CH zones

[Robert]

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?

[Ron Lowe]

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.

[ARWadsworth]

Crude maybe, but TRVs CAN be very effective. My guest bedroom has a TRV that is turned off until I get guests. It is manually controlled but simple and effective.

Cheers

Adam

[Steve Walker]

No, not new build - 1935 semi.

The existing system had all the upstairs radiators fed from under the floor within 3 feet of the airing cupboard (where the pump and existing diverter valve were), so I made up a "manifold" in the airing cupboard from 22mm pipe, tees and albows and installed 5 valves on it (3 bedrooms, bathroom and hot water). I built a box containing the relays, etc. which switches the valves and the microswitch in each valve feed back to operate the boiler and pump.

A single length of 3-core and earth runs from the box, downstairs, carrying L, N, E and "run" to a second relay box under the floor downstairs, where three further valves were installed for the living-room, hall and kitchen.

Each room has its own timer/stat, mainly installed right next to doorframes, so that the cable from the stat to the "local" box can run straight down the edge of the architrave and under the floor.

It's difficult to tell on the bills front, as we improved the system specifically because we were having a baby (three now!) and therefore have been using more heating and hot water. From the flexibility and comfort point of view, it's great though.

At ages 6, 4 and 2 they don't mess with the stats and can't reach the windows!

Once programmed, changes are not very common and it only takes 5 minutes twice a year to change the clocks.

That is my eventual aim - Dallas 1-wire temperature sensors (or similar), PIC or AVR control and a couple of LCD screens.

We are planning a conservatory and may use underfloor heating - if we go this way, there will be temperature sensors embedded in the slab ready for any future use.

SteveW

[Andrew Gabriel]

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.

[Andrew Gabriel]

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.

[David Hansen]

On Thu, 11 Mar 2010 18:07:00 +0000 someone who may be Robert wrote this:-

A thermostatic valve that "does not switch off" may be faulty, but it may also be doing its job very well.

On/off is not the only form of control. A thermostatic valve may be able to match heat losses in a room, in which case it will open the radiator up fully if it is cold enough and as the room gets up to temperature it will reduce output slowly, eventually matching losses. It will then vary the output by small amounts, to small to notice with a hand on the radiator, to match losses and heat gains. Whether it can do this or not depends on the particular circumstances, just one factor being how well it senses room temperature.

[David Hansen]

On Thu, 11 Mar 2010 21:13:09 GMT someone who may be "ARWadsworth" wrote this:-

In the right circumstances they are all that is necessary. I have a number in the common areas of my house. When any of the zones is calling for heat these valves are regulating the temperature in the common area they are in. The greatest mistake many people make with them is to treat them as on/off switches and constantly fiddle with them, turning them up full if they feel hot and down fully if they feel cold, entirely wasting the thermostatic action.

[David Hansen]

On Thu, 11 Mar 2010 18:12:31 +0000 someone who may be Robert wrote this:-

All that is needed is one run of three core and earth, which is looped from one room to the next.

As well as neutral and earth this cable carries a live supply (which may be switched by a master time clock) and a wire energising the pump. The live supply goes to the thermostat and also to one side of the switch in the motorised valve. If the thermostat is calling for heat then that sends the live on to the valve and when that is open the switch closes and connects the live supply to the pump wire. If one or more of the valve switches is closed then the pump will be energised. Hot water is the same. The boiler fires either directly, or better it only fires when a thermal store is depleted.

[David Hansen]

On Fri, 12 Mar 2010 02:32:30 +0000 (UTC) someone who may be [e-mail] (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.

[chris French]

In message , Robert writes

In essence though, it's a fancy version of a TRV - which do the same sort of job.

There are systems available with a central controller to control each room temp.

[TheOldFellow]

My view is that if it has a zone valve controlled by a thermostat, then it's a zone. But I didn't count it my post.

R.

[TheOldFellow]

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.

[Andrew Gabriel]

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.

[David Hansen]

On Fri, 12 Mar 2010 08:35:55 +0000 someone who may be chris French wrote this:-

Yes and no. If the thermostat is just a thermostat then yes. If the thermostat is programmable then no.

If the thermostat has optimum start control then it will save even more fuel and if it has PI control then it will match the set temperature more closely, at the expense of operating the zone valve/boiler frequently. These thermostats, really advanced controllers, are coming down in price, but still over twice the price of a programmable thermostat. Are they worth it? Perhaps for a living room.

[David Hansen]

On Fri, 12 Mar 2010 13:02:55 +0000 (UTC) someone who may be [e-mail] (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.

[dennis]

There is some requirement to "zone" conservatories.

[dennis]

TRV only limit the maximum temp, they do not allow timed operation or control the minimum temp as a zone can. They are a bodge and should not be used in new installations IMO.

Yes.

[Kostas Kavoussanakis]

This is indeed the limitation that affects me: they cannot call for heat.

(I believe that they are also not as accurate as thermostats; note that they do not present an interface in C or F, just a generic indication from 1-5 or something).

[ARWadsworth]

So you have met the girlfiend's parents then?

I changed their back boiler that had only ON/OFF controls and no programmer for a combi boiler with TRVs and a wall stat in the hallway last October.

The girlfriend's Dad buggers about with the TRVs and the hall stat as soon as the radiators cool down. And they have left the TRV in the empty bedroom on the No 3 setting so that the room is aired!

Adam