Hot Water Heat Pump - A Project

michaels

So there has been some discussion about using A2A for space heating (as well as cooling) but of course this doesn't cover hot water.

We are coming from a slightly different direction, we got a second hand heat pump (LG 12kw £380) to heat our above ground pool and then the gas boiler broke and rather than getting it replaced I decided I wanted to go house heat pump but this was going to take a decent amount of time so as a temp measure I drilled two holes through a wall and teed into a pair of radiator tails and connected up the pool heat pump. This turned out to work rather well and we are now entering our third winter (along with using it for water rad cooling in the summer).

Of course just like an a2a system, this does not cover the hot water. We already had a pressurised tank so switched to using the immersion. Not as mad expensive as it sounds as we used EV/E7 tariff at less than 7p per kwh, with any reheat needed in the day coming out of out battery which is also topped up overnight.

However we remain big hot water users - at least 20kwh worth a day so even at 7p per kwh this is still £500+ a year at a COP of 1 so moving to a COP of 3 would save £340 a year.

Hence the new project:

We picked up a Ochsner Europa Mini IWP for £100 on eBay (badged as Groundsun, brand new but sitting for several years) and will be fitting it over the next week or two. It is a bit of an undertaking as we are putting it in the loft (where the cylinder is) and will need to enlarger the hatch. Then we will put it on a sound damping mat on a 'table suspended by spring mounts from the rafters to reduce noise and vibration with vents down into the eaves and out (and in) through the soffits. We will also need to create an insulated enclosure because the loft is outside the normal thermal envelope of the house and these units apparently don't like sub-zero temperatures. The unit in question is not unfortunately wifi controlled but we will probably timetable a lower day and higher over night tank temp so it mostly heats during the off peak window for morning showers but still tops up in the day for our evening showers.

The unit draws about 500-700w and outputs between 1.1kw and 3kw depending on outside air temp (according to the spec) so even at the coldest it should still give us more than enough for our 20kw daily demand but we still have the immersion as back up. I am also planning to add an alternative air route drawing form in the house and returning the cooled air back inside which I will use in the summer when hot to provide 'free' cooling upstairs off the back of the hot water heating.

My plan is to keep the board informed especially on how well it works in reality to see whether this is a good route to potentially provide hot water along side A2A heat pump systems. Obviously our capital cost is not realistic but there are equivalent Trianco units on eBay currently for £550.

michaels

Progress so far is to attach the Ochsner where the LG joins the central heating to check it actually works - test passed although the output (at 10c air temp) was not enough to make a lot of difference to the house.

Next step is to cut the loft hatch trimmer and get it up into the loft - 47kg unit so not too bad.

Magnitio

Looks like a fun project. How will you deal with the condensation drainage? Do you have somewhere to plumb it in?

michaels

https://forums.moneysavingexpert.com/discussion/comment/82173113#Comment_82173113

Cos the cylinder plumbing is all there in the loft already there is a PRV, tundish and drain so I can tee into that :)