Thermo-mechanical cylinder stats any good???

[Ric2013]

Danfoss Randall RAVI - VMT 25/2 28mm Cylinder Valve For Gravity Primaries

Those!

Met potential customer the other day with zombie oil boiler running semi-gravity system.

Modern cylinder, but complaint that water too hot. Measured outlet from cylinder at 65°C with open tap. No thermostatic control except boiler stat and customer understandably doesn't want to set this down further as the guy who does his boiler told him to use the setting he is using.

My feeling is that using a thermo-mechanical valve like this won't help as Danfoss want it on the return and since it's not a snap open/close valve, more like a TRV, I won't be able to achieve 60°C with accuracy. Also, the boiler would still dry-cycle so won't even save much oil.

I think customer ideally needs a conversion to C plan if he insists on keeping that boiler. But I think that the best advice would otherwise be to just accept that the cylinder will be at 65° and fit TMVs to outlets as 65 will still be 'too hot'. The kitchen sink would need the hot pressure boosting to get the within the desired 1:5 pressure imbalance, or a dedicated low pressure cold feed for the TMV.

Question for those slightly less weird than me: am I making sense or would you do it differently? Ta!

 

[ShaunCorbs]

Need one of these mate

Drayton Cyltrol Valve 1"BSP Straight

Took me a while to remember what they were called

 

[Ric2013]

They seem to be the same thing except that your link senses return temperature while mine has a remote sensor which can be strapped to the cylinder?

 

[ShaunCorbs]

They seem to be the same thing except that your link senses return temperature while mine has a remote sensor which can be strapped to the cylinder?

Your one needs to be in a dry pocket

 

[Old Account]

Need one of these mate

Drayton Cyltrol Valve 1"BSP Straight

Took me a while to remember what they were called

What does this do shauni?

 

[ShaunCorbs]

What does this do shauni?

Read the links description there's also a link in there

http://www.uk-plumbing.com/brochure/drayton/CyltrolData.pdf

 

[Ric2013]

Ah, okay I see. Had hoped it could clip on to the outside of the cylinder, bit of thermal grease etc. Thank you.

So if I use your type, back to the question of would you bother fitting one rather than full conversion to C plan, or just fit TMVs to taps, and would it be reasonably easy to get a consistent 60°C? If not, customer will say they paid me to fit a stat that makes no difference (as current stored temperature is only 65°C)!

 

[ShaunCorbs]

upto you but you need to get the temp of the stored water down to safe limits / stop over heating

 

[Ric2013]

Perhaps I should clarify. I have done no work on this house whatsoever. I am merely quoting on possible resolutions to legacy work carried out in the past and want to give good advice. So I don't have to do anything. I could just decline to quote and walk away.

Since the people with this system are well familiar with it, and are likely to continue to operate the system as at present, then the water will remain at 65°C. (Of course, they might decide to set the boiler to max and the water would then reach 80). 60 isn't good at point of use, but it's not far above the ideal storage temperature. So I'd have to adjust the stat to allow 60°C at the present lowish boiler temperature setting because water MUST be stored at at least 60 (despite legionella dying off in an hour at 50: I don't make the rules).

My experience of TRVs is that they tend to settle at a low flow, keeping the radiator barely warm. If the mechanical valve works the same way (which would appear to be the case) then this trickle would allow a small quantity of hot water into the boiler. If the valve is working off the return temperature instead of the cylinder, then it MUST be allowing a trickle through in order to keep itself hot enough to keep shut.

Since the amount of heat in that steady trickle depends on the boiler temperature, then it follows that, like a TRV, the cylinder temperature (like the room temperature) will vary a bit if the boiler setting is changed. So my feeling is that if I set the valve to maintain 60, then the water temperature in the cylinder could still vary a bit, and, main concern here: the restriction caused by the valve shutting progressively will slow down the gravity flow resulting in the cylinder taking longer to warm up.

Or does your experience contradict this? - that's my main question here.

 

[ShaunCorbs]

Perhaps I should clarify. I have done no work on this house whatsoever. I am merely quoting on possible resolutions to legacy work carried out in the past and want to give good advice. So I don't have to do anything. I could just decline to quote and walk away.

Since the people with this system are well familiar with it, and are likely to continue to operate the system as at present, then the water will remain at 65°C. (Of course, they might decide to set the boiler to max and the water would then reach 80). 60 isn't good at point of use, but it's not far above the ideal storage temperature. So I'd have to adjust the stat to allow 60°C at the present lowish boiler temperature setting because water MUST be stored at at least 60 (despite legionella dying off in an hour at 50: I don't make the rules).

My experience of TRVs is that they tend to settle at a low flow, keeping the radiator barely warm. If the mechanical valve works the same way (which would appear to be the case) then this trickle would allow a small quantity of hot water into the boiler. If the valve is working off the return temperature instead of the cylinder, then it MUST be allowing a trickle through in order to keep itself hot enough to keep shut.

Since the amount of heat in that steady trickle depends on the boiler temperature, then it follows that, like a TRV, the cylinder temperature (like the room temperature) will vary a bit if the boiler setting is changed. So my feeling is that if I set the valve to maintain 60, then the water temperature in the cylinder could still vary a bit, and, main concern here: the restriction caused by the valve shutting progressively will slow down the gravity flow resulting in the cylinder taking longer to warm up.

Or does your experience contradict this? - that's my main question here.

most of that is answered in the spec sheet i put up

"Cyltrol Valve senses return water temperature and varies the primary flow until the
desired domestic hot water temperature is reached. At this point it will shut off
the primary flow, ensuring that hot water does not reach dangerously high levels,
thereby offering protection particularly to the young and elderly."

and its ment for a gravity system so shouldnt effect the flow rate at all

 

[Ric2013]

The spec sheet says nothing about accuracy of temperature maintained or hysterisis. It was the vagueness of that spec sheet

'Temperature range Factory-set, approximately 46°C to 60°C (115°F to 140°F)'

that raised my concern.

That said, it does say 'at this point it will shut off' which does suggest a positive snap close, rather than the progressive throttling down I'd have expected from a wax capsule.

But I think the fact that no one on here has come up with first-hand experience says it all

That said, I'll contact Drayton and see if they can give me a positive answer, in the hope that their technical department is better than Honeywell's.

Thanks Shaun!

 

[ShaunCorbs]

The spec sheet says nothing about accuracy of temperature maintained or hysterisis. It was the vagueness of that spec sheet

'Temperature range Factory-set, approximately 46°C to 60°C (115°F to 140°F)'

that raised my concern.

That said, it does say 'at this point it will shut off' which does suggest a positive snap close, rather than the progressive throttling down I'd have expected from a wax capsule.

But I think the fact that no one on here has come up with first-hand experience says it all

That said, I'll contact Drayton and see if they can give me a positive answer, in the hope that their technical department is better than Honeywell's.

Thanks Shaun!

I've fitted/ replaced a few on back boilers no complaints

And will take some time to set up but should be near enough each time

 

[Ric2013]

Brilliant. That was what I wanted to hear. Thank you!