Optimization of Bivalent Heating Systems Considering Time-Of-Use Tariffs for Electricity

• The cost for producing energy differs a lot due to the load coupled to the distribution grid. In Sweden the load has its maximum during the winter because of the climate. The cost for producing one extra unit of energy is then about 0.50 SEK kWh−1 (1 US$ = 6 SEK), while during summer the cost can be ten times lower. In order to encourage the consumers to save energy during the winter when the cost is high, it may be important to introduce a time-of-use tariff, which reflects the cost for producing the energy. Such a rate is present in Malmö, Sweden. when retrofitting buildings it is of course important to consider the applicable rate for energy, in order to decide the optimal retrofit strategy. In the time-of-use rate the peak load is expensive and a heating system that will use less of the peak energy becomes very desirable. A bivalent heating system, where the base load is provided by a heat pump and an oil boiler takes care of the building peak load can sometimes be found to be the best solution. In this paper two different methods are used for the optimization of such a bivalent heating system. One method uses derivative considerations, the OPERA model, while the other uses linear programming.

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