ground source vs air souce for new build

[Mur Huwcun]

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?

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.

You won’t need the DHW as hot as 60degree. We have ours at a range of 38-45 which is more than enough for a shower. The systems usually work by pumping the heating water through a coil in the hot water tank. Heat pump coil will be a much larger coil with more surface area. As mentioned they ‘suggest’ that you should periodically run the water up to 65 degree to kill legionell. You can do that with the immersion or the HP will do it by working harder for half an hour

 

[Mur Huwcun]

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

Our GSHP has suffered seriously but because of the easterly wind, it’s not the systems fault but our house and location. We don’t usually have problems with freezing temperatures it’s just the wind. Our old stone house is not airtight enough and the stone walls really need to be insulated somehow!! It’s been running a lot of hours and dropping efficiency seriousl, worst was when the loop was exiting the compressor at minus 5!!!

 

[MikeNeaverson]

Our GSHP has suffered seriously but because of the easterly wind, it’s not the systems fault but our house and location. We don’t usually have problems with freezing temperatures it’s just the wind. Our old stone house is not airtight enough and the stone walls really need to be insulated somehow!! It’s been running a lot of hours and dropping efficiency seriousl, worst was when the loop was exiting the compressor at minus 5!!!

Does GSHP get signficantly less efficient the more you run it? Presumably your energy demand might be very high in weather like this, but the units of energy in per unit of heat out should be pretty consistent?

 

[Dave645]

Our GSHP has suffered seriously but because of the easterly wind, it’s not the systems fault but our house and location. We don’t usually have problems with freezing temperatures it’s just the wind. Our old stone house is not airtight enough and the stone walls really need to be insulated somehow!! It’s been running a lot of hours and dropping efficiency seriousl, worst was when the loop was exiting the compressor at minus 5!!!

Old houses are tricky, are you happy to lose some space internally?
If so insulated plaster board maybe a option. it can be dot and dabed onto existing internal walls.

a second choice is framing timbers and insulating the framing with high grade insulation, Before plater boarding again.
Also foils can be good to help form air barriers, but they have to be sealed on all edges, if you use kingspan type insulation, expansion foam should be used on all your joints as one gap ruins the insulation value.
another area that Is often neglected is the area between floors the joints often stick into the walls and can allow air into the building also this area is often not plastered or sealed in anyway so can allow air movement that finds any cracks or holes where light fittings sit allow air into the home.
Fire places, while not often used in new houses, old houses often use open fires, these again are bad even when in use, they draw a massive amount of air into the house they often create negative air pressure in the room they are in and actively pull cold air into the home, all fireplaces should be replaced with stoves that have built in air supplies which remove the need to have vents installed in the room. This is basicly a stove with an air pipe that draws air directly into the stove from outside. So no negative air pressures in the home.

Ok air tight, this is hard it takes lots of small details, this may start in your floors. Now old houses tend to be solid floors, with zero insulation in them, you may or may not have already done this.
If hollow that are under ventilated, these are very bad for insulation as basically it’s often only the carpet that insulates the room from the cold air circulating under the floor. Again this can be improved.
Use rubber grommets on all pipes and connections that break the air barrier eg the plaster Finnish. So the sink drains all need rubber grommets, etc etc.
Air tight is only suitable for homes with heat recovery ventilation, but bathroom style units are available these are to help with old home that haven’t got full ventilation.
But making a single room air tight is no problem, if you have a cold spot in your home.
for best results you would insulate all the external walls internally if that’s your preference, but if solid walls run inside the home that link to external walls, then these are basically large thermal bridges that will also create heat loss, so you may want to insulate them even if it’s with the thinnest insulation available an alternative would be drilling out mortar near the wall joints and using expanding foam to reduce the thermal bridge and increase air tightness so the heat is less likely to travel out via those internal walls. This is maybe not the safest solution and would have to be done carefully.
The game is reduce thermal bridging anywhere you can and stop air movement where you can.
old house are always hard to do unless your willing to strip them back.

 

[chickens and wheat]

On my gshp the efficiency defiantly drops when pump is running lots of hours warming the fresh batch of broiler, as soon as demand drops efficiency climbs quickly.
When birds are bigger and heat use is sporadic I get over 4:1
Recently when working hard it dipped to 2.5:1.
First year of rhi metering is nearly over and effiency is at 3.52, going up slightly every day as I have just come out of a high demand time
£7500 worth of electric used.
Previous lpg was at least double that

 

[Dave645]

Does GSHP get signficantly less efficient the more you run it? Presumably your energy demand might be very high in weather like this, but the units of energy in per unit of heat out should be pretty consistent?

GSHP are happiest producing heated water at relatively low temperatures, and the lower the temp difference between the incoming water temp and the required the better, that said they happily push water down to below freezing.
They are differential machines taking heat out of water that’s at minus 1 is still possible you just make it minus 5 you still draw 4c of heat out. It’s just the efficiency of doing it that drops.

if anyone out there has suffered a frozen ground loop ( undersized loop) as in you have pushed the incoming waters to below freezing then it may pay to add a thermal buffer, for when the air temps rise above the ground loop, this can be as simple as an old combine radiator, that sits in the sun sat in a mini glass house, you move the water from the loop around the radiator it picks up the suns heat and or air temps and put them into your ground loop as it’s imperative you unfreeze your ground loop as fast as possible, as sub zero temps in the ground loop freeze ground water and stop the ground warming ups fast as it could with water moving through the ground.
This can also be done with solar hot water panels. And a mini pump loop that can pump water around your ground loop when the solar water panels are producing warm water. Your looking for any way to add heat into the loop that is free, a radiator is basically a high efficiency air to water heat exchanger. Even drawing water in from the loop into the heat pump through the radiator allows the radiator to pull warm airs heat into the cold water.
You could design a bypass to allow you to control when or if the radiator was used in the intake side of the heat pump water circulation system.

 

[Dave645]

On my gshp the efficiency defiantly drops when pump is running lots of hours warming the fresh batch of broiler, as soon as demand drops efficiency climbs quickly.
When birds are bigger and heat use is sporadic I get over 4:1
Recently when working hard it dipped to 2.5:1.
First year of rhi metering is nearly over and effiency is at 3.52, going up slightly every day as I have just come out of a high demand time
£7500 worth of electric used.
Previous lpg was at least double that

If You want to reduce demandsI would supplement my home with an air sealed log burning stove, if it could be tapped into that thermal store you use, then even better, on the coldest days when you see the lowest efficency you light a wood fire and boost your rooms up and boost your thermal store as well. But only if I have a good supply of wood available to me.
The other choice is as you said improve your insulation and or airtightness.
good luck with it.

 

[BBE]

GSHP are happiest producing heated water at relatively low temperatures

What would be the ideal, 30 degrees?

 

[Mur Huwcun]

Old houses are tricky, are you happy to lose some space internally?
If so insulated plaster board maybe a option. it can be dot and dabed onto existing internal walls.

Half our house is old stone part, other half is a new built extension. It’s the old part that suffered. We have solid floors with kingspan and underfloor heating on top of the original floor slab, we had enough head room. We were warned many times not to dot and dab external walls so avoided that. Did stud one gable end to square the room off or the engineered wood floor would show it up. That’s a different room so really should look at doing other gable end with 75mm kingspan between CLS timber. I did seal around any timbers going into walls but most were on joist hangers on another perling running along the wall. Chimneys are concrete lined so should not be an issue. every pipe etc was sealed and been around them checking. I have an idea where a problem could be I think it will be a rip plaster boards off job to check and or rectify!!!

 

[Dave645]

What would be the ideal, 30 degrees?

I am not actually sure what the ideal is, to be honest, I assume it can vary from heat pump to heat pump, it’s likely that they operate on a curve, based on input temps of the water in the loops and the output temp your asking for.
But I would suggest the lower the temp you can run at the better as this always keeps the temperature Difference to a minimum. Again each home will be unique, and vary because of how that heat is delivered into the home that’s why underfloor systems win out because your creating massive emitters and so you only require them to run at temps that just keep Pace with heat losses in your home. Thats the advantage of 24/7 heating the demand is only the heat loss not the ramp up from cold that normal homes with normal system do. Where the radiators can be 60c or more in fast bursts and heat just the air up quickly. I say air because bursts of heat don’t heat the home the same way that constant heating from underfloor do.

I liked the fact I can light a fire when I want, I find if I do the heating cycle slows down the heating kicks in less often, while I haven’t been cold without a fire just sat here in a tee shirt the fact I had a fire even without it being connected in any way to my heating system it reduced the number of runs my heating made by 50% over 6 hrs the warm room. Doesn’t cool the water in the underfloor system as fast so the heating system runs less.

 

[Hampton]

What is the equivalent air source pump to oil boiler?
For example, is a 16kw heat pump equivalent to a 50/70 oil boiler?
Most people I’ve spoken to say they’d need to do a full survey, but surely that survey has already been done an manifested itself in a 50/70 oil boiler?

 

[Exfarmer]

Oil boilers are not designed to run 24/7 Heat pumps are. In fact that is one query I would have on them.
We turn off our underfloor overnight because the house is too hot but I had to put my own time clock in

 

[Hampton]

Oil boilers are not designed to run 24/7 Heat pumps are. In fact that is one query I would have on them.
We turn off our underfloor overnight because the house is too hot but I had to put my own time clock in

I understand that, but surely if the previous pumber has done the workings and decided you need a 26/32 oil boiler, then surely the heat requirement of the house won’t change, so you can say “well, that needs a 12kw heat pump.
it’s got to have some relevance, surely?
What size heat pump do you have, and what size was your old boiler?

 

[Exfarmer]

I understand that, but surely if the previous pumber has done the workings and decided you need a 26/32 oil boiler, then surely the heat requirement of the house won’t change, so you can say “well, that needs a 12kw heat pump.
it’s got to have some relevance, surely?
What size heat pump do you have, and what size was your old boiler?

Sorry should have been clearer, I do not have a heat pump running the house heating. That is gas

 

[Water Wheel]

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?

Stratification ? 60 Degrees at top , 30 Degrees much lower down , cold at bottom?

 

[BillyBobs]

Some great posts really interesting, it springs to mind how on earth is the 'average home with average resident's' ever going to convert. Adding a bit more insulation in the loft is great but it's hardly going to make air source or ground source work especially with rads in the house.

I am looking at all the options as we speak and sadly the complexity makes it look like an oil boiler and invest the £30k installation cost and use the returns to pay the oil bill. Not great for the planet I agree and it doesn't feel 'right'......

 

[br jones]

Some great posts really interesting, it springs to mind how on earth is the 'average home with average resident's' ever going to convert. Adding a bit more insulation in the loft is great but it's hardly going to make air source or ground source work especially with rads in the house.

I am looking at all the options as we speak and sadly the complexity makes it look like an oil boiler and invest the £30k installation cost and use the returns to pay the oil bill. Not great for the planet I agree and it doesn't feel 'right'......

But with the boiler oil or gas you know its going to work

 

[BBE]

Stratification ? 60 Degrees at top , 30 Degrees much lower down , cold at bottom?

But if the ground source is only heating to 30 degrees, temp at top of tank must be limited to 30 degrees, how would I get DHW hot enough?

 

[Mur Huwcun]

But if the ground source is only heating to 30 degrees, temp at top of tank must be limited to 30 degrees, how would I get DHW hot enough?

The HP works harder for 30 minutes to heat the hot water, ours is set between 38 degree(cut in) and 45 (cut off). DHW will only run for 30 minutes before refering back to heating. All this can be set in the control panel