twin immersion tank fed from solar pv diverter

[cypher007]

scratching my head a bit. ive got a plumber fitting a rm stelflow 250l with twin immersions. my idea is to feed the top one first then the bottom one once the top one has tripped its stat setting. the problem is most stats seem to have only normally closed contacts, I need normally open. one idea I had was to feed a contactor from the top immersion, but that wont work as the supply to the immersion will be pulsed from the pv diverter. could I leave the thermal cut out in series with the top immersion and then use the top immersions stat to control the contactor? or is this a safety risk?

 

[SimonG]

Do not mess with the safety devices on an unvented cylinder.

 

[Centralheatking]

Wee said SimonG - there is a nice video by Plymouth Plumbers which will make you think centralheatking

Do not mess with the safety devices on an unvented cylinder.

 

[Ermintrude]

When the top is hot the bottom is about 10c cooler . Convection will smash that in about 5 mins. Don't worry yourself. As soon as u open tap lots of lovely cold water comes in so it will hit equilibrium but then it all goes in a few seconds.

Fit a large bottom immersion and an immersun and forget it

Engineer or rocket scientist? Answers on a postcard please

 

[cypher007]

maybe I could just fit this to the top outlet pipe:

PTS1 Pipe Thermostat - Drayton Controls

it has a change over contact rated to 15A.

one thought ive had is a cylinder stat, but the rm stelflow is covered in insulation and then a plastic cover.

 

[chris watkins]

What part of the above posts did you not understand ?

DO NOT RE-WIRE IN ANY WAY SHAPE OR FORM AN UN-VENTED CYLINDER it is both illegal (under the Building Regulations AD Part G) & potentially very dangerous.

Your "Plumber" who is installing the cylinder must by Law hold a Part G / un-vented ticket they would / should have explained all that you need to know.

You will get no further help or advice on here for this reason.

 

[cypher007]

which part of my post did you not understand? if Im switching between the 2 immersions using an external thermostat im in no way compromising the safety of the 2 immersion heater stats. that's like saying you cant fit a changeover time switch to heat the top first then the bottom. why make a cylinder with 2 immersions?

 

[chris watkins]

could I leave the thermal cut out in series with the top immersion and then use the top immersions stat to control the contactor? or is this a safety risk?

which part of my post did you not understand? why make a cylinder with 2 immersions?

I understood perfectly your post right from the off, the words "or is this a safety risk?" told me all that I needed to know.
Now you may well of copped the hump by my tone but were safety is concerned sometimes you need to be blunt to get the point across.

You may well have the electrical knowledge to wire what you want however that is not the issue is it, the requirement is that you understand how this all relates to the workings of an un-vented cylinder & the inherent risks of making modifications to such.
Like I said speak to your man on site who is competent & can see what you are doing !!! If he can't or you haven't, then get one quick.

 

[cypher007]

hes taking the line I only plumb. he leaves the electrical stuff upto his electrician. to be honest I think what im doing is beyond your run of the mill plumber, even rm were a little out of there depth, but said my idea of using a pipe stat to switch between immersions should work. part of that idea has to go to a member on another forum who suggested using a contactor and external stat. with the pipe stat listed above I don't need a contactor, as its rated to 15A and has changeover contacts.

 

[chris watkins]

Go on then, although it goes against my better judgment, what are you trying to achieve by this ?? If the PV is used to heat the lower immersion then hot water will accumulate at the top of the cylinder, the longer it heats the more of the cylinder water gets heated until the temp gets to 60-65 at the lower stat.
Top immersion is only used as top up on economy 7 cylinder or back up heating if no sun depending on cylinder type.

 

[cypher007]

the reasononing is in the shoulder months there will only be enough pv to heat the top. I suppose another way would be to have a manual changeover switch, kinda like a summer/winter thing.

 

[chris watkins]

No, just wire to the bottom only, what is available is what is available, & it will all accumulate at the top of the cylinder anyway under convection. You are over complicating it.

What is your back-up heat if sun not enough to provide for your HW needs ?

Top element on a timer or is there a coil (indirect cylinder)

 

[cypher007]

indirect gas boiler feed. why do they fit 2? I thought it was so the tank could be part heated?

 

[rpm]

See post #10