Posted by: @allyfish

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@roamingbull or disable weather compensation for a short period and revert to constant higher flow temperature. My 10kW Aerona is defrosting every 45 minutes or so, and as a result is not reaching target leaving water temperature. It should be 45degC at 0degC but it’s about  41. Still doing the job, but the house is a couple of degC cooler as a consequence. Log burner had just been lit to boost for the evening….

Thanks for the info.
We do have a decent log burner but what’s the point in these systems if they struggle heat homes when it gets cold or we all hoping the climate cycle will help us out with warmer weather?

2104 is set to zero and all the other figures are as your previous post with 2102@35c. Guess if I set it to a minus figure will this make any difference?

@mab I must admit, I've never looked at the state of the fins. Too bl**dy cold to be outside. I'm just assuming all is working okay. I would have thought that the 'frost protection' measure would help to some extent, but that's only active when the HP isn't heating.

@mikefl i think the frost protection is a completely independent thing, and there are settings to tweak for that. I've got that enabled as my installer didn't want to use antifreeze (contrary to grant recommendations and my preference) but having read about HPs here and elsewhere there do seem to be 2 schools of thought on antifreeze.

With frost protection enabled i think an OAT of -10 could triger the HP to come on (heating) to keep the circulating water from getting too cold.

@marvinator80 also has observed about 45min defrost intervals which adds to my thinking there's a minimum runtime - but i was out at work today when my HP was running so don't know what it was doing.

@mab I've done some brief analysis of some minute-by-minute data and the defrost cycles seem to be around 40-45 minutes apart, possibly triggered by the sensor detecting any sub-zero reading (I initially thought it needed to be below -10, but I can see cycles triggered when defrost temp is only -5); the defrost lasts between 4 and 6 minutes, but it might it ends when the defrost temp exceeds 20C as that is always the reading at the end of the 4 to 6 minute period.

@mikefl @mab, if it helps at all, here's today's data on my Grant 17kW model. The defrost cycles are depicted by the cliff edge drops in the flow temp (red) versus normal cycling where flow gradually cools towards return temp (green). DHW run between 17:00 and 18:00 hence the flow spike.

Some defrosts are about an hour apart, some closer to three so I don't think there is a system parameter that determines defrost cycle frequency.

@mikefl @aceshigh
Thanks, more data always helps. I still don't know what it uses to trigger a defrost,  but i do think that there's a minimum run time between defrosts of about 40mins. I was trying to judge what the shorter intervals in your data are - I'm guesstimating 40 - 45mins.  I did stay at home today and monitored what mine does: 

In the morning when it was cold it was icing up more slowly and de-icing every 40mins (plus de-icing time), which seemed reasonable, but as the day progressed it seemed to ice up quicker, but still stuck with 40mins runs, but as the hx clogs with ice,  the defrost temp drops, the Dt of the HP output drops from 5c down to 4, 3 or even 2c, and the power draw actually drops slightly, rather than cranking up as i thought (from 2400w with a defrost temp of -5c and output Dt of 5c to 2200w at a defrost temp of -20 and an output Dt of 2 or 3c. (OAT about 0c)).

The cop drops a bit as you might expect with a defrost temp of -20c but as I'm using the numbers from the chofu display it's hard to be precise .

I guess an OAT between 0 and 5c is about the worst case as below 0 there's less water in the air  and above 5c the hx might hold above 0c depending on power level.

I'm tempted to try running off the grid (cosy octopus) overnight to see if the low temp makes for fewer defrost cycles (forecast -8 tonight), but i won't be awake between 4 and 7am to monitor.

Disappointed with the Ashp tbh. We live in the countryside with minimal noise. 
Coldsnap is here and that quietness has been broken. 
The Ashp is running hard for minimal gains. 
Set to 35c flow rate but obviously could go higher but guess that means the Ashp will run harder. More noise. 
From 35c flow rate we are barely seeing 20c inside. And all the while blasting through 70 kw minimum per day for whole house electric. 

Had the Grant 17kw Ashp 3 years now and on RHI. Once the RHI is finished I will be seriously considering an alternative. 

@roamingbull I share your sentiments. My Grant ASHP spends most of its time in a cycle of frosting up and defrosting as the air temperature drops below +1C.  Electricity consumption goes progressively off the scale. It struggles to keep the house at 20C. I've tried various strategies such as setting timer to off through the night when temp is lowest, to only using the ASHP for UFH and then the immersion heater ( cheap rate at night) to heat the water. If I switch off at night (internal temp drops about 1C) the pump then struggles to recover this during the day, if it's still below 0C outside. My RHI ends this month - 7 years has gone quickly. That's another £110 per month to find.

Over this period what I have failed to learn is whether our unacceptably poor performance at low air temps is due to:

i) The make of pump - is it a Grant problem?

ii) Incorrect configuration of the pump's settings.

iii) Badly designed overall installation (I have UFH and am fully insulated, cavity walls, internal wall insulation, double glazing etc.., so it's not a leaky building)

iv) UK climate - high humidity (typically around 95% in West Oxon) not good for ASHPs

v) Heat pumps just don't work well at low temperatures - contrary to everything the mainstream media tells us about them.

Even on this forum with all the well documented problems (the technical details of which largely go over my head) it's clear that there are users who are happy with their pump's performance. We are told, too, that they work well through much of Europe where the installed base is bigger and longer standing in the UK. I also follow the debate in Canada where there is a gov't push to adopt ASHPs. Unless you live in Vancouver (as I once did and the climate is milder) winter temperatures can easily be -10C and below so presumably the expectation there is that ASHPs will still perform effectively. (Electricity in much of Canada is also dirt cheap compared to UK as it's often hydro power).

So what are the differences between those with good and bad ASHP experiences? I would love to know.

In 2022 January and December accounted for about 1/3rd of my total annual electricity consumption of about 10,500kWh. 2023 is shaping up to be the same. I estimate savings of about 1,500kWh p.a. if we could fix this problem.

I'm not prepared to spend any more money on heating engineer visits to try and resolve it. I long ago concluded that the ones in my area (including those on Grant's website) don't have a clue. They are traditional plumbers who know how to do gas and oil boilers but are now doing ASHPs without a real understanding of their technicalities. MCS certification just means they are certified for the paperwork around the RHI process. It's not an indicator of technical expertise. There is no gas in our village so switching to an oil boiler is the only alternative. Not a attractive choice.

Given everything I read on this forum I can't see ASHPs being an acceptable product for mass market installation in the UK. There are still too many ways in which they can fail to meet performance expectations. The typical consumer wants something that works "out of the box" like their existing gas or oil fired boiler. So do I!

 Mike

@mab Sadly, lower temps aren't helping me at all - entered the night at -7C and left at -2C.

I tried dropping target LWT yesterday (the theory being that if I could hit that LWT, HP would modulate down, and "less energy required" = "less energy taken from air" = "fewer defrosts") but that didn't help, as I still didn't hit the target overnight. Running thru the night I just about maintained 18C downstairs, and 16C upstairs, but I'm needing extra heating to feel comfortable.

Defrost every 40 or so mins. It's the recovery from defrost which is the issue I feel. I'm wondering if stopping the secondary pump during a defrost cycle would help, as I'm circulating the cooling LWT which might be cooling the radiators faster than they'd be losing heat to the rooms? It might not be a simple yes/no answer though.

@mike-patrick I couldn't agree more. It might be the case that, eventually, given lots of tweaking and work by the home owner, you get decent performance (and at the end of the day the only important factors are 1: are you comfortably warm at home, and 2: do you have any money left) but it shouldn't require this amount of effort to achieve that. It's evident that most people on this forum are doing way beyond what a typical home owner would be doing. They don't seem fit for purpose for the general public yet.

Having said that, it feels to me like the Grant has more issues than most, but maybe I think that because I have a Grant, and others are feeling equal pain. The open source monitoring site https://heatpumpmonitor.org/ doesn't appear to favour one manufacturer over another much, so maybe it is all an installation problem, and performance is just hit and miss, based on that. The industry needs to sort itself out if this is meant to be a mass replacement for on-grid gas boilers.  

Posted by: @mike-patrick

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@roamingbull I share your sentiments. My Grant ASHP spends most of its time in a cycle of frosting up and defrosting as the air temperature drops below +1C.  Electricity consumption goes progressively off the scale. It struggles to keep the house at 20C. I've tried various strategies such as setting timer to off through the night when temp is lowest, to only using the ASHP for UFH and then the immersion heater ( cheap rate at night) to heat the water. If I switch off at night (internal temp drops about 1C) the pump then struggles to recover this during the day, if it's still below 0C outside. My RHI ends this month - 7 years has gone quickly. That's another £110 per month to find.

Over this period what I have failed to learn is whether our unacceptably poor performance at low air temps is due to:

i) The make of pump - is it a Grant problem?

ii) Incorrect configuration of the pump's settings.

iii) Badly designed overall installation (I have UFH and am fully insulated, cavity walls, internal wall insulation, double glazing etc.., so it's not a leaky building)

iv) UK climate - high humidity (typically around 95% in West Oxon) not good for ASHPs

v) Heat pumps just don't work well at low temperatures - contrary to everything the mainstream media tells us about them.

 

Even on this forum with all the well documented problems (the technical details of which largely go over my head) it's clear that there are users who are happy with their pump's performance. We are told, too, that they work well through much of Europe where the installed base is bigger and longer standing in the UK. I also follow the debate in Canada where there is a gov't push to adopt ASHPs. Unless you live in Vancouver (as I once did and the climate is milder) winter temperatures can easily be -10C and below so presumably the expectation there is that ASHPs will still perform effectively. (Electricity in much of Canada is also dirt cheap compared to UK as it's often hydro power).

 

So what are the differences between those with good and bad ASHP experiences? I would love to know.

In 2022 January and December accounted for about 1/3rd of my total annual electricity consumption of about 10,500kWh. 2023 is shaping up to be the same. I estimate savings of about 1,500kWh p.a. if we could fix this problem.

I'm not prepared to spend any more money on heating engineer visits to try and resolve it. I long ago concluded that the ones in my area (including those on Grant's website) don't have a clue. They are traditional plumbers who know how to do gas and oil boilers but are now doing ASHPs without a real understanding of their technicalities. MCS certification just means they are certified for the paperwork around the RHI process. It's not an indicator of technical expertise. There is no gas in our village so switching to an oil boiler is the only alternative. Not a attractive choice.

Given everything I read on this forum I can't see ASHPs being an acceptable product for mass market installation in the UK. There are still too many ways in which they can fail to meet performance expectations. The typical consumer wants something that works "out of the box" like their existing gas or oil fired boiler. So do I!

 

 Mike

Cheers Mike for the response and clearly you have the similar thoughts to myself.

I had an Elite Heat Geek for the 2nd time prior to the cold snap last week. Told him that I was starting to warm to the system as when it was in plus figures it was working well. But it's a heating system it should work well when it's cold.

Fast forward 5 days and the ashp is blowing it's arse out for minimal gains. 

We have a Stuv logburner which belts out the heat but for me that's not the point.

It's minus 3-4c here this morning but as I have just been out dog walking it feels like a a really damp cold. We ski every year over in Banff and have Ski'd Whistler and know Vancouver quite well. Lovely place so lucky you to have lived there.  But when in Banff it's a dry cold.

First Winter we have tried the Grants commissioned strategy that it was set up and leave it alone. EHG stated it wasn't set on WC and going full steam from start up. Large Bill.

2nd Winter tried the I will put it on timed heating just like I used to on our boiler in previous house. Worked better than above and was cheaper.

Start of 3rd Winter with it set to WC and a flow rate of 35c. Like I stated above great when it's warmer but drop below the dreaded zero and hang on a minute home owner do I have to work harder for you scenario comes from the ashp.

I just can't see the masses going for these systems and tbh they aren't. 

Seems this forum obviously has become busy now that we have a cold spell which speaks volumes. Wonder what percentage are totally happy with:- 1. The temperature of their home 2. The KW usage and bills 

Lucky we have the RHI because gas is so much cheaper and you do actually get a warm house to boot without having to think how can I optimise my ashp system to actually keep the house to try and get 20c.

 

We too live in between villages with no gas so this is the route myself and the Architect went down as we have a heavily insulated house but as its modern inside not the best home to heat due to the high ceilings/glass etc.

 

So Mike what's your thoughts going forward? Stick with the Ashp and hope folk that have an ashp are looked after in the future with lower electric prices than gas or seek to install a gas tank and go back to being warm in your house?

 

 

 

Posted by: @mikefl

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@mike-patrick I couldn't agree more. It might be the case that, eventually, given lots of tweaking and work by the home owner, you get decent performance (and at the end of the day the only important factors are 1: are you comfortably warm at home, and 2: do you have any money left) but it shouldn't require this amount of effort to achieve that. It's evident that most people on this forum are doing way beyond what a typical home owner would be doing. They don't seem fit for purpose for the general public yet.

Having said that, it feels to me like the Grant has more issues than most, but maybe I think that because I have a Grant, and others are feeling equal pain. The open source monitoring site https://heatpumpmonitor.org/ doesn't appear to favour one manufacturer over another much, so maybe it is all an installation problem, and performance is just hit and miss, based on that. The industry needs to sort itself out if this is meant to be a mass replacement for on-grid gas boilers.  

People are going way and beyond which is great if you have the time and patience to tweak and analyse the graphs etc which becomes obsessive. If I had truly known that I would be going into the 3rd winter still thinking that Ashp was a huge mistake I would have buried an oil/gas tank in the garden.

And as you correctly state re having money left! Can you imagine getting to pension age knowing that you have to set aside a small mortgage to pay to barely keep warm? At least with gas you know you will be warm and it won't cost no where near the price of electric.

As we have 4 years left on RHI not only will I be thinking wonder if I can ever get this system tweak correctly but I'm as well thinking what will be my alternatives come 4 years time.