Portable split air to air

QrizB

Lots of good questions, hopefully my answers are up to snuff 🙂

Do you have sufficient battery capacity to last the day though if you switch to electric heating, or do you plan to run it mostly overnight during cheap rate from the grid?

I've got 16kWh of batteries (one Fogstar unit). If domestic use is around 6kWh/day, that leaves me 10kWh that will provisionally be available for the heat pump.

Any idea what your heat loss (gas usage on coldest day / 24) is and the heat output of the unit?

Our highest-gas-use day last winter was a bit of an outlier; we used 100kWh on the day we got home from our Christmas break, but we'd turned the thermostat right down while we were away and so we had to reheat the entire structure from 10C to 20C.

Other than that, we were under 80kWh a day for the whole of December through February.

Some of that will have been for hot water, so I reckon heat loss was closer to 3kW? 72kWh/day?

It's rated at 12k BTU (3.5kW) so I should have a chance at keeping up, as long as the Fogstar battery lasts. If the battery goes flat I'll be paying IOG datime rates of 36p/kWh and I'll probably switch to gas.

how do you give your portable split … access to the outside air without creating a huge (counterproductive) draft though the open window?

It's quite a small window (45x60cm, small enough that I had to take the handle off to fit the outside unit through it). In the summer I stuffed the gap with bubble wrap. This winter I'm starting the same way, but ...

Sheet of PIR cut to fit?

... I do have some insulation board in the shed!

NedS

Yes, with a heat loss of ~72kW on the coldest days, and an assumed COP of around 3 on those colder days, you may need ~24kWh of electrical input, of which 10kWh can potentially come from battery and an amount can come directly from the grid during the overnight cheap rate period, but you will likely need to let the gas boiler do the heavy lifting on the very coldest off days.

Where it will be very efficient and beneficial is in the warmer periods where you need some heating but the outside temp is above 7C. The heat pump will be efficient to run and may provide all the heat you require. I see the main issue being how well that provided heat is able to disperse around the property, particularly the ground floor space. It will be interesting to hear how you get on.

Martyn1981

PIR is pretty easy. Just don't use a new saw to cut it, as it's abrassive and will take the edge off.

Bit of watered down PVA to coat/seal the edges, then some duct tape over it. Job done.

Perhaps a couple of small holes with a length of string/rope through them, to help with removal. And you could cut in half (or more) using duct tape as a hinge, for easier storage.

I even once made 'armoured' versions for the local animal rescue, adding a layer of PVC, to reduce cat-scratch damage. That way they had open (wire mesh) panels for the warmer weather, but easily closed off for cold weather. About 8m2 in total, and a few rope straps hanging from above, to easily store the panels away …… though some of the more timid cats, did find their way up there to hide!

michaels

Google seemed to be happy with my suggestion of purchasing a 3-4cm shorter double glazed sealed unit and then 3d printing an infill fillet for the top or bottom of the window through which you run the pipe. I am on the look out for a split unit or two at non-summer heat wave prices on ebay.

May have suggested this above but I think this approach plus leaving gas in place for hot water and the coldest days may well be the quickest and easiest way for the UK to decarbonise quickly (avoids running hp when COP is lowest, avoids overloading the grid when supply is tightest), the carrot being that as well as cheap and non-disruptive it gives AC as well.

Reed_Richards

It's quite a small window (45x60cm, small enough that I had to take the handle off to fit the outside unit through it). In the summer I stuffed the gap with bubble wrap. This winter I'm starting the same way,

A picture would help. I'm curious because we have a workroom at the back of the garage which needs heating in winter and something like this would certainly be more economical to run than the electric heater we use at present, if there was a good way to deal with the exhaust hose. Although, as we only use this room intermittently, it's harder to tell how long it would take to payback the cost.

QrizB

I ran the split in heating mode for nine hours today, to check that the location was going to work and see how it got on. Results are positive; it kept the house warmer than it would otherwise have been, and the flow of air was gentle enough not to cause any issues.

With the split set to a target of 20C, the hall, dining room and lounge a (largely open-plan space) were kept around 21C. It was wet and dull here and the outdoor temperature fell from 13C to 9C over the same period.

Total energy consumption was 3kWh.

I have a few adjustments to make but on the whole I'm happy with these results.

michaels

https://forums.moneysavingexpert.com/discussion/comment/82161982#Comment_82161982

This would so work for us. Annoyingly the big room we would want to put it in only has bifold doors and I am struggling to come up with a suitable way of running the pipework. Have seen units as cheap as 400 second hand on eBay. Typically how long is the linking pipe?

QrizB

Ran the split for 12 hours today. During that period it was our only space heating. It used 4.2kWh.

When it was actively heating it was drawing about 400-450 watts, but there were times when it would idle drawing ~15 watts and just run the circulating fan when its internal thermostat said the house was warm enough.

During that time it held my living area at 19-20C. The area is just over 40 square metres (roughly 7m x 6m) and includes an open stairwell to the first floor and an open doorway into the kitchen.

Typically how long is the linking pipe?

On mine, the umbilical is a little bit less than 2m long. About 1m80-1m90.

A picture would help.

I'll see what I can do.

Edit to add a screenshot showing the temperature in my living space today. I turned the split on around 0900.

QrizB

My split has been providing all my space heating since Sunday (3 days) but this evening we're back on gas.

For some reason my battery isn't charging fully overnight - probably my inverter settings, which I'll investigate when I get some time at the weekend. That isn't a problem when we get decent sunshine as I can top up the last 20% from solar, but today it's been dull all day. Couple that with the inverter deciding the battery's flat when the BMS says it still has 30% in it (again, probably my settings) and I've only got half my capacity to play with.

The split used 7kWh from 0900-2200 on Sunday, 5.5kWh from 0900-2200 yesterday and since ~0630 today it's used 6kWh. That's entirely reasonable, in my books, and if I can sort out my battery settings to let me use more of the 16kWh that's theoretically available, I should be able to make it last through the day even when it's dull.