Energy-efficient HVAC solution-sets for low-energy apartment buildings in Nordic climates - An analysis of an affordable housing project

Sammanfattning: To meet the aims of the Paris climate agreement, it is necessary to reduce energy use in buildings. Efficient HVAC systems are a critical part in achieving a low delivered energy use. However, there is a lack of comparative information of the best HVAC systems for apartment buildings, which represent an increasing share of newly built floor area in the Nordic countries. Elements of HVAC systems were found through a statistical review of national EPC databases and a literature review. Resulting solution-sets were analysed through simulation of an affordable housing project in Sørum, Norway, built using a modular construction. The solution-sets were compared for energy use and energy cost. The potential for energy flexibility using thermal energy storage was also examined. The solution-sets were comprised of five heat emitter options, three ventilation options, six schedules and seven energy supply systems. Thermal energy storage was also identified as an important element in the sizing of the energy supply system. Underfloor heating and fan coils were the most efficient heat emitters. Fan coils were a more practical solution for the case study. Solutions using balanced ventilation system were more efficient than those with exhaust ventilation, although the difference could be offset by using an exhaust air heat pump. Maintaining a constant setpoint or allowing it to setback 2 °C during the night affected both the energy demand and peak demand. The constant setpoint required more energy but had a lower peak demand, allowing for a smaller heating system. For systems with a fixed size or low system cost, a variable setpoint was better. All the energy supply systems could have lower energy costs than the standard system used in each apartment, a 100 L electric immersion water tank. For exhaust air heat pump systems, this was only possible when combined with district heating. Ground source heat pump systems had the lowest delivered energy and energy costs. Using solar thermal collectors to provide DHW and recharge the boreholes reduced the total borehole depth while increasing the temperature of the brine. The improved heat pump performance resulted in a further reduction of the delivered energy and energy cost. Compact systems offered a low energy cost and the best thermal comfort with the possibility of heating and cooling all year round. However, its use was hindered by a high price and practical issues. The potential of consumer driven energy flexibility was shown to be limited due to the small cost savings possible and the large tank sizes required. An optimisation of the demand profile to use the lowest hourly cost of electricity did produce savings but these were outweighed by the higher charges for the high peak demand. When applied to the base case with a minimum tank temperature of 55 °C, a 5 % energy cost saving was possible.