thermodymic panel for water heating

zeupater

1echidna wrote: »

Remember the water starts out at 10C approx perhaps which is where modern control systems could come into play for this part of the heating cycle.

Coming back to your 18kWh in 5h that does seem out of kilter and I'm wondering if there can be some misinterpretation here.

Hi

All of the logic and source references are in the previous posts.

If there's any misinterpretation it's between the manufacturer and their marketing department.

HTH
Z

Martyn1981

Still reading with interest guys. More questions (sorry).

I appreciate that the COP being quoted / suggested is pretty high. But at what point does this technology have a place?

Am I right in thinking that leccy is roughly 3 times the price of gas, but with gas heating inefficiencies a comparison of 2:1 is fairer?

So would a COP of 2 (or more) make this technology comparable (ignoring initial costs)?

It appears to me that the cost of a single panel system will chiefly be determined by the non-panel costs, so such a system gets proportionately cheaper as more panels are added, just like PV.

Last question, if wall mounted, wouldn't these panels operate in a similar fashion to radiators (in reverse) cooling the wall behind, which transfers (shares) that energy differential outwards with the rest of the wall. I'm not trying to argue the suggested COP, just trying to consider some possible variables. It also occurs to me, that in this application you would definitely want a cavity (and insulated) for winter use.

Last question (again), what about rain, whilst air temp may be lower than during a sunny spell, would the water actually help to warm the panels up as the denser liquid 'removes' more cold (unless it freezes)?

Apologies for piggy-backing this thread, just trying to learn more.

Mart.

grahamc2003

zeupater wrote: »

Hi

All of the logic and source references are in the previous posts.

If there's any misinterpretation it's between the manufacturer and their marketing department.

HTH
Z

Hi Z, I looked at the reference material which surprisingly seems to come from the manufacturers. I looked quickly at the typical figures they claim for a single panel domestic system and yes, just about every single figure on there is absolute nonsense (and self contradictory), and a very quick bit of deduction implies those unbeleivable average high cops you previously mentioned.

Talking to the 'salesman' (who was about as knowledgeable as you could expect) who quoted for my system, (the same lot who installed my PV where I received good service and no BS at any stage), didn't mention any of those figures in that referenced material, and neither in the written quote were any figures like that mentioned. (BTW the 'salesman' was the company MD, I suspect all the proper salesmen have now been downsized along with the downsizing of the PV fit).

These panels qualify for the rhi, and as such have limitations on sales statements. Certainly, if that referenced document is used or quoted from then something is seriously wrong. The question is why should a potentially adequate system (albeit probably beaten by existing solar thermal technology in almost every respect for dhw heating) manufacturer produce such a ridiculous (and potentially illegal?) information brochure?

zeupater

grahamc2003 wrote: »

Hi Z, I looked at the reference material which surprisingly seems to come from the manufacturers. I looked quickly at the typical figures they claim for a single panel domestic system and yes, just about every single figure on there is absolute nonsense (and self contradictory), and a very quick bit of deduction implies those unbeleivable average high cops you previously mentioned.

Talking to the 'salesman' (who was about as knowledgeable as you could expect) who quoted for my system, (the same lot who installed my PV where I received good service and no BS at any stage), didn't mention any of those figures in that referenced material, and neither in the written quote were any figures like that mentioned. (BTW the 'salesman' was the company MD, I suspect all the proper salesmen have now been downsized along with the downsizing of the PV fit).

These panels qualify for the rhi, and as such have limitations on sales statements. Certainly, if that referenced document is used or quoted from then something is seriously wrong. The question is why should a potentially adequate system (albeit probably beaten by existing solar thermal technology in almost every respect for dhw heating) manufacturer produce such a ridiculous (and potentially illegal?) information brochure?

Hi

This exactly reflects my own thoughts ... 'why' ? ....

I can only deduce that the answer is rolled-up somewhere between customer performance expectations and supplier margins ... an expectation of a low COP describes a low return therefore a low price ... simply add to the expectation and the value to the customer increases, thus adding to the available supplier margin. Publishing a COP and publishing expectations are two different issues, both technically and legally - how long has it taken to reach consensus regarding the implied COP & how many potential buyers would actually think about doing this ? .... Seems to be a pretty typical smoke & mirrors marketing approach ....

HTH
Z

1echidna

Hi Martyn

If we are talking about a variable speed compressor it is possible for the compressor to increase mass flow when suction pressure increases or when discharge pressure reduces. The effect will be higher flow of refrigerant and higher COPs for these operating conditions. Of course to achieve these changes in pressure the evaporator and condenser have to be able to cope (either due to more evaporator panels and higher ambient temperature and/or low tank water temperature). The cost benefits of an additional panel are not simple to analyse.

I suspect that most of the heat transfer will be to the air and the bricks behind will have their surface cooled to a limited extent. I'm still very unsure about ice/frost on these panels but read that the problem of ice/frost build up has been dealt with elsewhere in the world. I don't know how.

zeupater

Martyn1981 wrote: »

Still reading with interest guys. More questions (sorry).

I appreciate that the COP being quoted / suggested is pretty high. But at what point does this technology have a place?

Am I right in thinking that leccy is roughly 3 times the price of gas, but with gas heating inefficiencies a comparison of 2:1 is fairer?

So would a COP of 2 (or more) make this technology comparable (ignoring initial costs)?

It appears to me that the cost of a single panel system will chiefly be determined by the non-panel costs, so such a system gets proportionately cheaper as more panels are added, just like PV.

Last question, if wall mounted, wouldn't these panels operate in a similar fashion to radiators (in reverse) cooling the wall behind, which transfers (shares) that energy differential outwards with the rest of the wall. I'm not trying to argue the suggested COP, just trying to consider some possible variables. It also occurs to me, that in this application you would definitely want a cavity (and insulated) for winter use.

Last question (again), what about rain, whilst air temp may be lower than during a sunny spell, would the water actually help to warm the panels up as the denser liquid 'removes' more cold (unless it freezes)?

Apologies for piggy-backing this thread, just trying to learn more.

Mart.

Hi M

Regarding gas, if you currently have gas then there's no additional investment required and even allowing for heating inefficiencies (combustion & distribution) I'd still look at the breakeven COP being 3. E7 would be different, but the main effect would simply be to extend payback period, for example, taking the reference material recently discussed and working on E7 being one-third the cost of daytime electricity, even if a COP of 8.4 was possible the manufacturers's claimed 'Payback total' changes from 4.89 years to ~15years ...

Regarding the costing of larger systems, I agree .... the price/performance chart should not be linear, but doubling the panel area will not provide double the heat exchange duty as the first panel in series will always be the coldest, it's a normal law of diminishing returns .... if you look at the document which we have been discussing you'll note that all savings are stated as 'per cylinder', which makes me think that the range of standard offerings are limited (250l/1000l ?) and that larger or intermediate systems are simply created by installing a cluster of standard systems in parallel, therefore the economies of scale will simply be related to installation efficiencies and margin aspirations ....

Regarding walls, yes, the panels will quickly 'suck' energy out of the walls, effectively reducing the efficiency of 50% of the surface area of the unit to collect radiated heat, that's if you believe that radiated heat absorption is how these panels collect the majority of their energy ...

Regarding rain ... that actually brings another dimension to the discussion. Rainfall will immediately freeze upon contact with the panels and this will have a two-stage effect on the panel performance. Initially, the performance of the panel will improve due to the relative desity of water to air, however as the ice thickens it will act as an insulator (ice being a relatively good insulator), therefore the performance will drop significantly.

Something which I would be even more concerned about is rainfall and moisture on materials behind the panels. Consider a brick wall which is exposed to condensation and rain and then freezing and thawing at a frequency which would probably represent a typical winter in a week ... I'd probably be looking for a small pile of sand below the panels on a regular basis ....

HTH
Z

zeupater

1echidna wrote: »

.... I'm still very unsure about ice/frost on these panels but read that the problem of ice/frost build up has been dealt with elsewhere in the world. I don't know how.

Hi

The solution is pretty simple, you just provide heat to the evaporator circuit and the ice slides off leaving a pile of (slushy) snow on the ground, I've seen it happen ... the problem is that in maritime climates this happens pretty regularly .... this also is part of what is missing from the calculation of the COP, the effect of the defrost cycle.

On a similar note, also missing is the realisation that there's an anti-legionella boosting immersion heater in the HWC too :eek: ... I wonder whether that's been mentioned relating to Air/Water heatpumps and their actual COP on this forum and elsewhere before ....

HTH
Z

Kernel_Sanders

Martyn1981 wrote: »

leccy is roughly 3 times the price of gas, but with gas heating inefficiencies a comparison of 2:1 is fairer?

It might be with an old back boiler, but I'm not sure the ratio would decrease by that magnitude with a modern boiler.
I resist using my CH backboiler not only because some of the heat is going up the chimney, but because I can't stop it heating the bottom of my cylinder. I live on my own and only have short showers, so I only use the water from the top. Even now, on the wrong side of the Equinox, I can still heat the 2.9 kW element using solar PV alone, but come the winter Economy 7 will be cheaper than even the 'hot water only' setting on the CH.

1echidna

Out of interest I made an enquiry to a local firm. Indicative cost was £5000 for the system. I was sent a FAQ sheet which seems to correspond with this http://www.greenerdeal4u.co.uk/energy-solutions/solar-dynamic/dep-faqs.

Some salient points are:

- costs based on 390W input 7hrs per day

- compressor power input 390W to 550W output 1690W to 2900W for hot water at a COP of 4.3 to 5.2 for 7C ambient

-panel size 2m x .8m x .02m

Based on the information I wouldn't like to say it can't perform as promised.

zeupater

1echidna wrote: »

Out of interest I made an enquiry to a local firm. Indicative cost was £5000 for the system. I was sent a FAQ sheet which seems to correspond with this http://www.greenerdeal4u.co.uk/energy-solutions/solar-dynamic/dep-faqs.

Some salient points are:

- costs based on 390W input 7hrs per day

- compressor power input 390W to 550W output 1690W to 2900W for hot water at a COP of 4.3 to 5.2 for 7C ambient

-panel size 2m x .8m x .02m

Based on the information I wouldn't like to say it can't perform as promised.

Hi

I'd want to see a a set of performance curves detailing COP vs cylinder water temperature at varying levels of irradiation, something similar to what's available for pv panels before I would believe COPs at those levels for water heating ....

Air source heatpumps which are dedicated to heating water from a range of global Japanese household-name manufacturers, known collectively as 'Ecocute' systems, seem to claim an average COP for heating water to 55C of 1.8 at -15C ambient, 3.1 at 7C ambient & 3.75 at 20C ambient and even products supplied by these global leaders often struggle to perform at anywhere near these published figures under long-term test conditions ...

A heat pump is a heat pump and it's very likely that compressors used in the plate units under discussion are made by the same manufacturer as ones used in the Japanese units raised above, the mechanism for transferring heat from the refrigerant to the water will be exactly the same and the cylinders will be insulated to the same standards .... that leaves the only difference being the passive plate exchanger vs a blown heat exchanger so we're left with a the detrimental effect of running a fan vs potential irradiation gain if the panels are in sunlight when there is a heating requirement ....

Given the high temperature of the cylinder and the figures above, I'd expect the compressor to be working as hard as it could to provide heat into the already warm cylinder because the refrigerant return temperature to the evaporator would be high, so how does a COP at 7C ambient of 1690/550 from the abovequoted figures look .... it seems to be 3.1 ... what a surprise, it seems to be exactly the same as Japanese 'Ecocute' systems ....

HTH
Z