Discuss 2 Cylinder thermostats on a Y plan System in the Central Heating Systems area at ElectriciansForums.net

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J

jarob

Hi All - can anyone please help me?

I have a Y plan heating system with the boiler, wiring centre and three port valve located in the basement of the property. The hot water cylinder is located on the first floor. A three core cable is running from the wiring centre to the cylinder thermostat and linked to the common, no demand and heating required terminals of the thermostat.

At some point a second cylinder has been added next to the original to increase the volume of stored hot water. The new cylinder does not have a cylinder thermostat fitted and is therefore only being controlled by the thermostat on the first cylinder.

I would like to ensure that each cylinder has thermostatic control but would like to link this via the existing wiring to the three port valve. I've searched on the internet but have been unable to find a solution.

My thoughts so far involve using thermostats linked to two port valves, with a relay to ensure they are both satisfied before sending a signal to the wiring centre. (See attachment of rough schematic)

I would appreciate any thoughts on this (or better solutions).

Thanks

James
 

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Hi All - can anyone please help me?

I have a Y plan heating system with the boiler, wiring centre and three port valve located in the basement of the property. The hot water cylinder is located on the first floor. A three core cable is running from the wiring centre to the cylinder thermostat and linked to the common, no demand and heating required terminals of the thermostat.

At some point a second cylinder has been added next to the original to increase the volume of stored hot water. The new cylinder does not have a cylinder thermostat fitted and is therefore only being controlled by the thermostat on the first cylinder.

I would like to ensure that each cylinder has thermostatic control but would like to link this via the existing wiring to the three port valve. I've searched on the internet but have been unable to find a solution.

My thoughts so far involve using thermostats linked to two port valves, with a relay to ensure they are both satisfied before sending a signal to the wiring centre. (See attachment of rough schematic)

I would appreciate any thoughts on this (or better solutions).

Thanks

James



"Hello James",

I am a Heating Engineer / Plumber / Gas Engineer so I am giving You these details from my point of view - what I have written below are facts - the way the Cylinder installation should have been done - not a `way out` of installing an additional Cylinder Thermostat - another Cylinder Thermostat is NOT needed:


IF the Flow and Return Pipework to the 2 Cylinders is done correctly the Hot Water will heat up at approximately the same rate - so only one Cylinder Thermostat would be required.

The CORRECT installation /`Twinning` of 2 Hot Water Cylinders means that it is VERY important to get the pipework correct - this is particularly important for both the Flow and Returns to the Cylinder Coils and for the Cylinder Cold Feeds and Hot Water `Draw Off` / distribution pipework.

It is important that the Cylinder Coils receive equal Flow / Return in order that the Hot Water heats up at a very similar rate within each Cylinder.

It is important that the Cold Feeds to the Cylinders are piped correctly to cause an equalisation of pressure and the shared Cold Feed should be no smaller than 28mm even if the Hot Water outlets from the Cylinders are only 22mm.

IF there is a High demand for Hot Water these sizes should be increased and the Cylinders / Cylinder connections should have been specified to allow for the increased sizes of Pipe connections.

Also it is important that the Hot Water outlet pipework from the Cylinders is run so that the `Draw Off` point is centralised - this should cause the Hot Water draw off rate from the Cylinders to be roughly equalised.

Because the Heating Coils to the 2 Cylinders are being supplied
from a 3 Port Valve this may well cause the Cylinder Heat Up / Recovery time to be longer than expected when both the Heating and Hot Water systems are operating - this is because of the shared Flow through the 3 Port Valve giving quite a low Flow rate through the 2 Cylinder Coils.


I would NOT use a 3 Port Valve in this situation.


I hope that this is helpful James - although You might find it awkward to establish whether my points above have been adhered to by whoever installed the Cylinders / Second Cylinder - ?



But regarding the Cylinder thermostat - just one will be sufficient IF my points above are the way the Cylinders / Plumbing & Heating Pipework have been installed - otherwise there could be problems - But in that case they would not be correctly solvable by You / an Electrician.


Regards,

Chris
 
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2 Cylinder thermostats on a Y plan System cylinders - EletriciansForums.netHi Chris

Thank you for responding to my post with details of how the cylinders should be set up. I'd like to explain a little more about the system and the history to my request. Firstly in response to the current setup.

I'm happy that the heating coils to the cylinders have been set up correctly (in parallel) and are delivering equal heat to each of the cylinders.

The cold feed to the cylinders was originally plumbed in 3/4 inch steel but has been converted to 22mm copper (just by the cylinders).

There are two hot water draw off's from the cylinders.

- The one to the left of the green cylinder is 22mm copper which feeds a 2 bar shower pump to the upstairs en-suite bathroom and the kitchen downstairs

- The one in-between the green and blue cylinder is also in 22mm copper and feeds a 1.5 bar pump supplying the downstairs bathroom.

We do find that air is being drawn into the pump supplying the downstairs bathroom. We were advised by a plumber that because this pipe work is attached to a surrey flange and then T'd into the vent pipe that this could be the source of the air problem.

His advice was to remove the T into the vent pipe and just run the pipe work from the surrey flange on the pump on the downstairs bathroom. This would then eliminate the equal draw off between the two cylinders which would in effect leave us running half of the house on one cylinder and half on the other. This is why he suggested adding the thermostatic control for each cylinder with two 2 port valves.

We are happy with the supply to the en-suite shower room which although it is taken from the top of the tank, it doesn't appear to be drawing air into the system.

We also haven't noticed any problems with the heat up time of the hot water. I have set up the hot water to come on before the heating so that might be why.

I appreciate It's very difficult for you to understand the system with one photo and short explanations but I have a couple of questions.

The cold feed to the cylinders is obviously not ideal being only 22mm. Is it essential for this to be changed or if the system performs as required at present would it be OK to leave this ?

Both of the hot water draw off's are supplying pumps (the bathrooms have thermostatic mixer valves). Most pump manufactures recommend that a dedicated supply is taken from the tank via a surrey or essex flange. This leaves me a problem as I don't have a hot water feed from an equal distance between the tanks. Is there and alternative way to balance the tanks ?

Thanks again for your help

James
 
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"Hello again James",


I could not see the Photo for some reason.



I have tried to be `Brief` with this message - but I did not achieve that !

I hope that I have been `Clear` with my descriptions - obviously You will decide whether to implement ANY of my suggestions:



The Cold Feed to 2 Cylinders should definitely be no smaller than 28mm from the Cold Water Storage Tank - and that would be borderline depending on the maximum rate of Hot Water `Draw Off`.

You should think about when the TWO Pumps drawing off Hot Water simultaneously:

The Pumps will be `pulling out` Hot Water from 2 X 22mm outlets from the Cylinders but the replacement Cold Water is coming from ONE 22mm Cold Feed to the Cylinders - which I think I am reading is connected close to the Cylinders to what is a probably internally rusted / reduced bore [?] 3/4" Iron Cold Feed Pipe ?

Because of the Cold Water Storage Tank that feeds the Cylinders that Cold Feed should not run dry - depending on the capacity of the CWS Tank and the Volume of the Water Mains Supply to the Tank - BUT the suction effect on the Cylinders could easily be `pulling` on the Expansion / Vent Pipe which has very little water within it in a normal sized Home.

Although the level in the Cold Water Storage Tank would normally `balance` the water level in the Expansion / Vent pipe - not if there are TWO Pumps `pulling` onto it AND an inadequately sized / possibly reduced bore Cold Feed to the Cylinders.


Could You please explain why when using a Surrey Flange which has 2 Ports the Pump Supply is then Teed into the Vent pipe ?

Surrey Flanges should have been used on both Cylinders - the 1" size - the dedicated ports for a Pump should have been used for the Pumps ONLY - reducing those ports to 22mm and the Top connections - 28mm [with a 1" Male Iron to 28mm Copper] should have been used to connect the Cylinders together and for the other Hot Water supplies and Expansion pipe / Vent.

AND of course the 28mm Cold Feed should have been installed.


Can I assume that You have 2 Cylinders which are not larger that 1050mm X 450mm = approximately 32 Gallon / 145 Litre capacities each - ?

Regarding the correct method of balancing the Hot Water draw offs from the 2 Cylinders:

Firstly I have to advise that a 28mm Cold Feed MUST be installed - all the way from the Cold Water Storage Tank - without this any `Upgrade` to the Hot Water Pipework sizes would NOT be beneficial.


It IS preferable to supply Hot Water / Twin Pumps by using Essex or Surrey Flanges - but the Pump connections can be done from each Hot Water supply pipe just after it leaves the Cylinder.

I giving You a Link below to a Pump Installation instructions PDF where on page 7 there are Diagrams of some options for taking the Hot Water supply to a Pump which should enable You to work out how to re-pipe the Hot Water from the Tops of the Cylinders to supply both Pumps - the other non-pumped Hot Water outlets and the combined Expansion / Vent Pipe and combine the pipework to balance the Hot Water `draw off`.

When the tops of the Cylinders are joined and have a shared Cold Feed Pipe and Expansion / Vent Pipe ANY Hot Water draw off will cause the Hot Water contained within the 2 Cylinders to equalise in levels - this is why it is important to get the Pipework correctly installed - including the Flow and Returns to the Cylinders to achieve equal Heat Up / Recovery times.


These diagrams are from the Stuart Turner Monsoon Pump range Installation Instructions - in MY Opinion Stuart Turner are the `Masters` of Domestic Water / Shower / Twin Impeller Pumps and I have installed many of their Pumps in my Plumbing systems.

Here is a link to a PDF Copy download webpage of the Stuart Turner Monsoon range Installation Instructions that I mentioned above which might be useful: http://www.stuart-turner.co.uk/media/4331-Monsoon-Universal-Twin.pdf





BUT
- To correctly achieve a good supply to the 2 Pumps and other Hot Water outlets - plus a combined Expansion / Vent Pipe the Pipework exiting the top of the Cylinders should be increased to 28mm - teeing off / down in 22mm for both Pump supplies [see Diagram options].


OR USING 1" SURREY FLANGES AS I DESCRIBED ABOVE.

The pipework connecting the tops of the Cylinders should be in 28mm with reducing Tees for other non-pumped Hot Water outlets - AND - Very Importantly the combined Expansion / Vent Pipe should also be in 28mm.

I am assuming that the Pumps are the TWIN Impeller type - Do You have separate Cold Water Supplies to both Pumps ?


I hope that this is of some help - I cannot really advise You on how to improve the Hot Water supply at your Home without suggesting these alterations.



Please excuse my overuse of the Highlighted Text James - I only noticed how unprofessional it looks when I posted it - But as it took Me a long time to compose and type this - I am a ONE Finger `typist` - I have now not got time Tonight to alter the highlighted paragraphs.


Regards,


Chris



EDIT: I HAVE NOW SEEN YOUR PHOTO JAMES AND I CAN SEE WHY YOU WOULD NOT BE ENTHUSIASTIC ABOUT TRYING TO GET A 28mm COLD FEED TO THE 2 CYLINDERS - AND A 28mm EXPANSION / VENT PIPE FROM THEM TO ABOVE THE COLD WATER STORAGE TANK.

THAT IS APART FROM ALL OF THE OTHER ALTERATIONS THAT I SUGGESTED !

HOW HIGH ABOVE THE CYLINDERS IS THE BOTTOM OF THE COLD WATER STORAGE TANK ?

CHRIS
 
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Hi Chris

Sorry for the delay in responding and thanks again for your help

The distance from the top of the hot water cylinder to the bottom of the cold water storage tank is about 1.3m

The old pipe work runs behind a stud wall in the bathroom and then up through a sloping ceiling to a small space in the loft. It's all very tight and i'm scratching my head to think how I can do it. Guess thats why the guy's that installed it didn't bother.

I know you have advised using at least 28mm pipe to run the vent and cold water feed. If I could get another 22mm feed for the cold and another 22mm vent so that each tank had it's own supply and vent would that have the same effect or do they need to joined in order to maintain the balance ? (still not sure how I'd manage that but It might be easier)

If that wouldn't work and I had to run more pipes would you go larger than 28mm ? and if so how big ?

I had a look at the PDF's that you attached from the stuart turner installation instructions detailing pump draw off configurations. I still can't work out why they have attached the surrey flange to the vent pipe. Either one would appear to be an acceptable method but both ? I think there is a problem that the vent pipe dips towards the connection in the middle of the two tanks which is why I'm getting air drawn through the pump. I think the reason for this may be because the installers couldn't connect the two tanks with an upward sloping pipe and still connect to the old steel vent pipe. Do you think if the T to the vent pipe was removed, I would lose the balance of the system ?

I live here with my wife and two very young kids so we're fortunate to never have two showers running at the same time. I think thats why we haven't seen a problem with the pumps so far.

Just in answer to your previous question

-Yes both of the pumps are twin impeller and have separate water feeds from the CWSC.

Thanks again

James
 
Hi Chris

Sorry for the delay in responding and thanks again for your help

The distance from the top of the hot water cylinder to the bottom of the cold water storage tank is about 1.3m

The old pipe work runs behind a stud wall in the bathroom and then up through a sloping ceiling to a small space in the loft. It's all very tight and i'm scratching my head to think how I can do it. Guess thats why the guy's that installed it didn't bother.

I know you have advised using at least 28mm pipe to run the vent and cold water feed. If I could get another 22mm feed for the cold and another 22mm vent so that each tank had it's own supply and vent would that have the same effect or do they need to joined in order to maintain the balance ? (still not sure how I'd manage that but It might be easier)

If that wouldn't work and I had to run more pipes would you go larger than 28mm ? and if so how big ?

I had a look at the PDF's that you attached from the stuart turner installation instructions detailing pump draw off configurations. I still can't work out why they have attached the surrey flange to the vent pipe. Either one would appear to be an acceptable method but both ? I think there is a problem that the vent pipe dips towards the connection in the middle of the two tanks which is why I'm getting air drawn through the pump. I think the reason for this may be because the installers couldn't connect the two tanks with an upward sloping pipe and still connect to the old steel vent pipe. Do you think if the T to the vent pipe was removed, I would lose the balance of the system ?

I live here with my wife and two very young kids so we're fortunate to never have two showers running at the same time. I think thats why we haven't seen a problem with the pumps so far.

Just in answer to your previous question

-Yes both of the pumps are twin impeller and have separate water feeds from the CWSC.

Thanks again

James



"Hello again James",


Sorry that I have not replied to your last message sooner - I have been away for the Weekend.


The situation with your Hot Water Cylinders / Pipework is one of those where if the Pipework cannot be `Upgraded` to the correct configuration advising anything less would just be an `Educated Guess` - especially without Me being able to actually follow the various Pipe routes to look for any further `Pitfalls`.


THIS NEXT OPTION IS THE MOST EXPENSIVE `NEXT BEST` PIPEWORK CONFIGURATION - BUT MAY NOT SOLVE ALL PROBLEMS:

IF You decide to run new pipework to the Cylinders - either both Cold Feeds and Expansion / Vent Pipes or just add one extra Cold Feed and Expansion / Vent Pipe it would then be better to separate the Plumbing to the Cylinders with one Cylinder supplying Hot Water to each of the Domestic Twin Impeller Pumps.

BUT - Then You would need to have the Heating System altered to have separate Zone Valves and Cylinder Thermostats for EACH Cylinder and another for the Heating Circuit - and confirm with the Electrical Experts on here what is required regarding wiring an `S Plan` Heating Controls wiring plan that has 2 Cylinder Zone Valves and 2 Cylinder Thermostats.

This is because with the Cylinders supplying separate Pumps / Hot Water draw offs obviously the Hot Water would be used at different rates and because of that the Cylinders would need reheating at different rates.


I am fairly sure that the wiring plan will not be too complicated [?].

HOWEVER AS I MENTIONED ABOVE THAT WOULD BE FAIRLY EXPENSIVE.


Although I don`t really want to recommend doing this:

In order to try and save quite a lot of Work and Money - You could try leaving the Cylinders connected and having separate Cold Feeds and Expansion / Vent Pipes to each Cylinder - IF the new Cold Feed and Expansion / Vent Pipe take the same routes as the existing pipes in order to maintain something like `Equal Pressure Zones` within the Pipes.



The problem with getting Air being pulled through one of the Pumps is probably caused by what I previously described about a Pump `pulling` Hot Water out of a Cylinder which has a Cold Feed connected to an [old ?] Iron pipe which may be restricted with Rust regarding replacing the Hot Water draw off - and an inadequate Expansion / Vent pipe which may be allowing Air into the Cylinder.

AND - Now Your further information about the Cold Water Storage Tank bottom only being 1.3 Metres from the top of the Cylinders shows that there is very little `Head of Water` at the Cylinder Hot Water draw off connection / Expansion / Vent Pipe connection point - even IF the Pipework was Perfectly sized and installed.

When the original - ONE Cylinder / Hot Water Tank Cold Feed and Expansion / Vent Pipework was installed it was obviously only supplying a Gravity Hot Water system - now there are TWO Cylinders and TWO Twin Impeller Pumps - this is a massive difference in the demands on these Pipes.

The Pump may well be having a detrimental effect on the Expansion / Vent Pipe causing Air to be drawn into the top of the Cylinder and with the Hot Water - through the Pump.



Regarding leaving the Cylinders connected together for the Hot Water draw offs:

Because my original advice about increasing the sizes of the Cold Feed - Expansion / Vent Pipe and the connecting pipework between the 2 Cylinders was the only correct way to rectify your Hot Water supply problems and get the Hot Water system configured to supply both of the Pumps correctly - I cannot really advise You any further than the above on how to alter the existing Cylinder Pipework with the 2 Cylinders connected and improve matters.

Remembering that the problem with Air passing through the Pump almost undoubtedly WILL get worse IF You do use both Pumps at the same time - and that this could cause further problems with the Cold Water supply and Expansion / Vent Pipes to the Cylinders.

It would be worth trying to investigate this by having BOTH Pumps running and having people watch the Showers and listen to the Cylinders / feeling the Hot Water outlets from the Cylinders to TRY and establish whether a lot of Air was being drawn into the Cylinders.

You MIGHT be able to feel a temperature change in the Hot Water outlet Pipes - or hear the Air being drawn in / out to the Pumps - ?




Regarding your question about running larger Pipes if it were possible:


THIS IS OBVIOUSLY DEPENDANT ON HAVING A ROUTE TO RUN 35mm and 28mm PIPEWORK:


IF I was installing for example 2 x 200 Litre [approx. 45 Gallon] Cylinders in your Home - which were connected together - AND which were supplying 2 x Twin Impeller Pumps - I would be running a 35mm Cold Feed from the Cold Water Storage Tank and teeing off in 28mm to feed each Cylinder from a centralised pipe drop between the Cylinders.

I would be connecting the top of the Cylinders with 28mm Pipework from 1" Surrey Flanges - Teeing off centrally between the Cylinders for a 28mm Expansion / Vent Pipe and using the 22mm Pump outlet from the Surrey Flanges for the Pumps - and Teeing off the 28mm separately in 22mm for any non-pumped Hot Water draw offs.



I hope that my messages have been helpful James - as usual with Plumbing / Heating that has been either installed or added to incorrectly it will probably be quite expensive to rectify the problems with your Hot Water Cylinders and get the installation into `Perfect Working Order` to supply 2 x Twin Impeller Pumps etc..


Regards,


Chris
 
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