GSHP - I need help with making it as efficient as possible!

QrizB

matelodave said:

It's pretty easy to get through a lot of water, even when showering - I know mine consumes 6litres a minute because I've checked it by filling a bucket and timing how long it takes to fill. That menas a two minute shower uses 12litres and ten minute shower will use 60 litres. However there are lots of showers that can use 10-15 litres a minute and a decent rain shower even more., you could easily empty your hot water tank.
It's reckoned that a bath can use 60-80 litres, washing machines and dishwashers usually use cold water and heat themselves rather than using water from the hot tank.

Agreed; we've got an Aqualisa Quartz pumped mixer shower, and it puts out around 8-10 litres a minute.
A short shower uses roughly half a bath's worth of water but a long one can equal a bath. (My showers tend to be cooler than my bath, so there's probably less hot water used even if the total volume is the same. I can't speak for the other members of my household, though!)

Reed_Richards

ACV Smart E Plus 300 https://origin.acv.com/gb/product/XB303000-466/smart-e-plus-300

• Reduces legionella risk due to temperature: hot water stored at > 60°C

That's NOT what you want!  Not with a heat pump.  If it's true it probably means you are using an immersion heater on top of the heat pump.

Reed_Richards

If you want chapter and verse, here is a huge report on Domestic Hot Water Consumption: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/48188/3147-measure-domestic-hot-water-consump.pdf

matelodave

Theres a calculator on this page which makes it easy https://bloglocation.com/art/water-heating-calculator-for-time-energy-power

220litres from 10 to 55 degrees will require 11.5kwh however if your heatpump is doing its job then assume a COP of around 2.5 then you should only consume 4-5kwh.

You might also mix some cold in with the hot and so might not use a whole 220litres in which case the temp rise could be between 40-55 degrees.

countryhouse39

@Reed_Richards - that’s not the right tank, not sure the one we have is still made mind you, but once I’m home again I can take a picture of the manual.
it does do a superheat once a week for legionella - but I thought all tanks do by default? It does have the possibility of immersion but the immersion is switched off at the fuse board, so no chance that is sneaking on. 

I’m trying to figure out with DHW if we were to be fairly excessive with our usage and use 2 tanks a day, that should surely only equate to 18kwh if direct electric heating, but assuming a poor 1:2 ratio, 9kwh for using the GSHP… so 30+kWh for daily usage at this time of year seems v high… really need the pump meter replaced so I know if it’s actually anything to do with the pump or if it’s some rogue appliance! 

Reed_Richards

countryhouse39 said:

....it does do a superheat once a week for legionella - but I thought all tanks do by default? It does have the possibility of immersion but the immersion is switched off at the fuse board, so no chance that is sneaking on. 

My heat pump cannot manage 60 C on its own so it cannot do the weekly Legionela cycle without the aid of the immersion heater.  Have you ever actually said what your hot water cylinder temperature is set at?  I don't remember that you have.

countryhouse39

I think from memory it’s set at 44 usually, weekly legionella blast, which I have no idea how it does tbh. Will have to check. 

matelodave

Most heatpumps are limited to 50-55 degrees and anything over that requires the use of an immersion heater.

A lot of systems were set up (or tweaked by their owners) to increase the flow or hot water temperatures and consequently were pretty unhappy about their energy bills. The Legionella cycle only runs for a few minutes and as the HP does most of the heating to 55 it only need the immersion heater to raise the temp from about 55 to 60 degrees so it isn't really a major drawback.

In my case the legionella cycle heats the tank on a Saturday and the tank temp stays hot enough to avoid the hot water reheating on Sunday, so it probably balances out

Reed_Richards

countryhouse39 said:

I think from memory it’s set at 44 usually, weekly legionella blast, which I have no idea how it does tbh. Will have to check. 

It may not be able to do this at all if you have the immersion heater switched off at the fuse board.

countryhouse39

Right - having had a thorough check in the pump room, I think I have worked out the issue regarding the 'immersion'. when you refer to the immersion, I expect you mean what we call the 'auxillary' heater that is part of the heat pump? We have this, but we also have an 'immersion' which is attached to the HW tank. What we call the immersion is switched off, if it was on it would just work continuously until we switch it off and we'd have boiling water in our HW tank and vast bills. We have had it on for short periods of time when the pump stopped working as it meant we still had HW while waiting for pump to be fixed.

The auxillary (which I know is an immersion too) is currently set to come on when outside temp is 4deg or lower - I assume it is this that does the legionella blast once a week? but how it does that I'm not sure - all I know is that the super-heat definitely does happen, as the HW is v hot on the Saturday morning (when it does it in the middle of the night on Friday).

We have actually switched off the underfloor heating completely today (it was barely on, but its now switched off at the socket in the pump room) since 9am to see if our usage is reduced, but in those 3 hours we have used 4kwh, with only thing of note being the dishwasher (its power consumption is meant to be approx 1kwh for a full cycle).

I've attached the monitor we had for the pump meter to our main meter now and we are generally getting a background rate on the main meter of about 210w (I assume this is for lights, computers, phones, fridge, etc), but every so often it goes really high and I can only think this is the HW ( I know there are short spikes with kettle etc, but these are longer). I cant work out why we are using over a kwh per hour with no heating... and we seem to be doing the same in the middle of the night too (although will see how that goes tonight with heating completely off) as when I looked at the monitor at 7:30am we had already rattled through 9kwh since midnight....