Thermostatic Radiator Valves whats the point?

[Readingplumber]

Hi Perhaps i am missing something,

Say in a house some one puts on TRV on all the rads except the one where the room stat is, - how can this save money?

The boiler will always be on regardless of if the TRVs are open or shut - isnt it governed by timer and room stat for one room?

At a guess please tell me if im close - if just one rad was on where the room stat is (assume trvs have been satisfied) the boilers temperature will get hot and cut off and then come back on when temperature drops again (cycling but isn't that bad for the boiler - shouldn't it be left running constantly to work best)?


Thanks!

 

[stevetheplumber]

r sat should control the room with no trv this prevents boiler cycling to a system thats satisfied

 

[doitmyself]

The boiler will always be on regardless of if the TRVs are open or shut - isnt it governed by timer and room stat for one room?

Firstly TRVs are not either open or shut. They are proportional devices which adjust the flow through the radiator so the heat given off matches the heat loss from the room.

As each TRV closes down more of the flow is available to feed the rads which are open more.

Provided the Room stat is not in a location which heats up quickly, all TRVs will have reached their operating point before the room stat turns the boiler off.

Room stats react to heat gains from the sun, room occupants, TVs etc.

the boilers temperature will get hot and cut off and then come back on when temperature drops again (cycling but isn't that bad for the boiler - shouldn't it be left running constantly to work best)?

It all depends on how long the boiler is on and off. If it's one minute on and one minute off, that might cause a premature failure of some components; but if its five minutes on and 15 minutes off, that's no problem.

Modulating boilers help as they can just modulate to a lower output instead of turning on/off. But once they reach the lower level of modulation they have to go into on/off mode to provide any lower output.

If you take your suggestion to its logical conclusion you would not fit a room thermostat, just rely on the boiler thermostat. Fortunately this has been found to be wasteful of fuel, which is why current standards require the fitting of a boiler interlock, which turns the boiler off when room temperature has been reached.

 

[payney1974]

What about the obvious reason that you can have certain rooms at lower temperatures ie. bedrooms. This makes it more efficient.