Association Stockholmshem

Ground source heat pumps without bedrock reduce district heating costs.

The background

The association “Stockholmshem” owns about 26,000 apartments making it the second largest housing company in Sweden. With hundreds of properties across Stockholm, it also finds itself with exorbitant heating costs to the tune of about SEK 260 million a year! The company is now determined to cut these costs and has decided to invest in ground source heat pumps - without bedrock. It has about 350 heating systems and an annual heating bill of approximately SEK 260 million.

Gunnar Wiberg of Stockholmshem explains, “The heating systems in our various properties run on district heating, pellets and bio-oil. And we’re talking about huge amounts of energy. Some of our systems are larger than the district heating systems in a small Swedish town. District heating covers a substantial share of the heating demand for Stockholmshem’s properties. The company has now decided to invest in heat pumps as a complementary heat source and thus achieve substantial energy savings.”

Solution

District heating covers a substantial share of the heating demand for Stockholmshem’s properties. Stockholmshem has determined on a solution that is becoming increasingly popular among large property owners - that of combining exhaust air with a ground source heat pump - but without bedrock. “We are currently in the process of installing no less than 140 heat pumps in line with this method. Instead of placing pipes in a borehole or a coil in the ground, we will be using a heat exchanger to extract the heat from the exhaust air.”, says Gunnar.

The equipment being installed is not exhaust air heat pumps, but NIBE’s largest unit, the NIBE F1330, which is normally used for bedrock or ground source heating.

The exhaust air is conducted via the normal ventilation system to a heat exchanger coil. The heat transfer fluid passes through this coil to the heat pump. The temperature of the heat transfer fluid becomes higher than in a bedrock/ground source heating system which subsequently results in an even higher coefficient of performance (COP ).

Results

Gunnar Wiberg of Stockholmshem explains “The performance of the systems that we’ve been running for a while has surpassed even our most optimistic projections. There is much more energy in the air than we had originally supposed. In some cases, we estimated that we would be extracting up to 120 kW but in fact the figure has been almost as high as 160 kW!

We are using our NIBE F1330s as supplementary systems and this has proved to be a very economical solution. Our district heating bills have fallen by as much as 40% and our annual energy consumption is down by about 70 kWh per square metre.

This means that the new system will have paid for itself within 3 or 4 years perhaps.”