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

A question about : Discussion ... ASHP(Air/Air) with Solar pv ....

Hi All

The combination of a small ASHP(Air/Air) with Solar pv seems to be a valid pairing of complementary technologies which has been raised a number of times on this forum.

The idea of this thread is to encourage discussion of this combination in order to validate what an appropriate equipment specification would look like in order to maximise performance benefits in a typical domestic environment.

Obviously, it is well understood that a typical domestic-scale solar pv system will not generate sufficient energy to provide winter heating, but should be considered as being a 'shoulder' months supplementary heat source for well insulated properties ... it is therefore best to concentrate on Spring & Autumn as being the target periods for heat provision, with an additional benefit of provision of cooling in heat-wave conditions such as we've been experiencing recently.

HTH
Z

Best answers:

• Okay, to kick-off the thread ...
  We have a ~4kWp pv system and currently use some power to provide heating to living areas using a small oil radiator (~400W/600W/1100W) and/or fan heater (~1kW/2kW) at times, just to take the chill off in Autumn/Spring when either lighting the log-burner or turning the GCH isn't justified ....
  During the recent hot weather we've used a portable air-conditioning system (hose through window type) which provides a theoretical ~2kW of cooling whilst using ~1kW of electricity .... this is a pretty old unit which isn't used much, but has proven to be extremely useful when elderly relatives have been visiting over the past few weeks ...
  Over the last few years I've looked at a split system Air/Air heat-pump system and have a number of ideas on what we would require from the system, but hopefully these will also be requirements which others would raise as part of the on-going discussion ... so I'll leave it there for the moment ...
  Enjoy the learning process, I'm sure I will ....
  Z
• My wall mounted aircon unit uses about 1.2/3kWh per hour. I would consider swapping it for an updated version as with all technologies they're advancing very quickly.
  Maybe its also time for me to look at getting around to purchasing a Wattson to compliment things as most of these systems are plug and play types. At least then I wouldn't be using any more power than I was generating.
  They're probably going to be a better option than oil fired heaters. At least these units will use 1kWh and turn it into 3-4kWh of heat. I can honestly say I haven't looked into portable units so probably should do a little more research(skulks off to do a bit more net nerding)
• Hi
  The portable unit we have is about 10 years old (possibly more) & cooling only, although there was a reversible version available according to the manual. The overall efficiency of the heat exchanger is (/was) probably much better than 2:1, but venting hot air out through the window means that there's always warm external air being drawn into the house to replace it thus reducing overall cooling .... there are portable split units available, I bought one for a specific application once, but they're not as efficient as wall mounted inverter systems.
  To pair a heat-pump to solar pv so as to ensure that they are well matched, the HP would need to be pretty controllable in terms of manual variability of power consumed to match pv generation rather than overall heating/cooling duty .... all of the specifications I've seen never detail the consumption and efficiencies at various speed settings, just a general range, if that !! ..... talk to an installation company and they have no idea other than the manufacturers' specifications so it would be good if someone has any actual comparative test data to share ! ... it's my opinion that it would be better to 'right-size' a heat-pump to the pv system's capabilities than to 'over-size' or 'under-size' it - that way it becomes a more useful addition to the household.
  HTH
  Z
• @ Zeup and Tunnel, many thanks for the info and comments from the other thread. TBH, I was a little shocked that my slightly odd idea was considered even remotely rational, not that that has stopped me before (PV @ WNW!!!!!!).
  So to keep things contained, here's what I pondered:
  Quote:
• Taking for example https://www.orionairsales.co.uk/toshi...rter-490-p.asp (I have no relationship to this seller).
  This is a toshiba top-of-the-line heatpump costing Ј899.
  For the 'shoulder' months - I looked up the performance at various temperatures.
  15C 3000W 6.1
  10C 2700W 5.8
  7C 2500W 5.7
  0C 1700W 4.6
  As you can see - for this sort of heat pump, for the 'shoulder' months - you get about 5 times the output per watt as a resistive heater.
  Assuming for the moment your heat pump throttles according to the output from the solar panel.
  Taking for no particular reason a 4kW panel in london.
  Quote:
• With being on LPG the priority was to dump that ASAP as although it was working the whole system [boiler, rads & pipework] was old and in need of replacement. Having lived with oil in the past that was not a contender either. So that narrowed the choice to electricity, renewables and solid fuel.
  The first year in the house was that of a stunning summer followed by the worst winter in years which was a terrible experience. LPG cost a fortune, we were not exeprienced/prepared for the one new log burner fitted in Oct so ended up using oil rads to supplement.
  The priority then was a new heating system to fit in with our renovations... Going through all the options I gave serious consideration to air to air with electric underfloor in the bathroom. Given the cost to do our house then revamping DHW with a new tank and solar thermal/immersion it was quite an expensive solution when compared to an ASHP with proposed RHI.
  I sometimes think of our ASHP which is coupled to fancoils not disimilar to air to air. With hindsight it was a good choice and has transformed the house despite the non existant RHI.
  Now that we have added a second log burner, PV and solar immersion we are sorted. Just need to build a log store now... The one I fancy costs Ј616 from the posh shed company so I'll make a couple just like it I plan on buying in a shed load of wood/peat/coal for this winter.
  If we built on a conservatory air to air and another log burner would be a definite. But that would be expensive as would have to match the style of a 1906 station....
• Hi
  Following on from the previous post, the performance curve & figures for a range of T0shiba Air/Air units look like this ... https://toshiba-aircon.co.uk/assets/u...P-E_DSK6_5.pdf ...
  What I find really confusing with the engineering performance figures is that data is given for min, nominal & max capacity & partial loading conditions, but this has little commonality to the controllability available in the relevant user manuals .... https://toshiba-aircon.co.uk/assets/u...s%20Manual.pdf ... which only refer to low/med/high control on fan speeds.
  What we would be looking for is a unit where the power drawn would be limited by manual control, something like limiting low to 250W, medium to 500W and high to 1000W in order to match pv generation with the heat output being directly linked to the COP available at these settings in various temperature conditions .... of course, being able to control this automatically depending on generation would be ideal, but talking directly to Toshiba a couple of years ago I was informed that this wasn't currently possible on their small Air/Air systems.
  HTH
  Z
• Unless I have missed it, nobody has mentioned the noise issue with Air to Air HP.
  It might be worth looking at some American websites on these heaters. They are very common in cheapish motels and trailer homes.
  De-icing units can severely dent the COP figures.
• You should scan through this 'sticky' thread.
  https://forums.moneysavingexpert.com/....php?t=1464827
  I wouldn't have thought icing would be a problem 'during daylight operation Mch/Apr & Sept/Oct '
  The Air to Air A/C(and heating) in my apartment in the USA(installed 2003) is very loud but as the external unit is on the roof so doesn't matter. Internally the air is ducted to all rooms so the fan noise is muted.
  The latest technology will probably make the units quieter. You can also research acceptable noise levels, however I am surprised that your proposed units can be as loud as 54db:
  Quote: