Use of the waste heat from the chillers for the heating of Läkerol Arena in Gävle

Abstract

Every day, huge amounts of energy are used by all sectors of the economy. From transport to industries, energy constitutes the base of development and people’s way of living. Besides, the energetic demand of millions of individuals must be satisfied with resources that are in constant depletion while the consumption is growing at a 2% rate every year. The consequence of such increase is that in the last decade energy costs have risen extremely fast. Societies must now find a way of maintaining the actual social-economic growth whilst reducing the energy demand in order to ensure sustainable development. Ice hockey arenas in Sweden have an average energy consumption of more than 1000 MWh per year, and around 42% of the total is used by the refrigeration system to cool the rink surface. The core of these units is the chiller, a machine that removes heat from a cold refrigerant and as a product of this chilling process, waste heat is generated. This energy can be exhausted to the environment or recovered for heating purposes. The main aim of this study is to investigate the uses given to the waste heat in Läkerol Arena, in Gävle. Some alternatives have been proposed and analysed in order to diminish the amount of rejected heat. Other objectives set in this project are to examine the possibility of reducing the dependence on district heating and to determine the efficacy of insulating the ground below the heating pipes that prevent permafrost. Nowadays the heat recovery system is used to preheat tap water until 30ºC and then up to 60ºC, to warm the air sent to the main rink area and to prevent the creation of permafrost in the ground below the main arena. The unused energy is sent to ambient with six big fans placed on the roof. The first additional use for waste heat proposed in this study is to design a heating system just for the resurfacing water. The current method in Läkerol Arena is to mix hot tap water with cold water. The problem is that the first one is three times more expensive than the second, so installing a unit that warms only cold cheap water up to 30ºC would result into saving 18760 SEK per season. Although this solution does not reduce the waste heat sent to the environment, it does reduce the demand of the desuperheater and increases the demand in the glycol circuit by 7%. Another option is to build a pit to melt the snow generated in the ice rinks. This solution would increase the use of the waste heat by 26% and bring annual savings of 32198 SEK, since it would not be necessary to rent any transport service to remove this snow. Besides, the emissions of CO2 would be reduced by 43774 kg. The possibility of sending part of the produced heat to a nearby building has also been investigated. The suggestion made in this study is to use part of the waste heat to warm the air for the ventilation of the Gefle Tennisklubb, an indoor tennis facility located at 150 m of the ice hockey arena. It has been calculated that this ventilation unit has an average heating demand of 9,1 kW. Results showed that in average this would represent 2% of the total heating capacity of the chillers and annual savings of 39858 SEK and 6880 kg of CO2 sent to the environment. The option of installing a heat pump in the hockey facility has also resulted beneficial. The purpose of such equipment is to cover the demand of district heating from the arena, which is currently used for radiators, radiant floor and 4 small ventilation units. After analysing average consumptions and talking with an expert, it has been decided that the best option is to install a ground source heat pump with a heating capacity of 415 kW. The interesting aspect about the heat pump is its efficiency, being it over the 300% (COP of 3,26). Although it means an important economic investment, this technology would save the arena around 239264 SEK every year and reduce CO2 emissions by 58331 kg. Finally, the installation of an insulation layer below the heating pipes has been analysed. The purpose was to see if this measure would be energy efficient. A simulation has been done with the educational version of the software ANSYS 14.5, and the results show that with a 100 mm insulation layer placed under the heated sand below the tubes, the heating demand is reduced by 44 kW (–54,6%), while the cooling demand increases by 5 kW (+1,1%). At the end this alternative has been dismissed since the installation would be too expensive and more heat would be sent to the environment, which is counter-productive. To sum up, with all the measures being installed, the arena would reduce the waste heat sent to the environment by 175,5 kW. It would represent the 49% of the total capacity generated (currently it is around 85% of the total waste heat). Besides, the annual emission of CO2 would decrease by 109 tonnes, the equivalent to 22 American cars. Finally, in terms of money, all the measures would bring total savings of 68880 SEK per year. The study concludes with three suggestions to continue with further research. The ideas are to investigate the possibility of introducing a filtering system for the water obtained in the snow pit, the viability of installing renewable energy sources to supply the electricity for the heat pump and study the efficiency of reducing the condensing temperature of the chillers.