Posted by: @arundalep

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You could use Home Assistant with a cheap wifi or Zigbee switch and essentially make whatever rules or conditions for the target temperature you want (This is how I control an oversized Samsung).

 

Posted by: @irmartini

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Ideally if I could I would like thermostatic control within these windows as well, but the thermostat I use to control the on off periods does have programable hysteresis

I would probably set off @ 21.0 on @ 18.5 this would deal with solar gain as well as short weather fluctuations rather than me knocking an hour or two off or on to cope, if anyone knows of a thermostat with programable hysteresis like this I'm all ears.

 

True, but the average householder isnt going to do this.

Posted by: @editor

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But really, this whole conversation shouldn’t even be happening. The fact that so many people are having to come up with workarounds to make their oversized heat pumps behave just proves that installers are still getting the basics wrong.

Indeed so. 

Does it even need to happen though?  Those who have responded want to 'take control', but does this actually save anything over just leaving the heat pump to do its thing.  Heat pumps can, after all, deal with being oversized but the enthusiasts on this forum presumably believe they can do better than the heat pump designer.  Are they right, or are they wrong.  Given the state of the industry we really need to know!

Any answers from anybody?  I certainly dont know!

@editor This isn't just about poor design and installation; it's also about the products used. The fact that some heat pumps can have a modulation range between 1.5 - 8 kW, and others with the same nameplate capacity only modulate between 4-8 kW is a problem. These specs are rarely published but are key to designing a system that is the most efficient for a given situation. The problem is that it is only by installing and monitoring the behaviour of different heat pumps (learning the hard/expensive way) that we will know which operates better at these low-load conditions in the real world.

Heat pump manufacturers have also economised with their product range by creating software-limited models, exasperating the problems further by narrowing the window of efficient operation, especially at lower compressor frequencies.

It would be impossible to achieve without mandating manufacturers to provide this data, along with the system volumes required to achieve them, but maybe MCS design criteria should also include low-load conditions in a bid to encourage manufacturers to work a bit harder in this area.

Posted by: @arundalep

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The fact that some heat pumps can have a modulation range between 1.5 - 8 kW,

Thats an interesting one - as a matter of fact which (is it the Ecodan twin compressor model?)

Posted by: @arundalep

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Heat pump manufacturers have also economised with their product range by creating software-limited models, exasperating the problems further by narrowing the window of efficient operation, especially at lower compressor frequencies.

Indeed, loads of 'models' but in fact only one or two!

Exactly this! There is a lot of talk about this, but very little hard evidence either way. 

Posted by: @jamespa

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Are they right, or are they wrong.  Given the state of the industry we really need to know!

Any answers from anybody?  I certainly dont know!

 

I use Home Assistant to provide a "Thermostat" signal to my Samsung heat pump; it wasn't required, but it has allowed me a lot of control to take advantage of TOU tariffs, solar generation, weather forecasting, integration with Tado etc, which wouldn't otherwise be available out of the box.

Posted by: @jamespa

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the enthusiasts on this forum presumably believe they can do better than the heat pump designer

Yes, I believe so, 🤣 . Definitely, in the case of Samsung, who I give credit for using PWM circulation pump control, but it could have been so much better, as I have demonstrated.

I believe systems should be hydraulically, as simple as possible, with the greatest active volume possible for the application and with the least amount of external influence, controls etc.

However, I would say system controls, in general, have massive room for improvement, and many existing controllers and installations could benefit from bespoke geekery to mitigate some of the controller design limitations to allow greater efficiencies, reliability and running costs.

Posted by: @arundalep

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However, I would say system controls, in general, have massive room for improvement, and many existing controllers and installations could benefit from bespoke geekery to mitigate some of the controller design limitations to allow greater efficiencies, reliability and running costs.

Oh definitely.  Getting the WC curve optimised is a key part of the commissioning which, realistically, installers cant be expected to do because it needs to be done over a period of several days when its cold.  So far as I can gather most just set it well above the optimum, invoke a thermostat/temperature sensor to compensate, and then instruct the householder to not to touch anything.  I can understand why installers do this, expecting a typical householder to deal with the typical 4 point WC setting is unrealistic and so is coming back every day for a fortnight, but it leaves us in a situation where by default systems are sub optimal, possibly by a significant amount.

Added to this many (not all) heat pumps have limited (or no) ability to schedule setbacks or set forwards by varying the WC curve, leaving no option but to abandon setback/set forward altogether (which in many cases is the best option) or to use an on/off approach.  Some heat pump manufacturers have worked out how to present setback/forward by altering the WC curve in a way that the ordinary householder can understand; this should be universal.  Homely of course addresses that, but why cant the heat pump manufacturers.

@jamespa Homely does address many of these issues, but unfortunately, because of how it operates, it removes a lot of the flexibility options (Dynamic TOU tariffs like Octopus Intelligent, for example).

I would still recommend Homely in 99% of use cases.