Combi - 2 heating zones

[pauliepie]

Is it possible to have the heating circuit off a combi split into

zones, one for a ground floor the other for upstairs. If so, what controls are required, etc,etc?

cheer

-- pauliepie

[John Stumbles]

2 * 2-port valves etc, but you'll also need a bypass (e.g. pressure relief bypass) so when the last valve turns off and tells the boiler to stop theres somewhere for water to go while the boiler keeps the pump running as it cools down

[Doctor Evil]

Yep. Two 2-port valves and two Honeywell C67 programmer stats. The CM67s energise the zone valves and the end switch of the valves switch in the boiler. The combis will have two terminals for the room stat. The stat simply switches the two terminals and the combi fires. That is in normal one stat configuration. One of these terminals will give a live. Have a permanent live from the fused spur switch to the combi to the CM67s. Out of the CM 67s run a wire to the zone valves. Then take a wire from the live of the combi terminal to the end switches of each zone valve. The ends switches then have wire back to the combi's other terminal. Simple.

Or you could have one combi do upstairs and another do down. Combine the flows to give zippo flowrates that fill a bath pronto. No zone valves then, and if one boiler drops out, you still have another.

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[Doctor Evil]

That is only if there are rad valves on all rads. If the rads do not have rad valves there is no need for it, unless the maker states one for heat dissipation reasons.

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[Andrew Gabriel]

I did it using a mid-position valve, so there is no mode in which there's no flow path, without needing a bypass. I did however design a circuit to drive the mid-position valve and boiler demand, using two stats as input controls.

[Roger]

The message from "Doctor Evil" contains these words:

Am I being particularly dim this morning or has DrivEl laid another class 1 brick. ISTM that it doesn't matter a toss whether or not the radiator circuits have TRVs as the 2 port vales would close each circuit off entirely.

[pauliepie]

I suppose that the bedroom circuit (upper floor) needs a seperate roo

stat and timeclock to control the heating circuit. I guess a programmable room thermostat will do the job with a honeywel cm controller downstairs

-- pauliepie

[John]

No Roger its not you . Apart from your comment its usual to have "rad valves on all rads" in this reality

[Doctor Evil]

You are dim.

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[Doctor Evil]

You are dim.

He is dim, he said so.

Nothing says you need to have thermo rad valves on a two zone system.

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[Doctor Evil]

Good idea if the boioer has an auto heat disipation function. But two 2-port valve are a lot simpler and more reliable than one mid-position 3-way valve.

If you have TVRs on all rads and close the pump will be pumping nothing. So, it is wise to have the rads where the stat or programmers stats are with no TRVs fitted.

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[Christian McArdle]

No problem at all. Wire up as S-Plan. This is compatible with all types of combi. Some won't handle Y-Plan without external relays, as they often expect "volt free" contacts on their room thermostat input.

You will need for each zone a 22mm 2 port spring return zone valve and a programmable room thermostat of your choice.

Simply plumb each zone valve into the circuits for each zone. Obviously, the feasibility of this will depend on your existing layout. If the upstairs radiators come of a central trunk, with the downstairs dropping from the same, you are unlikely to have a suitable layout. The ideal situation is if near the boiler, the pipework splits into two, with two pipes going up to the upstairs rads and two pipes going down to the downstairs rad.

Wiring up is simplicity itself. Wire a permanent live (fused at the same point as the boiler, and preferably using a live out from the boiler, if available) through the terminals of the room thermostat into the motor terminals of the appropriate zone valve. Then, take the contact terminals of all the zone valves, parallel them together and attach to the "room thermostat" terminals of the boiler.

You may need an automatic bypass valve as well. This will depend on the model of boiler. They're not expensive.

Christian.

[pauliepie]

Sorry to complicate things but....

If a combi is used with a vented cylinder, then 2 zone valves ar required, one for the heating and one for the hot water, BUT what if want to split the downstairs heating from the upstairs heating....

Can this be done, the only problem is the heating in the house i existing on a semi gravity system.

Is it best to use the honeywell cm67 wireless package!!!!!!

cheers guy

-- pauliepie

[Christian McArdle]

The hot water cylinder forms a zone, just like a radiator zone. Each zone needs a 2 port valve and a thermostat, whether it be a cylinder thermostat or programmable room stat. If you had a cylinder and 2 heating zones, you'll need three 2 port valves. The existing pipework will determine if it is easy to divide into upstairs and downstairs zones.

It is very well regarded, but a little ugly, and very pricey if you start having multiple zones.

Christian.

[Doctor Evil]

If heating a low pressure vented cylinder, run the showers off the combi for high pressure performance.

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[Tim S]

I've been planning a multi zone setup for some time, due to never being very satisfied with single zone setups.

I was considering wireless once. My conclusion:

X10: would do quite well in theory, nice DIN rail contactors available. But not much in the way of timer-thermostats. Would end up being very kludgy. This system is really geared to the US with some European penetration (slow). For example, if you want to install an X10 filter at the supply then the biggest single phase filter available is 63A, so a

100A supply would need the 3-phase 200A massive filter block. Or hope no-one in the wrong third of households down the road decide to play with X10 too...

Wireless: Better. But I need in some cases, 2 contactors remotely positioned on each channel/zone. One to control a fan-convector or rad valve and the other to contribute to a demand signal centrally. Apparantly possible, but only 2 makers sell the receivers as separate items: Siemens and Danfoss (and the latter do do multi-channel receivers). But as you say, very pricey and having a bank of 100x80mm receivers commoned up at the boiler end looks hideous.

Other systems:

produce a very nice modular system, but I haven't the balls to ask how much it is! They don't appear to sell parts either, preferring to offer a one-stop consult+install service. Mucho wonga without much doubt.

So eventually, I thought, if I'm going to run light duty signal cable everywhere for something like the smartkontrol system, why not go back to basics and make something custom.

Essentially, a central relay box (using DIN rail for ease and neatness),

24V DIN PSU, bit of cat5 (have loads and it's fairly tough) to remote room programmer/thermostats and wire all the relays in common for the demand signal. Tee off to remote relays in nice tidy little boxes for fan-convector or electric rad-valve control.

I like this solution. I have to run wires, but not heavy ones and the system is mains-isolated and fused low so I can string the cables anywhere I like. DIN gives neatness, wide variety of modestly priced components and enough ease to wire a safe (mains one half, 24V other half, proper DIN connector blocks to present the external wiring to) neat little unit which is easy to maintain and expand.

Plus, I'm not tied to anyone proprietry set of thermostats.

Can't think of a better way. But I'm always open to more ideas.

Tim

[Ed Sirett]

.... and only needed if the hassles/costs/disruption of running a wire makes it attractive.

[Andrew Gabriel]

Also, for pump run-on, and boiler auto-start for frost protection, and daily pump exercising.

Indeed, the radiators in the rooms with the stats have lock shield valves at both ends, i.e. no TRV and no hand operated valves.