Smart TRVs but only on selected rads

[DBSNOOR]

Some help please, I want to get some smart TRVs for certain rooms to restrict those rooms getting heated whilst the other rooms without the smart TRVs get heating when the main thermostat calls for heat.

Is there a solution for this scenario, I'm assuming evohome and wiser are based on certain tvrs calling for heat and then initiating the boiler, whereas I want to maintain the existing controls and just restrict certain rads getting heated.

Many thanks

[OutInTheShed]

I was doing exactly this about 20 years ago, using Pegler programmable TRVs.

We had a big lounge which we didn't use in the mornings.

I don't know what's on the market right now, but FWIW, someone is flogging the CURV TRVs on ebay for under a tenner each, a swift look at their website suggests you can just set a schedule on each TRV, but I can't guarantee that.

We got bored of needing AA batteries and the faff of programming in the days before aps and all that.

[Murph7355]

Why do you need "smart" trvs?

Turn "dumb" ones in the room you want heated to max, turn the others to min. (Shades in between as desired). Job done.

Programming times and days in needs you to adjust your boiler's on/off times (to on!). And invariably the "smart" won't be smart enough to combat "wife and kids" v1.0.

[nyt]

I have upstairs fitted with Sonoff (Amazon) smart TRVs

I can turn then off (14C) or on (19C) with Alexa commands.

I also have a routine to turn then on 30 minutes before usual bedtime so that it's not cold when we head up.

[simon_harris]

You can achieve that with evohome quite easily, I would expect any smart TRV with a connected app would do the same.

[alangla]

You could do it with Wiser, but it’s a lot of expense for what seems to be a relatively simple setup. You would, however, get a 7 day timer and variable temps for your “master” system stat.

If you wanted to do this you’d probably fit the Wiser room stat next to your existing system stat, create a room called Master or Hallway or wherever the system stat is fitted and set up the times and temperatures you want for the system as a whole.
Add your TRVs to your target radiators and set their timers. The issue you’ll have is that if you’ve got a situation where one of your TRV fitted rooms is below the target temp then it’ll start the whole system up. This might not be too much of a problem if your conventional TRVs are set correctly, if your rooms are set to shorter run times than the master and if you’ve got comfort mode turned off. You may find that your hallway, or wherever you’ve got uncontrolled radiators, gets a bit warmer than you’d like.

If you put Wiser’s smart modes on then all bets are off and literally anything can happen.

As mentioned, this does seem a bit like overkill unless you can get the kit cheap and you basically want your target rooms to heat on a subset of the master times.

[rossmc88]

I used Tado in my old house for this and it worked well

[Sheepshanks]

Also have Tado's on all rads, except the bathrooms. so if any rad (apart from the hall) calls for heat then the bathrooms warm up. Our hall loses a lot of heat and has a huge rad in it, so I have that Tado unlinked from the boiler controller and then the hall only warms up if another rad is calling for heat.

In summer I use the room 'stat. set to max to control the boiler and then only the bathroom rads get warm.

[VictorSeven]

Yes we use Tado to do exactly what you are asking about.

Tado Smart TRVs in the bedrooms, they are set to NOT trigger the boiler (easy in the settings for each TRV) so only restrict the heat in the room during the day when we don’t use the rooms.

[clockworks]

Surely any "smart" TRV could do the job, just don't wire it up to the boiler if you want to keep the existing room 'stat and boiler control.

I went from an oil boiler with a full Evohome setup, to a heat pump. I've kept the Evohome TRVs on some of the radiators, so they can act as "smart" limiters in bedrooms and my workshop. I've left the Evohome boiler relay connected, as well as the heat pump's own remote thermostat. The heat pump can be controlled by either system while I'm "experimenting" with operating modes to find the best balance of comfort and economy.
The way it's running now, the Evohome is just continually calling for heat as a wired thermostat, and the manufacturer's wireless controller is altering the flow temperature by modulating the compressor.

The Evohome system will work fine without being physically wired to the boiler - as long as it can communicate with the boiler relay, it's happy. It has no idea if the relay is wired to the boiler or not.

[Wildfire]

I did this for a while with Hive (had the thermostat for ages before getting the TRV). Hive has a feature called Heating on Demand that calls for heat from the boiler, but this doesn't work too well if you don't have the TRV's on most of your radiators.

I had a few rooms that we don't use much, so I put the TRV's on a schedule and when the heating came on, I had them shut so those rooms weren't being heated up (e.g. the bedroom during the day).

Any smart system should be able to do that.

[dhutch]

Yeah, as said, almost any 'smart' thermostat system could do this.

Fitting the smart stats to the lesser (weekend only?) used rooms actually make good sense if you can then program in a 7day schedule to save turning them on and off manually.

However while we use a Wiser system, we just have high spec conventional 'dumb' TRVs and just turn off the annex bedroom when not in use.

[B'stard Child]

alangla said:

<snip>

If you put Wiser’s smart modes on then all bets are off and literally anything can happen.

Not wrong there!!

alangla said:

As mentioned, this does seem a bit like overkill unless you can get the kit cheap and you basically want your target rooms to heat on a subset of the master times.

Yep

[B'stard Child]

DBSNOOR said:

Some help please, I want to get some smart TRVs for certain rooms to restrict those rooms getting heated whilst the other rooms without the smart TRVs get heating when the main thermostat calls for heat.

Is there a solution for this scenario, I'm assuming evohome and wiser are based on certain tvrs calling for heat and then initiating the boiler, whereas I want to maintain the existing controls and just restrict certain rads getting heated.

Many thanks

My advice is be careful when shrinking the CH circuit by having too many rads "Off"

If your boiler can't modulate low enough and starts to cycle any "saving" is quickly eroded by short cycling

If it's just a couple of rads out of a circuit of say 10 it might be OK but you'd need to monitor your energy usage/boiler behavior to ensure it's happy

The other issues are

1. In allowing those rooms to get much colder than other rooms beside them the rads in the heated rooms have to work harder to cover off the heat escaping to the colder rooms

2. The warm up time to get a room back to temp is a lot longer

I have 9 rads on 24/7 heating but 4 rooms on scheduled heating because either the heat loss in those rooms is a bit severe (3 external walls and north facing) and or they are little used areas

[Sheepshanks]

B'stard Child said:

If your boiler can't modulate low enough and starts to cycle any "saving" is quickly eroded by short cycling

Ours does that as the lowest it will go is 7.5kW. Is it really a significant issue though? The boiler just cycles so its average flow temp and average gas consumption could be similar to a boiler that can go lower.

[dhutch]

B'stard Child said:

If your boiler can't modulate low enough and starts to cycle any "saving" is quickly eroded by short cycling

See also reducing the overall size of the emitters/rads by turning half of them off, while not having sufficient internal insulation to have a significant temperature reduction in the room with the turned off rad.

Can work well if you have an layout that means the room you are turning off has a lot of external walls like 3 or 4, and or a poorly insulated flat roof or something, and or horrendous air tightness, especially if the internal wall separating it is also brick and or insulated.

However in a modern well insulated house, and a room with only 1-2 external walls, and an uninsulated stud wall internally, and or door with stops an inch from the floor or is opened a few times a night, you likely will see no savings or even an increase in fuel consumption.

[B'stard Child]

Sheepshanks said:

B'stard Child said:

If your boiler can't modulate low enough and starts to cycle any "saving" is quickly eroded by short cycling

Ours does that as the lowest it will go is 7.5kW. Is it really a significant issue though? The boiler just cycles so its average flow temp and average gas consumption could be similar to a boiler that can go lower.

I disagree with some evidence - not being preachy here and I appreciate I had a really miss-matched boiler as a result of improvements done to the house.

My old boiler was 24kW and a 10kW min

When it was short cycling it could fire more than 10 times an hour - this meant I was forced to heat to a schedule with the house never really reaching the correct temp because once it started short cycling it was very uneconomical to leave the boiler running.

I had to run it at 55 deg because it couldn't cope with much below that flow temp boiler efficiency was maybe 90% when running for initial house warm up

Each time it fired it fired up at 70% of max output (regardless of any range rating) for 120 secs before modulating down

That's 120 secs of 17 kW of energy going into the HE - a lot of that energy going out the flue before it's had chance to do much.

The schedule was built around keeping the house warm enough without getting it to short cycle -

weekdays morning then off and then evening with off at night

weekends morning then off, middle of day then off and evening then off overnight

Current boiler 16kW fires once per hour - fires up at 60% of max (16kW) for 60 secs before modulating down to it's minimum of 3.2 kWh (house heat loss at -2.4 is 4.5 kWh)

That's 60 secs of 9.6 kW of energy going into the HE being offset by a burn at low modulation that can be anything from 20 mins to 50 mins depending on OAT

As a result of this boiler change I'm heating 24/7 at a flow temp of between 28 and 32 deg C for an 8% increase in annual cost. Boiler efficiency is close to 98% with a 23 to 26 deg return

Edited to correct error

Edited by B'stard Child on Wednesday 12th February 13:13

[B'stard Child]

dhutch said:

B'stard Child said:

If your boiler can't modulate low enough and starts to cycle any "saving" is quickly eroded by short cycling

See also reducing the overall size of the emitters/rads by turning half of them off, while not having sufficient internal insulation to have a significant temperature reduction in the room with the turned off rad.

Can work well if you have an layout that means the room you are turning off has a lot of external walls like 3 or 4, and or a poorly insulated flat roof or something, and or horrendous air tightness, especially if the internal wall separating it is also brick and or insulated.

Exactly my drivers in the rooms where I still heat to schedule

3 external walls - limited loft insulation above one of them (I'm currently resolving that) - internal walls are brick/breezeblock - no IWI or EWI basically they have excessive heat loss - combined with occasional use (ie not a lived in area) I manage the heat loss by intermittant heating only at times when they might be used.

dhutch said:

However in a modern well insulated house, and a room with only 1-2 external walls, and an uninsulated stud wall internally, and or door with stops an inch from the floor or is opened a few times a night, you likely will see no savings or even an increase in fuel consumption.

Agreed you need to understand your house - just turning off rooms thinking it must save energy can sometimes not be the actual case

[Sheepshanks]

B'stard Child said:

When it was short cycling it could fire more than 10 times an hour - this meant I was forced to heat to a schedule with the house never really reaching the correct temp because once it started short cycling it was very uneconomical to leave the boiler running.

Ours is set for 20mins anti-cycle time.

[chrisch77]

Wildfire said:

I did this for a while with Hive (had the thermostat for ages before getting the TRV). Hive has a feature called Heating on Demand that calls for heat from the boiler, but this doesn't work too well if you don't have the TRV's on most of your radiators.

I had a few rooms that we don't use much, so I put the TRV's on a schedule and when the heating came on, I had them shut so those rooms weren't being heated up (e.g. the bedroom during the day).

Any smart system should be able to do that.

We have the same, Hive valves on rooms we don't want to heat in the daytime (e.g. bedrooms, living room) and on our home office. The office valve is the only one set to heat on demand, so that the boiler comes on to keep the office warm if the main thermostat has reached target, but otherwise the main Hive thermostat controls the boiler.

In answer to an earlier question about 'why not use ordinary TRVs', any smart TRV system allows setting of different temperature targets at different times of the day, so you can have more control over when you want those rooms to be warm or not. Working pretty well in our house for the last year or so.