Global heating is being caused by the emission of greenhouse gases from sources like industry, transport and power generation. One source of emissions that’s often overlooked is heating, which contributes 20% of the UK’s total¹. All across the country and world we need to stay warm and we currently burn a lot of gas doing it.

What's a heat network?

Over history people have tried loads of things to stay warm, and more recently efforts have been concentrated on doing this without also heating the planet. There are solar thermal panels which warm up water, biomass technologies and Iceland realised ages ago that geothermal power is great (especially if you live near a volcano). But with ever-increasing concentrations of people living in high-density urban areas, there’s a technology that could completely change how we heat our buildings: heat networks.

Conventionally we pipe gas to homes and buildings to get burnt in lots of small gas boilers. Dense buildings like apartment blocks and schools often have one large boiler and share the heat – this is called a communal heat network. (It’s more energy efficient and saves space and money!)

District heat networks take this further and share heat between buildings, with a large heat plant supplying hot water to lots of nearby homes or businesses.

The Climate Change Committee (CCC) thinks that about 20% of UK heat needs to come from heat networks by 2050 to meet carbon targets² – I recently went to a talk by members of a team working to bring district heat networks to Bristol, UK.

Building a district heat network

The Bristol council set itself a target of being net-zero by 2030 and realised this was going to take some serious change. The sort of change that doesn’t involve every building in the city burning gas every day. There’s three main phases to the project:

1. Design the network

   Work out where in the city the biggest demand for heat is, where heat could be generated and how likely this all is to change. Also, work out where the pipes are going to go. Rivers get in the way.

2. Install the network

   Basically, put in lots of well-insulated pipes all around the city without digging up anything best left alone – like water mains, sewers, wires, archaeological sites etc.

3. Make some heat

   Once the network’s set up it needs something to keep it hot. Actually, using lots of different sources is best, and they should be spread out across the city (decentralised) to make it all more efficient and robust.

4. Get people and businesses to use it

   Gas heating is going to be illegal for new homes past 2025³, but for everyone else it’ll take some persuasion. The aim is to make it cheaper than gas heating.

How do you generate the heat?

The heat network needs to be heated and this is the main bit from a climate perspective. Bristol doesn’t have a great supply of geothermal power like Iceland (or, to a lesser extent, nearby Bath) so there’s still a challenge in making low-carbon heat.

Combined Heat and Power (CHP)

This is the tried and tested option. The idea is basically burn gas to make electricity, but also use the waste heat in the network. The UK has been using these in council houses, factories, hospitals and universities (communal heat networks) since the 50s and have had mixed reputation because they sometimes heated buildings in summer! Anyway, CHP obviously still burns gas so it’s not a long-term solution.

Heat Pumps

Using some clever engineering, Heat Pumps use electricity to suck heat from the environment (be that water, ground or air). Heat pumps make about three times more heat than electric heaters for the same amount of electricity and as our electricity supply becomes greener they’re looking like an increasingly good option. Bristol is planning on building a big Water-Source Heat Pump to take a bit of heat from the river Avon.

Waste-to-energy…and heat?

The Bristol council has its eyes on the nearly-finished Avonmouth Waste-to-Energy just outside the city. When it’s done they’ll be burning waste to generate electricity and the idea is if it was connected to the heat network it could help keep the city warm, too – like CHP.

So…

The answer is: generate heat from lots of different sources and keep up with the latest technology. But burn less gas. In the words of the team “we aren’t waiting for a silver bullet, we aren’t waiting for fusion, we’re using the technology of today”.

What else?

How do you get the heat into buildings?

Instead of a boiler, buildings connected to a heat network have something called a Heat Interface Unit. Basically, it exchanges heat from the water in the network into the water in the building, which can then be used for heating and hot water. But it pretty much looks like a different white box.

What about variability?

Just like the electricity grid, heat networks have to constantly balance supply with demand. When the temperature drops there can be a quick ‘peak’ demand for heating¹. The UK also uses way more heating in the winter than the summer. Engineers have come up with solutions for this too – when it’s hot, they pump heat underground to be called upon when it’s cold4. Nice.

How is it funded?

The UK government has made capital available to support the creation of heat networks through the Heat Networks Investment Project (HNIP) - £320m in total⁵. Bristol is hoping to borrow the other half privately. The council’s also expecting to earn £12.5m from the government’s Renewable Heating Incentive (RHI)⁶, which is due to expire in 2021 (hence the rush…).

Is this part of a bigger trend?

There’s a lot of anger at the big energy companies and some communities think they can do better by taking control of their energy and heating. This is called Community Energy⁷.