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Passive house school in Knivsta in Sweden!
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October 10, 2016

Passive house school in Knivsta in Sweden!

Passive house school Högåsskolan in Knivsta in Sweden

A new passive house school Högåsskolan was built in Knivsta, about 50 km from Stockholm in Sweden. The architect´s company designing the school was the Archus Architects, Margareta Löfgren and Anna Kovács. The high school was completed in year 2014 and it was build as passive in order to minimize the cost of school from a life cycle perspective. Högåsskolan is built using passive house technology including requirements that the building is optimally positioned on the plot, it has a thermal bridge free structure, optimum day lighting, solar shading around the window and get the entrances to reduce drafts.

The Högåsskolan in Knivsta has an integrated gymnasium that meets curriculum requirements up to grade 6, as well as a preparation kitchen. The building is relatively square with three floors, which provide very good conditions for achieving passive house standards in a cost effective manner.  The heat requirement for the school is below 15 kWh/(m².a). The school cam accommodate up to 450-500 children. The heated temperature (Atemp) is about 5,000 m². The building frame consists of concrete slabs and I-joists with cellulose insulation. Passive House windows were installed with installed U-value of 0.64 W/(m².K).

During much of the year warms the school only by solar radiation and the heat generated from people, lighting and appliances. In the winter additional heat is supplied via a hydronic heating systems that are supplied by means of so-called passive geothermal heat. In the school building plot there are 28 boreholes in 250 meters. The drill holes also help cool the building on hot summer days.

In June 2015 the school was awarded the International Passive House certification.

dlAir tightness test report of Högåsskolan in Knivsta, or Lufttäthestprovningsrapport (link here)

February 2015. Report by IG Passivhus is in Swedish. A passive house school in Knivsta needs to have a good air tightness (n50<0.6 h-1) to be certified as a passive house according the Passive House Institute and German definition of a passive house. Blower door equipment is used to test the air leakage. The results show that air leakage at 50 pa is q50 = 0.06 l/(s.m²) and air permeability is n50 = 0.07 oms/h. The report shows locally occurring small air leaks at the provisional seals at the unfinished details. The shortcomings should be addressed through adjusting the frame / sash and seal between the frame and the wall. The assessment for the building as a whole is that it is very tight and no air leakage is expected to cause defects in the thermal climate.

dlThermography test report of Högåsskolan in Knivsta, or Termograferingsrapport (link here)

February 2015. Report by IG Passivhus is in Swedish. Report describes the procedure how to test the Högåsskolan in Knivsta with thermographic camera including the evaluation of results and images, and the floor plans of school where the images were taken. In the three lower floors the exterior walls are made of the concrete which means there is a temperature inert material. No leakage of air or cooled surfaces could be noted for this type of wall. On the 4th floor is exterior walls of lightweight construction with a stud frame and mineral wool insulation, air and vapour-proof barrier on interior and wind shield on outside.

Exterior walls are then lined with sheet material. No leakage of air or cooled surfaces could be noted for this type of wall. Roof images are generally satisfactory surface temperature and temperature distribution. No air leakage was observed onto adjacent walls. Windows are generally well sealed and no abnormal air leaks between the sash and frame or between the frame and the adjacent walls. On the single window are local minor shortcomings that should be addressed. In summary, the building as a whole performed well regarding air tightness and insulation.

dlPresentation about Högåsskolan in Knivsta (link here)

September 2015. Presentation by Archus Architects is in English. The presentation describes the compactness of two adjacent buildings with the enclosing area towards total floor area (7,997 m3 / 6,235 m2 = 1.3), optimal placement on the building site in respect of getting the most of daylight conditions and three entrances with enclosed areas. The solar shading is fixed with canopies around dining room, boxes around windows and porches at entrances.

Furthermore, the exterior walls for floor 1 (underground) are built from load-bearing concrete structure of 200 mm and insulating layer 300 mm of expanded polystyrene (U-value = 0.12 W/(m².K). Exterior walls for floors 1-3 are made of load-bearing concrete structure of 150 mm, insulating layer of 350 mm, and lightweight stud and cellulose insulation resulting in U-value of 0.115 W/(m².K). Exterior walls for floor 4 consists from load-bearing structure of 145 mm made from timber stud with 45 mm insulation, insulating layer 350 mm lightweight stud and cellulose insulation resulting in total U-value of 0.10 W/(m².K).

Ground slab is made from 300 mm insulation located under the concrete slab resulting in U-value of 0.12 W/(m².K). Flat roof has 600 mm of insulation (U-value = 0.065 W/(m².K)) and pitched roof has 400 mm of insulation (U-value = 0.10 W/(m².K)). Windows/glazed facade are triple glazed filled with argon with average value: 0.67 W/(m².K) and external doors have U-value of 0.90 W/(m².K). The building services are supplied by photo-voltaic system (30,000 kWh/year).

Images by IG Passivhus.

Find more Swegon Air Academy Building Case Studies here (link).