weatherproof frost stat

M cebee

i'm looking for an external frost stat

http://docs-europe.electrocomponents.com/webdocs/064a/0900766b8064a115.pdf

http://radionics.rs-online.com/web/p/products/4407972/

this one seems to be a stat in a moulded box

i'm wondering is this the best way of making one up and would you need to compensate for the enclosure when setting it?

cast_iron

With a couple of well placed small holes to prevent water build up, I can't see a problem. The temp shouldn't vary much if it's placed correctly on a north facing wall.
Though it's operating range seems a little tight...just to -5 degree C?

M cebee

-5 to +25

why would you need anything outside that range for water

cast_iron

M cebee wrote: »

-5 to +25

why would you need anything outside that range for water

I was just kinda thinking that.:) I think I may have misread what that meant. I was coming from the angle of it's operating temp (as opposed to the user settings). So will the stat still operate at say -20 dg C? I couldn't see an operating range in the spec.

M cebee

cast_iron wrote: »

I was just kinda thinking that.:) I think I may have misread what that meant. I was coming from the angle of it's operating temp (as opposed to the user settings). So will the stat still operate at say -20 dg C? I couldn't see an operating range in the spec.

yes

Bruthal

What you using it for, central heating anti freeze setup?

M cebee

ya

just so i don't get caught out with outside boiler and pipework coming in

i might do something with 2 stages

a higher temp for circ pump and a lower temp for boiler


in additional to any other frost ,comfort controls


that weatherproof stat appears to be a standard box and stat

i wonder would it need holes or adjustment to compensate for enclosure

Bruthal

Yea the 2 stage thing would work well. You could get the frost stat bringing on the boiler to close a relay to operate the boiler. This way you can have an indicator light come on when the stat operates, to show its switching, even if your using the heating normally. This would give you a good idea of how the stat is behaving.

The switch wire from the frost stat to relay could also go through a pipe stat set at a temperature so the boiler just ticks over rather than going up to full temp for times that the frost stat alone is bringing on the boiler to prevent freezing.

Just some ideas anyway. Probably have better ones yourself.

A stuffing gland in one of the knockouts with a metal rod in through it and into box would ensure the air temp in the box is equal to outside anyway.

M cebee

ya il have a pipe stat on return

do you mean a metal rod or tube

Bruthal

M cebee wrote: »

ya il have a pipe stat on return

do you mean a metal rod or tube

A solid metal rod will work. The inside of the box may get close to outside temp anyway, but with anything metal going from outside to inside, the inside temp will definitely stay equal to outside, once its never in the sun.

M cebee

ill have it facing north

so a metal rod will equalize the temps inside and out

Bruthal

M cebee wrote: »

ill have it facing north

so a metal rod will equalize the temps inside and out

Yes it should do, it just conducts the heat in, or out, depending if the inside of the box is cooler or hotter than outside. Let it go right into the box to touch the opposite side. And stick out of stuffing gland too.

A good few 4mm holes in the bottom of the box would work also.

M cebee

i think this will do with 1 frost stat
it's a basic oil boiler no valves
i wired the pump to stay on in frost so i added in A1

LeBash

Spelsberg make them. You should be able to order it from any wholesaler.

M cebee wrote: »

i'm looking for an external frost stat

http://docs-europe.electrocomponents.com/webdocs/064a/0900766b8064a115.pdf

http://radionics.rs-online.com/web/p/products/4407972/

this one seems to be a stat in a moulded box

i'm wondering is this the best way of making one up and would you need to compensate for the enclosure when setting it?

LeBash

Spelsberg make them. You should be able to order it from any wholesaler.

M cebee wrote: »

i'm looking for an external frost stat

http://docs-europe.electrocomponents.com/webdocs/064a/0900766b8064a115.pdf

http://radionics.rs-online.com/web/p/products/4407972/

this one seems to be a stat in a moulded box

i'm wondering is this the best way of making one up and would you need to compensate for the enclosure when setting it?

Bruthal

M cebee wrote: »

i think this will do with 1 frost stat
it's a basic oil boiler no valves
i wired the pump to stay on in frost so i added in A1

Is the high limit stat not bypassed there by the timer and room stat? im probably looking at it wrong.

M cebee

I may have phrased it wrong
thats a pipe stat

Bruthal

M cebee wrote: »

I may have phrased it wrong
thats a pipe stat

A yes the stat to set the temp the boiler runs at if the frost stat alone is running it. Keep it ticking over just.

M cebee

only spent ten minutes on it
It may not be necessary to have pump stay on

Bruthal

If that stat i mentioned is to open to cycle boiler on and off, the boiler wont go off, the A1 contact looks like it will act as a hold on contact and keep the relay on once the frost stat stays closed, and so the boiler will continue to run via the A1 contact.

M cebee

yes I see that
im prob safe enough to feed pump from stat on return instead

Bruthal

You could replace A1 with a n/c contact from relay, and also remove the leg just above A1 going to above limit stat, and just have the A1 n/o contact linking L1 and L2 of the pipe stat controlling the pump. So a dpdt relay would be needed.

Then have the relay coil supplied by the frost stat sw instead of room stat. Think that would work. Simple enough if i drew out myself, or if you took more than a couple of minutes yourself, but just based on your drawing there, that looks like it would do it.

This will mean the pump will start immediately even with just the room stat/timer bringing it on, via the leg where A1 n/c will be.

If just frost stat closes, this would close relay, connecting L1 and L2 of over run stat, and opening A1 n/c so the boiler will go off when the limit stat opens. So once the frost stat is closed, the pump would always run, which is not a bad thing.

If boiler was working without pump running until over run stat closed, then that leg where A1 is now, could be completely removed and no need for A1 n/c contact where A1 n/o is at present in drawing.

Bruthal

Could also probably just power a dpdt relay direct with the frost stat, and get one contact to power boiler through that limit stat, and the other contact to switch on pump.

Does current setup only have the boiler pump come on when the boiler heats up a bit?

M cebee

no pump on constant when frost stat or timer+rm stat close

the overrun just ensures pump is on above set temp

Bruthal

Using a n/c A1 where you have the n/o in drawing so, remove little link just above it, put A1 n/o linking L1 and L2 of 2 way over-run stat, and feeding A1 relay coil from the frost stat should work so.

The now n/c A1 contact can have an indicator light from its n/o spare terminal if you wanted a visual of when the frost stat has closed, handy to see that to judge how its working, during times the heating would be on anyway.

M cebee

i scrapped the pump overrun as i think it may tend to cool the hot water as i've no valves

Bruthal

The over run is there to allow the boiler to cool after it stops firing due to time clock going off. It is much better to include the over run.

The water in the boiler will stay hotter alright when it stops flowing when the room stat opens, but the water in the rads circuit will now cool anyway, so keeping it circulating is better,

In systems where zone valves close, there will be a bypass to allow the water to circulate through boiler.

Its not as vital in older heaver domestic oil boilers, but definitely recommended.

Bruthal

All you now have to do to re-include the over-run in new drawing is connect the boiler pipe stat across the A1 contact feeding the pump.

M cebee

i suppose i can turn it up if i have the rads turned off to stop it circulating and cooling cylinder

i wonder what the correct temp setting is

Bruthal

The over-run wont have a bearing on cooling the cylinder too much. It will only cause the boiler to run a few minutes after the timer stops the boiler firing.

The frost stat is always going to have to circulate the water anyway, and this would cool the hot water cylinder alright.

If you put the frost stat controlled pipe stat at something like 40c it wouldnt be too bad. If you want it to maintain cylinder at the usual when frost stat comes on, then about 65c

If you were leaving house empty for a week etc, you could lower it a bit then.

M cebee

ive put the overrun back in
il check to make sure everything functions

Bruthal

It should do, your circuit looks perfect.

My setup is like your own, no valve on the HW cylinder coil. Radiators have one where the feed out from boiler splits at the cylinde, but that never closed of the water properly. One of these days i will get round to sorting it all.

M cebee

it wouldn't be the usual way of protecting the system as the stat doesn't respond to the boiler on

but still i'd prefer it if the pipework is dodgy coming in
hopefully that's the right sketch with the overrun back in

Bruthal

Yea thats it now. Would of been exact same just to parallel the over-run stat n/o contacts with the A1 contact feeding the pump in your last drawing either.

If your going to be leaving the house for days etc, id say 20 degrees would do on the return pipe stat controlled by frost stat. Minimise oil use.