Ah, but who would set the setback?  The thing reads like something a marketing manager would write, not an engineer.

Posted by: @shapingstuff

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Hi,

 

I'm just looking for a little advice on Setback. I have a Grant Aerona 17kW and a Hive Thermostat.

Grant suggest having a Setback:

 ‘Setback’ control operation should be used instead which allow the heat pump to keeping running. This involves the system being in ‘energised’ mode during the hours when you are at home, running at the required higher flow temperature, and then it operates in ‘setback’ mode, setting to a lower flow temperature during the night and when you are away from the home. Using this cycle of ‘energised’ and ‘setback’ temperatures, the heat pump can operate very efficiently and can effectively keep the home warm.

They suggest 'setting a flow temperature' but this has nothing to do with the temperature of the thermostat which simply turns the heat pump on/off, which is exactly what they are suggesting you don't do? How exactly do you achieve this? Grant doesn't seem to provide any flow temperature controls.

https://www.grantuk.com/about/blog/how-to-control-your-heat-pump/

I feel like I might need to get myself another degree to make sense of this 😀 

Cheers.

Having read the blog and watched the video, it has convinced me to never buy anything from grant. 🙄 

Posted by: @shapingstuff

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They suggest 'setting a flow temperature' but this has nothing to do with the temperature of the thermostat which simply turns the heat pump on/off, which is exactly what they are suggesting you don't do? How exactly do you achieve this? Grant doesn't seem to provide any flow temperature controls.

Hi @shapingstuff - you can't set back a Grant ASHP overnight by changing the leaving water temperature setpoint. Ideally, a climate curve offset could be scheduled to drop the LWT by 2 or 3 degrees overnight, but the Grant [Chofu] controller does not have this functionality. All you can do is adjust a room thermostat down, but that will cause the ASHP to cycle on and off, which is not an efficient way for it to operate. It's best not to control the ASHP using a room thermostat at all, but via weather compensation and radiator/flow balancing. That's by far the most efficient way to run an ASHP.

We switch our Grant ASHP off for a few hours overnight, which isn't that efficient first thing in the morning, but it works for us as we like the bedrooms cooler overnight. The added energy to pre-heat the system volume from cold in the morning is less than if we left the ASHP running 24/7. We have all radiators, so the pre-heat time is relatively quick. We use HIVE programmable TRVs as simple on/off room/zone control. We don't modulate on the TRVs but set them to avoid room overheating.

When I came across Grant's 'How to control your heat pump' blog, advertised in LinkedIn, I contacted them advising them that what they were saying was not possible with their equipment. They admitted that directly to me, but have not corrected or amended it.

@derek-m knowing what I now know about Grant and their products, I'm inclined to agree. Their technical competency isn't very good, their installation schemes are 'bastardised' Y or S plan designs, very much borrowed from fired combustion boiler installations, and not designed to maximise the efficiency of low delta T high flow renewable heat sources. Grant specify low loss headers and secondary pumps even for simple single zone heating circuits where they are not necessary - the built in circulating pump in the Aerona ASHP is pretty powerful and capable, most 3-4 bed home heating single zone circuits with 28/22/15mm Cu pipe would be fine using the built-in circulator.

Their Grant G1 accredited installers seem to struggle to comprehend the fundamental differences between installing and commissioning boilers and installing and commissioning heat pumps. Grant seem to regularly not enable weather compensation when commissioning ASHPs, but commission for a fixed LWT. This is contrary to MCS certification requirements. The Chofu controller is very capable, but Grant bypass a lot of the functionality by fitting inappropriate external room thermostats (e.g. HIVE with far to narrow a hysteresis to control ASHPs) and digital 7-day water timers. The Chofu controller has much more advanced in-built control, and includes features such as night [quiet] mode and low tariff modes, which Grant don't use. The Chofu controller is complicated to use however. There is light at the end of the tunnel, they are partnering with Homely, and a new controller will launch next year which will be more intuitive and simpler, for both Grant installers and end users.

The Grant Aerona3 is a quality ASHP, very quiet, well designed and very reliable. Something about the Japanese OEM culture there and their technical competency. There are very few reports of Aerona ASHP failures and no known defects, which can't be said of many ASHP products on the market, but it does freeze up very quickly in our mild but humid climate needing to defrost every hour.

Thanks @allyfish for you extensive answer.

Frustrating that a lot of people wouldn't question this information, and should really have to.

I'm happy with unit to be honest it belts heat around our underfloor heating quite efficiently. Hopefully like you say it runs without problems for years to come.

I've had a lot of problem with installers and recently had various bits rewired costing more.

I don't yet have the confidence to set it to run all the time with weather compensation. We use the Hive thermostat. Was it easy enough to adjust and get the right house temperature? I've got weather compensation on but it tends to heat the house too much currently. Any guidance would be appreciated. I've not entered had the confidence to play with parameter codes yet.

In terms of defrosting have you tried the immersion in the low loss header yet? I've had it wired but not set it. We  struggle to get enough heat when below zero and it ends up on all the time anyway.

Cheers.

Posted by: @allyfish

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Ideally, a climate curve offset could be scheduled to drop the LWT by 2 or 3 degrees overnight, but the Grant [Chofu] controller does not have this functionality. All you can do is adjust a room thermostat down, but that will cause the ASHP to cycle on and off, which is not an efficient way for it to operate.

Just to add an observation on this: I did in fact manage to do this, in the cold snap last December, by using the room stat: normal target IAT is 19 degrees C, setback target was 12, 2200 to 0400 if I recall, and, given my house's relatively large thermal mass, it dropped to 16 point something during the setback - ie a 2-3 IAT (not LWT) drop, with the heat pump off throughout the setback, ie no cycling. In warmer weather cycling is even less likely, as the house will cool down more slowly, and never trigger the room stat.In effect, the room stat operates as a timer. The problem I then had was the painfully slow recovery, which is what I am hoping to address with my DIY auto-adaption, as described in other threads.

I can't remember whether Grant has a controller that you can connect to using modbus - the fact that Homely are going add Grant to their list suggest it may be possible, as that seems to be Homely's modus operandi. If you can, then you might be able to set the Weather Compensation Curve endpoints that way, and get a lower LWT during the setback.   

Posted by: @allyfish

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The added energy to pre-heat the system volume from cold in the morning is less than if we left the ASHP running 24/7.

Interesting, as I am sure you know, this is a matter of hot debate elsewhere on the forum. Do you have actual measurements? Some eg @derek-m appear to be firmly of the opinion, based on their modelling, that this is a mug's game, the hills are always bigger than the valleys. I am still sitting on the fence, awaiting the results of my own experiments, but my hunch is there should be some saving. 

Is programmable thermostat not your answer. I have one in the house ,i  have it set above desired temps for when i want heating, 2-9pm and set to @18 from 9pm until 2pm following day and heat pump is off then as i know temp wont drop below18 to switch it back on.

Posted by: @cathoderay

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Posted by: @allyfish

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Interesting, as I am sure you know, this is a matter of hot debate elsewhere on the forum. Do you have actual measurements? Some eg @derek-m appear to be firmly of the opinion, based on their modelling, that this is a mug's game, the hills are always bigger than the valleys. I am still sitting on the fence, awaiting the results of my own experiments, but my hunch is there should be some saving. 

 

Hi Ray,

I actually didn't state that using setback would be a mug's game. Please don't miss quote me.

Any reduction in IAT will reduce heat loss, reducing your IAT by 1C throughout the whole day could produce electrical energy savings in the order of 8% to 10%.

The problem comes when trying to retain the savings made, and bring the IAT back up to the desired level.

Hi @shapingstuff, there is a recent post on enabling and adjusting Grant Aerona weather compensation. It’s trial and error as every house has a different heat loss and heating profile. Easy to lower the maximum LWT if overheating is your concern. With WC enabled the ASHP modulates beautifully.

I would avoid using the immersion as supplementary heating during periods of defrost. I tried it and my electricity consumption went through the roof. You’re better off using direct electric supplementary heating roomside. At least that way your getting 100% efficiency from the supplementary heating rather than a fair percentage of it supporting defrost cycles.

@newhouse87 the disadvantage of using a room stat to set back the ASHP is that the room stat is a digital on/off device controlling a ASHP which modulates using analogue proportional control. You’re switching the compressor on and off rather than modulating it on inverter control. That uses a lot more electricity. Digital programmable room thermostats are poor control devices for modulating heat sources. The very narrow hysteresis of electronic thermostats cycles the compressor on and off far too often - the ASHP never gets a chance to establish stable modulation control.

@derek-m

Posted by: @derek-m

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I actually didn't state that using setback would be a mug's game. Please don't miss quote me.

I didn't quote you (no quotation marks, and my wording is 'appear to be firmly of the opinion', not X said Y), I paraphrased you, or you might say, expressed an opinion about an opinion, and although I can't in an instant find it, there is a comment of yours which says in effect the recovery plus boost will (almost, there are always exceptions) always use more energy than the setback saves, which suggests that trying to save energy by using setback plus recovery boost is a mug's game.

The trouble is we don't yet know the answer, let alone to how many homes that particular answer applies, ie is it a universal answer? Much of the recent debate has been about how to set about getting the answer: modelling vs real world measurements? Naturally we are trying both methods, indeed, not to do so would be another mug's game. I for my part have tried to counter the blind faith in the modern religion of modelling by pointing out that, however elaborate the model and elegant the formulae, it is still at heart no more than whatiffery, and is heir to error, as no less than the biggest whatiffery of them all, the weather forecast, has shown us in recent days (eg Wed (1st Nov) 0600 inshore waters forecast for Selsey Bill to Lyme Regis for 0600 to 1800 Thursday was 'Cyclonic 5 to 7 becoming west gale 8 to storm 10', where 8 - 10 is 34-55 knots, Thurs 0600 forecast effectively the same, 'Cyclonic gale 8 to storm 10, becoming west 7 to severe gale 9', actual winds at Chichester entrance during that period 0600-1800 Thurs 2nd Nov mostly 30-40 knots or less). The weakest link, and it is a serious weakness, in my preferred experimental approach is that the studies are invariably observational rather than controlled, as in I can't control all variables except one, and vary that single one to see what happens; instead, I have to observe what happens while nature keeps on twiddling the settings, giving ample room for bias and error.

Te recap: the research question can be boiled down to this. Most if not all of us accept that under steady state conditions, keeping a house at 20 degrees for 24 hours uses more energy than keeping the same house at 20 degrees for 12 hours, and then turning off the heating for the other 12 hours, during which the house indoor temp might fall to say 16 degrees. We therefore need a boost at the start heating period to get the house warmed up again, and the fundamental problem is that heat pumps are not good at boosts, they prefer to run low and level. The only way we can get the boost is by increasing the LWT, and, because of the nature of a heat pump, that lowers efficiency, with the consequence that we end up both putting more energy in and putting that energy in at a lower efficiency, during the recovery, @derek-m's double whammy. Quantifying the energy saved during the setback is easy enough, the hard one is quantifying the excess (over and above what would have been used anyway) energy used during the recovery. If the latter is greater than the former, then setback plus recovery boost is indeed a mug's game, whether we call it so or not.       

Edit: I've managed to find the comment referred to above in the first paragraph, it is here ("I hate to burst your bubble, but what you propose will not be possible to achieve, since it would defy the basic Laws of Physics and Thermodynamics....").  

Posted by: @allyfish

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Hi @shapingstuff, there is a recent post on enabling and adjusting Grant Aerona weather compensation. It’s trial and error as every house has a different heat loss and heating profile. Easy to lower the maximum LWT if overheating is your concern. With WC enabled the ASHP modulates beautifully.

I would avoid using the immersion as supplementary heating during periods of defrost. I tried it and my electricity consumption went through the roof. You’re better off using direct electric supplementary heating roomside. At least that way your getting 100% efficiency from the supplementary heating rather than a fair percentage of it supporting defrost cycles.

@newhouse87 the disadvantage of using a room stat to set back the ASHP is that the room stat is a digital on/off device controlling a ASHP which modulates using analogue proportional control. You’re switching the compressor on and off rather than modulating it on inverter control. That uses a lot more electricity. Digital programmable room thermostats are poor control devices for modulating heat sources. The very narrow hysteresis of electronic thermostats cycles the compressor on and off far too often - the ASHP never gets a chance to establish stable modulation control.

 

Posted by: @allyfish

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@newhouse87 the disadvantage of using a room stat to set back the ASHP is that the room stat is a digital on/off device controlling a ASHP which modulates using analogue proportional control. You’re switching the compressor on and off rather than modulating it on inverter control. That uses a lot more electricity. Digital programmable room thermostats are poor control devices for modulating heat sources. The very narrow hysteresis of electronic thermostats cycles the compressor on and off far too often - the ASHP never gets a chance to establish stable modulation control.

Isn't this possibly over-complicating things, as I pointed out earlier, using a room stat setback acts in effect as a timer (at least it does in my house, with a large thermal mass, and a large setback, say from 20 degrees daytime to 12 degrees during the overnight set back).

Still very interested to know if you have the data behind your earlier statement ("The added energy to pre-heat the system volume from cold in the morning is less than if we left the ASHP running 24/7.")