Gravity circulation idea

[Nostrum]

Possibly the wrong section for this as it has very little to do with solid fuel, but as gravity circulation plays a big role in the idea I thought the solid fuel section may be more appropriate.

I've got an idea for a problem and I can't for the life of me figure out if it will work or not. Appreciate any feedback on the idea.

The problem:

using a top entry immersion heater a standard cylinder is only heating the top half before the immersion stat clicks off. The problem seems to stem from over stratification and the fact the immersion stat is sat at the top of the tank.

The idea was to de stratify the tank enough for the whole tank to warm up to maximise efficiency of solar P.V generation.

ok so i'm wondering if this would work




basically, TMV fitted in between hot and cold feed to enable the cylinder to circulate via gravity. The other option is a de-stratification pump but I was trying to keep it as simple as possible.

A couple of things i'm not sure about though. Will a blending valve allow the circulation to creep by or will there be insufficient flow for this?

Secondly, when a hot tap is run, a certain amount of hot will be required to go through the TMV in order for the cold feed to fill the cylinder, can you think of any negative effect this will have on the hot outlet?

Or anything else i've missed completely and not even realised! (quite possible)

Cheers in advance!

 

[peteheat]

Hi Sambotec,

There should be no problem fitting a TMV, for gravity I find it has to be one size bigger example 22mm pipe = 28mm TMV or flow will be restricted.

You might get better information Here they use a similar system for stratifying for both the immersion and solar syphon.

They do work we have a working model on display in our showroom, I use it to test different solar panels.

 

[Nostrum]

cheers for the reply peteheat.

I'm struggling to figure out if/how circulation will take place unless a hot tap is run as the TMV inlets will both be under equal static pressure or will the valve sit in the open position in this state? If so how do they avoid cross contamination in a normal setting?

 

[Nostrum]

actually forget that, i think i'm over thinking the idea, the non returns are in the inlets arent they nothing to do with the thermostat?

 

[peteheat]

I think you might be "over thinking" the idea, when you look at the thermosyphon system they push the heat in at the top of the cylinder + about 300mm, it circulates through the Essex flange at the bottom of the cylinder, also notice it is opposite the cold feed to help stratification.

Maybe I am "under thinking" it?

 

[Best]

Not sure if any interest to you, but take a look at Willis immersion heaters on the internet. They are external small cylinders with a 3kw 11" element & they heat rapidly & whole cylinder if needed. They work by gravity.

 

[Nostrum]

Hi peteheat,

I've looked at the link you sent me with some detail. It differs slightly to my idea as the heat source is at the bottom. Also I wouldn't want to fit a flange to the bottom of the cylinder if I could help it. Good idea though, any idea how much they cost roughly?

My idea is more like a pre heat I suppose, which may still work depending on usage patterns etc. Wish I had a set up to test it out on, might haver to wait until I come across the problem before finding the answer!

Cheers

 

[Nostrum]

Hi Best, sorry missed your post. The willis was also mentioned by peteheat.

The reason for the question was because a growing number of people are looking into immersion controllers fed from their solar P.V to utilise as much of the free electricity as possible to maximise on payback etc

The controllers monitor the P.V output and the usage in the home and feed the excess to the immersion, very clever.

Over on the sparkys forum (i'm on there as well) a post was made regarding a standard 120 litre cylinder with a 27" top entry immersion, plenty of energy available but only half the cylinder was being heated as the stat was clicking off before the bottom was heated.

I've had this problem a few times when people have switched the immersion on as a top entry immersion is not really designed for full use, more a back up in my opinion (hence the economy 7/direct cylinders have 2x horizontals)

So this is where the idea came from. The problem is adding to much additional cost the the install may mean it is no longer a viable solution. If something like this would at least help, it's easily installed and cheap enough, it could be the solution.

Whether or not it will, i'm still not overly sure !

 

[Best]

Sorry Sambotc, I didn't see Peteheats link earlier.
I think the Solar syphon has the advantage of putting usable hot water to top of cylinder on a dull day. As to the Willis immersion heaters, - they have been going for years in N.Ireland & are very good provided they are piped properly with the flow rising well above the top of cylinder at least 0.6m IMO. The 1/2" drain tapping does for bottom connection (has to be 22mm for solar syphon return). Only disadvantage I see with their electric immersions, is the water is up to full heat immediately, so very hot at outlets always.
I recently removed an original Willis which is over 60 yrs old!

 

[peteheat]

Hi peteheat,

I've looked at the link you sent me with some detail. It differs slightly to my idea as the heat source is at the bottom. Also I wouldn't want to fit a flange to the bottom of the cylinder if I could help it. Good idea though, any idea how much they cost roughly?

My idea is more like a pre heat I suppose, which may still work depending on usage patterns etc. Wish I had a set up to test it out on, might haver to wait until I come across the problem before finding the answer!

Cheers

Hi,

If you look at the Video Here you can see it is a heat exchanger the cylinder side deposits the heat at the the top of the cylinder heating from the top down.

I would have to be in the office for the prices but a guess would about €70 for the immersion, and €180 for the solarsyphon.

 

[Best]

The Willis immersion, (copper body + an 11" element with stat) is £30 here in N.Ireland.

 

[Nostrum]

Cheers for the replies. I think it would work out to be to expensive. £180 for the syphon, £30 for the immersion , essex flange install & fitting it all + the initial cost of the immersion switch unit would see a bill over £700 I reckon which will increase payback rate to much. Plus taking on the liability installing the flange and potentially ruining the tank or at least being blamed for doing so if it failed in 6 months time for what ever reason.

Can see the potential in a new installation, but wouldn't want to retro fit onto an existing cylinder for the above reasons.

 

[Best]

Very wise IMO to not want to fit Essex flanges. Nasty things that have washers that perish with heat. Better a new cylinder with necessary extra tappings.

 

[peteheat]

Cheers for the replies. I think it would work out to be to expensive. £180 for the syphon, £30 for the immersion , essex flange install & fitting it all + the initial cost of the immersion switch unit would see a bill over £700 I reckon which will increase payback rate to much. Plus taking on the liability installing the flange and potentially ruining the tank or at least being blamed for doing so if it failed in 6 months time for what ever reason.

Can see the potential in a new installation, but wouldn't want to retro fit onto an existing cylinder for the above reasons.

For an experiment you only need one of them, the immersion is badly named because it's not immersed in anything it sits outside the cylinder.

My thinking was if the immersion and syphon would work what is to stop you trying a similar set up using just 22mm pipe, the idea is to improve stratification, note that both products are fitted a minimum 100mm up from the bottom of the cylinder.

 

[markfxy]

Instead of using the stat on the immersion couldn't you use a cylinder stat to control the immersion you'd need to figure out the right position for the stat but you could get it lower that way

 

[tamz]

Instead of using the stat on the immersion couldn't you use a cylinder stat to control the immersion you'd need to figure out the right position for the stat but you could get it lower that way

You would need one that was rated for 15 amp