30 May 2005

DEVELOPMENT OF A TWO-CIRCUIT HEAT PUMP FOR HEATING AND DOMESTIC HOT WATER SUPPLY


Advanced heat pump systems use low temperature heat sources of renewable energy from the
ambient or / and of waste heat in an efficient way to provide heat on demand. Typical applications are
space heating, domestic hot water supply and – to an increasing extent – combined heating and cooling
with one device. This is possible either by direct cooling with ground coupled heat pumps or with
reversible heat pump units. Due to better thermal insulation of the buildings the heat demand at low
supply temperatures nowadays for floor heating is decreasing. In contrast the demand for a domestic hot
water (DHW) supply at required temperatures of at least 60°C (to avoid possible growth of harmful
bacteria) is increasing greatly.
The development of a heat pump is described. With the so called Two-Circuit Heat Pump it is
possible to serve two different heat demands at different temperature levels. In parallel operation the heat
of lower temperature from the condenser is fed for instance in the floor heating while the hot water tank is
charged by the circuit of higher temperature from the desuperheater.
The design of a pilot-heat pump installation is described, measuring results obtained at a customer
installation will be discussed and possibilities for optimisation pointed out. The coefficient of
performance (COP) at different working points and the seasonal performance factor (SPF) will be
discussed. The described heat pump system is a ground coupled (bore holes) brine / water heat pump
supplying a low temperature floor heating and domestic hot water production.