While most heat sources do not directly affect the building energy demand, the energy balance calculation will take into consideration the origin of such source as to determine whether it should be considered an energy efficiency measure. As stated in chapter 2.3.3, the suggested definition of nZEB will consider biofuel and district heating to be a more sustainable energy source, and therefore suggest energy factors that will be beneficial in a building energy balance. Biofuel and district heating have been granted energy factors of 0.37 and 0.43 respectively (Table 2.5), which means that heating demand covered by these sources will be reduced by 63 % and 57 % when calculating the energy balance. The heat pump is assumed to have a COP of 3.5, which is chosen due to being used in some recognised reports (Ramstad, 2011). The proposed nZEB definition use an import/export balance, which means that utilising an energy source with lower energy factor will be calculated as an energy efficiency measure rather than production. Alternatively to these heat sources, heat pumps may be utilised to reduce energy demand. Heat pumps run on electricity, which has an energy factor of 1 (Table 2.5), but as they required less electric energy per delivered heat energy, it will be considered an energy efficiency measure in an import/export balance.
Choice of Heat Source as an Energy Efficiency Measure
Table 9.1: Influence on energy balance for some suggested heat sources
Reduction [%] 66.7 57.0 58.8 68.4 57.0 60.2 66.5 57.0 58.7
Net delivered energy [kWh (kWh/m2)] 9419 (9.4) 12167 (12.2) 11646 (11.6) 4117 (4.1) 5595 (5.6) 5167 (5.2) 12745 (12.7) 16359 (16.4) 15730 (15.7)
Energy factor / COP* [-] 3.5* 0.43 0.37 3.5* 0.43 0.37 3.5* 0.43 0.37
Coverage of total heating demand [%] 93.4 % 100 % 93.4 % 95.7 % 100 % 95.7 % 93.1 % 100 % 93.1 %
Heat Source Ground source heat pump District Heating Biofuel Ground source heat pump District heating Biofuel Ground source heat pump District heating Biofuel
Combined heating demand [kWh (kWh/m2)] 28296 (28.3) 13012 (13.0) 38045 (38.0)
Building Minimal large ‘shoebox’ Optimal large ‘shoebox’ Minimal large ‘C-shape’
Choice of Heat Source as an Energy Efficiency Measure
Table 9.1 presents the effect the heat source has on total heating demand in a few buildings simulated in SIMIEN (same as in chapter 8) – where combined heating demand is the sum of space-, water- and ventilation heating. District heating is assumed to cover the total combined heating demand, as the heat is delivered from a central location, a boiler is not required to be sized according to peak demand to cover the entire heating system. The biofuel boiler and the ground source heat pump is dimensioned to cover 40 % of the peak load, which translates to approximately 90 % of the total annual load (Appendix B), and the peak load is assumed to be covered by an electric boiler. SIMIEN does however only provide boiler-sizing for this heat source when hot water is not included, but in this report it is assumed that the heat source is dimensioned to cover both the water heating and 40 % of the remaining peak load. As can be seen by the results in the table, the percentage-wise reduction of heating demand remains very similar regardless of building fabric and –shape, ranging 57-68.4 % depending on heat source. The heating demand in the buildings simulated in this study makes up between 22.6 % and 47.5 % of the total energy demand, depending on building fabric and –shape, which means that the introduction of such an energy source could reduce delivered energy (as defined in import/export balance) by 13-32 %.
Despite the options being relatively close in terms of demand reduction, the investment price may differ greatly. Districting heating also requires an existing infrastructure to be in place, but if this is the case, it could prove to be the most cost efficient. The water based heating system would be connected to the existing grid and a substation would be installed, but the maintenance can largely be left to the district heating supplier. Biofuel systems are likely the other cost effective system of the three, and is very flexible compared to the other two. It can be placed in building without the availability of district heating or the outdoor space for heat wells (for the ground source heat pump). Ground source heat pumps require a substantial investment, but are also the most effective in terms of energy demand reduction. This option may prove to be cost effective over time, but do require both significant up-front investment and available outdoor space.
Choice of Heat Source as an Energy Efficiency Measure
Figure 9.1: Approximation of energy demand after adjusted for new heat source.
The green area represents nZEB energy goals
If the cases studied in previous chapter integrate an improved energy source, the assumed energy demand would significantly decrease. Figure 9.1 show an approximate plot adjusted for an upgraded heat source and clearly show an improved efficiency for every case. The difference between the two limits of the (yellow) area also shrink, which suggest that the installation of such a heat source would make greater impact on a building with worse building fabric. This follows previous results, as the percentage-wise reduction from a new heat source remains fairly similar regardless of building fabric design. The plot does also show that while this energy measure creates a significant improvement, the energy demand remains higher than the requirements of nZEB – meaning additional energy efficiency measures, and/or on-site production is required to meet this standard.
Case Studies of Ambitious High Energy Performance Buildings