Off grid house build Orkney

Builder has been taking their time on things and submitted a rather large invoice for not a lot being done. Told him just to focus on the outside and my dad and I are just going to tile the house ourselves to save paying him any more for it.

They have again got their quantities wrong and so don’t have enough of the silicone render to finish the last gable.. 3 weeks because the colour is a special order..

The renewables guy came out and fitted the turbine inverter yesterday. Had a chat with him and the sparky about this ongoing heat pump issue. Problem seems to be that there isn’t a two way control to the heat pump to tell it to not draw power when there isn’t there to draw. We think we could probably find a way around it manually, not demanding hot water and thermostats down to whatever ambient temperature there is in the house so as not to make it switch on. Talking with them though there does seem to be an inverter which can put the heat pump on a separate part of the system so it can only be switched on when certain demands are met (ie. Producing x kw and batteries at x% full).

CURRENT THOUGHTS – make it work with ASHP now? Or live with only using the immersions and woodburning stove until next year and try and add a heat pump or work out an alternative solution?

We want to avoid making an expensive mistake with the heat pump, so thinking adding it next year (if possible at all) may in many ways be preferable, we would also then have plenty of data as well as an understanding of living in the house how additional components should be incorporated. But if we can make the original plan work now (with reasonable confidence) it would certainly be great. I’ve read a couple of case studies on line with heat pumps integrated in off-grid Victron systems – which lends me to believe the Victron controller can treat the heat pump as a separate AC load from the rest of the house loads, and there is the scope to program the controller..

If a heat pump is installed, my thoughts around operation are something like this:
· ASHP should run fairly consistently in winter months – production dependent – we can live with manually adjusting timers and thermostats based on current and expected daily weather. Also, we will look to prioritise DHW only on low production days, by using the wood burning stove to provide most or all of the space heating (and possibly cooking).
· If battery storage available drops below 50% say, triggers a normal shutdown of the ASHP? i.e. Switch to allow ASHP to turn on only when battery storage is above this threshold. Allowing priority of other house loads over hot water when storage is low. Avoiding situation on low production days or at night, the heat pump running down the batteries and us having no power (also potentially avoiding the heat pump to hard shut down if power runs out)
· ASHP is not used as a dump in the sense of programming it to come on or do more when we have excess production – as this seems risky and might not be achievable anyway. We could increase load manually on high generation days by increasing DHW demand or increasing thermostats… but could a immersion be used as a dump instead, raising the water temperature of the thermal store so less is required of the heating system later? Limited by only having 3kW immersions at the moment (and assuming we can use one of them in this way). If smaller immersions can’t be added limits this dump to only when production > demand by 3kW – but could still provide a good use of excess power on very windy days. Would need some temperature sensor control for this immersion if used in this way.
· Manual management of high power ASHP legionella cycle – will need to plan this around when we have available power (and mitigate by decreasing other loads during the high power cycle).

If it’s not going to be possible to add a heat pump at this stage we will need to use immersions for water heating this Winter. We will have to rely on our wood stove for primary space heating (unless it’s windy and sunny I think) and ration our hot water use – but I think it will be liveable (we don’t have central heating in the place we have been renting for the last few years, and it’s no where as insulated as our new house and we’ve been fine). In this scenario we will want to use the immersion as a dump to take any excess production (after house loads and batteries full), which if there is plenty of wind should mean we manage to heat the water reasonably well those days?

Got the floors cleared for starting on the tiling when dad shows up this weekend too.

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