Keeping tabs on a Mitsubishi Ecodan heat pump

[Gary68]

Here is a video on how to set the weather comp curve.

 

 

[joth]

11 minutes ago, Garald said:

On a different note - I think I may have improved my shower settings (improved for my comfort, possibly destroying the planet in the process and/or doing very minor damage to my wallet) by accident while fiddling with the settings yesterday. The maximum temperature in my shower is usually acceptable but sort of lukewarm (mid-30s). Now and then it behaves like a proper hot shower without warning. This morning the temperature was glorious (mid-40s?) - my girlfriend was delighted.

 

This is what my settings look like now.

 

 

 

Is everything in order?

Looks like you've set tank temperature to 56° and turned on the immersion heater (Choc thermique?). That will hurt your wallet. 

You should be able to get acceptable shower temps of 48° or so without needing the immersion on all the time. 

[Gary68]

Video on how to set your hot water temp.

 

 

[Garald]

13 minutes ago, joth said:

Looks like you've set tank temperature to 56° and turned on the immersion heater (Choc thermique?). That will hurt your wallet. 

You should be able to get acceptable shower temps of 48° or so without needing the immersion on all the time. 

 

I thought "choc thermique" set as it is is just for legionella? At any rate, I'll follow the video so as to fix things.

[Garald]

23 minutes ago, Gary68 said:

Video on how to set your hot water temp.

 

The problem is that; while my controller looks just the same, it doesn't give me all those wonderful detailed options in the heating menu. On the left, I can just choose between two modes - "Normal" and "ECO". I may have set it on "Normal" yesterday. I just set it to "ECO". No idea what temperature range that corresponds to - I'll see tomorrow morning.

 

As for "choc thermique", I thought it was necessary to keep one of the two arrows checked to kill legionella?

 

[Gary68]

Are you sure you are pressing and holding the menu button until the menus come up, its a press and hold to get to the settings a quick press doesn't get you there its at 2.28 in the video

[Garald]

On 02/02/2024 at 15:50, PhilT said:

You are in "read only" mode. If you want to change any settings, from the FTC6 main home screen you need to press and hold the bottom left button for a few seconds. After that the domestic hot water settings window on the left in your last photo above will also show an edit symbol next to the two arrows in a circle. You should then also be able to change your WC settings. There are several YouTube videos on how to do this

 

Ah, will try that then, thanks.

 

So, I should set the hot water temperature to 48C, and leave the "choc thermique" (to protect against legionella) activated?

 

Also, what is a sensible curve? 45C was enough at -4C (even though it stayed under 0C for several days). I did all computations so that the house would be fine with a flow temperature of 40C even at -7C (leaving myself a margin of safety, obviously - but by a factor of less than 2). 

 

If I leave the flow temperature at 50C for an outside temperature of -15C, and set the flow temperature at a notional -30C for an outside temperature of 35 C (the only parameter I can currently control), that means that the system will bother to turn itself on when the line

 

y = 50-((50-(-30))/(35-(-15)))*(x-(-15)) = 26 - (8/5)x

meets y=x,

and it is to see that that happens when x=10, i.e., when the outside temperature is 10 C. A pretty sensible value in a well-insulated house, I'd say, no? It's slightly silly for the system to draw that as a line all the way to the right when it should be something \_ - shaped, but hey. At the same time, the flow temperature when it is -5C outside will be 34C, which seems to be low-ish.

 

(It does make perfect sense for the "curve" to be a line for the most part: for the sake of equilibrium, you want the difference between flow temperature and room temperature to be proportional to the difference between room temperature and outside temperature, so flow temperature has to be an affine linear function of outside temperature.)

 

Let's say I go with 40C at -5C, and that I'm happy letting the heat-pump work (with a flow temperature of 15C) starting when it's 15C outside. (In theory, that should really be 19C or whatever one's ideal temperature is, but that's a bit daft and eco-unfriendly.) Then the flow temperature at -15C should be 47.5 C, and the flow temperature at 35 C should be -10C. Does this sound good?

Edited February 4 by Garald

[Garald]

If I remember correctly, the factory setting (or the installer's setting) had a flow temperature of 50C for an outside temperature of -15C; and a flow temperature of -15C for an outside temperature of 35C. That would correspond to a flow temperature of 37C for an outside temperature of -5C, and the heating would go on when it's about 13.25C outside. If anything, that sounds like a very sensible baseline. Maybe that was the factory setting for a reason, and I should go back to it (not that I am feeling cold now, far from it.)

[PhilT]

19 minutes ago, Garald said:

If I remember correctly, the factory setting (or the installer's setting) had a flow temperature of 50C for an outside temperature of -15C; and a flow temperature of -15C for an outside temperature of 35C. That would correspond to a flow temperature of 37C for an outside temperature of -5C, and the heating would go on when it's about 13.25C outside. If anything, that sounds like a very sensible baseline. Maybe that was the factory setting for a reason, and I should go back to it (not that I am feeling cold now, far from it.)

Do you have a radiator circuit? My max is set to 50degC flow temp at -3degC outside temp, minimum 35degC flow temp at 15degC outside temp.

BUT - If you plan on switching to Auto mode this range is not critical, because the max flow temp is governed by the room temp - mine rarely goes above 40 and from what you said I don't think yours will either. At time of writing here it's 11degC outside and the flow temp is 33degC. As you can see from the chart below this is how Auto mode reacts as room temp is reached.

 

Domestic hot water temp is down to personal choice, no. of inhabitants, size of tank, lifestyle etc. Mine is set to 42degC and I never run the legionella cycle.

 

 

Edited February 4 by PhilT

[Kelvin]

I’ve switched the legionella cycle off. Do your own research on this though before deciding one way or another. 
 

But as above you need to put it into edit mode which gives you access to the weather compensation curves. 

[Garald]

Right - I was misunderstanding things because I was in read mode (so semi-ignore my previous mode).

 

Now I understand that the curve is indeed flat-linear-flat - at the maximal temperature at which the system goes on, it goes on with a flow temperature of 25C.

 

Now I've set things as follows:

- I've set the flow temperature to be 47C when it's -15C and 22C when it's 15C, so that it's about 40C when it's -7C; this seems like sensible values; above 15C, there doesn't seem to be much of a point in keeping the heating on, even at very low flow temperatures;

- Before, the maximum water temperature was 50C (I've kept that) and what I take is the maximum temperature drop-off was 10C (so the minimum temperature was 40C). I've decreased the maximum temperature drop-off to 7C. (By the time water gets to my shower-head, I take it will a couple of degrees colder.) Planet, forgive me, but I'm doing much more by reducing flow temperatures. I could take the maximum temperature down to 49C or 48C if that helps energy consumption.

- By default, the legionella cycle is 65C, once every 15 days. I've kept that for now, but shouldn't it be run weekly?

 

Edited February 4 by Garald

[PhilT]

38 minutes ago, Garald said:

Right - I was misunderstanding things because I was in read mode (so semi-ignore my previous mode).

 

Now I understand that the curve is indeed flat-linear-flat - at the maximal temperature at which the system goes on, it goes on with a flow temperature of 25C.

 

Now I've set things as follows:

- I've set the flow temperature to be 47C when it's -15C and 22C when it's 15C, so that it's about 40C when it's -7C

 

22 is a very low minimum for a radiator circuit, and the badly named (as you rightly implied) WC "curve" is probably on the conservative side, but try it out to see if it keeps your house at the temp you want. 

[Garald]

2 hours ago, PhilT said:

22 is a very low minimum for a radiator circuit, and the badly named (as you rightly implied) WC "curve" is probably on the conservative side, but try it out to see if it keeps your house at the temp you want. 

 

Would it be better to have the circuit go on only at 12C, with a flow temperature of 25 C? There's nothing terrible about not having heating at 13C (I grew up in a place where everything was made out of brick, nothing was or is insulated, there is no heating, and temperatures stay at a damp 10C for a month or two, with no solar gain) but it seems a bit (self-)unkind.

(Which curve is on the conservative side? The one I have chosen? Do you mean I should set it lower?)

Edited February 4 by Garald

[PhilT]

10 hours ago, Garald said:

 

Would it be better to have the circuit go on only at 12C, with a flow temperature of 25 C? There's nothing terrible about not having heating at 13C (I grew up in a place where everything was made out of brick, nothing was or is insulated, there is no heating, and temperatures stay at a damp 10C for a month or two, with no solar gain) but it seems a bit (self-)unkind.

(Which curve is on the conservative side? The one I have chosen? Do you mean I should set it lower?)

Depends on what type of emitters you have. 25 minimum might be ok for UFH but probably too low for radiators unless they are well oversized. If you have radiators try minimum flow temp 30 at 12 outside, up to maximum flow temp 50 at -8 outside, which rather neatly works out at matching increments of exactly one degree for both flow and outside temps. You need the max/min to both be higher than required in case there is a situation where the room temp drops further than normal below target room temp, otherwise it will take too long to get room temp back to target. For normal day to day operation, Auto mode will override WC and keep the flow temp limited to only that required to keep your room temp on target.

Edited February 5 by PhilT