Energy cutting/efficiency questions

Spoonie_Turtle

We are all-electric, annual usage is ~10,000kWh.  Prime suspects are very old appliances, and the heat pump, although we are of course auditing all of our usage.  Thanks to a few other extremely informative 'why is my energy use so high?' threads we've been able to start investigating, learned how to work out how much things cost, etc.  But I have some questions for which I think it would be simplest to start my own thread.  (The most pressing questions right now are about the heat pump but no doubt I'll end up needinf to ask about other areas too.)

I'm not sure which model the heat pump is, it's Ecodan, monobloc, the whole thing is outside and the water cylinder inside.  Installed c.2019 I think.  We have a manual but it's basically for installation and is more along the lines of "your installer has set it up for you, don't change the settings" - and we left it in the cupboard so it didn't get lost, but I need help to access it and that's why I couldn't find out the model before posting.  I'm going to try to get in there this afternoon though.

At the moment the hot water is set to 55℃, and heating set to 18℃.  Currently both are 'always on', not ideal for the hot water I know but I don't fancy having to debate my Dad on that one until it's the only issue left - he's convinced it's cheaper to make it heat a little at a time rather than a whole lot at once, on a timer.  Although if anyone has any firm evidence either way, please do let me know!

Questions:
- What is the weather compensation curve on a heat pump?  How do I find it, and what should it be set to (or roughly)?
- What is the flow temperature (flow return?), what does it mean and what should that be?
- We have a water cylinder; how do I know whether there is an immersion heater component?  The cylinder and piping replaced where our immersion heater was before.
- How would I find out if it runs a legionella cycle?  If it does, we could probably turn the water down a few degrees.

Please, please, I've seen people link informative videos especially for heat pumps, but I need it explained simply and in writing so it's easy to refer back to - brain fog and lack of any spare energy makes it very difficult to make sense of things where I don't have a basic knowledge already from before, and heat pumps are a total mystery to me.

We've just started hearing the outside unit going again with it being colder the last few days, so that was my cue to get on with trying to understand what the system's doing and maybe set it to be more efficient.  Thanks in advance for any help!

BUFF

you may find some useful info on heat pumps in https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving

Coffeekup

I can't comment as I know nothing about these things, but I'm gonna link a couple of people that have them and know there stuff when it comes to these things.

@QrizB   @Mstty

FreeBear

Spoonie_Turtle said:  How would I find out if it runs a legionella cycle?  If it does, we could probably turn the water down a few degrees.

Legionella is a very small risk in the UK. About 250 cases are reported each year, and over half of those were contracted whilst abroad. In addition, the incoming water for your hot water will have been treated to kill bacteria at the treatment works, so unless you have a storage tank open to the elements, the chances of contamination is very remote.

Maintaining a temperature of 50°C or more will ensure bacteria will be killed - The higher the temperature, the faster the little burgers die. 60-65°C is the oft quoted temperature if you want to ensure instant death, but in reality, 50-55°C is equally effective.

Turning your hot water temperature down to say 52°C will save you a few pounds without compromising your health.

Spoonie_Turtle

BUFF said:

you may find some useful info on heat pumps in https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving

Thanks, I did have a quick look but 20 pages of the forum produced one short thread (not helpful to me) and one very long which I don't have the capacity to trawl through.

FreeBear said:

Spoonie_Turtle said:  How would I find out if it runs a legionella cycle?  If it does, we could probably turn the water down a few degrees.

Legionella is a very small risk in the UK. About 250 cases are reported each year, and over half of those were contracted whilst abroad. In addition, the incoming water for your hot water will have been treated to kill bacteria at the treatment works, so unless you have a storage tank open to the elements, the chances of contamination is very remote.

Maintaining a temperature of 50°C or more will ensure bacteria will be killed - The higher the temperature, the faster the little burgers die. 60-65°C is the oft quoted temperature if you want to ensure instant death, but in reality, 50-55°C is equally effective.

Turning your hot water temperature down to say 52°C will save you a few pounds without compromising your health.

That's good to know, thanks!

I've found a manual that looks familiar and now know how to identify whether it does run a legionella cycle or not - it will be useful to know, to understand the energy it uses (though it tells me nothing about how to change the more advanced settings tbh).

The manual is this one https://www.sourceenergy.info/wp-content/uploads/2013/05/Mitsubishi-control-homeowner-manual.pdf  far from comprehensive!

Mstty

Hi Spoonie,

When you can pop outside on a plaque will be the model number. Inside the controller you use will be an FTC 5 or 6.

If it's been left as installed by an engineer no doubt everything has been left turned up high with the backup electric heaters kicking in and boosting temperatures faster.

I was a bit flummoxed when you said you couldn't follow YouTube videos as that's where I learnt the most about getting round the controller menus but if you get the model number there are better instruction manuals that the one you have already found.

Mstty

Hi Spoonie,

When you can pop outside on a plaque will be the model number. Inside the controller you use will be an FTC 5 or 6.

If it's been left as installed by an engineer no doubt everything has been left turned up high with the backup electric heaters kicking in and boosting temperatures faster.

I was a bit flummoxed when you said you couldn't follow YouTube videos as that's where I learnt the most about getting round the controller menus but if you get the model number there are better instruction manuals that the one you have already found.

Spoonie_Turtle

Mstty said:

Hi Spoonie,

When you can pop outside on a plaque will be the model number. Inside the controller you use will be an FTC 5 or 6.

If it's been left as installed by an engineer no doubt everything has been left turned up high with the backup electric heaters kicking in and boosting temperatures faster.

I was a bit flummoxed when you said you couldn't follow YouTube videos as that's where I learnt the most about getting round the controller menus but if you get the model number there are better instruction manuals that the one you have already found.

Thanks, that hadn't even occurred to me

With the YouTube videos, it fluctuates.  And at the moment, just not happening.  It's extremely frustrating.

Spoonie_Turtle

Right.  Model number PUHZ-W85VAA, I can't seem to find anything more comprehensive other than technical schematics for the actual pump.  I don't know if I'm not looking up the right thing.

Water temperature, it turns out what I saw before was the current temp at the time I looked, not the actual setting.  So we know it goes up to 55℃ at least, right now it's 45℃ and the pump's on doing … something.  It did say defrosting but that's gone off and it's still doing something.  I don't know.  Oh, now it's the normal heat pump symbol, but the hot water's paused and heating shouldn't have kicked in as the thermostat still reckons it's 19℃ indoors.



I did try watching a short vid with the sound off, and it seems we're actually missing the option to change the water temp.



I'm now not sure what to do about the legionella cycle, not knowing how long the water does actually spend above 50℃.

This is the setup - what do these tanks at the top do?  Are either an immersion?  Does the legionella cycle use an immersion if there is one, or would it use the heat pump?


*sigh* I'm exhausted now despite haven't been able to actually do anything useful to it

Oh, also.
The consumption/delivery figures - why would it have used energy for heating during months when it didn't deliver anything?  And is that an indication to turn the heating off when it's consistently warm enough?  Not much we can do about it now, but good to know for next year at least.

It used 36kWh for DHW and 50kWh for heating in August!!! delivered 96kWh apparently, for HW. 
July the consumption was the other way round, and delivered 146kWh.

Again, thanks in advance for any help.  I am zonked and need a lie down.

Mstty

Nice work that gives us a start.

So when you are ready press and hold  down the menu button (don't just press once) marked with the red arrow below until it takes you to the next screen then let go of the button. 

You will then have options to edit your hot water and legionella settings when you click on the tap option.

Spoonie_Turtle

Mstty said:

Nice work that gives us a start.

So when you are ready press and hold  down the menu button (don't just press once) marked with the red arrow below until it takes you to the next screen then let go of the button. 

You will then have options to edit your hot water and legionella settings when you click on the tap option.

Ohhhhhh my word THANK YOU!

Turns out the water's set to 50℃ … it was during the first heatwave when we first checked which may explain why it as actually 55℃ at the time.   Edit: or it could have been after a legionella cycle.

[I've now changed it to Eco and 49℃.  If nobody notices I might try 48℃ in a few days.]

So … these are the current DHW settings


And legionella cycle settings


Are there any adjustments needed there to make it more efficient?
Esit: I've changed it to 3pm, in the hope the water will need less heating at that point.


I also found the compensation curve for the heating, really don't understand what it does or how it should be set if we were to use it.  The long-press of the menu opened up some options to tweak the shape of the curve, in addition to the temperature adjustment along the x-axis.

The heating has 3 options, going by the curve, going by the house temperature (which it currently is and I guess always has been), and another symbol I don't recognise:


Anyone know what that one means, please?  And again with efficiency, which one is best?  (Though admittedly we quite like understanding how it works at the moment, with the thermostat temperature.)