Posted by: @jamespa

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Boilers, incidentally, frequently cycle like mad! 

I think part of my problem is that I have idea in my own head what is 'acceptable' cycling per hour. At the moment it's 0c here. Once it's got to the flow temp of around 35c, electric use drops to about 1.5kw per hour and the compressor stops around 3 times an hour for 10 mins. Does that seem reasonable?

The other thing I've noticed today is the Room Influence setting has no effect whatsoever on flow temps. They are the same whether it's set to 1% or 100%. Maybe it's something that was disabled by design when installed along with the heatmisers. The flow temps only change when I manually change the target room temp on the front of the ASHP. Two steps forward, one back 😔 

Posted by: @barrovian1963

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At the moment it's 0c here. Once it's got to the flow temp of around 35c, electric use drops to about 1.5kw per hour and the compressor stops around 3 times an hour for 10 mins. Does that seem reasonable?

3 times per hour is reasonable.  Are you sure it isn't doing defrost rather than cycling because of overcapacity?

Posted by: @barrovian1963

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The flow temps only change when I manually change the target room temp on the front of the ASHP. Two steps forward, one back 😔 

As long as they follow the weather compensation I wouldn't worry for now,  You probably won't want room influence anyway.  If they aren't following the WC then you need to look into the settings further.

Posted by: @jamespa

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As long as they follow the weather compensation I wouldn't worry for now,  You probably won't want room influence anyway.  If they aren't following the WC then you need to look into the settings further.

With the outdoor temp at 0c yesterday I was able to fine tune the heating curve and offset to get a flow temp of bang on 35c with an indoor target temp of 20c. Opened up all the heat misers and TRVs and let the ASHP run. At 35c/0c the consumption settled at about 3kw per hour as opposed to almost 7kw per hour before adjustments. During the day as the outdoor temp rose I noted the flow temp decreasing. Not huge differences, but differences all the same. I'm assuming therefore that some sort of WC is going on. Would you agree? 

I'm not sure if the ASHP is still trying to match the Heatmisers set temp of 25c (set at that to ensure they continue to call for heat) or is running to keep its own target temp of 20c. The only reference I have for room temp is the heatmisers themselves and I'm not convinced they are all that accurate. I may have to invest in some small thermometers to dot around the house to try and get a better idea. It may be that I have to resort to using the heatmisers to stop the house getting too hot. Not ideal, but I've got to work with what I've got. 

But since midnight based on my back on my back of a fag packet calculations, and on my cheap overnight rate I've spent about £1.00 less. Not a lot, but it all adds up. Plus, the ASHP compressor sounds a lot happier and running at a reduced speed. No obvious cycling overnight (except defrost cycle) but will monitor that as the temp rises during the day. So overall  I'm very happy. With your help @jamespa, I feel like I've achieved more this weekend than I have done in the last three years so again, thank you so much for your time. 

Posted by: @barrovian1963

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With the outdoor temp at 0c yesterday I was able to fine tune the heating curve and offset to get a flow temp of bang on 35c with an indoor target temp of 20c. Opened up all the heat misers and TRVs and let the ASHP run. At 35c/0c the consumption settled at about 3kw per hour as opposed to almost 7kw per hour before adjustments. During the day as the outdoor temp rose I noted the flow temp decreasing. Not huge differences, but differences all the same. I'm assuming therefore that some sort of WC is going on. Would you agree? 

I would agree with your conclusion on the last point.  When you say 'target temp', thats set on the fujitsu controller in the plant room?

Posted by: @barrovian1963

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I'm not sure if the ASHP is still trying to match the Heatmisers set temp of 25c (set at that to ensure they continue to call for heat) or is running to keep its own target temp of 20c.

Hopefully neither!  Hopefully its simply adjusting the flow temperature according to the outside temperature, without caring about the inside temperature.  Thats how 'pure' WC works, and in many/most cases ignoring indoor temperature works well.

I haven't managed to find the user manual for your particular product so I cant advise on specific settings, only general principles.  If you have a link to it perhaps you could post it alternatively post a couple of pictures of the part dealing with weather compensation.

Posted by: @barrovian1963

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I may have to invest in some small thermometers to dot around the house to try and get a better idea. It may be that I have to resort to using the heatmisers to stop the house getting too hot. Not ideal, but I've got to work with what I've got. 

Except if you get high solar gain, that shouldn't be necessary if the WC curve is correct.  It would be good to see the relevant part of the manual so I can comment on any other settings you might need to change.

Posted by: @barrovian1963

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Plus, the ASHP compressor sounds a lot happier and running at a reduced speed.

Thats a good sign in itself.  You will probably find it cruises along at low speed most of the time except after a defrost, when and immediately after heating DHW and is its particularly cold.  If it does that you are where you should be and hopefully money will be saved..

@jamespa

Posted by: @jamespa

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When you say 'target temp', thats set on the fujitsu controller in the plant room?

Yes. From the front panel.

Posted by: @jamespa

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Hopefully neither!  Hopefully its simply adjusting the flow temperature according to the outside temperature, without caring about the inside temperature.  Thats how 'pure' WC works, and in many/most cases ignoring indoor temperature works well.

I think the temp setting on the Fujitsu front panel is affecting flow temps. As an experiment, I upped the target temp to 25c and noted the flow temp had jumped quite dramatically to 44c.  Dropped it back to 20c and the flow temp dropped back to around 35c. One thing that has occurred to me is that Room Influence setting. I'll try adjusting that again and see if it makes any difference now. Half the problem for me is remembering what settings do what and getting to grips with the terminology The front controller is very basic and isn't particularly intuitive (well, it isn't for me anyway)

Posted by: @jamespa

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I haven't managed to find the user manual for your particular product so I cant advise on specific settings, only general principles.

I'll attach a pdf of the user manual, which covers basic day to day use and the installation manual which is where I found the more detailed settings relating to heat curves, offsets and room influence. I'm sure it will make much more sense to you than me.

As ever, thank you.

@jamespa

Posted by: @jamespa

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When you say 'target temp', thats set on the fujitsu controller in the plant room?

Yes. From the front panel.

Posted by: @jamespa

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Hopefully neither!  Hopefully its simply adjusting the flow temperature according to the outside temperature, without caring about the inside temperature.  Thats how 'pure' WC works, and in many/most cases ignoring indoor temperature works well.

I think the temp setting on the Fujitsu front panel is affecting flow temps. As an experiment, I upped the target temp to 25c and noted the flow temp had jumped quite dramatically to 44c.  Dropped it back to 20c and the flow temp dropped back to around 35c. One thing that has occurred to me is that Room Influence setting. I'll try adjusting that again and see if it makes any difference now. Half the problem for me is remembering what settings do what and getting to grips with the terminology The front controller is very basic and isn't particularly intuitive (well, it isn't for me anyway)

Posted by: @jamespa

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I haven't managed to find the user manual for your particular product so I cant advise on specific settings, only general principles.

I'll attach a pdf of the user manual, which covers basic day to day use and the installation manual which is where I found the more detailed settings relating to heat curves, offsets and room influence. I'm sure it will make much more sense to you than me.

As ever, thank you.

PS. I'm away for a few days now, so If I don't respond to your reply straight away, I'm not ignoring you. 

Posted by: @barrovian1963

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I think the temp setting on the Fujitsu front panel is affecting flow temps. As an experiment, I upped the target temp to 25c and noted the flow temp had jumped quite dramatically to 44c.  

I think thats expected with the way this particular model works, see page 49 of the manual.  Adjusting the room temperature 'set point' shifts the WC curve, resulting in a different target flow temperature for any given OAT.  

However that is not the same to it responding to the actual measured indoor temperature.  Parameter 750 (I think) controls whether it responds to the measured indoor temperature, and since this is the temperature at the controller which is (wrongly) located in the basement, you want it not to respond. 

Unfortunately the description in the manual (which is very similar to the one in the Ideal manual) is ambiguous.   I think you want this set to 1% but if its currently set to 100% maybe leave it and watch the behaviour over time.  

My Vaillant works the same way but the manual is a bit clearer, so Im hoping the manufacturers that have adopted this approach have in fact implemented the same methodology, but I cant be sure because of the ambiguity of the fujitsu manual. 

Hope that helps.

@jamespa Back at home now so thought I'd just update with how things are going.

Posted by: @jamespa

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I think thats expected with the way this particular model works, see page 49 of the manual.  Adjusting the room temperature 'set point' shifts the WC curve, resulting in a different target flow temperature for any given OAT.  

Posted by: @jamespa

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However that is not the same to it responding to the actual measured indoor temperature.  Parameter 750 (I think) controls whether it responds to the measured indoor temperature, and since this is the temperature at the controller which is (wrongly) located in the basement, you want it not to respond. 

Having gone back throughout the day, as the outside temp varied, so did the flow temp. Not by much, but it definitely changed so it 'seems' like some sort of WC is going on. Maybe 🤔

Posted by: @jamespa

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Unfortunately the description in the manual (which is very similar to the one in the Ideal manual) is ambiguous.   I think you want this set to 1% but if its currently set to 100% maybe leave it and watch the behaviour over time.  

When the outside air temp was around 0%, Heating Curve at 0.5, offset at 0.5 the flow temp set point sat at about 35c. Once up to temp the compressor settled into a pattern of 15 mins on, 10 mins off. I didn't see the ASHP saying temp reached ( the room set point of 20c) it just kept running. The heat misers showed a room temp higher than 20c, but I've never been convinced of their accuracy so that adds another layer of uncertainty. 

As the outdoor temps have risen, the flow temps have decreased but the ASHP keeps running but now cycles more frequently, 10 mins on, ten mins off. 

I think what's happening is that the heat misers are in control. If just one calls for heat then the ASHP is ignoring its own room temp setpoint and trying to get to the temp set on the heatmisers so I've had to reduce the target temps on them to stop the unnecessary cycling. Not ideal, but overall better than it was before I started pressing buttons last week.

It seems like I'm stuck with the heatmisers being in control. One thing I'm considering is taking the actuators off all save one of the downstairs ufh heating circuits so they are open at all times. That way I think I'd effectively end up with downstairs being controlled by one thermostat. Or, I look at trying to find someone willing to source a Fujitsu room thermostat and retrofit it to my system, if that's even possible. 

My electricity consumption has certainly reduced and the house is much more comfortable. I've learned a lot about my system and you've given me the confidence to try different settings. I started out wanting to find a way of stopping the ASHP running at 7.2kw every time it switched on and we've achieved that. I could not have done it without you. So again, thank you. 

Posted by: @barrovian1963

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Having gone back throughout the day, as the outside temp varied, so did the flow temp. Not by much, but it definitely changed so it 'seems' like some sort of WC is going on. Maybe 🤔

I cant remember what your WC curve showed, but it should follow that.  This is only a few degrees change given that OAT doesnt vary that much

Posted by: @barrovian1963

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When the outside air temp was around 0%, Heating Curve at 0.5, offset at 0.5 the flow temp set point sat at about 35c. Once up to temp the compressor settled into a pattern of 15 mins on, 10 mins off. I didn't see the ASHP saying temp reached ( the room set point of 20c) it just kept running.

With room influence disabled it wont, it doesnt care about the internal temperature.  On/Off running is because the heat pump is oversized, it cant modulate down far enough to match the demand with a steady output, so switches on and off instead.  In other words its doing exactly what is expected!

Posted by: @barrovian1963

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As the outdoor temps have risen, the flow temps have decreased but the ASHP keeps running but now cycles more frequently, 10 mins on, ten mins off. 

exactly as expected, there will be more cycling at higher OATs because the demand is even less so the heat pump needs to spend more time off in order to reduce the average output.

Posted by: @barrovian1963

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It seems like I'm stuck with the heatmisers being in control. One thing I'm considering is taking the actuators off all save one of the downstairs ufh heating circuits so they are open at all times. That way I think I'd effectively end up with downstairs being controlled by one thermostat. Or, I look at trying to find someone willing to source a Fujitsu room thermostat and retrofit it to my system, if that's even possible. 

Im not sure why you say are are stuck with the heatimisers in control, you dont want to be.  Nor do you need the downstairs to be controlled by a thermostat.   You want the heat pump to be running on weather compensation with no room influence at all and either no further control (because you have adjusted the WC curve so it delivers the right house temperature) or external control only to shut down a part of the house suffering from excess solar gain (ie set well above the desired temperature). 

I know it seems counterintuitive that, in this mode, the heat pump doesn't know about the inside temperature (or at least doesnt respond to it, but it really doesn't need to.  All it needs to do is compensate for the loss from the house which is determined by the outside temperature.  My heat pump runs on pure weather compensation taking no notice at all of the inside temperature.  Its by far the most comfortable heating I have ever had, and more comfortable than when I had the same heat pump set to take notice of inside temperature.

Posted by: @barrovian1963

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Or, I look at trying to find someone willing to source a Fujitsu room thermostat and retrofit it to my system, if that's even possible. 

Or move the controller which is likely connected to the heat pump by a two wire bus?

Or just not bother as above.

Posted by: @barrovian1963

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My electricity consumption has certainly reduced and the house is much more comfortable. I've learned a lot about my system and you've given me the confidence to try different settings. I started out wanting to find a way of stopping the ASHP running at 7.2kw every time it switched on and we've achieved that. I could not have done it without you. So again, thank you. 

Thats good to hear.  If you keep the faith I think its highly likely you can get this running efficiently on pure weather compensation with influence from room thermostats, heat misers etc., without spending any more money.  With heat pumps KISS is very definitely the motto.  What you wont avoid is cycling, the heat pump is too large so cannot modulate down far enough.  It might be a good idea once you have got it fully tuned to explore parameters which increase the cycle period (you cant change the on/off ratio, thats determined by the ratio of demand to minimum output).

Feel free to post more, this feels like it could become a success

Posted by: @barrovian1963

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One thing I'm considering is taking the actuators off all save one of the downstairs ufh heating circuits so they are open at all times

Do you have a Heatmiser wiring centre that controls the actuators it’s a beige box with red lights on it would be above your ufh manifold.  

if so all of your Heatmiser thermostats are linked to this and open the actuators.  As you said you can remove all of the actuators as they hold the circuits closed.  Once removed all of the circuits will be open and when one of the thermostats calls for heat all of the ufh circuits will be engaged this will reduce cycling.

@jamespa Good morning, and once again I'm amazed at how generous you are with your time and willingness to help. Thank you.

Posted by: @jamespa

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I cant remember what your WC curve showed, but it should follow that.  This is only a few degrees change given that OAT doesnt vary that much

I got it down to a heatpump set temp of 35c at 0c outside with a heat curve setting of 0.5 and off set at 0.5

Posted by: @jamespa

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With room influence disabled it wont, it doesnt care about the internal temperature.  On/Off running is because the heat pump is oversized, it cant modulate down far enough to match the demand with a steady output, so switches on and off instead.  In other words its doing exactly what is expected!

Should there ever come a point where the ASHP decides it's reached temp and stops or does it just keep going? I'm just trying to understand what sort of behaviour to expect. For the past three years I've been used to it running at full pelt then turning off when the Heatmisers tell it to. 

Posted by: @jamespa

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exactly as expected, there will be more cycling at higher OATs because the demand is even less so the heat pump needs to spend more time off in order to reduce the average output.

This is part of my problem I think. I'm fretting about it constantly switching on and off and having read so much about how cycling is 'bad'. But I guess I just need to remember your fridge analogy.

Posted by: @jamespa

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Im not sure why you say are are stuck with the heatimisers in control, you dont want to be.  Nor do you need the downstairs to be controlled by a thermostat.   You want the heat pump to be running on weather compensation with no room influence at all and either no further control (because you have adjusted the WC curve so it delivers the right house temperature) or external control only to shut down a part of the house suffering from excess solar gain (ie set well above the desired temperature). 

I know it seems counterintuitive that, in this mode, the heat pump doesn't know about the inside temperature (or at least doesnt respond to it, but it really doesn't need to.  All it needs to do is compensate for the loss from the house which is determined by the outside temperature.  My heat pump runs on pure weather compensation taking no notice at all of the inside temperature.  Its by far the most comfortable heating I have ever had, and more comfortable than when I had the same heat pump set to take notice of inside temperature.

Again, I think this comes back to my concerns about cycling and trying to avoid it, but I've just got to get it into my head that it's unavoidable due to the size of the ASHP. Everything you read says it's 'a bad thing', but there are so many opinions as to how to define excessive cycling its hard for a complete novice like me to see the wood for the trees. 

Posted by: @jamespa

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Or move the controller which is likely connected to the heat pump by a two wire bus?

I don't have a controller as such. The only direct control is via the front panel on the indoor unit in the plant room. The only external controls are the various heatmisers dotted around the house.

Posted by: @jamespa

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It might be a good idea once you have got it fully tuned to explore parameters which increase the cycle period (you cant change the on/off ratio, thats determined by the ratio of demand to minimum output).

Oh lordy! More parameters to explore? What sort of thing should I be looking for before I start randomly pressing buttons? 

Once again, thank you for all your advice and support. It's been invaluable and has made me less afraid of the ASHP and I can already see the benefits both in comfort and cost. 

Regards,

John.