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On the potential of retrofitting scenarios for offices
Building and Environment 37 (2002) 557 – 567
www.elsevier.com/locate/buildenv
On the potential of retro#tting scenarios for o$ces E. Dascalaki1 , M. Santamouris ∗ GR-BES, Group Building Environmental Studies, Department of Applied Physics, University of Athens, University Campus, Build. Phys. V, 157 84 Athens, Greece
Abstract Within the framework of OFFICE research project the energy conservation potential of combined retro#tting actions was investigated for #ve building types in four di1erent climatic regions in the European continent. The studied actions involve interventions on the building envelope, HVAC and arti#cial lighting systems as well as integration of passive components for heating and cooling. Interventions a1ecting the performance of the building in the global aspect were also assessed. The potential of retro#tting actions proposed for each building type was assessed through energy simulations using high-accuracy computer models and climatic data from 10 locations in South Mediterranean, Continental, Mid-Coastal and North Coastal Europe. Analysis of the results revealed common trends in the energy performance of di1erent building types and permitted to extract information on the most suitable retro#tting interventions in each. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: O$ce building types; Retro#tting potential; Energy performance
1. Introduction Retro#tting of o$ce buildings has gained interest during the past few years mainly due to increasing energy and air-quality problems. Important work has been carried out by architectural and engineering groups to retro#t o$ce buildings and to improve their energy performance. Results show that cost-e1ective energy savings in the order of 20 –30% can be achieved in o$ce buildings, while there are indications for greater savings resulting from major retro#tting projects. Based on the existing experience, guidelines for energy-e$cient retro#tting of o$ce buildings have been published by various national and international organizations [1]. Existing energy-related retro#tting actions mainly aim towards a more rational use of energy in the o$ce buildings, neglecting aspects related to passive solar heating, daylighting and passive cooling of buildings. As a result of recent scienti#c research on passive solar heating, cooling and daylighting systems and techniques existing knowledge on the above topics has increased. Current research on ∗
Corresponding author. E-mail address: [email protected] (M. Santamouris). 1 Current a$liation: National Observatory of Athens, Institute for Environmental Research and Sustainable Development, Group Energy Conservation, I. Metaxa & Vas. Pavlou, Palaia Penteli, 152 36, Greece.
retro#tting involves studies of the energy conservation potential of combined actions applied in the existing buildings. Retro#tting actions involve combined interventions on the main energy-related aspects of the building, including its outer envelope and installed systems for heating, cooling, ventilation and lighting with a simultaneous incorporation of passive systems and techniques. The objective of such retro#tting actions is to optimize the energy performance of the building, while maintaining thermal and visual comfort as well as acceptable air quality for the occupants. The e1ectiveness of retro#tting scenarios on the energy performance of an o$ce building depends on speci#c characteristics related to its architectural structure, its operational features and relation to the surrounding environment. Despite the di1erences observed among o$ce buildings throughout Europe, it is possible to de#ne a typology, classifying existing buildings into groups presenting common energy-related features. This classi#cation permits the investigation of the energy behavior of di1erent building types, as well as the assessment of their response to di1erent retro#tting strategies. As climate is one of the main parameters a1ecting the energy behavior of a building, the e1ectiveness of a retro#tting intervention is strongly dependent on the climatic region of reference. The aim of this work is to investigate the energy conservation potential of selected retro#tting interventions on #ve
0360-1323/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 1 3 2 3 ( 0 2 ) 0 0 0 0 2 - 1
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o$ce building types in four di1erent climatic zones of Europe. In the following sections, the adopted methodology is presented, along with the particular characteristics of each building type. Retro#tting scenarios proposed for each building type are given and the variation of their energy-saving potential as a function of climate is discussed.
• Mid-Coastal: Kew (UK). • North Coastal: Trondheim (NO), Copenhagen (DK), Gothenburg (SE). In the following sections, the general trends regarding the existing situation as well as the potential of proposed retro#tting interventions for each building type are discussed.
2. Methodology In the framework of the OFFICE research project, 10 di1erent buildings were thoroughly investigated and their energy-related behavior was studied. The buildings were selected as representative examples of o$ces requiring retro#tting in each of the countries participating in the project. The present condition of the buildings was studied through in situ inspections and monitoring of the indoor thermal conditions. The buildings were classi#ed into different types according to the four criteria, namely: degree of exposure, thermal mass, skin dependence and internal structure. According to the adopted classi#cation, o$ce buildings can be • Free standing or enclosed, based on their location in the urban texture. • Heavy or light, depending on the kind of structure and materials of construction. • Skin or core dependent, according to the relative importance of the outer envelope and the installed systems in their energy performance. • Open plan, consisting of large spaces and minimum interior partitioning or cellular, consisting of small spaces communicating through corridors. Based-on a study of the typology of o$ce buildings in Europe [2], the investigated buildings were classi#ed into #ve categories: • • • •
Free standing=heavy=core dependent=open plan (Type A), enclosed=heavy=skin dependent=cellular (Type B), free standing=heavy=skin dependent=cellular (Type C), free standing=light=skin dependent=open plan (Type D) and • enclosed=light=skin dependent=cellular (Type E). Computer models were developed for the accurate description of each building using data from the thermal monitoring in each building. The models were used in order to assess the e1ectiveness of proposed retro#tting scenarios aiming to improve their energy performance. The impact of the climate on the e1ectiveness of a retro#tting action on a speci#c building type was investigated through simulations using meteorological data from 10 di1erent European locations that cover the four major climatic regions: • Southern Mediterranean: Athens (GR) , Florence (IT). • Continental: Berlin (D), Lausanne (SH), Bern (SH), Lyon (FR).
3. Description of the building types In the framework of the OFFICE project #ve di1erent building types were investigated. The particular features of each type determine the energy consumption and its variation with regard to the climatic region of reference. Fig. 1 illustrates the variation of the total energy consumption for the #ve building types as a function of the climate. As shown in Fig. 1, the total energy requirements of all building types increase with increasing latitude. Free-standing buildings (Types A, C and D) present higher total energy consumption than enclosed ones (Types B and E). Type A has the highest requirements for heating and lighting in all climatic regions and is ‘self-cooled’ except in the South Mediterranean. Type B is the low-energy consuming type; the largest part of the energy is consumed for heating. Types C and D present considerable cooling requirements in all climatic regions, though heating seems to become a critical issue especially when moving away from the warm climate of South Mediterranean. Type E has the lowest energy consumption of all other types; yet, cooling appears to represent more than half of the total energy consumption. Type A corresponds to the representative o$ce building in the warm southern European climate. By contrast, Types C, D and E are commonly met in the North Europe. As can be seen from Fig. 1, compared to the typical ‘south European’ o$ce building, the typical ‘north European’ presents significantly lower heating energy consumption, which compensates its higher cooling requirements in all climatic regions. Consequently, even in the warm climate of Southern Europe, the typical ‘north European’ o$ce building consumes significantly lower total energy than the typical ‘south European’ o$ce. A brief description of the energy-related characteristics of each building is given in the following paragraphs. 3.1. Free standing=heavy=core dependent=open plan Buildings of this type are characterized by a high volume-to-envelope surface ratio, open plan internal structure, massive Loors and ceilings and large glazed areas on the outer envelope. The installed power for arti#cial lighting and the number of operating hours is high. The buildings are equipped with a central HVAC system operating under a constant set-point.
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Fig. 1. Energy consumption of #ve building types according to the climatic region.
This type of buildings appear to be more energy consuming than buildings belonging to other types, under all climatic conditions. A representative building was found to have a total annual energy consumption ranging from 195 kWh=m2 in the Southern Mediterranean climate to 355 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 51% for heating, 39% for lighting and the remaining 10% for cooling. Due to the large air-conditioned volume the major part of the heating energy consumption is attributed to ventilation and a smaller part is attributed to heat losses through the envelope. Daylight penetration is insu$cient for the deep plan structure of the working areas, which makes the use of the arti#cial lighting system necessary throughout the working hours of the day. This results in an increased energy consumption for lighting purposes and, combined with the internal gains, it adds to the cooling load of the building. Accordingly, the annual total energy consumption of this building type is very high. Therefore, there is a strong potential for energy reduction, especially for heating and lighting purposes, through appropriate retro#tting actions. 3.2. Enclosed=heavy=skin dependent=cellular Buildings of this category are located in a dense urban environment and are fairly sheltered from the outdoor conditions by adjacent buildings of the same height or taller. Windows on the outer envelope are double glazed and opaque surfaces are insulated. The interior structure consists of small spaces communicating through corridors.
The HVAC system is centrally controlled and operates at a constant set-point. The installed power for the arti#cial lighting system does not exceed 18 W=m2 . A representative building was found to have a total annual energy consumption ranging from 69 kWh=m2 in the Southern Mediterranean climate to 153 kWh=m2 in the North Coastal climate. This building type presents a signi#cantly lower energy consumption than the previous one. The energy-end use breakdown of the total energy consumption includes: 89% for heating, 9% for lighting and the remaining 2% for cooling. The major part of the heating energy consumption is due to heat losses through the envelope as well as non-e1ective use of the HVAC system. 3.3. Free standing=heavy=skin dependent=cellular Buildings of this type have similar characteristics as the previous type (Section 3.2) but they are more exposed to the outdoor environment which increases the role of their outer envelope on the overall energy consumption. Their opaque surfaces are insulated and the windows are non-openable and double glazed. The interior structure consists of small rooms connected by a corridor and internal partitions, Loors and ceilings are massive. The cellular structure of the building creates shallow working spaces, where the daylight penetration is su$cient to provide comfortable lighting levels. The installed power for arti#cial lighting does not exceed 16 W=m2 . The energy performance of this building type is strongly related to the condition of the outer envelope. A
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representative building was found to have a total annual energy consumption ranging from 169 kWh=m2 in the Southern Mediterranean climate to 328 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 86% for heating, 8% for cooling and the remaining 6% for lighting. The major part of the heating energy consumption is due to heat losses through the envelope as well as due to the pre-conditioning of the ventilation air supplied in the working spaces for indoor air-quality purposes during summer and winter. 3.4. Free standing=light=skin dependent=open plan Buildings of this type have little or no shading from the surroundings. Due to the large, non-shaded external glazed surfaces, they have high direct solar heat gains, which increase their cooling requirements. Heat losses through window frames in bad condition, as well as excessive ventilation rates during summer and winter, increase the overall energy consumption of the buildings. Their internal structure consists of open spaces, while suspended ceilings reduce the effectiveness of the interior thermal mass. The installed power for lighting does not exceed 13 W=m2 . A representative building was found to have a total annual energy consumption ranging from 183 kWh=m2 in the Southern Mediterranean climate to 307 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 67% for heating, 23% for cooling and the remaining 10% for lighting. The major part of the heating energy consumption is due to heat losses through the envelope as well as non-e1ective use of the HVAC system. 3.5. Enclosed=light=skin dependent=cellular Buildings of this type have the lowest energy consumption. Their outer envelope consists of highly insulated opaque elements and air-tight double-glazed surfaces. Atriums are often incorporated into the building design to allow for a deeper daylight penetration. The structure of the internal partitions is light, minimizing the role of thermal mass in the thermal response of the building. Solar gains cover a signi#cant part of the heating needs, but inappropriate shading often increases their cooling requirements. Obviously, the energy performance of the building is dependent on its envelope and application of control strategies in the HVAC system. A representative building was found to have a total annual energy consumption close to 70 kWh=m2 in all climatic regions. This building type presents a signi#cantly lower energy consumption than the average energy use of the other types. The energy-end use breakdown of the total energy consumption includes: 48% for heating, 36% for cooling and the remaining 16% for lighting.
4. Retro tting strategies The e$ciency of energy retro#tting options in o$ce buildings is mainly related to the application of systems and techniques dealing with • the rational use of energy and • the integration of passive solar retro#tting options. Interventions may vary from individual actions a1ecting a speci#c building component, to combinations of actions (scenarios) on speci#c areas and global scenarios. Despite the importance of understanding the impact of an individual action on the building energy behavior, it is undoubted that the complexity of the phenomena a1ecting the latter requires application of combined actions in order to achieve a successful global retro#t. Scenarios include combinations of individual actions affecting speci#c areas that determine the energy performance of a building. Speci#cally, the main areas and interventions include: • Improvement of the building envelope: the aim of this group of interventions is to reduce the impact of the outdoor air temperature on the thermal performance of the building, minimize the heat losses, maximize the use of solar gains for heating and daylighting and reduce the cooling load by appropriate solar control in summer. • Use of passive systems and techniques: the aim of this group of interventions is to reduce the heating and cooling requirements of the building taking advantage of the solar heat gains in the winter and obstructing direct solar penetration during summer. Related retro#tting actions include the use of the thermal mass of the buildings as a heat sink and application of passive cooling techniques for the improvement of indoor thermal comfort conditions. • Installation of energy-saving lighting systems and use of daylight: this set of interventions aims to reduce the electric power consumption for lighting by introducing energy-e$cient lighting systems and to reduce the operating hours of the arti#cial lighting system through maximum daylight utilization. • Improvement of the heating, cooling and ventilation system: this set of interventions aims to reduce the energy consumption for heating and cooling through maximization of the e$ciency of the building services and utilization of heat recovery systems. Global scenarios consist of a combination of scenarios aiming towards total building retro#t. The proposed retro#tting interventions were selected according to the energy-related features and rehabilitation needs of each building type. Tables 1 and 2 summarize the scenarios proposed for each of the #ve investigated building types. The potential of the above scenarios on the energy behavior of the buildings was assessed through energy simulations. Results are discussed in Section 5.
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Table 1 Retro#tting scenarios for Type A (free standing=heavy=core dependent=open plan) and Type B (enclosed=heavy=skin dependent=cellular) buildings Scenario
Type A
Type B
Building envelope
• • • • • •
Improvement of insulation levels Weather stripping of windows=doors Replacement of window frames in bad condition Use of double glazing Use of additional shading (summer) Integration of passive solar and daylighting components (atriums—shaded in summer)
• Increase of wall insulation levels • Reduction of the air in#ltration rate • Replacement of existing windows
Passive systems and techniques
• • • • •
Use of additional shading devices in the 1st and 2nd Loor (summer) Night ventilation (summer) Use of ceiling fans in the major zones (summer) Use of an economizer cycle (summer) Use of an evaporative cooler to pre-cool the fresh air (summer)
• • • •
Lighting
• Use of high-e$ciency Luorescent lamps with electronic ballast and daylight compensation • Decrease of the general lighting up to 20 W=m2 and use task lighting • Use of time-scheduled control • Improvement of luminaries and installation of reLectors
HVAC
• • • • • • •
Global retro#t
All the above
Use of a BMS Decrease of the winter set-point Use of heat recovery of the return air Recovery of the waste heat from the boiler Lue gases Possible replacement of the existing boiler Use of a Lue gas analyzer and a compensation controller for the burner Recovery of heat from the condenser
5. Results and discussion A number of retro#tting scenarios (Tables 1, 2) were assessed for each of the #ve di1erent building types. Each of the scenarios proposed for Types A and B addresses one of the main energy-related aspects of the building mentioned in Section 4, namely: the building envelope, lighting and HVAC systems as well as the adoption of passive strategies for energy conservation. Scenarios proposed for building Types C, D and E are combinations of measures addressing more than one of the above aspects. In this case, some of the proposed scenarios focus on the reduction of the heating energy demand (heating scenario), others on the reduction of the cooling energy demand (cooling scenario) or on the reduction of the energy consumed by the arti#cial lighting and HVAC systems of the building. Global retro#tting interventions proposed for all building types involve combinations of the most e1ective retro#tting scenarios. The e1ectiveness of the above interventions on the energy performance of each building type was assessed through building thermal energy simulations. The role of climatic variations in the e$ciency of the proposed interventions was also investigated. Detailed results are given in [3]. In the following sections, the impact of the most successful interventions on each building type is discussed.
Use Use Use Use
of of of of
mechanical night ventilation (summer) external shading devices (summer) ceiling fans (summer) indirect evaporative cooler (summer)
• Use of a BMS • Use of air-to-air heat recovery system
All the above
5.1. Type A: free standing=heavy=core dependent=open plan As discussed in Section 3.1, retro#tting actions on this building type should mainly focus on the reduction of the energy consumed for heating and lighting purposes. Cooling energy consumption is small and restricted in the warm climate of Southern Europe. Fig. 2 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. Combined actions aiming to improve the building envelope were found to reduce the energy consumption for heating by up to 21%, but no signi#cant reduction was observed in the lighting energy consumption. As a result, the total energy consumption was reduced by an average of 13% in all climatic regions. Application of passive systems and techniques was found to reduce the energy consumption for cooling by up to 34% in Southern Europe, but the respective reduction for heating was very small. Consequently, the reduction in the total energy consumption is not important. The lighting scenario was found to result in a reduction of 66% in the energy consumption for arti#cial lighting. Due to
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Table 2 Retro#tting scenarios for Type C (free standing=heavy=skin dependent=cellular), Type D (free standing=light=skin dependent cellular) and Type E (enclosed=light=skin dependent=cellular) buildings Scenario
Type C
Type D
Type E
Heating scenario
• Replacement of existing windows with super low-energy windows (U = 0:9 W=m2 K) • Insulation of facade (U = 0:3 W=m2 K) • Use of heat recovery (air–air) • Reduction of winter ventilation rate (1.5 ACH) • Reduction of in#ltration rate (0.25 ACH) • Reduction of heating set-point during night and weekend
• Replacement of existing windows (U = 3 W=m2 K) with super low-energy windows (U = 0:9 W=m2 K) • Insulation of facade (U = 0:3 W=m2 K) • Use of heat recovery (air–air) • Use of heat recovery from condenser coil • Reduction of winter ventilation rate (2 ACH, initial: 3.4 ACH) • Reduction of in#ltration rate (0.25 ACH) • Reduction of heating set-point during day
• Reduction of heating set-point • Increase of cooling set-point • Use of an optimized night ventilation strategy
Passive systems and techniques
• Replacement of existing windows with openable medium reLective ones • Use of an e1ective BMS to control external shading system • Use of exposed thermal mass • Reduction of ventilation rate during summer and winter (1.5 ACH) • Use of natural venting to prevent overheating
• Improvement of the U -value of the envelope • Use of low-E windows Type B • Reduction of heating set-point from 22:5◦ C to 21◦ C • Use of automatic control of arti#cial lighting via daylight sensors • Use of exposed thermal mass • Use of chilled ceilings in connection with mechanical cooling • Use of e1ective external solar shading
• • • •
Lighting scenario
• Automatic control of arti#cial lighting lowvia presence sensors • Use of HF ballasts • Automatic control of arti#cial lighting via daylight sensors
• Replacement of existing windows with super energy windows (U = 0:9 W=m2 K) of higher light transmittance (light = 0:76; solar = 0:58) • Use of daylight responsive control of light + HF ballasts in o$ce area • Use of HF ballasts in the remaining part of the building
• Use of high-frequency ballasts in the general lighting system • Use of daylight responsive control of arti#cial lighting • Use of arti#cial lighting control according to presence
Ventilation • Reduction of winter ventilation rate (1.5 ACH) • Replacement of old fan system with modern e1ective system • Use of natural ventilation (summer) • Reduction of running time of ventilation system + night ventilation
• Reduction of ventilation rate (2 ACH, initial: 3.4 ACH) • Replacement of old fan system with modern e1ective system • Reduction of running time of ventilation system + night ventilation
• Use of an optimized night ventilation strategy • Improvement of the air distribution system
Global retro#t
• Insulation of the facade (U = 0:3 W=m2 K) • Replacement of existing windows with openable super low-energy windows (U = 0:9 W=m2 K) • Reduction of heating set-point during day • Use of air-to-air heat recovery • Reduction of ventilation rate (2 ACH, initial: 3.4 ACH) • Replacement of old fan system with modern e1ective system • Reduction of running time of ventilation system + night ventilation mode • Use of daylight responsive control of light + HF ballasts in o$ce area • Reduction of in#ltration rate (0.25 ACH)
• Use of e1ective solar shading • Use of high-frequency ballasts • Use of daylight responsive control of arti#cial lighting • Use of arti#cial lighting control accordingto presence • Reduction of ventilation rate • Reduction of the heating set-point • Increase of the cooling set-point • Use of optimized night ventilation strategy • Improvement of the air distribution system
• Use of openable clear super low-E windows (U = 0:9 W=m2 K) • Improvement of the U -value of opaque part of envelope • Use of air–air heat recovery • Reduction of ventilation rate summer and winter (1.5 ACH) • Improvement of fan e$ciency in ventilation system • No use of mechanical cooling • Use of e1ective BMS controlled external solar shading system • Use of natural venting to prevent overheating • Automatic control of arti#cial lighting in response to daylight • Reduction of in#ltration rate • Use of night ventilation and reduced running time of ventilation • Reduction of heating set-point during night and weekend
Use of e1ective solar shading Reduction of heating set-point Increase of cooling set-point Use of an optimized night ventilation strategy
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Fig. 2. Retro#tting scenarios for Type A buildings: Breakdown per energy-end use for di1erent climatic regions.
the reduction of the internal gains resulting from the use of energy-saving luminaires, the cooling energy consumption is reduced by 17%, but the heating energy consumption is increased by up to 16% in the North Coastal climatic region. Consequently, the reduction in the total energy consumption is not important. The scenario aiming to improve the HVAC systems was found to reduce signi#cantly the energy consumption for heating and cooling. Analytically, an average reduction in the heating energy consumption of 69 kWh=m2 was estimated for South Mediterranean conditions, while for the rest of the climatic regions the estimated reduction was close to 120 kWh=m2 . These values correspond to almost 60% and 42% of the initial energy consumption in the above regions, respectively. Cooling energy consumption in the South Mediterranean is reduced by 9 kWh=m2 , which represents 40% of the initial consumption. Consequently, a reduction ranging from 72 kWh=m2 in the South Mediterranean to 130 kWh=m2 in the North Coastal climates is observed in the total energy consumption, representing 35% of the initial energy consumption in all climatic regions. Global retro#tting results in the most impressive reduction of the total energy consumption in all climatic regions. The achieved energy savings result from reduction of the energy demand for heating, cooling and lighting. The reduction in the heating energy consumption ranges from 40% to 51%, the highest percentage corresponding to the warmer climates. The average reduction in the energy consumption for lighting is 68%. Cooling energy consumption in the South Mediterranean is reduced by 11 kWh=m2 , which represents 49% of the initial consumption. Consequently, the reduction
in the total energy consumption is estimated to range from 116 kWh=m2 in the South Mediterranean to 181 kWh=m2 in the North Coastal climate. These #gures represent 55% of the initial energy consumption. 5.2. Type B: enclosed=heavy=skin dependent=cellular Fig. 3 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for the four di1erent climatic regions. Cooling represents a small part of the total energy consumption and is only necessary in the warm climate of South and Continental Europe. Use of passive cooling systems totally eliminates the energy requirements for cooling in both South Mediterranean and Continental climatic regions. However, the reduction of the total energy consumption is negligible. As discussed in Section 3.2, retro#tting actions on this building type should mainly focus on the improvement of the envelope and HVAC systems. Increasing the insulation levels and the air tightness of the outer envelope and using clear glazing to increase passive solar gains was found to reduce the heating energy consumption by nearly 55% in all climatic regions. Due to the increased solar gains in the summer period this scenario results in a slight increase of the cooling energy consumption. As a result, the total energy savings achieved were close to 44 kWh=m2 . The scenario aiming to improve the HVAC systems was found to reduce signi#cantly the energy consumption for
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Fig. 3. Retro#tting scenarios for Type B buildings: Breakdown per energy-end use for di1erent climatic regions.
heating and cooling. The average reduction in the heating energy consumption was estimated to range from 35 kWh=m2 in the South Mediterranean to 84 kWh=m2 in the North coastal conditions. These values correspond to almost 55% of the initial energy consumption in all climatic regions. Global retro#tting, combining interventions on the envelope and systems as well as integration of passive cooling techniques was found to have the most impressive energy savings, reducing the total energy consumption by nearly 80% in all climatic regions. The heating energy consumption is estimated to range from 56 kWh=m2 in the South Mediterranean to 117 kWh=m2 in the North Coastal climatic regions. 5.3. Type C: free standing=heavy=skin dependent=cellular Fig. 4 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.3 retro#tting scenarios for improvement of the energy performance of this building type should focus on the envelope and the ventilation system. A scenario reducing the lighting consumption was found to have a negligible impact on the total energy consumption of this building type. The ‘passive systems and techniques’ scenario is a combination of passive measures focusing on the reduction of the cooling energy consumption of the building. The scenario was found to reduce the cooling energy consumption by nearly 30% in all climatic regions. Additionally, the
proposed reduction of the ventilation rate during winter contributed to the reduction of the heating energy consumption by nearly 20% in all climatic regions. Consequently, the ‘passive’ scenario was found to result in a reduction of 19%. The scenario accounting for better control and improved e$ciency of the ventilation system was found to result in a signi#cant reduction of both heating and cooling energy consumption. Accordingly, a reduction of nearly 38% in the initial heating energy consumption was achieved in all climatic regions and the savings in the cooling energy consumption were close to 85%, as a result of the implementation of a night ventilation strategy that takes advantage of the thermal mass of the building. The ‘heating’ scenario includes measures addressing the building envelope, supported by system control measures and utilization of otherwise wasted energy, aiming to reduce the heating energy consumption of the building. This scenario was found to reduce signi#cantly the total energy consumption. Accordingly, the average reduction in the heating energy consumption was estimated to range from 92 kWh=m2 in the South Mediterranean to 240 kWh=m2 in the North coastal conditions. These values correspond to almost 80% of the initial energy consumption in all climatic regions. The cooling energy consumption was slightly reduced mainly as a result of the reduction of the in#ltration rate. The estimated reduction was close to 8 kWh=m2 , representing close to 30% of the initial cooling energy consumption in all climatic regions. The set of measures included in the global retro#tting scenario was found to have a slightly greater reduction in the total energy consumption, due to the inclusion of measures that reduce cooling energy demand.
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Fig. 4. Retro#tting scenarios for Type C buildings: Breakdown per energy-end use for di1erent climatic regions.
5.4. Type D: free standing=light=skin dependent=open plan Fig. 5 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.4 retro#tting scenarios for improvement of the energy performance of this building type should compensate the envelope losses as well as increased heating and cooling energy consumption through the ventilation system. The ‘heating’ scenario includes combined measures for the improvement of the U -value of the envelope and the enhancement of the HVAC system e$ciency. New settings of the control parameters and installation of a heat recovery system results in a decrease in the total energy consumption ranging from 47% in the South Mediterranean to 77% in the North Coastal climate. The greatest part of the energy savings is achieved in the heating energy consumption which is minimized in all climatic regions. The cooling energy reduction, mainly achieved through reduction of the air in#ltration rate, was found to range from 24% in the South Mediterranean climate to 44% in the North Coastal climate. Additional measures for the improvement of the e$ciency of the ventilation and lighting systems and application of night ventilation were found to further improve the e$ciency of the ‘heating’ scenario regarding both cooling and lighting. Consequently, the ‘global’ scenario was found to be more e1ective than the ‘heating’ scenario, resulting in total energy savings ranging from 59% in South Mediterranean to 79% in the North Coastal climate. The ‘passive systems and techniques’ scenario includes measures for the improvement of the building envelope, combined with measures mainly aiming to reduce the
cooling requirements of the building. Proper use of solar control and the removal of false ceilings to enhance the e1ectiveness of the interior thermal mass of the building, reduces the cooling energy consumption by 78% in the South ◦ Mediterranean. Reduction of the heating set-point by 1:5 C, a measure included in this scenario, results in minimizing the heating energy requirements, even in the North Coastal climate. Use of daylight sensors for better utilization of the available daylight reduces the lighting energy consumption by almost 50%. Consequently, the total energy consumption is reduced by 80% in all climatic regions, which makes this scenario the most energy e$cient one for this building type. 5.5. Type E: enclosed=light=skin dependent=cellular Fig. 6 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.5 retro#tting scenarios for improvement of the energy performance of this building type should mainly focus on the application of control strategies in the HVAC and on the reduction of the unnecessary solar gains in the summer period. The cellular structure and highly glazed outer envelope of these buildings allow for a deep daylight penetration and the use of arti#cial lighting is usually controlled by the occupants. Therefore, despite the fact that the lighting scenario results in a signi#cant reduction in the lighting energy consumption, the corresponding reduction in the total energy consumption is not so important. The ‘ventilation’ scenario was found to reduce the cooling energy consumption by 30% in the South Mediterranean
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Fig. 5. Retro#tting scenarios for Type D buildings: Breakdown per energy-end use for di1erent climatic regions.
Fig. 6. Retro#tting scenarios for Type E buildings: Breakdown per energy-end use for di1erent climatic regions.
and the heating energy consumption by 14% in the North Coastal climate. A simple reduction in the heating set-point, proposed in the ‘heating scenario’ was found to reduce the heating energy consumption by 48% in the North Coastal climate. Application of the ‘heating’ scenario was found to result in a reduction of the total energy consumption ranging from 27% in the South Mediterranean to 37% in the North Coastal climatic region. The e1ectiveness of the ‘heating’ scenario is signi#cantly enhanced by the introduction of an e1ective solar
shading system to reduce the excessive solar gains during the cooling period. Accordingly, the scenario ‘passive systems and techniques’ was found to reduce the cooling and total energy consumption by nearly 40% in all climatic regions. The global retro#tting scenario, combining all the above interventions has the most impressive performance, resulting in a reduction of the total energy consumption reduction ranging from 48% in the North Coastal to 56% in the North European climatic regions.
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6. Conclusions A retro#tting intervention a1ects the energy performance of a building according to its characteristics and speci#c needs. Successful energy retro#tting of a building addresses speci#c aspects or combination of aspects taking advantage of the special energy-related characteristics of the building in order to improve its energy performance. A determining factor in this process is the climatic region of reference. The present study was based on the analysis of the energy-saving potential of retro#tting strategies proposed for 10 buildings that were classi#ed into #ve types representing the existing o$ce building stock in Europe. Each type was investigated under four di1erent climatic conditions, covering the main climatic regions of Europe. Apart from the expected energy gains, the cost e1ectiveness of the proposed retro#tting scenarios is of great importance when choosing the most appropriate retro#tting intervention on an existing o$ce building. The cost e1ectiveness of the retro#tting scenarios proposed for each of the 10 o$ce buildings investigated in the framework of the OFFICE project was studied and is reported in detail in [4]. Due to the particularities associated with each building as well as the regional climatic variability, it is not possible to generalize the conclusions drawn from the present study. However, it is possible to extract an indication of the trends observed in the behavior of each building type with regard to various retro#tting interventions. As expected, global retro#tting was found to have the highest reduction of the total energy consumption in all climatic regions and all building types. Type A buildings (free standing=heavy=core dependent= open plan) present impressive energy savings for the scenarios that a1ect the installed HVAC and lighting systems. This is due to their open plan interior structure and due to their large volume which minimizes their skin dependence, reducing the e1ect of scenarios improving the envelope. Application of the HVAC scenario described in Table 1 in a Type A building in Greece was found to have a simple pay-back period (SPBP) of nearly 33 years. A simple measure though, such as installation of a BMS system was found to have an SPBP of 10 years, with almost the same energy gains as the scenario. Application of the lighting scenario described in Table 1 in the same building was found to have an SPBP of 9 years, while a simple measure accounting for a reduction of the installed power from 121 to 20 W=m2 in the building was found to have an SPBP of 5 years with almost the same energy gains as the scenario. Type B buildings (enclosed=heavy=skin dependent= cellular) present impressive reduction of the total energy consumption for the scenarios focusing on the improvement of the envelope and HVAC system. Taking advantage of the building’s skin dependence, the scenario on the envelope improvement, described in Table 1, was found to signi#cantly improve the total energy savings of a Type B building in France. Further improvement was achieved
567
through application of the HVAC scenario in the same building. The estimated pay-back period for the HVAC scenario was close to 10 years. Type C buildings (free standing=heavy=skin dependent= cellular) have an impressive response to combined interventions a1ecting the building envelope and systems. Application of the ‘heating’ scenario described in Table 2 in a Type C building in Denmark was found to have an SPBP of nearly 10 years. Application of measures for the improvement of the building envelope combined with measures aiming to reduce the cooling requirements of the building have an outstanding e1ect on Type D buildings (free standing=light=skin dependent=open plan). Application of the ‘passive systems and techniques’ scenario described in Table 2 in a Type D building in Germany was found to have an SPBP of 15 years. Application of the ‘heating’ scenario described in Table 2 in the same building was found to have an SPBP of 9 years with smaller energy savings. Type E buildings (enclosed=light=skin dependent= cellular) have an impressive energy-saving performance when operating under scenarios combining control of their systems and solar shading to reduce excessive solar gains in summer. Application of the ‘passive systems and techniques’ scenario described in Table 2 in a Type E building in Sweden was found to have an SPBP of 7 years. Application of the ‘heating’ scenario described in Table 2 in the same building was found to have an SPBP of 0.1 years with very similar energy savings. Acknowledgements This work was carried out in the framework of the OFFICE research project partly funded by the EC (contract number JOR3-CT96-0034). The authors would like to acknowledge the European Commission for the #nancial support of this research. The above analysis is based on the results from an extensive number of energy simulations performed within the frame of the Design Guidelines task of the OFFICE project. The authors would like to thank the groups of ESBENSEN, LASH, ECD, EPFL, NTNU and GR-BES for their valuable contribution to this task. References [1] Balaras CA. A guide for energy conservation in o$ce buildings. CIENE, Dept. of Applied Physics, University of Athens, 1994. [2] Tombazis A, Vratsanos N, editors. O$ce building typologies in Europe. Report No. OF-1, OFFICE programme, JOR3-CT96-0034. [3] Dascalaki E, editor. ATLAS on the potential of retro#tting scenarios for o$ces. Final Report, OFFICE programme, JOR3-CT96-0034. [4] Hestnes AG, Kofoed NU, editors. Draft #nal report on the design and evaluation subgroup. OFFICE programme, JOR3-CT96-0034.
www.elsevier.com/locate/buildenv
On the potential of retro#tting scenarios for o$ces E. Dascalaki1 , M. Santamouris ∗ GR-BES, Group Building Environmental Studies, Department of Applied Physics, University of Athens, University Campus, Build. Phys. V, 157 84 Athens, Greece
Abstract Within the framework of OFFICE research project the energy conservation potential of combined retro#tting actions was investigated for #ve building types in four di1erent climatic regions in the European continent. The studied actions involve interventions on the building envelope, HVAC and arti#cial lighting systems as well as integration of passive components for heating and cooling. Interventions a1ecting the performance of the building in the global aspect were also assessed. The potential of retro#tting actions proposed for each building type was assessed through energy simulations using high-accuracy computer models and climatic data from 10 locations in South Mediterranean, Continental, Mid-Coastal and North Coastal Europe. Analysis of the results revealed common trends in the energy performance of di1erent building types and permitted to extract information on the most suitable retro#tting interventions in each. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: O$ce building types; Retro#tting potential; Energy performance
1. Introduction Retro#tting of o$ce buildings has gained interest during the past few years mainly due to increasing energy and air-quality problems. Important work has been carried out by architectural and engineering groups to retro#t o$ce buildings and to improve their energy performance. Results show that cost-e1ective energy savings in the order of 20 –30% can be achieved in o$ce buildings, while there are indications for greater savings resulting from major retro#tting projects. Based on the existing experience, guidelines for energy-e$cient retro#tting of o$ce buildings have been published by various national and international organizations [1]. Existing energy-related retro#tting actions mainly aim towards a more rational use of energy in the o$ce buildings, neglecting aspects related to passive solar heating, daylighting and passive cooling of buildings. As a result of recent scienti#c research on passive solar heating, cooling and daylighting systems and techniques existing knowledge on the above topics has increased. Current research on ∗
Corresponding author. E-mail address: [email protected] (M. Santamouris). 1 Current a$liation: National Observatory of Athens, Institute for Environmental Research and Sustainable Development, Group Energy Conservation, I. Metaxa & Vas. Pavlou, Palaia Penteli, 152 36, Greece.
retro#tting involves studies of the energy conservation potential of combined actions applied in the existing buildings. Retro#tting actions involve combined interventions on the main energy-related aspects of the building, including its outer envelope and installed systems for heating, cooling, ventilation and lighting with a simultaneous incorporation of passive systems and techniques. The objective of such retro#tting actions is to optimize the energy performance of the building, while maintaining thermal and visual comfort as well as acceptable air quality for the occupants. The e1ectiveness of retro#tting scenarios on the energy performance of an o$ce building depends on speci#c characteristics related to its architectural structure, its operational features and relation to the surrounding environment. Despite the di1erences observed among o$ce buildings throughout Europe, it is possible to de#ne a typology, classifying existing buildings into groups presenting common energy-related features. This classi#cation permits the investigation of the energy behavior of di1erent building types, as well as the assessment of their response to di1erent retro#tting strategies. As climate is one of the main parameters a1ecting the energy behavior of a building, the e1ectiveness of a retro#tting intervention is strongly dependent on the climatic region of reference. The aim of this work is to investigate the energy conservation potential of selected retro#tting interventions on #ve
0360-1323/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 1 3 2 3 ( 0 2 ) 0 0 0 0 2 - 1
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o$ce building types in four di1erent climatic zones of Europe. In the following sections, the adopted methodology is presented, along with the particular characteristics of each building type. Retro#tting scenarios proposed for each building type are given and the variation of their energy-saving potential as a function of climate is discussed.
• Mid-Coastal: Kew (UK). • North Coastal: Trondheim (NO), Copenhagen (DK), Gothenburg (SE). In the following sections, the general trends regarding the existing situation as well as the potential of proposed retro#tting interventions for each building type are discussed.
2. Methodology In the framework of the OFFICE research project, 10 di1erent buildings were thoroughly investigated and their energy-related behavior was studied. The buildings were selected as representative examples of o$ces requiring retro#tting in each of the countries participating in the project. The present condition of the buildings was studied through in situ inspections and monitoring of the indoor thermal conditions. The buildings were classi#ed into different types according to the four criteria, namely: degree of exposure, thermal mass, skin dependence and internal structure. According to the adopted classi#cation, o$ce buildings can be • Free standing or enclosed, based on their location in the urban texture. • Heavy or light, depending on the kind of structure and materials of construction. • Skin or core dependent, according to the relative importance of the outer envelope and the installed systems in their energy performance. • Open plan, consisting of large spaces and minimum interior partitioning or cellular, consisting of small spaces communicating through corridors. Based-on a study of the typology of o$ce buildings in Europe [2], the investigated buildings were classi#ed into #ve categories: • • • •
Free standing=heavy=core dependent=open plan (Type A), enclosed=heavy=skin dependent=cellular (Type B), free standing=heavy=skin dependent=cellular (Type C), free standing=light=skin dependent=open plan (Type D) and • enclosed=light=skin dependent=cellular (Type E). Computer models were developed for the accurate description of each building using data from the thermal monitoring in each building. The models were used in order to assess the e1ectiveness of proposed retro#tting scenarios aiming to improve their energy performance. The impact of the climate on the e1ectiveness of a retro#tting action on a speci#c building type was investigated through simulations using meteorological data from 10 di1erent European locations that cover the four major climatic regions: • Southern Mediterranean: Athens (GR) , Florence (IT). • Continental: Berlin (D), Lausanne (SH), Bern (SH), Lyon (FR).
3. Description of the building types In the framework of the OFFICE project #ve di1erent building types were investigated. The particular features of each type determine the energy consumption and its variation with regard to the climatic region of reference. Fig. 1 illustrates the variation of the total energy consumption for the #ve building types as a function of the climate. As shown in Fig. 1, the total energy requirements of all building types increase with increasing latitude. Free-standing buildings (Types A, C and D) present higher total energy consumption than enclosed ones (Types B and E). Type A has the highest requirements for heating and lighting in all climatic regions and is ‘self-cooled’ except in the South Mediterranean. Type B is the low-energy consuming type; the largest part of the energy is consumed for heating. Types C and D present considerable cooling requirements in all climatic regions, though heating seems to become a critical issue especially when moving away from the warm climate of South Mediterranean. Type E has the lowest energy consumption of all other types; yet, cooling appears to represent more than half of the total energy consumption. Type A corresponds to the representative o$ce building in the warm southern European climate. By contrast, Types C, D and E are commonly met in the North Europe. As can be seen from Fig. 1, compared to the typical ‘south European’ o$ce building, the typical ‘north European’ presents significantly lower heating energy consumption, which compensates its higher cooling requirements in all climatic regions. Consequently, even in the warm climate of Southern Europe, the typical ‘north European’ o$ce building consumes significantly lower total energy than the typical ‘south European’ o$ce. A brief description of the energy-related characteristics of each building is given in the following paragraphs. 3.1. Free standing=heavy=core dependent=open plan Buildings of this type are characterized by a high volume-to-envelope surface ratio, open plan internal structure, massive Loors and ceilings and large glazed areas on the outer envelope. The installed power for arti#cial lighting and the number of operating hours is high. The buildings are equipped with a central HVAC system operating under a constant set-point.
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Fig. 1. Energy consumption of #ve building types according to the climatic region.
This type of buildings appear to be more energy consuming than buildings belonging to other types, under all climatic conditions. A representative building was found to have a total annual energy consumption ranging from 195 kWh=m2 in the Southern Mediterranean climate to 355 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 51% for heating, 39% for lighting and the remaining 10% for cooling. Due to the large air-conditioned volume the major part of the heating energy consumption is attributed to ventilation and a smaller part is attributed to heat losses through the envelope. Daylight penetration is insu$cient for the deep plan structure of the working areas, which makes the use of the arti#cial lighting system necessary throughout the working hours of the day. This results in an increased energy consumption for lighting purposes and, combined with the internal gains, it adds to the cooling load of the building. Accordingly, the annual total energy consumption of this building type is very high. Therefore, there is a strong potential for energy reduction, especially for heating and lighting purposes, through appropriate retro#tting actions. 3.2. Enclosed=heavy=skin dependent=cellular Buildings of this category are located in a dense urban environment and are fairly sheltered from the outdoor conditions by adjacent buildings of the same height or taller. Windows on the outer envelope are double glazed and opaque surfaces are insulated. The interior structure consists of small spaces communicating through corridors.
The HVAC system is centrally controlled and operates at a constant set-point. The installed power for the arti#cial lighting system does not exceed 18 W=m2 . A representative building was found to have a total annual energy consumption ranging from 69 kWh=m2 in the Southern Mediterranean climate to 153 kWh=m2 in the North Coastal climate. This building type presents a signi#cantly lower energy consumption than the previous one. The energy-end use breakdown of the total energy consumption includes: 89% for heating, 9% for lighting and the remaining 2% for cooling. The major part of the heating energy consumption is due to heat losses through the envelope as well as non-e1ective use of the HVAC system. 3.3. Free standing=heavy=skin dependent=cellular Buildings of this type have similar characteristics as the previous type (Section 3.2) but they are more exposed to the outdoor environment which increases the role of their outer envelope on the overall energy consumption. Their opaque surfaces are insulated and the windows are non-openable and double glazed. The interior structure consists of small rooms connected by a corridor and internal partitions, Loors and ceilings are massive. The cellular structure of the building creates shallow working spaces, where the daylight penetration is su$cient to provide comfortable lighting levels. The installed power for arti#cial lighting does not exceed 16 W=m2 . The energy performance of this building type is strongly related to the condition of the outer envelope. A
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representative building was found to have a total annual energy consumption ranging from 169 kWh=m2 in the Southern Mediterranean climate to 328 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 86% for heating, 8% for cooling and the remaining 6% for lighting. The major part of the heating energy consumption is due to heat losses through the envelope as well as due to the pre-conditioning of the ventilation air supplied in the working spaces for indoor air-quality purposes during summer and winter. 3.4. Free standing=light=skin dependent=open plan Buildings of this type have little or no shading from the surroundings. Due to the large, non-shaded external glazed surfaces, they have high direct solar heat gains, which increase their cooling requirements. Heat losses through window frames in bad condition, as well as excessive ventilation rates during summer and winter, increase the overall energy consumption of the buildings. Their internal structure consists of open spaces, while suspended ceilings reduce the effectiveness of the interior thermal mass. The installed power for lighting does not exceed 13 W=m2 . A representative building was found to have a total annual energy consumption ranging from 183 kWh=m2 in the Southern Mediterranean climate to 307 kWh=m2 in the North Coastal climate. The energy-end use breakdown of the total energy consumption includes: 67% for heating, 23% for cooling and the remaining 10% for lighting. The major part of the heating energy consumption is due to heat losses through the envelope as well as non-e1ective use of the HVAC system. 3.5. Enclosed=light=skin dependent=cellular Buildings of this type have the lowest energy consumption. Their outer envelope consists of highly insulated opaque elements and air-tight double-glazed surfaces. Atriums are often incorporated into the building design to allow for a deeper daylight penetration. The structure of the internal partitions is light, minimizing the role of thermal mass in the thermal response of the building. Solar gains cover a signi#cant part of the heating needs, but inappropriate shading often increases their cooling requirements. Obviously, the energy performance of the building is dependent on its envelope and application of control strategies in the HVAC system. A representative building was found to have a total annual energy consumption close to 70 kWh=m2 in all climatic regions. This building type presents a signi#cantly lower energy consumption than the average energy use of the other types. The energy-end use breakdown of the total energy consumption includes: 48% for heating, 36% for cooling and the remaining 16% for lighting.
4. Retro tting strategies The e$ciency of energy retro#tting options in o$ce buildings is mainly related to the application of systems and techniques dealing with • the rational use of energy and • the integration of passive solar retro#tting options. Interventions may vary from individual actions a1ecting a speci#c building component, to combinations of actions (scenarios) on speci#c areas and global scenarios. Despite the importance of understanding the impact of an individual action on the building energy behavior, it is undoubted that the complexity of the phenomena a1ecting the latter requires application of combined actions in order to achieve a successful global retro#t. Scenarios include combinations of individual actions affecting speci#c areas that determine the energy performance of a building. Speci#cally, the main areas and interventions include: • Improvement of the building envelope: the aim of this group of interventions is to reduce the impact of the outdoor air temperature on the thermal performance of the building, minimize the heat losses, maximize the use of solar gains for heating and daylighting and reduce the cooling load by appropriate solar control in summer. • Use of passive systems and techniques: the aim of this group of interventions is to reduce the heating and cooling requirements of the building taking advantage of the solar heat gains in the winter and obstructing direct solar penetration during summer. Related retro#tting actions include the use of the thermal mass of the buildings as a heat sink and application of passive cooling techniques for the improvement of indoor thermal comfort conditions. • Installation of energy-saving lighting systems and use of daylight: this set of interventions aims to reduce the electric power consumption for lighting by introducing energy-e$cient lighting systems and to reduce the operating hours of the arti#cial lighting system through maximum daylight utilization. • Improvement of the heating, cooling and ventilation system: this set of interventions aims to reduce the energy consumption for heating and cooling through maximization of the e$ciency of the building services and utilization of heat recovery systems. Global scenarios consist of a combination of scenarios aiming towards total building retro#t. The proposed retro#tting interventions were selected according to the energy-related features and rehabilitation needs of each building type. Tables 1 and 2 summarize the scenarios proposed for each of the #ve investigated building types. The potential of the above scenarios on the energy behavior of the buildings was assessed through energy simulations. Results are discussed in Section 5.
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Table 1 Retro#tting scenarios for Type A (free standing=heavy=core dependent=open plan) and Type B (enclosed=heavy=skin dependent=cellular) buildings Scenario
Type A
Type B
Building envelope
• • • • • •
Improvement of insulation levels Weather stripping of windows=doors Replacement of window frames in bad condition Use of double glazing Use of additional shading (summer) Integration of passive solar and daylighting components (atriums—shaded in summer)
• Increase of wall insulation levels • Reduction of the air in#ltration rate • Replacement of existing windows
Passive systems and techniques
• • • • •
Use of additional shading devices in the 1st and 2nd Loor (summer) Night ventilation (summer) Use of ceiling fans in the major zones (summer) Use of an economizer cycle (summer) Use of an evaporative cooler to pre-cool the fresh air (summer)
• • • •
Lighting
• Use of high-e$ciency Luorescent lamps with electronic ballast and daylight compensation • Decrease of the general lighting up to 20 W=m2 and use task lighting • Use of time-scheduled control • Improvement of luminaries and installation of reLectors
HVAC
• • • • • • •
Global retro#t
All the above
Use of a BMS Decrease of the winter set-point Use of heat recovery of the return air Recovery of the waste heat from the boiler Lue gases Possible replacement of the existing boiler Use of a Lue gas analyzer and a compensation controller for the burner Recovery of heat from the condenser
5. Results and discussion A number of retro#tting scenarios (Tables 1, 2) were assessed for each of the #ve di1erent building types. Each of the scenarios proposed for Types A and B addresses one of the main energy-related aspects of the building mentioned in Section 4, namely: the building envelope, lighting and HVAC systems as well as the adoption of passive strategies for energy conservation. Scenarios proposed for building Types C, D and E are combinations of measures addressing more than one of the above aspects. In this case, some of the proposed scenarios focus on the reduction of the heating energy demand (heating scenario), others on the reduction of the cooling energy demand (cooling scenario) or on the reduction of the energy consumed by the arti#cial lighting and HVAC systems of the building. Global retro#tting interventions proposed for all building types involve combinations of the most e1ective retro#tting scenarios. The e1ectiveness of the above interventions on the energy performance of each building type was assessed through building thermal energy simulations. The role of climatic variations in the e$ciency of the proposed interventions was also investigated. Detailed results are given in [3]. In the following sections, the impact of the most successful interventions on each building type is discussed.
Use Use Use Use
of of of of
mechanical night ventilation (summer) external shading devices (summer) ceiling fans (summer) indirect evaporative cooler (summer)
• Use of a BMS • Use of air-to-air heat recovery system
All the above
5.1. Type A: free standing=heavy=core dependent=open plan As discussed in Section 3.1, retro#tting actions on this building type should mainly focus on the reduction of the energy consumed for heating and lighting purposes. Cooling energy consumption is small and restricted in the warm climate of Southern Europe. Fig. 2 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. Combined actions aiming to improve the building envelope were found to reduce the energy consumption for heating by up to 21%, but no signi#cant reduction was observed in the lighting energy consumption. As a result, the total energy consumption was reduced by an average of 13% in all climatic regions. Application of passive systems and techniques was found to reduce the energy consumption for cooling by up to 34% in Southern Europe, but the respective reduction for heating was very small. Consequently, the reduction in the total energy consumption is not important. The lighting scenario was found to result in a reduction of 66% in the energy consumption for arti#cial lighting. Due to
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Table 2 Retro#tting scenarios for Type C (free standing=heavy=skin dependent=cellular), Type D (free standing=light=skin dependent cellular) and Type E (enclosed=light=skin dependent=cellular) buildings Scenario
Type C
Type D
Type E
Heating scenario
• Replacement of existing windows with super low-energy windows (U = 0:9 W=m2 K) • Insulation of facade (U = 0:3 W=m2 K) • Use of heat recovery (air–air) • Reduction of winter ventilation rate (1.5 ACH) • Reduction of in#ltration rate (0.25 ACH) • Reduction of heating set-point during night and weekend
• Replacement of existing windows (U = 3 W=m2 K) with super low-energy windows (U = 0:9 W=m2 K) • Insulation of facade (U = 0:3 W=m2 K) • Use of heat recovery (air–air) • Use of heat recovery from condenser coil • Reduction of winter ventilation rate (2 ACH, initial: 3.4 ACH) • Reduction of in#ltration rate (0.25 ACH) • Reduction of heating set-point during day
• Reduction of heating set-point • Increase of cooling set-point • Use of an optimized night ventilation strategy
Passive systems and techniques
• Replacement of existing windows with openable medium reLective ones • Use of an e1ective BMS to control external shading system • Use of exposed thermal mass • Reduction of ventilation rate during summer and winter (1.5 ACH) • Use of natural venting to prevent overheating
• Improvement of the U -value of the envelope • Use of low-E windows Type B • Reduction of heating set-point from 22:5◦ C to 21◦ C • Use of automatic control of arti#cial lighting via daylight sensors • Use of exposed thermal mass • Use of chilled ceilings in connection with mechanical cooling • Use of e1ective external solar shading
• • • •
Lighting scenario
• Automatic control of arti#cial lighting lowvia presence sensors • Use of HF ballasts • Automatic control of arti#cial lighting via daylight sensors
• Replacement of existing windows with super energy windows (U = 0:9 W=m2 K) of higher light transmittance (light = 0:76; solar = 0:58) • Use of daylight responsive control of light + HF ballasts in o$ce area • Use of HF ballasts in the remaining part of the building
• Use of high-frequency ballasts in the general lighting system • Use of daylight responsive control of arti#cial lighting • Use of arti#cial lighting control according to presence
Ventilation • Reduction of winter ventilation rate (1.5 ACH) • Replacement of old fan system with modern e1ective system • Use of natural ventilation (summer) • Reduction of running time of ventilation system + night ventilation
• Reduction of ventilation rate (2 ACH, initial: 3.4 ACH) • Replacement of old fan system with modern e1ective system • Reduction of running time of ventilation system + night ventilation
• Use of an optimized night ventilation strategy • Improvement of the air distribution system
Global retro#t
• Insulation of the facade (U = 0:3 W=m2 K) • Replacement of existing windows with openable super low-energy windows (U = 0:9 W=m2 K) • Reduction of heating set-point during day • Use of air-to-air heat recovery • Reduction of ventilation rate (2 ACH, initial: 3.4 ACH) • Replacement of old fan system with modern e1ective system • Reduction of running time of ventilation system + night ventilation mode • Use of daylight responsive control of light + HF ballasts in o$ce area • Reduction of in#ltration rate (0.25 ACH)
• Use of e1ective solar shading • Use of high-frequency ballasts • Use of daylight responsive control of arti#cial lighting • Use of arti#cial lighting control accordingto presence • Reduction of ventilation rate • Reduction of the heating set-point • Increase of the cooling set-point • Use of optimized night ventilation strategy • Improvement of the air distribution system
• Use of openable clear super low-E windows (U = 0:9 W=m2 K) • Improvement of the U -value of opaque part of envelope • Use of air–air heat recovery • Reduction of ventilation rate summer and winter (1.5 ACH) • Improvement of fan e$ciency in ventilation system • No use of mechanical cooling • Use of e1ective BMS controlled external solar shading system • Use of natural venting to prevent overheating • Automatic control of arti#cial lighting in response to daylight • Reduction of in#ltration rate • Use of night ventilation and reduced running time of ventilation • Reduction of heating set-point during night and weekend
Use of e1ective solar shading Reduction of heating set-point Increase of cooling set-point Use of an optimized night ventilation strategy
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563
Fig. 2. Retro#tting scenarios for Type A buildings: Breakdown per energy-end use for di1erent climatic regions.
the reduction of the internal gains resulting from the use of energy-saving luminaires, the cooling energy consumption is reduced by 17%, but the heating energy consumption is increased by up to 16% in the North Coastal climatic region. Consequently, the reduction in the total energy consumption is not important. The scenario aiming to improve the HVAC systems was found to reduce signi#cantly the energy consumption for heating and cooling. Analytically, an average reduction in the heating energy consumption of 69 kWh=m2 was estimated for South Mediterranean conditions, while for the rest of the climatic regions the estimated reduction was close to 120 kWh=m2 . These values correspond to almost 60% and 42% of the initial energy consumption in the above regions, respectively. Cooling energy consumption in the South Mediterranean is reduced by 9 kWh=m2 , which represents 40% of the initial consumption. Consequently, a reduction ranging from 72 kWh=m2 in the South Mediterranean to 130 kWh=m2 in the North Coastal climates is observed in the total energy consumption, representing 35% of the initial energy consumption in all climatic regions. Global retro#tting results in the most impressive reduction of the total energy consumption in all climatic regions. The achieved energy savings result from reduction of the energy demand for heating, cooling and lighting. The reduction in the heating energy consumption ranges from 40% to 51%, the highest percentage corresponding to the warmer climates. The average reduction in the energy consumption for lighting is 68%. Cooling energy consumption in the South Mediterranean is reduced by 11 kWh=m2 , which represents 49% of the initial consumption. Consequently, the reduction
in the total energy consumption is estimated to range from 116 kWh=m2 in the South Mediterranean to 181 kWh=m2 in the North Coastal climate. These #gures represent 55% of the initial energy consumption. 5.2. Type B: enclosed=heavy=skin dependent=cellular Fig. 3 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for the four di1erent climatic regions. Cooling represents a small part of the total energy consumption and is only necessary in the warm climate of South and Continental Europe. Use of passive cooling systems totally eliminates the energy requirements for cooling in both South Mediterranean and Continental climatic regions. However, the reduction of the total energy consumption is negligible. As discussed in Section 3.2, retro#tting actions on this building type should mainly focus on the improvement of the envelope and HVAC systems. Increasing the insulation levels and the air tightness of the outer envelope and using clear glazing to increase passive solar gains was found to reduce the heating energy consumption by nearly 55% in all climatic regions. Due to the increased solar gains in the summer period this scenario results in a slight increase of the cooling energy consumption. As a result, the total energy savings achieved were close to 44 kWh=m2 . The scenario aiming to improve the HVAC systems was found to reduce signi#cantly the energy consumption for
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Fig. 3. Retro#tting scenarios for Type B buildings: Breakdown per energy-end use for di1erent climatic regions.
heating and cooling. The average reduction in the heating energy consumption was estimated to range from 35 kWh=m2 in the South Mediterranean to 84 kWh=m2 in the North coastal conditions. These values correspond to almost 55% of the initial energy consumption in all climatic regions. Global retro#tting, combining interventions on the envelope and systems as well as integration of passive cooling techniques was found to have the most impressive energy savings, reducing the total energy consumption by nearly 80% in all climatic regions. The heating energy consumption is estimated to range from 56 kWh=m2 in the South Mediterranean to 117 kWh=m2 in the North Coastal climatic regions. 5.3. Type C: free standing=heavy=skin dependent=cellular Fig. 4 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.3 retro#tting scenarios for improvement of the energy performance of this building type should focus on the envelope and the ventilation system. A scenario reducing the lighting consumption was found to have a negligible impact on the total energy consumption of this building type. The ‘passive systems and techniques’ scenario is a combination of passive measures focusing on the reduction of the cooling energy consumption of the building. The scenario was found to reduce the cooling energy consumption by nearly 30% in all climatic regions. Additionally, the
proposed reduction of the ventilation rate during winter contributed to the reduction of the heating energy consumption by nearly 20% in all climatic regions. Consequently, the ‘passive’ scenario was found to result in a reduction of 19%. The scenario accounting for better control and improved e$ciency of the ventilation system was found to result in a signi#cant reduction of both heating and cooling energy consumption. Accordingly, a reduction of nearly 38% in the initial heating energy consumption was achieved in all climatic regions and the savings in the cooling energy consumption were close to 85%, as a result of the implementation of a night ventilation strategy that takes advantage of the thermal mass of the building. The ‘heating’ scenario includes measures addressing the building envelope, supported by system control measures and utilization of otherwise wasted energy, aiming to reduce the heating energy consumption of the building. This scenario was found to reduce signi#cantly the total energy consumption. Accordingly, the average reduction in the heating energy consumption was estimated to range from 92 kWh=m2 in the South Mediterranean to 240 kWh=m2 in the North coastal conditions. These values correspond to almost 80% of the initial energy consumption in all climatic regions. The cooling energy consumption was slightly reduced mainly as a result of the reduction of the in#ltration rate. The estimated reduction was close to 8 kWh=m2 , representing close to 30% of the initial cooling energy consumption in all climatic regions. The set of measures included in the global retro#tting scenario was found to have a slightly greater reduction in the total energy consumption, due to the inclusion of measures that reduce cooling energy demand.
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Fig. 4. Retro#tting scenarios for Type C buildings: Breakdown per energy-end use for di1erent climatic regions.
5.4. Type D: free standing=light=skin dependent=open plan Fig. 5 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.4 retro#tting scenarios for improvement of the energy performance of this building type should compensate the envelope losses as well as increased heating and cooling energy consumption through the ventilation system. The ‘heating’ scenario includes combined measures for the improvement of the U -value of the envelope and the enhancement of the HVAC system e$ciency. New settings of the control parameters and installation of a heat recovery system results in a decrease in the total energy consumption ranging from 47% in the South Mediterranean to 77% in the North Coastal climate. The greatest part of the energy savings is achieved in the heating energy consumption which is minimized in all climatic regions. The cooling energy reduction, mainly achieved through reduction of the air in#ltration rate, was found to range from 24% in the South Mediterranean climate to 44% in the North Coastal climate. Additional measures for the improvement of the e$ciency of the ventilation and lighting systems and application of night ventilation were found to further improve the e$ciency of the ‘heating’ scenario regarding both cooling and lighting. Consequently, the ‘global’ scenario was found to be more e1ective than the ‘heating’ scenario, resulting in total energy savings ranging from 59% in South Mediterranean to 79% in the North Coastal climate. The ‘passive systems and techniques’ scenario includes measures for the improvement of the building envelope, combined with measures mainly aiming to reduce the
cooling requirements of the building. Proper use of solar control and the removal of false ceilings to enhance the e1ectiveness of the interior thermal mass of the building, reduces the cooling energy consumption by 78% in the South ◦ Mediterranean. Reduction of the heating set-point by 1:5 C, a measure included in this scenario, results in minimizing the heating energy requirements, even in the North Coastal climate. Use of daylight sensors for better utilization of the available daylight reduces the lighting energy consumption by almost 50%. Consequently, the total energy consumption is reduced by 80% in all climatic regions, which makes this scenario the most energy e$cient one for this building type. 5.5. Type E: enclosed=light=skin dependent=cellular Fig. 6 illustrates the impact of the proposed scenarios and global retro#tting on the energy consumption of this building type. Results are given in terms of breakdown per energy-end use for four di1erent climatic regions. As discussed in Section 3.5 retro#tting scenarios for improvement of the energy performance of this building type should mainly focus on the application of control strategies in the HVAC and on the reduction of the unnecessary solar gains in the summer period. The cellular structure and highly glazed outer envelope of these buildings allow for a deep daylight penetration and the use of arti#cial lighting is usually controlled by the occupants. Therefore, despite the fact that the lighting scenario results in a signi#cant reduction in the lighting energy consumption, the corresponding reduction in the total energy consumption is not so important. The ‘ventilation’ scenario was found to reduce the cooling energy consumption by 30% in the South Mediterranean
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Fig. 5. Retro#tting scenarios for Type D buildings: Breakdown per energy-end use for di1erent climatic regions.
Fig. 6. Retro#tting scenarios for Type E buildings: Breakdown per energy-end use for di1erent climatic regions.
and the heating energy consumption by 14% in the North Coastal climate. A simple reduction in the heating set-point, proposed in the ‘heating scenario’ was found to reduce the heating energy consumption by 48% in the North Coastal climate. Application of the ‘heating’ scenario was found to result in a reduction of the total energy consumption ranging from 27% in the South Mediterranean to 37% in the North Coastal climatic region. The e1ectiveness of the ‘heating’ scenario is signi#cantly enhanced by the introduction of an e1ective solar
shading system to reduce the excessive solar gains during the cooling period. Accordingly, the scenario ‘passive systems and techniques’ was found to reduce the cooling and total energy consumption by nearly 40% in all climatic regions. The global retro#tting scenario, combining all the above interventions has the most impressive performance, resulting in a reduction of the total energy consumption reduction ranging from 48% in the North Coastal to 56% in the North European climatic regions.
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6. Conclusions A retro#tting intervention a1ects the energy performance of a building according to its characteristics and speci#c needs. Successful energy retro#tting of a building addresses speci#c aspects or combination of aspects taking advantage of the special energy-related characteristics of the building in order to improve its energy performance. A determining factor in this process is the climatic region of reference. The present study was based on the analysis of the energy-saving potential of retro#tting strategies proposed for 10 buildings that were classi#ed into #ve types representing the existing o$ce building stock in Europe. Each type was investigated under four di1erent climatic conditions, covering the main climatic regions of Europe. Apart from the expected energy gains, the cost e1ectiveness of the proposed retro#tting scenarios is of great importance when choosing the most appropriate retro#tting intervention on an existing o$ce building. The cost e1ectiveness of the retro#tting scenarios proposed for each of the 10 o$ce buildings investigated in the framework of the OFFICE project was studied and is reported in detail in [4]. Due to the particularities associated with each building as well as the regional climatic variability, it is not possible to generalize the conclusions drawn from the present study. However, it is possible to extract an indication of the trends observed in the behavior of each building type with regard to various retro#tting interventions. As expected, global retro#tting was found to have the highest reduction of the total energy consumption in all climatic regions and all building types. Type A buildings (free standing=heavy=core dependent= open plan) present impressive energy savings for the scenarios that a1ect the installed HVAC and lighting systems. This is due to their open plan interior structure and due to their large volume which minimizes their skin dependence, reducing the e1ect of scenarios improving the envelope. Application of the HVAC scenario described in Table 1 in a Type A building in Greece was found to have a simple pay-back period (SPBP) of nearly 33 years. A simple measure though, such as installation of a BMS system was found to have an SPBP of 10 years, with almost the same energy gains as the scenario. Application of the lighting scenario described in Table 1 in the same building was found to have an SPBP of 9 years, while a simple measure accounting for a reduction of the installed power from 121 to 20 W=m2 in the building was found to have an SPBP of 5 years with almost the same energy gains as the scenario. Type B buildings (enclosed=heavy=skin dependent= cellular) present impressive reduction of the total energy consumption for the scenarios focusing on the improvement of the envelope and HVAC system. Taking advantage of the building’s skin dependence, the scenario on the envelope improvement, described in Table 1, was found to signi#cantly improve the total energy savings of a Type B building in France. Further improvement was achieved
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through application of the HVAC scenario in the same building. The estimated pay-back period for the HVAC scenario was close to 10 years. Type C buildings (free standing=heavy=skin dependent= cellular) have an impressive response to combined interventions a1ecting the building envelope and systems. Application of the ‘heating’ scenario described in Table 2 in a Type C building in Denmark was found to have an SPBP of nearly 10 years. Application of measures for the improvement of the building envelope combined with measures aiming to reduce the cooling requirements of the building have an outstanding e1ect on Type D buildings (free standing=light=skin dependent=open plan). Application of the ‘passive systems and techniques’ scenario described in Table 2 in a Type D building in Germany was found to have an SPBP of 15 years. Application of the ‘heating’ scenario described in Table 2 in the same building was found to have an SPBP of 9 years with smaller energy savings. Type E buildings (enclosed=light=skin dependent= cellular) have an impressive energy-saving performance when operating under scenarios combining control of their systems and solar shading to reduce excessive solar gains in summer. Application of the ‘passive systems and techniques’ scenario described in Table 2 in a Type E building in Sweden was found to have an SPBP of 7 years. Application of the ‘heating’ scenario described in Table 2 in the same building was found to have an SPBP of 0.1 years with very similar energy savings. Acknowledgements This work was carried out in the framework of the OFFICE research project partly funded by the EC (contract number JOR3-CT96-0034). The authors would like to acknowledge the European Commission for the #nancial support of this research. The above analysis is based on the results from an extensive number of energy simulations performed within the frame of the Design Guidelines task of the OFFICE project. The authors would like to thank the groups of ESBENSEN, LASH, ECD, EPFL, NTNU and GR-BES for their valuable contribution to this task. References [1] Balaras CA. A guide for energy conservation in o$ce buildings. CIENE, Dept. of Applied Physics, University of Athens, 1994. [2] Tombazis A, Vratsanos N, editors. O$ce building typologies in Europe. Report No. OF-1, OFFICE programme, JOR3-CT96-0034. [3] Dascalaki E, editor. ATLAS on the potential of retro#tting scenarios for o$ces. Final Report, OFFICE programme, JOR3-CT96-0034. [4] Hestnes AG, Kofoed NU, editors. Draft #nal report on the design and evaluation subgroup. OFFICE programme, JOR3-CT96-0034.