H&M was one of the very first companies to join Öppen Fjärrvärme in 2013. Through its co-operation with Stockholm Exergi, its cooling system at the data center was fitted with a connection to the district heating network. This enables the data center to recover excess heat on days when the ambient outside temperature falls below 7°C. This amounts to some 4,300 hours in a typical year.
Furthermore, the new installation and the agreement with Öppen Fjärrvärme now means that the data center has an extra cooling option, available as a reserve during the remaining hours of the year.
It was straightforward to connect H&M’s facility to Öppen Fjärrvärme. The existing cooling loop was connected to a heat exchanger and a circulation pump at the same time. The other side of the heat exchanger was connected directly to Stockholm Exergi’s district heating network.
Cooling of the data center now allows cooling water to be heated to a temperature of 20°C before excess energy is transferred to Stockholm Exergi’s system and transported to a large heat recovery plant in Hjorthagen, just outside central Stockholm. With help of four large heat pumps that have a combined recovery capacity of 24MW, the temperature of returned heat from the data center is increased to an intermediate level, prior to being mixed with high temperature water from the Hjorthagen plant’s cogeneration process for distribution to district heating customers.
Between 2013 and 2015, the data center’s load has virtually doubled. H&M is now able to recover energy and make annual deliveries of up to 1,700MWh in heat to Stockholm Exergi’s network. This amounts to the heat use of some 350 Stockholm inhabitants.
After several years’ experience of heat recovery at the data center, in 2017 H&M decided that their next data center, slated to go online in 2018, would also recover heat. For this data center, H&M is investing in an installation where they generate data center cooling themselves with heat pumps in a redundant N+1 solution and deliver excess heat directly to Stockholm Exergis district heating network. Under this model, Stockholm Exergi pays for capacity (kW) and energy (kWh) dependent upon outside temperatures. The data center is scheduled to have an IT capacity of 1MW, and projected to be able to heat some 2,500 modern apartments.