The TRV and what does what, how to select a new head.

[ericmark]

For me too late, I am not going to change them now, but I have made mistakes, and would like a thread that we can direct people to so they don't make the same errors.

I have hunted the internet, and no guide seems to either cover all, or even get it right. It seems everyone who writes about them has different ideas, but the start of the problem is how to set them.

We see charts like this, which may be a good start, but the problem is, the room temperature is dependent on heat loss with the mechanical head, so with a well insulated room 2.2 may equal 20°C but with a poorly insulated room, it may need to be set over 3, and the lock shield valve also has a bearing to room temperature.

Some systems have bi-pass valves, others rely on one radiator not having a TRV, some systems have modulating boilers, (can adjust output) and others simple on/off. Some pumps on the supply and some on the return, and the list goes on, and not talked about the varying ways the TRV heads is fixed onto the radiator.

So I will start with the valves I have used, and maybe others can add how theirs work, so someone new can read this thread, and have some idea of what they are buying. I would say the mechanical valve does work if the lock shield is set spot on. But for the DIY guy, near impossible to set the lock shield and a mechanical valve, what is wanted is one valve, either the lock shield or the TRV to be set spot on, so the other can be set by trial and error, so *123456 is useless, what is wanted is temperature in °C at least to start with.

Unless living in an open-plan house, one thermostat to fire or stop the boiler is unlikely to work, be it sun through windows, cooking, open fires, or wind direction, most home will need at least two thermostats which can fire the boiler. If using programmable TRV heads, then heads in a room used overnight, will need a different trigger to those used in the day. The idea of two zones has been around for some time, but use a bedroom as an office, or homework room, and the up/down split no longer works, but this does not stop two rooms with similar use from being paired.

But a thermostat on an outside wall will give a different result as to one on an inside wall, so in the main the radiator is fixed, so using wall or radiator mounted thermostats depends on what wall the radiator is mounted on. If the radiator is on the outside wall, the TRV can fire the boiler prematurely, once the air flow has been established then it will work A1, but it depends on how well insulated the wall is. The reverse applies to a wall mounted thermostat, that also does not want to be on an outside well.

So if the radiator is on an inside wall then TRV can do all the control, but on an outside wall one may want to trigger the boiler with a wall thermostat on the inside wall. So we have linked and non-linked TRV heads.

Next is how to control the TRV heads, it can be manual, using Bluetooth, or Wi-Fi. To use geo-fencing, it needs to be Wi-Fi, but I have found geo-fencing can turn heating off OK, but to turn it on again, by the time it detects the mobile phone is close, it is too late.

Recovery speed is really important, how fast can a room be re-heated? My living room has two large radiators, so around 2.5 kW, but the time it takes for the boiler to fired up and heat the radiators, and then in turn heated the room, I am looking at well over an hour, so unless the commute is over an hour, then only real option is time, or manually turning on the heating. (With the mobile phone, but manually select the app and turn on heating).

So we have the features, like window open detect (I use it to stop heating when unloading shopping) remembering how long it takes to heat a room, and starting heating that amount of time before the set time, anti hysteresis software (although that can be OTT) linking to another TRV head in same room, and producing graphs to show how well it has worked.

Also, using the target and current temperature report to help set up the lock shield valve. I have four electronic TRV head types (10 electronic TRV heads) and each has plus and minus points, and not linked to price. Some need hubs, others don't, some hubs link to the boiler, others don't, some the hub is also a wall thermostat, others the hub can be at the boiler, some hubs need hard-wiring to the router, other use wireless links.

But the problem is to find out what it can do before you buy. So a post per TRV head type, will help, I don't know what Tado, EvoHome, or Hive heads do today. I do know what Energenie, Kasa, eQ-3, and the old Wiser will do, and I will add to this thread and detail what they can do latter.

I looked at this report not a bad report, but it does not help to select which will suit me or you.

 

[ericmark]

Energenie was my first electronic TRV head, came with two threads, and two set travels, never sure if installed correct, there seemed to be not way to tell. Very little could be done manually, you needed the app or PC web page, the anti-hysteresis software was OTT, so had to set it at 22°C at 7 am and 20°C at 8 am to get around it.

Claimed it worked with Nest, but although it connected to Nest, it did not in any meaning full way. However, using the report, and closing the lock shield a tad if current exceeded target, the room temperature remained stable, as long as the boiler was running.

The program works, but in some ways the eQ-3 which is much cheaper does a better job, batteries last around 2 years.