District heating temperatures: How low can you go?

If you keep doing the same things, you’ll keep getting the same results – or so the saying goes. Yet in the case of district heating, using the same system specifications as 20 years ago could well see you lose out on potential energy savings and environmental benefits. But why is this the case?

Old habits die hard, and in the case of flow/return temperatures, there is still a trend for designers to request temperatures in excess of 80/70°C. What we need to remember however, is that modern buildings are much better insulated and boilers are much more efficient than before. This in turn creates less of a need to have radiators running at high temperatures and allows for larger difference between flow and return temperature. Thanks to current technology, lower temperatures can work perfectly well and maintain the same level of comfort for occupants.

Up until fairly recently it was best practice to keep the flow and return temperatures quite close, as older, non-condensing boilers struggled to cope with a significant difference. However, modern condensing boilers work well under these conditions, so if you’re tasked with designing a heat network, I’d urge you to use this to your advantage.

As the CIBSE CP1 Heat Networks: Code of Practice, suggests, for existing buildings, a system originally designed at 82/71°C could be rebalanced to run at 80/60°C. It is also advisable to use a minimum difference of 30°C between flow and return temperatures for new builds and 25°C for existing buildings.

Using a lower flow temperature than 65°C for your domestic hot water (DHW) means you’ll need to keep the legionella risk to a minimum by storing a minimal amount of water, but why not use a Heat Interface Unit to generate instantaneous DHW?

If you’re in need of a helping hand, training programmes such as our CIBSE-approved CPD in District Heating will soon have you applying the theory of modern heat networks to practice. By reducing operating temperatures and increasing the difference between flow and return temperatures, you really can avoid wasting money on unnecessary energy costs boost environmental credentials at the same time.

Richard Davies, Commercial Technologies Consultant at Bosch Commercial and Industrial