Discuss Thermo dynamics for hot water that runs off atmosphere in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net
the compressor doesn't create heat*, it merely concentrates it from a lower grade to a higher grade of heat. The original heat energy input that allows for the high COP's comes from the panels extracting heat / energy from the air and solar radiation.The thermo dynamic panels only require small amounts of heat to operate, the heat comes from the compressor to warm the water, not the panel.
basic laws of thermodynamics say you're wrong.not if your using gas it dont
I'm fairly obviously not saying that the compressor doesn't extract the heat energy and boost it up to the required temperature, but you seem to be denying that the heat energy actually has to originate in the panel, which is obviously wrong.The panels wont reach 55 degrees if the outside temp at night is -5. Thats why ASHP can work down to -20,
Absorbed Power 0,9 - 1,8 kW ; Thermal Power 3,6 - 7,3 kW
it's not a matter of degrees as such, it's a matter of total energy input into the system. and yes you could put the panel in a lake if you had one, but this is an alternative for those of us who don't have sufficient lakes or ground for a GSHP / WSHP to be an option.Yes but only a few degrees, stick the panel in the ground or lake it would still work, how do you think fridges work or cold stores, freezes.
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.
electrical input 390 - 550Wpower output 1690 - 2900W
anti legionella heater 1200W
the worrying thing to me about this conversation is that both of you install heatpumps, and I don't yet.
assuming you were using the energie system
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.Why? I am an air conditioning engineer and have been installing "heat pumps" for 25 years>
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.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.
fair enough.You have assumed incorrectly, perhaps the ones we installed have a larger compressor and a more efficient heat exchanger.
Steve
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.
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.
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
oh don't be like that ffs.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
that's not zero cost though is it.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.
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.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 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.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 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.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.
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.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.
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 ?????
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.And what happens to the heat at night time when no sun in the sky and its -5 outside ?????
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.and how does the system manage to keep the temp at 55 at night were is the heat coming from
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