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Discuss Gravity and vented thermal store. in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Apologies for the unusual question, as I am an interested DIYer.

The question is, why do you need a gravity coil, on a thermal store?

Surely, you'd get better flow rate from direct connections to the side, as there would be no friction and you could use 35mm or 42mm copper pipe, to a 2 inch direct tap in.?

Apologies if this is the wrong forum. First time here and it seemed the most appropriate.
 
Some thermal stores use coils to heat them (called indirect thermal stores) and others are direct stores and the heating system is same water as in store.
With an indirect store you can have a sealed heating system because the coil inside the cylinder keeps the open vented cylinder store water separate from the sealed heating system
 
Some thermal stores use coils to heat them (called indirect thermal stores) and others are direct stores and the heating system is same water as in store.
With an indirect store you can have a sealed heating system because the coil inside the cylinder keeps the cylinder store separate.


Yes. I'm familiar with the ideas.

I'm completely renovating a house, and in the loft, I was going to make use of the Multifuel fire.

I've 4 outputs on the back, and one diagonal was for pumped heating of a thermal store at ground level, this will be direct.

But the one in the loft, was to be used for a shower, if the power fails.

The thermal store will have a hot water coil, and if no power would mean I could still light the fire.

What I was wondering was, would gravity work direct, bearing in mind it's a thermal store. My guess what that the old indirect coils were used because the water in the cylinder was directly to the taps in the days of coal fires.

Nowadays since the hot water is direct with a thermal store, is there any need for a gravity coil? Or can you just make direct connections with a gravity system?
 
Yes. I'm familiar with the ideas.

I'm completely renovating a house, and in the loft, I was going to make use of the Multifuel fire.

I've 4 outputs on the back, and one diagonal was for pumped heating of a thermal store at ground level, this will be direct.

But the one in the loft, was to be used for a shower, if the power fails.

The thermal store will have a hot water coil, and if no power would mean I could still light the fire.

What I was wondering was, would gravity work direct, bearing in mind it's a thermal store. My guess what that the old indirect coils were used because the water in the cylinder was directly to the taps in the days of coal fires.

Nowadays since the hot water is direct with a thermal store, is there any need for a gravity coil? Or can you just make direct connections with a gravity system?


Sorry, when I said the hot water was direct to the taps, I meant direct in the sense that it goes straight without touching the tank water.

Obviously the tap water is indirectly heated, misuse of terminology on my part.
 
Google Akvaterm thermal stores, the U.K. is so far behind in terms of hot water storage. The Scandinavians/ Germans/ Austrians/ Swiss have been the innovator and purveyor of stores for years.
 
Thanks.

I have 5 big thermal stores to put in the new house, all duplex stainless. (There's no steel anywhere, as all the low pressure is pex, and any rads are stainless.)

#1 is to drive underfloor heating
#2 is the boiler proxy
#3, #4 & #5 will each power 2 rooms with a stainless towel rail with their contents, and by virtue of an l-type valve, in the winter, they'll also divert the water from the towel rail back via a long pex al pex pipe back and forth under the floor joists, thus giving underfloor heating on each floor in the winter.
#5 in the loft rooms will at 7 metres, receive the hot water from the wood stove.
#3,#4,#5 will be receiving a share of 10KW three phase solar, and will have two main capillary stats, so when below 60 degrees it circulates the heat using two circulators through an inner concentric coil in each one.

If any cylinder is over 70degrees, (from solar, or wood stove,) the circulation starts to distribute the heat to tanks 2,3,4,5, and the central heating goes on through a second circuit, meaning that the house is warmed by solar PV. This eventually powers the whole house for most of spring through to end of November, at which point, the boiler tank, #2, will start demanding heat from a pellet, oil, or gas boiler.

Since #1 is basically direct only, and has just a couple of stats for emergency house heating, I will get it made first at put it in the loft, to test if direct gravity works.

If it does, then I'll route both sets of pipes to the loft tank from the wood stove, which has a maximum heat to water of 7kw. The wood stove has four outputs, inch tapered, and if I put 35 mm pipe on all four, it should maximise the floor.

One of the two down pipes will go through four towel rails, and the two downs will split to allow several parallel non return valves, so I can bypass the valves and rads with a down pump.

This means if the electric's on, then I have pumped heating of the loft cylinder, and if off, I have gravity heating.

Cylinders one and two both have massively wide hot water coils at the top, and are lined in parallel. From there, they split with 28 mm pipe to the heating coils of the three localised stores #2,3,4 which provide water to the house. Thus we have an effective 1800 litre store for heating to any of the bathrooms.

(#2 will receive heating from boilers, #3, 4, 5 will get solar PV, and #5 from the wood stove. if any over heat, they turn on their heating, and the heat recovery will distribute it if the water doesn't circulate.)

All that's missing is an as yet non existent thermostat which has two inputs, one of which is the overheat stat on the local cylinder.

Six bed, six bath/shower, five zones on ground floor. Each has 1 timer thermostat, and right next to it, a tamperproof one which is driven by any tank which has overheated.

Thus the solar first powers the house, then three eddis or solic 200s divert each phase to their own cylinder until they reach temperature. When they get there, having reheated the energy lost to showers, and built up a 10 degree buffer, they then use the extra heat to heat the house.

In essence, during the winter, the solar PV (because it's oversized for just the electric,) still does all the electric during the day, and gas keeps the cylinders warm if nothing else does. As we head to spring, the contribution gets bigger and bigger, automatically, until eventually, the gas boiler doesn't even come on.

That's the plan.

So what I'll do is buy the cylinder for the underfloor heating first, and temporarily put it in the loft, to see the effect of direct, on the flow rate of gravity heating.

Thanks for the advice.

Google Akvaterm thermal stores, the U.K. is so far behind in terms of hot water storage. The Scandinavians/ Germans/ Austrians/ Swiss have been the innovator and purveyor of stores for years.
 

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