Final Program EXPRES 2012 - Conferences

‘wastage’. It is more favorable to use thermal water forheating, DHW production - and cooling if the temperatureis above 65 °C – as thermal water is a thermally lessvaluable heat source [1] [7] [8].In Hungary’s numerous cities, settlements and localgovernment buildings there are decentralized heat supplysystems with obsolete gas fired regular wall mounted orstanding gas boilers. These systems can be potentialconsumers for geothermal systems to be built in thefuture. In this article focusing on this prospect three of thenumerous different calculation results are described. Type’A’ is a regular gas boiler supplied radiator heatingsystem, type ’B’ is a compressor equipped ground sourceheat pump system and type ’C’ is heat exchangerequipped thermal water supplied system. We assumed atall three calculations that the temperature of heating fluidis controlled according to the outside temperature. Wehave calculated the energy and exergy efficiency for threedifferent operating statuses.ηn= ∏ i =X , FUNη1 X , FUN , iExergy efficiency basically is divided into two parts:η x,mech/el – includes mechanical and electricallossesη x,th – includes losses caused by temperaturedrop (irreversible change). Thus the resulting exergyefficiency of an element can be determined with thefollowing formula [1] [8]:ηX , FUN= ηX , mech / el⋅ηX , th(2)(3)Figure 3. Type ’C’ thermal heat supplied system via heat exchangerFigure 1. Type ’A’ regular gas boiler operated radiator systemFigure 2. Type ’B’ geothermal heat pump supplied radiator systemValue η x,th is calculated from temperature, while valueη x,mech/el. was taken into account from practicalexperiences. In the calculations the following values asboundary conditions were assumed [8]:- The energy efficiency of the regular gas boiler is: 0,9(which value is considered rather good). Theefficiency is assumed to be constant, although it isknown that it alters according to fluid and load.- Electric energy is produced by gas, the assumedefficiency is: 0,5- Loss factor of heat pump is: 0,6- Loss of a perfectly insulated heat exchanger is: 0- The assumed constant medium temperature of thermalwater is: 75 ºC- Primer side fluid temperature of the geothermal heatpump is: 10/7 ºC- Electric power used for thermal water exploitation is 5% of the overall heat exploited (with this assumedvalue the coefficient of performance is: 20)A complex system’s resulting energy efficiency:nη = ∏ η i = 1 i(1)A complex system’s resulting exergy efficiency:60