Heat Pump Sizing?

michaels

So now we are allowed to put the heat pump where I want it on the side of the house less than 1m from the boundary I have got another quote.

1. They only do Vaillant and are suggesting the 7kw is big enough - its specs show it can output about 8.5kw at -7 with a 45 flow rate which is probably slightly more than we need which is about 6.5-7 kw at a design temp of -3 and a flow temp of 43. The 10kw Vaillant is too noisy.
2. We use about 20kwh of hot water a day so basically an extra 1kw of output per hour needed to cover hot water usage which I would say is quite tight on this size Vaillant?

But the more fundamental issue is should we go ahead. Currently we are using a second hand heat pump (10 year old LG 12kw) that I had originally purchased to heat the kids pool, and immersion for the hot water.

Obviously the COP on the hot water is 1 currently and might go as high as 3 if we switch to heat pump? 20 x 365 x 6.5p per unit is £475 a year, reduce this by 2/3rds will save about £300 per year.

Space heating we used (input into heat pump) about 5500kwh last year at a cop of say 2.5. If this improves to 3.5 then that would save about 1600kwh at 6.5p = £100 per year.

Total saving £400 a year, cost with grant - perhaps £5000 seems to have a very long payback period. Of course currently we have a large battery so use 6.5p per unit night rate electricity most of the time, we can't be certain that will always be available. We don't know how long our already old heat pump will last, there aren't really any servicing or even repair options for a heat pump with no provenance - then again we also save at least £100 per year on servicing!

I really want to go for new and shiny but I can't make a sensible economic case to do so until either the current system fails or it looks like the grant might be going away or I guess cheap night rate disappears.

Anyone want to persuade me otherwise or point out something I have missed? Thanks

Alnat1

Why would you expect to get a heat pump grant if you already have a heat pump?

michaels

https://forums.moneysavingexpert.com/discussion/comment/81909760#Comment_81909760

Because it is just used to heat the kids pool.

shinytop

https://forums.moneysavingexpert.com/discussion/comment/81909741#Comment_81909741

I agree. I also can't see the 7kW Vaillant being enough. Your DHW isn't going be a steady 1kW load; it'll be much peakier Also when it's cold you'll lose output because of defrosts. I think you're likely to end up with a cold house and/or using the immersion. I doubt you'll get a DHW COP of 3; unless you have a huge cylinder, with your use you'll need it as hot as possible to dilute down.

Is there a bigger, still quite enough alternative?

NedS

What about the new Grant R290 range - they do a 9kW model. I know the 6.5kW model has been well received and has a great modulation range, but not seen much on the 9kW model yet.

michaels

Thanks, there are as far as I can see the following that are 57db or quieter and at least 8kw

LG 9kw

Samsung 8kw

Viessmann 8kw and 10kw

And the Grant 9kw and 12kw

Another to add, Ideal Logic Air