Modernising room heatng controls - what's available?

[Andy Burns]

ISTR some of them were sold in the UK by Conrad ... yes, here you go

But those are each standalone, rather than centrally controlled ...

[Bill Taylor]

Ah!, that's one of the disadvantages of the eq3 MAX system that I'd forgotten about. I don't think it has any boiler/zone/hw controls. Lots of district heating/communal heating systems on the continent, so isn't relevant to them.

My system uses a weather compensating controller with a large thermal store, the pump runs all the time until the outside temperature exceeds about 18C. There's a separate controller for water temperature control.

It wouldn't be too difficult to come up with a fairly simple control system using information from the dmitry-kazakov programme to control the boiler and pump, but that's possibly getting a bit too complicated, unless you like playing with that sort of thing.

The Honeywell systems are probably more suited to a UK style system, if rather more expensive, and they don't encourage DIY installation.

[Andrew Gabriel]

I do that with windows and doors. I have a 5 minute delay before an open window or door switches off the heating in that zone. Also, doesn't apply in bathroom, or if windows set in ventilation lock position.

The controls need to be more complex than this. A boiler won't work well if it gets separate and independant call for heat from one room at a time - the power output will be well below the boiler's minimum. Such a system needs to strive to have a minimum load, and this can be done by having a temperature range for each room, and waiting until, say, half the rooms are demanding heat before the boiler demand is asserted. If you have a hot water cylinder, you can also use this in the scheme as something that needs heating, but over a wide time, it doesn't care too much when that happens. Ultimately, if you have one room well below set point, you will have to heat that by itself, but boiler won't be efficient doing this and a clever control system will try to avoid getting in to that state.

Another way to do this would be to use a thermal store, which will happily heat just one radiator. However, a thermal store adds losses, so it's probably not going to payback those losses unless you make use of it for other purposes, such as feeding solar water heating into your system.

If you go for fine grained zoning, you might also want to use that for heating only part of the house if another part is unused. If you do this, do remember to allow for heat losses between internal rooms and floors in the house when one is heated and another isn't. Normal heat loss calcs wouldn't enable you to heat just the upstairs because up to half the heat comes through the floor from the heated downstairs, and you would need to allow for heating the upstairs without that contribution.

Generally, it's not the room stats which are compensated for this, but the central heating flow temperature, which effects the power output from the radiators.

Another compensation you can apply in a similar way is the building's core temperature, such as the temperature in the middle of a thick internal wall. When heating up a building from cold, you will need extra heat beyond the normal losses to heat up cold masonary.

[nospam]

Today I discovered that it's a single pipe heating system. with some of the pipes in the solid floor, so I've got more work than I realised and it's likely that I may as well replace everything.

[nospam]

Here's the reply from the manufacturer: "I guess you are looking for a boiler controller? Unfortunately the MAX! boiler controller has been withdrawn from the market due to poor customer uptake. We do not believe there to be any devices available in the sales channel. In the future a Boiler Controller will be included in our Homematic IP portfolio."

[nospam]

Thanks, Tim, for some useful answers and for sparking some ideas. I discovered a new challenge today: it's a single-pipe system. I might be able to feel a heat store sneaking up on me ;-)

[harry]

You can get pumps that automatically adjust themselves to a set pressure. ie, as radiators turn down /off they slow down. Eg:-

[nospam]

Is this with a home-brew controller?

I'm still struggling up the learning curve but it seems that the OpenTherm protocol allows the smart heating controller to control the boiler modulation and so reduce the problem of the boiler running inefficiently when a single rad calls for heat. Also, if some areas have regular TRVs (airing cupboard being the prime target, but maybe also the hall, landing and workshop) then those will always be heated (assuming the TRVs haven't shut off) when any smart bit of the system calls for heat.

Good point

Thanks - that's another step up the curve.

Perhaps that's a Bridge (or thermostat) Too Far ;-)

[nospam]

... snipped

I forgot to add: another way of solving the boiler efficiency issue would be to go back to the earlier suggestion of having two boilers and only bringing the second on line when needed (using a sequencer) or in the winter.