Use of Very Low Temperature Geothermal Water in Radiator Heating Systems

Abstract

This paper deals with the utilization of geothermal water of very low temperature. Experience gained in Iceland over 50 years of utilizing water in the 55 - 80?C temperature range in radiators with a focus on the low temperatures is described. The theory of performance of hot water radiators is reviewed and the method of evaluating the annual hot water requirements for space heating purposes is outlined, both in direct throughflow district heating systems as well as more complicated district heating systems with heat exchangers at users' stations. The question of sizing the radiators and individual controls is discussed as well as the optimization of temperature programs for radiators with and without heat exchanger substations. It is shown that by properly sizing the radiator and equipping it with the required controls one can utilize water directly even at inlet temperatures as low as By operating the system at these low temperatures and with a large temperature drop, heat losses from the system and pumping requirements are reduced. Measured values of supply and return temperatures in a sample of houses in various geothermal district heating systems in Iceland are presented which confirm that large temperature drops in radiators can be achieved in spite of low inlet temperatures.