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Solvärme för en skola i Lerum. Studier av olika systemalternativ.

Solar Heat for a School in Lerum. Analyses of different system designs

Martin Nordmark ; Joakim Lind
Göteborg : Chalmers tekniska högskola, 2012. 71 s. Examensarbete - Institutionen för energi och miljö, Avdelningen för installationsteknik, Chalmers tekniska högskola; E2012:07, 2012.
[Examensarbete på grundnivå]

Two elementary schools are now being built in Gråbo (in the municipality of Lerum), Röselidsskolan and Ljungviksskolan, which are both designed with solar thermal collectors for the schools domestic water heating. During the summer while the largest amount of solar heat can be generated, the activity hence the domestic water use in the schools are heavily reduced. Both schools are connected to the local district heating system which makes it possible to use the solar collectors to deliver heat to the district heating. The purpose of this thesis is to evaluate the two systems mentioned above and to determine which system is more suitable to apply on a school. The building which conditions were used for this evaluation is Röselidsskolan. A solar heating plant of each system type was dimensioned from the expected and known conditions of the building. The purpose with the dimensioning was to make the solar plants replace the ordinary energy source as much as possible. The solar plant for domestic water heating was dimensioned to cover 50 % of the annual energy consumption for heating domestic water. The plant for delivering heat to the district heating system was dimensioned from available space on the roof of the building and the summer load of the district heating system. The dimensioning resulted in the following systems: • Domestic water heating system: 35 m2 collector3 area, 2.6 m3 accumulation tank volume • Delivery to the district heating: 300 m2 collector area The solar plant which is built on Röselidsskolan has 126 m2 collector area and 4 m3 accumulation tank volume. The reason for the size of this system being this much larger than that dimensioned in this thesis is that the dimensioning for the built system was based on a estimated consumption of domestic water, much higher than that estimated in this thesis. The built system was dimensioned from an expected hot water consumption of 15 kWh/m2 per year, compare to 3 – 5,5 kWh/m2 per year that was found for this thesis by reweaving available statistics. However, the statistics for domestic hot water consumption in schools are very poor. 3 Aperture area IV The option of connecting the built solar collectors to the district heating is also evaluated in this thesis. This gives two additional systems: • Domestic water heating system: 126 m2 collector area, 4 m3 accumulation tank volume • Delivery to the district heating: 126 m2 collector area The four solar plants mentioned above have been simulated with computer software called Polysun. Due to the uncertainty of the domestic water consumption, the two systems for domestic water heating was simulated with three different heating loads within the span 3 – 5,5 kWh/m2,year. The yearly water consumption is distributed over the schools active time with a reduction by 20 % during the school holidays. Furthermore, the average cost for the solar energy for each solar plant is calculated with the annuity formula. The investment cost for a complete system where, with no regard to size, set to be 10000 kr/m2 solar collector for the domestic water heating systems and 7000 kr/m2 solar collector for the systems with delivery to the district heating. The investment cost, and the reasonable assumption of 20 years depreciation time and a cost of capital at 5 %, gave a relatively high cost for the solar energy. The most important results are:4 • The plant with 35 m2 collector area and 2.6 m3 accumulation tank volume is expected to generate 9 (12) MWh per year, and 260 (345) kWh/m2 collector area and year. The energy cost was calculated to 3,1 (2,3) kr/kWh. • The plant with 300 m2 collector area for delivery to the district heating is expected to generate 84 MWh per year, and 280 kWh/m2 collector area and year. The energy cost was calculated to 2,0 kr/kWh. • The plant which is built on Röselidskolan is expected to generate 13 (21) MWh per year, and 100 (165) kWh/m2 collector area and year. The energy cost was calculated to 8,0 (4,9) kr/kWh. • If the plant which is built on Röselidskolan instead was to deliver heat to the district heating it was calculated to generate 34 MWh per year. Following conclusions can be drawn: • For the alternative where the solar collectors deliver heat to the district heating, the potential for replacing the ordinary energy source is 6 to 9 times higher than the alternative to heat the domestic water supply. • The solar plant built on Röselidsskolan has been calculated to cover 70 to 80 percentage of the energy needed for hot water heating. This high coverage and the low hot water demand in the school during the summer makes the solar plant inefficient. If the plant instead was connected to deliver heat to the district heating it is expected to generate 65 to 170 percentage more useful energy.

Nyckelord: Solar heat, domestic hot water, school building, district heat, energy



Publikationen registrerades 2012-09-05. Den ändrades senast 2013-04-04

CPL ID: 162913

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