Why heat from parks?

Cutting carbon is an enormous challenge for government at all levels. For urban areas, renewable heat harvested from parks and green spaces could be an important part of the solution.

What is a heat pump?

Heat pumps differ from the other main heating technologies in that they principally operate by moving energy from one place to another, rather than converting energy directly from one form to another. Because they do this in a very efficient way, they can heat a building with a much smaller energy input than a gas boiler or electric heater requires to do the same job.

Ground source heat pumps use pipes buried in the ground – either coiled in loops in metre-deep trenches, or in boreholes that are tens or hundreds of metres deep – to absorb heat from the ground. Water source heat pumps use pipes or special heat-transferring metal plates to absorb heat from rivers, lakes or the sea. In either case, the heat that is extracted originally came from the sun’s rays warming the surface of the planet – and that energy is being continually replenished year after year.

Heat pumps vary widely in size and capacity, from domestic scale to machines capable of heating entire tower blocks or neighbourhoods. For small and medium systems, the heat pump unit inside a building is normally a box-shaped device similar to a fridge, and is installed in place of a boiler to provide heating to radiators and hot water to taps.

Did you know that the ground beneath parks, playing fields and public green spaces holds a secret renewable energy resource that could play a role in combating the climate crisis? Through harvesting some of the heat that the ground absorbs from the sun each year, and delivering it to buildings using heat pumps, greenspace can become a provider of low-carbon heat to reduce our reliance on fossil fuels. Water bodies like rivers, lakes and reservoirs also store enormous amounts of thermal energy from the sun from which useful heat can be generated – 100% sustainably.

The buried elements of ground source heat systems (whether coils of pipes or boreholes) can be thought of as long-term infrastructure, capable of supplying renewable heat year after year for many decades. As natural gas is gradually phased out as our main fuel for heating, this infrastructure will become more and more valuable as part of a town or city’s low-carbon heat supply.

Because heat pumps use small amounts of electricity to deliver large amounts of heat (see Box, right), they can offer a low-cost way to keep a building warm. In 2020, heat pumps are typically competing with another low-cost energy technology as the ‘business-as-usual’ choice: the gas boiler. Subsidies help to level the playing field between the two, but in many places ground- and water-source heat pumps struggle to decisively outperform gas boilers in short-term financial calculations. But when organisations are able to take a longer-term view, to account for externalities like the societal cost of carbon emissions and air pollution, to consider intangible benefits such as greenspace protection and improvement – or even to take fossil fuel heating off the table completely – then greenspace heat investments make clear sense.

Where? How? How much?

Whatever the type of heat pump, it is necessary to consider the characteristics of a building and its internal heating system to establish compatibility with a heat pump. In some instances, upgrades to radiators and pipework are required; likewise in poorly insulated buildings, it is normal to invest in some basic energy efficiency measures when the heat pump is installed. The more energy efficient the building, and the more suited the heat distribution system (i.e. pipes and heat emitters), the lower the temperature flowing through the network can be (the flow temperature), and the more efficient the heat pump will work. These additional requirements add upfront cost to a project, but typically pay for themselves in the long run. Most buildings are already heat pump-compatible or can be made so without excessively intrusive work.

The level of efficiency of the heat pump is referred to as the Co-efficiency of Performance (CoP) which refers to the number of units of heat which can be generated from one unit of electricity. A higher CoP means a more efficient system and a lower running cost.

Ground source heat pumps require open spaces that are largely free from large tree roots, buried services or extensive shading, and are ideally close to the point(s) of heat use. Lawns, playing fields, car parks or courtyards are often ideal. ‘Horizontal’ systems require substantially more space than ‘vertical’ systems, but are cheaper to construct. Water source heat pumps require flowing water or fairly deep static water (at least 2 metres). The size of the water body places limits on the capacity that can be installed.

Unless complicating factors are present (e.g. archaeology, complex internal heating systems, space-constrained access) the installation of a heat pump system could take only a few weeks, or a few months for a large commercial-scale installation.

Costs can vary substantially between projects, but as a rough guide (to be validated by obtaining quotes or through a bottom-up cost estimation exercise), simpler schemes might cost £1,000 per kW while complex schemes might cost £2,000 per kW. If heat is used for other purposes beyond space heating and hot water, the cost per kW might be substantially different.

Meanwhile, in spite of these declarations, the dominant heating fuel for urban areas – natural gas – is still being chosen in the vast majority of new-build, retrofit and equipment replacement situations. In the same way that petrol and diesel cars are to be phased out within a generation, heating is expected to change dramatically as carbon-reducing policies, regulations and fiscal (dis)incentives come into force. Additionally, challenges to business-as-usual thinking are increasingly forceful from within the organisations procuring heating technologies. 

Diverse organisations are accepting that new ways of planning and decision-making will be required for individual municipalities, regions and nations to achieve climate objectives and avert the most catastrophic forms of climate change. Many types of intervention will be delivered at the local level and fall within the sights of local authorities either as direct implementers or as facilitators of third-party developments. This is especially true for energy generation and transformation, with future energy systems becoming increasingly local in nature. Limited urban energy resources – and the land that hosts or adjoins them - will be in high demand. Urban green space accounts for most of the land area within towns and cities that is open, free of tree roots and buried structures – and therefore suitable for exploitation of the ground heat resource. Water bodies like rivers and lakes (‘blue space’) are often sited within, or next to parks and greenspace. 

Ground and water source heat are often the most prominent low-carbon heat resources available to a town or city. They are available in most urban areas and have important advantages over other resources like air source and solar thermal heat in terms of consistency of supply by continuing to work efficiently in cold weather. In practice, a combination of several or all of these resources will be required for each municipality to meet its energy needs from low-carbon sources.

Towns have often been planned or have evolved with green spaces located close to public buildings such as hospitals, schools and leisure centres that have high heat demands. This offers opportunities to match greenspace heat resources with specific, heat-intensive users.

Projects harvesting heat from greenspaces usually involve local government and administration in some capacity. With local authorities typically under intense pressure in the delivery of vital services, decarbonisation interventions that are simple, high-impact and revenue-positive are more likely to succeed. It makes sense that identifying opportunities for these greenspace heat pump schemes should form part of short-term (1-3 years) climate action plans for local authorities with significant urban populations.

Where technically feasible opportunities are found the benefits typically include:

• carbon savings of at least 70% relative to gas heating (and increasing to 100% over time as the electricity grid decarbonises);

• air quality improvements (mainly NOx emissions), especially where older, more polluting boilers are being replaced;

• eliminating a site’s direct use of fossil fuels;

• opportunities to engage the public on and demonstrate climate action;

• opportunities for cost-efficient and disruption-minimising coordination with other works, e.g. drainage improvements or building heating modernisation;

• opportunities to ‘protect’ greenspace from the threat of development by virtue of it hosting critical energy infrastructure.

Alongside clean heating, increasing the energy efficiency of buildings is a critical component of any area-wide decarbonisation plan. The two go hand-in-hand, as improving insulation and draughtproofing will increase the numbers of buildings that are heat pump-compatible. 

The UK market for heat pumps is currently small compared to the scale of uptake that is expected over the next decade under most official and academic heat decarbonisation scenarios. This means that capital costs are anticipated to reduce by around 18% as the industry matures. This is offset by the financial support available from Government for early uptake. 

The UK Government’s Renewable Heat Incentive (RHI) set to close to new participants (non-domestic RHI) in March 2022, and consultation has recently closed on the future support for low carbon heat (published 20 April 2020 until July 7, 2020). A new fund has been set up, the Boiler Upgrade Fund (BUF), to replace the Clean Heat Grant (April 2022). The BUF has been created to deliver grants to property owners to install air and ground source heat pumps to ensure the capital costs are the same as a new boiler system. Additionally, the Public Sector Decarbonisation Scheme (PSDS) provides finance for energy efficiency and heat decarbonisation projects in public sector non-domestic buildings. Lastly, the Green Heat Network Fund (GHNF) opens in April 2022, funding up to 50% of heat network projects’ commercialisation and capital costs (up to £1M). Until the PSDS replacement policy has been implemented and during the GHNF transition period, there is uncertainty over how the sector will be supported financially. However, heating our homes, businesses and industry is currently responsible for 1/3 of the UK’s greenhouse gas emissions, and the UK has set a legally binding target to achieve net zero emissions by 2050, so significant, concerted and co-ordinated action will be necessary.

The future direction of the gas and electricity prices on which financial performance calculations are made is highly uncertain, particularly when the possibility of carbon taxes and similar instruments is raised. This situation poses challenges for organisations wishing to develop robust and reliable business cases for investing in low carbon heat projects, particularly those with a long development period. 

However, the long-term view from the UK and devolved governments and their advisers offers some confidence that markets and policies for low carbon heat will be shaped to make business as well as environmental sense. Each positive, feasible opportunity for ground- and water-source heat deployment represents a fork-in-the-road choice for organisations involved in greenspace management. Opting for natural gas as the business-as-usual heating source risks locking a building in to a polluting technology with a clear expiry date. Wherever it is technically and financially feasible – and where ground- or water-source heat presents itself as the optimum low carbon option – the decision to invest in future-proof, climate-friendly infrastructure is a step forward towards the Net Zero world envisioned by the pledges of hundreds of local governments across the country.

Footnotes:

1. Equivalent to the heat demand of around 5 million homes – although these systems are able to heat non-domestic buildings too.

2. By December 2019, two-thirds of UK local authorities, in addition to the UK and devolved governments, had declared a climate emergency.

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