Two open vents on same system?

[Kenny.5]

Is there any reason why you can't have two open vents on the same system?

Under normal conditions the pumped circuit from the stove would feed the cylinder directly and in a power cut the gravity circuit could continue to operate via a coil, unaffected by the pump circuit, least that was the idea.
Any advice or comments appreciated.

P.S excuse the drawing!

 

[Ermintrude]

This looks a wee bit of a mess. That heat leak looks like it's in the wrong place tho!

It might not be upon closer inspection ! c

 

[Kenny.5]

As said, please excuse the rubbish drawing!
The heat leak should be lower down on the flow from the stove.

I'm open to any suggestions for a better way to have both gravity and pumped circuits feeding the cylinder. Not sure if an injection Tee would work?

I was trying to avoid having a cylinder full of DHW that we might not use so the storage route seemed like the better option and then we can use it for what ever we need at the time.

 

[Worcester]

You need a thermal store simples

:: AKVA

For example hydraulics (yep I know it has a solar coil, just be open minded, its an EXAMPLE : :: AKVA SOLAR

 

[Nostrum]

Your pump should on the return and then take the vent from the highest point ie the coil, but I'm struggling to understand what your purpose for such a complicated set up is?!

 

[Nostrum]

You could lose the gravity coil unless you are expecting frequent power cuts. Take a gravity feed to heat leaks through a 28mm normally open MV which is powered closed by the pump call signal.

That way the heat leak will only circulate in a power failure and you can put them anywhere you like. You'll need to notify building control about this installation as its a controlled service.

 

[Nostrum]

Sorry, to answer your question. There is no reason you can't have 2 open vents, it's just not required!

 

[Kenny.5]

I was just trying to devise a way of making best use of the stove, both in normal circumstances and during power cuts, we're out in the sticks and get several through the winter.

If I could be sure that the gravity circuit would be able to transfer all of the available output from the stove to the cylinder/store then I would forget the pumped circuit, but i'm not sure it would?
Or as you say, just have a heat leak on the gravity circuit to deal with the power cuts, but as mentioned, the idea was to try and cover all eventualities and have some means of heating and hot water during a power cut. If however it's going to prove overly complicated we may need to go back to the drawing board.

 

[SimonG]

Gravity only on the primaries, correctly sized and located heat leak in conjunction with a normally open and normally closed valve.

what kw to water is the stove?

 

[Kenny.5]

The stove was already installed when we moved in but due to how it had been piped, tight radius 90deg elbows directly off the back of the boiler, it would not circulate by gravity in the event of a power cut. It was 28mm all the way to the neutraliser but it didn't work very well.

There were Several times last winter when I had to put welding gloves on and shovel the fuel into and a big metal bucket! Then close all the vents down to stop it kettling during a power cut.

On wood, its supposed to put out about 8.5-9kw to water. The new heat leak radiator we've got is rated at 2.4kw with a 50'c delta

 

[Nostrum]

How often and for how long do you get power cuts? How big is the thermal store? What's the heat load and hot water requirements of the building?

 

[Kenny.5]

The last power cut we had lasted for about 3hrs, later found out to be caused by someone stealing the overhead lines a few miles away!
During winter, it varies, sometimes 30mins, sometimes 3-4hrs. Think we had 5 or 6 in the time we were using the stove last winter.

I didn't want to make the first post like War and Peace but we also have 30kw LPG combi which currently has it's own space heating circuit.
Using the Stelrad STARS app, we ended up needing about 14kw of radiators, corrected for a 40'c delta.
Hot water demand is currently 3 people, 1 shower room and 1 bathroom both fed off the combi at the moment.
The house is cavity brick and could benefit from some additional insulation which is work in progress.

We looked at putting in a decent size thermal store and linking everything through it but we didn't have anywhere to put it without losing the only cupboard we have and even then it would have been a real squeeze to get something in and pipe it up nicely.

The plan was for the stove to have it's own system comprising of a small store maybe 150ltrs, along with 4 radiators capable of dissipating the full output to water. The layout of the house lends it's self to having a few extra radiators that wouldn't be obtrusive. And a means to produce hot water if we need it. The mains pressure is about 4.5bar static, drops to around 4 with the bath tap on full.

 

[Nostrum]

My honest opinion is it sounds like a waste of time. I'd be inclined to rip out the wet side and stick with a wood stove in. Add more radiators through the combi if required.

The expense you'll go through adapting what's there will outweigh the gains to be had.

At best, I'd look at the design of the current system with neutraliser and try to improve its functionality.

What's the current set up?

 

[Kenny.5]

That option did occur to me, the existing stove is only a few years old so I would hope it still had a reasonable secondhand value.
The neutraliser has been removed and the combi is running it's own space heating circuit.
I guess by the time we re-plumb the stove we wouldn't be much different cost wise to sell it and buy a normal wood burner.
It would be nice to have some form of back up system but as you say, it might end up costing more than it's worth.
Food for thought

 

[Nostrum]

For the 3 hours you may experience a power cut, you'd be better off installing a hot water storage cylinder and running that off the boiler, then invest in some nice thick blankets. Or a generator and crack on with life as normal! :bulb2:

 

[plumben]

I'd just buy a generator if its only a couple of hours, if it was days on end then it would be differnet

 

[Unregistered]

Appreciate the replies and advice.


Made a bit of progress over the past few weeks.


The new LPG boiler has now been installed and commissioned.
Still need to do a bit more balancing on the radiators, ideally wait for the weather to get a bit cooler, but indications are that all the piping and radiator size calculations are spot on and we should be able to achieve a 20'c degree drop running a 60 flow/40 return.


With regards to the Stove, for this winter at least we're just going to use it for space heating and maybe revisit the hot water side of things next year.

The engineer that did the LPG boiler has had a quick look over the existing piping etc for the stove and has said the position of the F&E tank isn't really ideal and it could do with being closer to the stove.

Another very quick sketch but this gives a rough idea of the lay out.

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The upstairs has been converted so the only attic space left is at the far end of the house, which is where the F&E tank and now redundant CW cistern are. The existing pipework has been run with a constant rise all the way to the tank albeit there can't be more than a 1:35 maybe 1:30 rise

I could move the F&E tank above the heat leak radiator but it would be lower than it is just now, the bottom of the tank would only just be above the top of the radiator.
When the pump was running, I assume there wouldn't be a problem, (stove is essentially the neutral point?) but if there was a power cut and the heat leak was in use I expect the F&E tank would get warm but would that cause any issues? In that scenario I'd be wanting to get rid of heat anyway.

The engineer is going to come back in a few weeks to see what can be done but in the meantime I'm just curious to know what the options might be.

Thanks again,

Kenny.

 

[Kenny.5]

Oops, forgot to log in!