ASHP - Maximising Efficiency

nxdmsandkaskdjaqd

This will be my first season with a ASHP so looking for some advice on the best way to get the most efficiency out of the system.

The property is a 200sq m bungalow, with a large south facing family room with a large bi-folds (lots of solar gain).  There are 4 bedrooms, 2 bathrooms.  All rooms have their own heatmiser temperature controls.  Under floor heating and the building is well insulated and air tight.

Based on previous properties we like the living area to be 20C during the day, rising to 21 for the evening.  Bedrooms are fine at 20C.

So some questions:

Setback.

What time should I start the overnight setback, given the lag in the UFH? 

Then what time should the setback returned to normal for the morning. 

Also what temperature should I reduce the overnight setback to?  We have had a few cold nights of late (5C) and temperature in the house only dropped to 19C.

Zoning

Should I zone or not?  The large family room with bio-flolds is a potential heat gain during the day and loss at night.  With zoning being off work because of this?

Flow Temperature

As low as possible, starting point 30C

Balancing the UFH

I have the design criteria for the UFH, so I should check that I have a temperature drop of 7C on each of the circuits.  Is 7C the right drop?

matelodave

I have a 140m2 bungalow with a heatpump and an overlay underfloor heating. Each room has its own heating loop controlled by a room stat which controls the temp for that room.

After 14 years of fiddling and faffing I've come to the conclusion that its better to set all the stats to a degree or two above the desired temp so they operate as a high limit control. By adjusting the flow temps and weather compensation curve to match the heating requirements (means some tweaking of the room flow rates), we are much more comfortable. I found that zoning caused the heatpump to short cycle which increases it power consumption.

The problem we find with our living room which has high solar gain is that when the sun goes down and the temperature plummets, if the floor is cold then the room temp can take a long time to recover whilst the floor heats up again. We only set back by around three degrees at around 9pm and bring it back up again around 6am however with very low flow temps (ours runs at around 33-35 degree (weather compensation slope 30 at 15degrees  increasing to 42 at -5) it can still take to nearly lunch time to get the room temps back up if it gets everso cold outside.

What we do find it that we dont need 20+ degrees. 18 is about right for most of the rooms with a bit more in the lounge. Having underfloor heating means that there are no cold draughts and the temperature is even everywhere. Being home all day means it idles away for most of the day (and in the depth of winter sometimes most of the night)

In the end I found its best to turn it down util you are not quite warm enough and then make minor adustments untill you get it about right. As the response time is very slow because of the low temperature differential (deltaT) and the thermal inertial of your underfloor heating then you really need a day or two between tweaks to be able to gauge the effects.

We went away in the depths of winter just after we got ours installed and I turned it down to low - it took two days for the place to reheat. If we go away now I dont turn it down so low and use the holiday mode on the stats to get the place reheating 24 hours before we return. 

In the end, its just a case of tweaking, waiting to se what effect it had and then another minor tweak - keep notes on what you did, when you did it and what effect it had. Ideally take inside, outside and power consumption measurements as well so you can determine whether you are making things better or worse.

Our average annual power consumption 7200kwh* = approx 20kwh a day but in the summer its down to 8-10 and in the worst of the winter we've manage as high as 55kwh in a day.

*its been as high as 8600 and as low as 6000 but the 14 year average is 7200. 

nxdmsandkaskdjaqd

matelodave said: re zoning

How do you manage the living room temperature on days when the sun is out with no zoning?  Does the living room not get over heated with the sun and UFH?

FreeBear

nxdmsandkaskdjaqd said:

matelodave said: re zoning

How do you manage the living room temperature on days when the sun is out with no zoning?  Does the living room not get over heated with the sun and UFH?

As the room temperature rises, the ΔT between UFH and room drops. As heat output is a function of ΔT, the amount of heat being put out by the UFH drops. When running very low flow temperatures, the whole system kinda self regulates.

michaels

matelodave said:

I have a 140m2 bungalow with a heatpump and an overlay underfloor heating. Each room has its own heating loop controlled by a room stat which controls the temp for that room.

After 14 years of fiddling and faffing I've come to the conclusion that its better to set all the stats to a degree or two above the desired temp so they operate as a high limit control. By adjusting the flow temps and weather compensation curve to match the heating requirements (means some tweaking of the room flow rates), we are much more comfortable. I found that zoning caused the heatpump to short cycle which increases it power consumption.

The problem we find with our living room which has high solar gain is that when the sun goes down and the temperature plummets, if the floor is cold then the room temp can take a long time to recover whilst the floor heats up again. We only set back by around three degrees at around 9pm and bring it back up again around 6am however with very low flow temps (ours runs at around 33-35 degree (weather compensation slope 30 at 15degrees  increasing to 42 at -5) it can still take to nearly lunch time to get the room temps back up if it gets everso cold outside.

What we do find it that we dont need 20+ degrees. 18 is about right for most of the rooms with a bit more in the lounge. Having underfloor heating means that there are no cold draughts and the temperature is even everywhere. Being home all day means it idles away for most of the day (and in the depth of winter sometimes most of the night)

In the end I found its best to turn it down util you are not quite warm enough and then make minor adustments untill you get it about right. As the response time is very slow because of the low temperature differential (deltaT) and the thermal inertial of your underfloor heating then you really need a day or two between tweaks to be able to gauge the effects.

We went away in the depths of winter just after we got ours installed and I turned it down to low - it took two days for the place to reheat. If we go away now I dont turn it down so low and use the holiday mode on the stats to get the place reheating 24 hours before we return. 

In the end, its just a case of tweaking, waiting to se what effect it had and then another minor tweak - keep notes on what you did, when you did it and what effect it had. Ideally take inside, outside and power consumption measurements as well so you can determine whether you are making things better or worse.

Our average annual power consumption 7200kwh* = approx 20kwh a day but in the summer its down to 8-10 and in the worst of the winter we've manage as high as 55kwh in a day.

*its been as high as 8600 and as low as 6000 but the 14 year average is 7200. 

is that 55kwh of electricity use or 55kwh of heat pump output?  If the former, do you know the split between heat, hot water and other electricity use?  Thanks

matelodave

nxdmsandkaskdjaqd said:

matelodave said: re zoning

How do you manage the living room temperature on days when the sun is out with no zoning?  Does the living room not get over heated with the sun and UFH?

As I said, I set the zone stat in the lounge to a degree or two over the desired temp so it will close down the floor in the lounge when the sun shines and you do get a dip in temp when the sun goes down and the heating comes up.

matelodave

michaels said:

matelodave said:

I have a 140m2 bungalow with a heatpump and an overlay underfloor heating. Each room has its own heating loop controlled by a room stat which controls the temp for that room.

After 14 years of fiddling and faffing I've come to the conclusion that its better to set all the stats to a degree or two above the desired temp so they operate as a high limit control. By adjusting the flow temps and weather compensation curve to match the heating requirements (means some tweaking of the room flow rates), we are much more comfortable. I found that zoning caused the heatpump to short cycle which increases it power consumption.

The problem we find with our living room which has high solar gain is that when the sun goes down and the temperature plummets, if the floor is cold then the room temp can take a long time to recover whilst the floor heats up again. We only set back by around three degrees at around 9pm and bring it back up again around 6am however with very low flow temps (ours runs at around 33-35 degree (weather compensation slope 30 at 15degrees  increasing to 42 at -5) it can still take to nearly lunch time to get the room temps back up if it gets everso cold outside.

What we do find it that we dont need 20+ degrees. 18 is about right for most of the rooms with a bit more in the lounge. Having underfloor heating means that there are no cold draughts and the temperature is even everywhere. Being home all day means it idles away for most of the day (and in the depth of winter sometimes most of the night)

In the end I found its best to turn it down util you are not quite warm enough and then make minor adustments untill you get it about right. As the response time is very slow because of the low temperature differential (deltaT) and the thermal inertial of your underfloor heating then you really need a day or two between tweaks to be able to gauge the effects.

We went away in the depths of winter just after we got ours installed and I turned it down to low - it took two days for the place to reheat. If we go away now I dont turn it down so low and use the holiday mode on the stats to get the place reheating 24 hours before we return. 

In the end, its just a case of tweaking, waiting to se what effect it had and then another minor tweak - keep notes on what you did, when you did it and what effect it had. Ideally take inside, outside and power consumption measurements as well so you can determine whether you are making things better or worse.

Our average annual power consumption 7200kwh* = approx 20kwh a day but in the summer its down to 8-10 and in the worst of the winter we've manage as high as 55kwh in a day.

*its been as high as 8600 and as low as 6000 but the 14 year average is 7200. 

is that 55kwh of electricity use or 55kwh of heat pump output?  If the former, do you know the split between heat, hot water and other electricity use?  Thanks

My electricity use is around 8-10 kwh a day through the summer and probably a bit more in the winter (incl hot water) so 55kwh in a day probably equates to around 45kwh used by the heatmpump for heating (its very rare for the temp to drop so low as to require that amount of heat) but daily energy use  in the winter of around 35-45kwh isn't unusual.

My EPC reckons we should use around 12750kwh for heating and 2800kwh for hot water (ie around 15000kwh a year) and I reckon the heatpump uses about 4000-4500kwh out of our annual 7200kwh. I can't find my MCS certificate at the moment to find out what it says we should be generating.

I really only monitor my energy use on a weekly basis and its total household energy, I don't have the facility anymore to monitor the heatpump in isolation so its a bit random. Some of the higher days will include the use of the washing machine and tumbledryer which can put our daily use up to 15kwh or more  on a heavy washing day.

Looking back over my smart meter data the worst I've managed for a whole day was Saturday 9th January 2021 when we chewed through a total of 65.25 kwh but most days its more like 40-45kwh when its cold.

data for the past Januarys (which tend to be a bit colder than even December) are 2021 = 1373kwh, 2022 = 1028kwh, 2023 = 1135kwh, 2024 = 955kwh.

We aren't particularly frugal with our heating or use of appliances. For instance its pretty unlikely that any washing will ever get hung out, even during the summer, so its virtually all tumble dried. Some of our hobbies use a reasonable amount of leccy - my 3d printer for instance, a couple of computer are on all day and we keep a dehumidifier running in the garden office from about November to March to keep it dry.

Likewise the bungalow isn't exactly open plan but the lounge and dining room have a archway between them, its got a big hall and kitchen and trying to get my wife to keep doors shut is a lost battle although we do try to keep the bedroom doors shut and their temps are reduced to around 17 degrees.

We could do more but its not worth the arguments, especially over room temperatures. I prefer to pay a bit more for a quiet life.

if you understand the concept of "degree days" etc then here is a plot of my weekly energy use v weekly degree days although there will be some inaccuracy due to the fact it also includes other stuff as well as heating but it's pretty well representative of how well my consumption tracks the temperature. The green zero line is the forecast based on my heating history and the blue one my actual consumption. (the degree data is based on my local area)


for info on degree days have a look here - https://www.degreedays.net/introduction and if you want to gather your own put your location into here - https://www.degreedays.net/

akwexavante

I've had an ASHP for two winters now and another just around the corner.

For me, i've found that the more insulation the better.  Over the first winter, my house wasn't insulated as well as it could/should have been and leaked like a sieve. In time for the second winter, i insulated the house myself and plugged up all leaks.  What a difference this has made to my energy bill and the stability of comfort.

Keep doors closed, especially at the bottom of the stairs to slow down/stop all the heat downstairs all going up the stairs.

I've found that lowering the temperature on the room stat overnight and or when the house is empty at other times to be false economy, as the ASHP afterwards has to work hard and can take quite a while to push the temperature back up again.  With this, i've learned to set the room stat at a temperature i'm happy with and walk away and leave it 24/7.

I question the effectiveness of heat build up through windows on sunny days, which can turn the ASHP off.  The ASHP has to work hard and takes time to stabilise things again afterwards.  Little if anything gained.

I have a multi fuel stove and have to pay for fuel (logs etc) and again the ASHP goes off and has to work hard and takes time to stabilise things again afterwards........... convinced the ASHP is cheaper to run than the stove.  If the fire fodder was free though, things would be different!!   I suffer regular power cuts, so the stove is important to have.

Take time to adjust to having an ASHP as a heating system, it's a very different animal to get to grips with, be patient.

Spies

Why not try running full weather compensation, not using the room thermostat at all? That way solar gain won't screw things up. 

MP1995

Spies said:

Why not try running full weather compensation, not using the room thermostat at all? That way solar gain won't screw things up. 

I'm not sure outside temp is linked to solar gain and how many sun facing windows different houses have.

Reed_Richards

I'm not sure how not using the room thermostat can stop solar gain from overheating those rooms which benefit/suffer from it. 

Now if you have one thermostat in a room that controls whether a heat source is on/off for an entire zone then any external factor that influences the temperature in that room can mess things up.  That could be an open window or external door.  Or it could be solar gain or a secondary heat source.  Maybe that's what @Spies means?