@glyn.hudson I tried this yesterday and part of today. I love the idea of this setting - I see it as helping the flow temp to sortof “gravitate” toward the thermostat temp which is good.
Something I didn’t like - I set my thermostat to 21 and didn’t touch my hysteresis which is 0.4c (I haven’t ever touched this setting) and the result was obvious - the ASHP switched off when I hit 21 and then only turned back on again when I hit 20.6.
What I would prefer is that the thermostat didn’t deactivate the circuit but instead was used with the room temperature correction to sortof gradually guide the flow temp back down to where it needs to be to maintain the thermostat setting. Not sure if this is possible or not or whether it makes sense, it feels that it does in my head
Potentially my installer changed the hysteresis to 0.4, they certainly disable room temperature correction (if the default is indeed 4).
My thermostat pump blockade is disabled (set to NO).
So my thermostat was set to 21 which was resulting in a target temp of 30, then at 09:55 this morning it achieved 21 and then the target temp was set to what seems to be “off” which is 26, so the ASHP stopped and the flow temp just coasted (as it does) until 11:21 when the thermostat hit 20.6 and then the target temp shot back up to 31 which caused the ASHP to go full pretty much full whack (65hz, 700rpm fan) for about 25 mins until it got back up to target temp.
Yeh my pump runs when the system is idling, 14l/m it seems. Up until I saw your post I’ve been experimenting with using only the weather comp curve - e.g set thermostat to something it won’t ever reach and simply use the curve which does seem to work well.
I think if I did use the thermostat in the way intended and set a hysterisis of 1 I’d get some largish swings in temp - do you not find this?
When a target air temperature is set on the assigned thermostat, the smart controller calculates flow based on ambient temperature, heating curve and current circuit air temperature.
If ‘THERMOSTATIC PUMP BLOCKADE’ is enabled, the circuit demand will be stopped once the target air temperature set on the thermostat is reached.
If ‘THERMOSTATIC PUMP BLOCKADE’ is not enabled, once the target air temperature is achieved the smart controller will use decrease the flow temperature target by the ‘DECREASE WATER TEMPERATURE’ value, which is set correctly will maintain the target air temperature. Refer to 7.3.1.3 for recommended setback values based on heat emitters for the circuit
Section 7.3.1.3 is talking about night air temp setbacks so it doesn’t feel very applicable, but here is the setbacks:
I think they mean Decreasing fixed water temperature (confusing use of the word fixed there if they do), which is in Service Parameters → Installer controller →Circuit 1 H1 → Decreasing fixed water temperature.
What is this set to for you? Mine is 17 which I think may explain things (set by my installer, not me!), because that effectively would just shut everything down as soon as the thermostat hits its limit. I’m guessing yours is set to something far more modest.
Not directly related to previous, so maybe needs a new thread, but I have seen a couple of defrosts recently, which happened at about 7c ambient, 99% humidity, as the compressor ramped up fast. You can detect it in home assistant since the fan stops, while the compressor keeps running. Obviously flow and return temps swap too, but that can happen anytime to a small extent. This is what it looks like.The impact on house temp was small to none.
Fwiw, my (room temp) hysteresis is set to 0.2c, and I check 17 temp sensors in 5 main areas, to decide whether to start or stop the heatpump. With very low wc curve it only cycles off when the sun come out big time, else it just about holds temperature in the 0.2c range. If it does cycle, I may need more hysteresis, but at current ambient 0.2c works fine. Did need some fine tuning of wc curve though.
Heat pump doing pretty serious short cycling. It’s running general factory defaults (after updates) other than set-temps, wc heating curve 0.6 and room temp correction at 1.0.
The sharp ramp from 11-23l/m every 4 mins was causing a lot of noise, so I reduced the max pump speed to 70 (see next picture for impact). This resolved the noise and improved COP, but feel I’m mitigating the problem rather than solving it…
Mmm I’ve seen this before, an installer recently showed me the data from a recently installed 6.5kW Grant, it’s been doing this since day 1: Emoncms - app view
Out of interest, could you try increasing the WC curve to increase the flow temperature to see if this makes any difference. I think this could be some sort of software gitch.
Mine often seems to go into defrost at the beginning of a DHW cycle, not sure why since there’s no frost on the evaporator. Maybe it’s a preventative defrost? Emoncms - app view
Thanks for getting back Glyn, I agree that looks like an identical pattern to what I’m seeing, if it’s a new install it maybe running the same firmware. I’ll bump up my WC curve and see if that has any impact, frustrating as it’s already off for long periods as hitting temp.
