Heat banks (again!)

[IMM]

You were on about the whole cylinder and primary circuit being pressurised.

You have NOT Got a heat bank.!

You are confused.

[Andy Hall]

Exactly, and this one is not suitable for that.

On the heat input side there are the following options

1) Heat bank with no coil, run directly using boiler primary water, vented with integrated or loft F&E tank. Can be DIY. 2) Heat bank with no coil, run directly using boiler primary water, unvented and pressurised to normal > >

That's irrelevant. You haven't got a hundred acres.

I'm seldom confused and certainly not here.

.andy

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[Andy Hall]

Exactly, but would need a total of three pumps in the system.

.andy

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[Dave]

Thanks to all for the responses. It looks like the answer is a Worcester Greenstar running vented into a direct heatbank with a zone valve for the rads and a second zone valve for the towel rails and airing cupboard rad. The boiler and cylinder (of whichever type) will be in the garage so the F&E tank will need to be in the loft and the DHW will need a return pipe to ensure hot water doesn't take too long to reach the taps.

Any other comments? Dave S

[IMM]

They are available.

Not so. It depends on the application, such as having the boiler on the ground floor and the boiler dumping "all" its heat.

[IMM]

pressurised.

So?

It does not change the fact that you haven't got a heat bank and you say you have and say because you actually haven't it doesn't matter. You need therapy

Imagine your post on ripped paper and written in crayon and the scene is set.

[IMM]

Are you saying pressurised heat banks don't exist?

[IMM]

Good choice.

Sounds good.

Errm no. The rads taken off the heat bank using a pump and a check valve.

Taken from where? The boiler primaries? Could be. Is there a need for the zone valve when you want these on all year around? If off the boiler primaries (flow and return) then the rails only operate when the bioler does. If you want them on 24/7 then take then off the heat bank and use a pump and check valve.

Can be done with a couple of check valves and DHW circulation pump.

See above.

[Andy Hall]

One zone valve for the radiators and a second for the heatbank would be the most appropriate, or a diverter valve.

This is not the best way to connect the radiators. Apart from needing an extra pump, it is not the most efficient way for the boiler to work.

For the heatbank to be useful, it needs to operate at the highest temperature possible in order to store the maximum amount of energy. This is true throughout the year. The minimum useful flow temperature to the heatbank is 75 degrees, with 82 being better.

For the condensing boiler to run most efficiently during the much longer on times than the hot water requires, and accounting for the lower heat output requirement during spring and autumn, the return temperature needs to be as low as possible. The boiler will automatically modulate down to achieve that and the flow temperature can easily be below 50 and return below 40 degrees. The efficiency of a condensing boiler increases markedly with reducing return temperature and especially below the 54 degree dew point.

If you run the radiators from the heatbank, the flow temperature will be that of the heatbank (i.e. 76-82 degrees). The boiler will come on full periodically in order to replenish the heatbank and maintain the required temperature. It has no real way of knowing the difference between a DHW demand (a lot of heat for a short time) vs. the CH (relatively little heat continuously). Thus it will effectlively cycle on and off at around the ste point of the heatbank, not at what the radiator load requires.

If a conventional boiler were being used, then this would be a reasonable approach (because they are intended to run at a high single temperature, but for a condensing one it isn't. It is far better to connect the heat bank to the boiler and heat that rapidly at full power and then switch the boiler to the radiators where it can detect the heat load for the house directly and operate most efficiently

.andy

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[Andy Hall]

No - simply that some are not suitable for pressurised operation, and that if they are used pressurised that the regulations concerning large volumes of pressurised water apply - must be installed professionally.

.andy

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[IMM]

Located where?

Oh my God. It is the best way.

What the hell are you on about?

You split the cylinder with a flow and return on the upper DHW section and a flow and return on the lower heating section. The lower section can run at a lower temp than the upper. Best use an outside weather compensator and have the temp senor on the lower cylinder section. Both sections only need a pump and check valve each from the boiler, with the DHW having priority. The compensator will ensure the rad circuits will run at low temperatures most of the time promoting condensing efficiency.

< snip >

see above.

[IMM]

You should be certified. If they are pressurised heat banks then they are suitable.

[Andy Hall]

So the point is that there are some heatbanks that are not suitable for pressurised operation. That was all.

No, you need therapy. English lessons wouldn't hurt either.

I have never ever said that I have a heatbank. This does not, however mean that I haven't studied how they work (in detail) and haven't considered using one.

As I've told you on many occasions before, I don't have a good enough mains flow, so there is no value in my having one versus a roof storage tank and conventional cylinder. I am not short of space in the loft or the airing cupboard so for me there is no value.

I don't need to actually *have* something to know how it works and the most appropriate way to use it. This is not difficult stuff and ownership does not alter physics.

It doesn't mean either that somebody with a good mains water supply or who wants to redistribute space in their house won't derive benefit from a heatbank - there are cases where they are useful as long as they are appropriately connected.

Speak for yourself

.andy

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[IMM]

If it is designed to be pressurised then it is suitable.

You did.

When you made your so called informed decision you didn't know enough.

Imagine your post on ripped paper and written in crayon and the scene is set.

[Grunff]

Quite - we have pretty poor mains pressure (just under a bar - the reservoir is about 12m above the house), and no real space problems. The reason I put in the thermal store (or heatbank as it seems to be defined here) was becuse the oil boiler was short cycling, despite all my attempts to cure it. The thermal store solved this, and provided us with a nice on demand energy store.

[IMM]

There is a difference.

It is possible to use them with a cold water storage tank and a bronze pump to boost water pressure. Then no boiler short cycling if two cylinder stats are fitted. It is also possible to use a smaller boiler using a heat bank.

[Andy Hall]

On the boiler flow with one zone or diverted branch going to the heatbank and the other to the radiators.

How can I help you?

Not for a condensing boiler.

To circulate the water from the heatbank through the radiators and back requires a pump unless you use the one used for the DHW heat exchanger and zone or diverter valves.

You mean two separate flows and returns from the boiler? That would mean more complexity and the boiler is still unable to properly detect the heat load of the radiators, because the heatbank is still in the middle.

If you meant on the radiator connections, there is no value in having a reduced temperature flow and return to the radiators if the boiler is connected to the top and bottom of the heatbank. That simply reduces the rate of heat delivery to the radiators for a given water flow. It won't alter what the boiler sees, other than a reduced rate of energy use. To feed the heatbank it still has to attempt to meet the storage temperature.

The outside temperature sensor is simply another control term for the boiler when used for space heating. It doesn't alter the behaviour of the heat bank load which will effectively damp the detection that the boiler would have had of the return temperature directly from the radiators.

It isn't the operating temperature of the radiators that matters, it's what the boiler can see. Having a large energy store in the way, screws up the control that is intended for a condensing boiler - i.e. to see the heating load and modulate finely..

This is why the heat bank should be used as an energy store for the hot water and not to run the radiators when a condensing boiler is the main or only heat source.

.andy

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[Andy Hall]

What are you talking about? I clearly and consistently made the point that some heat banks are unsuitable for pressurised operation.

Logically that means that some are.

The point was that one should check before buying if pressurised operation is being considered.

Have you always been this obtuse or is it an acquired skill?

.andy

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[Andy Hall]

No shit, Sherlock.

Please provide the post where I have.

I knew and know precisely what was required. In order to improve the mains supply to make a mains pressure DHW system interesting would have cost about £5k. I have better places to spend that kind of money, especially when I can achieve what I want in different ways.

All of which is completely irrelevant anyway, because we are not discussing my application.

.andy

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[Andy Hall]

That's a good reason. Presumably the boiler has a large thermal mass and quite high non-modulated output and the previous cylinder was unable to take what it could deliver.

In this instance, a heatbank is ideal because it can swallow all the output.

.andy

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