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

Martyn1981

ASavvyBuyer said:

matelodave said:

You have to take into account what their "central assumptions" are predicting for 30 years hence. Did you read the whole paper or are just quoting the headline in typical Daily Mail fashion

It appears that by just reading that bald statement, they could be predicting that the price of gas is going to be extremely high and  leccy will be everso cheap but even then they can't make a case for hydrogen or fuel cells.

Just my take on a headline rather than reading through it all. 

I could not see the "actual" figures they were using, but apparently they were based on other studies predicting the future prices of energy. Those figures may be in the reference documents.

I understand that is why they did the "sensitivity" analysis to see what the results would be if those predictions were 50% out.

Looking at the paper, and I'll admit to not understanding a lot of it, it seems to be well researched / based on prior research, and the sensitivity analysis (fig 3) appears to show that the heat pump options are still by far the best solution (economically) out of the lower carbon future options.
Nice to know that the current direction of travel appears to be 'the best' based on current analysis, even allowing for significant future leccy/H2 price fluctuations. Thanks for posting.

[Edit - Silly comment, but was able to switch off the GCH boiler 30 mins ago, and switch on the A/C unit covered by PV generation. Even duller March days tend to allow steady HP heating through the day now. Roll on more sunshine. M.]

[Edit2 - Thinking about it, now that air temps are rising, I probably should have put the A/C unit on over night on E7, and switched the boiler off. Doh! M.]

ASavvyBuyer

Martyn1981 said:

[Edit - Silly comment, but was able to switch off the GCH boiler 30 mins ago, and switch on the A/C unit covered by PV generation. Even duller March days tend to allow steady HP heating through the day now. Roll on more sunshine. M.]

[Edit2 - Thinking about it, now that air temps are rising, I probably should have put the A/C unit on over night on E7, and switched the boiler off. Doh! M.]

Just checked through our records and the GCH has not been triggered by the thermostat to come on since 14th February. The programme in the GCH thermostat has not been changed, but careful tweaking of the programmes for the 2 ASHP's has meant that the bungalow has maintained a temperature that does not require the GCH to come on.

As we are on the Go-Faster tariff, we get cheap electric (5.5p/kWh) from 01:30-06:30 (usually the lowest carbon period for generation) so I programmed the ASHP's to set back to minimum temperature from when we go to bed until 05:30 when they change to a higher setting, for an hour, to boost the temperature (but on the cheap rate) and then back to normal for the rest of the day. Within that hour, on the cheap rate, their current draw has reduced back to a low level and then they just tick over usually drawing less than 250watts each.

So now that we are regularly getting PV generation above 500 watts from about 9AM - 4PM it covers most of the ASHP's use throughout the day.

Martyn1981

ASavvyBuyer said:

Martyn1981 said:

[Edit - Silly comment, but was able to switch off the GCH boiler 30 mins ago, and switch on the A/C unit covered by PV generation. Even duller March days tend to allow steady HP heating through the day now. Roll on more sunshine. M.]

[Edit2 - Thinking about it, now that air temps are rising, I probably should have put the A/C unit on over night on E7, and switched the boiler off. Doh! M.]

Just checked through our records and the GCH has not been triggered by the thermostat to come on since 14th February. The programme in the GCH thermostat has not been changed, but careful tweaking of the programmes for the 2 ASHP's has meant that the bungalow has maintained a temperature that does not require the GCH to come on.

As we are on the Go-Faster tariff, we get cheap electric (5.5p/kWh) from 01:30-06:30 (usually the lowest carbon period for generation) so I programmed the ASHP's to set back to minimum temperature from when we go to bed until 05:30 when they change to a higher setting, for an hour, to boost the temperature (but on the cheap rate) and then back to normal for the rest of the day. Within that hour, on the cheap rate, their current draw has reduced back to a low level and then they just tick over usually drawing less than 250watts each.

So now that we are regularly getting PV generation above 500 watts from about 9AM - 4PM it covers most of the ASHP's use throughout the day.

Thanks. I've still got lots to learn, and future opportunities. Currently still missing south facing gen which will help with the colder months. Covid has slowed my progress, but fingers still crossed for a small steep pitched ground mount ready for the autumn.
My E7 is not a very good deal (10p at night), but I got a free car charger, no £300 contribution, so in a year I should be able to find a better deal. But I'll start experimenting now to see if we can go GCH free, without of course leaving poor Wifey uncomfortable.
My main problem though is that the original A/C unit is in the conservatory, so I don't like using it till the sun is able to warm the room up, as I feel that's a waste of good green generation if it's sending too much heat outside. But it's OK now as temps and sun improve, and this morning it was warm enough (18C), and enough spare gen to switch it on (too) just after 8am. The second unit is fine as it's in the lounge, so does a great job any time.

Wolfbo38

Hi

Firstly forgive me if I mix kW and kW/h up below, I sometimes struggle to know which to put, but hopefully, you will understand what I’m explaining and asking, and don’t please shoot me down if I get the wrong measurement units!

So I’m hoping someone can answer this question for me, (sorry a very long pre-amble before the question as I want to explain where we are at currently!) we have a 10-year-old 3.5kW solar PV array, giving us around 3.07 kW/h max output, which we use as efficiently as possible, using the washing machine and dishwasher on sunny days when we are generating the most.  The house has a ‘base’ demand of around 250 to 300W/h, (lightbulbs (all LEDs), hands-free phones, the odd item on standby, the alarm clocks, cooker clock, our laptops, radio/TV probably the fridge freezer in that too, just ticking over, the router, etc. etc).  Given we don’t always have the dishwasher or washing machine on means there is often excess energy generated, particularly in summer.

To make the most of this we fitted a second-hand Solic 200, a Facebook bargain find, that diverts the excess energy through a ‘spare’ consumer unit that used to provide energy to the long since removed, storage heaters, meaning that in the bedroom and living room we now have separate sockets wired, using the old storage heater circuits, to this consumer unit that we plug heaters into, a 1950’s HMV Bakelite ‘Dalek’ 2kW heater in the living room and an 800W oil-fired heater of about the same age in the bedroom.   These heaters use the excess power generated and heat both the rooms.  This is of benefit, even in the summer, as we live in a rather cold 4 bed end terraced Victorian house, almost impossible to insulate, (except the loft where we have in excess of 300mm insulation), as we are in a conservation area, so could not have external insulation and also have many of the original Victorian features that we don’t want to lose in the interior, which would make internal wall insulation very difficult.  The two rooms are north facing each with two exposed walls and large original sash bay windows (which have or are about to have secondary glazing).  We do have central heating but I’m loathed to put it on year-round, my wife would have a different view on that, hence heating the main rooms we live in with the spare energy from the PV!

To improve how ‘green’ we are we had initially looked at replacing the combi boiler, only just over 2 years old now (replaced under insurance when the old one failed), with an A/W ASHP, however the heat loss through the walls would have been too great and it seemed to be the wrong thing to do given the boiler is so new.  We have therefore fitted a Solar Thermal system, with a new 115l tank, part-funded through the GHG scheme to heat the hot water minimising the amount of gas we use for our water heating.

I’ve recently had the thought of fitting an A/A  ASHP into the living room as a more efficient method of using excess energy than the Dalek heater, given we could expect a COP of 4 or more, which would allow us to heat the room far better on the ‘shoulder’ months, and perhaps let excess heat into the rest of the house in the warmer months by simply opening the living room door!  What I wonder is can we run the ASHP as we do the Dalek, ie on the excess energy through the Solic 200, ie sometimes only having 200W/h excess energy being supplied and other times well in excess of its requirements, or does it need a continuous level of energy to be delivered to it?  I know excess is not an issue, but wonder if less than its rated value would still allow it to function.  The Dalek heater simply runs slower and produces less heat when we have less excess solar energy available than the 2kW it is rated at.  So what I’m asking really is if say it is a 700W ASHP giving out say 2.8KW heat, would it work if just supplied with 200W/h and give out say 800W heat or does it always require 700W/h to operate? 

gefnew

Maybe not because the ashp  requires constant 240 v supply, you would have to use like you use your washing machine.
the solic 200 only works with a restive load.

QrizB

Wolfbo38 said:

What I wonder is can we run the ASHP as we do the Dalek, ie on the excess energy through the Solic 200, ie sometimes only having 200W/h excess energy being supplied and other times well in excess of its requirements, or does it need a continuous level of energy to be delivered to it?  I know excess is not an issue, but wonder if less than its rated value would still allow it to function.  The Dalek heater simply runs slower and produces less heat when we have less excess solar energy available than the 2kW it is rated at.  So what I’m asking really is if say it is a 700W ASHP giving out say 2.8KW heat, would it work if just supplied with 200W/h and give out say 800W heat or does it always require 700W/h to operate? 

As I understand it, while you can turn the output of an air-to-air heat pump up and down and the input power varies with it, this involves adjusting the fan & pumo speeds rather than simply modulating the AC supply (which is how I think the Solic works). You could install a AAHP system to give you the COP advantage you're looking for but you'd either need to manage it manually, or install a more sophisticated control system. (I suspect a Raspberry Pi or Arduino would do the job, but you'd need someone to put the logic together and I don't think I can really lend you my 17-yo son to do it!)

@Martyn1981 has solar PV and an AAHP that he runs in the shoulder months. He might be able to give you info on how his works for him.

Martyn1981

Hi Wolf and welcome.

As mentioned by others, I don't believe you can run the units as you hoped. But, there are many units that have an 'eco function' or similar type name, so run at reduced power, rather than say at 700W until the room reaches temperature, so that's an option for you.

What I would say having done similar to you, starting with a 400W oil rad, and a couple of 120W tubular heaters, there is an obsession with avoiding leccy import. But with the A/C units (I'll use A/C just to avoid any confusion) because of the huge energy out bump from the COP, it's less important to worry about leccy import - or to put it better 'don't let the perfect be the enemy of the good'. If you are buying 350W, but outputting 2,800W, then focus on the pluses, not the minuses.

So, whilst I'll try to use the units when there's enough spare leccy, I don't worry so much about buying some in. I also find that for a single room, they will modulate quite fast, so as the sun comes up, Wifey pops on the unit in the lounge (now her office, as she works from home), after an hour (probably far less) the temp will be fine, and the unit modulating, and also by that time, the small conservatory (facing E) will have warmed up from the sun, and I can open the door into the living room, and put on the A/C unit in the conservatory to pump heat around the living room. With say 1kW of generation, that will tend to cover all leccy demand from the two units and baseload most of the time, so long as you don't worry about a small amount of import - just think of the 4x COP, and the cost ain't so bad.

Another huge benefit, that one of the other posters pointed out, who installed an A/C before me, is that by heating the room(s) you are in, you reduce GCH by a greater amount, since you aren't heating the whole house (caveat - even with TRV's in all rooms, there will still be wasted heating at times).

Sorry if my waffle is confusing, but I'd suggest not worrying too much about some import, when generation is low, and then when gen is higher, open those doors (internal!) as you suggest and spread the heat through the house.

Martyn1981

Sorry Wolf, meant to add, but forgot, it's not just the shoulder months. Even in the winter, there are a lot of sunny days when the A/C unit can be used to keep the temp up (in the room(s)) between a morning and evening GCH burn. Obviously the sun is doing the heavy lifting, with all the solar gain through the windows, but rather than needing the GCH to run at low levels during the day, on those marginal heating periods, the A/C may be enough, and hopefully run from PV even if it only ticks along at ~1kW through the sunny period.

This system/idea also works quite well with a BEV, since you can charge the car at around 2.2kW from PV each day in the summer, when heating isn't needed, but when gen just isn't high enough to make it worth doing as you enter the lower 6 months, you can leave the excess PV for the A/C, and charge the car at 7kW off wind* at night.

*Just an expression, by moving to a green tariff, and charging when demand is lower, and wind generation is typically higher.

QrizB

Wolfbo38 said:

So I’m hoping someone can answer this question for me, (sorry a very long pre-amble before the question as I want to explain where we are at currently!) we have a 10-year-old 3.5kW solar PV array, giving us around 3.07 kW/h max output, which we use as efficiently as possible, using the washing machine and dishwasher on sunny days when we are generating the most.  The house has a ‘base’ demand of around 250 to 300W/h, (lightbulbs (all LEDs), hands-free phones, the odd item on standby, the alarm clocks, cooker clock, our laptops, radio/TV probably the fridge freezer in that too, just ticking over, the router, etc. etc).  Given we don’t always have the dishwasher or washing machine on means there is often excess energy generated, particularly in summer.

You probably don't want to read all 2800 pages of it but several of us give monthly summaries in the "Talking 'bout my generation" thread. Martyn's summary for August is here, for example (it makes mine, here, look puny!). If you have the numbers you can compare and see how you're doing.

I guess your system is on the 2011 FITs? If so, it should have paid for itself comfortably by now?

Wolfbo38

There is some great reading there!  I've never really monitored min that closely, but will from now on and publish for all to see!  My guess would be the with the Solic 200 we are feeding back very little to the grid now, and have a fairly significant reduction in our gas use as we heat a lot less of the house now, given the thermostat in the living room never switches the boiler on with the HMV Dalec keeping it above 20 deg most of the time.  The programable TRVs also keep the heating off in many rooms when not needed.

It is probably just under 10 years that we have had the system, as we just missed out on the 42p(ish) FIT rate and got the 22p ish FIT, however I think we are now just about approaching our break even on them.  Not sure we will ever do that with the solar thermal, but it seemed the right thing to do when GHG would fund part of the cost and is better for the environment.