Newbie to ashp - cost is scary!

[sirpatchuk]

Hi,

 

We have had a Grant ASHP 17KW installed since May.  We have solar panels and an iboost so haven’t taken much notice of the ashp because it hasn’t been on… until now.  As it has been mild I have resisted turning the heating on, using our log burner in the evenings.  

It has now been on for four days.

It is still relatively mild… and our KWH useage has gone from 5kw a day to 25kwh a day and that is with me keeping the temperatures low.  16 at night and 18 in day.

 

We have a 1950s detached, 4 bed house in a village.

No cavity wall insulation

Good loft insulation

Large radiators upstairs.

Underfloor heating downstairs. 

This was fitted retrospectively and is plates with celotex underneath, chipboard on top and either tiles (kitchen/diner, hallway) or carpet (lounge) on top.

 

The radiators upstairs come on nicely.

The underfloor heating obviously is working as the temperature has gone up but it takes about 12 or more hours to go up 1 degree.  It doesn’t feel warm to walk on and it cools very quickly.

The KWH usage is a lot.  I don’t know how to work out the COP.

 

My installer has not been helpful.

I am worried my ASHP is not working properly as it seems to kick in and out an awful lot - every 10 minutes or so and I can see the smart meter burning my money!

We have weather compensation turned on and the flow temperature low.

 

Can anyone help please!
 

Thank you.

[sirpatchuk]

I have also seen that the patio slabs are very wet (not from rain!) around the ashp… can anyone explain is this is normal…

 

[ReedRichards]

25 kWh per day is not too terrible, it's about the same consumption as keeping a 1 kW fan heater on all the time but that is keeping your whole house warm(ish).  For comparison, my worst monthly average was 27 kWh per day for last January and I keep my house at about an average of 20 C during the day.  But different houses can have very different heat requirements so a comparison with somebody else means very little.  How were you heating the house before you got the heat pump and how much energy did that use?

 

How do you control your heat pump?  Do you use a third party programmer or is it the one Grant supplied?  

 

Your heat pump will cool the surrounding air and this will cause condensation inside the body of the heat pump.  Ideally this would be piped to a nearby drain but in the absence of any drainage system it will drip onto the patio slabs.  If your brickwork remains dry then it's probably not an issue but if your house bricks get damp then I think something needs to be done.   

[Miek]

The moisture on the slabs could be the HP entering its defrost cycle. This happens at low outdoor temperature and high humidity and reduces the COP somewhat.  If the unit is short cycling then go out and watch the rear of the heat exchanger to see if it's frosting up. 

 

[JohnMo]

Just looking at the position where your pump is mounted does not seem to comply with Grants defined clearance requirements.  Which are, to the left 100mm that looks ok, but to the right they are looking for 600mm.  The issue you could have the heat pump is constantly recycling cold air which will affect the performance.

 

I would also make sure you don't have too many zones (areas with thermostats).

 

Did the installer, also install a buffer?

[SteamyTea]

1 hour ago, sirpatchuk said:

Underfloor heating downstairs. 

This was fitted retrospectively and is plates with celotex underneath, chipboard on top and either tiles (kitchen/diner, hallway) or carpet (lounge) on top.

How much celotex underneath?  You may be heating the ground more than the house, especially in the carpeted area.

 

Your 17 kW ASHP will only run for an hour an a half a day to deliver 25 kWh if it is running on full chat.  Hopefully it is modulating down to its minimum.

As @JohnMo askes, have you a buffer.

 

I have basic Economy 7 storage heaters, the first time I turn them on they gobble energy, twice as much as when they are running.  So don't fret too much about the initial usage after turn on.

[Gone West]

2 hours ago, sirpatchuk said:

Underfloor heating downstairs. 

This was fitted retrospectively and is plates with celotex underneath, chipboard on top and either tiles (kitchen/diner, hallway) or carpet (lounge) on top.

What type of ground floor do you have. Is it a concrete slab or suspended timber. What was the thickness of insulation fitted under the UFH. Does the carpet have a low tog rating. It could be that, as @SteamyTea says you may be losing the heat to the ground.

[sirpatchuk]

@SteamyTea thank you 

The underfloor is between 75 and 100mm depending on the size of the joists.

 

We do have a buffer.

 

I am not sure what you mean by “Hopefully it is modulating down to its minimum.”

[sirpatchuk]

@Gone West

 

It is a timber frame floor with between 75 and 100mm celotex. Not sure on the tog but both the tiles and carpet stated they were suitable for UFH

[SteamyTea]

4 minutes ago, sirpatchuk said:

I am not sure what you mean by “Hopefully it is modulating down to its minimum.”

Most modern ASHP can vary the power output, the kW.

So when they return temperature gets closer to the flow temperature, the unit reduces its output.  This means it is working less hard and uses less electricity.

Older ASHP tried to produce full power and then just stop, then when there was a call for heat again, full power.  This is very inefficient.

[sirpatchuk]

1 hour ago, ReedRichards said:

25 kWh per day is not too terrible, it's about the same consumption as keeping a 1 kW fan heater on all the time but that is keeping your whole house warm(ish).  For comparison, my worst monthly average was 27 kWh per day for last January and I keep my house at about an average of 20 C during the day.  But different houses can have very different heat requirements so a comparison with somebody else means very little.  How were you heating the house before you got the heat pump and how much energy did that use?

 

How do you control your heat pump?  Do you use a third party programmer or is it the one Grant supplied?  

 

Your heat pump will cool the surrounding air and this will cause condensation inside the body of the heat pump.  Ideally this would be piped to a nearby drain but in the absence of any drainage system it will drip onto the patio slabs.  If your brickwork remains dry then it's probably not an issue but if your house bricks get damp then I think something needs to be done.   

We have a Honeywell home control system.

Each room upstairs has its own thermostat. Downstairs we have three zones, hallway, lounge, kitchen diner.

 

I would be happy using 25 kW a day on the whole. It’s just that I have my thermostat set low and it’s still mild outside. Therefore I’m just worried about you said when it is very cold.

 

With regards to the short cycling to source heat pumps produce a report to show how they’re working?

 

I cannot compare yes a seat pump to what it used to be. We moved into our house in June 2021 and it was a dilapidated oil system with no thermostats etc. we struggled in the cold last winter without using heating. In January this year we had work done to our house which included the new radiators, UFH, ashp, solar panels, iboost. It was the 1st of May we move back in and as I say haven’t had I need to turn the heating on currently, until now. We are not on mains gas so that wasn’t an option. We either chose to stick with oil goes in a source heat pump which before was going to be the best long-term solution.

[billt]

On the face of it, without much information, that doesn't seem an unreasonable energy consumption. It would translate to about 75kWh of heat energy if the heat pump had a CoP of 3.

 

We live in a 190 sq.m. detached bungalow of indeterminate age, poorly designed for energy use but with as much insulation as is practicable and our energy consumption for heating and hot water has been 100-110kWhr for the last few days. (Maximum has been 170kWh.)

 

If the installer made a reasonable survey, the fact that a 17kW heat pump was specified implies that the property has quite a high heat demand. I reckon that we could get away with a 7kw heat pump in our house.

[AliG]

I agree, it sounds like you have never had to heat this house before and so maybe the heating requirement is coming as a surprise.

 

A 1950s house with no cavity wall insulation is going to cost a lot to heat.

 

I would assume around 2000sq ft and maybe UPVC double glazing?

 

Taking a guess at wall U-Value of 0.4 floor and roof at 0.15 and windows at 1.2 gives roughly 75-100kWh a day of heat input required at 21C depending on the outside temperature. Hot water on top of this will add a further maybe 15kWh a day. Your use is  consistent with this. The 5kWh a day you were using before was around 15kWh of hot water at a COP of 3 which sounds about right.

 

I would also think it is likely that the heating flow temperature has been set to a higher temperature considering the fact that you have radiators and a poor level of insulation. This will reduce the CoP of the ASHP and make it somewhat less efficient than it might be. You might get a COP of 3 instead of 3.5 for example. It does look as if it has maybe been installed in quite a tight corner which may not help. A wider picture would help.

 

[SteamyTea]

Just to elaborate on initial high heat demand when first turning on the heating.

Here is the last couple of weeks data for my place, turned the heating on 17^th November.

Settles down to around 14 kWh/day.  This includes DHW and everything else.

 

 

[ProDave]

1950's uninsulated house, ASHP would not be my first choice and neither would UFH.

 

What was there before? 

[ReedRichards]

1 hour ago, sirpatchuk said:

We have a Honeywell home control system.

Each room upstairs has its own thermostat. Downstairs we have three zones, hallway, lounge, kitchen diner.

 

 

Does your Honeywell Home Control know that it is controlling a heat pump?  Controllers usually have a setting for "heat source" although it can be hard to find.  If there is no option to set heat pump, the next best option would be Oil Boiler.  This should force your controller to use a minimum cycle time of 15 or 20 minutes so if the heat pump turns itself off after 10 minutes then the controller won't allow it to turn on for another 5 minutes or more.  That will limit your cycle time.

[sirpatchuk]

10 minutes ago, ProDave said:

1950's uninsulated house, ASHP would not be my first choice and neither would UFH.

 

What was there before? 

When we moved in it was an old oil system.

We are not on mains gas.

Choices we’re LPG, stick with oil or ashp. We wave gone with ashp so now we need to make it work!

 

[sirpatchuk]

31 minutes ago, SteamyTea said:

Just to elaborate on initial high heat demand when first turning on the heating.

Here is the last couple of weeks data for my place, turned the heating on 17^th November.

Settles down to around 14 kWh/day.  This includes DHW and everything else.

 

 

@SteamyTea

 

This is with your storage heaters as opposed to an ashp?

 

[ReedRichards]

You may have heard that UFH and an ASHP is cheaper to run than radiators  and an ASHP.  This is likely to be true because you typically need a higher water temperature for the radiators than for the UFH.  Unfortunately a combination of UFH and radiators is no cheaper to run than all radiators.  That's unless you have a sophisticated system that can work out when the radiator zones are not demanding heat and then reduce the water flow temperature.  I doubt that your Grant heat pump is capable of that and if it was it would need to be using its own controller, not your Honeywell system.  

[Radian]

4 hours ago, sirpatchuk said:

No cavity wall insulation

 

Any particular reason? If it's brick outer leaf, 50mm cavity and concrete block inner leaf with solid plaster then you're looking at a U-value of at least 2.5W/(m²K) in a 4-bed detached so typicaly 200m² floor area, 140m² wall area. Windows and doors may average out about the same if not airtight so a constant 3.5kw loss for a 10^oC inside/outside difference.

 

Insulating the cavity with blown-in EPS beads would take the losses through the walls down to around 0.5W/(m²K) i.e. 700W although the windows would then probably be the poorest performing part. Shame to loose the benefit of your good loft insulation. I assume 400mm rockwool?

[sirpatchuk]

1 minute ago, Radian said:

 

Any particular reason? If it's brick outer leaf, 50mm cavity and concrete block inner leaf with solid plaster then you're looking at a U-value of at least 2.5W/(m²K) in a 4-bed detached so typicaly 200m² floor area, 140m² wall area. Windows and doors may average out about the same if not airtight so a constant 3.5kw loss for a 10^oC inside/outside difference.

 

Insulating the cavity with blown-in EPS beads would take the losses through the walls down to around 0.5W/(m²K) i.e. 700W although the windows would then probably be the poorest performing part. Shame to loose the benefit of your good loft insulation. I assume 400mm rockwool?

I think the reason is too many horry stories on retrospective cavity wall insulation with damp getting in the house.

It is 300mm rockwool in the loft

 

[sirpatchuk]

Even tho we are all

at school and work Monday to Friday would it make sense to leave the heating on 24/7?

 

From reading other posts maybe just have one zone downstairs as opposed to three zones..

[SteamyTea]

52 minutes ago, sirpatchuk said:

@SteamyTea

 

This is with your storage heaters as opposed to an ashp?

 

Yes, but it highlights how the whole building, as well as the air in it, needs to be heated up from a lower temperature.

 

51 minutes ago, ReedRichards said:

You may have heard that UFH and an ASHP is cheaper to run than radiators  and an ASHP

Bit more complicated than that.

It is the ratio of heated areas to heat loss areas and that governs temperature difference.

But agree that you need relatively sophisticated control and monitoring to make a mix of UFH and radiators work well.

 

 

Edited November 28, 2022 by SteamyTea

[Ferdinand]

I think to address the bills you need to focus on two things - 1) The rest of your fabric, and 2) Heat loss caused by air leakage. ie Do the other half of the full renovation you have started - arguably all the right notes but not quite in the conventional order.

 

Your ufh celotex is about the same as mine, which is 90mm. Not quite as much as I would like which would be 125-130mm, but the previous owner restored and extended my bungalow by rebuilding from 3 walls and a hole in the ground.

 

1) is going to be Cavity Wall Insulation and/or IWI or EWI.

 

If you look at CWI, I would say do it carefully and go for phenolic, as it is much more insulative.

 

2) This is the normal process we all do in renovating, about which there is much material on the site.

 

Low hanging fruit is things like gaps in the wall, draughts around pipe entries and your postbox, insulated and sealed loft hatches and backdraught shutters in fans (or Heat Recovery fans). And it goes on from there, with things like unsealed tops to cavity walls such that your cavity is linked to the loft above the insulation, and hence the outside.

 

Are your floors well sealed for air leaks?

 

Then there is less obvious stuff like escapes through your cooker hood outlet - I currently have mice coming in through the external end of mine, which means I have a direct hole to the outside from within my heated envelope.

 

You will also need to consider ventilation.

 

3) One of our members did a heat loss calculator which may help you think and prioitise.

 

Here:

 

[Radian]

2 hours ago, sirpatchuk said:

I think the reason is too many horry stories on retrospective cavity wall insulation with damp getting in the house.

It is 300mm rockwool in the loft

 

 

You are quite right to be wary, but EPS beads are generally considered to be safe. Unlike fibre based products they don't wick water, don't compact over time and still allow a degree of airflow for drying out brickwork. Being spherical beads, they fill cavities very effectively with fewer injection holes. This makes them a good choice as the contractors that do the work are usually idiots - so an idiot proof system the best one to choose. Have a look at this energy saving trust document 

 

2 hours ago, sirpatchuk said:

It is 300mm rockwool in the loft

 

So a U-value of 0.14W/m²K  whereas your empty cavity walls lose nearly eighteen times as much heat.