Field experience with ULTDH substation for multifamily building

Ultra-low temperature district heating (ULTDH) substations may be an important enabler for integrating higher shares of renewables and waste heat in the district heating (DH) network. In the paper, we describe a concept and first experimental results for producing domestic hot water (DHW) at DH supply temperatures of 45°C. The substation utilises a heat pump for boosting the DH temperature up to approximately 60°C to an accumulation tank, after which the DHW can be produced on demand for temperatures up to 55°C. Additionally, the system included a separate heat pump to supply the DHW circulation heat demand. The DH accumulator tank provides load shift opportunities, which is important going towards the integrated, flexible and renewable based future energy system. The two heat pumps operate with a COP of approximately 5, which results in representative share of approximately 11-13 % electricity to supply the DHW including circulation.