A new developed solar heating/natural gas heating system was installed in a one family house with three inhabitants in Helsinge, Denmark, latitude 56°N, in July 2006. The house is shown in figure 1 before the installation of the solar heating system.

Before the installation of the solar heating system the house was supplied with heat from a Vaillant non condensing natural gas boiler from 1990 with a nominal power of 22 kW. For domestic hot water preparation the natural gas boiler heated a 50 l hot water tank, see figure 2.

The solar heating system installed in the house has 5 Velux solar collectors, type S08 with a total collector area of 6.75 m2. The collector orientation is 15° towards east from south and the collector tilt is 45°. The collectors have a start efficiency of 0.79, a first order heat loss coefficient of 3.76 W/m2K, a second order heat loss coefficient of 0.0073 W/m2K and an incidence angle modifier of 1 — tan3 9 (9 / 2), where 0 is the incidence angle.

The solar heating system is based on a technical unit and a heat storage unit produced by METRO THERM A/S. The technical unit includes a modulating condensing natural gas boiler from Milton A/S, type Milton Smart Line HR24, with a nominal power for space heating of 5.7-23 kW and a nominal power for hot water preparation of 5.7-28.5 kW, a heat exchanger producing domestic hot water, and all equipment needed to operate the solar collectors, the natural gas boiler and the heating system. The heat storage unit includes a 360 l solar tank which can be charged by means of the solar collectors and the natural gas boiler [5]. The tank insulation is partly PUR foam, partly vacuum panels.

Both the technical unit and the heat storage unit are built into 60 x 60 cm units by METRO THERM A/S. Due to this prefabrication, the installation of the system is easy and the risk of installation mistakes is reduced. The design of the units provides good operation conditions for the condensing natural gas boiler and for the solar collectors.

Figure 3 shows a schematic sketch of the two units as well as the solar collector loop and space heating system.

Figure 4 shows the house after installation of the solar heating system.

Fig. 4. Demonstration house after installation of the solar heating system. Left: From the south. Right: Solar

tank and technical unit in the basement.