Thermodynamic Panels


Introduction to Thermodynamic Panels

Thermodynamic panel on houseThermodynamic panels are designed to produce hot water for both domestic and commercial usage. These systems are more formally known as Solar Assisted Heat Pumps. This term helps to explain how and where this type of product fits into the renewable energy spectrum.
A thermodynamic panel is a halfway house between a solar panel and a heat pump. The primary purpose of this product is to provide heat energy in the form of hot water predominantly, but soon the systems will be adapted to provide space heatling (centeral heating) as well.
The products have been developed as a more efficient alternative to air source heat pumps by including the use of solar gain / radiation. This means that a thermodynamic system can benefit from both the ambient air temperature, like a heat pump, as well as the solar radiation, like a solar thermal system.

Thermodynamic PanelThis best of both worlds approach will often result in an improved COP (coefficiency of performance). These products have been designed with a life expectancy of roughly 20 years by some manufacturers, however they have only really started to take hold in the UK over the last 6-8 years.
Initially there was lots of scepticism and uncertainty surrounding this new renewable energy system as it found its feet in the UK. However, in early 2016 the first thermodynamic products were granted Microgeneration Certification Scheme (MCS) approval. This dramatically increased consumer and trade confidence.

How does a TD system work?

A thermodynamic system works by sending a very cold liquid refrigerant around a panel on the outside of a property. The temperature of the liquid is approximately -22°C when it enters the panel. As the liquid flows through the veins in the panel it absorbs heat energy from the air surrounding the panel. This is where the term Thermodynamics comes from, as it is a scientific terms used to explain heat energy and its movements. The liquid refrigerant will vaporise into a gas once its temperature reaches approximately -15°C. This is more commonly known as its boiling point. The gas exits the panel and is circulated back to a compressor inside the thermodynamic unit. The compressor job is to compress the gas and send it under pressure through a heating element or plate. When a gas is compressed is gives off heat energy. The heating element is a way of distributing the heat into the store of water. Once the gas has lost its heat it exits the element and passes through an expansion value, which releases the pressure. This drop in pressure and loss of heat energy means that the gas condenses back to a liquid for the cycle to begin again.
Thermodynamic panel system diagramThe higher the temperature outside the more energy a thermodynamic system will be able to absorb, due to the greater heat difference between the liquid refrigerant and the air. Therefore the sun will help but it’s not essential. This means that thermodynamic panels can be positioned on a side wall of a property as well as a roof, and face any direction. However if possible it’s advised to position the panels towards the sun to gain that bit of extra performance. The panels will however continue to work at night time due to the heat being absorbed from the air.

The water inside the thermodynamic unit /cylinder is constantly monitored and kept hot by a thermostat. The thermostat will switch the system off once it reaches its required temperature. Most thermodynamic suppliers will set the stored water temperature of a domestic unit at 55°C. This is considered to be sufficiently hot for domestic hot water purposes, yet remaining safe for use. However, this temperature setting can be amended if necessary. Commercial units can be set at much higher temperature if needed.

What is a TD System made of?

A thermodynamics panel is roughly about the size of a standard door, 2m by 1m. The panels are made from anodised aluminium. The anodizing is an electrochemical process that converts the surface of the metal panel into a non-corrosive, durable finish. Inside the property / premises there would be a main unit. This unit consists of two sections, one of which holds the electronics and working parts, the other contains a water storage area. Thermodynamic units come in lots of different sizes dependent on the amount of water needed and storage capacity. Inside the unit you would find a compressor, circuit board, wiring, heating plate or element, expansion value and a backup immersion heater. Some units also come with a secondary coil built into the storage tank so that the existing boiler or additional heat source can be connected up. Most storage tanks within the units are made from stainless steel, however some come with enamelled cylinders. There is little difference between the performance of these cylinders, however stainless steel is often considered to be the more durable cylinder.

Types of TD Systems?

Types of thermodynamic hot water systemsThere are two main ways that a thermodynamic unit can be set up for a domestic property. The first is to install a small thermodynamic unit, usually no larger than 50cm by 50cm, which is designed to work with a normal hot water cylinder. The water from the standard hot water cylinder is pumped to the thermodynamic unit and is heated over a heating plate. These systems are idea if you are restricted on space, for example a tight airing cupboard. However because the water is heated externally from the cylinder a pump is needed which slightly increases the power consumed by the unit (manufactures quote between 300-450w when in use). These systems can be linked up with a maximum of about 250lt cylinder capacity. Be wary of installing these types of thermodynamic systems onto a vented hot water system (low pressure, with a header tank). When installing on a vented hot water system the position of the thermodynamic unit is very important, it must be sufficiently lower than the header tank to prevent low pressure air locks. A rare but not unusually problem, which can be easily fixed. In this instance the unit will turn off and display an error message or red light.
The second and more common thermodynamic system set up is to take out the existing cylinder and replace it with an all in one cylinder/thermodynamic unit. These units come in a range of sizes and cylinder capacities (75, 150, 160, 180, 200, 210, 250, 280, 300, 500lt). This set up is the most efficient way of installing and running a thermodynamic unit, if you have the space. The water is directly heated by a coil/element in the storage tank within the unit. thermodynamic hot water system unitsThis means there is no heat loss from piping the water to an external heating unit. These systems can be fitted to both vented and unvented hot water systems. Quite often an old copper cylinder with poor lagging is replaced with the new thermodynamic unit, which means because of its modern insulation the heat is also retained more efficiently within the new cylinder. The larger 300lt & 500lt units are more commonly used for places with higher hot water demand, such as restaurants, B&Bs, hotels, hair dressers, farms etc…These larger units would often come with more panels, usually 2 or 4, which helps increase energy absorption and speed up recovery time. Manufacturers typically say that 200lt of water can be heated from normal tap water temperature up to 55°C in approximately 3-4 hours, but once achieved it is then constantly maintained.

Running cost of a TD System

The running cost of each thermodynamic unit is dependent on the size of the unit and compressor within, the volume of water being heated, the length of pipe run to the panels, the amount of hot water the property requires. Domestic systems will require between 300-450w of power when in use. An average domestic house would have approximately 200lt of storage capacity; this means that if the thermodynamic unit was running for 6 hours a day (2x complete fill & heating of 200lt tank) the unit would cost you approximately 30p. Most providers state that a typical house would expect to pay between £40-60 per year in electrical running cost. Commercial units will typically range between £150-£500 per year to run, dependent on specific hot water requirements.

Maintenance, Warranties and Lifespan?

Thermodynamic systems do not need any maintenance. This is because they have very few moving parts and are a sealed system. Once the gas lines and panel/s have been correctly installed and filled with the refrigerant there should be no need to top up or maintain the system in the future. A qualified F-Gas engineer should vac down the entire system (suck all air out of the system) prior to inserting the refrigerant. This process removes imperfections such as particles of dust or water vapour, which could hamper the performance of the unit. Once the refrigerant is put into the system a pressure test should then be undertaken to determine the correct level of refrigerant needed and to check for any leaks. Due to the complexity and skill required to install a thermodynamic system correctly we recommend using a qualified F-Gas engineer.

Warranties for thermodynamic systems can vary from company to company from 2 year up to 5 years. Some companies will break their warranty down into different section, for example 2 years on labour and install, 2 years on the unit and 5 years on the panel. The best warranty we have found to date is a 5 year fully inclusive warranty. The most important thing to check is that the warranty is back up, either by the product manufacture or by an independent insurance provider. This will help to give you better protection if the company that sold you the thermodynamic system is no longer around in the future. The estimated lifespan of a thermodynamic system is around 25 years.

Thermodynamic Panel Mounting Methods

Wall Mounted Thermodynamic panelThe most common and often cheapest way of installing a thermodynamic panel is to wall mount. This is achieved by using 6 stainless steel brackets that fix directly to an external wall.

Racked thermodynamic panelsIf multiple panels are needed for larger installations the thermodynamic panels can be racked. This is because they do not need sunlight to operated, and will work as long as there is sufficient air movement around the panels.

thermodynamic panel on roofThermodynamic panels can be installed onto a roof. This type of installation is very similar to how Solar PV panels are installed. Stainless steel runners will go along the roof for the panels to sit on and attach too. These runners are then attached to the joist via a metal clasp that slides under the tiles.

commercial thermodynamic panel on flat roofPanels can be installed on a flat roof using specially made a-frames. The panels must be louvered to a minimum of 15 degrees so that water can run off.

Will a Thermodynamic System Add Value to my House?

There is no concrete evidence to suggest with certainty that a thermodynamic system will add value to your property. However, since the introduction of the EPC (Energy Performance Certificate), which all properties must have when being bought or sold, consumer awareness of properties energy performance has greatly improved. If a property comes with a low EPC grade this could suggest to the buyer that investment may be needed to improve its energy efficiency once bought. In 2016 the first thermodynamic units were incorporated into SAP calculations, which meant that they would have an effect on a buildings energy rating.

If you are thinking of selling your house after having installed a thermodynamic system it may be possible to keep the system and take it to your next property. This is very much dependent on the type of system purchased and its set up. Thermodynamic systems are not designed to replace an existing boiler, just switch the domestic hot water off, therefore if a system were uninstalled the property could revert back to the existing boiler / heat source. Not all providers offer this option, and if they do consumers would have to factor in the additional labour cost of uninstall and re-installation.

Planning Permission

The installation of thermodynamic panels in England and Wales is classified as ‘permitted development’ which means that no planning permission is needed. There are however a few exceptions to this rule. If you are looking to install on a Listed Building you must take the necessary steps to obtain planning permission through your local council. If you live in an AONB (Area of Outstanding Natural Beauty) it is advised that you discuss your plans and panel positions with the local authority. If you live in a conservation area no planning permission is needed, however the panel/s must not be visible from the main highway / front of house.


MCS (Microgeneration Certificate Scheme) is the government backed approval of renewable technologies for application in the UK. Thermodynamic panels were first included on the MCS register back in 2013. The panels were however quickly rescinded from this approval, due to a false classification, resulting in them being de-registered. This removal from the MSC register knocked consumer confidence in the technology; however what consumers were not told was that the panels were registered under the wrong classification of renewable energy, Solar Thermal. In 2015 MCS created a new category specifically for thermodynamic panels known as ‘Solar Assisted Heat Pumps’. The first thermodynamic panel manufacturers and products achieved MCS approval in early 2016. This approval has helped the thermodynamic panel industry to flourish over the coming year. Furthermore news was released mid 2015 that Solar Thermal would be losing its RHI (Renewable Heat Incentive) payments in early 2017. This helped to further strengthen the appeal of thermodynamic systems over the ageing technology of solar thermal.thermodynamic heating system
Although thermodynamic panels are now MCS approved they do not qualify for RHI. Therefore the systems cost effectiveness needs to be judged on its energy savings along. Although an RHI payment would be good for consumers the general consensus among thermodynamic manufacturers is that they don’t want to repeat the turmoil of the Solar PV industry, with subsidies being given and then reduced / taken away. They hope that the systems will still make financial and commercial sense without payment assistance from the government. This will help to create a more stable industry able to stand on its own two feet, without being propped up by the government. Early signs of this seem positive.

Solar Thermal Vs Thermodynamic Panels

Solar Thermal Thermodynamics Panels
Requires solar radiation Works from air temperature & solar radiation
Is an assist to another heat source Can provide 100% of hot water
Requires a service every 2/3 years No servicing
MCS Approved MCS Approved
Has an RHI payment (Until early 2017) No RHI
Panel has to face south Panel can face any direction
Cylinder heats and cools dependent on sun Cylinder is constantly kept hot on thermostat
Life expectance 10-15 year Life expectance 25 years
Domestic install cost between 4-6k Domestic install cost between 7-10k


What are the Potential Savings of a TD System?

The savings for each individual thermodynamic system will widely vary, based on energy consumption, hot water consumption, location in the country and system set up. There are a few things you can do to maximise your systems performance, such as: Panels can be placed up to about 20m pipe run from the unit, however reducing this run can help save on the electrical running cost. If you can face the panels towards south in an open area you will also benefit from extra performance, due to solar gain. The average ambient air temperature will also play a part in the overall performance of each system. Someone living in Brighton would have high average air temperatures than someone in Edinburgh for example. This means that the unit in Brighton would absorb more heat from the air and recover the cylinder temperature faster, thus saving on the electrical running cost.

Despite these variances thermodynamic units appear to have a very low running cost, with manufactories displaying figures of 300w – 450w of electrical consumption when in use. This means that it would cost you between 3-4 pence per hour to run a thermodynamic unit. Systems typically only run for a few hours a day as when the water reaches temperature the unit will automatically turn off. Therefore the equation for working out savings would be as follows:

Domestic Hot Water Cost – Running Cost = Total Savings

The main variable in the equation is the domestic hot water cost. For some this is hard to decipher as it is all lumped into a gas, oil, electric or LPG bill. This will also vary based on the number of people in the property, hot water usage, boiler set up (combi or cylinder) and hot water system type (unvented or vented). Combi boilers will have a lower percentage of hot water on the bill compared to a cylinder system, as they only heat hot water on demand, whereas cylinders heat and maintain the entire water volume within. As an average guidance hot water can represent between 30-40% of a typical domestic properties fuel bill.

How Much Does a Thermodynamic System Cost?

The cost of installing a domestic thermodynamic panel system will vary, however you can expect to pay between £7000 and £10000. This cost would include full installation, parts, labour, scaffolding if needed, warranties and a reduced VAT of 5%.

commercial thermodynamic panel systemPotential differences in the initial costings will vary from project to project. For example, plumbing costs may be higher if the building has a complicated or antiquated water system. The installation costs could be significantly higher if scaffolding is required. The size of system (number of panels and water cylinder capacity) you will need depends on the hot water demand of your home, business or organisation. A general rule of thumb is that you’ll need 1m² of hot water for each person living in the building. The average person will use around 50 litres of hot water each day; a normal 3/4 bedroom house would require a 200 litre unit/cylinder.
We strongly recommend using a professional company with experience and the correct installation qualifications (F-Gas Engineer). Thermodynamic systems shouldn’t be installed by conventional plumbers alone. This is why the DIY thermodynamic panel market doesn’t really exist.

Commercial Water Heating

commercial thermodynamic panel systemA thermodynamic panel system could be very beneficial to a business or premises that use large volumes of hot water, for example hair dressers, restaurants, hotels, B&Bs, dairy farms swimming pools and sports clubs. These types of installations will often pay back the initial capital invested through energy savings within the first few years of owning the system.An individual investing through a business also has the added advantages of claiming the VAT back and using the initial installation cost as a business expense / investment.


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