## 3 Results
### Benefits of Low-Temperature Heating  
In the previous section, it was shown that the rate of thermal insulation of a building had a large impact on the operational mode of space heaters and their capability to be operated with a low-temperature water supply. In this section, another factor that has also an important impact on the system performance will be explored, namely, the thermal efficiency of the space heaters. Figure 4a shows variation of heat loss with outdoor temperature for a typical Scandinavian single-family dwelling built up to 2000. In the figure below, Figure 4b, the supply water temperatures required to compensate for the heat loss shown in Figure 4a, for a conventional radiator, for baseboard radiators, and for floor heating are shown, respectively. By following the red line in Figure 4b, it can be observed that the selected baseboard radiator system was able to cover a heat loss of about 29 W/m\({}^{2}\) per floor area using a 46 \({}^{\circ}\)C/36 \({}^{\circ}\)C system. According to Figure 4a, this heat loss would occur at an outdoor temperature of about \(-1.7\)\({}^{\circ}\)C in the selected single-family dwelling. Figure 4b further reveals that used floor heating could compensate for the same heat loss with an approximately 10 \({}^{\circ}\)C lower supply temperature. That is, by using a 36 \({}^{\circ}\)C/31 \({}^{\circ}\)C system. With a conventional radiator, 51 \({}^{\circ}\)C/41 \({}^{\circ}\)C system is required to cover the same loss. This implies that, to overcome the same heat loss (29 W/m\({}^{2}\)floor area), the chosen conventional radiator must be operated with 5 \({}^{\circ}\)C and 15 \({}^{\circ}\)C higher supply water temperatures, respectively, than the selected baseboard and floor heating system. Furthermore, the data in Figure 4a,b indicates that all three analyzed space heaters would be able to cover a heat loss of about 20 W/m\({}^{2}\)floor area with water supplies lower than 45 \({}^{\circ}\)C. This means that most current heating systems could be operated with low-temperature supplies if the heat loss from a building would be sufficiently low. The change of HSPF with water supply temperature used in Figure 4b is illustrated in Figure 4c, and the change of CO\({}_{2}\) emissions with HSPF used in Figure 4c was shown in Figure 4d. Figure 4d shows that both HSPF and CO\({}_{2}\) emissions are affected by the water supply temperature used in a heating system. According to Figure 4c, the HSPF increases by approximately 1.3%/\({}^{\circ}\)C for a decrease of supply temperature from 55 \({}^{\circ}\)C to 30 \({}^{\circ}\)C. This increase rate of HSPF corresponds to the reduction rate of CO\({}_{2}\) emissions in Figure 4d. Therefore, by replacing conventional radiators with floor heating in the considered dwelling, the HSPF would be increased by 17% and the CO\({}_{2}\) emissions would be reduced by about 70 kg per heating season. In order to better understand and to get a greater insight into how the parameters presented in Figures 2, 3 and 4a-d are interconnected, Table 3 gives a brief summary of the mutual interconnections. It can be observed that increased outdoor temperature, improved thermal insulation of the building envelope would lower the heat loss of the building, this together with efficient space heaters would decrease the total electricity usage for heating and CO\({}_{2}\) emissions from the building. It should be noted, however, that the rate of thermal insulation of a building and the efficiency of its heating system are not always necessarily interdependent. Figure 4: (**a**) Variation of heat loss versus outdoor temperature for a Scandinavian single-family dwelling built before 2000. Room floor area = 20 m\({}^{2}\). (**b**) The required supply water temperatures for conventional and baseboard radiators and floor heating to cover heat loss from the considered dwelling. (**c**) The variation of HSPF with supply water temperature for a 6.4 kW GSHP installed in the considered dwelling.