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Measurements & Experience
with Solar Air Heating

Measurement results: solar air collector

The Technical University of Denmark (DTU). Summary of DTU report no. 94-1.

Measurements are made on a 14 years old SV Model, which in size corresponds to the actual SV 14 model – even though the actual SV14 model has an even better output.

Output figures for the actual size corresponding SV14 model are marked in italic.

Excerpt from the test’s conclusions:

At full sun, the system warms up the air with a power of between 700 and 750 Watts (New SV14 reaches approx. 1000 W) and the temperature of the injected air is raised by approx. 30 degrees centigrade in relation to the outdoor temperature.

The solar cell starts up the fan at a light intensity of between 80 and 95 Watts/m². At a solar radiation of 300 Watts, the volume of air amounts to 50 m³/hour, increasing to 60 m³/hour at full sun.

At an air flow of 60 m³/hour, the temperature of the injected air is raised by approx. 30 degrees centigrade in relation to the outdoor temperature (New SV14 approx. 110 m³/hour raised approx. 32 degr. Celsius).

According to the test, the performance of the solar cell and the fan is not greatly affected by the angle of incidence of the sun. The air flow is only significantly reduced at incidence angles above 60 degrees centi-grade and the fan stops altogether at an angle of almost 80 degrees centigrade.

With regard to woodwork and holiday cottages

In the winter, a cold wooden holiday cottage will absorb approx. 15% water. This corresponds to a relative humidity (RH) of 75%. The woodwork will act as a damp buffer and attempt to maintain 75% RH when the house warms up or dries out. The evaporation from the wood-work will continue until the wood has reached a water content of approx. 10%.

If the wood is to dry out, the water content must “evaporate”. This requires energy. The latent heat of water at 0 degrees centigrade is 2490 Joules/gram.

In reality, more damp is eliminated

There is approximately 1000 kg of wood in a 60 m² wooden holiday cottage. 50 kg of water must evaporate for the humidity of the wood to be reduced from 15% to 10%. At an output of 700 Watts, the “holiday cottage package" will eliminate
700 x 3600/2490 grams of water per hour = approx. 1 liter.

In practice, much more than 1 liter per hour will be eliminated as the solar radiation on 1 m² of a window facing the sun corresponds to approximately 800 Watts.
In addition, a large proportion of the system’s operating hours are in periods during which the humidity of the outside air is relatively low (in cold, clear weather).

The measurement was conducted on a 3-component model in which the solar cell and fan are not integrated into the absorber. The model was produced and sold between 1985 and 2003 and the area of the solar panel was 1.4 m².
The measurement was conducted by , DTU.

About improved output in the newer SV14 model compared with earlier model: The increased effect on SV14 is partly caused by an improved airflow inside the panel. But also because the widespread and very even air-intake through the many small holes spread all over the back plate, makes it possible to drag a lot of extra heat from wall- or roof behind the panel.


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