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December 6, 2012

Swegon Air Academy in Tallinn on renovation of multi-residential buildings – Part 2: The right application of renovation measures is the key!

Application of renovation measures lower the lifecycle costs in time and the most beneficial investments are seen as a package of measures. Adding more measures will increase costs and therefore the lifecycle cost will increase, and thus, the renovation measures will not be so much profitable. In Sweden, the major step is to keep the district heating and apply the profitable measures, yet Sweden must also focus on measures which are has lower energy-profitability to get to the national goal as described in previous article. Here is the continuance of Åsa Wahlström´s presentation that she gave in Swegon Air Academy seminar in Estonia.

The new building regulation divides Sweden in 3 climates zone with various requirements for energy. Over 80% of all buildings are situated in climate zone III (Southern Sweden up to the level of Stockholm). New construction requirements (for heating, comfort cooling, domestic hot water and electricity operation of buildings´ services) applied in 2013 based on electric heating vary from 95-130 kWh/(m2.a) or other types of heating vary from 55-90 kWh/(m2.a) depending on the climate zones. Typical is to have a heating/cooling with power of 10 W/m2 which enables to install heat pump and then the building complies with same regulation as for the district heating that is of course lower than electric heating.

Most common technologies in Sweden are heat recovery (air-to-air or exhaust air heat pump) and measures addressing DHW provision (energy-efficient taps, meters, etc.). Also the lighting is in focus with demand-controlled system and installation of energy-efficient bulbs in staircases, attics and common laundry. Furthermore, the measures include loft insulation, window replacement and facade insulation. Additional energy is usually obtained from solar energy – solar thermal and PV panels which produce electricity.

As example the building in climate zone II is taken and various applied measures and their efficiency are described. Air-to-water heat pump and ground source heat pump have good effects if applied with small amount of measures to achieve 50 kWh/(m2.a) required for climate zone III. Facade insulation and window replacement will reduce energy consumption, but they have high costs, and thus, long payback time. The most important measures is heat recovery in order to meet energy consumption requirements and that what Swedish Energy Agency has considered and made renovation procurement to get better systems available in the market.

Åsa said: “In Sweden, at the beginning there were no building owners asking for heat recovery and no entrepreneurs who could give the whole package from design, operation to service. That is why we have placed air-to-air heat exchanger in 3 buildings and air-to-water heat pumps in 4 buildings to make a market which did not exist and to introduce the companies producing such technology and solutions. It was a development of ordinary techniques but focused on cost reductions and operation experiences (installation, service and maintenance). Many service building people were not used to do anything about the systems and they were afraid that this will require more knowledge from the staff in multi-residential sector. Main requirements were energy efficiency, costs, indoor environment, design and function, installation and operation with maintenance.”

Åsa stated also obvious facts which are often forgotten and are important part of the process: “When you install something, it must be acceptable for tenants and architecturally right. It needs to have a function and work properly. When the tenants are still living in the apartments, the work must be done during 1 week and do not disturb tenants. The new installation usually does not work properly for the first year after installation; therefore there is a need for commissioning. This is also about finding the space to install heat recovery and implementation of techniques which can be repeated in all types of apartment buildings.”

The exhaust air heat pump can be used as an outdoor heat pump with improved efficiency by a condenser which improves efficiency. This solution has been widely used in single family houses but not so much on multi-residential buildings in Sweden. As shown in many examples by Åsa, the storage tank can be situated in cellar where the ducting is lead through the formerly used waste shafts. These former waste shafts are not allowed to be used today as Sweden wants to focus on recycling.

The indoor climate must be improved at the same time which means that we must make the building´s envelopes tight and have control. The control is easier applied with heat recovery then formerly used exhaust air heat pump which was usually located with air supply behind radiators. The current air inlet is lead from the ceiling all the way down across the room to get a good mix of air. That way the exhaust devices must be installed directly above the doors and this also required invention of some new exhaust devices for better mixed ventilation.

The typical energy savings compared for two different techniques are approximately 35 kWh/(m2.a) but resulted in increased electricity consumption. In this case, the evaluation must be made if it is better to use electricity or district heating. The facade improvements are still rather difficult to apply in Sweden as the industry might not be ready to give a decent solution today. The prefabricated thin elements for facade are one way to do it where the whole element is put on exterior without disturbance of tenants. The only thing to do from interior is to take away the old window and sealed the new window in the new façade elements. Another idea with profile system elements made from aluminium and steel structure has been used in new large buildings in Lund. In this case every second element is glazed and every second element is fitted with PV panels. However, this method is not ready to be used in renovation so far. There was also another invention where the manufacture thinks that he can have both elements integrated, i.e. the ducting are installed in the facade and insulation is put on the top covering the whole façade and ducting.