Technologies for a Low-Carbon Future

Heat Pumps

21st November 2023

heat pipes

In this series, following our guidance on how CEO’s can boost net zero investment, Anthesis’ energy team share insights into the technologies needed to support the low-carbon energy transition. In this first article, Ronald Tomlinson, Principal Engineer for Industrial Decarbonisation, examines heat pumps, their potential to support a low-carbon future, and how they can meet the challenges of industry.

With around half of global energy consumption being used for some form of heating, whether it’s space heating and hot water for human comfort or heating for industrial processes, it is clear that if net zero targets are to be met within the timescale required, this will necessitate a substantial and rapid shift away from burning hydrocarbon fuels to generate this heat. Key to meeting this target will be the widespread deployment of affordable, efficient and well-proven low or zero-emission alternative technologies. In this context, heat pumps are an obvious choice to meet a significant proportion of the world’s heating needs going forward.

How are heat pumps being deployed?

Although heat pumps have only risen to public prominence over the last decade or so, the technology is over 150 years old, widely available and can be installed in a range of sizes and configurations depending on the available heat source. Heat pumps have a long track record of being deployed for the provision of space heating and hot water, whether for individual properties at a scale of a few kilowatts or as part of large district heating schemes generating 10s of megawatts of heating as is common across Scandinavia and Central Europe. Increasingly, industrial heat users are also seeking to deploy heat pumps for process heating, potentially taking advantage of existing process cooling requirements which generates waste heat which can then be upgraded with a heat pump to meet process requirements.

Even though heat pumps are more efficient when delivering lower-temperature heating, the technology continues to develop, pushing the temperature threshold further upwards to capture more of the industrial heating market, with some technologies already capable of operating at +150°C or higher.

How do heat pumps work?

Whilst burning fuel to generate heat is obvious and intuitive, a potential barrier to adoption by individuals may be a lack of awareness as to how a heat pump works. However, a heat pump simply operates in the same way as a domestic fridge; it extracts heat from the contents of the fridge (the heat source) by evaporation of a liquid refrigerant which is then compressed to form a high-pressure, high-temperature gas which is subsequently condensed back into a liquid via a coil at the back of the fridge exposed to ambient air (the heat sink). Whereas a domestic fridge is purposed to make beneficial use of the cooling caused by evaporation of the liquid refrigerant, a heat pump makes beneficial use of the heat rejected by condensation of the gaseous refrigerant.  A compressor at the heart of the system is driven by an electric motor to compress the gas from its low-temperature, low-pressure condition to its high-pressure, high-temperature condition.

For a typical heat pump, around two-thirds of the energy transferred into the hot circuit is extracted from the heat source (which could be the air, a source of water or heat from the ground) whilst only one-third of the energy comes from the compressor drive motor. In other words, for one unit of electrical power input, a typical heat pump would deliver three units of heating, though it can be considerably higher depending on the application. This is referred to as the Coefficient of Performance (COP). The COP is improved by using as warm a heat source as possible (although it should be noted that appropriately designed air source heat pumps can still operate effectively at sub-zero ambient temperatures) and by heating to as low a temperature as is suitable for the intended application. Where waste heat is generated as part of a separate process, such as from data centre cooling or from sewage treatment plants, this presents an opportunity for extremely efficient heat pump operation and therefore improves the economic viability of this technology.

How do heat pumps support the transition to a low-carbon future?

It seems increasingly likely that heat pumps will be one of the foundational technologies to assist in eliminating reliance on fossil fuels for the purposes of heating.  As the grid continues to decarbonise, the indirect emissions associated with the electricity required to operate the heat pump will fall as well. In Norway, where around 98% of electricity is generated from renewables, heat generated in this way is almost emissions free. Using large-scale heat pumps in combination with large-scale thermal storage can also act as a thermal battery to make use of electricity generated by windfarms at times when the energy could otherwise not be used. This allows the heat pump to operate when the carbon intensity of the grid is at its lowest and switch off at peak times when the carbon intensity is highest.

How can heat pumps be used now?

Heat pumps can be used for almost any space heating or hot water application now. However, heat pumps are not all the same and careful selection of all component parts of the system is required, from the heat pump technology itself to the working fluid used and optimised sizing of ancillary equipment relative to peak loads.

Getting all of these factors right is key to ensuring the project meets both decarbonisation and financial objectives. Optimisation of all system parts can be complex and seeking specialist advice can often ensure better outcomes.

Whilst there are limitations to currently available heat pumps, particularly where the desired temperature exceeds 100°C, the majority of global heating needs can be met with existing heat pump technology.  A major barrier to wider adoption relates to the cost of the heat pump itself and the cost of electricity required to operate the heat pump relative to the counterfactual case, but end users should consider whether this appropriately accounts for the cost of doing nothing.

Heat pump project economics are highly location dependent with the UK for example seeing a slower uptake of heat pumps compared to much of Europe due to less favourable pricing structures. Whilst government policy and wider energy markets have a significant impact on project viability beyond the control of the average end user, this emphasises again the importance of optimising the complete system design to tip the balance in favour of heat pumps.

The International Energy Agency (IEA) estimates that to achieve net zero emissions by 2050, approximately 500MW of heating capacity generated by heat pumps needs to be installed globally every month for the next 30 years. This covers all sectors including higher-temperature industrial applications for which heat pump technology is not yet proven. Meeting this target will be challenging and will require both public and private organisations to rethink their approach to heating to maximise the potential opportunity to deploy clean heating technology.