CH zone control

[Adrian Godwin]

I'm in the process of looking at a replacement heating boiler and want to take the opportunity to get the heating working properly at the same time.

The house is a 4-bed '70s detached with an 80,000 BTU conventional boiler. I'm intending to replace it with a conventional condensing boiler and replace the hot water storage tank with a better-insulated one having 2 heating coils. At some time I may then add solar water heating.

I don't like the house too hot so tend to keep the thermostat at about

15 degrees. It's located in the hall which, while not particularly drafty, does have a single-glazed door with no outer porch. It also has a large square stairwell between the thermostat and the hall radiator.

The result is that the boiler runs to warm up the hall, but by the time it's up to temperature the air rising up the stairwell has made the upstairs stifling unless the outdoor temperature is very low. TRVs are fitted but mostly seem to have jammed up so probably aren't helping. There are three other rooms downstairs, two of which tend to be a bit cold as a result of this. The third is the kitchen which is warmed by the boiler and pipes - this may not still be the case if I resite the boiler to the garage.

I think I can isolate the upstairs and downstairs pipework to make two zones, and I could obviously replace the faulty TRVs. But this might not be enough - although it would help if I could avoid putting heat upstairs when it's already hot, I can't stop the hall heating the landing. My best guess is to move the downstairs thermostat to the lounge, add another thermostat for an upstairs zone, and try to regulate the lounge and landing temperatures while leaving the hall cold. However, this may mean the study ends up cold as well. Or, I could leave the thermostat in the hall and use the lower temperature to keep the downstairs zone running, then rely on TRVs to regulate the other rooms. Perhaps also a separate actuator on the hall radiator to make it follow the upstairs zone.

Any ideas ? Any suggestions for a good, flexible, 3-zone controller that could handle this ?

-adrian

[dennis]

8<

Best way is to fit a zone valve and a timer/stat on each room. Its easy to do from a control point of view but does require more cable and pipes.

On mine I have mains to individual timer + stats that are battery powered (last about three years).. the live from the stat operates a spring return zone valve and the end switches on each valve are just wired in parallel to the boiler on. Its not cheap but it makes control easy.. you just set the times and temps you want in a room and forget it.. it works spring, summer, winter, anytime without you ever having to do anything.

[The Natural Philosopher]

Do consider a mains pressure stored hot water system. If you like showers and baths that really fill up fast, its worth it.

Then put a/the stat upstairs....

Ok..

You don't need a three zone controller as such. Unless you want to time the zones independently.

What you need s a lot of wires and zone valves. So when each bit is shut off the pipework is isolated.

The microswitches on the valves are all wired in parrallel to run the boiler and pump, so there is not 'master stat' as such. Any area that is below temp can call for heat, and any area that is hot enough will shut itself down: when all are shut down, the system shuts off the boiler.

You can run this little lot of a single controller zone for timimg purposes. Only if you want your (say) upstairs coming on at a different TIME from downstairs do you need a 3 zone controller.

In essence (conceptually) every TRV can be replaced with a room stat/motorized valve combination. You need to run a three wire+E to that lot..one wire is the live from your timer, then another is the return from the microswitch which gets wired to the boiler/pump. And of course a neutral and earth.

If you are ripping and relaying pipes, I strongly suggest you do this. Or at least put on the wires.

You can use radio stats to avoid *some* wiring issues. But you still need to run wires back from the motorized valves to the boiler and pump.

I wish I had done this myself.

[The Natural Philosopher]

Yes. That is even better. Every room has its own stat and timer and valve.

It would be instructive to work out how cost efficient that is, given the cost of fuel is high and rising and never likely to come down.

[Doctor Drivel]

Use an integrated heat bank (thermal store. Ideal for solar). Avoid unvented cylinders and they need annual service charges.

Have both CH zones of the cylinder using TRVs on all rads (no wall room stat) and a Smart pump on the CH circuits. It gives mains pressure DHW. The boiler operates in a superior hydraulic environment

Look at:

an explanation. Get back if you have queries.

If you were not going solar I would recommend using two Atmos Intercomi combi boilers (RR quality), one doing one CH zone and one the other. Combine the DHW oulets for the baths only for very fast fills. The most cost effective route and saves lots of space too. Easy to fit. Simple wiring and piping and DHW. A back up if one is down (very rare with an Atmos).

[Adrian Godwin]

Tricky, as the downstairs piping (which is where this would be most useful) is set in the concrete floor. So although I think I can interrupt it where it comes away from the boiler (and the upstairs piping goes off in the other direction) it's hard to split it up further. Individual actuators on the radiators would be easier, if a bit expensive, but not all are easy to get wiring to either.

-adrian

[Adrian Godwin]

Difficult to estimate without some accurate measurements of room heating times and the effect of outside temperatures. An interesting project, but one I'd never get around to completing ..

-adrian

[Adrian Godwin]

We almost always use showers, so bath fill time isn't an issue. I'm not sure it's worth the extra hassle when a shower pump will do the job.

Good point. It would be an advantage but certainly not essential in a fairly small house.

Unless there's a smarter controller available, that would not just turn on at a specific time but set itself forward according to how much heat is needed, or some other trickery that would help it guess that the downstairs was overheating the upstairs. Do such things exist or are they all just simple time controllers ?

It's a good way to do it, but I doubt I'd like the cost. And really, TRVs ought to do it, provided that I also had a few thermostats in parallel to keep the boiler on until all the rooms were warm. But I've never been that impressed with TRVs - is that a common experiance, or are some better than others ?

-adrian

[Roger Mills]

You don't need a 3-zone controller - you can do it with one which controls CH and HW (which you've presumably already got), plus 2 programmable room stats. You then implement an S-Plan+ system (see

) with 2 heating zones and

1 hot water zone - requiring three 2-port zone valves.

Use the timer in your existing controller to control the HW zone. Set CH to constant on the controller, and feed the two programmable stats from the CH output, and use them to control the two heating zone valves. The timing for the heating is then controlled by the programmable stats - and the 2 zones can be on at different times if you wish.

It might be an idea to use wireless programmable stats rather than the hard-wired variety. You can then easily experiment with moving the stats to different positions to see which works best.

[John Rumm]

If you zone up and downstairs separately, then a A programmable stat to cover each zone would seem to solve many of your problems better than trying to do it all with a simple timer / controller.

[The Natural Philosopher]

Yep. At some point commons sense and cost benefit analysis tells you 'this is going too far'

[The Natural Philosopher]

In my experience mains pressure hot water does it about twice as well.

I costed it out in my new install, and by the time I had wired in all the pumps etc, the cost of the pressurised tank was actually LESS than the pumps and installations thereof.

I helped a friend do another one..there the plumber raised another point

- the HW tank was an ail in one with header "If you pump that mate, you will empty the header faster than it will refill, and there's barely a showers worth in there as it is"

The cost of retrofitting a PHW tank to his EXISTING boiler was 1300 quid, and the results exceeded all expectaions.

As others have pointed out, at that pint you want to buy a smart STAT, and get rid of the master controller altogether.

As fuel gets expensive, and chips get cheap, the old idea of 'time switch, master stat and maybe a few TRV's as well' starts to look antiquated.

If I were doing any extensive work even tho my systsem is only 5 years old, Id go for bloody valves and stats everywhere, and no time clocks at all for upstairs. It has merit downstairs only in the UFH and then only in spring and autumn. In winter it has to be 24x7 as the rate of temp rise is so slow that i never gets warm enough otherwise. In summer its off anyway.

Upstairs we use rooms on a pretty random basis..and they are low thermal inertia. I would really like to walk into a room at 12C and simply 'turn it up' to 20C and settle down in it, and switch it back to 'frost' after I have left it.

I may yet do it. Being upstairs most of the wires could go into the loft, and that's where most of the CH plumbing is too. One big junction box and a 4 way cable down to the boiler would be all it needs.

I could do it as and when each room needed decorating..