Blog Layout

How do heat pumps work? Mesh Energy explains

Doug Johnson • 4 August 2020

In the first of our Mesh Energy Explains series of blog posts, we’re looking at just how heat pumps work; specifically, how energy is harvested and transported into the home using little more than an electrical supply. Those of us working in the renewable technology sector often forget that sometimes we need to return to basics and explain some of the fundamentals to those just entering into the field or researching for their personal provision. So, here goes…


A brief history of heat pumps and the basics

In the 19th Century, William Thompson, otherwise known as Lord Kelvin (of temperature scale fame), pioneered the concept of the heat pump using a refrigerant cycle to prove that heat energy could be used to cool. In fact, he foresaw use in air conditioning and refrigeration.


In the 1940s, Robert C. Webber is credited with creating the first modern day heat pump and we haven’t looked back since. Today’s heat pumps work in exactly the same way; with developments in efficient compressor technology and refrigerant gases incrementally improving operational efficiency of the units.


Heat pumps are often described as “fridges working in reverse”. Energy in fridges is extracted from the enclosed interior of the fridge, keeping your food cool and using a tiny amount of electrical energy to power a small compressor. This extracted heat is “processed” and ultimately expelled at the back of the fridge via an element.


A heat pump uses an identical principle and strips low-grade energy from the natural environment using the process of gas evaporation. Once compressed by the compressor cycle, it is during its condensation phase that high temperature energy is exchanged into your under floor, radiator or domestic hot water system.


The diagram below shows the basic cycle.

Heat Pump Cycle

As a general rule, heat pumps as we know them today use three distinct mediums to harvest energy: earth/ground, air and water. Being pedantic, it is the water moisture in all of these mediums that helps with energy transfer, but for clarity we will stick with these three.


So, it is the changing heat source that helps the evaporation phase of the refrigerant cycle that gives heat pumps their name.


Ground source heat pumps

Ground source heat pumps (also known as geothermal heat pumps) use two practical methods for harvesting energy.


The first method is horizontally buried pipework in the ground which has a glycol/water mixture pumped around it to stop it freezing. The pipes are buried at approximately 1.5m below the ground level and the ambient heat of the earth (nominally 8ºC-12ºC) provides energy to the liquid flowing through the buried pipes. The fluid, which warms up just a few degrees in its journey in the ground, heads back to the heat pump. The water that heads back to the heat pump from the ground collector is often only around 5ºC but this small temperature is passed through a plate heat exchanger and with a significant flow rate, boil the gases in the ground source heat pump refrigerant circuit and impart large quantities of thermal energy to the home using an electric compressor.


Alternatively, the second method uses vertical boreholes (circa 100m) which can be drilled and which require significantly less ground area. These still rely on the ground’s low level thermal energy to warm the fluid but, because of the depth, much more stable ground temperatures are found, and the efficiency of the system improves.



Typical ground source heat pump efficiencies year-round are around 400%.


Air source heat pumps

Air source heat pumps use an external fan unit to draw air across the evaporator unit, which exits at the back of the unit cooler than it entered. Because of varying seasonal air temperatures, these heat pumps are less efficient than their ground source cousins. As a rule, the colder the outdoor air gets, the harder the system has to work to strip energy from the air and elevate it to heat the home.


Air is sucked into air source fan units using a single fan (or fans) and refrigerant pipes strip heat from the air. The air exits the fan units at a cooler temperature. You may be surprised to hear that air source heat pumps can successfully extract energy from the air down to well below -20ºC. Because the refrigerant in the heat pump boils at such a low temperature, even air well below freezing temperatures can give up its heat.


Due to energy in the air affecting outputs from air source units, the efficiencies of these systems typically vary from 450% efficient in the summer and 250% efficient in the winter months. This means that even in the winter one unit of electricity can supply 2.5 units of heat to the home using ‘freezing’ cold air and some clever physics!

Air Source Diagram

Water source heat pumps

Water source heat pumps are so called as they are used in lakes, ponds and streams to harvest energy.


“Open loop” and “closed loop” systems are used. Open loop systems can be likened to a hoover sucking up water and using this direct energy to transfer to the evaporator via a plate heat exchanger. The closed loop system is basically a ground source system with loops or panels buried or pinned under water to harvest energy from the body of water. There are many advantages regarding the amount of energy that can be harvested from pure bodies of water, especially streams and rivers, as flow rates are high and ensure an almost endless supply of energy to the heat pump.


Due to the high levels of energy in the water, water source heat pump efficiencies can exceed 500%.


Still have questions? Speak to us!

So, there you go. A whirlwind introduction to the magical, yet practical basics behind the increasingly common heat pump!


If you still have any questions about the wondrous world of heat pumps and the part they could play in your low-energy home, please don't hesitate to get in touch with the Mesh team today.

SHARE THIS POST WITH YOUR NETWORK

by Doug Johnson 24 March 2025
Mesh Team Blasts Half Marathon for Cancer Charities
by Doug Johnson 24 March 2025
Offsite housing specialists TALO and building performance consultants Mesh Energy have announced a collaboration agreement to accelerate the delivery of ultra-low energy homes. The collaboration will combine TALO’s advanced timber superstructure technology from Finland with Mesh’s experience of providing net zero building performance and engineering services for housebuilders, architects and residential property developers. Working closely together, TALO and Mesh will aim to significantly increase the energy efficiency of new homes for market sale, rent and affordable housing, exceeding both Passivhaus energy standards and Future Homes standards, in compliance with the latest regulations. Doug Johnson, Director of Mesh Energy: “TALO’s timber superstructure solutions for low rise housing are the very best we have seen in the UK in terms of energy efficiency, air tightness, cost and quality. Their latest projects are achieving at least a 30 per cent improvement on Passivhaus energy standards and at no cost premium. We don’t believe there is anything like this on the market today and yet it is very needed. Some of the biggest issues facing housebuilders and developers are managing risk and addressing skills shortages. TALO’s system addresses both of these challenges extremely well. New regulation is coming which will make it increasingly difficult for developers to balance the rising cost of building new homes to the required energy and air tightness standards and the risk of non-compliance. New homes simply need to perform better. And yet the risk for developers is in the fabric and performance of each home. Our new collaboration will give housebuilders the benefit of much greater certainty of delivery to the required quality, air tightness and energy standards from the inception of a project. Our work on the energy strategy, data and compliance will support TALO’s extremely efficient way of building new homes to reduce risk for residential property developers.” TALO and Mesh have already collaborated on a number of projects. Under the new agreement, both businesses can leverage their respective experience to enhance the efficiency and economics of new residential projects. Dr Anthony Greer, Corporate Strategy Director of TALO said: "Our vision is to transform UK housebuilding by taking proven technology which has been used to build thousands of units in the Nordics – in one of the most extreme climates in the world. Our goal is to address some of the difficult problems that have been challenging the UK construction industry for many years – skills shortages, speed of delivery, sub-standard quality, and poor energy efficiency. Our ultimate goal is the offsite construction of high quality, ultra-low energy homes that can eradicate fuel poverty and snagging. By radically reducing time on site, developers can achieve a faster return on investment. They need fewer trades on site because we are using highly efficient offsite technology. Our processes are entirely dry – from forest to site – which means better air tightness performance and more accurate programme scheduling for the fitout phase to further reduce risk. Homes built by TALO exceed Passivhaus energy and air tightness standards at no cost impediment. This means homeowners and tenants will have hugely reduced energy costs that are verified by A-rated EPC certifications. Our housebuilding solutions will be enhanced with our collaboration with Mesh, helping to solve the technical and economic challenges that are constraining the sector and compounding the housing and cost of living crises.” In the new arrangement, Mesh will provide the energy strategy, data analysis and compliance work to support TALO’s delivery of the offsite superstructures for low-rise housing projects – which range from terraced housing, semi-detached family homes and larger executive schemes for developers and housebuilders across the UK.
by Pablo Jiménez-Moreno 29 April 2024
Discover the critical role of a feasibility study in integrating renewable technologies into your home. Learn how to make informed decisions for sustainable living.
by Doug Johnson 11 January 2024
As we come out of our end of year hibernation period for 2023 and try to both digest and interpret what 2023 had in store for us, how we dealt with it, and what we would change if we could; we drag ourselves out into the blinding light of 2024 and hope for a less tumultuous year in the UK’s sustainable construction sector. I am an optimistic person and ‘glass half-full thinking’, as well as doing my best to gaze into the future, is my default position. When working with a team on the sharp end of sustainable building design, there are some trends which simply cannot be ignored and hold great promise for 2024. The following trends are in areas we’ve seen growing design time and client fees being spent to great effect, and that’s why these are my top four sustainable construction prediction of 2024.
by Doug Johnson 7 December 2023
In recent years, sustainability has seen a massive increase in priority within the construction industry. As climate change and its effects worsen around the world, architects, builders, and developers are now feeling more compelled to adopt more environmentally friendly practices. While pursuing sustainable building design is definitely a commendable course of action, the process itself has its own set of challenges; introducing potential risks to the construction industry that must be addressed.
by Rebecca Boehme 3 August 2023
In May 2023, we discovered we’d been included in The Sunday Times’ ‘Best Places to Work in 2023’ list . This phenomenal achievement was the icing on the cake of what’s been a great few years for Mesh as an employer. From achieving our B Corp in November 2021, to being recognised in B Corp’s ‘Best in the World’ category for workers in March 2022, to growing the business to the 22-strong team it is today, it’s been both incredible to see our recognition grow, and a mammoth effort to get here.
by Doug Johnson 27 July 2023
Incorporating low-energy solutions like solar PV, battery systems, and other energy-efficient technologies into commercial buildings offers several key benefits. We cover the top 5 in our latest blog.
by Doug Johnson 20 July 2023
In this second blog on the technology behind low-energy commercial projects, I'll be exploring why solar PV, energy storage, EV charging systems, and LED lighting are crucial assets to any low-energy commercial building.
by Doug Johnson 13 July 2023
It's estimated that commercial buildings contribute around 8% of the UK's total annual carbon emissions, and carbon associated with heating, ventilating, and cooling buildings makes up about 40% of a building's total annual energy usage.
by Lewis Caudy 5 July 2023
When it comes to sustainable and energy-efficient building design, architects are increasingly turning to geothermal technology as a viable option.
More posts

Subsribe to memo from mesh

Share by: