District heating is a viable low carbon solution to heating large numbers of homes, businesses and public buildings. It connects them all to a shared source of heat via a network of very well insulated pipes carrying heat for hot water and space heating.
There are various approaches to district heating, however, and with the rise of heat pumps as a source of decarbonised heat and hot water, district heating is being seen in a new light.
In this blog we’re going to discuss how traditional district heating works, how heat pump district heating works, and what the benefits and use cases might be.
How Does Traditional District Heating Work?
In its traditional sense, district heating is a system where heat is generated at one central location – for example, a biomass boiler, and distributed to multiple buildings through underground piping. The original source of the heat could be anything – from natural gas to geothermal – although if district heating is being used as a low carbon alternative to traditional heating, clearly the choice of source matters significantly.
This heat arrives at buildings at a temperature of around 55-90 degrees C and so can be used for both space heating and domestic hot water.
What are the benefits of traditional district heating?
There are two main benefits to using district heating in this sense, over conventional individual boilers in each building.
The first is efficiency. It’s more efficient to have a large source of either cheap or low carbon heat rather than an individual boiler in each building. Generating heat at scale also offers the opportunity to utilise CHP, waste heat or other technology that only works at scale.
The second is adaptability. One source of heat can more readily be swapped out for new, lower carbon alternatives without massive infrastructure overhauls such as digging up roads or replacing people’s boilers.
How Does Heat Pump District Heating Work?
The rise of heat pump technology as a low-carbon source of heat has re-ignited the discussion around building heat networks. The UK government is moving forward with proposals to promote the use of district heating with zoning and incentives.
Heat pumps are a very flexible technology that can be applied to many types of district heating. There are some great examples in Denmark and other countries. They can be retro fitted to second generation as well as being used as part of what’s called Fifth Generation District Heating:
- First generation district heating relied on steam, at 120 degrees C.
- Second generation district heating relied on boiling water, at 95 to 100 degrees C.
- Third generation district heating relied on hot water, at 70 degrees C.
- Fourth generation district heating relied on low temperature flow (50 to 60 degrees C) with a return of 35-40 degrees C. (we discussed flow/return and delta temperature in this blog).
- Fifth generation district heating works with heat pumps to work with piped water temperatures as low as -5 degrees C.
The lower the temperature of the water in the pipes the less the heat loss but the pump energy consumed rises. The designer has to balance many different things, including the suitability of the connecting buildings with their respective heating systems. With modern heat pump technology, it’s possible to employ heat pumps as the single heat source, as a booster on the network or in each property in an ambient loop system.
Third and fourth gen system heat pumps
A central heat pump generates heat for the whole network, it can use the air, ground or water as a heat source. The use of waste heat, e.g. from a data centre, is also a brilliant concept that’s starting to find traction with examples in Europe.
A central heat pump has the advantage of being able to benefit from grid flexibility to reduce input power costs. It also keeps maintenance costs down for home owners by centralising activities and provides an easy route to upgrade in the future.
New build district heating and retro-fit present very different challenges with different temperature profiles and demand cycles. Fortunately heat pump technology is adaptable and can be applied to both scenarios.
A fully optimised heat pump-based fourth generation district heating system is a big step towards realising the idea of the smart city.
Fifth gen systems
In fifth generation district heating with heat pumps, low grade is heat generated from the ground, air or even from waste heat processes and circulated in pipes. Small individual heat pumps in each building use this circulated water as a source of heat. With a little electricity, they’re able to warm buildings and provide domestic hot water.
What are the benefits of heat pump district heating?
The benefits are enormous and will be a huge part of decarbonisation:
-Lower energy bills. Smart electricity purchasing, and system efficiency deriving from economies of scale, mean heating bills for buildings in a fifth generation district heating system should be much lower.
-Decarbonised heat. With system-wide deployment of heat pumps, an entire town or community could move to decarbonised heat and hot water.
-Low maintenance. No more surprise boiler replacement bills for individual families. These systems are resilient, and maintenance will be far easier and cheaper. Heat pumps typically last decades before needing to be replaced and the costs could be pooled.
-Improved local air quality. No more combustion gasses pumped into the local air. NOX, particulates and other contaminants are increasingly being proven to damage health in particular for children.
What are the use cases of heat pump district heating?
This kind of approach to heating communities has wide-ranging uses. But in the immediate future, the most obvious ways to use it would be:
-New developments. In new development schemes, a modern district heating set-up could help developers achieve and exceed carbon reduction targets.
-Housing associations. For housing associations, district heating can help alleviate fuel poverty, and are compliant with modern carbon-limiting regulations.
-City centre decarbonisation. Large buildings in cities are a massive carbon challenge, limited space and other factors conspire against individual heat pumps. District heating is a viable technology that works and is scalable right now.
Clade is working with the leading UK district heating providers on a wide range of projects. Please do get in touch to discuss what we can do for you.