INFLUENCE OF THE AIR T° IN TUNNELS BY MEANS OF THE "ACCUMULATING EFFECT" OF A WATER MATTRESS
In relation to all kinds of other materials like soil, stone, or air, the heat capacity of water is hight.
For a temperature rise of 1°C of 1 dm3 water 1 kilogram calory is required. In comparison with this, a temperature rise of 1°C of the same volume of clay soil asks 0,304 kcal and of sand stone 0,370 kcal.
For a rise of temperature with 1°C of 3,5 m3 air only 1 kilogram calory is required.
In the morning after sun rise the temperature of the soil surface as well as the air temperature rises rather quickly. The warming up of a water mattress, especially when this mattress is thick, demands much energy, so that the temperature rises slower. By a same quantity of radiation energy the temperature of a thin water mattress rises higher than that of a mattress with a thicker water layer.
Just like in a greenhouse, where the temperature rises quickly by "direct" sun radiation, this happens too in a water mattress of transparent film. Because of the fact that the contents of the mattress exists of water, the temperature rise passes much slower. As soon the ambient temperature decreases the temperature of the water mattress delivers heat to the surroundings. A thin water mattress which is increased higher in temperature, attains this point of delivery at an earlier stage than a thicker, but less warm, mattress.
Towards afternoon there is a time that the thin water mattress loses already more heat then it receives by radiation, while the thick mattress does not deliver any heat but still absorbs.
Towards evening the thick water mattress contains much more kilogram calories than the thin mattress which can be calculated in an easy way from the following measured water temperature figures in september 1965.
|Thickness of the water mattress||4 cm||8 cm||10 cm
|vol. of water pro m2 soil surface||40 dm3||80 dm3||100 dm3
|Temp. 22–91965,16. 30 h||25,5° C||23,4° C||22,8° C
|Temp. 23–9–1965 8.00 h||11,4° C||11,8° C||12,0° C
|Fall in temp.||14,1° C||11,6° C||10,8° C
|Delivered in kcal/m2||564,0||928,0||1080,0|
Now from these temperature data the effect of the water mattress has been proved, the following question can be posed.
What is the effect of a water mattress on the air temperature in a tunnel covered with plastic film?
For this aim two tunnels of an equal size were erected and of one the ground surface was provided with a water mattress.
In order to record the air temperatures calibrated thermographers were used. See obtained thermogram, figure 1.
The thermogram go far to prove, that - by the action of the water mattress - the temperature rise of the air is reduced by day while at night the temperature falls less by heat delivery from the water mattress to the air in the tunnel.
By a not complete covering of the surface with a water mattress a row of beans could be planted out on both sides of the mattress in the tunnel. So long the plants were small there was not ventilated. No damage was caused by sunburnt. Late in May, when the danger for night frost was averted and the