Heat recovery integration with district heating

Heating a Supermarket utilizing Heat Recovery of the Cooling system

Cooling systems are normally rejecting the cooling energy into the ambient air. This is a big loss which also has a lost heating opportunity. To optimize heat recovery it is especially good to integrate with district heating systems as there may be an opportunity to sell heat in periods where the supermarket cannot use all the heat by itself.

In the current case a supermarket of 3500 m2 utilizing a CO2 based refrigeration system of 350 kW cooling capacity. The supermarket is located in Kerteminde, Denmark.

During the warm periods, the supermarket cannot utilize all the heat and the surplus is sold to the district heating grid. In the cold months, the heat provided by the cooling system is not sufficient to heat up the store and extra heat is purchased from the district heating grid. The taxation rules did not allow for an optimization procedure to produce more heat during the cold months which would have been a possibility to totally eliminate the purchase. The test period was between Jan-Oct 2018. Before the installation, the shop expected to use 290 MWh heat for the period ( 390 MWH for a full year). The results show estimated savings are in line with actual performance i.e. the actual purchased energy consumption for heating has been heavily reduced with 60%.

The total cost of the project was 24.000 € and the payback will be less than 2 years.

The technical outline of the heat recovery installation

Technical details:

  • GHG savings: 55 Ton CO2 per year. (If it natural gas 180 kg CO2/ MWH can be assumed. 305 MWH times 180 kg = 55 Ton CO2 per year.)
  • Energy savings : 305 MWH per year. (165 MWH from Jan to Oct – an average of 25 MWH/ month. In the summertime heat is exported to the district heating grid. Yearly demand is 390 MWH of which 215 MWH has been saved with heat recovery (60%). On top of the saving 90 MWH was exported to the district heating grid which makes the amount of recovered heat to be around 305 MWH )
  • Heating capacity:  25 MWH per month as demonstrated – could be more
  • COP: 6 (Not measured (unique systems) but scientific papers reports yearly actual cooling COP is around 3. A combined heating and cooling COP will be 6.)
  • Refrigerant: CO2
  • Heating source: District heating to top up demands in the cold months and to absorb heat during the months where there is a surplus of heat recovery.
  • Supplied temperature: 75 °C