The installation was at the start of March. We were very impressed. A team from the Valleys hit the house like a (well-oiled) train and it was all done in two days, they took on board some requests (e.g. about fixings) and really knew what they were doing. We’ve had a few trades in the house since, including a plumber, who have praised the configuration and pipework. Given that this was grant funded and so we had no control over that side of things I feel we’ve been very fortunate.

The system has performed fine so far but obviously we haven’t been in the winter months. I’ll try to remember to give another update come December. The one issue has been the new Grant smart controller – there were significant teething problems. The installers, and Grant engineers, were learning the product themselves on the job, but on the plus side that has meant that we’ve had their attention, and so far the customer service has been very good. It’s working fine now, but again, we’ll see how it goes through its first winter.

That’s right. You would have a pair of wires for each feature - connect the two wires of either pair together (e.g. with a timeswitch or smart switch) to activate either feature. 

I would hope that the new Grant smart controller has a built in means of doing this without additional switching hardware - but I don’t know. 

You might also be interested in this link:

https://energy-stats.uk/what-size-heat-pump/

Definitely HTC gave me the best measurement of heat loss and was at 4.5KW @-2C, way below the MCS estimate of 7.5KW. Quite why they sized the heat pump at 12KW is a bit of a mystery but at least I am using long cycling on off peak tariffs to get the most economical way of running it and still achieving SCOP around 3.5 for combined heating, hot water and weekly pasturisation.

As Ian stated, get the radiators as large as you can but do match the room heat losses to the rad output at the set flow temp for a given outside temp, otherwise some rooms won’t get up to temperature at a given flow rate, whilst the rest of the house will be fine. Weather compensation and modulation will take care of the rest.

And watch out for pipe sizing, as I think this is a limiting factor in my house and huge disruption required to upgrade. I have 28mm from the heat pump, 22mm splits upstairs and down, but quite a few long 15mm runs with several rads connected at the end. Upsizing them may not give me the benefits I hope and the guidance of how much heating power can be delivered by each pipe size is useful.

“There isn't a set back function on the Grant controller, you can't knock the LWT down 2 or 3 degrees overnight, which is a shame. If you could I would do that. If you turn a master room control thermostat down you start cycling the ASHP on and off, and that's not good or efficient control.”

The Grant does in fact have a couple of potentially interesting features which could offer set back and boost functionality:

Night Mode - which will reduce the compressor frequency (essentially dial down the power a bit) to reduce noise and power consumption.

Low Tariff Mode - which will increase the target temperature by a set amount over whatever the current value is.

Both of these modes are configurable (you can set the max compressor frequency for night mode and the target temperature adjustment amounts) but unfortunately these modes can only be enabled by closing an electrical contact which therefore needs to be physically wired up to some sort of time-switch or smart switch.  So you either need to get the installer to do it or you need to open up the wiring panel on the heat pump and start tinkering around in there yourself.

I don't have these connected up on my system so I've no idea how effective or useful they might be in practice. 

I could potentially see some benefit though - I have the Octopus half hourly tariff which has expensive electricity between 4pm and 7pm every day - that's when I would trigger the night mode - at present (if it's not too cold) I just programme lower thermostat temperatures for that period which tends to switch off the heat pump completely.  It might be better to keep the heat pump running at a lower compressor frequency rather than have it switch off and then on again - but who knows.  

@rupes, thanks for your message above. Just to be clear, if I can get these two functions wired up at installation it'll mean I'll have the option of activating them, or not - it's not that they'd then be on all the time?

@iancalderbank:

on this , although you say you aren't a natural techie, try downloading and reading the manuals for the user-facing controller for each. For samsung, its this. I don't think either has a reputation for being that user friendly to be honest. however both units are supported by a 3rd party control system called Homely , custom developed in the UK for heat pumps, which seems to be a good way to bring a really user-friendly control system into the picture, have a read of their stuff, there are write ups by users of it on this forum.

Thanks @allyfish, I’ll certainly request the new Grant smart controller. How would this interface with the Homely system recommended by @iancalderbank, is it a case of one or the other, and Grant’s upgrade should do away with the need to use Homely, or would you use them in tandem?

Thanks @allyfish, I’ll certainly request the new Grant smart controller. How would this interface with the Homely system recommended by @iancalderbank, is it a case of one or the other, and Grant’s upgrade should do away with the need to use Homely, or would you use them in tandem?