Hot water: The technology behind thermodynamic panels

Kya deLongchamps teases out the technology involved in getting a quality hot water feed from alternative technology in the wet and overcast Irish climate.
Hot water: The technology behind thermodynamic panels

There is a legion of sustainable energy devices appearing on our walls, roofs and abroad on our sites, some familiar and some head-scratchers.

It’s exciting to see that the change towards zero energy, suburban housing development across the country has really started, with the inclusion of not just solar plate panels or solar tubes but photovoltaic panels (generating DC current transformed instantly to AC current by domestic scale technologies).

Reputable Irish suppliers are harvesting everything the climate and geology this wet little country has to offer.

This year, 12 homes in the Madeira Oaks estate in Enniscorthy, Co Wexford have achieved the first A- BER rating, including PV as standard.

Heat pumps are still a relatively new range of products and we took a look at the established products group of air, ground and water sourced pumps on the market in January, from €8,000 for a fully commissioned air to water heat pump to provide central heating and some hot water.

Here, I wanted to answer a few questions regarding the latest thermodynamic panels for domestic hot water, another form of heat pump that tends to be confused with flat panel solar arrays.

Detractors claim this is due to strategic marketing, but there’s more to this warming story.

What are thermodynamic panels?

They are close in type to an air source heat pump, and year round can utilise both ambient heat in the outside air and rain and sun to heat all our domestic water.

A low carbon technology, you are most likely to run across them at a self-build trade show.

Unlike solar panels, thermodynamic panels can gather energy 24 hours a day, and although sun contributes — air and rain are also thermally generous.

This technology can work in compromised conditions, even sub-zero temperatures.

Thermodynamic panels (one is standard) can be fixed to the roof, flat or pitched, or to a wall, preferably a south or south-east facing wall.

They are black, thin in profile, semi-gloss in texture with an imprinted ‘circuit’ look of veins, and very discreetly sized around 80cmx1m of surface area set on brackets to your chosen surface.

How do they work?

The technology is roughly that of a fridge, but in reverse. Using the exterior panel (the collector) a chilled refrigerant F liquid of -20c to -30c is circulated and transformed by the warmth in the atmosphere into a warmed gas.

The gas is channelled through a narrow gauge copper pipe to a compressor which increases its temperature further returning it to liquid form.

A heat exchange coil in the hot water cylinder then warms the hot water supply.

On rare occasions where the supply does not reach safe temperatures of 55c, an integrated immersion boosts the result, and most systems are routinely pushed to 60c on set dates in the year to deal with any dangers from Legionnaires’ disease.

There is no water in the collector panel as there would be with solar tubes, and there is no powered fan as with a conventional air-to-water heat pump.

However, a relatively small amount of electricity is needed to run the compressor, and that can vary depending on usage.

Retrofit systems can even utilise appropriate existing 100l and 200l cylinders, the condenser/heat exchanger being sited with the cylinder.

The panel outside is only around 8kg, eliminating the need to strengthen the roof structure.


This is new technology lacking the extensive, independently verified testing of more conventional solar and air/water/geothermal heat source products.

Performance figures for a thermodynamic array are expressed as COP, common to heat pumps (Coefficient of Performance), a reading of how many units of usable energy is produced, using one unit single unit of electricity.

Air source heat pumps run at a moderate COP of 2-4 but deliver a massive saving on the greater expense of home heating and domestic hot water (water makes up only 15% of a standard billing cycle).

Thermodynamic panels are said to have a comparable average seasonal performance.

There has been only one independent test of a these panels, The Narec/National Renewable Engery Centre test in 2014 which showed a disappointing COP spread over January to July of 1.6-2.2, still likely to offset the expenses of a conventional electric immersion by 50%, industry sources say.

Claims in the industry itself vary from 70%-100%, and Irish sustainable energy service technicians I spoke too (without panels to promote) agreed that 100% was viable ‘dependent on individual domestic hot water usage’.

This could give a potential annual saving for a standard home of about €200.

Financing the technology

Thermodynamic panels are currently not covered by the SEAI Better Energy Homes Grant as a single panel, but according to Richard White of LVP Renewables, some qualify in multiples, which he agrees, does not make any economic sense.

Following further, appropriate independent industry-acceptable testing of thermodynamic products, there’s every reason to believe they will be accepted here for grant aiding in the future, and compare in price to solar water heating systems.

The €1,200 SEAI grant currently offered for retrofits, is for conventional flat plate solar collectors and evacuated solar tubes which will handle 50-60% of your hot water needs depending on individual usage, and cost €4000-€6000 (SEAI).

Thermodynamic panels suppliers registered with Revenue for the Home Renovation Incentive Scheme, qualify for inclusion in this VAT relief scheme (happily now extended for two years by the 2017 Budget),

Comparisons with other systems

Solar panels require detailing at around €200-€250 every three to five years including glycol replacement.

Despite claims by suppliers that thermodynamic panels are maintenance free, service professionals I spoke to were sceptical, claiming they with the potential for ice build up and refrigerant leak, they were ‘not bullet-proof’.

They cost less to run than other air source heat pumps, but such comparisons are flawed, as air source heat pump systems (€8000-€10,000 installed) offer most if not all of your space heating needs and can contribute to the hot water supply too.

There’s little argument, that ranged against conventional solar panels and tubes, panels have less moving parts to go wrong and won’t suffer problems with water stagnation in times of high sunlight and low water usage.

They also take up a fraction of the roof space (solar needs 1-1.5m² per person), and their inclusion will satisfy the Part L requirement of the Building Regulations for sustainable energy in a new build.

Hot Contender

LVP Renewables installed the first thermodynamic system in Ireland in 2008 in one of its family homes.

Since then, it has over 2,000 installations across the country and was featured on About the House with Duncan Stewart on RTÉ television.

Richard White, sales director at LVP was happy to answer some direct questions on the technology.

Can a thermodynamic panel really deliver 100% of domestic hot water to a standard family home year round?

Yes indeed it can. Assuming temperatures don’t fall below circa -5°C. Also, when we say 100%, we assume one tank of hot water minimum per day.

Is this augmented by an electric immersion in the system?

No. The system comes with a few modes. Ordinarily, it is set on ‘Eco’ mode where the immersion will never kick in unless manually turned on.

This can be automated if desired by the customer. There is a small compressor that will consume a nominal amount of electricity.

What are the potential savings? 

It fluctuates massively, and economies of scale play a part, along with the system in place. We have seen savings of €300 and €1,500 per annum.

What is a reasonable coefficient of performance with a thermodynamic system? Is this measurement of performance fair?

According to EN16147, The Eco 250 has a coefficient of performance of 3.78. The measurement is not a fair reflection as it doesn’t take solar gain into consideration. This can improve performance by 30%.

What are the prime advantages of thermodynamic over conventional solar arrays?

In Ireland, where the weather is so unpredictable, thermodynamics is a preferential technology as it doesn’t require sunlight to operate. It will work every day of the year. Only one panel is needed for 100% hot water and the panel can be east, west, or south facing.

Pricing — new and retro-fit for a standard 2,000ft four-bed family home?

New builds are difficult to price as we need an xml file to ensure compliance but in a retrofit situation, a typical installation would cost €5,000 fully inclusive of new installation, plumbing and Vat.

Retrofit time to fit and commission?

Generally speaking, we will have everything done and dusted in one working day.

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