A technical evaluation of the thermal solar collector systems at Bo01 in Malmo

Ten thermal solar collector systems for heating buildings and domestic hot water at Bo01 in the Western Harbour of Malmö were taken into operation during the Spring of 2001. The solar collectors are designed to cover about 20% of the total heat demand in that area, with the remaining 80% mainly covered by a heat pump that brings in heat from a local aquifer.

There are two different kinds of solar collectors in Bo01; a plane conventional type Solsam LGB-2 AR, and a tube formed (vacuum) type Viessman 200 D. Pumps and valves etc in the solar collector systems are controlled and monitored by remote controlled computers at “Energifabriken” (G). The information can be displayed from any place if access-code and connection to the Internet are available. Nine of the solar collector systems are connected to the district heating system of Malmö. The tenth system heats the hot well of an aquifer system. Unlikely many other solar collector systems in Sweden, there is no heat added from any other production unit to raise the temperature post the solar collectors. Either the solar collectors deliver heat by their own (at 65ºC), or there is no heat output at all.

The systems at Bo01 are reliable solutions with convenient software. Each system consists of only one type of solar collector, and they also have the same angle and orientation. In this way they are kept “simple” which makes it easier to control the pumps and valves, and decreases the risk of oscillation.

Theoretically, about 12% or 84 MWh/year of the heat from the sun’s radiation is lost due to non-optimal angles in the solar collectors of Bo01. This is due to the architecture of the buildings with some roofs being tilted towards the East and the West, or solar collectors that are not tilted optimally. In reality the heat loss is much greater because of dirt on the solar collectors and the effect of shadows.

In Fränsta, the middle of Sweden, there are plans to preheat water with solar collectors and then add heat from electric water heaters to raise the temperature before it is used in the district heating system. This is an efficient technique with great future potential in Sweden.

In the village of Unbyn, northern Sweden, there are plans to build a thermal solar collector system probably never constructed before. A wood chip fired furnace supplies heat through a central heating culvert to customers just like in an ordinary district heating system. Solar collectors placed on the roofs of the customers´ houses supply heat primarily to that particular house. In each house there is also a hot water storage tank equipped with an electric water heater. The tank stores heat both from the remotely placed furnace and the solar collectors on that house. When there is a surplus of heat somewhere that a tank is unable to store, hot water is then passed into the central heating culvert to supply other customers with heat. An important advantage with this system is that the furnace can be shut down during summer when the demand for heating is low and solar energy output is high. This prevents the furnace from operating at low efficiency due to frequent start-ups and shut-downs.

Author: Jedensjo, Thomas

Source: Luleå University of Technology

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