CH zones

Robert wrote:

I have an upstairs zone and a downstairs zone and in addition the bathroom rad is in parallel to the bypass circuit so is on whenever the boiler is firing. The bathroom rad has a TRV so there is also a small radiator on the landing as a heat sink for the bypass when the bathroom is up to temp.
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On Wed, 10 Mar 2010 12:04:58 +0000 someone who may be Robert
Away from DIYers they are not common at all.

Yes, for large heating systems IIRC. Large houses upwards.
Zoning depends on the house. Where solar gain is high north/south is the best form of zoning. Where there is different occupancy ground/first floor is often best (assuming bedrooms are all on the first). Some combination may be best for a particular place.
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David Hansen, Edinburgh
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David Hansen wrote:

Oh cmon now. Data bus right round the house, to drive a valve for every heat source and pick up a stat in every room..all controlled by a centralised computer.
In fact, use the mains ring to do the bus, and make em all hotpluggable ethernet type devices..Hmm. I may actually build that one..
So what we need is individually addressable ethernet-over-mains motorized valves and independently addressable thermometers that also just plug into the mains.
then you could dial into your house using your mobile I phone app and make sure the heating was on for when you got there...;-)
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On Wed, 10 Mar 2010 15:07:34 +0000, David Hansen
That is what my experience suggested but since 4 channel programmers seem to be on the shelf at B&Q and Screwfix, I wondered whether things were changing.
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Our underfloor heating had three zones upstairs and three downstairs. When I replaced the leaking upstairs with radiators I didn't put zone valves in, but I might sometime. Or replace the TRVs with Honeywell CM Zone ones. Recommendations for alternatives recomended....
One of the downstairs zones could usefully be split in two, but not easily - the heating pipes from that manifold do two rooms, and the southern one is much warmer than the northern one. And another downstairs zone is currently waiting for me to swap an unused valve actuator from upstairs to replace a failed one.
(Fixing the fact that the boiler pump is permanently on is a higher priority than zoning upstairs. In theory it was switched by the thermal store cylinder thermostats, but in practice those do nothing. The zone thermostats do switch the underfloor heating pump (the upstairs ones are off, the radiator circuit has an auxiliary pump just switched by a timeswitch for now (I did try asking about controls here a while back, but no-one seemed to understand the question - professional plumbers who are actually looking at the system get confused by it too, so its not just my description))).
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Why are you zoning? More accurate and separate temperature control, or ability to heat only part of house? These have different design considerations.
I designed with upstairs, downstairs, and (downstairs) bathroom. Bathroom is connected directly across boiler, so it's the logical 'OR' of the upstairs and downstairs zones. (Boiler only does central heating anyway, and not hot water.)
Be careful making too many tiny zones - boilers aren't efficient at providing 600W for one radiator at a time, and going to a thermal store is significantly extra complexity and very questionable in any efficiency gain claims.

Nor do I, not even in large houses.

Yes for large houses, but never implemented as far as I've seen in professional installs. I don't think it's something many domestic installers would understand. Indeed, it's rare that they do the electrics/controls anyway - usually get an electrician in to do it IME.
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On Wed, 10 Mar 2010 18:11:16 +0000 (UTC) someone who may be snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote this:-

Extra complexity, yes. Significant, I don't think so.

You reckon? Simply by avoiding short cycling (and modulation if the boiler has it) it will increase efficiency. The proof of the pudding is the lower gas bills.
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David Hansen, Edinburgh
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Modulation isn't an issue. Short cycling can be, but needn't be (more intelligent boiler firmware control can eliminate it).
Additional pipework and storage facilities will result in additional losses. Also much greater volume of water to be heated before heat is available to the room, and that larger volume of heat to be lost when heating is no longer required.

when compared to a similar installation but without a heat store, but also installation and maintenance costs over lifetime of system. It is a failure of KISS, for gains which are not clearly commensurate; in some cases they may be, in other cases they won't be.
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On Thu, 11 Mar 2010 10:46:03 +0000 (UTC) someone who may be snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote this:-

And who was it who said, "boilers aren't efficient at providing 600W for one radiator at a time"?

Assuming the system is designed properly the additional pipework is negligible.

While no insulation is perfect, the sort of insulation provided on a thermal store is fairly good. One should only drop by a few degrees overnight. As long as that heat goes into the building this is no great problem.

You don't understand thermal stores. Heat is available almost instantly in the room, as it was heated before heat was needed in the room. Depending on how much heat is taken out and the initial conditions, at some tome the boiler will fire to recharge the store.

Thermal stores are very simple. An extra pump and a few control elements are just about it. An advantage is a simpler boiler, which is less likely to go wrong, no need for modulation with a thermal store.

Well yes, in some cases the gains are worth it and in other cases they are not. That is where proper design comes in, if the gains are not worth it then the designer should go for something else.
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David Hansen, Edinburgh
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There aren't any that modulate down to 600W. Somewhere around 4kW is the lowest I think I've seen.

I'm talking about returning to a cold house, but then my usage wouldn't work with a thermal store, hence my point about not being suitable in all cases.

Does anyone make a condensing boiler which doesn't modulate? Oh, and the extra parts needed you list are the most frequent to fail.
When I was looking to add additional complexity and cost to my system design to improve efficiency, I was looking for significantly better efficiency gains than a thermal store would give me.

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On Fri, 12 Mar 2010 02:32:30 +0000 (UTC) someone who may be snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote this:-

If one has been out for the day then this is not a problem, the heating can be left off and when one returns a button pressed to activate heating. The radiators will be hot in a minute, due to the stored heat.
If one has been away for a long time and the boiler programmer/remote control is not flexible enough to warm the store up before arrival then that would be a slight problem. How big a problem partly depends on the size of the store.
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and not forgetting all the heat you lost as it cooled down.
Like I said, if you have money to spend on extra efficiency, find something more effective to spend it on.
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Andrew Gabriel
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On Fri, 12 Mar 2010 13:02:55 +0000 (UTC) someone who may be snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote this:-

Not as great as you might think. If going away for a long time one can run the store temperature down easily enough, by setting the boiler off or suitably low, for a suitable period on the last day.

They are very effective, as I have demonstrated.
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David Hansen, Edinburgh
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On Wed, 10 Mar 2010 18:11:16 +0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

I was thinking of doing up/down zoning, so I only need to heat half thee house we are in. Couldn't temperature control be achieved through balancing and radiator sizing?
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If you are thinking of not heating half of the house for long periods, remember to allow for the extra heatloss between the heated and unheated parts of the house, or you'll find you can't actually heat just half the house because it's losing too much heat into the cold areas.
If this is simply heating downstairs during day and upstairs in the evening, it's not so much of an issue, but ideally you should still take into account extra heat lost from downstairs into colder upstairs rooms, depending how much they are likely to cool down between heating periods.

Balancing, no. Radiator sizing, yes, and that's how it used to be done, but that's not how it tends to be done nowadays, as it requires more accurate heat loss calcs than are now typically carried out. Radiators are now oversized and controls such as TRVs or thermostats superimpose control to compensate for that, and that also compensates for other things such as having had a door open, etc.
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On Fri, 12 Mar 2010 02:19:24 +0000 (UTC) snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

This is really important. When I designed my zones, I planned for extra insulation in the dividing walls - 60mm Quinn-Therm in my case. It's not so bad if one zone is set at 18 and the next is 21, but between a 14 (guest-suite when there are none) and a 21, there is a big gradient.
R.
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This summer I will fit motorised valve/s to the upstairs bedroom circuit controlled by a timeswitch so that it shuts about 9AM then re-opens about 9PM. Main problem is cost of motorised valve (I'm using 2nd hand ones) and need to lift carpet. Savings should be significant as many days CH is on all day.
Much better return than solar cells/wind farms. Not sure why the govt dont push this a lot harder.
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On Wed, 10 Mar 2010 19:34:26 -0000 someone who may be "Mitch" <x> wrote this:-

Probably for the same reason that they don't insist on the radiators being resized when a condensing boiler is fitted, so that it condenses for an appreciable time. Modifications to pipework are more difficult.
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David Hansen, Edinburgh
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Three zones, ground, first and second. Strangely, specified by the people who restored the property just before us who cut lots of corners elsewhere.
Two boilers in parallel with no check valves to prevent water going the wrong way through one of them when the pump is stopped. We have only ever used one at a time with the other isolated. Four zones including water, originally using a triple and single time switch with a contactor.
I have replaced the time switches with a homebrew PIC micro based controller that has remote control stations with temerature sensors on a CAN bus. As we are moving this will be replaced with simple time switches again as I don't want to have the responsibility for it. The HIPS inspector was well impressed and gave us some credit for the zoning and control in his report :-)
Pete
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On 10/03/2010 12:04, Robert wrote:

In my last house, I had 3 zones: Upstairs, Downstairs and Hot Water. In this house, I have only 2: CH and HW; but that may change.
How you modify your zones depends on the layout of your house, how you use the space ( eg in daytime is downstairs occupied, but upstairs not ); how easy it is to modify the pipework, and what benefit you get.
There's no simple answer.
The electrical wiring is trivial, as is the plumbing, if you have access to the necessary pipework.
You could go gold-plated, and have seperate zones for each room, fed from a central manifold with a dozen zone valves, each individually controlled by a thermostatic timer on the wall of each room. Probably overkill, and a similar result can be got with TRVs.
--
Ron









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