CLIMA edition:2013 location:Prague date:16-19 June 2013
Thermal energy storage (TES) is regarded as one of the key technologies to enable a higher penetration rate of renewable energy sources in the electricity supply. A typical example in the residential sector is the combination of heat pumps with passive TES such as floor heating. Floor heating provides flexibility at demand side since it allows heat pump operation to be shifted in time. The idea of demand side management (DSM) is to access this flexibility by means of a time-variable electricity price. From a consumer perspective, the question arises which floor heating storage capacity minimizes the annual electricity costs for heating a dwelling. This optimal capacity is a trade-off between conflicting effects. On the one hand thermal capacity increases the potential for load shifting. On the other hand it induces larger transients which in turn result in higher heat losses. This paper investigates this design problem for a residential building with an air-coupled heat pump for a broad range of scenarios, among which occupancy profiles and electricity price scenarios. All design cases are evaluated with an optimal control strategy. The building dynamics are represented by lumped resistance-capacitance models in Matlab. It is found that for most of the scenarios, the thicker the floor heating system, the higher the energy cost. Hence, the cost reduction of extra load shifting does not compensate for the efficiency reduction associated with higher heat losses. This observation motivates research on the combination of heat pumps and active TES instead of passive TES in the framework of DSM and smart grids.