Worth of OpenTherm and/or Smart TRVs with 2 zone heating

[karlbbb]

Hi all,

Looking to get a bit of a sanity check here. I have a new-ish (2017) build house, which is an Ideal Logic Combi C35 boiler, with 2-zone heating (upstairs and downstairs split). The wiring centre and zone valves live in the airing cupboard upstairs, mid-way through the house from the boiler. The two thermostats are wired (but battery powered) ESi ESRTP4 programmable units. Upstairs thermostat in the main bedroom, which is (unfortunately) south-facing and has no TRV, and downstairs thermostat at the bottom of the stairs, again with a rad having no TRV. It seems normal wisdom that the room with thermostat should have no TRV, yes?

Now, looking at future upgrades, it seems I should be looking in two areas - OpenTherm and Smart TRVs.

OpenTherm
This one is easy - modulate the heating flow temperature to avoid cycling. The hard part seems to be that our 2-zone heating complicates matters somewhat, with seldom few "smart" systems being able to run 2 heating zones and OpenTherm. I found EPH thermostats that claim they can, a few internet posts saying the Drayton Wiser system maybe can, and Ideal's own Halo system certainly seems like it can. The Ideal system looks like the easiest fit, as the boiler control can be fitted right next to it and so a very short, invisible, and easy fit run for the OpenTherm cabling as the zone control unit would go upstairs in the airing cupboard where the current wiring centre and motorised zone valves are. Other systems look like we'd need to run extra cables over cupboards and through walls as their control units effectively replace the wiring centre upstairs - this could be messy with the layout of the house. This aside, how much could I really expect to save with OpenTherm?

Smart TRVs
Again, very easy concept to understand. What I can't see is exactly how much energy saving I'd get from switching our system over to smart TRVs. It seems their concept is one of ultimate and fine control. This is great, but when I have 8 rads currently with TRVs, and packs of 3 heads cost £200, that cost is rising very quickly, even before getting the requisite receivers etc. This also doesn't take into account that I'm struggling to find a hard "yes" to systems that could control 2 zone valves on top of smart TRVs. So, it would seem to go to smart TRVs, I'd somehow have to bypass the two zone valves or somehow fudge them to actuate together so the house was acting like a traditional single-channel system. This seems sub-optimal.

On the surface, it seems I could make a bit of a saving (though how much?) if we got some kind of OpenTherm system in, but using Ideal's own Halo as an example, I'd be looking at about £350 or so, and that's before getting a GasSafe engineer to come and re-wire some bits - all of which I'd be happy to do myself, it's just the boiler cover has to come off to get to the electrical connections, so GasSafe it is. Looking at smart TRVs, it seems I'd be looking at a minimum of £600 before any required wiring or zone-valve fudging, again likely needing a GasSafe engineer to plumb into the OpenTherm connectors in the boiler controls.

I guess I'm just looking for any input from wisened members, or perhaps harder numbers as to what I could expect to save. It seems I have a ludicrously sized boiler for our house size (roughly 100m2), so I'm just looking to make the best of the current setup.


Thanks!

 

[Swwils]

Look into weather comp. C35 is likely a massively oversized boiler for size of your house.

 

[muggles]

Honeywell T6 can do two OpenTherm zones. You'll save a bit but the modulation on the Logic is very poor and its minimum output likely exceeds your maximum heating requirements

 

[ericmark]

I have never had a home which could use OpenTherm, and although it claims to gain more latent heat by using it, not sure if enough to be worth while.

As to TRV in the room with wall thermostat I was told you don't fit a TRV in the room with the wall thermostat, but when I did it transformed my mothers heating. In the hall opening the front door the hall rapidly cooled, if I opened the lock shield valve so hall heated faster, then other rooms in the house got too cold, but once I had fitted the TRV setting it to 17ºC and wall thermostat to 19ºC the hall would recover fast, but slow up before it got to the point of switching off boiler, since the radiator TRV is lower than the wall thermostat found by experiment needed about 2ºC difference in the settings.

In mothers house I fitted 4 Energenie MiHome TRV heads, and they worked well, I was told they would work with Nest, but once the TRV heads were set up, they were spot on, no real need for Nest. On my mothers death and selling the house, new owners did not want the wifi TRV heads so swapped back to wax, now all the lock shield valves set, the old wax heads worked well, and the wifi heads were fitted to this house, but more rooms so I got a further 5 eQ-3 bluetooth heads at £15 each, so 9 programmable heads in this house, they did not work as well with the oil boiler being simply on/off no modulating.

However the main problem was the triple and earth cable from main house to flat where the boiler is had one core open circuit, so needed to find a way to control CH and DHW with just two cores, so went for Nest Gen 3 as claimed it worked with Energenie, well the Energenie app would work both the wall thermostat and TRV together, but the schedule temperature changes did not change the TRV and turning dial on Nest didn't either, plus seemed wrong way around, thought TRV should tell wall thermostat heat required, not the wall thermostat setting the TRV's, and a phone call to Energenie found Nest support was withdrawn when Google bought out Nest.

So I have 9 programmable TRV's not linked to the wall thermostat, I simply use the same schedule for wall thermostat and TRV in the hall. It has not worked very well, the main problem is the hall cools too slowly, I can with lock shield valve adjust how fast it heats up, but not how fast it cools down.

But the eQ-3 TRV's are if anything better than the Energenie, they have window open detect, so in the kitchen when we unload the shopping it auto turns of heating in kitchen for ½ hour while I unload shopping. The Terrier i30 is also stand alone, the bluetooth makes it easier to program and means when two radiators are in same room they can be linked, but not really required, unless two radiators in the same room.

The big question is when the lock shield valves are correctly set, with a modulating boiler, how much better are linked TRV heads to stand alone? I would say likely want one or two linked, but rest can be stand alone.

Nest USA do temperature sensors, I had hoped these would be released for the European version, having sensors in two rooms would transform my control, but it seems only way is to fit two thermostats in parallel, I use motorised valves as the flat as a whole is rarely used in Winter, but can't see the point of spiting the main house like that, as I have four upstairs rooms, two used as bedrooms, one a craft room and one an office, so times when I want to use the 4 rooms are not the same.

What I could do with is larger radiators, so I can set a sequence when arriving home first kitchen, then dinning room, then living room then finally bedrooms, but with a 20 kW oil boiler no point heating just kitchen to start with as radiator can't sink 20 kW.

But moving from our small open plan gas central heated home to this house with three floors and nearly twice the size oil fired I was surprised to see fuel bill drop. I expected to pay more. How it will work out now price has gone up I don't know.

The boiler is C Plan, so summer no thermostatic control of DHW just set it to ½ hour 3 times a week. It runs for around 20 minutes.

 

[karlbbb]

Thanks both.

Look into weather comp. C35 is likely a massively oversized boiler for size of your house.

Looking at the Ideal manual, it seems that adding in their weather comp sensor turns the flow temperature dial into a room temperature dial, and the boiler attempts to maintain the room temperature based only on the outdoor temperature, not using room stats, needing only an external timer. But surely if I kept in the current thermostats, it'd just knock off the heating once the rooms were up to temp? Seems a touch confusing.

Honeywell T6 can do two OpenTherm zones. You'll save a bit but the modulation on the Logic is very poor and its minimum output likely exceeds your maximum heating requirements

Thanks. The units look nice but would require me running a cable across the house to carry the OpenTherm signal, which I was hoping to avoid for both aesthetic and convenience purposes, hence looking at Ideal's own which sits next to the boiler.

With regards to size of the boiler, the spec sheet says minimum output is 7.1kW at 70C flow, and 7.5kW at 40C flow. Certainly seems very high for the size of house and how well insulated it seems to be - we're yet to drop below 19C in the house even with the cold nights we had last week. I suspect the home builder just got a huge job lot to cover the highest demand in whole estate as there are a number of 4 and 5-bed homes which are larger than ours.

Is it looking likely we should just do some "manual" OpenTherm and start at a lower flow temp and then raise it as we get deeper into winter if the house isn't get up to temp? We'll be setting the stats to 19C so expecting demand to still be very low even on the coldest of days.

 

[vulcancontinental]

Is the combi the only source of hot water? you mention you have an airing cupboard and automatically I assume there is a hot water cylinder in there rather than say a radiator. Am I incorrect in supposing there might be a hot water cylinder? It is certainly possible for the configurations to be that way.

ErP data suggests a 3% saving on space heating if you use a modulating thermostat (OpenTherm).
Weather compensation is a 2% saving but I believe the Ideal is one temperature WC which can be annoying when setting a comfort temperature with only an OFF setting rather than a setback temperature. delays in reheat times can be frustrating.

 

[karlbbb]

Is the combi the only source of hot water? you mention you have an airing cupboard and automatically I assume there is a hot water cylinder in there rather than say a radiator. Am I incorrect in supposing there might be a hot water cylinder? It is certainly possible for the configurations to be that way.

ErP data suggests a 3% saving on space heating if you use a modulating thermostat (OpenTherm).
Weather compensation is a 2% saving but I believe the Ideal is one temperature WC which can be annoying when setting a comfort temperature with only an OFF setting rather than a setback temperature. delays in reheat times can be frustrating.

Sorry, forgot to mention that. Yes, it's hot water from the boiler only. It has the "domestic pre-heat" option but we have that turned off, as it obviously only accounts for a small amount of water. I say airing cupboard as it's where a hot water tank would generally be (cupboard on the upstairs landing), and we're keeping towels in there. It does have the heating send/bypass/zone valves so it'll get a little heat in there when the heating is on, I suppose. I imagine we'd have to sacrifice the storage space for a hot water tank in the future should we get a heat pump system in.

Could you expand a little on "one temperature WC", please? Looking at the Ideal WC guide, page 7 explains the WC sensor being present operates as follows:

"The On and Off time control of central heating should be controlled by a separate timer.

During programmed On times the Central Heating Radiator Flow Temperature is controlled by the boiler relative to the Outside Temperature as shown in the diagram. The Room temperature can be adjusted using the Central Heating Temperature Control Knob on the boiler as follows. Essentially rotating the knob clockwise increases the room temperature and rotating the knob anti-clockwise decreases the room temperature.

The Room Temperature Setpoint in the associated graph is not directly related to the Actual Room Temperature but is the Nominal Room Temperature during a programmed CH period."

It also gives a graph of external temp to flow temp curves. It seems that for a "comfort temperature" of 20C, with an outdoor temp of 15C it's set a flow temp of 37C. The way it's described really seems that it expects only a timer device for CH periods, in which case it would always run and expect that the compensated flow rate would maintain the house at the requested temp. Surely that's far too simplistic, and we should keep a programmable stat around? So if the house gets up to temperature it'd still cycle the heating as needed. And if that's the case, is that what you refer to as the delay in reheat times - when the stat calls for heat again, the low flow temp would likely take a while to get the zones back up to set temperature?


The WC sensor kit is certainly the cheaper option at only £50 (plus getting an engineer to wire in), but if they provide the flow temp curves, I could probably achieve similar by keeping an eye on average outdoor temps, and use a flow temp a little higher than their curves?

 

[vulcancontinental]

Weather comp control is not when the heating is ON, that temperature is achieved by adjusting the climatic curve and it's a nominal 20 degrees insude. When the timer or room thermostat contacts are open the heating is OFF with single temp WC. House grows cold, heating comes back on at modulated flow temperatures and delays in achieving comfort can occur with swings in temperature.

Dual temp means in an 'OFF' period the boiler dos not necessarily stop working (although it will) the boiler simply recalculates a flow temperature to achieve a lower setback temperature (overnight or while the house is empty). By avoiding having to reheat the whole property this retains the thermal store of heat in the house and on restart the boiler has in essence only to raise the air temperature. Overall it is more fuel efficient in my experience.

 

[karlbbb]

Weather comp control is not when the heating is ON, that temperature is achieved by adjusting the climatic curve and it's a nominal 20 degrees insude. When the timer or room thermostat contacts are open the heating is OFF with single temp WC. House grows cold, heating comes back on at modulated flow temperatures and delays in achieving comfort can occur with swings in temperature.

Dual temp means in an 'OFF' period the boiler dos not necessarily stop working (although it will) the boiler simply recalculates a flow temperature to achieve a lower setback temperature (overnight or while the house is empty). By avoiding having to reheat the whole property this retains the thermal store of heat in the house and on restart the boiler has in essence only to raise the air temperature. Overall it is more fuel efficient in my experience.

Thanks, that makes more sense. So if I went for WC, I'd have to try and guess a happy medium "room temp" on the boiler that would try and negate the delay in reheating. I guess that would be the beauty of an OpenTherm system as it would negate the delay that WC would cause. So it would seem, due to the limitations of the Ideal boiler (ironic name, in this case, both in size and functionality), that OpenTherm would be the way to go.

That said, only looking at a 2-3% saving against an upfront cost of likely £300-400 doesn't really make sense against an top-end estimated gas bill of £900/year on the new 10p rate. Maybe I'd be better just experimenting with flow temp manually and find a temp as low as I can that still meets heating need in good time.

 

[vulcancontinental]

Thanks, that makes more sense. So if I went for WC, I'd have to try and guess a happy medium "room temp" on the boiler that would try and negate the delay in reheating. I guess that would be the beauty of an OpenTherm system as it would negate the delay that WC would cause. So it would seem, due to the limitations of the Ideal boiler (ironic name, in this case, both in size and functionality), that OpenTherm would be the way to go.

That said, only looking at a 2-3% saving against an upfront cost of likely £300-400 doesn't really make sense against an top-end estimated gas bill of £900/year on the new 10p rate. Maybe I'd be better just experimenting with flow temp manually and find a temp as low as I can that still meets heating need in good time.

Do not dismiss the comfort improvements of OpenTherm and weather compensation, they cannot be quantified in monetary terms. I personally have a system that incorporates both in a property type hideously difficult to heat but not on a basic Ideal boiler and I play with options.

I recommend doing what you suggest as a start, you'll be surprised how well it can work, it's how much patience you've got to be doing this all the time because new build housing will not have oversized radiators so you will need to monitor things as the weather changes.

 

[Swwils]

The WC sensor is a cheap thing to get and install, about £60 (or £3 if you just get a equivalent NTC). At least then you will have some modulated flow temp based on actual heat demand.

Unfortunately yes the ideal is very basic. It's possible your house will never see a heat demand above 7kw so you will always be cycling and never in steady state.

Load comp vs weather comp will be a debate until the end of time. I prefer weather comp but in some houses load comp (or both) very much make sense.

As mentioned above as soon as you have a modulated control in the picture the whole thing is a different way of heating the house, try to forget about TRVs and think more along the whole house heating envelope.

 

[karlbbb]

I assume some of the better units that can do OpenTherm can also get the local weather and effectively do both load comp and weather comp together, without needing the local sensor actually attached? I'd say the current local weather should be accurate to within a degree or two of the actual outside temperature...

Thanks again for all your inputs, I've learned quite a lot over the last day or two of looking into new control systems. I'd never have thought have a large boiler would be an impediment before now.

 

[vulcancontinental]

An independent test house used several brands of boiler to assess the efficiency losses through cycling. 12% if the boiler fired in 10 second bursts but 1.5% if the firing time of the boiler could be configured to exceed 3 minutes.

 

[Swwils]

I assume some of the better units that can do OpenTherm can also get the local weather and effectively do both load comp and weather comp together, without needing the local sensor actually attached? I'd say the current local weather should be accurate to within a degree or two of the actual outside temperature...

Thanks again for all your inputs, I've learned quite a lot over the last day or two of looking into new control systems. I'd never have thought have a large boiler would be an impediment before now.

Yes they can but generally the weather data is very granular and often quite far out. Local sensor is very much superior since it reflects the actual heat demand for the location in real time.

You've done your research and now probably better informed than 98% of plumbers.

 

[vulcancontinental]

Yes they can but generally the weather data is very granular and often quite far out. Local sensor is very much superior since it reflects the actual heat demand for the location in real time.

You've done your research and now probably better informed than 98% of plumbers.

Agreed though maybe 80%