Ecodan COP thoughts

[JohnMo]

19 minutes ago, ReedRichards said:

 

No, it's terrible, but I am struggling to think how an installer could get this wrong.  

 

22 minutes ago, dpmiller said:

monitor the flow temp to the tank during the DHW heatups. You'll likely find the ASHP is maxed out, and the top third of your tank will end up at those temps...

No, check the home brew monitor system first. 

 

Set cylinder to heat once maybe twice per day only. There are 3 different target temperatures for the cylinder in a 24 hour period. Set once for a cheap electric period and once middle of day for best CoP, all other times set to 10 degs so DHW doesn't fire up unnecessarily. Always heat to same temperature or don't heat at all. Target 47 to 50, anything higher is a waste of energy.

 

The temperature monitor is at the bottom 1/3 of the cylinder, its temperature dropping a few degs means nothing on a 400L cylinder, you still have 300L of super hot water.

[Gary68]

I have an Ecodan with a 210L tank we only heat once a day to 47C and don't reheat, its fine for 2 showers and a bath, with a 400L tank you definitely don't need to reheat during the day.

[puntloos]

OK Inline, I'll do heavy editing to keep it shortish

14 hours ago, SteamyTea said:

Tap DHW, Immersion, overheating, stop heating

currently 40 (sensor says 42), no immersion. Overheating, interesting, I might check the top if I can. Stop> worth an experiment.

12 hours ago, JohnMo said:

Strong suspicion there will be a bit of shite in, shite out going on.

 

It looks like from your bottom trend, the cylinder temp goes up about 7x in a 24 hrs period on the 19th, if you are actually heating that many times, you maybe getting a rubbish CoP as everything is occurring at high temperature. A lot of energy being moved aboard not much work being done?

 

You seem to have the same CoP for DHW over a whole day, wouldn't expect hot generation to be over a whole day, just one or two heats. When you start projecting a CoP that occurs for an hour over 24 hrs you get rubbish out 

 

How exactly are you measuring CoP for DHW?

 

How many times do you heat the cylinder per day?

Poor measurement, yea Mitsu only provides energy consumption over a day. And yes, the device switches on fairly often per day because the temp seems to drop below the treshold (eg set to 42, dropped to 36) but indeed seems to be done heating quite quickly, it seems to say it heats "the 400L tank" (again, sensor in the lower pocket) 6 degrees in 12 minutes, en then switches off. 

 

Also, one thing I noticed is that even if we're not using hot water, there's a somewhat immediate steep drop of tank temperature after heating, only then to mellow out:

 

Could it be the heating is pretty focused around the area where it measures, and then when the tank mixes, it starts averaging out, only then to drop more gently?

 

12 hours ago, dpmiller said:

monitor the flow temp to the tank during the DHW heatups. You'll likely find the ASHP is maxed out, and the top third of your tank will end up at those temps...

By "maxed out" do you mean it's heating at a super high target temp? 

12 hours ago, ReedRichards said:

No, it's terrible, but I am struggling to think how an installer could get this wrong.  

 

11 hours ago, JohnMo said:

 

Set cylinder to heat once maybe twice per day only. There are 3 different target temperatures for the cylinder in a 24 hour period. Set once for a cheap electric period and once middle of day for best CoP, all other times set to 10 degs so DHW doesn't fire up unnecessarily. Always heat to same temperature or don't heat at all. Target 47 to 50, anything higher is a waste of energy.

 

 

The temperature monitor is at the bottom 1/3 of the cylinder, its temperature dropping a few degs means nothing on a 400L cylinder, you still have 300L of super hot water.

Will try setting it to 50 (cheap) 10 (noncheap).. maybe that will help. I worry that the sensor might think we reached 50 too early and just stop, but if we're coming from a low temp it might work

 

10 hours ago, Gary68 said:

I have an Ecodan with a 210L tank we only heat once a day to 47C and don't reheat, its fine for 2 showers and a bath, with a 400L tank you definitely don't need to reheat during the day.

Yes, seems like we have the same consumption yet I seem to struggle (although of course bigger tank, more heat loss)

[JohnMo]

3 minutes ago, puntloos said:

6 degrees in 12 minutes

Sounds like it's doing very little unless you have a huge heat pump. 

 

Are you on an external plate exchange or internal heat coil?

 

Sounds like the cylinder is just getting stirred up and cylinder thermostat says I'm hot enough. Heat pump does work at high temperature with no benefit 

8 minutes ago, puntloos said:

one thing I noticed is that even if we're not using hot water, there's a somewhat immediate steep drop of tank temp

Even more evidence the tanks just getting stirred 

 

10 minutes ago, puntloos said:

Will try setting it to 50 (cheap) 10 (noncheap).. maybe that will help. I worry that the sensor might think we reached 50 too early and just stop,

Just give it an 1.5 hrs window to heat and see what happens

[Gary68]

I believe a 400L tank should have 2 sensors 1 towards the bottom and 1 towards the top, there is a setting in the hot water menus to set the cylinder to std or large.  Large will mean it uses the bottom sensor if its set to std it will be using the top sensor only and only heating the top third of the tank.  If you have enough HW this probably isn't the case but worth checking, the std and large settings are under DHW recharge in the menu

[puntloos]

Not a huge heat pump (8.5kw - decent?) but indeed I think the major problem the device has is that the temperature (as measured, at least) in the tank fluctuates so quickly that when the ASHP thinks it's done, the next time it needs to start up is pretty soon after. 

 

As can be seen in the graphs the pump really only runs for ~20 minutes, regardless of what target temp I set it to. Case in point:

 

 

At 11:09 the difference between target and actual is 5C, and the ASHP (mitsu logic) switches off at 23:25 or so, almost immediately when it hits the target temp. 

 

What I am wondering here - if the ASHP is being asked to provide 40C water, and the tank approaches that 40C, can't it just keep running at 40C for a decent amount of time? Or will not being able to lose the coolant heat to the tank heat quickly enough be more inefficient still? 

 

Frankly I'm still trying to make sense of the overall temp in my tank. The amount of temperature loss due to a short shower is massive. Eg this is my kid today showering for, it seems, about 10 minutes, and the tank drops from 48 to 30. The showers are clearly not "eco" but they are also not excessive wrt the amount of water we are talking about. (also my water pressure is 3bar)

[joth]

As I've suggested before, add monitoring/logging for the high and low pockets in the tank, I expect you'll see the top stays permanently at/above target and the bottom around 10°C or smth

 

[puntloos]

5 hours ago, joth said:

As I've suggested before, add monitoring/logging for the high and low pockets in the tank, I expect you'll see the top stays permanently at/above target and the bottom around 10°C or smth

 

Indeed, it's on the todo list - I'm sure we'll get to it when things get moving again.

[ReedRichards]

On 24/03/2025 at 18:09, puntloos said:

Frankly I'm still trying to make sense of the overall temp in my tank. The amount of temperature loss due to a short shower is massive.

 

If the water coming out the shower had dropped to 30 C I'm sure your kid would have let you know!  The only logical explanation I can think of is that the sensor is right at the bottom of the tank, for some unknown reason.  That's pretty much was @jothis saying.