TRV systems

[rustyh]

Hello,

Is is a MUST requirement to have one radiator with out a TRV?

Im currently installing a Honeywell Evohome system with HR80 radiator valves and BDR91 boiler controller.
The room thermostat was previously in the hall way on the an old glowworm ultimate system (boiler now been changed to a Baxi Solo 15HE). But the hall way radiator has now been removed. This leaves two radiators downstairs (Kitchen and lounge) which I plan to fit the HR80 TRVs on to. All the upstairs radiators will also have HR80's on.

So questions would be
1) Is a fully TRV system ok?
2) Do you need a room thermostat if running full TRV
3) If you need at least one radiator with out a TRV then it would probably be the kitchen one I would choose, would I need to more the room thermostat to this room?

Further information - Boiler is a Baxi solo 15HE, Hot water cylinder in the loft, and system uses a mid-positon valve (think this is called Y-Plan??)

 

[Armo74]

The room with the room stat in should not have a TRV,
Not advisable to have the room stat in any room where there are other heat sources like a kitchen.

 

[rustyh]

Ok, so from that I gather a fully TRV system is a no

There are 3 rooms down stairs (Lounge, Kitchen and Hall). The Kitchen as you8 said I cant have the room stat in, and the lounge has a log burner as another heat source. The hall has no radiator

Upstairs there are 4 rooms (3 bedrooms and a bathroom), all radiators are currently TRV'ed

Where would you suggest to have the room stat and which radiator would you not have a TRV on?

 

[jeff the gasman]

The baxi solo can be run with all radiators fitted with TRVs. Your pump must be wired directly to the boiler though. Consult the installation instructions it is detailed in there.

 

[rustyh]

Hey Jeff,

That was going to be my next question, querying page 14 of the baxi manual that shows a Y Plan full TRV system.

So basically, I rewire the pump the the p/f terminal of the solo 15, and that allows a fully TRV system and removes the need for a room thermostat....correct?

Another question though, the room thermostat control when the boiler turns on and off (based on room teperature), so what tell the boiler to turn off if all the room are at set temperature if there is no room stat, does the boiler monitor heating system water temp or something??

 

[45yearsagasman]

The boiler will not switch off unless the switched live is interrupted. That is usually done via a room stat. It will short cycle on the boiler stat, thus wasting energy.

 

[rustyh]

Ok Im a bit lost now

I plan to use this honeywell evo home system, which is basically a 7 day programmable wireless system.

Say I program it to come on for 3 hours in the winter evening. Whilst on, all the rooms come up to temperature, will the evo system turn the boiler off its self, or will the boiler sense it no longer need heat demand until a room cools and thus turn off

 

[tiptoptrump]

The Evohome system can be set up so that all the TRV's act as boiler interlocks. So theoretically when the last TRV in the circuit closes, the boiler/pump will switch off, allowing you to have a full TRV system. However on my electronic TRV's I have found that as you get to that point, the noise from the pump trying to push the water through a nearly closed valve (despite having a bypass valve) was excessive. I ended up leaving one of my bathroom valves open to compensate. Plan is to fit an auto variable speed pump, which I hope will offset my problem.

 

[rustyh]

Now Ive got ya, make sense now

Did you have to use two BDR91's, one for heating and one for hot water, or does one BDR91 control the two?

 

[tiptoptrump]

Hi Rustyh
I have the Danfoss Link control. I have an S Plan system and use the boiler relay to control heating and a simple relay to control the hot water.
Looking at the Evohome they offer a separate relay for the hot water control, but using a separate BDR91 should also be possible. You will need to programme them to provide two different switching sources. The Honeywell would guide you through that.