Discussion ... ASHP(Air/Air) with Solar pv ....

Coastalwatch

Hi Ken, From the searches I carried out prior to having ours installed the prices appear reasonable to me.

Incidentally, how does the cost of the new clean energy system compare to a tank of heating oil!

JKenH

Coastalwatch wrote: »

Incidentally, how does the cost of the new clean energy system compare to a tank of heating oil!

Last tank fill up was 13/08/18 1800 litres @ £52.80 plus 5% vat -total £997.92
Previous fill up was 30/10/17 so annual usage probably 1900/2000 litres - about £1050/1100 pa.
Our leccy use in the last 2 full years before solar averaged 6900 units pa. Only one (the larger) of our hot water cylinders was heated by the oil boiler, the other is solely electric. I have the option to heat the larger tank by solar PV as there are two immersion heater elements in it but the controller failed a couple of decades ago and I never got round to fixing it. Next job is to try and get the IBoost to heat both tanks (in the summer). That should reduce the oil usage.

The house is a bit bigger than average and we are at home all day so we’re ideal candidates for solar and ASHP but I am not sure full ASHP C/H would be worthwhile. My biggest regret is not getting more solar panels installed on day one but I am thinking of adding some even though I won’t get any more FiT. I think we could absorb 10 kWh/day of PV in our hot water system when it is available and adding the soon to be installed aircon/heater will absorb a bit more in summer, spring and autumn. Our daily base load is about 5 kwh. Looking at the stats from the old Moixa Dashboard our average daily usage in September was 15 kWh of which 10 kWh came from solar. With the Iboost we really do use every kw generated at this time of year but it will be more cost effective to use the heat pump because a) it is much more efficient, b) we can use E7 to heat the hot water and c) we lose some of the energy (to cooling) in the 15 or so hours between the tank being heated and our using the hot water for showers in the morning.

It is really difficult to calculate payback from the heat pump and any additional panels but I think they will complement each other. Every extra kWh solar for the six coldest months of the year can hopefully be turned into 3kwh of heat displacing oil usage. If I spend £2500 on 4 more so on 4 extra panels and ASHP I would need to save £250 pa for a ten year payback. As the majority of saving will come from displacing oil usage at say 6p/kWh I would have to generate/use about 1400 kWh of solar PV (based on a COP of 3) or 1050 kWh based on a COP of 4. Only about 500 kWh would come from an extra 1200 kw of panels so the rest would have to come from replacing IBoost consumption with E7. So I would need to be able to take 550 to 900 kWh from my existing solar. PVGIS says I will produce 1474 kWh October to March. During these months the solar might cover 8hrs base load which would equate to 300kwh so there would be 250 to 600kwh to operate the heat pump during daylight hours. I would need a COP of 4 therefore to make it work for a 10 year payback. (I realise that the sun wouldn’t necessarily shine when I wanted the heating on and vice versa but I might still get some benefit from the heat pump operating from the grid during April and September when I didn’t want to put the C/H for the whole house on. My daytime leccy rate of 13.7p would mean that it would pay me to use the heat pump anyway as it works out cheaper than oil so I could just shut the radiator valves off in the living room and let the C/H do the rest of the house while the heat pump warmed the lounge.

I am hopeful that it should all be cost effective but I anticipate someone can find a flaw in my calculations.

mgbond

ukenergysolution dot com/pacsystem/

What do people think of this as a system ?
(I’m not allowed to post links as a new member)

JKenH

Thanks for that- looks interesting.

Here is the link
https://www.ukenergysolution.com/pacsystem/

zeupater

JKenH wrote: »

Thanks for that- looks interesting.

Here is the link
https://www.ukenergysolution.com/pacsystem/

Hi

<Cough> ..... sorry, only interesting until you take a first look at the presentation of efficiency claims on the site <Shrug shoulders> ... needs realistic headlines without the unobvious caveats before I'd even bother looking into the detail (again!) ...

HTH
Z

JKenH

zeupater wrote: »

Hi

<Cough> ..... sorry, only interesting until you take a first look at the presentation of efficiency claims on the site <Shrug shoulders> ... needs realistic headlines without the unobvious caveats before I'd even bother looking into the detail (again!) ...

HTH
Z

Are quoted COPs not to be trusted? I am looking into an ASHP for the house at the moment and there seems to be quite a range of COPs.

I was wondering myself how the combined panel and heat pump would work efficiently in the middle of summer when the sun is belting down and the aircon is working full blast.

mgbond

I suspect it will have a refrigerant within it like the all the other heat pumps so regardless of the heat hitting the roof it should still be able to cool?

So apart from their figures are there any fundamental floors with it.

Positives I can see is that it takes heat from the panels when std air/air heat pump rely on the refrigerant system. So this system gains an advantage (assuming it also has refrigerant£. Also it would be situated in the loft and can be position to each room (upstairs at least)

They are coming round Monday so will let you know

zeupater

JKenH wrote: »

Are quoted COPs not to be trusted? I am looking into an ASHP for the house at the moment and there seems to be quite a range of COPs.

I was wondering myself how the combined panel and heat pump would work efficiently in the middle of summer when the sun is belting down and the aircon is working full blast.

Hi

I like the idea of convergence, however ....

.... for example 57.1% thermal collection efficiency on the standardised 1000W/sqm looks good, probably somewhere in the region of our own thermal panels, but they're vacuum insulated which effectively insulates the heated surface from ambient temperatures & wind-chill thus allowing the majority of the energy absorbed to be collected & utilised .... the performance graphic doesn't seem to recognise that of the 57.1% collected there would be an immediate heat loss to the atmosphere/surroundings.

To gauge the relative system heat-loss, in full sun the water in our thermal panels will rise to well over 180C in bright conditions when not required to heat the DHW, in similar conditions the PV panels on the same roof will be over 130C cooler, so not particularly thermally efficient ...

To make any kind of reasonable comparison the panel heat loss needs to be considered within their display, but, of course this immediately reduces the consumer's expectations ...

It's also relevant to note that the '*simplified interpretation' test conditions are pretty artificial & don't really represent the flash test conditions of 1000W/sqm at the same standard temperature & pressure as applied to PV .. also that the test conditions had absolutely no wind .. and, of course, anywhere near 1000W/sqm for sustained periods is pretty rare ...

My interpretation is that the system COP as stated is when running in the range of conditions described in the test which wouldn't be representative of average conditions which apply when heating is required, this is where the consumer should be looking to compare performance at typical conditions, ie ambient temperature, internal temperature and at various levels of irradiance (which at night includes zero!) or the SCOP (average SeasonalCOP) for the unit ...

---

What needs to be recognised is that the performance of air source heat-pumps is heavily dependent on ambient temperatures, flow temperatures and the relative internal heat exchange (think oversized radiators etc!) - to get an idea of what the range can be, have a look at the engineering specs (post #86) for our system as it's easily the best source publication I came across & reference the data table on P9 where you'll see a COP range (output/input) of between ~3.30 & ~6.8 ... it's currently 7C outside and our unit is ticking over & consuming ~120W, so operating at a COP of approx 5.2 and maintaining a temperature in here of 20.3C (set 20C) ...

Regarding Aircon on full blast ... we hardly ever use ours on aircon & when we do it only ever ticks over to make the house a little more comfortable when temperatures suddenly shoot up or to provide a higher level of dehumidification on 'muggy' days ... when working overseas I really hated leaving an over-cooled air conditioned building or car and stepping outside into what felt like an oven just to freeze again later, I'd rather acclimatise slowly whilst remaining comfortable!

HTH
Z

mgbond

Thanks Z

They do actually state the test conditions in small print at the bottom.

265Wc panel 1650x990 temp 15C wind 0 air flow 87.6m3/h

My only concern with the wall mounted Air/Air heat pumps is that they will create a warm spot. My lounge is approx 25’x 17 that links to the kitchen 25’ x 10’ will it not make the lounge feel warm due to the air flow.

My main concern is up stairs. It can feed one room (say bathroom) and the you have to leave all the doors open. Could it not just be piped in the loft to feed each room?

Martin

Exiled_Tyke

mgbond wrote: »

Thanks Z

They do actually state the test conditions in small print at the bottom.

265Wc panel 1650x990 temp 15C wind 0 air flow 87.6m3/h

My only concern with the wall mounted Air/Air heat pumps is that they will create a warm spot. My lounge is approx 25’x 17 that links to the kitchen 25’ x 10’ will it not make the lounge feel warm due to the air flow.

My main concern is up stairs. It can feed one room (say bathroom) and the you have to leave all the doors open. Could it not just be piped in the loft to feed each room?

Martin

I have similar issues in that I've got a large house with many rooms and I don't know where I would site a unit to be most effective.

I did however see a reasonably priced system (I think at Appliances Direct) with 3 'outlet units' (not sure what they are called!) working from one external unit for £1,100. They also link to installers so presumably a reasonable installed quote can be achieved?