Weather compensation - indoor temperature sensor placement

[Nick Thomas]

Bit of a consistent pattern with my Grant Aerona3 6kW, installed with a thermostat in the downstairs hallway (radiators, volumiser, not the ideal setup - maybe switching to UFH next year) - the house would be below the requested temperature, and the heat pump would be running below capacity, but never get the house quite up to the expected temperature (20C during the day; 18C at night). In general we were comfortable anyway, but with the cold snap it's been more of a pain these past few days. Today, after 4 hours of the house sitting at ~18.5C, I decided to go poking around upstairs. Think I've cracked it.

 

The grant controller had been screwed to the front of the hot water cylinder, in a poky airing cupboard, and was registering an inside temperature of 29°C. Fortunately it had lots of spare cable, so I've moved it to the upstairs landing where it's now registering a cool 22°C indoors, 1.5°C outdoors. The downstairs thermostat has almost immediately moved from ~18.5 to ~19, presumably because the heat pump now has more accurate information for weather compensation (CH is off for 2 hours now while the pump switches to DHW, I'll be interested to see how quickly it climbs to 20°C once that's done).

 

My working theory is that the weather compensation algorithm is now far more accurate, so it can do a better job of heating the house. Will be interesting to see the knock-on effects on energy consumption.

 

Professional installers, eh 😬.

[JohnMo]

Grant use a heat pump made in Japan by Chufu, and generally simplify the install and make an S plan system, the same as a gas boiler would have. Basically to make it simple for a bog standard plumber to install. They seem happy to stuff a controller full of good features in an in appropriate place.

 

If you are switching to UFH make sure you do it fully informed, doing it badly will make it very expensive to run due to the downward heat losses.

 

Post a specific question with all the information you have such as proposed floor buildups etc.

 

Other than that is the Grant heat pump good? I am looking for a heat for cooling more than heating, but when installed will do both. (a feature the grant heat has but they tell you about it)

[Nick Thomas]

No specific question, just sharing information really ^^.

 

I don't have much to compare the Grant with, but it's making hot water cheaply. I'm not really keen on the skunkworks stuff to get extra data / functionality out of it. Given another go-around, I'd probably do a load more research and get one with such bells and whistles as first-class features.

 

At the last house we had an A2A heat pump that did both heating and cooling, and it was pretty good at both. Trying to use this to pump cold water around the house seems pretty inferior by comparison.

[Nick Thomas]

Yup, after this one change, the house got up to a nice 19.5°C long before the setback to 18°C came along.

 

As far as I can tell, the heat pump is being told to achieve a temperature of 40°C by the stock grant controller, and then the external thermostat turns it on and off when it reaches 18 or 20. Might try fiddling there next - it seems like that would mess up weather compensation also.