Posted by: @Anonymous

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WC just changes the flow temperature in line with the energy likely to be lost on lower temps outside.

Hate to burst people bubbles, but WC will never match the house heat loss. The only way to do that is by using the internal house temp and adding / removing heating as required and inorder to do that you have to either understand your own house or automate it by controlling the flow temp.

Even a well setup WC will add more or less heat, rather than the correct amount and keeps needing changes to work. When people say they are using "setback" overnight the system is either turned off or the WC never got to the correct temp anyway. Only a few HP actual turn down the WC to match the setback.

As for costing, we use 1300kwh over 150 days. The house covers over 500m2

Posted by: @uk_pete_2000

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Hate to burst people bubbles, but WC will never match the house heat l

On what do you base that assertion please?

There are plenty of people on this forum running on pure wc achieving comfortable and stable house temperatures.  Properly adjusted it works remarkably well in many, possibly most cases (maybe with a temperature limiter set a couple of degrees above target to deal with solar gain). This is not surprising because it follows the science.

@jamespa 

Yes there are a lot of people running WC  and there are a lot of people who make changes to those WC curves during the winter as the house gets too hot or cold.

WC has its place and its good in the back ground, but it should not be seen as the only reliable way of running a HP.

How many times did you adjust your WC curve ?

WC does not take  into account the number of people in the house, which equipment is turned on. Nor does it take account of wind or rain or snow. It depends on where the temp sensor is place, which direction it is facing. Solar gain.

By running on internal temp, once you reach the correct temp you take down the flow temp, say 3°. Once internal temp goes down increase 2°. After a few small changes the flow temp will match the heat required. Then as house gains / loses heat flow temp is adjusted.

Posted by: @uk_pete_2000

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By running on internal temp, once you reach the correct temp you take down the flow temp, say 3°. Once internal temp goes down increase 2°. After a few small changes the flow temp will match the heat required. Then as house gains / loses heat flow temp is adjusted

My boiler had that control, unfortunately with thick screed UFH, the boiler spent the whole time completely out of sink with the house needs. Was pretty rubbish.

But you can do that with a simple low hysterisis thermostat connected to your second set point connection. Your only issue is the whole inertia of the floor. Basically have a low and high WC curve. When you hit target temp you go on low curve and below target high curve. Running UFH floor will buffer heat quite easily for a higher than idea flow temperature. 

But why bother with the complexity a simple 0.1 hysterisis thermostat works way better. Just set flow temp to suit coldest day.

Where do you live - are you getting a big swing in outside temperature?

Posted by: @uk_pete_2000

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Yes there are a lot of people running WC  and there are a lot of people who make changes to those WC curves during the winter as the house gets too hot or cold.

How many times did you adjust your WC curve ?

I'm answer to all of that, my house is much more stable run on pure WC than it ever was on a temperature sensor (with a boiler or a heat pump).  This is without adjusting it once it was set up, unlike my trvs/thermostat which needed adjustment on average probably weekly, often daily.

You are ignoring the fact that an indoor temperature sensor is a rear view mirror, it tells your boiler or heat pump controller about the driving factors a long time after they have happened, which leads almost inevitably to instability because the house takes time to respond to the heating controllers corrective action.

Do you have any knowledge, however basic, of control theory.  That particular branch of engineering helps explain why WC is a valuable, arguably essential, in the control of heating systems and why control based on indoor temperature alone is, in most cases, flawed. Our more enlightened European neighbours realised that 20+ years ago.  We didn't and as a result have been paying perhaps 10% more for our heating than we needed to and enjoying less comfort as a result.

Posted by: @uk_pete_2000

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WC does not take  into account the number of people in the house, which equipment is turned on. Nor does it take account of wind or rain or snow. It depends on where the temp sensor is place, which direction it is facing. Solar gain

Several of those are irrelevant.  For the ones that are relevant, if you work out the energy difference due to these, it's mostly negligible compared to the heat capacity (stored energy) in the house, so these generally result mostly in  minor temperature deviations which are mostly much less than the error caused by the delay in a indoor sensor based control loop.  That's not saying they don't sometimes matter (even though often they don't), but an IAT based control loop alone won't sort it and a WC based control loop is likely to be closer.

Posted by: @uk_pete_2000

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WC has its place and its good in the back ground, but it should not be seen as the only reliable way of running a HP.

Nobody, so far as I know, says it is.  But to run a hp (or a condensing boiler for that matter) without WC as the principal control loop is sheer madness in most cases (obviously there are always some exceptions to a general rule)

I am not sure you have understood fully why WC (largely) works nor the reasons why a control based solely on internal temperature is likely to be less stable than one based substantially on WC.  If you have example situations where your assertions are correct, it would be interesting to discuss them.  As I say above there are always some exceptions to a general rule.  Maybe your house is, for some reason, an exception?

Several of those are irrelevant.  For the ones that are relevant, if you work out the energy difference due to these, it's mostly negligible compared to the heat capacity (stored energy) in the house, so these generally result mostly in  minor temperature deviations which are mostly much less than the error caused by the delay in a indoor sensor based control loop

Hi James, I would slightly disagree with this and maybe we are outliers due to our location but wind is a huge factor for us, which means I also agree with you very much that a control based system is the way to go (again for us!).

This is why I am trying to factor in IAT, OAT, weather forecast, weather actual, solar days, etc whilst giving Commander in Chief Domestic granular control if she is too hot or too cold! And as my tiny mind can only cope with so much, I am using AI to try and help me solve this problem.

Posted by: @grantmethestrength

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Several of those are irrelevant.  For the ones that are relevant, if you work out the energy difference due to these, it's mostly negligible compared to the heat capacity (stored energy) in the house, so these generally result mostly in  minor temperature deviations which are mostly much less than the error caused by the delay in a indoor sensor based control loop

Hi James, I would slightly disagree with this and maybe we are outliers due to our location but wind is a huge factor for us, which means I also agree with you very much that a control based system is the way to go (again for us!).

This is why I am trying to factor in IAT, OAT, weather forecast, weather actual, solar days, etc whilst giving Commander in Chief Domestic granular control if she is too hot or too cold! And as my tiny mind can only cope with so much, I am using AI to try and help me solve this problem.

 

This is how I would set it up

Firstly a WC curve tuned to house. Start at 20 Deg outside and min flow temp of heat pump  20 or 25. End point at your design outside temp say -3 or -5, for radiators set to 45 and UFH at 35. For the windy days where the house temperature drops more than expected, the Grant/Chofu heat pump has a set of terminals for a second set point, connect a wireless thermostat that. Set the set point 1 or 2 deg above the normal WC base temp. Computherm do a nice variable hysterisis thermostat Q20RF can get from Amazon.

So your general heating is all done via WC, if the house drops in temperature your second set point comes into play and adds heat for you automatically.

Tuning

In heating season, set second point thermostat out of the way set to max, tune only once every 24 hrs, if to warm tune only the high flow temp setting down 1 Deg, repeat every 24 hrs. Until comfortable, then bring in thermostat , you will need to run hysterisis to suit your comfort, under and overshoot.

No weather forecast which are usually crap, sensors that decides to go off line, and a system no-one can fix except you. Smart stuff has a place, but it isn't for control of heating systems.  We were supposed to 30kWh of yesterday, but it was foggy all day, got nearer 3kWh. Shelly H&T also went offline for no reason for a couple of hours then came back on, but only use to to log data, that will be going as well pretty soon.

Sorry what you are doing is fine for monitoring only, but utter rubbish for heating control, it just isn't robust enough. Been there, done it, got the bloody tee shirt, wife utterly pissed off. KISS wins every time, heating has never run better, getting rid of the useless tatt, additional pumps, no buffers, no mixers, no internet anything, you don't even need a thermostat really.

Make sure your outdoor sensor on the ASHP doesn't get affected by the sun would be my input.

@johnmo 

Having never had a gas boiler, I can not commit on that. All I understand about them is that they run high temp to warm up a house, within 15 mins and they turn off / on to maintain that temp. 

I (and my parents, when I was growing up) had electric UFH, so it's a concept I understand.

Posted by: @Anonymous

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Basically have a low and high WC curve. When you hit target temp you go on low curve and below target high curve

Is that "target" not the internal temp of the house ?

We live in the west Midlands, so no real swings in outside temp

@grantmethestrength With respect to weather forecasts, I used to have my "DHW hour" fixed at 3-4pm, for obvious reasons, but have changed it to look at the hourly weather forecast for hours between 10:00 and 14:00, and schedule the DHW for 1 hour after the peak in that period. So far, it's never picked an hour other than 15:00 😀  Maybe I can go later in summer, but in summer it's not that important. Especially now.

@jamespa 

Posted by: @jamespa

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You are ignoring the fact that an indoor temperature sensor is a rear view mirror

Yes the basic principle is correct, but by using that mirror and knowledge you know that if the temp is falling / gaining then x amount of heat will correct it.

Posted by: @jamespa

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Do you have any knowledge, however basic, of control theory

To some extent yes, but then there are lots of differences in control a HP. My way is one, yours is another.

Posted by: @jamespa

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Our more enlightened European neighbours realised that 20+ years ago.

So on that principle we should never have progressed beyond the stone age. Our neighbours have different house, different heating needs, different weather.

Just because it works for them, does not mean it will work for us

Posted by: @jamespa

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Several of those are irrelevant.

To you, and others, they may be, to us they can make a difference as out house is very well insulated and air tight.

Posted by: @jamespa

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I am not sure you have understood fully why WC (largely) works nor the reasons why a control based solely on internal temperature is likely to be less stable than one based substantially on WC

I understand WC very well thank you and know why/how it is used and to me it never does what it says on the box.

Even looking back over old forum listing, people (and I was one), would change those settings one way or another and they would work till the weather got too warm or cold and off people would go and change them. Hopefully after some time things settled down and it worked, or they where happy to have the house warmer anyway and lost interest.

People would talk about "setback" as a way of resetting the internal temp, ready for the next day's heating.

So once again, internal temp comes up as the deciding factor. How you get to that temp and maintain it will always be debated, but all heating / cooling is done by deciding that internal temp. So why not start and work with that, rather than trying to match the external temp to what it might be/not be to achieve it

@johnmo Interesting, I wasn’t sure what the second setpoint was for but I like this strategy! 

In heating season, set second point thermostat out of the way set to max, tune only once every 24 hrs, if to warm tune only the high flow temp setting down 1 Deg, repeat every 24 hrs. Until comfortable, then bring in thermostat , you will need to run hysterisis to suit your comfort, under and overshoot.

I am a bit confused by this though. Do you mean connect the second thermostat to the second set point terminals (22-23 I believe). Then set it to say 30c so it doesn’t trigger, then tune my main WC down (which we are pretty happy so far at about 34c @-3c and 23c@16c, so that would be my start point, but as it was installed at the start of Jan we still have some tweaking to do). Once happy bring the second stat into play and set it at a lower temp so say 18c so if the house drops to 18c that second WC curve kicks in?

Do you know the params to set the second set point?

Also how does this switch back to regular WC?

Is this controlled by the LWT or room temp?

The hysteresis you mention is that param 21-41 Hysteresis of water set point in Heating and DHW?

Thanks in advance.

Am I right in thinking the second set point is configured using the zone 2 settings?