Thermal Store (DPS), UFH, Multi Zone

[the-moog]

Hi,

I'm trying to get the right design for a CH system as a complet replacement for the existing.

We are modernising and extending our house and in the process want t replace and update the heating and hot water systems.

It is going to have to be some sort of mains pressure HW system as th tank has to go. I've decided on the DPS Pandora, any body ha experience of these?

The new bathroom and conservatory lack wall space, I though UFH may b the solution, but I'm unsure if, given the small areas that it wil provide enough heat, any views?

I'm new to plumbing systems (I'm a electronics product designer) wha are the differences, advantages, fallbacks of the Y and S plans, how d I decide which is right?

Its only a three bedroom house, with a dining room, large bathroom lounge, kitchen and small conservatory. Is it sensible to still us multiple zones?

Is it sensible to zone the UFH (if used?) as I think it would b necessary to warm the conservatory on cold summer nights (to kee plants happy).

Any other suggestions?

Regards, Jason

-- the-moog

[the-moog]

Hi,

I'm trying to get the right design for a CH system as a complet replacement for the existing.

We are modernising and extending our house and in the process want t replace and update the heating and hot water systems.

It is going to have to be some sort of mains pressure HW system as th tank has to go. I've decided on the DPS Pandora, any body ha experience of these?

The new bathroom and conservatory lack wall space, I though UFH may b the solution, but I'm unsure if, given the small areas that it wil provide enough heat, any views?

I'm new to plumbing systems (I'm a electronics product designer) wha are the differences, advantages, fallbacks of the Y and S plans, how d I decide which is right?

Its only a three bedroom house, with a dining room, large bathroom lounge, kitchen and small conservatory. Is it sensible to still us multiple zones?

Is it sensible to zone the UFH (if used?) as I think it would b necessary to warm the conservatory on cold summer nights (to kee plants happy).

Any other suggestions?

Regards, Jason

-- the-moog

[Doctor Evil]

Christa> The new bathroom and conservatory lack wall space, I though UFH may b

S is better as Y has a mid-position valve which are more troublesome Using an integrated heat bank, you don't need any of these plans. .

Its only a three bedroom house, with a dining room, large bathroom lounge, kitchen and small conservatory. Is it sensible to still us multiple zones?

the-moog Wrote: Is it sensible to zone the UFH (if used?) as I think it would b necessary to warm the conservatory on cold summer nights (to kee plants happy).

More than two zones may be over top, but I would do upstairs and down a separate zones. Take both zones of a heat bank with a pump on each. Th heat bank makers will install two flow and return tappings on the botto of the heat bank for the two CH zones. The best way

-- Doctor Evil

[Christian McArdle]

I would always put the conservatory on its own zone, even if conventionally heated, rather than UFH. Like all zones, but specifically in this case, it should have its own programmable thermostat, so that the conservatory is only heated when it is needed.

Also, if you use a fan convector in the kitchen, they work better on their own zone, as they can hog the heat even when off, otherwise.

Although if the zones start to multiply, you can always share a tapping on a pumped circuit, if you're careful.

Personally, if I was designing a system from scratch, I'd be tempted to have one tapping, one pump, a "manifold" and an S-Plan system, rather than go multiple pump, which can have issues with parasitic circulation (or noisy valves to cure such) in some cases. Also, zone valves can be cheaper than pumps, which may be an issue on multiple zone systems.

Finally, S-Plan-Plus allows long distance unzoned trunking, which can be more efficient in pipework (and hence energy efficiency through primary circuit losses). (i.e. you can have the zone valves near the point of delivery and have a single trunk pipe snaking around the house, rather than a pair of pipes for each zone, running alongside each other).

Christian.

[Christian McArdle]

Y-Plan = cheaper, smaller

S-Plan = more adaptable, subzonable, reliable, easier to understand, install and troubleshoot.

Christian.

[Doctor Evil]

A heat bank/thermal store, presents you with a wonderful neutral zone. Pumps are not expensive and are far more reliable than 2-port zon valves. You put a check valve on each CH zone to prevent bac circulation. Each pump can have its speed set to the needs of th zone. There will be no parasitic circulation if each zone has its ow flow and return tapping off the store

-- Doctor Evil

[the-moog]

This is another point of confusion for myself.

To take the CH and/or UFH from the store or the boiler circuit. Obviously, to take it from the store means instant heating, bu depletes our DHW source. The other way means that we are 'steeling' heat from the input to th store, so it will take longer to replenish.

Any other factors in deciding which side the heating should come from?

The only thing I can think of is the need for more than one pump.

J

-- the-moog

[Doctor Evil]

Take it from the store. If the store is sized well enough it will no deplete the store. Also the CH flow and return are taken near th bottom, leaving the upper DHW untouched. You could have it a priorit system. Wheh the DHW is called the CH pump(s) is switched off. Th boiler operates independently heating the store of water to pre-defined temperature. Have two stats on the heat bank so as t avoid boiler cycling. Have the klargest boioer you can afford. therml store/heat bank is not fussy what sized boiler heats it. Mak sure the flow and return pipes are 28mm.

Two CH zones: Either:

1. Two pumps (both directly off the store)
2. One pump and two 2-port valves. (only one pipe off the store)

Taking all zones directly off the store eliminates a balancing ac between two zones

-- Doctor Evil

[Christian McArdle]

But the boiler is capable of replenishing at a far greater rate than the radiators extract heat, so there is no massive effect. Just make sure that store isn't already marginal in size.

Direct heating has a considerable advantage when running with a condensing boiler capable of open venting. You lose the advantages of sealed pressurised operation, such as easy refilling, but you get a more efficient system. The heatbank is designed to be heated to 75C. With direct heating, with no heat exchanger differential to maintain, this allows a 75C flow temp, rather than 82-85C. It also frequently provides a low return temperature, with a nice large differential. This provides good condensing action in the boiler.

Christian.

[the-moog]

Please explain what a check valve does - any weblinks with nic pictures?

I did a search and found lots of people trying to sell them, but I'v still no idea why I would want one.

-- the-moog

[John Rumm]

except you don't want to be running your heating off the store with a modern boiler....

[Tim S]

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long efficient burns?

Tim

[Andy Hall]

This depends on the type of boiler in use.

If you are talking about a conventional one operating at 82 degree flow and 70 return, then there *could* be a benefit in the approach of running the heating circuit from the store on the long efficient burn argument.

However, with a condensing boiler, the greatest efficiencies occur when the burner is modulated down rather than on/off and when the operating temperature is lower.

In the intended set up with a HW cylinder (or store for that matter), the boiler, in HW mode, operates balls-out to replenish the cylinder quickly and at high temperature. Although this is one long burn, it is not in the most efficient operating range. The heating circuit is intended to be connected directly to the boiler and the boiler will modulate down as the load reduces when TRVs begin to close. Ideally, the system should reach an equilibrium with boiler running continuously at lowish power to match the radiator load. This avoids cycling and runs the boiler in a more efficient temperature range.

If you insert a store in between boiler and radiators, you effectively defeat this arrangement and force a cycling situation. The radiators gradually drain heat from the store, and at a certain point the boiler is brought on to replenish it using a high temperature burn as for hot water.

There *may* be exceptions to this if you want to bring in additional heat sources such as solar, or possibly if you want a source of lowish temperature water for UFH (although that can be done with a blending valve)

Other than that, it is better to keep the store for DHW and let the boiler drive the radiators directly if it's a modulating condensing model.

[Doctor Evil]

A non-return valve. Flow can go one way but not the other.

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[Doctor Evil]

Many heat banks run at 75C and many condensing boilers have a flow/return

22C temp differential. If two stats are used to ensure no boiler cycling, the stores water is quite cool when the boiler is called to re-heat. Most of the burn the boiler will be operating very efficiently. The overall operation is very efficient. There is also the simplicity of having the CH zones off the store (a neutral point). One circuit does not interfer with the other and are simple to balance. The CH flow & returns are taken off the bottom of the cylinder where it is cooler.

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[Christian McArdle]

It's a one way valve. A standard check valve needs too high a pressure and can be very noisy in this application. Instead, you need a much harder to locate flap type valve, preferably unsprung.

Christian.

[Doctor Evil]

Running two CH circuits from the store of water, there is no need for check valves. Not all check valves buzz.

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[Andy Hall]

This implies that the boiler would be operating in its most efficient range with 75 flow (and by your numbers) 53 return.

While the return temperature implies that condensing just about begins, this is not the most efficient part of the range by a long way.

That is achieved by operating the boiler as cool as possible and by allowing it to match its output to the continuous requirement of the radiators at as low a temperature as possible.

Putting a store in the middle, with however many thermostats simply won't achieve this objective. The radiators (and UFH if used) will cause heat to be extracted from it at a continuous rate lower than the peak output of the boiler. The boiler will then come on in cycles at full output and replenish the store. The principle is exactly the same as would happen if a hot tap were left on a low flow rate.

While this method of working matches a conventional boiler quite well and can be useful if heat is being introduced from another source, perhaps at lower temperature, it is not at all suited for a modern, modulating condensing boiler which will operate far more efficiently if allowed to drive the heating loads directly and continuously at low power.

The boiler will be switched over to heating the store (used for hot water production only) at full output power when required.

It is a pointless and inefficient exercise to connect the radiators to a thermal store when a modulating condensing boiler is in use.

[Andy Hall]

This is misinformation if a modulating condensing boiler is used.

[Andy Hall]

This is only true if a conventional boiler is used or if there is a need to introduce heat from another source such as solar or possibly some form of stove.

It is not an appropriate technique to use if a modulating, condensing boiler is the primary or sole heat source since the boiler will not be allowed to ever operate in its most efficient temperature range.