I have a Grant Aerona 290 15.5 kW with the Smart Controller.  I have radiators throughout the house and no underfloor heating.  I am running on Shift = 1 and Heating Curve = 0.8.  Obviously, the right numbers depend on how well the house is insulated.  

Our system was installed in August and I soon discovered that the water circulation pump was on all the time.  Since the heating was hardly on at all, this seemed to impose unnecessary wear on the pump and waste electricity.  In the summer, one solution is to reduce the temperature at which Winter Mode activates.  However, that is not appropriate in winter.

Grant recommends that Pump Blockade should be set to No, if you are using weather compensation.  In the colder months, I think this makes sense.  Ideally, the heat pump compressor should be running 24 hours per day, so the water pump must be designed to handle that level of work.  When the compressor turns off, the water is still hot, so it is good to keep it circulating to impart the maximum energy to the house.  It also enables the heat pump to measure the temperature of the water and thus to decide when to turn back on again.  

We are not using a set back temperature at night for a couple of reasons:

1. We are on the Intelligent Octopus Go tariff, which costs only 7p at night, compared to almost 30p during the day.  Therefore, it makes sense to make the house as warm as possible while the cost is a quarter of what it is during the day.
2. By running at the same temperature all day, we minimise the required flow temperature, which again keeps our costs down.

If you prefer your bedrooms to be colder, maybe you could use flow regulating valves or lock shield valves to reduce the water flow in those rooms?

I ran it last winter 24/7 with no stat. Feeling smug, I told Grant that for over 14 weeks my heat pump only cycled once. That was met with Whoaa! that could wear out the compressor, please let it cycle a few times per day. So I started to question compressors and pumps running 24/7 and the overall feedback I received was that its not a good idea. There should be a balance between efficiency and longevity.

I put the stat back because the WC still requires constant attention. This is despite using a combination of curves, circuit temp correction, and set point correction to fine tune it. The stat acts like Grant intended, a safety net if the internal temp climbs too high. For example, yesterday was a steady 5 degrees outside, and 21 inside. When the outside temp dropped to 3 degrees, my internal temp shot up to 23. If I fine tuned that out, then it would cause issues with the start of the day. Even Grant having looked at my Data concede that it will be an ongoing issue for me so the stat was put back.

If only I could find a way of having pump blockade on without it shutting down the 2-port valve.

@unsure you make an interesting point about longevity.  Most of what I have read and heard says that compressors are worn out most by starting up and not by continuous running.  Apparently, they are designed to handle so many thousand on/off cycles.  If you run a compressor for 24 hours per day and it stops once for 10 minutes per hour, then that reduces its run time by 16%, which is pretty marginal.  On the other hand, it adds 24 start stop cycles.   

Do you have any concrete evidence for the view that continuous compressor run time is a problem?

I don't quite follow your comment about weather compensation.  You said that you managed to run your compressor continuously for 14 weeks, which is very impressive.  You also said that you can't adjust weather compensation to keep a constant indoor temperature.  Does that mean that you spent 14 weeks continually tweaking it? 

My experience is that weather compensation cannot hold to an exact temperature, because of various factors that WC cannot detect - e.g. solar gain on a sunny day, closing the curtains at night, a gaggle of relatives arriving and leaving the front door wide open while they bring in all their luggage...

Having said that, I have found that weather compensation alone can probably keep the temperature within 1C of the target. It is harder when the outside temperature varies a lot, but I have adjusted the Shift and Heating Curve and I think I am fairly close now.  The key is to get the slope right and not just set the flow temperature at a specific outdoor temperature using Shift.

@grahamF

Posted by: @grahamf

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Do you have any concrete evidence for the view that continuous compressor run time is a problem?

Only the comments I've received from old school HVAC engineers in the states and nordic countries. There is a logic to what they're saying, but I'd be interested if any scientific evidence exists.

Posted by: @grahamf

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 Does that mean that you spent 14 weeks continually tweaking it? 

Yes ! My first heat pump experience during the winter. A kind of obsession creeps in with graph paper, calculations, and reaching heat pump nirvana. Then reality sets in. No work gets done around the house, waking in the night to tweak the EcoNET app whilst in bed annoys the partner, and you find a new mental health medical condition starts to emerge.....Heat Pump Mania.

Posted by: @grahamf

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My experience is that weather compensation cannot hold to an exact temperature, because of various factors that WC cannot detect - e.g. solar gain on a sunny day, closing the curtains at night, a gaggle of relatives arriving and leaving the front door wide open while they bring in all their luggage...

Having said that, I have found that weather compensation alone can probably keep the temperature within 1C of the target. It is harder when the outside temperature varies a lot, but I have adjusted the Shift and Heating Curve and I think I am fairly close now.  The key is to get the slope right and not just set the flow temperature at a specific outdoor temperature using Shift.

I came to the same conclusion as you, hence why I reinstated the stat to prevent temp runaway. You can fine tune the HC with 'Decreasing Fixed Water Temperature',  'Circuit Temp. Correction', and 'Set Point temp. Correction' in Service settings > 0000 > Main Heat Source and Circuit 1. It takes a lot of time and experimenting, but I did achieve some good results during Jan/ Feb this year. But once the temp swings during the day and the sun is strong it all goes to pot.

I'm confident that in the near future with AI and a few more sensors, we will be able to enter the room temperature and it will remain constant without have to touch the controls for at least a..................day 🙂

Posted by: @unsure

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the sun is strong it all goes to pot.

Posted by: @unsure

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I'm confident that in the near future with AI and a few more sensors, we will be able to enter the room temperature and it will remain constant without have to touch the controls for at least a..................day 🙂

 

Not unless either you allow the AI to turn on cooling when the sun is strong, or you give it control of the windows and curtains also!

No amount of fiddling with heating controls alone will deal with sunny days at the ends of the season when the potential solar gain well exceeds the loss yet there is still a big diurnal swing.  Perversely this problem gets worse for lower loss houses because there isnt the constant drag of heat escaping.