The heating system for a small house with the ground plan 50 m2 and the fit up attic was constructed. It consists of a 2,7 m2 open thermal heat collector designed for heating of swimming pools [6]. The heat collector surface is protected in a distance of 10 cm from the absorbing area on the front side with the transparent plastic sheet and on the back side with plywood board. The lower and upper parts of the heat collector are opened, so that the air can freely flow in the interstitial space.

The heat pump, type GvP-25 [7], is dimensioned for the delivery of 2,5 kW heat for the floor heating. It is connected to the heat collector via flat heat exchanger. The heat exchanger is placed between the throttle valve and 60m long copper tube through which flows the expanded heat pump fluid. The tube is placed horizontally at the bottom of the excavated pit 4 x 8 x 1 m in a pattern depicted in Fig. 1 (loop 5). The distance between the parallel sections of the tube is 50 cm. The pit is filled with the excavated earth to the half of the depth and a second tubing system is laid at this height. It consists of two 32 mm diameter polyethylene tubes, situated along the long sides of the pit. These tubes are connected with 20 parallel tubes 16 mm i. d. (Fig 1, loop 9). This tubing system is used for warming the soil in the pit with excess heat from the SHC.

20 cm above this pipe system is laid drainage pipe system with a pattern similar to the previous one (position 12 in the Fig. 1). The pit is then filled to the full height of 1 m with the soil. The drainage pipe system distributes the rain water collected from the roof of the house.

Temperatures at critical parts of the system, insolation and relative humidity of the air are measured every third minute. Five measurements are averaged and the results are stored in a data logger [8]. 10 m from the edge of the pit, 1 m below the northern part of the house, is situated the sensor measuring the natural variations of the soil temperature. Temperatures are measured with Pt 100 sensors. Solar irradiation is measured with the pyranometer Kipp & Zonen, model CM3 [9] and the relative humidity with the EMS 33 sensor [8].