The enlightened among us are well aware that heating and cooling for domestic, industrial, and commercial buildings are a major source of carbon dioxide emissions. Thermal energy – including heating and cooling for space, water, cooking, industrial processes, air conditioning, and refrigeration – is reckoned to account for around half of the world’s end-use energy and 40% of its energy-related global carbon dioxide (CO2) emissions.
As such, thermal energy merits a prominent place in any low carbon strategy. But this begs an important question – what are the best systems to forge a sustainable path?
There are essentially two systems that offer low carbon heating and cooling: combined heat & power (or combined cooling, heat & power) – CHP and CCHP – and heat pumps.
How can CHP/CCHP & heat pumps work together?
Conventional wisdom dictates that C(C)HP and heat pumps are rival systems, and never the twain shall meet. In fact, there is nothing preventing the two technologies from operating together. Indeed, there are powerful synergies associated with this arrangement, of which more later.
Both technologies are currently used as an alternative to traditional systems such as boilers and electric heaters, but, unlike these legacy systems, they are also both sustainable options for providing heat to district heat networks.
Each technology individually also offers benefits. An advantage of CHP is that it can guarantee security of supply by supplementing the use of heat pumps when the grid is unable to provide enough renewable energy.
Other gains associated with C(C)HP include the fact that it typically has an efficiency of over 80% with operators regularly saving around 20% on energy bills. They can also save up to 30% on carbon emissions, transmission, distribution losses are reduced, and there is an increase fuel supply security.
Furthermore, C(C)HP can generate heat and power simultaneously, reducing carbon emissions by up to 30% compared to the separate means of conventional generation via a boiler and power station.
But C(C)HP is not alone in having advantages over more conventional forms of heating and cooling; heat pumps also offer a host of significant benefits. For example, they are particularly energy efficient, versatile, and offer consistent comfort. They also provide significant environmental benefits by reducing the harmful greenhouse gas emissions traditionally associated with heating and cooling.
Both C(C)HP and heat pumps are also considered valuable options for boosting the functionality of the district heating systems that distribute heat generated centrally through insulated pipes. And it is when they work together that C(C)HP and heat pumps really come into their own.
Indeed, the combination of CHP and heat pumps is increasingly seen as the most efficient solution, overcoming the traditional quandary of choosing one over the other.
A research paper published in 2020 – On the value of combined heat and power (CHP) systems and heat pumps in centralised and distributed heating systems: Lessons from multi-fidelity modelling approaches – compares the performance of CHP with that of heat pumps. The results imply that, although centralised CHP energy is currently a particularly profitable option, this can’t be certain in the future. However, the research also reveals how including heat pumps in the energy mix offers the potential to create significant heat decarbonisation.
Integrating heat pumps and combined heat and power
Integrating the two technologies essentially means employing the residual heating or cooling produced by a C(C)HP system to drive a heat pump, thereby increasing the overall efficiency of energy use. In other words, C(C)HP systems can enable the operation of heat pumps in situations where the grid cannot provide enough renewable energy.
Indeed, at times when renewable sources of electricity generation such as wind and solar photovoltaic power generation are insufficient, C(C)HP systems can offer a flexible power supply.
As well as providing electricity, they also produce useful heat or cold, allowing heat pumps to operate at a lower capacity than they otherwise would. So, the combination of these technologies results in a win-win – simultaneously decreasing and generating the power requirements within the building or network while maximising efficiency.
When used in heating applications, heat generated by CHP could preheat water or air before it enters the heat pump, reducing the amount of electrical energy needed to achieve the desired temperature. This not only increases the coefficient of performance of the heat pump but also ensures smoother, more consistent and reliable heat output.
Furthermore, combining these technologies can help balance the energy grid by providing flexible demand response capabilities. CHP can provide heat and power when renewable energy production is low while the heat pump can operate during times of surplus renewable energy generation. This hybrid approach can prevent fluctuations in energy supply and demand.
Applications for combined heat and power and heat pumps
The combination of C(C)HP and heat pumps holds enormous potential for innovative solutions in various sectors, including industrial applications and heat networks which distribute heat or cooling from a central source or sources, and deliver it to a variety of different customers such as public buildings, shops, offices, hospitals, universities and homes.
