Study on waste heat recoveries and energy saving in combined energy system of ice and swimming halls in Finland

Abstract

Ice and swimming halls annually consume lots of energy and produce significant amount of potential waste heat in Finland. In this paper, utilization of four possible waste heat sources (ice refrigeration, dehumidification of air, Gray water and exhaust air) is studied by simulating combined energy system of ice and swimming halls locating in Helsinki. Four cases were simulated including the reference case, one case with waste heat recovery and two cases with both waste heat recovery and two different exhaust air heat pumps. In addition, thermal energy storage tanks are used to store the excess waste heat from the ice hall, while the high temperature exhaust air heat pumps can raise the waste heat temperatures for all heat demands. The results show that up to 99% of the purchased district heat can be replaced by the waste heat in the ice hall at the cost of only 9% purchased electricity increase. The combined utilization of excess heat transferred from the ice hall and the waste heat from the swimming hall can result in 72% reduction of purchased district heat and 37% electricity demand increase in the swimming hall. In the combined energy system of the studied ice and swimming hall, altogether 77% waste heat is utilized, bringing in 82% purchased district heat decrease and 25% electricity increase, while the total consumed energy reduced by 42%. In addition, the total annual energy cost savings reach 133 k€ (-29%), while the saving of the energy cost of the combined system can make up the maximum cost of the profitable investment. During three repayment periods (7, 10 and 15 years), the energy cost savings and maximum cost of profitable investment for the ice hall alone and combined ice and swimming halls are between 510 k€ and 970 k€ and between 700 k€ and 1 580 k€, respectively.