We’ve very recently had an air sourced heat pump (ASHP) fitted and there are lots of gems on the forum (and elsewhere) which I have been looking at to remind me of some key things to consider.
There are a few items which I can’t see an answer to and as yet don’t know the pros and cons about.
Circulation pump - on demand or continuous?
Heating - set a schedule or not?
Setback - useful overnight or not?
Quiet Mode - does this affect efficiency?
DHW - schedule and reheat or just schedule?
I realise a few things are personal preference but there will be some who have more knowledge from experience.
Best answer by hydrosam
@BPLightlog welcome to heat pump ownership, a world of joy and frustration at the same time! :-)
Circulation pump - I settled with on demand. But this is mainly because my heat pump is so oversized, and normally only needs to be on for half the day. With a properly sized system, continous should be the way to go.
Heating - set a schedule or not. Depends on two things. House occupation, if you are in the house most of the time I’d run the system continuously with a well dialled in weather compensation curve, if the house is only occupied morning and evening, then a scehdule makes sense. The second consideration is… You guessed it, its whether the heat pump is sized correctly. If the system is significantly over-sized you’ll want to operate a schedule to avoid the house over-heating. Our house is occupied 24/7 (work from home) but I have a schedule to turn off mid morning and then on again mid-afternoon till 9pm, otherwise the house over heats most of the time (below 0C being the exception).
Setback - useful overnight or not. If it’s a Daikin you might find the start up surge wakes you up, as Jason mentioned. Daikin’s have an annoying habit of running at 100% on every startup to get up to temperature, it can do this often if the pump is running during regular defrost operations (typically +5C to -2C outside). If you are sensitive to noise it’ll bother you. If not, then run a set back. There are ways round this through diving deep into the settings, but that’s not for this thread, and is Daikin specific.
Quiet Mode - does this affect efficiency. Yes. Typically it restricts output capacity by limiting the fan speed, so efficiency will take a dive. There are caveats to this, and some people have found it useful during DHW cycles on better quality heat pumps like Vaillants, but not something to explore at this stage I’d suggest.
DHW - schedule and reheat or just schedule? Depends on DHW usage. As Jason said, early afternoon will get the best efficiency due to warmest part of the day, however if you have a ToU tariff and cheap electricity overnight it may make sense to make use of this. The other consideration is how quickly you get through the water and what you set your reheat settings at. I have a large 300l tank, I’ve settled on reheat only with a 20C hysteresis. We heat to 48C, and when the tank stat reads 28C we can just about get away with a short shower (top of the tank is more like 35C), and it’ll reheat the tank. Sometimes it’ll reheat the tank every couple of days, sometimes twice a day, it depends what the teenagers are up to. The house is well insulated enough we don’t ever miss the heating being off for an hour. If you don’t have a well insulated house you might miss an hours heat during a cold day. However if you are running the heating continuously it’s likely the thermal mass of the building will see you through that time.
Hope that gives you something to think about. *note much of this is also applicable to running a system boiler efficiently.
I haven’t made any change to the way the circulation pump runs so I assume it runs on demand.
I’ve tried various schedules for running the heating but now just have it targeting a constant indoor temperature 24/7.
Overnight setback - not at the moment. We have a lower tariff for 6 hours overnight and it is of course colder at night. Takes a bit of getting used to but bedroom radiator is sized to keep that room cooler than the rest of the house.
Quiet mode - never tried it.
DHW - I have schedule and reheat. Heated at night during cheap rate and again at midday, when peak solar from our roof. It very occasionally triggers the reheat when tank sensor detects lower than 30 degrees.
I'm actually testing quiet mode overnight and although I’ll need to try in mid winter, this morning was near freezing and it worked well. I think it just adjusts the top end running from what I’ve read so far.
Circulation pump - on demand or continuous? As far as I am aware ours runs continuously, but I haven’t delved deep to understand this in detail
Heating - set a schedule or not? We use our wall stat just as an on off switch with a high temp shut off for those days where sunshine makes the house too warm. We run weather comp with a target of 20°, with high shut off being 22°
Setback - useful overnight or not? We don’t use this and just let the house cool down between 2100and 0500. I did try set back in early days but found it was waking us up when triggered overnight
Quiet Mode - does this affect efficiency? Yes definitely - it murdered efficiency! Tried it this winter but gave up straight away
DHW - schedule and reheat or just schedule? We run schedule 1300-1500hrs to take account of warmest part of day and solar PV. Programme allows for reheat if DHW temp drops below 38°, but that rarely happens. At last service DHW temp suggested at 48° rather than 50° which has made a small improvement in efficiency
hope that helps and feel free to ask further questions.
Circulation pump - I settled with on demand. But this is mainly because my heat pump is so oversized, and normally only needs to be on for half the day. With a properly sized system, continous should be the way to go.
Heating - set a schedule or not. Depends on two things. House occupation, if you are in the house most of the time I’d run the system continuously with a well dialled in weather compensation curve, if the house is only occupied morning and evening, then a scehdule makes sense. The second consideration is… You guessed it, its whether the heat pump is sized correctly. If the system is significantly over-sized you’ll want to operate a schedule to avoid the house over-heating. Our house is occupied 24/7 (work from home) but I have a schedule to turn off mid morning and then on again mid-afternoon till 9pm, otherwise the house over heats most of the time (below 0C being the exception).
Setback - useful overnight or not. If it’s a Daikin you might find the start up surge wakes you up, as Jason mentioned. Daikin’s have an annoying habit of running at 100% on every startup to get up to temperature, it can do this often if the pump is running during regular defrost operations (typically +5C to -2C outside). If you are sensitive to noise it’ll bother you. If not, then run a set back. There are ways round this through diving deep into the settings, but that’s not for this thread, and is Daikin specific.
Quiet Mode - does this affect efficiency. Yes. Typically it restricts output capacity by limiting the fan speed, so efficiency will take a dive. There are caveats to this, and some people have found it useful during DHW cycles on better quality heat pumps like Vaillants, but not something to explore at this stage I’d suggest.
DHW - schedule and reheat or just schedule? Depends on DHW usage. As Jason said, early afternoon will get the best efficiency due to warmest part of the day, however if you have a ToU tariff and cheap electricity overnight it may make sense to make use of this. The other consideration is how quickly you get through the water and what you set your reheat settings at. I have a large 300l tank, I’ve settled on reheat only with a 20C hysteresis. We heat to 48C, and when the tank stat reads 28C we can just about get away with a short shower (top of the tank is more like 35C), and it’ll reheat the tank. Sometimes it’ll reheat the tank every couple of days, sometimes twice a day, it depends what the teenagers are up to. The house is well insulated enough we don’t ever miss the heating being off for an hour. If you don’t have a well insulated house you might miss an hours heat during a cold day. However if you are running the heating continuously it’s likely the thermal mass of the building will see you through that time.
Hope that gives you something to think about. *note much of this is also applicable to running a system boiler efficiently.
Thanks all - very useful and as I expected, although I had researched the whole topic, I’m learning as I go. We have a Daikin 9kW Monobloc unit which just matches the 8.7kW heat loss reported on our survey. I did a Heat punk calculation and came up with a similar figure. We have a void under the house (due to local geology) and I think that is one factor which makes the figure higher than I expected. Without tearing up all the floorboards, I can’t see how to insulate that part any better.
The Daikin is running well - I’m almost pleased with the recent freezing temperatures first thing as it allows me to see and test how it all copes. We run the house at 21deg all day and set 19 deg overnight which seems to fit our needs.
The DHW seems to be always hot enough even though I’ve set it to heat once first thing. It heats to 45 deg and seems to maintain well. The monitoring point is mid-tank (180L) and so perhaps it actually reaches a little higher.
I'm trying the quiet mode first thing (midnight to 7am) and I can imagine a lower efficiency at that point but it does the job early on and working with the Cosy tariff it fits the need. We seem to be getting a CoP of between 3.2 and 4.8 (depending on factors) but I’ll know better once I get my monitoring system fitted - ESPAltherma based on an ESP32 Arduino dev board feeding into Home Assistant.
No doubt I will have a few more hurdles to overcome but I’m quite happy so far.
@hydrosam good to hear from you. Have you managed to sort out a service contract now Reina’s obligation has ended? I am minded to go with the full beans Daikin service pack for £360, given the problems we had last year
My plan moved from Reina to Daikin early on in the trial, as Reina were only brought in to deal with the issues with my setup. Servicing was carried out by an approved sub-contractor, there isn’t much to the service but they knew what they were talking about, and turned up when they said they would.
The Daikin deal is a little more expensive but it covers cost of parts if they are needed. Depends on level of reassurance you want.
I am not renewing with Daikin, I had considered going direct to their sub-contractor for servicing, but I’ve decided to swap out the pump for a small heat pump, 7kw from a different brand. Knowing what I know about heat pumps now, I want something properly sized to my house.
@jason.lewis I’ve bought the Gold service contract from Daikin, paying monthly starting on 1st Jan. They’ve been taking the money but I’m yet to hear from them regarding the “initial inspection” which should be done in the first 90 days, which will be up next week. Hmm. Cutting it fine!
@juliamc that’s not ideal. Mine is due a service in May so I best get my skates on.
looking around locally I can only find service offers at around £250-300 which is disappointing, hence the gold package looks good value and offers peace of mind in the event of another breakdown
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