@mab I think most have changed their low end to 0 from -4, I have. I guess once you're at zero, you'll need 'high LWT'.

I'm getting the figures from the Aerona unit, via its RS485 interface (basically, a serial interface), which allows all of the parameters to be read, and updated (where possible), following info I found on this page. I've wired up some network cable to the outside unit, and the other end of have this, which is connected to a Raspberry Pi sitting in an upstairs cupboard. Then I just run a bit of code every minute or so, to record at least the 10 values available easily(!) from the controller, and write them to a database, for analysis and graphing as and when.

The IT is fairly straight-forward. Figuring out what's happening...

Making that change has really made a difference for me, Mike. But then I had to be patient and stop tinkering. Once I did that it has worked.

that and balancing my radiators. We added a new building, a garage with a room above it and the heat for the upstairs room runs off the pump. I turned that off completely last night and today I have turned that on gradually and balanced it with the house upstairs radiators. 

result is that it is currently 1 degree outside but the house and garage loft are both toasty. It IS still doing regular defrost cycles but in between it is getting to 39/40 degrees which is enough. 

-3 degrees outside and the entire house is sitting at an average of 20 degrees. Feels very comfortable, particularly the underfloor. 

this is probably the first time I’ve really felt the different type of heat from UFH as previously it was powered by an oil boiler. 

if anything 20 from the rads upstairs feels a bit too warm whereas 20 from the UFH feels perfect. 

I am grateful to this forum and the people on it. Have had so much help and my understanding of these complex systems is finally improving. 

@mikefl

Posted by: @mikefl

↑

@mab I think most have changed their low end to 0 from -4, I have. I guess once you're at zero, you'll need 'high LWT'.

Is the low end what the Grant manual calls 'min outdoor air temperature corresponding to max outgoing water temperature (Te1)'? Also, what does 'high LWT' mean? Sorry for the dumb questions 😑 

And here's another one - should the outdoor temperature at which the defrost cycle starts be lowered from 4C to 0C? If so, does this come under 'Start temperature of frost protection on outdoor air temperature' and/or 'Start temperature of frost protection on flow water temperature'? It may have been answered earlier in this thread but I'm struggling to find it.

@sentinam Yes. Parameter '21 04'; the temperature at which the HP will be aiming at the high LWT value set in parameter '21 02'. By 'High LWT' I meant just the '21 02' parameter value. So you're just saying "at this low temperature, and below, target the highest LWT I want you to use, as set in '21 02'. My current values are 0C and 45C - it's the 45C you can possibly lower to improve economy.

The  "frost protection" parameters (the '43 nn' ones) are not about the defrost cycles. It's not clear if there's any way to influence the defrost cycles (and possibly a bad idea to be able to - you have to let the HP remove ice build up from the fan, or it'll stop working).

These parameters are the ones which trigger the pump in the HP to just carry on running in low temperatures. It seems to just cycle whatever water is in the heat pump continuously around to the LLH and back again, probably just to stop anything seizing up in cold weather. By default, as you say, it starts when outside temp hits 4C, and stays on until it goes over 7C. Mine was triggered on 24th Nov and has been running ever since. You could lower the numbers to get the pump to stop running, but I'm loathe to do anything which might risk something seizing up, and it's just an extra 2.4kWh/day, which isn't much compared to what's been used of late.

@mikefl

Thanks, that’s very helpful and also interesting about the ’43 nn’ parameters - I did wonder if ‘frost protection’ meant just that and not ‘defrost cycle’ as both have separate symbols on the control panel. Having said that, an engineer (not our own installer) told us you can lower the outdoor temp at which the system defrosts from 4C to 0C but I wonder if they meant a Grant person has to do this for warranty reasons. 

The other thing I wasn’t clear about is @allyfish saying to set a third party thermostat to 30C and let it run. We have a Hive and anything above 20C would make the windows melt 😓 It does tend to do its job quite keenly. 

Posted by: @sentinam

↑

The other thing I wasn’t clear about is @allyfish saying to set a third party thermostat to 30C and let it run. We have a Hive

Hi again, if Weather Compensation [WC] works right then your heating will regulate based on that. Hive thermostats cycle the ASHP on and off far too frequently (I’ve got one). I have it set to 24degC to prevent overheating the house. WC regulates around 19-20degC normally. The thermostat in the Grant controller can be set to 30degC to make sure it doesn’t override anything. Hive is a poor stat for ASHP control, too narrow a control band, OK to use them for timed on/off control and room temperature display.

@allyfish

Hi Ally, thanks for reply - and here's another simple question coming up.

The Hive is at 24C now and the system is on WC (as per your suggested parameter 21 settings earlier in this thread). Does this mean we should see the room temp stick at 19-20C and not go above this?

We use the Hive as a sort of set-back function, i.e. room temp 16-17.5C overnight (exact setting dependent on outdoor temp), and 19C during the day. It’s also programmed to turn DHW on/off at mid-day. As a whinge, we don’t like the Hive; would prefer an all-in-one control unit/thermostat which we’re used to. 

Posted by: @sentinam

↑

The Hive is at 24C now and the system is on WC (as per your suggested parameter 21 settings earlier in this thread). Does this mean we should see the room temp stick at 19-20C and not go above this?

In theory, yes. You may need to adjust the WC parameters, or the flow rate to certain emitters to fine tune it. Every house and heating system is different. When it's there or thereabouts, the WC will do the heating temperature regulation with the HIVE stat or other internal zone thermostat controllers there to prevent overheating.

Expect to regulate +/-2degC of your ideal temperature on WC. It's reliant purely on outdoor air temperature as a reference point for heating flow temperature, it doesn't take into account sunlight through south facing windows, etc. On a day like today, bright and sunny, that adds a degree or two onto the room temperatures subject to solar gain through windows.

It's all this commissioning that Grant doesn't do. But the Grant system control is very primitive using an impossible to understand ASHP controller and simple thermostats like HIVE which are really suited for controlling gas boilers not ASHPs.

Homely are working on a controller for the Grant Aerona range, it should launch next year. Homely will be more intelligent and take much of the manual guesswork out of setting up WC. It will also be much simpler to use, hey it can't possibly be more complicated. 😉 It might be retrofittable, I don't know. Fingers crossed.

@allyfish

OK, many thanks for that, think I’ve got it now. Is the WC ideal room temp at ’21 05’? And does the system read the room temp off the control panel (as shown on its screen)?

As you say, just seen on Homely’s Facebook page back in June that they’re partnering with Grant - ‘coming soon. watch this space for further details’. We will ‘watch this space’ expectantly and hopefully.

WC works completely autonomously, it doesn't reference room temperature. Parameter 21 05 is the maximum outdoor air temperature at which, with WC enabled, heating is disabled. 21 05 default is 20degC, if the outdoor air is above this, the unit won't provide heating. Put simply, WC is a heat energy balance - the lower the outdoor air temperature the higher the heat loss from indoor to outdoor, so the higher the heating supply temperature to balance this. It's doesn't always balance first time using Grant default settings. Most of us Grant owners have found that we need to raise parameter 21 04 from -4degC to 0degC. Probably because UK houses are comparatively poorly insulated with higher heat loss compared to most other countries.

@allyfish

Hello Ally, thanks for your help. My knowledge has increased exponentially through your guidance and that of the other kind posters on this thread. 👍