Heat exchanger possibility?

[martyc]

Hi there.
Had our attic converted last year- I stuck a rad in there and ran the pipes to the hot press but never tied them in (and now it’s winter -lol)
Anyhow- current system is vented F&E, so would need to seal it etc. I know what needs to be done but I’m reluctant TBH as I fear it could spring a few leaks.

Anyhow was just thinking if there is such a thing as a small standalone heat exchanger that I could utilise to tie into my existing system

The plan (in my head) would be to have one side of the heat exchanger on my current vented system(and therefore not having to pressurise it), and the other side with a small pump and small expansion vessel on its own sealed loop just feeding the rad in the attic, which I’d be confident wouldn’t leak as it’s all new.
Does something like this exist (outside of my head)?

 

[cross thread]

Yes ,plate heat exchanger

 

[martyc]

Thank you- I’ll look them up, are they fed the same as a rad or are they fed in-line on the supply side?(I guess that would just cool down the whole supply side so maybe not a good idea and I’ve prob answered my own question)

 

[Johntheo5]

Hi there.
Had our attic converted last year- I stuck a rad in there and ran the pipes to the hot press but never tied them in (and now it’s winter -lol)
Anyhow- current system is vented F&E, so would need to seal it etc. I know what needs to be done but I’m reluctant TBH as I fear it could spring a few leaks.

Anyhow was just thinking if there is such a thing as a small standalone heat exchanger that I could utilise to tie into my existing system

The plan (in my head) would be to have one side of the heat exchanger on my current vented system(and therefore not having to pressurise it), and the other side with a small pump and small expansion vessel on its own sealed loop just feeding the rad in the attic, which I’d be confident wouldn’t leak as it’s all new.
Does something like this exist (outside of my head)?

How much higher is the water level in the feed&expansion cistern above the top of the attic rad, even if only 0.25M higher then its possible that you can circulate water through that rad once you can fill it.

Of course, you can raise the F&E cistern, mine was always above the CWSC which gives ~ 0.7/0.8M from the F&E cistern water level to the top of the attic (converted to bedroom) rad, with excellent circulation.

 

[martyc]

How much higher is the water level in the feed&expansion cistern above the top of the attic rad, even if only 0.25M higher then its possible that you can circulate water through that rad once you can fill it.

Of course, you can raise the F&E cistern, mine was always above the CWSC which gives ~ 0.7/0.8M from the F&E cistern water level to the top of the attic (converted to bedroom) rad, with excellent circulation.

Hi John- Thanks for taking time to reply.
The new rad is basically at the same level as the F&E, the rad might even be a couple of inches higher than it and I have no head room to raise the wee tank- it’s in the eaves and it’s a v small attic so I do need to pressurize at least this 1 rad.

I looked at those plate exchangers - doesn’t seem to be a huge variation in sizes/KW like it’s one small rad thats 1.3kw and the exchangers are all like 15kw and up.
But maybe that’s just its max ability to heat transfer.
Interested to hear from anyone who has used a HX in this kind of scenario (1 rad)

 

[Johntheo5]

Personally, I find it hard to imagine how that would even work.

I would seal the system and wouldn't have any fears really of springing a leak if its done properly.
I would install a 12L EV (expansion vessel) on the ground floor, pre filled to 0.6bar pressure and charged to 0.75bar, assuming your system contents (say 8 to 10 rads) at 100L then the final pressure when whole system fully heated will still be less than 1.1bar, I would also use a 1.5bar pressure relief valve instead of the normal 3.0bar, this will ensure that the system can never exceed 1.5bar. The present OV system neans you have a pressure/head of 0.6/0.65bar anyhow on the ground floor?. If you have plenty of room you could install a 18L EV which would give a final hot pressure of less than 1.0bar (0.95). How many double/single rads are installed?.

 

[martyc]

Personally, I find it hard to imagine how that would even work.

I would seal the system and wouldn't have any fears really of springing a leak if its done properly.
I would install a 12L EV (expansion vessel) on the ground floor, pre filled to 0.6bar pressure and charged to 0.75bar, assuming your system contents (say 8 to 10 rads) at 100L then the final pressure when whole system fully heated will still be less than 1.1bar, I would also use a 1.5bar pressure relief valve instead of the normal 3.0bar, this will ensure that the system can never exceed 1.5bar. The present OV system neans you have a pressure/head of 0.6/0.65bar anyhow on the ground floor?. If you have plenty of room you could install a 18L EV which would give a final hot pressure of less than 1.0bar (0.95). How many double/single rads are installed?.

Hi John- yeah small enough house and I have an 18L EV already got.
4 double rads and 3 single currently, I was thinking something similar originally, reducing the pre charge, I was going to go a bit lower again as vessel would likely end up in the hot press 2nd floor and above all existing rads, but about a meter below the newest rad in the attic - I was thinking about .3 bar precharge and then fill the system cold until the rad in the attic is just full, nip it up and give it a fraction more charge, say .1 bar - good idea on the PRV too .
I’m still reluctant however for some reason!

 

[Johntheo5]

Yes, try that anyway, should be fine as long as 0.4/0.5 bar is sufficient to push the diaphragm back home against the water end, there must be some resistance from the diaphragm as its only shoved into the EV like a baloon, some come with the diaphragm in the middle of the EV I think.

 

[Johntheo5]

You might also consider installing a EV isolation&drain valve, saves draining/partially draining down the system to check the pre charge pressure or for trouble shooting, you do have a nice little water reserve of 1.29L with pre/fill pressures of 0.3/0.4 bar but your attic rad will quickly start running cold or "half" cold in the event of any pressure loss, for whatever reason.

 

[martyc]

That’s a good idea too thank you John- very helpful.