Rad Valves + Room Stat problem

[seanpen]

Hi
We have TRVs on 6 of the 8 radiators in our house. I have a problem - the wife uses a room stat in the hall to control the central heating (sets it at 21C). I think I should be bypassing that? I remember someone years ago saying that if u have trvs and a room stat, turn the room stat up full and then adjust the Trvs to get the suitable temperature.

Can you help - What should we do? Thanks in advance for any advice.
Sean

 

[Nige F]

Hot wire the roomstat while she`s out

 

[nstreet]

Do the rads in the hall have trvs on them?

In normal practice you wouldn't have trv's on the rads in the area where the room stat is located.

 

[ricarbo]

It's the other way round!!!!! Open the TRV's fully in that room only and set the roomstat to the temperature you want. Then the room warms up to the desired temp, the system stops until your critical room is too cold, then starts again. If your roomstat is not in your 'critical room', move it!!!!

 

[scatmanjohn]

ricardo wrote:

It's the other way round!!!!! Open the TRV's fully in that room only and set the roomstat to the temperature you want. Then the room warms up to the desired temp, the system stops until your critical room is too cold, then starts again. If your roomstat is not in your 'critical room', move it!!!!

So what you are saying is that the critical room dictates the temp in every other room?

Whats the point in having trv's then?

 

[ricarbo]

Well, you choose your 'critical room' and put your thermostat in it. Perhaps the living room. The other rooms will be cooler, for example bedrooms, and halls, so the TRV's control them. Some rooms will need to be hotter, for example the bathroom. Again the TRV does it's job. When your critical room reaches temperature, the boiler stops. So if, in the example given, the system stops when the living room is satisfied, the assumption is that that everything else is ok - perhaps erroneous.

Can you devise a better methodology?
An alternative is the system used in commercial (office and large buildings), where each area is measured for temperature and the system controls work in response. The way to do all this is not very difficult to work out, but it's a question of cost effectiveness in a house or flat. How far do we go with the controls? Generally, the normal arrangement satisfies most users, so is ok, if you will accept some degree of compromise.
Perhaps you can think of a better way.
It's up to you.

 

[scatmanjohn]

ricardo wrote:

Can you devise a better methodology?



Perhaps you can think of a better way.

No, thats why i asked .

 

[seanpen]

Hi Guys, thanks for your thoughts, in particular Ricarbo, Your comments explain a lot.
With the room stat being in the hall I guess that why it rarely switches off, because of its proximity to the front door (cold).
Q. I will follow your advice but should I remove the TRV from the radiator in the hall?
Thanks again, much appreciated
SEAN

 

[nstreet]

Hi Guys, thanks for your thoughts, in particular Ricarbo, Your comments explain a lot.
With the room stat being in the hall I guess that why it rarely switches off, because of its proximity to the front door (cold).
Q. I will follow your advice but should I remove the TRV from the radiator in the hall?
Thanks again, much appreciated
SEAN

It may not switch off because the trv cuts in before the temp reaches that set on the room stat, therefore the bolier is never satisfied as the room stat is always calling for heat. Personally I would remove it, if thats not an option keep it on its maximum setting.

If the radiators in the rest of the house have been sized correctly there is no reason for the hall to be cold. As each of the trv's shut down more heat will be available for the hall, rising the temp for the room stat to cut in, thus shutting down the boiler.

 

[ricarbo]

If you move the roomstat to the living room, leave the TRV on the hall rad. You don't have to remove the TRV's in the living room either, PROVIDED you leave them (it) fully open on max. Then the roomstat can do it's job of controlling the boiler and saving you money.
Scatmanjohn, I see why you say why bother with TRV's at all. The answer is it is very difficult to get the temperature of the rooms where there is no roomstat just right without them.The ordinary valves can let through 90% of the max heat when they're just 10% open. This means it's very difficult to get, say, 70% heat (this is called 'poor valve authority'), but a TRV will go wide open when the weather is cold, get the room to your chosen heat and then maintain it as the outside temp goes up and down. Why not TRVs on all rads? Because the boiler will never get told to stop, so will keep firing to satisfy it's own thermostat, even though all rooms are ok, and this wastes fuel. You can fit TRV's to all rooms if you have a flowswitch which tells the boiler there is no flow when all the TRVs are shut down and interrupts the firing signal. This will prevent the boiler starting unless there are some electronics to start the pump, see if there is a flow, and if there is, then fire the boiler. This is built into some boilers. The thing about this is the flowswitch can't tell if the flow is to a demand (e.g. rads or cylinder) or just going round the bypass, unless the bypass is also internal to the boiler. So you can't just add a flowswitch externally to any system unless it's in the right place and working with some electronics.