The energy- and cost-efficiency of buildings and areas can be improved by combining a ground heat pump with solar heating, according to the results of a project led by VTT Technical Research Centre of Finland. VTT used ecological hybrid solutions to enhance the efficiency of heat and electricity production in buildings and found that a hybrid solution combining a ground heat pump with solar heating is the most efficient and has lowest lifecycle costs.
The goal of the distributed energy systems (DESY) project was to use hybrid solutions to produce energy in close proximity to the consumption site. Hybrid production was developed by combining primary energy sources — electricity, district heat or oil — with local solar, wind, biofuels and ground heat pumps.
VTT found that solar power was particularly efficient when combined with ground heat in terms of profitability, with a payback period between five and six years. If solar power is used to reduce the amount of sourced electricity required in addition to a ground heat pump, the payback time is around nine years.
Solar combined with district heating is also profitable if the solar energy replaces boiler capacity, which involves higher production costs between spring and autumn. The local district heating network can also be used for the temporary storage of surplus heat produced by buildings.
Solar energy is also useful to produce additional heat and electricity in buildings that are close to being zero-energy.
The study also found that the consumption requirements for passive-energy buildings (15 kWh/m2v) are difficult to achieve through the addition of insulation only. An efficient ventilation system and heat recovery from exhaust air and hot water is also needed. However, this does not necessarily reduce payback time. In addition to the above, seasonal thermal energy storage is also required for buildings that are close to being zero-energy in order to neutralize the annual need for primary energy.
Adding more than one local hybrid solution to a building is not profitable, VTT found.