ASHP. We've only gone and done it again!

HappyMJ

Geotherm wrote: »

Yes, as the outside air temp reduces, the COP lowers. 70C is high for a rad system, it is usually based @ 55C. A buffer tank is normal for rad systems, to stabilise the heat level.

The 70C was for the domestic hot water.

lovesgshp

HappyMJ wrote: »

The 70C was for the domestic hot water.

Too high, not required. Put your hand under 70C!!! 50C normal with boost to 65 for bacterial cleaning.

TiredGeek

OK, a lot to try to clarify, remind me if I miss something

At the moment DHW temp is set to 58'c which is very hot to the hand and easily enough for a bath/shower/washing up. Set for two hours a day, but the full 28kw is used for DHW so it heats the 300L cylinder from fully cold (just filled) to 58' in just about an hour. As it's a holiday/retirement home the DHW is only utilised once or twice a year so is usually set to off.

Until the new controller arrives the heating is set to weather compensation, flow temp of 30' @ ambient 17' ranging to 50' @ -10' ambient. Calculations show the system capable of heating the house to 21' @ -15'. Our area does go lower than that but only for 1% of the year or less. This can be adjusted for by reducing the temp in unused rooms with TRVs to allow the used rooms to hit full temp.
We usually keep the house at 18' during the evening going down to 15' for the rest of the time. To us this feels comfortable. We also have wood burners in the two main rooms for added heat in case of power cuts etc.

We know the bills will be high, it's an old place, hopefully they'll come in a fair bit lower than friends we have up there in similar houses (~4000L/year oil). We'll take it as a year bill to balance it out.

Yep, the same 28kw setup, two 14kw Ecodans. No buffer tank fitted - ~8 litre low loss header is all that is required. Flow rates are 32L/min through the heat pumps, 25L/min around the rads. System volume is around 300litres with glycol protecting down to ~-22'c.

Electric is Scottish Hydro - 12.xx pence/kWh. We're looking to switch if we can, two domestic full rate meters often confuses companies

lovesgshp

TiredGeek wrote: »

OK, a lot to try to clarify, remind me if I miss something

At the moment DHW temp is set to 58'c which is very hot to the hand and easily enough for a bath/shower/washing up. Set for two hours a day, but the full 28kw is used for DHW so it heats the 300L cylinder from fully cold (just filled) to 58' in just about an hour. As it's a holiday/retirement home the DHW is only utilised once or twice a year so is usually set to off.

Until the new controller arrives the heating is set to weather compensation, flow temp of 30' @ ambient 17' ranging to 50' @ -10' ambient. Calculations show the system capable of heating the house to 21' @ -15'. Our area does go lower than that but only for 1% of the year or less. This can be adjusted for by reducing the temp in unused rooms with TRVs to allow the used rooms to hit full temp.
We usually keep the house at 18' during the evening going down to 15' for the rest of the time. To us this feels comfortable. We also have wood burners in the two main rooms for added heat in case of power cuts etc.

We know the bills will be high, it's an old place, hopefully they'll come in a fair bit lower than friends we have up there in similar houses (~4000L/year oil). We'll take it as a year bill to balance it out.

Yep, the same 28kw setup, two 14kw Ecodans. No buffer tank fitted - ~8 litre low loss header is all that is required. Flow rates are 32L/min through the heat pumps, 25L/min around the rads. System volume is around 300litres with glycol protecting down to ~-22'c.

Electric is Scottish Hydro - 12.xx pence/kWh. We're looking to switch if we can, two domestic full rate meters often confuses companies

DHW temp seems high @58c, we normally set to 50c, with peak boost every 14-28 days. Suprised no buffer tank with a rad system to keep it stable. Have the rads all got bypass valves?

TiredGeek

Geotherm wrote: »

DHW temp seems high @58c, we normally set to 50c, with peak boost every 14-28 days. Suprised no buffer tank with a rad system to keep it stable. Have the rads all got bypass valves?

Nope, about half have TRV and the others are just slightly open to allow flow to be pretty balanced around the lot.
The low loss header takes care of flow to the heat pumps. Allows for the system to adjust quicker to temperature fluctuations as well.

[Deleted User]

TiredGeek wrote: »

Until the new controller arrives the heating is set to weather compensation, flow temp of 30' @ ambient 17' ranging to 50' @ -10' ambient. Calculations show the system capable of heating the house to 21' @ -15'. Our area does go lower than that but only for 1% of the year or less. This can be adjusted for by reducing the temp in unused rooms with TRVs to allow the used rooms to hit full temp.
We usually keep the house at 18' during the evening going down to 15' for the rest of the time. To us this feels comfortable. We also have wood burners in the two main rooms for added heat in case of power cuts etc.

All the best with the new system!

Great to hear you settings so I can compare

Our flow temps are 35c @ +15c to 45c @ -3c. DHW to 50c but thinking of changing it to 45c then boost to 50c with imersion (65c once a week)... 13 smartrads, 1 normal rad and 1 room ufh. House heated to 20c with overnight setback to 17c. Even in winter the house does not normally drop to 17c so Ecodan doing nothing overnight.

Last year the stove was not used spring summer autum but this year the stove has been on every evening what with the all the rain. Mad! Running the stove means the Ecodan does not come on except when very cold. Never worked what is cheaper, running the Ecodan at this time of year or a bucket of coal and free wood everyday???

Currently paying npower £84pm but should come down as little as we owed them a debt of £120 odd pounds and not had the solar for a full year yet. Unfortunately with the wife watcing endless soaps, the hairdryers for two ladies and computers etc I doubt it will come down that much Energy efficient bulbs just can't compete.... Still cheap for a big old house in the hills I guess.

Cheers

Cardew

TiredGeek wrote: »

OK, I'm not going to pretend I understand all the calculations, but there's been a second, much more thorough inspection carried out and then calculations were done. Results are thus:

Heat Pump Space Heating Mode Annual Space Heating Energy Requirement (kWh) 59414
Annual Space Heating Energy Consumption (kWh) 16975
Annual Cost of Space Heating from Heat Pump £2,037.04
Annual Space Heating CO2 Emissions of Heat Pump (kg CO2) 8810

Heat Pump Hot Water Mode
Daily Energy Requirement for Water Heating (kWh) 11.77
Total Energy to be delivered to Cylinder Daily (kWh) 12.35
Total annual hot water demand (kWh) 4509
Annual Energy Consumption (kWh) 1961
Annual Cost of Hot Water Heating from Heat Pump £235.26 Annual Hot Water CO2 Emissions of Heat Pump (kg CO2) 1018

Total annual energy requirement of dwelling (kWh) 63923
Total annual energy consumption of Heat Pump System (kWh) 20026
Total annual run cost for Heat Pump System £2,403.15
Total annual Heat Pump System CO2 Emissions (kg CO2) 10394

With the same numbers oil would come in at £5935!
It's looking very much like the previous £13/day is actually a probability, however, the old system never actually made it through a winter without failing horribly. This one is pretty much guaranteed to survive Also, that £13/day previously was when the system was trying to keep the house at 10'c frost setting...
Hopefully it will come in at less than expected running costs as we tend to keep the house cooler than the temps the calculations were based on, but we'll give it a full twelve months before we work out the numbers.

BTW, there's now 39 radiators fitted (! couldn't find room to round it up to 40 )

I really will be surprised if your system manages to achieive an annual overall COP of 3.5 for heating including defrost cycles. I have seen no confirmed results that get that performance anywhere. Especially as your house is in one of the coldest areas of UK and, by your own admission, is far from the ideal property for installation of a heat pump in terms of insulation etc.

That poor insulation to a certain extent is confirmed by a heating requirement(without Hot Water) of 60,000kWh pa. for a house of 170 square metres.

So what happens if your system falls well short of that COP = 3.5? Is there any guarantee from Mitsubishi/your installer?

Can you explain how you state:

With the same numbers oil would come in at £5935!

Your total consumption is estimated at 63,923kWh. That for oil would mean 6,267litres of heating oil.(1 litre contains energy equiv of 10.2kWh)
Taking a new oil boiler as being 90% efficient that is approx 7,000 litres pa

On the 'oil price thread' in this section of MSE people are reporting prices from 50p to 55p a litre which would mean a total price of £3,500 to £3,850.

However even that comparison is to ignore the biggest disadvantage of heat pumps when comparing running costs. Because of the low water temperatures produced by an ASHP, it is necessary to have the system running very long hours, if not 24/7!, when heating is required. So the system is consuming electricity when you are away from the property, or asleep in bed. If you let the temperature of the house drop too far, water at 30C to 35C will take ages to bring it up to temperature.

So in effect there is a lot of 'wasted' heat.

This simply isn't the case with gas or oil CH, which with water at over 80C can bring the house back up to temperature quickly.

The Energy Saving Trust have confirmed the above.

It is also pertinent to point out that with water at 80C you perhaps would not need the 39 radiators you require with water from an ASHP

Please don't think I am making any criticism of your choice, but you did ask us to discuss.

[Deleted User]

mindovermatter wrote: »

Hi
your setup looks amazing.
We are just about to sign up for an ASHP.
How did you arrange for Mitsubishi to supply and fit the monitoring equipment?
Have you got any other tips for a new install?
We are replacing an ancient LPG boiler
Best wishes
Mindovermatter

Mitsubishi may contact you post install to invite you to take part in monitoring. I can PM you a contact if you like to make prior enquiries?

HappyMJ

Do you really need the heating set at 10C if you aren't actually in the property?

Me...personally I'd turn the heating off and let the place freeze (turning the water off). Then only use the heating when you are in the property.

I'm just saying it doesn't need to be that warm. My house barely uses 80kWh/m2/year and I live in it all the time. The kitchen has no heating and never drops below 5C in the winter. Yes it's very cold but it's not freezing. I rarely use the kitchen and when I do the cooking (slow cooker on a lot) keeps it warm enough. I'm on a very tight budget so only heat one room at a time. All other rooms the heating is off all year round.

I would have just purchased a whole lot of electric heaters. With a 28kw maximum draw from heating plus whatever other usage you have it isn't a standard domestic electrical installation which has a maximum continuous current of 100Amps at 230V (23kw). You said there are 2 supplies. Is that a 3 phase supply?

TiredGeek

Yes we could turn off the heating and let it drop naturally. In the past we've seen -9'c on our indoor high/low thermometer. This resulted in frozen and split pipes even though we'd drained down as much as possible. You'll never fully empty pipes in a house like this, there's always going to be pockets of water left.

Cold goes hand in hand with damp in an old stone house which then causes deterioration of furnishings and things like the kitchen cupboards and wood worktop. A bit of warmth, 10', isn't all that much but it is enough to prevent the worst of the damp and damage whilst, hopefully, not costing too much. Pay now for heating or later for repairs....

The place was a hotel many moons ago and had two domestic supplies fitted. We have two 240v lines, two meters and two fuse boards....made the rewire intersting to avoid 415v potentials. The heat pumps output 28kw, not suck it in, max current is about 40amps AFAIK.

Cardew, no offence taken
The oil suppliers up that way are currently wanting 66p/litre. My friends have just had a 1000 litres delivered ready for Autumn.
We'll have to see how it performs in the next twelve months to see what running costs really are. So long as it's no more than oil, we'll be content

Your point about longer running times, agreed. For us though it's moot. If we're there we want it warm all day, if we're not we want it to maintain 10'c 24/7. Ideal situations for heat pumps, long run times with little cycling. For a normal property with people out most of the day then you have a case
We do indeed need so many rads due to the lower flow temps and higher temps would need fewer, but we don't mind, and the more water in the system the longer it takes to cool off (but conversely to heat up as well) and this helps reduce the "house too hot, house too cold, too hot" cycles you sometimes get.