Posted By: Peter_in_HungaryIf the 140kWh/day is the assumption what size ASHP would be needed

Well 140 kWh/day = 5.83 kW so a 7 kW or so HP should be big enough in theory. 14 kW is easily available, so it should certainly be possible to do something. Worth doing some more detailed calculations I would say.

Posted By: djhWell 140 kWh/day = 5.83 kW so a 7 kW or so HP should be big enough in theory. 14 kW is easily available, so it should certainly be possible to do something. Worth doing some more detailed calculations I would say.

How do you make the leap from 140kWh/day to 5.83kW?

More detailed calculations are difficult due to the number of unknown variables. Walls vary from 800mm stone/rubble to 500mm variable what came to hand and some porotherm type blocks of unknown make. Windows vary from ancient to modern and then there are the losses from the thermal store which is outside the heated envelope. I have no idea of the weight of the firewood burned (it comes from my forest) and even if I did the calorific value is so variable a calculation of input would be impossible.
Hence I settled on the temp. rise of the TS as a simplistic calculation that I could manage without too much brain ache.

Will
Thanks for the links, I will give the sizing spreadsheet a go but there still seem to be a lot of unknown variables that can't go into the spreadsheet so I'm not sure how valid any results would be.

If I have to resize the radiator then that would probably make the project a non-starter due to cost. I was hoping to be able to run the rads. at 50 deg. for longer (instead of the 60 as present)

Which makes of ASHP can manage an output temp of 50 deg. without destroying the CoP

Posted By: djh140 kWh/day = 140 kWh/day / 24 hours/day = 5.83333 kWh/hour = 5.83 kW

Would this figure of 5.83kW imply 24 hour running to get the 140 kWh/day ? If so would a 10 kW unit be more appropriate ?

Posted By: djhSorry, I should have been more explicit. Worth getting a supplier or somebody else qualified to do the calculations and who is willing to stand by the results. (e.g. insured against the risk of being wrong)

Last time I had to do that over here was for a property needing a CH system. The supplier came in and looked at each room and noted a rad. size (no measurements taken) and a few days later gave me the requirements. When I challenged the lack of measurements he said "I know what I am doing". I then calculated everything and found that I could reduce the rad sizes by 50% and the boiler size by half. When I showed him the calcs. he said "You do what you like, I know mine will work". The point being over here to ensure success and to avoid complaints everything is grossly over specified.

I do have an EPC for the main house that is 10 years old and shows a heating load of 160 kWh/m2/year which was then increased to 190 kWh due to 'system losses'. this is over a 165 m2 house which if you take the annual figure over 6 months (heating season here) you get 190 x 165 /180 = 174. So 174 kWh/day for the main house but this was before various windows were changed and 100mm EWI added.

I would expect the EWI to reduce the heating load by probably 40% but that is a guess and of course it was an EPC figure to start with and EPCs do not have a good track record of being accurate.

Peter, how did you calculate the 150kWh per day?

How long does your 40kW boiler run for each day during winter? How about during summer?

Posted By: owlmanPeter have you done a cost comparison with heating your buffer by immersion heater? I did just such an experiment, with my very similar system, in late winter/early spring this year which was fairly successful.
I assume you get your buffer tank up to 70/75+, ( I've had mine up to 90 on occasion ) with wood. My suspicion, when I considered A-W heat pumps was that they would still need immersion boost to adequately serve both the existing hydronic CH and DHW Phx.
After your years of having that large reservoir of very hot water at your disposal you may be disappointed with any HP however good the manufacturers claims. They simply can't compete with those temperatures but then their MO is different and trying to configure it as a log-gas replacement simply won't work IMO.

Based on my own simple experiment here's what I'd do:-
Ideally 2 x immersions @ 1/3 and 2/3 way up the tank. If you've got 3 phase, that'd be great. Having the two immersions, separately controlled gives you greater seasonal control, e.g. just heating a small amount of water at the top 1/3 if demand is low.

I run the system by firing the boiler when the TS is down to 60 deg and heat it up to 90 - 95 deg. this then feeds the CH directly and the DHW via an indirect tank. The rad temps are mixed down to 60 deg. The wood comes from my own forest and I an happy with the way the system works but the cutting of the fire wood and fuelling the boiler at my age of 72 is getting difficult so I am looking for an easier option.
Immersion heater(s) would not be an option as I can't get the power needed for the estimated 150kWh/day and whilst the TS losses are less of an issue using my own wood the expense of those losses on the electric bill I think would be too high, not to mention the cost of running the CH on resistance heating even at night rate (about 280 quid a month).

Posted By: WillInAberdeenPeter, how did you calculate the 150kWh per day?

How long does your 40kW boiler run for each day during winter? How about during summer?

I calculated the 150kWh/day by taking the energy needed to get the TS from 60 deg. to 90 deg. which are my usual from - to operating temps. for the TS. Last December and January the 2 bed house (less well insulated than 4 bed house) used 38 kWh/day and 47 kWh/day respectively. (I have a heat meter on the CH for that house to bill the tenants for the heating)

The boiler will run up to 6 - 8 hours in the winter, but then it takes an hour+ to get up to a temp. whereby the laddomat starts mixing water from the TS and then output drops as the wood burns down and drops a bit more if I have to add additional (cold) firewood whilst that comes up to temp.
Whist it is rated at 40 kW as you pointed out above with your comments about heat pumps - more so with wood burners, the rated output is under ideal conditions and I doubt that 40 kW is ever achieved other than a short period mid-burn.
During the summer I run the DHW on an immersion heater running on night rate electricity. When I have run the boiler for DHW only then I lit it every 3 days or so but I had to keep the TS above 65 - 70deg. to get 60 deg in the indirect tank and at that temp. the DHW indirect pump was running continually. And 3 days of unknown thermal losses from the TS need to be accounted.

Thanks for the info about heat pumps, they look interesting.

Yes the cheap fit up option might be immersion heaters but I cant get the amps to run that much. My farm is at the end of the grid line and the nominal 230v drops to 190v with a 20a load. We already have 3 phase split between the demands, every thing is single phase with the phases spread around because you don't get 3 phase toasters.
If we tried to run the immersions we would get our own personal brown outs.
A heat pump would reduce the load by 3-4 times and make that option feasible - along with reducing the electric by the same proportion.
I've been speaking to the gas co. as a gas boiler would be the 1st choice but so far they are not interested at any price.

At the moment the CH is program timers and is on for 12 - 15 hours a day spread between morning, midday and evening. The plan would be to run the ASHP direct to the rads, leaving out the TS as I think the losses with the TS would be too expensive in terms of extra ASHP size to make up for the losses and therefore running costs. (The TS is outside the heated envelope) Both houses have additional wood burner stoves in the main room of each which can be used if needed or for feature (and in the autumn and spring to avoid the CH)

Also The electric co. wouldn't give us enough amps to run resistive heating because they know the problems we have and they have their power standards to maintain.

Many heatpumps are available that have options to work with 3ph supplies - eg that Daikin 3 3HT is available in 1ph and 3ph options.

Thinking ahead - any plans to get EV charger(s) ? Might need some amps for that.

Posted By: jms452UNTIL we're away and need to warm the house up from cold...

Our emergency plan for warming the house up is a bunch of random electric heaters - fan heaters, radiant heaters etc - that we happen to have lying around. Given the expected low usage, I don't feel able to justify anything more sophisticated/efficient/ecological.

Won't help Peter in his constrained electricity supply position though :( Bottled gas burner? We have a little gas camping stove we also keep for emergencies. Or just thermal underwear and a bunch of jumpers

Posted By: owlmanI hadn't realised you planned to run the two properties direct from the heat pump and bin the buffer tank altogether.
I came across all the A-W problems, and there are others besides water temperature, which don't get mentioned on this forum; when I thought of doing it myself. Which is why in the end I opted for A-A.

When thinking this through I couldn't see the point of using the TS with a heat source like a ASHP which would come on when needed and without the constraints of a batch burning wood boiler especially when the TS losses are taken into account. A2A would not be an option because of the locations of the ASHP and the 2 houses.

Posted By: WillInAberdeenThinking ahead - any plans to get EV charger(s) ? Might need some amps for that.

An EV is some time away (when my current car reaches end of life) and by then grid issues will either be resolved or in terminal decline.
At the moment 50% of electricity here is nuclear with an expansion planned, otherwise it will be solar or perhaps geothermal 'cos there is lots of that here if there is an easy way to get electricity out of 90 deg geothermal water (but not where I live ). No real option for wind unlike the UK.

Posted By: jms452Peter have you considered how long it will take to heat the house up from cold?

Yes, current lifestyle means that we don't go away for more than a weekend during the winter and now I make sure the TS is loaded before we go. I would probably leave the heating on night temps (as now). The other house has tenants so for longer periods in either house arrangements could be made.

Posted By: owlmanPeter what is the distance between your proposed HP and the two dwellings, that you mention above?

The proposed HP would be behind the main house on the hill at sort of 1st floor level (both houses are built into the hill) The current 'boiler house' is at house ground floor level between the house and the hill. The HP would be behind and above the boiler house.
The smaller house is to the side of the main house by 3m. seperation

The first thoughts are one ASHP to do both houses and I have assumed that an ASHP would modulate the output. Currently the two CH system run independently without zones drawing off water from the TS and I have assumed that I could run the ASHP with one zone for each CH system using one pump and zone valves or 2 pumps. Either way each CH system would have its own programmable thermostat as today.

I think two ASHPs would be a more expensive option.

I have a sneaking suspicion that you will need at least two outside units. That is, if you can find a single large enough inside unit capable of accepting input from two condenser/compressors.
Were you thinking monobloc?

Two thoughts, if you're limited by the supply:

(1) two (or more!) units would allow a smaller start up current peak

(2) batteries could power the start up peak without overloading the mains?

I'm a bit sceptical Peter, my nature I guess, but;-
You're; ( mid-winter, I presume ), currently heating 2 tons of water to 90-95C on a daily basis.
You're throttling that down to 60C to supply on demand, to two dwellings, for both CH and DHW.
You want to leave the current rads. and supply network in place.
Even accounting for supply and storage losses, some of which are NOT going to disappear with a HP. I can see a HP struggling to replace all that "on demand comfort", even with a lower temperature, longer running regime; call me old fashioned.
I have visions of you constantly having to boost the store temp with immersion heating in order to end up with anything other than lukewarm rads. That cuts right across your electricity supply problems. I obviously have no idea of your planned system layout but the distance between condenser and store need careful consideration, more especially if it's a monobloc system.