Is this article a Red Haddock ???

[ericmark]

That's fine if you have a wall stat it every room (but then you wouldn't need TRVs, anyway!).

The TRV can connect to a sensor, so can measure the temperature remote to the TRV head, but you can also have a display,

the problem today is working out what will best do the job. We tend to jump to the idea that a wall thermostat controls the boiler, this is not always the case, it can control the TRV head.

I have repeated many times, the problem is finding out what product will do what, and keeping up with the changes. So 5 years ago when I moved in here, Hive would not work with OpenTherm, and Tado had also removed their OpenTherm versions from the UK market, and Nest would work with Energenie, all this has changed, Tapo and Kasa now both use same hub and the TP-Link products seem to be taking the market by storm. I keep mixing up Tapo (TP-Link) with Tado which is a completely different make.

There are two very different ways to control a boiler, one is electric, the other is with the return water, many uses both, and in both cases they can control the boiler in an analogue manner, which is better, or a digital manner (on/off) commonly referred to as mark/space. With my boiler it can only work with mark/space, but modern boilers using mark/space makes them inefficient, as every time a wall thermostat turns the boiler off, it has to start again from scratch setting how much to modulate to gain the latent heat from the flue gases.

The homes have improved heat loss wise, and I know turning my heating down overnight it is very rare the boiler will ever fire, so turning the boiler completely off with a programmer will likely have in the main same result as turning it down with a programmable thermostat.

Turning the heating up again, I found not so simple, before fitting Wiser, I used a Nest Gen 3 thermostat, it could only go in the hall, as that was where the wires to power it went, turn from 16°C to 20°C and the heating would likely run for an hour, and over shoot, so I set it to advance in 0.5°C steps, around once every hour, this resulted in it taking 8 hours to reach 20°C so would hit it at around 4:30 pm, but same result could have been done with a simple time switch. In fact, likely better. As it depended how much the hall had cooled overnight as to when the heating turned on in the morning, it was a useless thermostat, at least for my home, I can see why wiring did not go into living room, the living room has an open fire, The only option is to have multi-thermostats able to turn on the boiler, which I now have.

But we all seem to be looking for a one system to suit all, and although Wiser may be flexable enough to do that, it's expensive, and there are home where one thermostat is enough. This

thermostat would have worked well in my house, it uses a mark/space ratio to stop over shooting, but completely useless when used with a modulating boiler.

 

[Harry Bloomfield]

But we all seem to be looking for a one system to suit all, and although Wiser may be flexable enough to do that, it's expensive, and there are home where one thermostat is enough. This

thermostat would have worked well in my house, it uses a mark/space ratio to stop over shooting, but completely useless when used with a modulating boiler.

On/off is not the very best way to control a heating system. Better to sense an actual temperature, so that the boiler's output can more precisely match the demand for heat.

 

[ebee]

Please see the PS I added to my

My understanding, from a Heating Engineer is that with TRVs a Room Stat is still required and is used as a "High Limit Stat".

Edited a PS - at least that positions as was explained to me a few years back anyhow.

(the part in bold italics')

 

[ericmark]

On/off is not the very best way to control a heating system. Better to sense an actual temperature, so that the boiler's output can more precisely match the demand for heat.

I did say my boiler does not modulate. So on/off only option for me.

But I looked at mother's gas boiler, and it did not modulate that low, around 12 kW, max output 35 kW, why anyone thought it needed a boiler that big I don't know? Today we see boilers which can modulate down to 6 kW, even that's high for a small house, but agree, all controls need to be analogue where possible. So the whole idea of two zone valves which are either open or closed is flawed, maybe 9 would work, as likely one always open, but EPH is the only OpenTherm thermostat I have found which can be set master and slaves to work multi zone valves.

So in the main, the TRV is the only option for most homes.

 

[Harry Bloomfield]

I did say my boiler does not modulate. So on/off only option for me.

I didn't suggest yours could..

But I looked at mother's gas boiler, and it did not modulate that low, around 12 kW, max output 35 kW, why anyone thought it needed a boiler that big I don't know? Today we see boilers which can modulate down to 6 kW, even that's high for a small house, but agree, all controls need to be analogue where possible. So the whole idea of two zone valves which are either open or closed is flawed, maybe 9 would work, as likely one always open, but EPH is the only OpenTherm thermostat I have found which can be set master and slaves to work multi zone valves.

Probably, most boilers installed, are bigger than needed. My demand seems to be around 6Kw, once settled, when it's cold, but I have an 18Kw. Luckily, it can modulate down to around 5Kw.

 

[SUNRAY]

The room I am in now has 3 radiators.

So you think that if I want to change the temperature it is not better to only have to adjust one wall stat than it is 3 TRVs.

OK.

In a system there has to be some form of thermal control, in a conventional system of rads and balanced lockshields that'll be a space stat or two and room by room the temp will be reliant on the balancing action.
With 'all dumb' TRV's the Time clock calls for heat which the boiler provides and when all TRVs are satisfied a sensor on the return pipe stops the boiler, this is far too often incorrectly left to the boiler sensors (not so much these days). IE; the boiler overheat stat operates. – A poor system as the boiler may be constantly going through a heating and long cooling cycle and not be available when a TRV opens. Adding a room stat is complex as the room monitored could be the first to reach TRV set point so one has to work out what temp to set the stat to – yada yada yada.

With a 'zoned' system where each zone has a space stat and motorised valve, (Imagine a block of flats with a communal heating system).

With a 'full intelligent TRV' system one is effectively creating a series of zones and each can call for the boiler to provide heat and can be used in isolation.

However one now has to look at the situation where there are multiple heat sources in a space; if that's a radiator and some other such as a log burner or blacksmiths forge then it's fairly easy as the space stat will be satisfied and stop heating the rad when the second heat source excedes the stat temp. Multiple heat sources on the same system is a different thing, consider a large open plan office space with East and West facing windows, (a situation I'm extremely familiar with) in the morning there will be a significant temperature gradient where the solar energy is warming the East windows but not the West and in the afternoon the opposite is true. the requirement becomes a minimum of 2 zones with independant thermal controls (and silly as it sounds the big possibility of requiring heating at one end and chilling the other)

So I've wandered a tiny bit from DIY territory but returning to a system with multiple rads in a room there are several options if one wishes to adjust the temp on an ad hoc basis, the three most obvious to me as I sit at the keyboard:
Use a motorised valve and space stat to create a zone for the multiple rads.
Use intelligent TRVs which can be paired so they act as master/slave to control the others.
Use a single TRV (dumb or intelligent) as the zone valve. Afterall said and done it is only a metal thing installed by a wetpants.

 

[ericmark]

Probably, most boilers installed, are bigger than needed. My demand seems to be around 6Kw, once settled, when it's cold, but I have an 18Kw. Luckily, it can modulate down to around 5Kw.

Yes, that does seem to be a major problem. But the other is the fitting of on/off zone valves, why would anyone in their right mind fit on/off zone valves with a modulating boiler? OK exceptions, like this house with a granny flat, where one wants to turn off whole flat for an extended time. But I can't think of any home where up-stairs rooms are never used during the day.

We have a craft room, and an office upstairs, last house kids did their homework in the bedrooms, and the list goes on, in nearly every home, unless open plan, we have rooms downstairs hardly ever used, or rooms up-stairs used during the day, so the only real option is to select room by room areas heated, which in turn means control by TRV heads. Which since work as analogue controls, also better control the boiler to allow more latent heat to be gained.

There is a reason to turn heating completely off, when one leaves the house for example, and geo-fencing will do that for you. But it is the turning back on which is the problem. Living room radiators are around 2 kW each so 4 kW in all, it does not matter how big the boiler is, or how fast it can heat the water, from 16°C to 20°C will take around an hour, so it needs to start the heating even in a built-up area in Wales at least 20 miles from home, in England 30 miles from home, and in the country 40 miles from home. But that would only work if going over 20 miles from home to start with. My geo-fencing waited for me to be about to step through the door before turning back on, basic when your phone connects to local cell.

Switch it on manually, and it will turn off again as you're not home. So unless you can set the distance, geo-fencing is next to useless. My thermostat has a built in PIR and it will override the geo-fencing if it detects movement in the house, but darn thing turned heating off when EE cell site damaged in high winds. My geo-fencing has been turned off ever since.

The TRV head is held in place with a 32 mm thread, so very easy to swap and change, and the home can be adapted when a bedroom becomes an office, or dinning room a bedroom, very quickly, nearly as easy as swapping bulbs, one would hardly base an energy rating for a home on what bulbs are being used. Ups, they do don't they, even when so easy to swap them.

 

[ericmark]

Thank you, @SUNRAY very well put, the problem is we have intelligent TRV heads able to work out how long it takes to heat a room, and turn the heating on at the correct point to get the room heated in time, including firing the boiler, then we have a series of other TRV heads which slowly get dumber and dumber until they only control the room to within a couple of degrees, and people want to regard them all as being the same.

 

[SUNRAY]

Thank you, @SUNRAY very well put, the problem is we have intelligent TRV heads able to work out how long it takes to heat a room, and turn the heating on at the correct point to get the room heated in time, including firing the boiler, then we have a series of other TRV heads which slowly get dumber and dumber until they only control the room to within a couple of degrees, and people want to regard them all as being the same.

An issue I have is most of my 'recent' heating experience is commercial where the heating pumps may easily be a number of KW (up to 75KW) and motorised valves are often on 4" pipes (up to 12") and boilers are measured in tens or hundreds of KW.
Effectively the thought of the wireless TRV you refer to is a big no-no in such systems so my comments are frequently based on 3rd hand info and compared with my commercial experiences (hence the east-west office reference and block of flats). I just have 2 TRVs and both are dumb in bathroom and downstairs WC. However I keep hearing from others about the issues their domestic automation causes (one recently where a battery went flat in a paired temp sensor and the system stayed calling for heat which overheated the secondary hot water cylinder within the combi boiler system. I feel happy with KISS I'm afraid.

 

[JohnW2]

However I keep hearing from others about the issues their domestic automation causes (one recently where a battery went flat in a paired temp sensor and the system stayed calling for heat which overheated the secondary hot water cylinder within the combi boiler system. I feel happy with KISS I'm afraid.

I'm not sure that either of us need to be "afraid" about this, but I am largely with you on this one.

There is a lot of very clever and potentially valuable technology around these days, but my personal inclination is to only make use of it when it really does fulfill a true 'need' (and/or provide a useful net benefit), rather than just "because it is possible/available". Apart from anything else, 'dumb' things are usually far less likely to 'go wrong' that the 'clever'/complex alternatives, thereby diminishing 'net benefit'

 

[plugwash]

why anyone thought it needed a boiler that big I don't know?

The main reason for wanting high power output on a combi is to allow running a bath in a reasonable length of time.

 

[JohnW2]

The main reason for wanting high power output on a combi is to allow running a bath in a reasonable length of time.

Indeed - or even to provide hot enough water at a sensible flow rate from taps - the energy required for adequate instantaneous water heating (at reasonable flow rates) is usually much greater than that need for space heating.

 

[ericmark]

Yes, very aware of problem with discharged batteries. One reason for going with Nest to start with, the 12 volt DC comes from the hub, so the battery in the thermostat is only to keep it going with a power outage, and the use of two thermostats, removes the problem should either fail.

Also, aware of limited battery size, the 6.4 kWh are allowed to drop to 10% so only have 0.64 kWh by the end of the day, which will not keep boiler and refrigeration units running for long, and the TRV head which is linked to boiler will lose the socket adaptor required to relay the signal to the hub.

The eQ-3 TRV heads tell me they will fail open with a discharged battery, and the others tell me the battery state on this PC.

I do look at the one pipes heating system used where I work, total manual control, someone decides how much steam to allow from the boiler through the carriages, and the waste produces a nice ambiance around the carriages with the Santa specials. I know a few boilers did use condensers so could reuse the H2O, but they were mainly in South Africa so it does lay a question, if one pipe has no return, what is the one pipe system I hear plumbers refer to?

Since Brexit the cost of electronic TRV heads has gone up, but at £15 each when I got the eQ-3 heads, why would anyone be still using mechanical heads? Yes I see the KISS, but main point with the electronic heads is they exercise the TRV pin, so the whole unit lasts a lot longer, but does need a pair of batteries every year or two.

I would like to replace the bluetooth TRV heads, so we can both control the temperatures of rooms with our phones, I look at aqara W600 in Insights DIYnot and at £50 may as well pay a little extra and get Drayton Wiser. Kasa and £30 look nearly the same as Aqara, but £30 is still expensive even if half the price of Drayton Wiser, MOES down to £22.29, and uses ZigBee which I already have.

But Wiser also Zigbee, and it did not use same hub as rest of my Zigbee stuff. But at £22.29 only 10 times the price of mechanical from Temu (£2.99) or Drayton £12.29 but this which one is the problem

the Kasa links to internet, and the Eqiva is manual same as the Terrier

but with MOES undercutting them price wise and with internet connected I would think the days of the non-internet TRV heads is numbered.

 

[Harry Bloomfield]

However I keep hearing from others about the issues their domestic automation causes (one recently where a battery went flat in a paired temp sensor and the system stayed calling for heat which overheated the secondary hot water cylinder within the combi boiler system. I feel happy with KISS I'm afraid.

I am somewhere in the middle, on this. I do like my fancy tech, but the tech has be reliable, fail-safe/good, and offer a worthwhile advantage. I would want TRV's, which needed yet more batteries to be regularly replaced, or they stop working - one set of batteries, to keep my heating in operation, is enough. Note - my thermostat/time control unit, needs a set of AAA's to be replaced every couple of years.

 

[Harry Bloomfield]

Apart from anything else, 'dumb' things are usually far less likely to 'go wrong' that the 'clever'/complex alternatives, thereby diminishing 'net benefit'

That is the way I try to evaluate things!

Over the years, the most troublesome part of our heating system, has been the 3-port valve actuator. A basically simple device, but under tremendous strain, from a spring, wound up by a constantly powered, stalled clock type motor, to retain the valve open. Such a daft idea, I had it in mind to design something better, and more reliable, to operate the valve.

Then I found an updated version, called a MOMO actuator. Researching those, I found they used some fairly simple electronics, but only ran the motor, when a change of position was required, and didn't need a spring. The motor was simply powered, for the short time needed to change the position, then switched off, so a small power and waste heat saving too.

Thus, it offered several advantages, for a slight bit of extra complexity, but reliable electronic complexity. It has so far proven to be 100% reliable, compared to the older designed constantly needing a spare actuator to be kept available to fit.