Vaillant Unistor cylinder - or not

[mk1_man]

Thanks for the input re the cylinder.  I have decided to bite the bullet and go with a Joule Cyclone high gain, 3m2 coil, 28mm fittings, bonus is that they do the 250l in a 'short' 600mm diameter so height is only 1400mm, this is beneficial as my small plant room is in the loft (warm roof) with restricted headroom.

 

[JohnMo]

3 minutes ago, mk1_man said:

room is in the loft

Make sure the diameter isn't an access issue, if you are going through a loft hatch

[mk1_man]

Just now, JohnMo said:

Make sure the diameter isn't an access issue, if you are going through a loft hatch

 

We have a nice 800mm entry to loft room with stairs - use it as a den for my lad, door off that to ' plant room '

[sharpener]

On 11/04/2024 at 17:49, mk1_man said:

It is frustrating as my existing cylinder is a Warmflow solar 250l with twin coils....  I am hoping I can convince them that my existing cylinder is fine and swap it out afterwards if proven not.  The Vaillant R290 shows good efficiency even at 65 - 75 degrees, if that is the case I don't see why anyone would have to swap out their cylinders.

 

Sorry to learn you have lost the battle against the MCS orthodoxy @mk1_man.

 

Edited April 13 by sharpener

[HughF]

I’ve got the smallest vaillant cylinder, the 150 slimline (1m2 coil) being driven with a 9kW ashp - works perfectly…

 

Glyn Hudson uses the same on a 5kW Samsung, again no issues.

 

The vaillant cylinder is a decent one, coil is at the bottom for maximum efficiency.

[mk1_man]

The ongoing indecision of Vaillant or Joule cylinder continues.  On paper the Joule heat pump cylinder appears superior i.e. 28mm coil diameter v 22mm, 3m2 v 2.4m2 for Vaillant,  immersion when required is lower down, both do 595mm diameter so shorter than normal for 250l which is what I need.  Vaillant has a better insulation with a B rating.  My big doubt is that feedback on Internet is very poor for Joule customer service with what appears a high failure rate after just 2 or 3 years?   What are peoples thoughts / experience?  

 

Regarding the coil area etc not sure why so much emphasis is placed on this with coil capacities of 40 - 42kW being quoted.  If the heat pump can only output 6 - 9 kW why does this make such a difference?

 

Thanks all.

[JamesPa]

2 hours ago, mk1_man said:

Regarding the coil area etc not sure why so much emphasis is placed on this with coil capacities of 40 - 42kW being quoted.  If the heat pump can only output 6 - 9 kW why does this make such a difference?

For the simple reason that many, possibly most, heat pump installers will insist on replacing a cylinder with a coil area less than 3sq m.  They are, in many cases, wrong to do so but sadly its a case of Resistance is Useless (well almost).  So if you are installing a cylinder and planning later to install a heat pump, it's the 'safe' choice.

 

I'm not sure how kW capacities of coils are measured, but I suspect its at a higher flow temperature than is typical of a heat pump (noting that ht heat pumps can reach 75) so you probably can't make a direct comparison.

 

Nevertheless the frequent insistence on 3sq m remains unjustified in many cases.  Of course for the grant chasers it provides an excuse to spec a new pre plumbed cylinder which means rookie plumbers are less likely to make a mistake.  

Edited Friday at 17:44 by JamesPa

[JohnMo]

Heat geek - love or hate them, have done a couple recent videos on cylinder heating may be worth checking it out.

 

Of note is Telford do a cylinder designed by heat geek and mixergy have changed their heat exchanger (bigger) and control logic in line with what is discussed on the video.

 

For me bigger is better (m2).

[sharpener]

3 hours ago, mk1_man said:

The ongoing indecision of Vaillant or Joule cylinder continues.

 

From the other thread I thought you were now doing the job as DIY with a friendly plumber under an MCS umbrella. Will they not allow you to keep the original Warmflow? As I recall it has twin coils which you were planning to connect in series. If you choose the 5kW HP I am sure it would be more than adequate, as posted elsethread it will turn down to about 2kW when delivering at 55C.

 

I have recently had a quote from an (otherwise reasonable) installer who is very keen on the Heat Geek cylinder which is made by Newark. I have looked at this and think it is over the top. Also some of the stuff in the first HG video is IMO plain wrong, I think keeping the tank mixed as it heats up is thermodynamically the better thing to do. Maybe @JamesPa has a view on this?

 

Yes I have read that Joule have poor quality control, and also that Gledhill are not 100% pressure tested at the end of the line with leaking joints being reported on arrival. So I would pick Newark's ordinary range or Telford.

[JamesPa]

11 hours ago, sharpener said:

, I think keeping the tank mixed as it heats up is thermodynamically the better thing to do. Maybe @JamesPa has a view on this?

Mixergy have a blog on this and claim so. I read the argument, it's plausible but I haven't examined it critically.

 

Keeping the tank mixed means you can heat more to target temp, but the top of the tank presumably takes longer to warm so maybe it seems like the recovery time is a bit longer.

 

I have been wondering what happens when you call for water during a heating cycle.  There is possibly a risk of getting cold water.  I'd be interested in views/experiences of this.  Presumably it's dependent on pipe layout

Edited Saturday at 06:51 by JamesPa

[JohnMo]

1 hour ago, JamesPa said:

wondering what happens when you call for water during a heating cycle

Doesn't mixergy plan heating cycles around your normal life style, monitoring what you when and circling with hot water?

[JamesPa]

3 minutes ago, JohnMo said:

Doesn't mixergy plan heating cycles around your normal life style, monitoring what you when and circling with hot water?

I think so, but I'm thinking of the DIY assemblies with a pump for mixing, such as @sharpener has spoken of (and may be planning to implement), or any of the cylinders that use a phe instead of a coil (ideal, Mitsubishi, maybe others)

[JohnMo]

I noticed my cylinder heating occurs about 10 to 20 mins after say a shower. So suspect cylinder is all stratified, prior to opening hot tap, cold water comes in at bottom and mixes with water at bottom of cylinder all the time you use water, thermocline rises etc.  then it needs time to stratify again and then thermostat says time to heat.

[JamesPa]

7 minutes ago, JohnMo said:

I noticed my cylinder heating occurs about 10 to 20 mins after say a shower. So suspect cylinder is all stratified, prior to opening hot tap, cold water comes in at bottom and mixes with water at bottom of cylinder all the time you use water, thermocline rises etc.  then it needs time to stratify again and then thermostat says time to heat.

Makes sense.

 

So in a system with pumped mixing similar would probably happen, unless you take a shower during a timed re-heat period or a second shower shortly after the first.  

[sharpener]

3 hours ago, JamesPa said:

I think so, but I'm thinking of the DIY assemblies with a pump for mixing, such as @sharpener has spoken of (and may be planning to implement), or any of the cylinders that use a phe instead of a coil (ideal, Mitsubishi, maybe others)

 

Yes. This pump will move 400l/hr on its lowest setting, which is faster than ideal but it will be in the middle of the night anyway. Plan is to tee off from the outlet pipe and pump into cw feed at bottom. I have seen the opposite proposed, that would surely feed the c.w. straight to the outlets if anything is drawn off . Hence there will also be an NRV to prevent reverse flow through pump when it is not running.

[JamesPa]

On 04/05/2024 at 12:45, sharpener said:

 

Yes. This pump will move 400l/hr on its lowest setting, which is faster than ideal but it will be in the middle of the night anyway. Plan is to tee off from the outlet pipe and pump into cw feed at bottom. I have seen the opposite proposed, that would surely feed the c.w. straight to the outlets if anything is drawn off . Hence there will also be an NRV to prevent reverse flow through pump when it is not running.

The argument for the opposite I think is to avoid the possibility of sucking air out.  Not sure if this is a real risk or not.

 

Edited Sunday at 20:44 by JamesPa

[sharpener]

1 hour ago, JamesPa said:

The argument for the opposite I think is to avoid the possibility of sucking air out.  Not sure if this is a real risk or not.

 

I thought for a moment you were talking about sucking air in via an open tap. Then I remembered the whole is pressurised to >3 bar anyway so unlikely, pump only develops a head of 1m even on max setting.

 

Don't see any possibility of sucking air out, where would it have come from in yr scenario? All academic as pump will only run while water is being heated and that will be in the small hours so little likelihood of simultaneous draw-off.

[JamesPa]

6 hours ago, sharpener said:

 

I thought for a moment you were talking about sucking air in via an open tap. Then I remembered the whole is pressurised to >3 bar anyway so unlikely, pump only develops a head of 1m even on max setting.

 

Don't see any possibility of sucking air out, where would it have come from in yr scenario? All academic as pump will only run while water is being heated and that will be in the small hours so little likelihood of simultaneous draw-off.

I'm thinking of the air at the top of the tank (if any).  Agree it's unlikely unless (I suppose) the expansion vessel is over pressurised, pushing the air bubble down into the tank.

Edited Monday at 04:34 by JamesPa

[sharpener]

Interesting point which I had not thought of, as it is an OSO tank with internal expansion space. Don't know exactly what the construction is, I suppose I have assumed that the outlet pipe which physically emerges from the very top of the tank has its mouth some way down inside leaving an air space.

 

Any air which the pump sucks in will get re-injected at the bottom. If the pump flow is too great I can partially close one of the isolation valves on it. As above, the min setting will turn the tank over twice an hour.