7. Passivhus Norden Sustainable Cities and Buildings. Comparison of five zero and plus energy projects in Sweden and Norway A technical review

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1 Copenhagen, August Passivhus Norden Sustainable Cities and Buildings Brings practitioners and researchers together Comparison of five zero and plus energy projects in Sweden and Norway A technical review Tor Helge Dokka 1, Bjørn Berggren 2 and Niels Lassen 1 1 Skanska Norge AS, Norway 2 Skanska Sverige AB, Sweden * Corresponding bjorn.berggren@skanska.se SUMMARY In order to share knowledge and experiences on how to design and construct high energy performance buildings, this paper presents an analysis, comparing five different projects built in Sweden and Norway by Skanska. The five projects are named: Solallén, Skarpnes, Juvelen, Väla Gård and Power house Kjørbo. All projects have applied energy saving measures before considering energy generation. The building envelopes in all projects are well insulated. Furthermore all projects have balanced ventilations with heat recovery and are designed to reduce the load from the sun during summer in order to reduce the cooling demand. All projects, except Juvelen, have used ground source heat pumps to supply the buildings with heat for hot water and space heating. All projects use PV to achieve the ambition for net zero- and plus energy ambition. KEYWORDS Net Zero Energy Building, Technical review, Design strategies, Energy performance INTRODUCTION The concept of Net Zero Energy Buildings (Net ZEBs) has existed for a while. In the Nordic countries, a limited amount of built buildings exists today, but more are being planned. However there exists no common international standard for this type of buildings, and there are no official national standards in Sweden or Norway. In order to share knowledge and experiences on how to design and construct high energy performance buildings, this paper presents an analysis, comparing five different projects built in Sweden and Norway by Skanska. A comparison of passive measures of the building envelope, the thermal supply system and the renewable electricity production is undertaken. Simulated energy performance and lessons learned will be discussed. This first section gives an introduction to the study and the projects. The following section describes the technical solutions used within each projects comparing building envelope, heating, ventilation and cooling system (HVAC), lighting and plug loads and renewable energy supply. Investigated projects The five projects are named: Solallén, Skarpnes, Juvelen, Väla Gård and Power house Kjørbo. Solallén, see Figure 1 (left), is built in the middle of Sweden, in Växjö. The project consist of seven one story-terraced houses with three dwellings in each house. The buildings were designed during 2012 and are formed as a housing cooperative. Initially there was a requirement from the municipality, who owned the land, that the buildings should be designed according to the Swedish passive house criteria (Sveriges Centrum för Nollenergihus, 2012). However, the project thought that it was more cost effective and environmental friendly to achieve a Net ZEB balance instead of trying to fulfill the passive house criteria. This meant that the project, after applying passive design features considered reasonable, the project invested in a Page 1/10

2 geothermal heat pump and PV-panels instead of spending the last share of the budget on increased amounts of insulation. In this project Net ZEB balance is including energy use according to the Swedish Building regulations, meaning that lighting and plug loads are not included. All dwellings are now occupied and measurements of the energy performance started in March The Skarpnes project, see Figure 1 (right), is currently built in Arendal, the southern part of Norway. The project consist of seventeen single family houses (SFH), and 20 apartments in 2 buildings. The SFH is currently under construction, and the apartment buildings have planned construction start in The first SFH was taken in use in November Figure 1 Left: Picture of one of the buildings at Solallén, Right: Illustration of the buildings in the Skarpnes development Juvelen, see Figure 2 (left), is designed to be built in Uppsala, close to Stockholm. The building is a result from an architectural competition conducted in The municipality (Uppsala kommun) stated in the conditions for the competition that it was their opinion that it was possible to create a plus energy building. It is also the municipality's belief that solar energy will have an important function in such a building. Hence the result was a building designed as a Net ZEB. In this project Net ZEB balance is including energy use according to the Swedish Building regulations, meaning that lighting and plug loads are not included. The energy use is weighted, using primary energy factors. Väla Gård, see Figure 2 (right), is a two-story office building, is situated in the south of Sweden. The overall design concept may be described as two main buildings with double pitched roofs, connected by a smaller building with a flat roof. The design phase started in 2009 and the construction started in The building has been in use since The building has proven to outperform the goal of being a Net ZEB, see Energy performance. Figure 2 Left: Illustration of Juvelen. Right: Picture of Väla Gård Powerhouse Kjørbo, see Figure 3, located in Sandvika outside of Oslo, consists of two ordinary office blocks from the 1980 s that have been transformed to an up-to-date and modern office facility. The goal over the lifetime of the buildings is to produce more energy than they use during the whole lifetime (60 years). Page 2/10

3 Figure 3 Power house Kjørbo A summary of the five investigated projects are describe in Table 1. Table 1 Summary of investigated projects Project Location Annual mean temp ( C) Sollallén Skarpnes Juvelen Väla gård Powerhouse Kjørbo Växjö, central part of Sweden Arendal, southern part of Norway. Uppsala, central part of Sweden Helsingborg, southern part of Sweden km west of Oslo 6.3 Type of building and reference area 7 Terrace houses, new construction. 7 x 257 m 2 17 Single family houses, new construction. 17 x 154 m 2 1 Office building, new construction m 2 1 Office building, new construction m 2 2 office buildings. Retrofit project m 2 DETAILED DESCRIPTION OF PROJECTS Building envelope and building structure s for exterior walls and roof is calculated according to EN 6946 (Swedish Standards Institute, 2007a) and EN ISO (Swedish Standards Institute, 2007b). Normalized heat capacity is the internal heat capacity (according to EN ISO (Swedish Standard Institute, 2008)) normalized by conditioned/heated floor area. See equation 1, below. κ j A j Aheat (1) 3600 Where κ j is the internal heat capacity per area of the building element j, element j and A j is the area of the A heat is the conditioned/heated floor area, i.e. floor area which is mechanically heated. The ground construction in Solallén is a concrete slab with EPS insulation between the concrete slab and the ground. The exterior walls are insulated and prefabricated wood frame constructions, using mineral wool. The roof construction was built on site with timber roof trusses, insulated with mineral wool. In Skarpnes the slab on ground is a concrete slab with EPS insulation. Cellar walls is made of core insulated light weight aggregate blocks. The roof construction is made of prefabricated trusses. The external wall is a prefabricated construction (36 x 198 mm) with additional insulation layers both on the inside and outside. Page 3/10

4 Juvelen, as mentioned earlier, is still in the design phase. This means that the final design of the building envelope and building structure may change. Currently the building is designed with a concrete foundation with EPS insulation. All load bearing walls, external walls and the roof construction are concrete constructions. External walls and roof is designed to be insulated on the exterior side with EPS insulation. At Väla Gård, the ground construction is also a concrete slab with EPS insulation between the concrete slab and the ground. The external walls were prefabricated concrete walls with graphiteenhanced EPS insulation. On site an additional layer of mineral wool were mounted before the wood façade were mounted. The double pitched roof construction was built on site with timber roof trusses, insulated with mineral wool. The flat roof is a corrugated steel sheet, with EPS insulation and mineral wool on the exterior side. Power House Kjørbo is a building renovation project where the existing load bearing concrete structure has been kept unchanged, while interior, facades, windows and technical systems have been renewed. The building envelope above ground level is insulated to passive house standard, while walls and floor under ground level is insulated as good as practically possible. The slab between the basement and ground floor has been insulated to reduce the heat loss to the ground. Table 2 Summary of building envelope for all five projects Foundation Exterior walls Roof Windows Doors Average Insulation (mm) Insulation (mm) Insulation (mm) Solallén Skarpnes Juvelen Väla Gård Power House Kjørbo Air tightness n 50 (h -1 ) Normalized heat capacity (Wh/m 2 ) Passive measures for solar energy At Solallén, there are large windows in the living rooms, which are facing south or west (depending on the orientation of the building). All windows and glazed doors in the livings rooms were given external solar shading (screens). The residents are also provided with solar window film, which they may apply in their bedrooms if they want to. Concerning the Skarpnes project, due to poor experience with a lot of south facing windows in Norway, giving to high temperatures already early in the spring, the window size and distribution is normal and more oriented towards giving adequate daylight conditions in different rooms. External solar shading (screens) is applied for solar exposed windows facing east, south and west. Page 4/10

5 In the design of Väla Gård, solar shading where carefully considered. The direct effect was the initially glazed gables where instead designed as walls with regular windows. All windows were mounted >200 mm in, from the facade, giving them a small external solar shading. Furthermore, all windows facing south-east and south-west (no windows directly towards south) were also given additional external solar shading. At Juvelen windows facing south-east to south-west are designed to be mounted >300 in, from the facade. The choice of glazing will be further studied. At Powerhouse Kjørbo the building volume and placement, orientation and of windows was locked to the original design as the façade is historically protected. The size of the windows is somewhat larger than the original windows. To avoid overheating in the summer, the building has been equipped with automatically activated external sun screens. Technical installations At Solallén the ventilation is designed as balanced ventilation with heat recovery. The standard ventilation rate is according to Swedish building regulations but may be increased if the indoor temperature or relative humidity exceeds a certain level (chosen by the residents). The residents may also manually choose to increase the ventilation rate. Each building at Solallén (containing three dwellings) is equipped with a ground source heat pump (GSHP) and a PV panel installation. The GSHP provides the buildings with heat for space heating and hot water. During summer, free cooling from the bore holes are utilized and supplied to the dwellings via the ventilation system. The PV panel installation at each building is designed to generate the same amount of energy needed for the GSHP and the ventilation system. The ventilation solution for Skarpnes is a balanced ventilation system with a rotary wheel heat recovery. In addition the fresh air is preheated in the winter with the ground source brine loop, which also can be used to cool the air slightly in warm periods (not taken into account in the energy simulations). The total efficiency of the rotary wheel and the preheating system is estimated to be 90 %. The thermal supply system is a GSHP based on a 90 m deep borehole for each dwelling, covering both the space heating, the demand for hot water and also supply hot water to dishwasher and washing machine (hotfill machines). The peak load is covered by an electric element. The electric renewable production is provided by a high efficiency mono-crystalline PV-system. Juvelen is also designed with as balanced ventilation with heat recovery. The main part of the building is designed to be ventilated with constant air volumes, running during normal office hours (starting 2 hours before office hours and running 2 hours post office hours). However, meeting rooms will be equipped with variable air volume ventilation. Heat for space heating and hot water is obtained via the district heating network in Uppsala. Cooling is obtained by using free cooling from bore holes. The bore holes are also used during winter to pre-heat the ventilation air, minimizing the risk of frost in the ventilation units. A high energy efficiency ratio (EER) is expected due to that the supply system for cooling is designed to use a high temperature on the brine for the cooling system. The PV-panels at Juvelen are designed to cover 50 % of the energy consumption. The project will invest in off-site windmills to cover the remaining 50 % of the energy consumption. Väla Gård is equipped with two ventilation units, providing the building with balanced ventilation with heat recovery. The ventilation system is designed as a variable air volume system which runs between 6 AM an d 6 PM during weekdays. Otherwise they are completely shut down. They start at a rather low ventilation rate but increases the ventilation rate when necessary, based on CO 2 and temperature. The building has a geothermal heat pump system, with four heat pumps located at the building site. The heat pumps have variable speed compressors, enabling the system to adjust the speeds (and heat production) depending on the varying heating loads. Hence, the system reduces energy losses caused by stopping and starting. Furthermore this enables the heat pumps to manage more than 100% of the estimated peak load. Free cooling is extracted from the bore holes during summer. No electrical chillers are installed. Roofs facing south-west are equipped with PV-panels. At Powerhouse Kjørbo, the design process emphasized interdisciplinary collaboration and the design of technical solutions is therefore closely linked to the general building design. For example, the floor plans are planned to allow optimal zoning and sensor placement for automatic lighting and ventilation control. Electrical outlets at each desk are also controlled by occupancy sensors to reduce energy use. The ventilation concept utilizes the displacement ventilation and hybrid ventilation concepts and is Page 5/10

6 designed for low air volumes and minimum pressure drop. The air handling unit is placed on the top floor and the central stairwell doubles as an exhaust air shaft. Fresh air is taken from the façade on the north side of the top floor and brought in to large vertical shafts with an overpressure of just 20 Pa before it is brought in to air diffusors at floor level in the core of each office space. For office cubicles the air is applied through ducts to each office. Exhaust air flows from the office-areas to central communication areas and out through an overflow vent to the central stair shaft. Here it rises partly due to the stack effect and is exhausted through the air handling unit where the heat is recovered on cold days. On hot days when there is a heat surplus the air is exhausted directly out through hatches in the roof and the staircase. The exhaust fan in the air handling unit only draws enough air to heat the fresh air through heat recovery. All windows can be opened manually by the occupants. Due to overpressure inside the building air will flow out of the window and the applied amount of fresh cooled air via the air handling unit will be larger. The building is equipped with a GSHP which also delivers cooling. However free cooling from the ground is sufficient in most conditions, and the cooling machine is seldom used for cooling. All cooling is applied via the ventilation system, and there are no local cooling units. Heating is applied through the ventilation system and a small number of large radiators placed centrally in the building. There are no radiators under the windows and no radiators in the office cubicles. The door to small offices must be left open on cold nights to supply these rooms with heat when there is no heat load from the users. Table 3 Summary of technical installations for all five projects Ventilation Fixed lighting Solar energy (PV-panels) Energy supply Heat recovery (%) Specific fan power (kw/m 3 s) CAV/ VAV Installed effect (W/m 2 ) Control strategy* Installed effect (Wp/m 2 A heat ) Solallén Skarpnes Juvelen Väla Gård Power House Kjørbo VAV CAV CAV & VAV VAV VAV No No No D+AO D+AOO D+AOO Type** GSHP GSHP DH & FC GSHP GSHP SCOP, heating EER, cooling * AO = Automatic switch-off, AOO = Automatic switch on/off, D+AO = Daylight dimming + Automatic swtich-off, D+AOO = Daylight dimming + Automatic switch on/off ** DH = District heating, FC = Free cooling, GSHP = Ground source heat pump DESIGN PROCESS At Solallén, the initial design concept from the architect, al roofs were rather flat (7 ) and facing north. Due to the fact that the municipality were asking for energy efficient buildings, this had to be changed. Changing the roof pitch, facing towards south and south-west and increasing the pitch, was one of the first decisions made. Thereafter the work were carried out as an integrated energy design process with a small team consisting of an architect, an energy designer, the project developer and a contractor. The work was initiated with an energy meeting were the energy goal was defined and any quarries were discussed. The designed work than evaluated different measures following the Kyoto design principle which means that measures to reduce energy demand are evaluated and applied before energy generation is considered. One scenario of using heat from the local district heating network and exporting electricity from the PV-panels were investigated. However, the project estimated that it would result into a rather extensive communication effort. Explaining the concept of a Net ZEB Page 6/10

7 balance using primary energy weighting factors, which was the case here, for potential buyers who may not have any knowledge within the field. Therefore, when the investment for district heating turned out to be almost the same as for GSHP, the project decided to choose the design concept with GSHP. The aim of the Skarpnes project is to demonstrate that it is possible to build zero energy and zero emission residential buildings in Norway. Further it should use affordable and available technical solutions but used in an innovative way, giving optimal solution with regard to energy use, renewable energy production, costs and comfort (indoor climate). The buildings is designed according to the ZEB-O definition (see where the carbon emission due operational energy use should be zero during an annual balance. All energy items, also plug loads, is taken into account. The design process was a collaboration between Skanska, experts from the ZEB research center, the architect (Rambøll) and the HVAC engineer (Siv.ing Øivind Berntsen AS). Even though the form and architecture is rather conventional for new construction of dwellings in Norway, the roof construction is asymmetric to enhance solar production (PV). Different solutions for energy supply was analysed, both more central solution and solutions for each dwellings. After the evaluation, a solution with a GSHP together with a large PV installation was chosen, based on robustness and cost effectiveness. Solar thermal collectors, in addition to the GSHP, was also considered. However, before the construction start, they were rejected due to complexity of installation, size of the heat storage and costs. Initially the architects behind Juvelen had ideas of concepts where the ratio between the building envelope and the conditioned floor area was rather high. Meaning that the transmission heat transfer losses were high. A work shop were then initiated where an energy goal was defined and the definition of Net ZEB were discussed. After the meeting, the energy engineer compiled a short memo, two pages. The memo gave the architects two important design ratios which they had to consider: window to wall ratio and building envelope to conditioned floor ratio. Furthermore, they were asked to define a solar strategy ; meaning that they had to already before they started to design the building had to consider how they should consider solar energy in their design. In addition to the design features, the memo also defined performance requirements for the building envelope and the technical installations. This gave the architects a scope to work within. The final design drastically reduced the window to wall ratio and building envelope to conditioned floor ratio. Furthermore, the quantities of windows were reduced towards south and increased towards north. The building is still in the design phase, meaning that the projects is currently evaluating different solutions for the building envelope. At Väla Gård the initial design had a lot more glazing compared to the final design. Therefore a number of simulations were conducted, evaluating the indoor climate end energy performance. The results served as a basis for the architects to reduce the quantities of windows and glazed areas. Just as in the Juvelen project, the energy engineer compiled a short memo with performance requirements for the building envelope and the technical installations. The contractor then took a rather simple and effective decision. He decided to outperform all performance requirements. This saved the project a lot of time during the design phase. The time savings were achieved due to that decisions were easy to make. Instead of evaluating different options and asking the energy engineer to do energy simulations for different aspects. The contractor always choose a solution which was slightly better compared to the performance requirement set in the memo from the energy engineer. The Powerhouse Kjørbo process is a product of the Powerhouse collaboration which started as the CEO s of several companies, among them building owner Entra, Construction firm Skanska and architect Snøhetta, signed an intent to build the world s first energy positive office building. The collaboration led to the Powerhouse definition, making a clear and ambitious goal for the environmental standard of the building. The Powerhouse definition states that a Powerhouse must produce more renewable energy through its lifetime than it consumes for production of materials, construction, operation and disposal. The definition relates to measured energy, which means that its fulfilment must be documented through measurements. As project development was initiated both the energy goal and the team was given by the Powerhouse collaboration. The design concept phase was organized and led by a dedicated process leader from Snøhetta, and interdisciplinary workshops were held regularly. The team had a clear philosophy that the key factor for finding solutions to achieve the energy goal lay in an interdisciplinary design process. In addition to workshops there were held a number of workgroup meetings. The participants were divided into interdisciplinary workgroups with responsibility for a specific task. Each workgroup had a designated leader, and a matrix was used to keep track of resources, tasks and responsibilities in the team. Parallel to the concept phase an additional team started work on project development. This team had responsibility for further development and quality control of the ideas from the concept Page 7/10

8 process and then led the project development on to the general building permission. From this point on the project was organized as a traditional turnkey project, although a number of the key participants from the design phase also followed the project in this phase. ENERGY PERFORMANCE Energy simulations In Table 4, the results from simulations for all projects are presented. For all projects energy demand (ED), delivered energy (DE) and primary energy (PE) use is presented. For all projects, the following primary energy factors are used: District heating: 0.8 Electricity: 2.5 Table 4 Summary of calculated energy performance for all five projects Solallén Skarpnes Juvelen Väla Gård Power House Kjørbo ED DE PE ED DE PE ED DE PE ED DE PE ED DE PE Heating (kwh/m2a) Cooling (comfort) Cooling of machines Hot water Auxiliary energy Electricity for lighting Electricity for plug loads On-site Energy generation Total ED = Energy demand, DE = Delivered energy (considering SCOP and EER), PE = Primary energy demand Energy metering As mentioned earlier, measurements of the actual energy performance in Solallén has just begun. Skarpnes and Juvelen are not finalised yet. For Väla Gård and Powerhouse Kjørbo results from actual energy use during operation is available. At Väla Gård, initially the metering could not start due to minor mistakes in the installation of the metering system. As mentioned earlier the measured energy performance is better compared to the results from the simulations in the design phase. Some major conclusions from the metering of Väla Gård are: Initially, one of the ventilation units was having difficulties to find the balance when it started every morning. After fine-tuning the ventilation could be adjusted and the ventilation rate in the morning was not too high. The energy demand for cooling is lower than expected. Page 8/10

9 Comparing the results for the PV-panels, simulations and measurements, they show high agreement. The simulations were expecting 64 MWh, the measurement shows 68 MWh. As the Powerhouse definition states that the fulfilment of the definition should be documented by measured results, the Powerhouse Kjørbo is instrumented for detailed energy metering and energy use is followed up closely. Operation and measurements started in April 2014, and results for the first year of operation are now available. Total consumed energy shows a surprisingly high correspondence in sum between calculated and measured energy. However, the results deviate more when different energy purposes is analyzed. The results have not been corrected for climate variations and user variations. Further they have not yet been fully analyzed and are not fit for making exact conclusions. The building is in a 2 year test phase and undergoing adjustments to optimize the energy use, and several adjustments have already been made. Examples are: Energy for lighting was too high as the lights were activated when the solar screens went down. This has been corrected by programming the screens to not roll all the way down. The energy for domestic hot water was too high as the electric heating element kicked in too soon. This was solved by adjusting the thermostat. The heat pumps have too many starts and stops which will shorten service life of the compressor. The heat recovery unit has lower efficiency than expected due to too low air flow rate. This fact was previously unknown to the manufacturer. DISCUSSION AND CONCLUSION Comparing the technical solutions and design philosophy for the five projects there are several similarities: All rely on high performance building envelope with low s, low air leakage and negligible thermal bridging However some of the projects have a lower performance building envelope than is required for Passive house standard in the respective country. It is reasonable to conclude that better than passive house building envelope is not a requirement for net zero energy houses. In the office projects the exposed thermal mass is high giving high heat storage capacity which lowers the cooling demand, but also lowers the heating demand. All use some sort of external solar shading, either building integrated and/or artificial shading (e.g. screen). All projects use high performance balanced ventilation with high efficiency heat recovery and low specific fan power. All use measures to reduce the electric energy demand, e.g. low energy lighting or ventilation systems with low energy demand for fans. All projects use ground source heat pumps for the heating demand, except Juvelen which applies district heating. All projects use the ground as a free cooling source. All projects use PV (Photovoltaics) to achieve the net zero- or plus energy ambition. To some degree all projects use the same design philosophy, which can be summarized in four points: 1. Reduce the thermal demands (heating and cooling). 2. Reduce the electric demands. 3. Use high performance thermal supply systems to cover the heating and cooling demand. 4. Use building integrated or on-site renewable solar power production (PV) to achieve the desired energy ambition. Page 9/10

10 For all projects, collaboration between different actors in the design phase has been an important action, to be able to reach their goals. For the two projects with metered energy results, Väla Gård and Powerhouse Kjørbo, the measured energy use is close to or better than the simulated energy use. Indicating that the chosen design strategy for these office projects works well in practice. ACKNOWLEDGEMENT This work has been financed by Skanska AB. REFERENCES International Energy Agency (IEA). (2011). Towards Net Zero Energy Solar Buildings. In SHC Task 40/ECBCS Annex 52 IEA (Ed.). Swedish Standard Institute. (2008). EN ISO 13790:2008 Energy performance of buildings Calculation of energy use for space heating and cooling (pp. 180). Stockholm. Swedish Standards Institute. (2007a). EN ISO 6946:2007 Building components and building elements Thermal resistance and thermal transmittance Calculation method (pp. 44). Stockholm. Swedish Standards Institute. (2007b). EN ISO 13370:2007 Thermal performance of buildings Heat transfer via the ground Calculation methods (pp. 64). Stockholm. Sveriges Centrum för Nollenergihus. (2012). Kravspecifikation för nollenergihus, passivhus och minienergihus, from %20bostader%20jan.pdf Page 10/10