Zones,how do they work with modulating boilers?

[ericmark]

This is pure interest, no intention of zoning my central heating, but was told today central heating must be split into zones, which I assume means motorised valves?

So without zones my understanding is every radiator has an electronic TRV head which tells the central thermostat how much heat is required, and in turn the central thermostat tells the boiler what output is required. So we have systems like EvoHome which using OpenTherm do this.

However with zone valves it would need each TRV head to tell a Thermostat which in turn told the zone valve how far to open and then the zone valves would tell a master thermostat how much they were open and then that would tell the boiler, however I know of no such system.

I have not even seen a motorised valve which can regulate how much fluid passes through it.

And to be frank can't see any good reason for fitting zone valves where programmable TRV heads are fitted.

I can see how it would be cheaper maybe to split the house into zones than to fit all programmable TRV heads, but can't see how this would work with a modulating boiler? Unless that is no wall thermostats are used and the boiler uses the return water temperature to control the amount of modulation, then we have age old problem how do you tell the boiler not to come on as it's a warm day.

So what is the crack on this splitting into zones?

 

[Dan Robinson]

What kind of modulation are you talking about?

 

[D_Hailsham]

Zoning using motorized valves is the simplest way of controlling areas with different time/temperature requirements, e.g living space and bedrooms. TRVs are used to prevent rooms overheating due to solar gain, TVs etc so they do not need to be able to control the boiler.

Electronic TRVs which can communicate with the boiler are a step up as they allow control of individual rooms.

Evohome allows you to mix and match; i.e have a zone controlled by a thermostat with standard TRVs, as well as having radiators in other "zones" each of which can request heat irrespective of what is going on elsewhere.

All requests for heat go via the central controller which calculates the flow temperature necessary to meet all requirements. What it cannot do is supply water at different temperatures to different parts of the system. This is where TRVs come in to play.

The fact that the boiler may be modulating is not relevant. All modulation does is to vary the heat supplied to the water so the correct water temperature is obtained.

Standard motorized valves do not control the flow, they are open/closed devices. If you want to do anything more sophisticated you need specialized valves, for example the mixing valves used with underfloor systems which maintain a lower temperature, e.g 45C, in the U/F section even though the boiler is putting out water at 70C for radiators in the rest of the house.

There is no need to provide zone valves if all rads are controlled by e-TRVs.

 

[Dan Robinson]

Partly correct