Mitsubishi Ecodan pre plumbed hot water cylinders - Thoughts and views ?

[mk1_man]

Hi all, just wondered if anybody had any experience with the Ecodan pre-plumbed hot water cylinders.  They use an external heat exchanger instead of an internal coil for faster re-heat times (supposedly)

 

https://les.mitsubishielectric.co.uk/products/residential-heating/cylinder/ecodan-r32-ftc6-monobloc-pre-plumbed-standard-cylinder

 

Am I asking for trouble going this route or are they a good option alongside quoted 8.5kw Ecodan heat pump.

[Kelvin]

It’s what we have. We’ve barely used any hot water so I can’t comment much about it. I noticed that it reheats the water fairly regularly after use (which might just be how it’s been set but not looked) and there’s no drop off in water temperature when you draw off hot water. 

What size of cylinder are you looking at as the benefits of plate heat exchangers vs large coils reduce as the tank gets bigger. 

 

 

Edited March 20 by Kelvin

[JohnMo]

1 hour ago, mk1_man said:

Ecodan pre-plumbed hot water cylinder

Don't look that cheap, unless you are getting a good deal. Plumbed for 2 zones, good if you need two zones, bit of a waste for a single zone.

[mk1_man]

Looking at the 210L and that's a full 210L as there is no large coil inside taking up space.  On a standard 250l cylinder with 3m2 coil how much usable water is left?  We have a 250l non heat pump compatible cylinder at mo and am a little concerned about dropping down to 210 litre

[JohnMo]

There is two of us and we have a 210L HP cylinder (with 3m2 internal coil) heated to 50 - never had it running out.  If more than two of you you may need bigger, or we had consecutive showers straight after washing up, that may be a different story.

[Kelvin]

The benefit of a heat exchanger is you have more usable hot water in the tank as it heats the whole tank up. But you need to size it on the number of people in the house. In our previous house, with a 250l tank and four of us, we’d occasionally run out of hot water if everyone had a shower especially as the bin lids were in the shower for ages. 

[JamesPa]

14 hours ago, mk1_man said:

Looking at the 210L and that's a full 210L as there is no large coil inside taking up space.  On a standard 250l cylinder with 3m2 coil how much usable water is left?  We have a 250l non heat pump compatible cylinder at mo and am a little concerned about dropping down to 210 litre

If you already have a 250l UVC and are considering buying one with a phe, why not add a phe and pump to your existing cylinder to 'upgrade' for heat pump compatibility.  £400 vs £1200.

 

Thats what all heat pump installers should be offering where there is an existing DHW cylinder IMHO.

[JohnMo]

26 minutes ago, JamesPa said:

If you already have a 250l UVC and are considering buying one with a phe, why not add a phe and pump to your existing cylinder to 'upgrade' for heat pump compatibility.  £400 vs £1200.

 

Thats what all heat pump installers should be offering where there is an existing DHW cylinder IMHO.

I think if I remember correctly a PHE with 1m2 surface area is equivalent to a coil with around 3m2. Then all you need is a small pump suitable for domestic water (not a CH pump). Tee into the cold feed in and hot feed out of the cylinder.

[JamesPa]

2 hours ago, JohnMo said:

I think if I remember correctly a PHE with 1m2 surface area is equivalent to a coil with around 3m2. Then all you need is a small pump suitable for domestic water (not a CH pump). Tee into the cold feed in and hot feed out of the cylinder.

Or for a sort of ready made solution buy the mixergy heat pump add on kit and throw away the interface module (or use it if you can work out what it does).  I'm not sure what the best control strategy for the pump is, probably just on/off based on a temperature sensor on the flow from the heat pump as it enters the phe.  Set a pipe stat to say 50C, job done.  Might need a relay to reverse the sense if you can't find a pipe stat with changeover contacts.

Edited March 21 by JamesPa

[mk1_man]

The problem I have been fighting is the insistence of what i consider to be an overly large heat pump. The solution currently proposed is an 8.5kW Ecodan plus their 210 cylinder with heat exchanger.   From what I have read the re-heat time doesn't appear that different to a normal cylinder with 3m2 coil.  As cylinder is in loft concerned about now having three pumps going and noise issues etc.  I would prefer single system pump within the monoblock so as to keep pump noise external.  If using an external heat exchanger was so good / efficient why are there not more solutions like this?

[JohnMo]

18 minutes ago, mk1_man said:

From what I have read the re-heat time doesn't appear that different to a normal cylinder with 3m2 coil

Better or worse?

 

Just looked at a cylinder datasheet and the usable volume (heated) for a 210L HP cylinder is 189L for a normal shape cylinder and 183L for a slimline. A 250L is 228L and 300L is 268L.

[JamesPa]

51 minutes ago, mk1_man said:

The problem I have been fighting is the insistence of what i consider to be an overly large heat pump. The solution currently proposed is an 8.5kW Ecodan plus their 210 cylinder with heat exchanger.   From what I have read the re-heat time doesn't appear that different to a normal cylinder with 3m2 coil.  As cylinder is in loft concerned about now having three pumps going and noise issues etc.  I would prefer single system pump within the monoblock so as to keep pump noise external.  If using an external heat exchanger was so good / efficient why are there not more solutions like this?

Oversizing seems, sadly, to be endemic from what we hear on this and other forums.  It's a backside covering exercise by people who don't know how to design a system properly.  The whole industry is just to accustomed to shoving a 28kW gas boiler into an 8kW house, leaving the flow temperature turned up beyond the point at which the condensing feature actually works, shoving in trvs and letting them sort it out.  Nobody complains because the house isn't cold and, until recently, nobody cares a fig about the efficiency of gas boiler systems.

 

So with no skill in system sizing or design, the safe route is to oversize heat pumps too, because people don't complain if the house is warm.  Except that those currently getting heat pumps do care about efficiency, hence the damage being done to the reputation of the technology.  Worse still oversizing frequently drives unnecessary components and costs, eg buffer tanks, unnecessary pipework upgrades and the like.  It's a dreadful state of affairs.

 

As regards the phe solution at least one other hp manufacturer also sells a similar product (Ideal I think), and the installer I hope to use if I ever get planning consent for a heat pump fits them as standard.  They are unfamiliar to your average plumber and there is a pump to worry about, furthermore they provide a way to reuse an existing cylinder which the industry certainly doesn't want to countenance.   Hence why they are not popular afaik.  

Edited March 21 by JamesPa

[JamesPa]

7 hours ago, JamesPa said:

Oversizing seems, sadly, to be endemic from what we hear on this and other forums.  It's a backside covering exercise by people who don't know how to design a system properly.  The whole industry is just to accustomed to shoving a 28kW gas boiler into an 8kW house, leaving the flow temperature turned up beyond the point at which the condensing feature actually works, shoving in trvs and letting them sort it out.  Nobody complains because the house isn't cold and, until recently, nobody cares a fig about the efficiency of gas boiler systems.

 

So with no skill in system sizing or design, the safe route is to oversize heat pumps too, because people don't complain if the house is warm.  Except that those currently getting heat pumps do care about efficiency, hence the damage being done to the reputation of the technology.  Worse still oversizing frequently drives unnecessary components and costs, eg buffer tanks, unnecessary pipework upgrades and the like.  It's a dreadful state of affairs.

 

As regards the phe solution at least one other hp manufacturer also sells a similar product (Ideal I think), and the installer I hope to use if I ever get planning consent for a heat pump fits them as standard.  They are unfamiliar to your average plumber and there is a pump to worry about, furthermore they provide a way to reuse an existing cylinder which the industry certainly doesn't want to countenance.   Hence why they are not popular afaik.  

In fairness I should add that there clearly are 'good guys' out there who know what they are doing and do it well.  I certainly don't have the information to speculate whether the good guys are the majority or the minority (they were definitely on the minority when I was getting quotes, but that might have changed with time or may be a local phenomenon). 

 

There is likely also a bias in the 'reporting', people who are unhappy may be more likely to speak about it, those who are happy just get on with something more interesting than their heating system.