Passive houses for the Northern climate

Passive houses for the Northern climate Jyri Nieminen Customer Manager VTT Technical Research Centre of Finland Finland Jyri.Nieminen@vtt.fi Jouko Knuutinen Regional Director TA Yhtymä Finland Jouko.Knuutinen@TA.fi Summary A passive apartment house and a similar reference building that fulfills the national building code requirements are under construction in the City of Oulu in Northern Finland. Oulu locates at the latitude 65,01 o. The aim is to compare energy performance and construction costs of a very lowenergy building and a typical building in a cold Northern climate. Special attention has been paid on performance verification by a monitoring program, passive building s heating and ventilation systems and design for an airtight building envelope. The buildings will be connected to district heating. Solar thermal systems will provide heat for hot water in summer. Dynamic energy simulations show that the developed concept fulfils the heating and primary energy demand requirements set for a passive house in Northern Finland. The buildings contract offers show that the extra costs of the passive house are low, less than 4% compared to typical. Keywords: Include list of keywords (maximum of ten keywords) 1. Introduction Passive house is one of the approaches to build very energy-efficient buildings. It is not a standard, and so far any country has approved a passive house as a national building code requirement. A passive house is an approach to reduce building's energy demand down to a minimum by economically attractive extra costs. Figure 1 compares the present Central European passive house requirements to passive house defined for Finland [1, 2]. The heating demand in Nordic climates is much higher than in Central Europe, Figure 2. The rationale behind the Finnish definition for a passive house is that the building has to fulfil the national building code requirements on ventilation rate, indoor climate and hygrothermal performance of building structures. Therefore, e.g., ventilation heating system with subsoil exchanger with ground to air heat exchange (Figure 3) does not fulfil the requirements for purity of supply air. The impact of this type of a system on hygiene or health has not been identified (condensed moisture in the pipeline, mould, dirty pipes, etc.) [3]. Passive house as an approach bases on performance requirements. There are no specific energy requirements on building components. The design team has to ensure the conformity of the design solutions to required energy efficiency level by energy simulations. However, there are number of recommendations on very low-energy buildings such as a passive house that need to be taken into account in the design of the building. Window area, e.g., should be 15-20 % of the floor area depending on the building type to ensure adequate natural lighting. Passive houses suit well on building sites with low solar access. A passive house utilizes passive solar energy efficiently, but at the same time efficient passive cooling methods should be implemented to avoid cooling demand in summer. Air tight building envelope is a key figure of a passive house. Therefore all installations

and routing of technical installations should locate inside the building's thermal envelope for reduced number of penetrations in the air tight layer. Heating demand, kwh/m 2 Heat demand, W/m 2 Primary energy demand, kwh/m 2 Over heating hours/year Temperature > 25 o C, % Air tightness, n 50 1/h Germany 15 10 120 10 0,6 Finland South Central North 20 25 30-130 135 140-0,6 Functional unit, area m 2 Energy calculation method Treated floor area PHPP Gross floor area Optional Fig. 1. Passive house definitions. The Central European definition is rather difficult to be reached in cold climates and, thus, a country based approach is required. Fig. 2. Heating degree days of European countries according to Eurostat method [4]

Fig. 3. Ventilation heating aim as reduction of costs of heat distribution system. If a building's heat demand is in the range of 10-20 W/m2, ventilation supply air can be used as a heat carrier into rooms. In cold climates 10 W/m2 is very difficult to be achieved, and typically ventilation heating requires boosting during peak demand to quarantine the required heating efficiency. Preheating of fresh air helps for reducing the need for defrosting of heat exchanger. Subsoil heat exchangers are not recommended in Finland due to possible health risks. 2. Passive apartment building in Oulu 2.1 Project aims The project aimed at assessment of a very low-energy apartment house concept requirements for a Nordic climate. The feasibility of the Finnish definition for a passive house was studied in the climate of Oulu (latitude 65,01 o ). The project produced a solution to fulfil the requirements for Northern Finland (Figure 1). The phases of the project were: Design targets for energy demand, indoor climate and construction costs Definition of the concept Design solutions Dynamic simulations for conformity assessment Special design for buildable building envelope solutions Monitoring plan Construction Guidelines. Two apartment buildings with similar architecture and typology are being built in Oulu. One of the buildings follows the requirements of the National Building Code, and the other is a passive apartment buildings. Both buildings will be monitored to assess the performance and conformity to requirements set for the buildings. 2.2 Design characteristics Table 1 shows the properties and simulated energy demand of the buildings. The energy demand

assessment bases on modelling of the buildings and dynamic simulations. Table 1. Building properties and energy simulation results. Building Gross volume, m 3 4287 Heated gross area, m 2 1219 Heated floor area, m 2 942 Structures m 2 W/m 2 K (BC 2010) 1) Exterior wall 795 0,15 (0,17) Roof 433 0,09 (0,09) Base floor 433 0,14 (0,16) Widows - South - East - North - East - North - West - South - West 82 8 51 16 0,85 (1,0) Doors 39 0,9 (1,0) Ventilation Design value (BC 2010) Minimum ventilation, m 3 /s 0,595 (0,595) Air tightness n 50, 1/h 0,6 (2) Infiltration, m 3 /s 0,016 (0,08) Ventilation heat recovery (minimum), % 75 (45) Energy simulation: electrical energy Household electricity, kwh/m 2 25 Fixed lighting, building services, kwh/ m 2 12 Water Cold water (total), m 3 /a 1750 Hot water, m 3 /a 700 Heating demand Space heating, kwh/m 2 28 (64) Hot water heating, kwh/m 2 29 Heat demand Space heating, kw 29 Space heating W/room-m 2 31 1) Building code 2010 requirements and corresponding performance characteristics in parenthesis. According to the energy simulations the buildings heating demand is 28 kwh/m 2, hot water heating demand 29 kwh/m 2, and total electrical energy demand is 37 kwh/m 2. The present Finnish estimated primary energy factors for grid electricity and district heat are 2,2 and 0,7 accordingly. This gives a total primary energy demand for the passive building 122 kwh/m 2 which is well below the required level. 2.3 Pilot buildings The pilot buildings locate in a block of four buildings. The buildings form a condominium of rights of occupancy residences. Technical room for all the buildings is in building no. 3 (Figure 3). The district heating system is supported by solar thermal system, and part of thee pilot buildings' heating bases on solar energy. The solar thermal system includes collector area of 40 m 2 and a storage tank of 5 m 3. The buildings' heating bases on district heat. Heat distribution system is low temperature floor heating supported by ventilation heating. Room based temperature control allows for individual conditions in each room.

The buildings are under construction in spring 2010. The load bearing structures, floors and load bearing external walls are concrete structures. The non-load bearing structures and roof are lightweight wooden structures. The floor plan of the passive building is in Figure 4. The building has one to three room apartments with kitchen with total area of 881 m 2. Basic kitchen equipment and furniture are provided by the builder. The buildings are under construction and they are completed in autumn of 2010. Reference building Passive building Technical services Figure 3. Site plan and facade images of the buildings (passive building on the right). Figure 4. Passive building, floor plan, 2 nd floor. 2.4 Monitoring The buildings will be monitored according to a monitoring plan shown in Table 2. The monitoring intervals range from one hour to one day depending on the measurement. The aim is to compare the passive building's performance with the reference building. The commissioning procedure includes air tightness tests and infrared surveys. Performance of the ventilation will be ensured with measurements and control actions.

Table 1. Monitoring plan for the passive and reference buildings Electrical energy Water consumption 1) heating energy Electrical energy for building services Electrical energy for building services out side the building Household electricity, whole building Household electricity, selected apartments Building level Apartments Building level Selected apartments Total consumption Ventilation units (staircases, storages) Fixed lighting Plug loads Pumps Laundry Lift Lighting and plug loads Car heaters Energy for melting of outside pathways Extractor fan/kitchen hoods Plug loads and electrical appliances Lighting Saunas All ventilation units Plug loads and electrical appliances Lighting Sauna Ventilation unit Cold water Warm water Cold water Warm water District heat, total Space heating Water heating Space heating, floor heating Space heating, ventilation heating Hot water heating 1) Ventilation Selected apartments Ventilation rate, supply and exhaust Extractor fan Building level Rate Solar energy Energy from the collectors Temperatures Building level Staircases Storage rooms Selected apartments Outdoors Room temperatures Ventilation systems: all ducts at machines 1) Warm water circulation may have an impact on the accuracy of the measurements 2.5 Construction costs The construction costs of the passive building are 3,3% higher than with the reference. This assessment bases on contract offers from contractors. The extra costs are well in the range with other very low-energy building projects where the extra costs are typically between 2 and 7 % compared to reference level. 3. Conclusions The Finnish passive house definition bases on climate dependent assessment of energy demand levels that can be reached with acceptable costs, and at the same time the building fulfils the building code requirements for ventilation and indoor air quality. A passive house's conformity with both the definition and building code requirements can be presented with the energy statement

required from new buildings within the building permission processes. The passive apartment house in Oulu, although it is under construction at the moment, shows that cost-efficient reduction of space heating energy demand is possible. Pilot buildings are necessary for general acceptance of energy-efficient building concepts and wide market penetration of the principles of very low-energy buildings. According to the analysis carried out the pilot building in Oulu (latitude 65,01 o ) fulfils the requirements for a passive house in Northern Finland. References [1] PEP - Promotion of European Passive Houses. EIE/04/030/SO7.39990. Final report [2] NorthPass - Promotion of the Very low-energy house Concept to the North European Building Market.IEE/08/480/SI2.528386 [3] Ståhl, F: Pre-heating of ventilation air through an earth tube system. Building Physics 2002-6th Nordic Conference [4] U-values for better performance of buildings. Report established by ECOFYS for EURIMA