Thermo dynamics for hot water that runs off atmosphere

[steve k]

The heat is magicked from the compressor, from the heat of compression. Imagine a bicycle pump, why do these get hot in use? kinetic energy to heat enegry.
All the evaporator plate/panal is for is to allow the refrigerant to boil and change state from a liquid to a gas, so that the vapour compression cycle can start again.

The gas does not care weather it is 10 deg C, 50 deg C or -10 deg C as long as it can change state in there.

I will try to simplify Jason's explanation:

When a fridge (which is essentially what these are) is switched off the gas in side them will be in a saturated condition; part liquid, part gas.
When we switch it on here's what happens, the compressor starts and does what it does i.e. compresses the gas in the system, as the gas is compressed it heats up and comes out of the compressor in the hot gas discharge line. It is this hot gas line that wraps around the cylinder full of cold water, as the heat flows from the hot gas to the cold water obviously the gas cools down, and then condenses from a gas into a liquid.
The trouble now is that we have liquid refrigerant that we need to turn back into a gas so that it can be compressed again. Then we can utilize the heat of compression to heat our bloody water up. Are you all with me so far???

To do this we send the liquid refrigerant through an expansion valve that will allow the liquid to expand and lower its pressure (think spraying mister muscle in the kitchen) this happens just before the evaporator (the panel), now that the liquid refrigerant is in small particles, like a mist, it will now boil/evaporate easily back into a gas using any heat around as long as it is above the gases boiling point of -26 deg C.

The process can start again..

It's all clear in my head:sifone:, I hope it will help someone understand it all a bit better.

 

[Gavin A]

ok, the heat is effectively created by the compressor, but the energy isn't.

there is the same energy difference in joules between the incoming and outgoing gasses to the energie unit from the panels as there is between the incoming and outgoing heating fluid to the tank plus part of the electrical input to the compressor.

but that's clear from what I originally wrote anyway, in terms of the compressor concentrating low grade heat energy into higher grade heat energy.

and of course it matters what temperature the incoming gas is at, as this dictates how much energy is available - why else would the efficiency and heat output from heat pumps rise with temperature of the incoming gasses?

the worrying thing to me about this conversation is that both of you install heatpumps, and I don't yet.

 

[Gavin A]

I have installed a few of these systems and these are the facts:

Ambient air temp - 6 deg C
Water entering temp - 8 deg C
200l of water 8 deg to 55 deg = 2 hours
amp draw = 9amps

Now i'm no mathematician, but what does this calculate into?

Steve

200l at a little under 50deg temp rise needs around 11kWh of energy input.

9amps x 230 v = 2kW x 2 hours = 4kWh

COP = 11 / 4 = 2.75

a COP of 2.75 at 6 deg c ambient air temperature is reasonable, but not particularly impressive for a heat pump tbh, though it at least demonstrates that it's considerably better than an immersion heater, and maybe just about on a par with a condensing gas boiler.

So possibly worth it for those on full electric heating.

something has been bugging me about these figures, and I've just worked out what it is.

These are the ratings for the 200l energie unit

electrical input 390 - 550Wpower output 1690 - 2900W
anti legionella heater 1200W

assuming you were using the energie system, it's pretty clear from these figures that you must have had the 1200W immersion switched on when you were heating the system up from cold, as there's no other way you could have got anything like 5.5kW heat output from it, or 2kW electrical input. I'd been thinking the electrical input figures seemed extremely high.

http://www.thermogroupuk.com/thermogroup_pdfs/TDY_ECO_Data_Sheets_v1.0.pdf

 

[steve k]

the worrying thing to me about this conversation is that both of you install heatpumps, and I don't yet.

Why? I am an air conditioning engineer and have been installing "heat pumps" for 25 years>

assuming you were using the energie system

You have assumed incorrectly, perhaps the ones we installed have a larger compressor and a more efficient heat exchanger.

Steve

 

[Gavin A]

Why? I am an air conditioning engineer and have been installing "heat pumps" for 25 years>

have a read through Jason's posts and your recent post then, and the answer should be obvious. You don't seem to be understanding, or at least you're not describing very well where the actual energy input originates in these systems, or allocating any importance to it.

it will now boil/evaporate easily back into a gas using any heat around as long as it is above the gases boiling point of -26 deg C.

yes, this is where the actual additional energy input into the entire system (over the electrical input) comes from, not from the compression / expansion cycle itself. This energy input to the otherwise closed cycle* of the heatpump comes from the panel collecting energy in the form of heat from both the air and the solar radiation, and is directly proportional to the actual heat energy output from the other side of the compressor as is clearly shown in the graph posted.

You have assumed incorrectly, perhaps the ones we installed have a larger compressor and a more efficient heat exchanger.

Steve

fair enough.



*well, not entirely closed as the energy is obviously being extracted at the other side into the hot water tank, which balances out the heat energy input from the panel + the most of electrical energy input.

 

[steve k]

I am lost for words so I shall gracefully bow out of this discussion and look forward to reading it instead. I will also carry on installing these things without worrying too much about the if's, but's and why's of a simple fridge that simply works..

Steve

 

[The Solar King]

Normal Solar Thermal has zero costs for energy production and pretty low running costs - a fluid change every five years and a pump if you are unlucky during it's lifetime.

not entirely true - the electricity to power the pump can easily cost £5-10 a year depending on the set up, efficiency of the pump etc. Unless it's a PV powered pump, or I guess if the customer also has solar PV installed.

The pump on a solar thermal system will not operate before there is sufficient temperature differential to ensure that more energy is being transferred into the hot water cylinder than the pump is consuming giving a permanent net gain. How you account this will depend on the calculation used for the performance of the ST system. It should be showing the net energy provided.

There is a lot of hard work going on with DECC to make normal ST viable under the proposals for the RHI. If this is successful and IF the questions raised about thermo dynamic equipment can be answered by the manufacturers, then at some stage it may be included. However, the complexities currently involved in the RHI consultation over issues such as bi-valency, and issues surrounding what this technology is finally defined as may still exclude it.

snigger... the same numpties who killed the solar thermal industry immediately the tory government got into power by pulling the plug on the previous grant scheme then taking 3 years to fail to implement RHI? That's not my definition of hard work to make ST viable, quite the opposite, but yes maybe they will eventually come up with something that makes it viable again.

​

Anyone who has bothered to actively engage in the consultation process and negotiation surrounding the domestic RHI would find this comment somewhat at odds with reality. Patrick Allcorn of DECC who is lead on the domestic RHI is certainly no numpty, far from it, and has only had responsibility since earlier this year. He is doing everything he can to drive the process to make the RHI a success. This is a hugely complex piece of work covering different technologies. It is confronted by several policy constraints that make this a daunting task. If there is a stumbling block, it will be the Treasury.

He is not the only person working extremely hard. Interested trade bodies have been walking the extra mile in consultations and negotiations to provide evidence based information, and solutions to issues raised. This is especially so for solar thermal for which the impact assessment shows a zero uptake under the initial proposals. I am hopeful of a positive outcome as DECC acknowledge the position outlined in the consultation document is not that desired.

With regard to market size, yes it will be niche and therefore very small. The bottom line is how much it costs to run for the energy produced. We still do not know this. Hot water is the one energy element in properties that cannot be insulated away. When costs are known a fair comparison can be made between technologies. My money is still on traditional ST. There are other technologies around that are developing fast (and cost effectively) such as waste water heat recovery that reduce daily requirements still further. This will also affect equipment choice in the future.

Use in conjunction with other technologies means it would need to to be compatible with a multi-coil thermal store or hot water storage vessel, not just a dedicated tank. If it is not compatible, you are possibly in to a two tank design, with all the space implications that entails.

that entirely misses the advantage these systems have over solar thermal in that they do not need a secondary heat source other than an immersion for the very few days of the year when the system can't operate due to extreme low temperatures. So no they don't need a second coil to be combined with another heat source​

Using an immersion as an auxiliary heat source may not be the most cost effective method of providing a secondary heat source. Until we have validated performance data we do not know how much 'very few days' is. It may be much more than anticipated. The question of how the system is controlled to satisfy part G of the Building Regs also need to be addressed.

One of the mistakes often made when assessing the suitability of a property for for renewables is a failure to take a holistic approach to total energy requirements due to the compartmentalisation of skills and registrations for differing technologies. There is also an inherent assumption that the equipment performs in a cost effective manner which we still do not know. One of the question sets within the RHI consultation is to do with bivalency. There is recognition that in some circumstances two or more technologies working in conjunction with each other are more effective than they are on their own. This could well be the case here. How technologies interact is important to getting the best from each.
​

 

[Gavin A]

I am lost for words so I shall gracefully bow out of this discussion and look forward to reading it instead. I will also carry on installing these things without worrying too much about the if's, but's and why's of a simple fridge that simply works..

Steve

oh don't be like that ffs.

I don't understand why it is even slightly controversial to say that the actual energy input into this system that gives a COP of over 1:1 is from the panel absorbing energy from the air and solar radiation.

yes the compressor then raises the temperature to something more useful, but the actual energy input itself comes from the panel absorbing heat from the air and solar radiation.

This should be a simple statement of fact, not the basis of a 2 page argument at the end of which a time served air conditioning engineer flounces from the thread.

 

[Gavin A]

The pump on a solar thermal system will not operate before there is sufficient temperature differential to ensure that more energy is being transferred into the hot water cylinder than the pump is consuming giving a permanent net gain. How you account this will depend on the calculation used for the performance of the ST system. It should be showing the net energy provided.​

that's not zero cost though is it.

Anyone who has bothered to actively engage in the consultation process and negotiation surrounding the domestic RHI would find this comment somewhat at odds with reality. Patrick Allcorn of DECC who is lead on the domestic RHI is certainly no numpty, far from it, and has only had responsibility since earlier this year. He is doing everything he can to drive the process to make the RHI a success. This is a hugely complex piece of work covering different technologies. It is confronted by several policy constraints that make this a daunting task. If there is a stumbling block, it will be the Treasury.

He is not the only person working extremely hard. Interested trade bodies have been walking the extra mile in consultations and negotiations to provide evidence based information, and solutions to issues raised. This is especially so for solar thermal for which the impact assessment shows a zero uptake under the initial proposals. I am hopeful of a positive outcome as DECC acknowledge the position outlined in the consultation document is not that desired.

I attempted to engage, but got no response at all to my email asking them to clarify exactly how they were planning to calculate the 7 year RHI payments, and asking for a worked example (actually I supplied them with 2 alternative worked examples for the 2 possible ways of interpreting it to make it easy for them), but yes I have completed the 75 consultation questions last night.

And anyone who's read the consultation document that took them 2.5 years to produce could only conclude that it was written by people who don't really know what they're doing, especially as it followed on from 2 years of the industry being told / hinted at that everything was going to have to be metered, then presumably as a result of the trials of the meters they seem to have changed their minds. What did they discover in the trials that wasn't obvious before them to anyone who knows anything about heat metering?

If they aren't clueless then they've spent a good 3 years doing a very good impression of an organisation that is, when they should have been rolling out a workable scheme instead.

I particularly liked the bit in the consultation where they blamed the economic climate for the reduction in domestic renewable heat installations since 2010, nicely ignoring the fact that the recession started in 2008, and the downturn in the renewable heat market only happened 2 years later when DECC pulled the LCBP funding a year early, then spent the next 2 years repeatedly delaying the launch of the RHI scheme, during which time they attempted to partially rectify their previous mistake by launching a temporary grant scheme to replace the one they'd killed 18 months earlier. But of course, it's the recession that was to blame not DECC.

 

[The Solar King]

There were a number of mistakes made in DECC in the past. Yes there are things written that niggle. Those who got right up their own backsides over heat metering have now 'left' DECC. It used to be that you did not need to be the sharpest knife in the drawer to work in DECC. The clever people went to DEFRA when the two departments were set up. Fortunately there have been some changes with the reduction in staff numbers.

The greatest shame is that Patrick Allcorn did not get the lead on this on day one. We then might have had a more workable and attractive non-domestic RHI. Yes, I do rate the guy, but do not envy him his task. If the RHI is not everything everyone wants, it will not be for lack of effort from those involved, but more the intervention of the treasury or political masters.

Sorry you did not get the information you sought. Sometimes it is finding the right person to give the answer. It is a pity you were unable to attend one of the road shows that DECC put on around the country. Patrick Allcorn would have been quite willing to provide the information you were looking for. He has been very accommodating in his approach. He genuinely wants as many as possible to respond to the consultation.

With luck, there may be a degree of separation between the RHI and the Green Deal. I get the feeling parts of DECC view GD as having a few shortcomings.

If it was how the 20 year payment was compressed in to seven, the calculation is based on a net present value discounted cash flow giving a 6 to 8% return. My own trade body worked this through to look at various scenarios and the optimum we can propose for ST based on the constraints facing DECC. (namely the cap imposed by off-shore wind). The original consultants report to DECC for the RHI suggested ST needed a tariff of around 95p/kWh! This is clearly bonkers and included a high level of so called barrier costs that may exist for other technologies but not ST. However 17.3p is way too low. If we could achieve a level equivalent to an up to 4kWp FIT over 7 years, ST will be viable.

There was an interesting meeting on deeming last week where a new appendix to SAP was presented which may be know as GDsap. Like RdSAP, it's a "front end" that goes onto SAP and modifies some of the inputs. In the case of GdSAP it takes real occupancy into account, and therefore should benefit Solar Thermal.

Hot water use is calculated based on what the occupants tell you about their hot water use, or if they can't tell you how many showers a day they have you calculate it based on the actual number of occupants (a bit like the new MCS).

Maybe we will finally get a hot water usage calc everyone agrees on and is used uniformly across technologies. Currently, how much hot water a household uses and at what temperature depends on which technology and MCS document is being used!

If you want a copy, please pm me.

 

[Gavin A]

There were a number of mistakes made in DECC in the past. Yes there are things written that niggle. Those who got right up their own backsides over heat metering have now 'left' DECC. It used to be that you did not need to be the sharpest knife in the drawer to work in DECC. The clever people went to DEFRA when the two departments were set up. Fortunately there have been some changes with the reduction in staff numbers.

I hope they rot on the dole, like those they've forced onto the dole with their ignorant policies and years of procrastination. If the idiots truly have gone then that at least is something to be thankful for I suppose.

If it was how the 20 year payment was compressed in to seven, the calculation is based on a net present value discounted cash flow giving a 6 to 8% return. My own trade body worked this through to look at various scenarios and the optimum we can propose for ST based on the constraints facing DECC. (namely the cap imposed by off-shore wind). The original consultants report to DECC for the RHI suggested ST needed a tariff of around 95p/kWh! This is clearly bonkers and included a high level of so called barrier costs that may exist for other technologies but not ST. However 17.3p is way too low. If we could achieve a level equivalent to an up to 4kWp FIT over 7 years, ST will be viable.

I still have zero idea what this means in practice. Why DECC can't actually give worked examples is beyond me - if you do know for sure what they're actually proposing, I'd appreciate it if you'd tell me which of the following worked examples is correct.

so a standardish 5m2 of solar thermal panels generating 868kWh* a year get's 17.3p x 868kWh = £150 a year for 7 years = £1050

or does it get 20 years worth of heat output at 868kWh a year x 17.3p per kWh = £3003.28 total split over 7 years = £429 per year for 7 years

There was an interesting meeting on deeming last week where a new appendix to SAP was presented which may be know as GDsap. Like RdSAP, it's a "front end" that goes onto SAP and modifies some of the inputs. In the case of GdSAP it takes real occupancy into account, and therefore should benefit Solar Thermal.

Hot water use is calculated based on what the occupants tell you about their hot water use, or if they can't tell you how many showers a day they have you calculate it based on the actual number of occupants (a bit like the new MCS).

Maybe we will finally get a hot water usage calc everyone agrees on and is used uniformly across technologies. Currently, how much hot water a household uses and at what temperature depends on which technology and MCS document is being used!

If you want a copy, please pm me.

This about sums up the sort of idiocy and incompetence I'm referring to. How hard is it really to come up with an agreed common standard for how much hot water a house should be expected to use. This is not rocket science, it's basic stuff that should have been agreed years ago. I do include BRE in my bunch of incompetent numpties assessment btw for coming up with sap assessments based on floor area instead of anything actually related to likely water use such as number of bedrooms, bathrooms, occupancy levels etc. SAP has obviously never been fit for purpose for solar PV or solar water heating purposes (amongst other things), yet instead of starting from scratch and coming up with something sensible all we get are slightly rehashed versions of the same outdated / wrong methodology.

If they are now finally going to sort that out then that at least can be one item I'll remove from my list of complaints, but for every day they dither more good people end up on the dole as a direct cause and effect to their dithering.

ps We've now lost more than half our staff as a direct result of DECC's FIT cuts policies combined with the RHI depts decision to postpone the launch of domestic RHI from this september, which we were expecting to cushion the impact of the August and October FIT cuts when they actually did the FIT consultation. So yes I'm extremely angry at the incompetence / negligence I've witnessed from all sides of DECC over the last 3 years - if I actually went to a meeting with them I doubt I'd be able to restrain myself from kicking the **** out of them tbh, which is partly why I haven't been to any meetings with them. I did go to one meeting with them prior to the first round of FIT cuts, and the arrogant, ignorant posh git from DECC at that nearly made me implode with fury. I'm generally not a violent man, but I'd make an exception for him.

 

[Gavin A]

sorry for the rant, but the impact of their policies is really coming to a head right now, and I suspect that's a fairly industry wide thing.

On a more positive note, from what you're saying it does sound like they actually might have someone in charge now who might be able to get this thing launched, so do you see the timetable within the RHI consultation as actually being something that's likely to happen - ie a spring launch for the legislation and RHI levels, and late summer / autumn launch for the scheme proper?

I'm glad it sounds like there have been some people / organisations working away in the background to try to sort this mess out and get something workable out of it, hopefully that will bear some fruits when the final scheme is announced.

 

[jason121]

oh don't be like that ffs.



yes the compressor then raises the temperature to something more useful, but the actual energy input itself comes from the panel absorbing heat from the air and solar radiation.

QUOTE]

And what happens to the heat at night time when no sun in the sky and its -5 outside ?????

 

[Gavin A]

And what happens to the heat at night time when no sun in the sky and its -5 outside ?????

that'd be it absorbing heat from the air without the solar radiation component, hence the difference in the daytime and night time energy output on the graph I posted.

At night it's just like an ASHP except it relies on natural air circulation over a large surface area instead of large volumes of air being forced by a fan over a smaller surface area.

I was thinking I might have somehow misinterpreted your postings, but I see I haven't.

 

[jason121]

and how does the system manage to keep the temp at 55 at night were is the heat coming from

 

[Gavin A]

and how does the system manage to keep the temp at 55 at night were is the heat coming from

As I said earlier, I think we're talking at cross purposes because of confusion over the difference between heat and temperature. The compressor creates the higher temperatures, but it doesn't create the heat energy itself* (as energy can't be created or destroyed, just changed from one form to another), this heat energy input originates from the panels, or more properly, from the absorption of energy from the air blowing over the panels and when available from radiated solar energy.

Understanding this matters because someone with some time on their hands (and probably a bit more data than I've found so far) could then use this to calculate the actual additional heat that can be expected to be produced over and above the electrical input from such a system given different levels of air temperature, wind speed and sunlight levels. As I keep saying, the heat exiting the compressor is directly proportional to the heat input to the panel, as is clearly shown on the graphs I posted.


*although the compressor does also directly converter electrical energy into heat, which is why I've repeatedly referred to the additional heat energy on top of the electrical input.

 

[jason121]

but were does the 55 degrees come from to heat the water on a cold night

 

[Gavin A]

ok, I'm getting a bit bored of this now. If you're not on a wind up then I suggest you go and learn how the ASHP technology you install works, as this works on the same principle just with the panel replacing the fan unit.

If you're asking how it heats the water to 55 when the air temperature is below its lowest operating temperatures then I'd expect it would use the inbuilt 1.2kW immersion, though I've not installed a unit and am not 100% sure of the control settings etc.

 

[jason121]

thermodynamic panels works on vapour compression cycle to create heat = heap pump.

 

[jason121]

This is why MCS have suspended them and classed them as a heat pump, heat pumps under the RHI must be able to provide space heating and hot water.
They can be used if filled with water/glycol mix and be registered under MCS (no idea how they work like that)

not disputing on the low COP but they are a heat pump just like Ground and air

 

[Gavin A]

thermodynamic panels works on vapour compression cycle to create heat = heap pump.

they create heat do they?

best write a rebuttal paper to Einstein et al then as he and the whole of physics since have obviously got things wrong.

but yes they work on the vapour compression cycle and as such are heatpumps (and AFAIK nobody on this thread has disputed that), and as shown on this diagram, they absorb heat from the atmosphere in the liquid>vapour phase, which is then raised to a more useful temperature via the compressor.

 

[Gavin A]

This is why MCS have suspended them and classed them as a heat pump, heat pumps under the RHI must be able to provide space heating and hot water.

that though is a problem with RHI / MCS classifications, not the technology itself.

 

[jason121]

you have just repeated what Steve K said a while back.

 

[jason121]

it can draw heat both from the air and from solar radiation falling on the panel, an ASHP can only draw heat from the air,


You words not mine
This is partly true but again heat is from compressor not from panel like ST

 

[Gavin A]

it can draw heat both from the air and from solar radiation falling on the panel, an ASHP can only draw heat from the air,


You words not mine
This is partly true but again heat is from compressor not from panel like ST

which bit of that statement is false?

where does the heat come from intially? where does the heat come from to evaporate the liquid back to a gas again? It comes from the absorption of heat from the air and sun within the panel.

this is like pulling teeth.

 

[jason121]

yes but only requires a few degrees to boil the gas thats why thay can work at night and dont need a sunny day to reach 55

 

[Gavin A]

yes but only requires a few degrees to boil the gas thats why thay can work at night and dont need a sunny day to reach 55

so the statement is true then?

in which case why have you just spent several hours arguing against it?

Also, degrees are units of temperature not energy, and the boiling of that gas itself will absorb significant quantities of energy in the form of the latent heat of evaporation, which is then released on the condenser on the form of latent heat of condensation, so a few degrees of temperature change around the boiling point of the gas will require the absorption of much greater quantities of heat energy than warming the gas by a few more degrees.

To reiterate it, all the additional energy that comes out of the warm side of the heat pump (on top of the electrical energy) has first been absorbed from the air and sunlight (if available) in the panel, as shown in this diagram.

The compressor takes affect between points 1 and 2, raising the pressure and therefore the temperature of the system, but having no impact on the overall heat energy / entropy of the system. All the increase in heat energy / entropy within the system occurs between points 4>5>1, which in the energie system is in the panel.

eta - Either I or Wiki has got a bit mixed up about whether it's entropy or enthalpy along the bottom of this diagram.

This is also why this graph is as it is - it clearly shows the direct relationship between air temperature and the heat energy output from the other side of the heat pump. And in relation to your query, at -5 at night it will take roughly twice as long to raise the temperature of a full tank of water to 55deg as it will at 35deg outside air temperature in sunlight because the energy output from the system 3.5kW instead of 7.2kW.

There is something odd going on with the day time levels on that graph, as there is potentially 6.4kW solar radiation input to the 4 panels on that system at 1000W/m2, but yet the increased heat output vs no sun ranges from around 2kW at low ambient air temps to 1kW at high ambient air temperatures, so there's obviously something else going on within that system that limits the transfer of solar energy through the system as this is that is the opposite to what would be expected with a normal solar water heating panel. This was the sort of thing I was hoping I might have spent the last few hours discussing rather than the basics of how a heat pump works.

 

[Vegelen]

Energy transfer normally occurs from a hot source (B) to a colder source (A).

A heat pump does the opposite, transfering energy from a cold source (A) to a hotter source (B).

This can only happen once work is imparted on the system to help move energy from A to B.

If no work is done on the system, energy wouldn't flow from A to B, but from B to A until the temperatures between the 2 systems equalised.

A cold refrigerant liquid with a temperature substantially lower than the ambient air temperature outside the panel, enters the solar thermodynamic panel.

This cold refrigerant liquid extracts energy from the warmer ambient air surrounding the panel, causing it to change state.

This gas then enters a compressor (which does work on it) pressurising it, increasing its temperature.

The hot, pressurised gas then passes though a coil in a water filled tank.

The water inside the tank is colder than the gas in the coil, thus energy flows from the hot pressurised gas to the cold water.

Over time this incremental energy transfer from hot to cold, raises the tanks water's temperature.

This pressurised gas gets passed through an expansion valve, which reduces its temperature and pressure further, reverting the refrigerant back to its liquid state.

This liquid then gets passed into the solar thermodynamic panel and the cycle recommences.

An energy transfer is taking place from a cold source (ambient air) to a hotter source (water in the tank) by virtue of work being done on the system.

If the ambient air temperature drops to -5C, energy will still be transfered from the ambient air to the refrigerant liquid (at a far slower rate) because the ambient air is at a higher temperature than the refrigerant liquid it surrounds (-15C).

We think of air at -5C as having "little or no energy" but it has lots of energy relative to absolute zero.

Jason121 uses the word "heat", when he should be using the words energy / energy transfer.

 

[Marvo]

All the evaporator plate/panal is for is to allow the refrigerant to boil and change state from a liquid to a gas, so that the vapour compression cycle can start again.

The gas does not care weather it is 10 deg C, 50 deg C or -10 deg C as long as it can change state in there.

The compressor cares what temperature the returning gas is, all compressors are designed to work within certain superheat ranges. Most commercial compressors rely on there being a small amount of saturated vapour returning back on the suction line for sub-cooling. If a solar panel in direct sun is being used as an evaporator how is it possible to control the system superheat and ensure the lifespan of the compressor?

 

[Gavin A]

There is something odd going on with the day time levels on that graph, as there is potentially 6.4kW solar radiation input to the 4 panels on that system at 1000W/m2, but yet the increased heat output vs no sun ranges from around 2kW at low ambient air temps to 1kW at high ambient air temperatures, so there's obviously something else going on within that system that limits the transfer of solar energy through the system as this is that is the opposite to what would be expected with a normal solar water heating panel.

I think I've now answered my own question.



I'll try to explain...

A is the maximum energy increase from air at -5 deg, assuming all liquid is vapourised. Note, no increase in temperature or pressure of the vapour
B is a rough estimate of the maximum energy increase from and air temperature of 30, and solar input. Note significant increase in both temperature and pressure.
C is the amount of additional pressure required from the compressor to raise the vapour to 55deg from point A
D is the amount of additional pressure required from the compressor to raise the vapour to 55deg from point B
E is the end of the condenser and point where the high pressure fluid passes through the expansion valve

The line at the top between D>C is effectively the additional heat energy output from the heat pump resulting from the additional energy input from the higher air temps and solar.

Now compare that diagram with this one

The top diagram explains (to me at least) why the additional solar input can only result in a relatively minor increase in actual energy output vs the available solar energy to the panels, and why the additional input from the solar decreases as the input from the air increases.

What it also shows though is that there is a significant additional benefit from the solar input though in terms of doing the majority of the work of the compressor by actively pressurising the vapour and raising it's temperature before it enters the comnpressor, resulting in the compressor needing much less energy input.

This explains the high top end COP figure claims for the Energie systems theoretically, which matches with their energy performance figures

Absorbed Power 0,9 - 1,8 kW ; Thermal Power 3,6 - 7,3 kW

The low end absorbed power figure of 0.9kW will be at the highest energy output figure of 7.3kW because much of the compressors work is being done by the additional energy input in the form of solar energy heating the vapour in a closed system and pressurising it.

7.3 / 0.9 = a max COP of 8.1, which actually does look plausible from the diagram above.



* I fully acknowledge that the diagram is very rough and ready, and I don't know what the exact figures are for the working pressures, what temperature the solar input will raise the panel to etc but I hope it works as an illustration of the principle on which these panels operate.

 

[Gavin A]

Actually thinking about it, this is probably a more accurate diagram, as the pressure would be pretty much equal across the low pressure side of the system so in full sunlight and high ambient air temps, rather than the pressure dropping all the way down then being raised up by the extra energy input it would simply not fall as far as it wouldn't need to fall that far in order to extract the heat from the air and solar input. It will effectively sit at a dynamic equilibrium point instead - point F on this diagram.



The energie system's main benefits over an ASHP then is that in full sunlight the system will be able to reach a dynamic equilibrium temperature that is almost at the ambient outside air temperature. This means the operating pressure on the low pressure side of the system is significantly raised, and the energy input required in the compressor can be as much as halved.

On top of this the actual energy output from the system can be increase by up to 12% at the top end in summer, and around 35% in the depths of winter.

These benefits would obviously be diminished for space heating purposes if they're largely not being used during the day, but they should be very real benefits for water heating systems as long as they're set to largely heat the water during daytime hours when they'll benefit the most from the solar input.

 

[Gavin A]

Those diagrams are a bit complex and took me a while to sus out, but for those not wanting to spend that time working it out, essentially the theoretical data seems to match well with the performance data supplied by Energie, so I see no reason to doubt the energie data I've given isn't accurate.

One note of caution though would be that the output relative to the air temperature alone will be far more dependent upon wind speeds than for standard fan driven ASHPs, as if the air isn't moving rapidly across the panel then it will become cooled by the panel, so the air surrounding the panel will be at a lower temperature than the actual ambient air temperature.

This is going to be one of the factors that makes it impossible for energie units to be tested under standard ASHP test procedures, as they need to be tested at different different combinations of air temps, wind speeds and solar input levels. This ought to be possible to do, but it could well be that the standard ASHP test labs aren't kitted out to do it - they'd probably need to use solar PV test labs to carry out the tests as they do have to simulate all those factors when testing solar PV panels under STC.

 

[The Solar King]

Gavin
re RHI.
The calculation of 17.3p/kWh over 7 years is equal to I think 8.3p over 20 years. The 8.3p relates to the subsidy level paid for offshore wind over 20 years which is the most expensive subsidy in ROCS. This gets referred to as the 'value for money' cap.

Clearly 17.3p times whatever figure of output you choose (I know my 4.4sqM system actually produces 1200kWh/a) does not provide a realistic incentive. Even if you factor in the savings relating to the efficiency of the back-up fuel used, (as the new MCS ST standard will), you still only get to a notional output with a gas boiler of 1600kWh/a.

One of the areas examined has been the additional energy savings generated by changing the hot water cylinder. Moving to a part L compliant cylinder adds a large additional saving due to the reduction in standing loss which is currently not accounted for when calculating the total benefits of ST. A tank scrappage scheme giving an upfront grant of £600.00 in addition to to 17.3p would give the equivalent of around 27p. This would have the benefit of an upfront payment in addition to the 17.3p. This is among our proposals.

The other side of this is deeming. How much energy does a system produce? It is OK having a decent tariff, but useless if it is deemed at too low a level. The methodology of MCS 3001 draft may form a basis coupled to an agreed daily hot water requirement, possibly GDSap.

With regard to not losing ones rag with DECC, after the FITs debacle this time last year, as a trade body, the STA decided to actively enter a constructive dialogue with them. Through our then chair, we had been at the forefront of challenging the decisions taken over FITs in the courts. However continuing a combative approach was not going to gain anything. It also meant DECC had not listened to sound advice in the past which could have avoided the worst of what happened over FITs. It is just as well we did. FITs was set to be capped on the same 'value for money' basis as already mentioned. Due to the tireless efforts of Ray Noble who I think had a camp bed in DECC, we ended up with the scheme now in place which is as good as could be hoped for. There have been extensive ongoing discussions over large scale PV. I am not close to this, but would surmise from recent press releases the lack of announcement on ROCs and those schemes at a lesser level is political and due to intense lobbying by the enemies of renewables. The subsidy level required for large scale PV is less than 2 ROCS and cheaper than onshore wind. The cost effectiveness of large scale PV, and associated developments starts to undermine the case and subsidies (sorry tax incentives) for unconventional gas.

What this dialogue does mean is there is a route through our expert working groups to engage on all policy and technical fronts with DECC, Gemserve, BRE, Government ministers, Politicians and whoever else we need to address. Everyone has the same frustrations, and many share your views on DECC's past performance. There is also now a much better understanding of the constraints under which DECC operates which allows work within the framework of the possible.

That we have this dialogue has been hugely helpful with regard to the domestic RHI. We are after all the experts in the field (as are those in trade bodies representing other technologies).

The expertise so readily shown in this forum by several contributors would be more than welcome within the STA and could then feed directly in to the work on both policy and technical standards.

If anyone wants to know more, please PM me or talk to our CEO Paul Barwell. Contact details are on the STA website.

 

[Gavin A]

I was a member of BPVA. I quit following their failure to notify their membership about the G83/2 changes or do anything to assist me in raising this point with Ofgem despite me asking them to do so a month before the deadline. In the end, I and others from on this and other forums formed virtually all, if not all of the objections to the policy relating to close geographic area defintion and the requirements for stage 2 applications (no STA involvement either as far as I could see), and only as a result of our intervention we've actually got that policy changed to something that is eminently more workable.

SO I'm not against productive involvement in the decision making process, and if STA are open to actually taking advice from and taking up initiatives proposed by their membership, and are actively engaging in the decision making processes, then I would consider joining, as long as I don't get sat next to that stuck up ----- from DECC at a meeting.

 

[The Solar King]

Gavin

You don't even have to sit next to me!!

 

[The Solar King]

For info, STA response on Thermodynamics in RHI
Q 10
Do you agree with the proposed eligible technologies set out above? Are there others that should be considered for inclusion?

So-called “thermodynamic solar panels” which use a refrigerant in the solar panel should be considered for inclusion, subject to reinstatement to the MCS scheme. However, these technologies should be supported by the RHI as an air-source heat pump, since the product is essentially an air-source heat pump with the evaporator being the panel rather than a fan-blower unit.

 

[Gavin A]

I said something similar, though I think I suggested they needed their own category due to the extra test data required for COP with solar input, wind speed etc. plus the F-gas cert and the need to actually have working at heights, roofing experience etc.

 

[peteheat]

but were does the 55 degrees come from to heat the water on a cold night

The immersion heater that can't be switched off by either the home owner or the installer in fact if the immersion breaks the system stops working altogether.

I don't know where the figure of -15 came from, it automatically switches off the heat pump at 1 > 2c and reverts to the immersion.

The big problem is they are not being sold with any degree of honesty and in the UK at grossly inflated prices.

The story about switching on at 8c can not apply to the energias system because they call for the system to be pre-heated using the immersion to a minimum of 30c when commissioning the system.

One thing the MCS action has shown that is very worrying is the panel passed the Solar Keymark test with water as the transfer medium, basically fit a standard radiator painted black and it will achieve the Solar Keymark.

 

[peteheat]

they create heat do they?

best write a rebuttal paper to Einstein et al then as he and the whole of physics since have obviously got things wrong.

but yes they work on the vapour compression cycle and as such are heatpumps (and AFAIK nobody on this thread has disputed that), and as shown on this diagram, they absorb heat from the atmosphere in the liquid>vapour phase, which is then raised to a more useful temperature via the compressor.

Do you mean Thermodynamic Laws formulated by the French physicist Carnot theories?

 

[jason121]

[h=3]How it Works[/h]

The sun isn’t always out. In winter the days have an average of 7 hours of light with only 3 to 4 hours of sun which constitutes a constraint on the operation of traditional solar panels. ENERGIE Thermodynamic Solar Panels have managed to overcome this constraint, making it possible to raise the temperature of the water with great efficiency and major energy savings on rainy days and even at night. One of the innovative aspects lies in the fact that an ecological fluid passes through the solar panel at a temperature of -20ºC, thereby allowing the collection of solar energy and greater absorption of atmospheric energy, in other words from the sun, rain and wind, 24 hours a day, 365 days a year. The ecological liquid which circulates on a closed circuit at negative temperatures collects the heat at the solar panels and then releases it into the water by way of a heat exchanger. This facility, whereby we combine technology with a law of Nature, demonstrates the potential of ENERGIE solar systems and that they really work. This were my info came from, if its true, in what your saying, they are a waste of money.

 

[Gavin A]

Do you mean Thermodynamic Laws formulated by the French physicist Carnot theories?

These laws?

More specifically, the First Law encompasses several principles:

• The law of conservation of energy.

This states that energy can be neither created nor destroyed.

You can raise the temperature of a gas in a fixed volume via a compressor, but you can't actually create energy itself, that has to come from somewhere in the first place, namely the panel extracting heat energy from the air and sun.

 

[jason121]

what would be the temp from the expansion valve and suction line

 

[peteheat]

what would be the temp from the expansion valve and suction line

They did manage to con their way onto the Irish grant scheme for renewables, at the time the grant for heat pumps was much higher than that for solar.

So we investigated why not call it what it was and qualify for the higher grant?

The consultants we hired came back with a report that basically said the COP was too low to qualify which meant the data supplied to us by the manufacturer was not "Complete" or inaccurate.

The system will work by absorbing any heat around the panel (top and back) which is why some claim the panel is actually twice it's size.

Too much smoke and mirrors being used for our liking so we took the consultants advice and left them, we do however advertise them simply because they are great for bringing visitors to our web site, we also price them for all to see at less than €5,000.00 including VAT supplied and fitted using a stainless steel cylinder (not mild steel) and with a coil for a second heat source.

If we were to sell them at that price we would be making a respectable profit not just a days pay.

 

[SibertSolar]

Always interesting to see such thorough discussions on new technologies, very interesting thread. Just spotted that Ecoskies are offering training courses on thermodynamic "solar" panels.....have they provided any input here as yet? According to their article in the current REI magazine, although "installers will need an F-Gas engineer to commission the system, the vast majority of work, once understood, can be carried out by any solar thermal installer already qualified to a standard recognised by MCS"

 

[Vegelen]

It automatically switches off the heat pump at 1 > 2c and reverts to the immersion.

Thus, Thermodynamic Solar Panels are currently very expensive, take an unrealistic

time to economically pay back and during periods of extreme cold weather,

UK householders will be saddelled with increased electric bills to heat their water.

 

[The Solar King]

We are still going round in circles on this. The theory of their working has been ably shown and discussed in this thread. We are still back to speculation as to their likely performance with contributors in one camp or the other. Things are still coming up that are already covered in the letters from MCS. The controls of the system is one of them.

This is getting to be like QI, where the answer to the question is 'nobody knows'. I feel like Alan Davis with a score of minus 46!

 

[Gavin A]

Thus, Thermodynamic Solar Panels are currently very expensive, take an unrealistic

time to economically pay back and during periods of extreme cold weather,

UK householders will be saddelled with increased electric bills to heat their water.

This is probably true for anyone on mains gas. It's definitely not true for anyone who's on full electric heating with no gas option, which is several hundred thousand households in the country. It's not a one size fits all solution, but then practically nothing is - it should however have a valid place in the market and could save a significant minority of people a significant amount of money.

 

[Gavin A]

The consultants we hired came back with a report that basically said the COP was too low to qualify which meant the data supplied to us by the manufacturer was not "Complete" or inaccurate.

did the consultants actually take measurements themselves for this report, or attempt to calculate the COP?

 

[Gavin A]

We are still going round in circles on this. The theory of their working has been ably shown and discussed in this thread. We are still back to speculation as to their likely performance with contributors in one camp or the other. Things are still coming up that are already covered in the letters from MCS. The controls of the system is one of them.

This is getting to be like QI, where the answer to the question is 'nobody knows'. I feel like Alan Davis with a score of minus 46!

indeed. I'm wondering if our finances will stretch to buying a unit we can set up to test through this winter.

 

[Vegelen]

Excerpts From A Consumer Focus Report: Off Gas Consumers

- "21 million homes in Britain are heated by mains gas (83 per cent of all homes): 84 per cent in England, 76 per cent in Scotland and 79 per cent in Wales."

- "2.3 million homes in Britain are heated by electricity (9.3 per cent), 1.1 million (4.4 per cent) by heating oil, 310,000 (1.2 per cent) by solid fuel and 170,000 (0.7 per cent) by LPG. In total, 3.9 million homes in Britain rely on other heating fuels to mains gas to heat their homes."

- "Electricity is the second most common heating fuel after gas in England and Scotland, whereas heating oil is the second most common in Wales. However, the largest number of heating oil consumers (828,000) live in England, reflecting its larger population."