Monitoring Grant heat pumps on https://heatpumpmonitor.org

[TrystanLea]

Hello

Thanks for setting this up. I read your post on https://forum.buildhub.org.uk/topic/25579-grant-ashp/ with interest.

I've setup monitoring on two Grant Aerona systems installed through Eco4 by Baxter Kelly.

• System 1: https://heatpumpmonitor.org/system/view?id=57
• System 2: https://heatpumpmonitor.org/system/view?id=97

The Honeywell T3 TPI control excessive cycling can be clearly seen. On system 97 for now the owner is setting the room temp target to 25C and just tuning the thermostat fully on/off manually. I'm keen to explore using the Chofu own controller to see what difference that makes.

I will report back here with any results.

There is another Grant on https://heatpumpmonitor.org with a different room thermostat that is working better, it's in the top 5! https://heatpumpmonitor.org/system/view?id=10 (WC + 3rd party thermostat EPH CP4M) shows how well these Grant heat pumps can work which is promising, not that the other two are performing particularly badly, they are doing quite well really.

Thanks for compiling this resource!

[TrystanLea]

Here's a few screenshots of the data to illustrate the TPI cycling issue:

1) Wider view with a mix of decent runs and then some of the TPI cycling periods:

2) Zooming in to the TPI cycling periods,the COP is about 3.6 and if that was overnight, that would likely be an issue for the noise sensitive as you say in your piece:

3) Contrast that with the performance when it's running nice and steady, COP of 4.3 :)

[TrystanLea]

How did you get on with using the Chofu own controller?

[caliston]

Thanks, that's really interesting. I can only ready-reckon my COP from the pump-speed because I just have an analogue flow meter (that I have to read by pulling a pin) so very useful to get some hard data.

Comparing my compressor speed with the Honeywell Lyric T6 controller:

to using the heat pump's own controller:

For the first one I don't have the local temps but a weather station a few miles away says that day was min 5C, max 8C. For the second one (today) the temp according to the ASHP was min 8C max 11C, so not too different. On the second you can see the compressor running much less often. Also, at about 5am (when someone may have bumped the target room temperature which caused it to run a bit harder) you can see it ran at max speed and then ramped down the speed after a while. You can see the same behaviour on the first plot but only for a couple of periods in the morning which is when the hot water ran (ie the Lyric was not in control so not cycling it).

Noise-wise it's night and day different. Before it would be revving up like a jet engine, only to then rev down again a short while later. Now it just purrs gently. In my kitchen I can stand about 1 metre from the fridge and 1 metre from the ASHP (with the window open) when one or other are on and the noise level of the fridge and the ASHP are very similar.

The Chofu controller is fine: it's actually not hard to wire up - there are two outputs 'pump 1' and 'pump 2' that can be configured for 'zone 1' and 'zone 2' on an S-plan (plus) system, and there's a '3 position valve' output that goes live when it hot water mode, so that does for the hot water valve control. They're all on relays only rated at 1A which is a bit weak so I've installed a boost relay for each one. The pump is wired via the switches on the valves in the normal S-plan way.

I fitted a hot water cylinder thermistor which works for that and means the ASHP will heat the hot water up to its demand temperature and then switch back to central heating, rather than a fixed runtime as per Grant's install. I also fitted a buffer tank thermistor but it turns out the control mode for that only has a fixed target temperature (default 60C) and ignores weather compensation, so I've disabled it.

There are a few settings to configure to enable these things in the right way: I must write it all up.

The room controller is a bit unfriendly - it's like an old school wall controller but with a lot of settings via holding down buttons and numerical codes - you need to have the manual to hand to set anything. It seems like most settings can be done via Modbus which is another way. Some kind of touchscreen frontend is on the todo list, but TBH it's mostly set-and-forget these days - I only have to change the clock twice a year.

One thing that isn't well documented is the hot water has two temperatures: 'Comfort' and 'Eco'. The idea is that you can boost it to a higher temperature when you want. The room controller looks like a traditional time clock (setting on/off times over a 24h/7day period) but actually the timer flips between 'Comfort' and 'Eco' temperatures - when 'off' it actually heats to Eco temperature and there's no setting to turn it fully off. What I've done is set Comfort to my desired water temp (44C) and Eco to 15C, which means the water is never heated when in Eco mode, and so it behaves like a regular timer. Similarly there's a hot water button which can be held for 3 seconds to engage Comfort mode - we use this to run the hot water outside the scheduled times (you have to remember to turn it off afterwards, otherwise it'll keep the water at Comfort temp as long as it's on).

Thanks for compiling this resource!

And thank you for all the info you've put out there - your site was one of the ones I started with on my heatpump journey.

[TrystanLea]

Thankyou @caliston that all sounds great, I look forward to seeing how different the ramp up is once I've got this wired up.

I reconfigured the cylinder plumbing today, removing pre-plumbed 2x 2 way zone valve setup + bypass, replacing it with a single 3 way diverter valve (bypass not needed as all rads are fixed open, some fully open without the option to turn down with TRV's, it's a small enough house for that to be sensible).

I just need to do the wiring side now.

Did you connect to the AC 3-way valve terminals? What is phase and signal? I've got live, neutral and earth on my diverter and the micro-switch outputs. How did you connect these up?

I've also bought the 10k NTC temperature sensor.

I need to have a good read through the manual to work out what changes I might need to make to the controller settings once I switch over.. the house only has one zone so no need for any complication on that front.

Im making these change on system https://heatpumpmonitor.org/system/view?id=97 this is my Mums house :)

[caliston]

Here's my wiring setup:

The 3 way valve terminals are fixed live (pin 51), fixed neutral (pin 50), and pin 52 goes live when the ASHP is in hot water mode. So I've wired this (via a relay, as all the ASHP outputs are only good for 1A and I wouldn't vouch for startup currents) to the hot water zone valve (red wire).

For the other pins, blue is neutral, brown and white are the Pump1 and Pump2 outputs which go to the zone valves of zone 1 and 2 respectively, pink goes via a relay and contactor to the immersion heater, and yellow is unused and parked in a spare terminal. The indoor pump live is looped through the microswitches on the zone valves in the usual S-plan way. I only have one zone but I have a secondary controller and zone valve to fit in future.

The foreground orange twisted pair is for the hot water cylinder thermistor. The foreground brown pair is for the buffer thermistor (which I have disabled in settings but the unit may actually still use). The background orange pair is Modbus + and -, the lower green pair is Modbus ground. The upper foreground blue/green/brown pairs are as my installer put it in, they're twisted together to be single wires and used for the DHW on remote contact and the on/off contact from the Honeywell boiler controller (we disable both of those in settings below), and the background blue and brown are the wires to the room controller, which I moved to the hall rather than the back of the airing cupboard.

Setting	New value	Old value	New description	Old description
5119	0	1	use room controller for DHW	use remote contact for DHW
5120	0	1	use room controller for heating	use remote contact for heating
5107	1		use DHW tank thermistor
3140	1	0	enable legionella cycle
3141	6		legionella cycle run Sunday
3142	17:00		legionella cycle run 17h00
5111	0	0	disable buffer thermistor	disable buffer thermistor (forces buffer setpoint mode if enabled)
4100	0	1	room set point	water set point
4200	1	0	main water pump based on buffer temp	main water pump always on
4220	2		additional water pump as main but disabled for dhw
3112	15		DHW ‘economy’ temp = 15C (don’t heat water in economy mode)
3111	44		DHW ‘comfort’ temp = 44C (desired DHW temp)
3113	6	3	DHW hysteresis 6C – don’t heat unless dropped 6C from setpoint (ie 38C), avoids turn on during the night

There are a few things to note here. One is that enabling the buffer thermistor (5111=1) also forces the unit into buffer setpoint mode. This tries to maintain a set buffer temperature, irrespective of load or weather compensation, and by default the target is 60C. This roasted everyone! So I disabled the buffer thermistor (5111=0) and switched to room set point mode (use the room controller's internal temperature sensor as a thermostat) - this keeps weather compensation running.

Another complication is I wanted the unit to be silent when turned on but not heating. That means no central heating pump running, no ASHP internal pump running. The default setup (setting 4200=0) is to run the ASHP pump all the time, which I didn't like. The alternative (4200=2) is to run 'sniffer cycles', ie to turn the pump on, pump water to the ASHP and measure the temperature there. This is worse from a noise perspective because it turns the pump on for a short period every so often, and the pump spinning up/down is more distracting than it running constantly. There is a third setting (4200=1) which is 'run based on buffer temperature'. While I have disabled the buffer thermistor, this setting seems to work as I want. (Perhaps I should try unplugging the buffer thermistor and see if it changes anything)

As I mentioned above, the hot water timer on the room controller looks like a digital version of a mechanical time clock but it selects between 'comfort' and 'economy', rather than 'on' and 'off'. So I have configured the 'economy' water temperature to be 15C so that the hot water is never heated in economy mode, making it equivalent to 'on' and 'off'.

Normally I have the hot water run in the morning, but sometimes it's drained and I want some extra hot water. I hold down the 'hot water' button on the room controller for 3 seconds and it switches to 'comfort' mode, heating the hot water up to the comfort set point (44C in my case) and then switching back to heating mode. This is in contrast to the way the Honeywell was wired where you could run the hot water for an hour and house would never get heated during that time, even if the water was already hot.

The thing here is you have to remember to switch back to 'economy' (hold for 3 seconds) otherwise it'll heat the water again if it falls 3C below the comfort set point. I have increased this hysteresis to 6C because we lose about 4-5C in hot water temperature over night, and if I forgot to switch back to economy that was causing the ASHP to fire in the middle of the night just to heat the hot water.

I also enabled the legionella cycle for the immersion, which can only be set to run once a week at an hourly granularity. It will first heat the hot water with the ASHP up to the maximum temperature it can (55C I think) and then run the immersion to bring it up to 60C. I have also some external relays to run the immersion, eg periods when electricity is free.

I think that's everything. Once done it operates a bit more like a boiler (being silent when not running, only heating when it's told to), and we just use the room controller to bump the room set point up and down, with a manual setback at night.

[TrystanLea]

Thank you @caliston that's really helpful. I will get back to you shortly once I have this up and running. Will be going back to finish this later in the week.