Central Heating Prefabrication - e.g. DPS

[Andy Hall]

But surely if one breaks it would be a win-lose situation.......

.andy

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[IMM]

That is good. That is an improvement.

[IMM]

You will still have heat. Haven't you figured that one out yet?

[Andy Hall]

How many domestic installations do you truthfully know of that are like this?

It's a bit like welding two cars together in case one breaks.

.andy

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[IMM]

I don't care how badly "plumbers" design and install heating. I have met none who I would consider good enough. They should stick to drains.

What a stupid analogy. If one breaks the car doesn't go as they are together. If one boiler drops out, one still works. Think hard about that. There is the cost advantage too.

20 years ago I specified three wall mounted, forced flue, copper heat exchanger boilers on a sequence controller instead of one 300k BTU/hr commercial cast-iron boiler that required an expensive conventional flue. They said "but they are domestic boilers" I said parts are available on every street corner and if one drops out the others work, and it will be cheaper to run as on part load the sequencer will take one boiler out at a time, the two small boilers do not take up lots of needed space and they are as reliable as any commercial boiler. I got my way and the customer was delighted.

They same approach can be used for larger domestic applications. Put a sequence controller on two modulating boilers and the range of heat delivered is far wider than any one boiler. That will give you, depending on boiler, anything from 3 to 7 kW to 60 kW, all nicely delivered exactly to the heat load for 90% plus of operational time.

It is called looking at the problem from a different angle. Even Keston recommend using a number of domestic boilers for commercial applications these days.

[Andy Hall]

Ganged boiler installations are extremely common and have been for donkey's years.

I don't think that you can claim any originality for that.

So you are describing a larger domestic installation (actually a very large one). As soon as you use a single controller with two boilers, it is no longer a redundant system, which was your main point.

...as do a lot of manufacturers producing boilers in the 50-100kW bracket. Big deal. Nothing new there.

.andy

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[IMM]

I don't. I do claim originality to installing small capacity domestic boilers in a commercial situation in the environment I was. The mentality was that only Fed Dibnah cast iron lumps would do, and that only boilers with a "commercial" tag would do. It was getting the Ludites to shift their ingrained prejudices.

On the Continent they were using this set up for decades.

It is a redundant system. One drops out and the other still works. The controller calls boilers one (this is down),, not enough heat is detected (well none in fact) so No. 2 is called. That is what sequencers do.

They didn't do it 20 years ago. They didn't put "domestic boilers in "commercial" situations.

I saw one setup in the City of London in a smallish revamped building that had air handling units local to the zones. Each one had a Neataheat domestic boiler heating the copper duct coils. It worked fine and saved a ton of money finding room for a large boiler. The service guys always had Neataheat parts in stock in the building, as they were so cheap and easily available. Imagine having the controls of a comercial boiler hanging around.

[Andy Hall]

... and when the sequencer fails?

If the system depends on anything run in common like a controller, it isn't, by definition, redundant.....

.andy

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[IMM]

You can always have a simple by-pass switch.

[Stephen Fasham]

OK, so lets say I take the point, and I do. It is fair to say that if the heating is only calling for 1 zone out of 4 then this will be below the bottom end of the Keston C40 when modulated down (11kW) so there will be boiler cycling. The two issues I then need help with are, will it still all fit? I am planning to put the boiler, tank, valves and controls (except for the room stats!) all in the airing cupboard (not a lot of space for airing!). This is plausible as the ceiling height is almost 3m (hence the high heat loads for the house) and I can have as large a floor area as I want, but obviously this eats into the bathroom. I know I can fit in a big tank and a C40 but say 2 Celsius's will definitely take up more space. If I were to do it, how do I set up the sequencer and controls, and does the extra complexity not wipe out any savings. As regards breakdown I'm not particularly concerned as a) I'm hoping the Keston will be reliable and b) I live near a couple of large towns so the list of gas installers in the yellow pages is long so getting someone in to fix it shouldn't be too bad and I will have immersion back-up on the hot-water.

The real question I guess is whether it is worth the hassle given that a C40 will modulate down to 11kW anyway? A quick look at pricing say's that 2xC25=1xC40 so there's nothing in it economically.

Alternatively, since DPS are getting a reasonable level of recommendation from the group generally (apart as far as I can see for shipping one guy a secondhand part - subsequently replaced) do I just put the heat-loads, zone layout and HW requirement to them, and see what they suggest?

Stephen

[Andy Hall]

I think so, unless you were to split the house in two and use one boiler for each part. However, the C25 modulates down to 7kW so you wouldn't resolve the cycling issue. As it is, the boiler's controller will deal with that aspect.

You would also have two boilers to service, which will cost more than one.

Exactly. You might want to ask Keston for details of fitters who are approved by them in those towns.

.. plus you have to add the controls and extra fittings.

I don't see the point. If you needed 100kW or more, it might be a different issue

I would send it to them and to at least one other such as Albion and see what they say

.andy

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[IMM]

A deal can be struck which will give a good deal on two serviced as the boilers are next to each other.

Not a big issue.

[IMM]

See below re: heat bank.

As you are stuck for space there are two approaches:

1. Assuming two bathrooms here. View two combi boilers. One doing two zones of heating the other doing the other two zones. Each boiler will have two 2-port zone valves operated by a programmer/stat for each zone, preferably a Honeywell CM67, or equiv. Combine the DHW outlets using non-return valves, which will fill a bath pronto and give good power showers for two showers.

See a) . below, a previous post of mine.

1. An integrated "direct" heat bank (this supplies DHW and the CH zones) with two Glow Worm "heating" boilers heating it. Glow Worm make excellent condensing boilers.

See b) below:

a) With combi's the most important figure is the flowrate. 11 litres/min is fine for showes and the odd slow filling bath. Here is a recent post of mine...

For an even better flow rate and cheap too for what you get, assess using two Worcester-Bosch Junior combi's.

For high flowrates it is cost effective to use two Juniors and combine the DHW outlets. Worcester-Bosch will supply a drawing on how to do it, or ask me here. Two Juniors are available for around £1000 to £1100 depending on what sized units you buy. They have 24 and 28 kW models, you could use two

24kW or two 28 kW combi's or one of each. That is cheaper than the Worcester HighFlow 18 litres/min floor mounted combi and can deliver about 21.5 litres/min and never run out of hot water. The highest flowrates of any infinitely continuous combi is 22 litres/min, which is the ECO-Hometec which costs near £2K.

Have one combi do the downstairs heating on its own programmer/timer (Honeywell CM67 or equiv) and one do upstairs. Natural zoning, so you don't have to heat upstairs when you are not up there saving fuel. The running cost will be approx the same as a condensing boiler heating the whole house. No external zone valves either, and simple wiring up too. The Juniors are simple and don't even have internal 3-way valves.

Also if one goes down you will have another combi to give some heat in the house and DHW too. Combine the outlets for the DHW bath pipes and all the baths you want very quickly and no waiting. Best have the showers on separate combi's. It will do two showers no problem at all.

The Juniors are not condensing combi's, yet overall heating costs will be equivalent to a one condensing boiler as the upstairs will not be heated most of the time.

A win, win, situation.

Its advantages are:

- space saving (releases an airing cupboard). Both can go in the loft, or at the back of the existing airing cupboard.

- never without heat in the house,

- high flowrates (will do two showers and fill a bath in few minutes,

- No waiting for a cylinder to re-heat

- Natural zoning, one does upstairs and one does down

- hardly any electrical control work (running a wire to a programmers/stat and power to each,

- simple no brainer installation,

- minimal components used.

- less piping used

- cheap to run overall as upstairs would be off most of the time

- etc.

b) An "integrated" CH and DHW "direct" heat bank heated by two Glow Worm boilers "directly. I would have the heat bank company (DPS or Range, Albion only do thermal stores) provided two boiler flow connections of 28mm and two

28mm boiler return connections. Both boilers heat the heat bank independently. This way the boilers are isolated from the heat demand of the CH circuit and only re-heat the heat bank cylinder. So modulating down is not an issue as cycling is eliminated. Have a two stat setup on the cylinder to elimiate cycling altogether.

If the maker will provide two sets of bpioer flow and return tappings one set of 28mm tappings will do as this can provide about 70kW of heat, so two bioerds can be coupled to this.

The CH flow take off will have 4 zone valves, each operated by programer/stat, CM67 or equiv.

Also see

They will custom make, or adapt a model nearest to your needs, as will DPS.

[IMM]

spell checked..

[IMM]

DO NOT mate a Keston Celsius with a thermal store or heat bank. They are not suited.

[Neil Jones]

Actually, the documentation for the Celcius says

"Where thermal stores are to be used the thermal store supplier should be consulted as to the compatibility of the thermal store with a Keston Celsius 25. Thermal store units where the boiler directly heats an open vented thermal store are not suitable for use with the Celsius 25."

I think the key word is 'directly'

Neil

[IMM]

I would say none of them are.

[Neil Jones]

You might say that, but Keston don't. Why should an indirect heat bank be inappropriate vs a regular vented cylinder?

Neil

[Dave Plowman]

Wonder what your definition of original thought is then? Reading it off a corn flakes packet?

[IMM]

Why should this boiler not operate on direct with anything from 180 litres onwards to run through it? I believe the problem is their load compensation control circuit which is programmed to operate on rads.