Thermo dynamics for hot water that runs off atmosphere

[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