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

Abstract

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.

Popular Abstract

The most energy-efficient combination of HVAC systems for apartment buildings in Nordic climates.

There has been limited comparative study of the many possible combinations of systems to provide mechanical heating and ventilation to apartment buildings, which represent an increasing share of newly built floor area in the Nordic countries. Reducing the energy required from the electric and district heating grids is an important part of the energy transition required to tackle global heating. From a consumer perspective, the system choice greatly impacts the ongoing cost for energy. The solution found to require the lowest delivered energy over a year included: a ground source heat pump combined with solar thermal collectors, balanced ventilation with heat recovery, fan coils and a variable setpoint schedule. The lowest energy cost was achieved by the same system but with a constant setpoint schedule due to smaller peak demands.

Interesting trends were found within each of the studied categories (heat emitter, ventilation, heating schedule, thermal energy storage and heating supply). These were consistent when parameters in other categories were changed. Lower supply temperatures for heat emitters reduced energy demand, although this was counteracted by higher pumping power. Solutions using a 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. Ground source heat pump systems had the lowest delivered energy and energy costs. Using solar thermal collectors to provide domestic hot water and recharge the borehole field, 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, where a heat pump providing hot water is integrated in a balanced ventilation system, offered the best thermal comfort with the possibility of heating and cooling all year round. However, its use is hindered by a high initial cost.

The potential for consumer driven energy flexibility using thermal energy storage was also examined. Under the current energy pricing, only small cost savings were possible, and these required large tank sizes. Although optimisation of the demand profile to use the lowest hourly cost of electricity did produce savings, these were outweighed by the higher charges for the high peak demand. When applied to the 100 L immersion tank with a reduced setpoint temperature of 55 °C, a 5 % energy cost saving was possible.

The studied systems were found by analysing the energy performance certificates of low-energy buildings in Norway, Sweden and Finland. The effect of each system component was then analysed through parametric simulation of an affordable housing project in Sørum, Norway. The systems, including five hydronic heat emitter options, three ventilation options, six heating schedules and seven energy supply systems. Thermal energy storage was also identified as an important element in the sizing of the energy supply system, as it can buffer the peak demand.

The results and models developed in this research will be used for life cycle costing of the systems to determine which provides the most cost-effective solution. This is an important consideration as the most energy efficient option is the one that is economical enough to be practical.

• author: Gibbons, Laurence
• supervisor: Saqib Javed
• organization: Division of Energy and Building Design; Department of Architecture and Built Environment
• course: AEBM01 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Heating, Ventilation, Free cooling, Borehole, Ground source heat pump, Compact unit, Solar thermal collector, District heating, Underfloor heating, Radiators, Convectors, Thermal energy storage, Norway, Sweden, Finland.
• language: English
• id: 9061757
• date added to LUP: 2021-07-26 09:59:57
• date last changed: 2023-07-28 13:06:26