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sharpener asked

Control of heat pump on 5k MultiPlus II

I am planning to add a 12kW Vaillant Arotherm Plus to my setup which has a 5k Multiplus II, 6.9kW of PV and 10.65 kWh of Pylons.

The HP has a max starting and running draw of 23.3A. The ideal scenario is to power it as follows:

  1. from Economy 7 cheap rate at night
  2. from Solar PV during the day
  3. from the Victron battery system during the evening

I hope to get as close as I can to this using the following control strategy

  1. Scheduled Charge to 100% from 2300 - 0000 and 0100 - 0700 (these bizarrely are the E7 times in my area of S Devon).

    From 2300 - 0400 (say) the HP will be on night setback to reduce noise.
    From 0400 - 0530 it will be on a slightly high setting to charge up the floor slab at cheap rate
    From 0530 - 0700 it will charge a 210 litre thermal store to 55C and heat the hot water

  2. During the day and early evening (0700 - say 2000) use Scheduled Charge set to 10% to prevent the HP discharging the battery. This will keep it fully charged and so available in case of a power cut. Any PV generation will reduce peak rate consumption from the grid. If there is prolonged fine, cold weather I can reduce the overnight target to less than 100% to leave room for surplus PV.

  3. Late evening (2000 - 2300) terminate the scheduled charge to allow the HP to run down the battery. Use the thermal store to heat the radiators in the bedrooms. Adjust the start time of 2000 so the battery is just out of useful charge when the cheap rate starts again at 2300. Possibly I could automate this last step with Node Red, all the rest can be done with standard ESS settings.

I would be grateful if anyone can suggest improvements or alternatives to the above. Particularly @Jason - UK who IIRC has a similar setup with a Mitsi Ecodan.

Would the new predictive ESS help with all this or is it an irrelevance?

TIA

Multiplus-II
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2 Answers
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nickdb answered ·

Hi. You have a fairly small inverter for such a HP. Ignoring other loads, 23A is already beyond the inverting ability of the 5kVA, it would require mains to cover the gap.

The brochures state they have a control unit for app control, it should be using some form of public framework that could be controlled via node red, and hopefully allows more creative control of the appliance.

Mine uses a tuya based controller, so I have full visibility and control of the pump - though I mainly, turn it on at a fixed time, and once it detects the desired temp it is deactivated for the rest of the day.

Ultimately, the inverter can't differentiate between loads, the new DESS, would provide some flexibility into when the system pulls/pushes to/from mains, but this is more beneficial for varying rates, alternatively, as you stated, the existing scheduling tools, or using node red for applying more advanced logic.


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sharpener answered ·

Yes, it will need the grid unless running on reduced power. But the Multi's passthrough rating is 50A and it copes OK with my 7kW EV charger. (There is a bypass switch which will enable me to use this at the same time as the HP.)

Fortunately we have an oil-fired AGA we use all through the winter so there is no cooking load.

By "The brochures state they have a control unit for app control" I assume you are talking about Vaillant. We will be getting their internet access module but I don't think it will help integrate with the Victron setup.

Some more detail of yr tuya-based configuration might be interesting if you are willing to share...

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nickdb avatar image nickdb ♦♦ commented ·

Their app module (VR700/VR900) says it supports Alexa. Usually they are based on a generic platform which means you might be able to use an API via node red for control from the GX. I do this for my Tuya based system. Not familiar with this HP though, but if you dig around, you will probably find someone who has integrated it with an automation platform.


Mine I use to dashboard some data, and to force it to only run a heating cycle and then turn off, so it doesn't constantly heat. It is a smaller 5kW appliance, heating 300L of water, which it does brilliantly in around 1 to 2 hours and consumes 1 to 2.4kWh.

I wrote a post on the modifications section about using Tuya. The concepts will be similar.

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