Thermodynamic panels: snake oil or worthwhile
Discussion
I've recently become aware of thermodynamic panel fed, domestic hot water systems.
On the face of it they look like a pretty decent, low maintenance option for our home.
Does anyone have any experience with this type of system? Are there any pitfalls? Is there anything else that I should take into account? Can you recommend an installer in East Anglia?
Thank you.
On the face of it they look like a pretty decent, low maintenance option for our home.
Does anyone have any experience with this type of system? Are there any pitfalls? Is there anything else that I should take into account? Can you recommend an installer in East Anglia?
Thank you.
Do you mean circulating water tubes that heat hot water?
Theoretically they are fine - much more efficient than solar PV, But, maintenance is an issue as a mate has found out. His are about 7 years old and now leak - all things with water in them leak eventually. The original company that installed it is long gone. Roofing companies say “nah, nothing to do with us”. Solar installers have zero interest in fixing 7 year old kit, unless they can sell you a new one.
Theoretically they are fine - much more efficient than solar PV, But, maintenance is an issue as a mate has found out. His are about 7 years old and now leak - all things with water in them leak eventually. The original company that installed it is long gone. Roofing companies say “nah, nothing to do with us”. Solar installers have zero interest in fixing 7 year old kit, unless they can sell you a new one.
normalbloke said:
What is the cool liquid?
Refrigerant.(Below nicked from a website)
In spite of being panels, they are closer to an air source heat pump than they are to a solar thermal panel. Basically, they are a freezer in reverse. Refrigerant enters the panel, absorbing heat from the atmosphere and becoming a gas as it passes through it.
Subsequently, the gas passes through a compressor that increases the temperature. Finally, it passes through a heat exchange coil inside the hot water cylinder. This heats the water within the cylinder to 55 degrees. It is approximated that roughly a quarter of the energy absorbed by a panel comes from the solar irradiation, the remaining from rain and air.
As I understand them, I'm yet to be convinced; so in the absence of more compelling expert evidence, I'm going to call snake oil.
As with any heat pump technology, they basically 'condense' the energy within their source, to feed it into your heating system.
In this case, they are 'condensing' the heat from a solar thermal panel. Thing is, that energy doesn't really need condensing... plain solar panels raise the temperature enough for it to usefully pre-heat the water before you boost it to DHW temperature without the need for expensive, (relatively) unreliable, and energy-consuming heat pump technology being bolted on top of it.
Furthermore, heat pumps work because when they 'suck' the energy out of their working material (be that ground, air or water), more energy flows in to replace it, either by conduction (ground) or movement of the source fluid (air or water). By contrast, the heat going into a solar panel is by solar radiation, and 'sucking' it up with a heat pump doesn't draw more energy in any faster... so you might as well just let the panel absorb it naturally at the rate it's being delivered, and use it 'unprocessed', instead of bolting on fancy gubbins to 'condense' it before use.
...and before the scientific pedants arrive: I'm aware that's a deliberately very simplistic explanation, hence all the words in inverted commas, in order to try to explain things simply.
As with any heat pump technology, they basically 'condense' the energy within their source, to feed it into your heating system.
In this case, they are 'condensing' the heat from a solar thermal panel. Thing is, that energy doesn't really need condensing... plain solar panels raise the temperature enough for it to usefully pre-heat the water before you boost it to DHW temperature without the need for expensive, (relatively) unreliable, and energy-consuming heat pump technology being bolted on top of it.
Furthermore, heat pumps work because when they 'suck' the energy out of their working material (be that ground, air or water), more energy flows in to replace it, either by conduction (ground) or movement of the source fluid (air or water). By contrast, the heat going into a solar panel is by solar radiation, and 'sucking' it up with a heat pump doesn't draw more energy in any faster... so you might as well just let the panel absorb it naturally at the rate it's being delivered, and use it 'unprocessed', instead of bolting on fancy gubbins to 'condense' it before use.
...and before the scientific pedants arrive: I'm aware that's a deliberately very simplistic explanation, hence all the words in inverted commas, in order to try to explain things simply.
We have these panels
We have no gas, and don't use oil.
So when looking around for something years ago to replace an underspecced, noisy, expensive and uselessly installed nibe air-air heat pump. we eventually chose energie thermodynamic panels. I think they were fitted around 2012, costing about £11k
They are basically an air source heatpump as Equus states.
We have 2 units
one has 2 panels and a pump/compressor for hot water with a 300l tank.
the other has 8 panels and pump/compressor gubbins with buffer tank for underfloor heating
We also have a log burner that we use for the lounge/living area in the colder months, as it does struggle to cope with the whole house when it gets below freezing, although the DHW tank has a back-up immersion. Would rather not use an immersion to back up the heating !!
Our house is very well insulated with 200-300mm blown cellulose in walls and roof, there are a couple of little drafts i'm hoping to slowly work on this year before ther winter comes back.
4 bed bunglow south facing (although panels are on the rear wall due to space required) think the floor area is about 150sqm
We have direct debit for £130 a month with bulb which covers the year as we use about that half that monthly in the summer and double that monthly in winter.
So i'd reckon the bill is avaerage and comparable to gas. Both units have been maintenance-free its been serviced once with no issues.
We upgraded the DHW compressor unit, which we can get RHI payment on i hope (just going through it all now)
Both needed regassing as we moved the panels from roof to walls in 2018, but thats it.
Luckily we have full whack fit payments for PV panels which pays for the electric bill.
If you are very well insulated with no gas i'd go for a heatpump, any type, preferably one where you can claim RHI
We have no gas, and don't use oil.
So when looking around for something years ago to replace an underspecced, noisy, expensive and uselessly installed nibe air-air heat pump. we eventually chose energie thermodynamic panels. I think they were fitted around 2012, costing about £11k
They are basically an air source heatpump as Equus states.
We have 2 units
one has 2 panels and a pump/compressor for hot water with a 300l tank.
the other has 8 panels and pump/compressor gubbins with buffer tank for underfloor heating
We also have a log burner that we use for the lounge/living area in the colder months, as it does struggle to cope with the whole house when it gets below freezing, although the DHW tank has a back-up immersion. Would rather not use an immersion to back up the heating !!
Our house is very well insulated with 200-300mm blown cellulose in walls and roof, there are a couple of little drafts i'm hoping to slowly work on this year before ther winter comes back.
4 bed bunglow south facing (although panels are on the rear wall due to space required) think the floor area is about 150sqm
We have direct debit for £130 a month with bulb which covers the year as we use about that half that monthly in the summer and double that monthly in winter.
So i'd reckon the bill is avaerage and comparable to gas. Both units have been maintenance-free its been serviced once with no issues.
We upgraded the DHW compressor unit, which we can get RHI payment on i hope (just going through it all now)
Both needed regassing as we moved the panels from roof to walls in 2018, but thats it.
Luckily we have full whack fit payments for PV panels which pays for the electric bill.
If you are very well insulated with no gas i'd go for a heatpump, any type, preferably one where you can claim RHI
Thank you so much.
We live in an C18th cottage with a C21st 'barn' addition. The house can't be insulated to the standards needed to heat source central heating. Hence, my specific HW system enquiry.
I assume that even with your panels facing north, there's enough in the system to heat your water?
We live in an C18th cottage with a C21st 'barn' addition. The house can't be insulated to the standards needed to heat source central heating. Hence, my specific HW system enquiry.
I assume that even with your panels facing north, there's enough in the system to heat your water?
In the colder months there may be an hours boost needed on the immersion for a 4/5th shower in quick succession, if we have friends over for example.
It does 3 of us fine 95% of the year without the immersion, HW temp is 55.
The panels probably will be more effiecient South facing as they will benefit from solar gain when the ambient air starts to drop below a couple of degrees (EDIT - If the sun's out that is !)
Not sure what the electric usage would be just for the DHW. Although I could put some sort of smart meter clamp on it to find out, but it will be pretty low i'd imagine until Oct time.
It does 3 of us fine 95% of the year without the immersion, HW temp is 55.
The panels probably will be more effiecient South facing as they will benefit from solar gain when the ambient air starts to drop below a couple of degrees (EDIT - If the sun's out that is !)
Not sure what the electric usage would be just for the DHW. Although I could put some sort of smart meter clamp on it to find out, but it will be pretty low i'd imagine until Oct time.
Blib said:
Can one buy a simple solar panel driven hot water heating system?
One can buy simple solar panel boosted hot water systems. Obviously, we don't get enough sunshine in this country to rely on solar as the only energy source for DHW.The basic idea is that you use solar to pre-heat the water to whatever level it can, with an alternative system (boiler, or whatever) to finish the job.
The fact that the systems generate maximum hot water when you least require it (in summer) means that they tend to have fallen out of favour in preference of solar PV (which can give benefit from as much electrical energy as it can generate, even if you don't use it all yourself, by feeding it back into the grid.
A conventional air to hot water heat pump has a fan that draws air through the evaporator, thereby collecting quite a lot of energy under all conditions.
If the evaporator is spread out over a couple of large panels and there is no fan, the output will be compromised in cold/dark weather, perhaps only 1kW output - therefore taking many hours to heat a cylinder
For a small family all this may not matter too much, depends how easy or difficult it is to install.
As soon as you need larger quantities of hot water, even under very poor conditions, an air sourced hot water heat pump is the way to go.
We have installed a 7.5kW output heat pump, that uses about 2 kW, supplying a 750 litre cylinder for 28 people.
No it isn't snake oil, but there are limitations.
caziques said:
If the evaporator is spread out over a couple of large panels and there is no fan, the output will be compromised in cold/dark weather...
This is an understatement, I think.Blib said:
(Below nicked from a website)
In spite of being panels, they are closer to an air source heat pump than they are to a solar thermal panel.
... It is approximated that roughly a quarter of the energy absorbed by a panel comes from the solar irradiation, the remaining from rain and air.
ASHP's use an efficient heat exchanger and a fan to blow a continuous source of air (contain energy) across it.In spite of being panels, they are closer to an air source heat pump than they are to a solar thermal panel.
... It is approximated that roughly a quarter of the energy absorbed by a panel comes from the solar irradiation, the remaining from rain and air.
Bearing in mind that these are basically still just flat, smooth panels, with no finned heat sinks or fans to pass air across them, to suggest that 75% of the energy absorbed by a solar thermal panel comes from incidental heat transfer from rain and air sounds like b
ks to me, and I'd want to see the test results to prove it.
In the absence of data to prove otherwise, I'm still calling snake oil.
The test data that I have managed to find from a quick Google HERE tends to actually support that conclusion.
The graphs look pretty, don't they:
What you've got to bear in mind is that a Coefficient of Performance of 1.0 means that you're getting as much heat energy out as the electrical energy you put in - so the same as a direct electric immersion heater.
So the graph appears to be showing that in the winter heating season months the heat pump is still only hovering around an average COP of ~1.1 (barely worth the effort - and meaning that the payback period will be very long). If someone tried to sell me an air or ground source heat pump on the basis of a COP of ~1.1, I'd laugh at them.
By comparison, you'd be expecting a COP of maybe 2.5-3.5, real world, from an ASHP (and even that's a lot lower than the purveyors of such systems would like you to believe that they deliver. And yes, I've read the FAQ linked from the page above, trying to tell me that comparison with ASHP is unfair, but frankly I don't give a f
k - all I'm interested in is how much energy the system is saving me, not excuses for why it's not doing so).Edited by Equus on Thursday 1st April 09:40
Equus said:
I see some interesting claims around the things, the only one that looks vaguely interesting is the hybrid photovoltaics with the evaporator bonded on the back. Might do something useful but the instinctive reaction is it looks complicated for minimal performance.
I've read about these panels before a decade ago. Let's face it - if they were any good, we'd see them all over the British Isles. The company quoted examples of efficiency in Portugal, where it's far warmer and sunnier than the UK. That rang alarm bells for me. The maker tried to get in the UK RHI scheme, but got chucked out as far as I remember.
There are reasons why they can't work effectively in the UK, and these may be mentioned in posts before me. I CBA to read them all, but just wanted to add my two penneth as I went into it a long time ago.
There are reasons why they can't work effectively in the UK, and these may be mentioned in posts before me. I CBA to read them all, but just wanted to add my two penneth as I went into it a long time ago.
pquinn said:
Equus said:
I see some interesting claims around the things, the only one that looks vaguely interesting is the hybrid photovoltaics with the evaporator bonded on the back. Might do something useful but the instinctive reaction is it looks complicated for minimal performance.
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