ASHP water leaving temperature control

[JohnMo]

1 hour ago, MechanicalBuilder said:

dhw is using 5-7kwh to heat a 300litre tank

Couple of things to look at

 

Heat DHW in a set window or two only. I found leaving to sort it self out used bucket loads of electricity.

 

Target temperature anything above about 50 degs target temperature the heat pump doesn't always hit target temp, so the immersion is switched on. The heat pump learns this then does it every time.

 

Depending on house DHW usage one 1.5hr heating slot is ok,  or if not enough a 1.5 and 1.0 hrs slots. Do a risk assessment do you need legionella cycles? If not needed, switch the immersion control off in the Daikin controller.

[Andrew D]

I have an Ecodan PUZ-WM85VAA.

I have this in Auto Adapt mode which uses indoor temperature, I believe combined with knowing the outdoor temperature, to learn what flow temperature to use.

This allows the flow to overshoot a bit more to allow a longer off period. This is much better than the Weather Compensation mode which tries to too tightly stick to the flow temp on the curve and doesn't have the ability to be configured to allow for a bit more over and undershoot to minimise this. This causes lots of cycles in shoulder months and on systems where radiators are undersized.

 

The Ecodan will keep the system pump on constantly between cycles, I guess so it can monitor the flow and return temperatures.

My pump's speed can be controlled by PWM so I have an ESP32 running esphome connected up to this to reduce the flow rate to a minimum between cycles to save energy. Then when the heat pump's compressor is running the flow rate is increased and increased further for DHW. I've also experimented with trying to use the pump speed to hit a delta T of 5K but this doesn't seem to improve things noticeably.

[PhilT]

1 hour ago, Andrew D said:

This allows the flow to overshoot a bit more to allow a longer off period.

Longer ON period?

[Andrew D]

On 16/10/2024 at 20:37, PhilT said:

Longer ON period?

Yea, It looks like it realises the flow temperature is getting too high (because emitters are unable to get rid of the heat quick enough) and so does one last blast, often increasing input power a bit.

This then results in it being a bit longer before the next cycle.

 

I think this is probably based on it learning how your room temperature reacts to this so if doing this doesn't make much difference to how stable the room temp is it probably does it more but if it was having an impact it might not do it so much and allow more cycles.

 

The FTC6 controller allows you to configure limits on the amount of over and undershoot to allow as well as a responsiveness time that can be adjusted to account for different types of emitters, like radiators being fast responding and UFH being slower.

 

Frustratingly there is no way to configure the over and undershoot when in Weather Compensation mode. This makes it fairly inefficient unless your emitters are sized appropriately and there is enough heat loss due to low outdoor temps.  

 

This is all based on my assumptions watching what it does.

[PhilT]

1 hour ago, Andrew D said:

Yea, It looks like it realises the flow temperature is getting too high (because emitters are unable to get rid of the heat quick enough) and so does one last blast, often increasing input power a bit.

This then results in it being a bit longer before the next cycle.

 

I think this is probably based on it learning how your room temperature reacts to this so if doing this doesn't make much difference to how stable the room temp is it probably does it more but if it was having an impact it might not do it so much and allow more cycles.

 

The FTC6 controller allows you to configure limits on the amount of over and undershoot to allow as well as a responsiveness time that can be adjusted to account for different types of emitters, like radiators being fast responding and UFH being slower.

 

Frustratingly there is no way to configure the over and undershoot when in Weather Compensation mode. This makes it fairly inefficient unless your emitters are sized appropriately and there is enough heat loss due to low outdoor temps.  

 

This is all based on my assumptions watching what it does.

Mitsubishi have just released a new firmware upgrade, which they installed on my ASHP and controller for free. It's designed to extend compressor lifespan, improve overall performance and efficiency. The difference is noticeable

[Andrew D]

9 minutes ago, PhilT said:

Mitsubishi have just released a new firmware upgrade, which they installed on my ASHP and controller for free. It's designed to extend compressor lifespan, improve overall performance and efficiency. The difference is noticeable

Do you know what versions you have?
You can find this out by going to the Installer Settings and Running Information. Then using the codes 90 and 91 you get the major and minor versions for the outdoor unit and 190 and 191 give you them for the FTC.

What behaviour changes have you noticed?

[PhilT]

15 minutes ago, Andrew D said:

Do you know what versions you have?
You can find this out by going to the Installer Settings and Running Information. Then using the codes 90 and 91 you get the major and minor versions for the outdoor unit and 190 and 191 give you them for the FTC.

What behaviour changes have you noticed?

90 = 5809

91 = 0000

190 = 2001

191 = 0000

The flow temp is modulated to extend comp run time eg at room temp target 20, actual room temp sits at 20-20.5 for longer before switching off comp at top of hysteresis 21, so in warmer ambients it gives a higher ratio of comp on vs. off time

[Andrew D]

On 18/10/2024 at 17:46, PhilT said:

90 = 5809

91 = 0000

190 = 2001

191 = 0000

The flow temp is modulated to extend comp run time eg at room temp target 20, actual room temp sits at 20-20.5 for longer before switching off comp at top of hysteresis 21, so in warmer ambients it gives a higher ratio of comp on vs. off time

Yes I have the same versions as you since the summer.
I appear to be getting better COPs than this time last year but I have improved a number of things since then.

I'm reserving judgment until we've been through a bit of winter so I can do a more fare comparison. Especially to see if it's better at getting into and maintaining long runs in colder weather.

With the old firmware last year there were lots of times where it looked like it should be able to maintain a long run but would randomly ramp up overshoot and stop.

[PhilT]

2 hours ago, Andrew D said:

With the old firmware last year there were lots of times where it looked like it should be able to maintain a long run but would randomly ramp up overshoot and stop.

It still does that at warmer outside temps, say 12 - 15, but not at around the 10 or lower that we had over a week ago. Looking at the power draw curve, the behaviour suggests that AA manages the compressor to run as near as possible to its efficiency sweet spot around 40% of maximum capacity, and if it can't, then if the run has been long enough (never less than 20 minutes), AA allows the compressor to ramp up and either switch off while keeping the flow pumps running, or when target room temp +1 is reached.