ground source vs air souce for new build

lost_in_paperwork · Feb 10, 2021

nev12345 said:
We are currently on second fix in our new house. We inherited a prepayment meter which has been fine for the build but now need to change it for when the air source starts up properly.

Is there a cleverer way to run airsource? We are underfloor heating downstars and radiators upstairs. The house is built to modern building regs standards, at least 150mm insulation in the floor, cavity and roof. Would it be more efficient to have an economy 7 tarriff for example, and run the heat pump with generally cheaper electric? What have others found?

We also have underfloor heating downstairs and radiators upstairs with air source. Works really well but it is quite costly on the electric front during the cold winter months. We also have solar panels which help on a bright sunny winters day and the solar runs does all our hot water in the summer so we actually turn the air source off Apr - Oct. So, over a 12 month average, the electric bill is probably about right but is quite painful during the winter.

Mur Huwcun · Feb 10, 2021

We had a bit of a bad day yesterday when the smart meter informed us we used £8 of electricity!! It’s the wind from the east that does it to this house and the GSHP has to wirk a lot harder.

MikeNeaverson · Feb 10, 2021

If you use £8 of any fuel on one of the coldest days of the year I’d say that’s pretty good going?

Exfarmer · Feb 10, 2021

My average use for gas during January was £3 a day and that is for quite a large house

Mur Huwcun · Feb 10, 2021

nev12345 said:
If you use £8 of any fuel on one of the coldest days of the year I’d say that’s pretty good going?

Well I wasn’t alarmed by it as we use about £3 in the summer anyhow but we’re usually averaging at around £5-6 per day since November.

Just checked, according to the devil (smart meter) we’re at aroud £30-35 a week. I woukd like it to be less but only half the house is a new build, it’s the old stone part that guzzles up the power!! We had a 2 bed terraced house before that was £80 a month annual average on dual fuel. We’re now on about £120 per month electric only with a house three times the size, shed, garage, extra freezer etc etc

Hampton · Feb 11, 2021

Timbo said:
If you're going with a heat pump type design, radiators wont work due to the system only running at 40-50c not the usual 60-70c as with a boiler. You'd also have a large thermal store so you can run the heatpump full bore using the cheapest source of energy - eg solar during the day or off peak at night.

I thought the trade off was to put in radiators 30% bigger than the old ones?

Timbo · Feb 11, 2021

Hampton said:
I thought the trade off was to put in radiators 30% bigger than the old ones?

Underfloor as a rule in a new build. The op asked about retrofitting a heat pump in an existing property tho.

Hampton · Feb 11, 2021

Timbo said:
Underfloor as a rule in a new build. The op asked about retrofitting a heat pump in an existing property tho.

That’s what I meant. If you were retrofitting then you need to swap existing radiators for rads 30% bigger to make up for them water in them being approx 25C colder (assuming you run rads at full pelt)

rogeriko · Feb 12, 2021

Delta T for radiators at 70 deg is 1.5. Delta T for radiators at 30 deg is 0.5. Look up any radiator calculator. In other words your radiators have to be 3 times larger for a heat pump, thats 300% larger. Underfloor heating only for heat pumps.

Hampton · Feb 12, 2021

rogeriko said:
Delta T for radiators at 70 deg is 1.5. Delta T for radiators at 30 deg is 0.5. Look up any radiator calculator. In other words your radiators have to be 3 times larger for a heat pump, thats 300% larger. Underfloor heating only for heat pumps.

True, but remember standard boiler will be on a timer, whereas pump is constant, therefore I think 3x would be overkill as the ambient temperature will be higher, compared to the cold/heat burst cycle you get with conventional heating.
You are right though, if in doubt go bigger. The flip side is that they may not fit in your rooms.

Dave645 · Feb 13, 2021

Hampton said:
True, but remember standard boiler will be on a timer, whereas pump is constant, therefore I think 3x would be overkill as the ambient temperature will be higher, compared to the cold/heat burst cycle you get with conventional heating.
You are right though, if in doubt go bigger. The flip side is that they may not fit in your rooms.

Heat demand is actually the factor that dictates radiators size, near passive houses built air tight, reqiuire so little heat that as you said, normal sized radiators will do the job.
My underfloor heating is Hardly above room temp.
On the curve if it’s 4c outside my heating set at 21c for room temp, the water will be at 23-24c and it will run the actual GSHP only a few times a day, I suspect if I had wanted radiators, I would find that normal sized ones running 24/7 as you said, would have been more than fine baring in mind even though I have underfloor through out my house 75% of its carpeted, only the bathrooms on the upper floors are tile the rest are carpet, to be honest we have a 4.2tog on our beds all year round any more and you can be over warm. Minus 10 c outside still using the same 4.2 togg bedding.
Yes the heating will have automatically ramped up but I have the heat curve set at it’s near minimum the underfloor I doubt ever reach 30c Even when it was -10 c outside.

the only factor that pushes a well built house to use underfloor is a safety net, and efficiency, the GSHP like long and slow runs, so the shear volume of water in the system helps it be efficient but that can be cancelled out with an over sized heat pump, mine was 10kw in a 300m2 home on 3 floors, and it’s over sized. The heating knocks off too soon it would have been better If it was Half the size running twice as long. It’s better for the ground loop and the efficiency of the actual GSHP. When heat is taken out of the loop slowly that means the loop can replace the heat as fast as it’s taken so the temp of incoming water is maintained more easily, and the fact the heat pump is running for longer means it gets past the start up inefficiency they are a bit like Fluorescent tubes great when on, very cheap to run but relatively expensive to start up.
I will note plumbers are required to use your heat calc likley provided by the building regs guys, hopefully these have got better at coming up with an accurate estimate, of heat loads.
The most over looked part of many builds is solar gain, even when it’s below freezing outside solar can heat me 700L of water to 30c in a day, if it’s nice and sunny.
That and you can feel the warmth coming in via the windows, the down side is without sun shading of those windows in summer it can also work against you. The simple fix is overhangs for south facing windows and actually west facing ones as well. I now use external blinds as I have no simple way to shade my south facing windows. They work great.

I look forward to the time when battery prices for home storage fall then I will link a large solar electric system to them and my home and I will be able to go as close to off grid as possible. That will never be possible with oil or gas. So those looking at going heat pumps, put that in your plus side of pros and cons, 10kw of solar is about £5-6k installed the only barrier left is battery storage costs when they fall to £50 kwhr even if that’s for second hand car batteries, then 50kwhrs of storage offers plenty to run my house for 2days on average without any solar activity or charging. My guess is for £7.5k I can basically go off grid, and likely be able to charge an EV for free as well, solar only makes sense when you can consume the majourity of the energy you generate. My guess is it will take the rest of this decade for Second hand car batteries to hit the market in the numbers needed to push them under the £50/kwh price. Unless we get a new battery tech break through that creates cheap grid storage that trickles down to consumers at that price.
while buying £2.5k of batteries sounds expensive, it will allow you to make use of solar that will only cost you 2p/kwhr not the 12-15p the national grid charge. My house averages out at £3.80 per day for all my electric that includes all my heating and hot water as well. If I go solar that drops to as little as 54p per day. So a 2year payback on the battery or 6 years on the whole kit, with an estimated 20 years life on the system even using second hand car batteries.

Exfarmer · Feb 13, 2021

Dave645 said:
Heat demand is actually the factor that dictates radiators size, near passive houses built air tight, reqiuire so little heat that as you said, normal sized radiators will do the job.
My underfloor heating is Hardly above room temp.
On the curve if it’s 4c outside my heating set at 21c for room temp, the water will be at 23-24c and it will run the actual GSHP only a few times a day, I suspect if I had wanted radiators, I would find that normal sized ones running 24/7 as you said, would have been more than fine baring in mind even though I have underfloor through out my house 75% of its carpeted, only the bathrooms on the upper floors are tile the rest are carpet, to be honest we have a 4.2tog on our beds all year round any more and you can be over warm. Minus 10 c outside still using the same 4.2 togg bedding.
Yes the heating will have automatically ramped up but I have the heat curve set at it’s near minimum the underfloor I doubt ever reach 30c Even when it was -10 c outside.

the only factor that pushes a well built house to use underfloor is a safety net, and efficiency, the GSHP like long and slow runs, so the shear volume of water in the system helps it be efficient but that can be cancelled out with an over sized heat pump, mine was 10kw in a 300m2 home on 3 floors, and it’s over sized. The heating knocks off too soon it would have been better If it was Half the size running twice as long. It’s better for the ground loop and the efficiency of the actual GSHP. When heat is taken out of the loop slowly that means the loop can replace the heat as fast as it’s taken so the temp of incoming water is maintained more easily, and the fact the heat pump is running for longer means it gets past the start up inefficiency they are a bit like Fluorescent tubes great when on, very cheap to run but relatively expensive to start up.
I will note plumbers are required to use your heat calc likley provided by the building regs guys, hopefully these have got better at coming up with an accurate estimate, of heat loads.
The most over looked part of many builds is solar gain, even when it’s below freezing outside solar can heat me 700L of water to 30c in a day, if it’s nice and sunny.
That and you can feel the warmth coming in via the windows, the down side is without sun shading of those windows in summer it can also work against you. The simple fix is overhangs for south facing windows and actually west facing ones as well. I now use external blinds as I have no simple way to shade my south facing windows. They work great.

I look forward to the time when battery prices for home storage fall then I will link a large solar electric system to them and my home and I will be able to go as close to off grid as possible. That will never be possible with oil or gas. So those looking at going heat pumps, put that in your plus side of pros and cons, 10kw of solar is about £5-6k installed the only barrier left is battery storage costs when they fall to £50 kwhr even if that’s for second hand car batteries, then 50kwhrs of storage offers plenty to run my house for 2days on average without any solar activity or charging. My guess is for £7.5k I can basically go off grid, and likely be able to charge an EV for free as well, solar only makes sense when you can consume the majourity of the energy you generate. My guess is it will take the rest of this decade for Second hand car batteries to hit the market in the numbers needed to push them under the £50/kwh price. Unless we get a new battery tech break through that creates cheap grid storage that trickles down to consumers at that price.
while buying £2.5k of batteries sounds expensive, it will allow you to make use of solar that will only cost you 2p/kwhr not the 12-15p the national grid charge. My house averages out at £3.80 per day for all my electric that includes all my heating and hot water as well. If I go solar that drops to as little as 54p per day. So a 2year payback on the battery or 6 years on the whole kit, with an estimated 20 years life on the system even using second hand car batteries.

Dave
a very good post , very interesting. A very good case for GSHP
A couple of points , I am afraid you are grossly underestimating the cost of your solar power. I am afraid experience suggests a figure far closer to 5p and possibly more is far more realistic for a domestic set up. You have not factored in inverter repair/ replacement nor panel replacement I am certain. Sadly, experience suggests that these 10/12/25 year warranties are not worth the paper they are printed on. There are one or two makers I would trust but capital costs for their Inverters/ panels are far higher and thus give a production cost closer to 10-12p per unit.
Secondly thermal gain in these houses on a hot day is a serious issue , which we experience not just through glass but also black walls, even on a very cold day when the sun appears our glass fronted rooms can soon get very warm with no heating. I cannot believe that anyone can live in an air tight house and stay healthy!

ollie989898 · Feb 13, 2021

br jones said:
Just built a 4 bed 160 sqm place ,ultra insulated ,last year it used £200 worth of gas for hot water and heating ,

This is the reality.

Insulate a new build and heat it with oil or gas and you will spend fudge all in reality. I absolutely hate being too hot in a house though, especially at night.

Dave645 · Feb 13, 2021

Exfarmer said:
Dave
a very good post , very interesting. A very good case for GSHP
A couple of points , I am afraid you are grossly underestimating the cost of your solar power. I am afraid experience suggests a figure far closer to 5p and possibly more is far more realistic for a domestic set up. You have not factored in inverter repair/ replacement nor panel replacement I am certain. Sadly, experience suggests that these 10/12/25 year warranties are not worth the paper they are printed on. There are one or two makers I would trust but capital costs for their Inverters/ panels are far higher and thus give a production cost closer to 10-12p per unit.
Secondly thermal gain in these houses on a hot day is a serious issue , which we experience not just through glass but also black walls, even on a very cold day when the sun appears our glass fronted rooms can soon get very warm with no heating. I cannot believe that anyone can live in an air tight house and stay healthy!

Numbers will always vary from install to install, for solar, my area with 10kw of panels over 20 years it can be as low as 2p but I except your correct that a more realistic price should be used by anyone planning an install that should be calculated by the installer, a 7.5 year payback would require a large % as close to 100% as possible of self consumption and me saving 10p unit over the grid price that’s available. It’s the batteries that make the difference that and having the consumption requirements like owning an EV. Make sense.
The more self consumption you can manage the more your saving. Pay back times will vary user to user.

most export prices are about 4-5p per unit. So solar for home users only makes sense for users planning to self consume over 50%, this is why grid companies are fitting it because that can charge consumers full price for solar.

ok on avaerage a 10kw solar will produces 8700kwhrs of electric in the uk your area may differ, if I can self consume 50% that means that saves me £615 plus export at 4p then that’s a 6 years payback. On solar just solar.
If I can up that to 75% self consumption then the numbers improve again so do if the grid price rises. If you hit 75% self consumption then your pushing at £1000 plus saving per year, and a payback of 7.5 years on the whole system including batteries, if self consumption can be over 75%, large cheap in home batteries alloware the key to making solar pay well.
Bare in mind the actual production panels can make will fall over time but are not going to be useless after 20 years they can push on for 30 years plus, but at some point newer more efficient panels will make the replacement of them a good choice.

the worst case is you use zero of your home production and export at grid set prices of 4-5p per unit. Then payback for solar is way out at 14 years just to reclaim your outlay, on solar panels.
Self consumption where your saying 12-18p a unit is the only factor to make solar a good quick investment, get an EV and a home battery of a good size 50kwh plus then your cooking on gas. You can even go to special tariffs and buy and sell electric wholesale. (This is possible now) charge batteries on cheap night rate and day rate electric prices and sell it at peak demand times.

My house is air tight it’s air test was the lowest ever tested in my area at the time, at a 1, when it was tested, but the whole volume of air in the house is replaced with clean filtered fresh air every 2hrs, via a heat recovery unit. That is rated at 95% efficient.
I use a ground pipe on its intake so it brings in nice cooled air even on the hottest days and it warms it on the coldest days on average air coming in to my house doesn’t vary in temperature much all year around. It sits at about 12c that’s before the heat recovery unit does its job. With a summer bypass.

Dave645 · Feb 13, 2021

ollie989898 said:
This is the reality.

Insulate a new build and heat it with oil or gas and you will spend fudge all in reality. I absolutely hate being too hot in a house though, especially at night.

It’s true, no mains gas in my area.
That said £200 per year can be misleading it can vary on lots of factors, number of people demanding hot water, and how warm you heat a home to, location, other renewables etc.
I will also note my heating system has earned me £275 per month for the last 7 years the net heating cost to my house is an income not a cost my electric is £1500 total, that includes my heating costs for hot water and heating to a nice 21c 24/7 and every other electric use in the house including tumble drying cloths, I made £1800 per year on top because I get £3300 per year with a GSHP.
That makes, that gas bill look expensive to me just saying.

I also hate being warm at night I tune my heating down at night and it’s the reason I carpeted my bedrooms it cuts the heat delivered by underfloor systems into the air basicly the thicker the carpet the smaller the output the underfloor delivers to the room. My bedrooms are closers to 18-19 at night with the knock back in the heating and its normally cooler outside at night.

honeyend · Feb 13, 2021

Dave645 said:
Heat demand is actually the factor that dictates radiators size, near passive houses built air tight, reqiuire so little heat that as you said, normal sized radiators will do the job.
My underfloor heating is Hardly above room temp.
On the curve if it’s 4c outside my heating set at 21c for room temp, the water will be at 23-24c and it will run the actual GSHP only a few times a day, I suspect if I had wanted radiators, I would find that normal sized ones running 24/7 as you said, would have been more than fine baring in mind even though I have underfloor through out my house 75% of its carpeted, only the bathrooms on the upper floors are tile the rest are carpet, to be honest we have a 4.2tog on our beds all year round any more and you can be over warm. Minus 10 c outside still using the same 4.2 togg bedding.

This how live with our air source. Most rooms run at 19-20C, the heating went off on Saturday night due to a problem, and it took two days for the house to get to 16C in the unheated rooms, the most exposed room which the utility with no extra heating only fell to 12C after four days.
When it went back on because of the demand, it overheated everywhere, so it when up to 21C. We have block and beam floors and traditional plaster walls to increase the thermal mass.
For four days we resorted to plug in electric heaters for the main room, which is a large open plan kitchen sitting room, with a vaulted ceiling, and a 4kw of heaters kept at 21C without them being on all the time. I liked the idea of solid fuel fire in a house living area, but unless you have a way to move the heat out, you would be cooking in an hour, because of the insulation
We went for air source because if it didn't work out it would be easier to replace. Our neighbours had a pellet system, and they have gone on to oil as even with a new well insulated house it was just too expensive to run.

Mur Huwcun · Feb 13, 2021

Dave645 said:
Heat demand is actually the factor that dictates radiators size, near passive houses built air tight, reqiuire so little heat that as you said, normal sized radiators will do the job.
My underfloor heating is Hardly above room temp.
On the curve if it’s 4c outside my heating set at 21c for room temp, the water will be at 23-24c and it will run the actual GSHP only a few times a day, I suspect if I had wanted radiators, I would find that normal sized ones running 24/7 as you said, would have been more than fine baring in mind even though I have underfloor through out my house 75% of its carpeted

Wish ours could cope like that! With this stupid Easterly wind over last week it’s been running about 18-20hrs a day and still struggles to keep house above 18 degree!!! Bring on the rain I say

BBE · Feb 14, 2021

Need some help understanding ground source and water temperatures. I've a well insulated conversion with underfloor heating throughout. Currently have an oil boiler that heats the thermal store to about 60 degrees, this is required for hot water. The water for the heating only ever needs to be 30 degrees (probably even less) yet its fed from the same thermal store. How does the heat pump work so you have water a 30 degrees for heating and 60 degrees for hot water?

MikeNeaverson · Feb 14, 2021

I know that our hot water cylinder will run at significantly less than 60C and the immersion heater is programmed to come on once a week for legionella control.

MikeNeaverson · Feb 14, 2021

How have others found their airsource energy coefficients over the last week in the cold?

ground source vs air souce for new build

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