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?