On Wed, 27 Jun 2007 19:46:29 +0100 someone who may be "Roger Mills" wrote this:-
Depending on the arrangement of the house and occupancy one might be able to do almost the same with three zones. Public rooms, bedrooms and rooms which are on whenever either or both of the first two is on. For each of the first two there is a programmer and valve. Other rooms have thermostatic valves.
The on and off times for each zone would involve the bedrooms being on first and last thing. The public rooms would be on in the evening, but go off before the bedrooms. Precise details would depend on occupancy.
Rooms which were not in use, some bedrooms and a dining room for example, would be set back via the thermostatic valve.
I initially resisted the idea that I would benefit from zoning as I have an open staircase leading from the living room but I eventually weakened and have not subsequently regretted it. FWIW I have effectively 3 zones. Downstairs with the programmable stat in the living room, upstairs with the programmable stat in the main bedroom and the bathroom where the radiator (with a TRV) is on the boiler bypass circuit and is thus supplying needed heat whenever the boiler runs. There is an automatic valve on the bypass circuit which can operate when the bathroom TRV is closed.
There are two basic types, both intended to sit on a TRV valve base in place of the normal manual head.
- Thermal drive e.g. AXT 111. This is basically a commercial version of John Stumbles' idea. They work reasonably well if one is happy with on and off control - fully open or fully closed. I tried to make one do proportional control and partly open the valve, but it wasn't all that successful - very non linear and variation between two units, so would have to be individually calibrated. However, they are about the same size as a TRV head
- Motor drive e.g. AXM 117S. These have a positioner and can be controlled by a DC voltage of 0-10v. They seem to be consistent as well. The motor body isw a bit larger but not obtrusive if the overhanging piece is pointed back towards the wall.
I zoned my house when I installed CH 25 years ago. Five zones five programmable stats (well they were timers and stats 25 years ago but I replaced them with more advanced digital timer stats a few years ago. Works very well and there is no change to the settings between winter and summer. I just wish the valves were more reliable as I have had to replace all of them now.
Well that's resolvable by matching radiator sizes to heatloss in each room, which should have been done anyway. The room with the thermostat could be relatively slightly undersized to ensure other rooms are normally all up to temperature before the thermostat switches off.
However, to go back to your main point, I installed central heating in an end-terrace house 5 years ago. I zoned it and I don't regret that one bit. I split it into 3 zones; downstairs, upstairs, and bathroom. The bathroom sticks out the back of the house and was prone to be cold and takes a long time to warm up. The bathroom zone is simply the logical OR of the upstairs and downstairs zones, i.e. the bathroom heating is on if either upstairs or downstairs heating is on.
Some things to bear in mind...
A small zone is likely to have insufficient heat output to absorb all the power of a modulating boiler even at lowest power output, so you will get boiler cycling. Some modulating boilers, particularly condensing with a system designed for efficient low flow temperature, are not all that good when cycling at low temperature. Even a medium sized zone will have this issue when only low heat output is required, and you will end up with periods where multiple medium sized zones end up taking turns with heating demand resulting in a long period of cyclic boiler running where fewer/single zone would avoid this. My own designed heating controller attempts to avoid this, but I don't know if there are any multi-zone commercial heating controllers which do that (and multiple single zone ontrols could not do that).
If you are intending to be able to operate the system with some zones switched off (or frost setting), remember to allow for the heatloss to a cold room from a warm room on a different zone, bearing in mind that rooms are often not well thermally insulated from each other. This is particularly important for upstairs verses downstairs zones. Often much of the upstairs heating comes from downstairs through the floor, but if you make that normal assumption in a heatloss calculator, you will find it difficult to heat the upstairs alone if downstairs is cold and not contributing.
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