Home Heating Networks

Heating accounts for about 40% of the energy used in the UK and to decarbonise we must switch to electricity for our heating. Sheffield Friends of the Earth organised a zoom meeting with manufacturers of household heat pumps, zero emission boilers and infrared heating to look at some of the solutions on offer. Click here to find out more. However, a completely different approach is possible where we use district heat networks to pump large volumes of hot water around the city to homes, businesses and public buildings. This solution does not rely on individuals buying and installing heating technology.

Heat Pumps & Sea Water

MAN Energy Solutions has provided two 50 MW heat pumps to a district heating system located in the port of Esbjerg, Denmark which has an average high temperature in December of 5°C and a low of 1°C. 

When the system starts operating in autumn 2024 it will extract heat from the Wadden Sea to provide 350,000 MWh of heat per year. It will deliver water to the district heating system at 90°C to keep 100,000 people in 25,000 homes warm.

The district heating network is currently powered by coal and an incinerator, but the new system will save 120,000 tonnes of CO2 emissions per year by converting renewable energy into heat, storing it, and sending it to customers when required.

There is a similar scheme due for construction in August 2024 with a start date planned for 2027. It is another set of 3 MAN heat pumps providing 550,000 MWh of heat annually to provide nearly a third of the heat required for Aalborg which is Denmark’s third-largest municipality.

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Heat Pumps and Sewage Wastewater

The warm water from a shower or a bath eventually finds its way to the sewers. The kitchen contributes too with hot taps, a dishwasher, washing machine and draining pans of hot water when cooking. Even human urine contributes to heating the sewers because it is around 37˚C. So why waste this heat? 

False Creek is a neighbourhood in Vancouver, Canada where they have decided to extract the heat from the waste water flowing in the sewers to heat their homes. And no, it does take the actual wastewater, it just extracts heat from it so there’s nothing yukky or disgusting about it.

The energy centre is sited next to the sewage pumping station so heat can be captured before sewage reaches the treatment plant. Heat pumps extract the 20°C water temperature and concentrate it to produce temperatures as high as 80°C. The system has an efficiency of 300% which means for every unit of electricity used three units of heat are produced.

By 2030 they hope to be fully sustainable by using renewable energy and thermal storage.

According to a BBC article, the London South Bank University estimated that energy from the UK's daily 16 billion litres of sewage wastewater could, in theory, provide more than 20TWh of heat energy annually which is enough to provide space heating and hot water to 1.6 million homes. To put this into context, the National Statistics Office states that there were 26.4 million dwellings in England and Wales in 2021 so that should heat 6% of those buildings. Due to the size of America, they flush an estimated 350TWh of energy down the drain each year which could heat 30 million homes a year.

Picture Source: Pixabay.com

The UK government's Green Heat Network Fund has granted £11 to Bolton to extract warmth from the sewers using a heat pump to heat almost 2,000 homes and businesses. The district heating network in Hull won 22m from the same fund to use excess heat from a nearby chemicals plant.

By harnessing sewage heat, wastewater treatment plants could become energy producers rather than energy consumers. The city of Aarhus in Denmark produces more energy than it needs to treat and distribute water for the 200,000 residents. It does this in a different way by recovering waste heat and processing waste sludge to produce biogas. If this was scaled up across Denmark it could provide carbon neutral heating for 20% of all households. 

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Heat Pumps in Coal Mines

90% of our largest urban centres are located above former coal mines and recent estimates suggest that a quarter of the UK's homes sit above abandoned coal mines. The earth naturally heats about 2 trillion litres of warm water which sits in old mines. If extracted, this heat has the potential to supply 2.2 million GWh of heat.

The Coal Authority has already got this technology working in the North East by partnering with the Gateshead Energy Company to use warm water 150m below Gateshead. A 6MW heat pump extracts the heat and supplies it to a 5km long network of pipes which feed a diverse range of buildings from colleges, art centres, offices and over 600 homes. Annual carbon dioxide savings are expected to be 1,800 tonnes CO2 per year.

At the start of 2024, the West of England Combined Authority (WECA) is hoping to replicate Gateshead’s success by investing in a £1.6m study to see if heat pumps could harness water in old pits around Somerset, Bristol and South Gloucestershire. They state that there is the potential to heat more than 100,000 homes, schools and hospitals using this technology.

The Coal Authority is exploring the feasibility of some 70 mine water heating projects across the UK.

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Heat Storage

The heat pumps used in the solutions above can be powered with renewable electricity but another option is to convert excess renewable electricity to heat and store it for later use.

In Berlin, a 45m high storage tank capable of holding 56 million litres of 98°C water has been constructed to store 200MW of energy. In layman’s terms, this is enough to fill 350,000 bathtubs.

The tank can provide hot water for 13 hours and can meet most of Berlin's hot water needs during the summer. In winter, as demand for heating increases, it is expected to supply about 10% of Berlin's hot water requirements.

The water can be heated from excess renewable generation, but currently most of it comes from the nearby Combined Heat and Power plant which uses incineration and coal. Both of these are bad for the environment but over time the storage tank will use more renewable energy and hook into other greener ways of generating heat.

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