling 355 699 325 982 325 551 350 570 375 991 326 408 314 818 Lighting 157 949 193 417 233 188 183 498 231 357 161 878 177 376 London Heating 60 199 61 521 61 745 60 509 60 222 66 570 71 330 Cooling 247 044 213 855 213 271 240 618 265 377 219 587 207 531 Lighting 180 347 207 529 249 631 200 695 247 641 183 981 200 326 Barcelona Heating 1 698 1 718 1 725 1 703 1 700 2 151 2 721 Cooling 482 203 431 920 430 321 470 358 503 427 438 271 416 853 Lighting 111 501 135 596 188 194 129 150 185 791 113 396 123 734 Helsinki Heating 570 942 582 359 583 760 573 217 570 078 585 790 596 327 Cooling 179 886 145 698 145 919 173 155 202 059 155 266 142 354 Lighting 201 233 237 555 289 808 227 218 288 473 203 088 212 931 It can be noticed that the highest heating and lighting demand is obtained for Helsinki and the lowest for Barcelona climate. From the other hand the highest cooling demand is for Barcelona and the lowest for Helsinki. The results for the medium climates also varies. It can be noticed that using shading devices the energy needs for heating, cooling and lighting are changing for every localization. The energy needs for different shading strategies are presented in Figure 2. 6

Heating demand [MWh] Cooling demand [MWh] 600 550 500 450 400 350 300 250 200 150 100 50 0 550 500 450 400 350 300 250 200 150 100 50 0 Basic S1 S2 S3 S4 S5 S6 Helsinki Heating Warsaw Heating Milano Heating London Heating Barcelona Heating Basic S1 S2 S3 S4 S5 S6 Helsinki Cooling Warsaw Cooling Milano Cooling London Cooling Barcelona Cooling 300 Artificial lighting demand [MWh] 250 200 150 100 50 0 Basic S1 S2 S3 S4 S5 S6 Helsinki Lighting Warsaw Lighting Milano Lighting London Lighting Barcelona Lighting Figure 2. Energy demand for different variants of calculation (top left heating; top right cooling, bottom left lighting) It can be noticed that for the every climatic data a pattern of energy changes is the equal for the same shading strategy. The energy for heating for every variant increases when the shading devices are applied. The only exception is for Helsinki and internal blinds with low reflectivity slats. This can be affected with additional artificial lighting demand. It can be noticed that for each climate and internal blinds with low reflectivity slats the energy demand for cooling increases. For other cases the energy demand for cooling is lower than for the basic variant. This is caused by additional artificial lighting demand and internal assembly of the blinds. The solar radiation is passing the windows and heats up the blinds inside an internal space. Thus the solar gains are not decrease efficiently and if the additional gains from artificial lighting will be added the energy demand for cooling gets higher. It can be 7

noticed that the highest reduction in cooling demand was obtained using louvre shading. However the lighting demand increases in those variants. The energy calculation are complex and if one of the demands decreases the other increases. Thus it is important to reduce energy results to a common denominator. The operational cost can be used as such parameter. 6. Cost analysis In order to compare energy results the operational cost for each variant were calculated. The calculation was based on fuel price for Poland. The heating source is gas boiler and the gas price is equal to 0.20 PLN/kWh. For the cooling and lighting demand the electricity price of 0.54 PLN/kWh was used. In Table 5 the results of the operational cost are presented. Table 5. Results of operational cost calculation for different shading strategy and climates Localization Cost of energy for heating, cooling and artificial lighting [PLN/a] Basic S1 S2 S3 S4 S5 S6 Warsaw 294 842 290 957 314 274 301 057 341 560 285 027 287 699 Milano 304 929 308 069 329 318 315 966 355 526 292 340 294 857 London 242 831 239 852 262 316 250 411 289 074 231 240 234 509 Barcelona 320 940 306 802 334 343 324 075 372 518 298 330 292 461 Helsinki 319 993 323 428 352 045 330 845 378 903 310 670 311 119 In Table 5 the variants for which operational cost are lower than for basic building were highlighted. It was showed that only shading strategy with overhangs (S5) and louvre (S6) allow for decrease operating cost in every considered climate. For shading strategy with external blind with high reflectivity slats the lower operational cost were obtained for Warsaw, London and Barcelona climates. For other variants the energy cost are higher than for the basic case. Even if the operational cost are lower than for the basic case the global cost can be higher as the extra investment cost are required for shading devices. Thus the global cost was calculated including an investment cost and discounted over 20 years operational cost. The results are presented in Table 6. Table 5. Results of operational cost calculation for different shading strategy and climates Localization Global cost in 20 years [PLN] Basic S1 S5 S6 Warsaw 5 932 896 7 998 222 5 962 185 6 244 242 8

Milano 6 149 389-6 123 341 6 402 742 London 4 901 085 6 984 794 4 895 127 5 189 505 Barcelona 6 483 860 8 342 228 6 255 757 6 365 858 Helsinki 6 418 744-6 457 912 6 694 861 The calculation was done for the basic variant and the variants where operational cost are lower than for the basic case. For this analysis the discount rate of 4% was used as it is recommended by Regulation no 244/2012 [3]. Also the evolution of energy prices was done according to Annex II [4] of this Regulation. The increase of fuel prices has been extrapolated for 20 years of calculation and it is equal to 3.9% for gas and 4.1% for electricity. It can be noticed that only for four variants from thirteen the global cost is lower than for the basic case. The result shows that for the Barcelona climate two shading strategies are economically viable: overhangs (S5) and louvre (S6). For the Milano and London climate the lower global cost was obtained for overhangs (S5) only. It was shown that using shading devices not always provide to decrease of the operational cost related to energy demand. Even if the operational cost are lower the global cost with included extra investment cost of the shading devices can be higher. 7. Conclusion The windows and shading devices play an important role in ensuring the comfort of indoor climate conditions. On one hand, they influence to a large extent the heating/cooling demand of buildings, on the other hand they are an irreplaceable source of daylight. In the paper the analysis of six different shading strategies under five European climates was examined for office building. The calculation was done for heating, cooling and lighting demand. It was showed that using shading devices all three demands are changing. In order to choose the best shading strategy the global cost as decision criteria has been estimated. The calculations were done only for the variants with lower operational cost than for the basic variant. It was noticed that only for four variants the global cost is lower than for the basic case. Those variants were overhangs (S5) for Barcelona, Milano and London and louvre (S6) for Barcelona. It was shown that using shading devices not always provide to decrease of the operational cost related to energy demand and even if so, the global cost in life time can be higher. 8. Acknowledgements Part of the work presented in this paper has been done under the IEE/11/989/SI2.615952 project called MaTrID (Market Transformation Towards Nearly Zero Energy Buildings Through Widespread Use of Integrated Energy Design). 9

9. References [1] Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (OJ L 153, 18.06.2010). [2] http://www.designbuilder.co.uk/documents/designbuilder-flyer-v1a.pdf [3] Commission Delegated Regulation (EU) No 244/2012 of 16 January 2012 supplementing Directive 2010/31/EU of the European Parliament and of the Council on the energy performance of buildings by establishing a comparative methodology framework for calculating cost-optimal levels of minimum energy performance requirements for buildings and building elements. [4] EC (2010) European Commission, Directorate-General for Energy. EU energy trends to 2030 UPDATE 2009. Luxemburg, 2010. 10