Utilization of excess heat from data centers.

Abstract

Digitalization has influenced the rapid growth of data centers around the world. The advancement of IT and telecommunication also played a vital role in is this expansion of data centers. Data centers facilitate the storage and access of data when required. Electric power is the main energy input and heat is the main energy output from the data center. This work is about the utilization of the excess heat which is the by-product of data center operation. To connect the heat from data centers to a district heating network, a heat pump might be necessary to increase the temperature of the heat. The economic potential for different conditions and different heat recovery solutions are evaluated. Simulations and economical optimization at different conditions in Aspen HYSYS were carried out. Especially three alternatives were evaluated. The first is an alternative without a heat pump in which the cooling water leaves the data center at 80 ºC and enters the district heat network at 70 ºC. The second is an alternative with a slight temperature increase in the heat pump. The cooling water temperature from the data center is 65 ºC and the temperature to the district heat system is 70 ºC. The third is an alternative with a higher temperature increase in the heat pump. The cooling water temperature from the data center is 65 ºC and the temperature to the district heat system is 80 ºC. The COP (Coefficient of Performance) in a heat pump for these alternatives were calculated using the refrigerant R-22 in the simulation program Aspen HYSYS. The estimated economic potential for each alternative was calculated by estimated values on electricity cost and district heat price. In one alternative, the electricity cost was specified to 0.1 EUR/kWh, and the district heat price was specified to 0.05 EUR/kWh. For the alternatives using heat pumps, the capital cost was estimated assuming that the heat pump investment was dominating. The COPs for the two heat pump alternatives were calculated to be 8.66 and 5.4, respectively. The economy for a large data center facility with recovered waste heat of 200 GWh/year was calculated for 10 years. For the specified conditions, the net present value was calculated to be large and positive for all the alternatives. As expected, the most economical alternative was without a heat pump, and the most economical heat pump was the one with the highest COP. Sensitivity calculations were performed to show dependencies of temperatures, district heating price, electricity cost, heat pump cost, COP, and pipeline cost. Pipeline cost is very much dependent on the length and the local conditions for which it was not possible to make a reasonable estimation. The calculations show that there is a large potential in using waste heat from data centers for district heating.