PLACING OF HEATING PIPES IN FREE PLANTED CROPS
The lecture will discuss the principles of the heat installations and the main results of the investigations.
As you know the heating pipes in new Danish glasshouses are of very small dimensions. In this way we try to make regulation easier and quicker and to provide the heat nearer to each plant.
Of course, for a long time we have discussed where the numerous small pipes must then be placed to give the best conditions for the plants and - if possible at the same time - the best heating economy.
We have tried for a few years now to investigate a part of the problem in two 12 meter wide 60 meter long single-span houses placed on an experimental station in a very open area. The orientation of the houses is east/west and the distance between them 10 meters. We have used tomatoes, of the same variety and under the same culture, as the experimental crop. The investigations have been made every day in the tomato season for two years. About 300,000 figures have been taken from the instruments. The material is not yet reported, and the results I give you here are not quite final.
I therefore have preferred not to give too exact figures, but to find the tendencies in the different aspects and to show them by simplified illustrations only. You will be able to have more concrete material from the special report when it is published. In the two houses we placed the 1" pipes as the plan seen here (fig. 1). There are four pipe lengths in each house side and two times eight pipes across the house. There are 117 cm between the pairs and 15 cm between the pipes of a pair. In the one house we have only low placed pipes, about 15 cm from the ground (fig. 1). In the other house the 16 pipes are hung up 250 cm from the ground. The heat is taken from a central boiler. Each of the houses has shunt-arrangement. The heat consumption has been controlled automatically by multiplication of the water quantity with the difference temperature. It has been a difficult problem, and we have later installed another system. The temperature has been set by day/ night thermostats, at 15–16°C at night, at 22–24°C day temperature in dull weather and at 27–30°C in sunny weather. The thermostats have followed the half plant-height.
The recording of the air and ground temperature has been made manually by help of thermoelements and a spot galvanometer, two times a day - eight and sixteen o'clock. Here (fig. 2) we have the 25 points for the elements. We have