Combi boiler with Drayton LP20RF & DIGISTAT+RF - upgrading to programmable or smart thermostat

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/82142450#Comment_82142450

You don't have to add Smart TRVs - that is entirely optional. You'd only fit these if you wanted individual control of rads, which you might, but don't need.

The EMS system will be more efficient than a conventional Smart programmer due to the way it communicates with, and controls, the boiler - much finer tuning.

In short, a non-compatible controller will have the required temps and timings programmed into it as you'd expect. The unit will sense the temp of the room it is in. If the unit 'calls for heat', then it'll tell the boiler to come on and provide CH. The rads will heat up, so will the house, and when the room temp reaches that called for by the unit, the unit will tell the boiler to turn off. The rads cool, the room temp drops, and the unit tells the boiler to come on again. Ie, it's a basic on/off system. (Some might work better than this, but that's the gist.)

Drawbacks of a non-fully-compatible Smart programmer are; the boiler doesn't know how close to the required temp it's getting, so provides CH at the boiler-set temp until then. So, the boiler works to provide this water temp until the Prog unit tells it to go off. That's a 'hot' boiler, with a hot return water temp, and that makes it less efficient (the cooler a modern boiler runs, the better.) The room temp achieved is also more crude - the boiler is turned on and off typically between a half and one degree temp swing (hysteresis).

So, what does a proper connection-protocol controller - like EMS - do? It doesn't just say to the boiler 'go on' and 'go off', but it can control how 'hot' the boiler runs. So, as the house temp is called for, the controller works out how far from the required temp the house is, and turns up the boiler accordingly. If the house is cold, the boiler will be asked to come on at full. If the house temp is only a couple of degrees below the required temp, the boiler will likely be told to come on more gently. (That's in basic terms. But the idea is to have the boiler run as cool as it can get away with.)

Then, as the required temp is approached, the controller tells the boiler to start turning down the flame - like adjusting a hob to reduce a 'boil' to a 'simmer' - so that the required temp is arrived at smoothly, not 'full on', and it'll then attempt to keep the boiler running gently, providing just enough output to maintain that requirement. So, there are far fewer temp swings, far fewer boiler ons and offs, and the boiler is always kept as cool as it can - just enough to provide the heat. That means less boiler wear, a more even house temp, and a cooler boiler = more efficient. (A cool boiler extracts more heat from the flame, as it'll 'condense' better.)

Worth it? Little question.

WIAWSNB

As for Smart TRVs, how many bedrooms do you heat? And how do you currently do this (ie, turn it on and off)?

I have only one Smart TRV fitted, and that's in the main bedroom. If I want the bedroom heated for a half-hour before retiring, and again a half-hour before get-up - and I do - what would this require? Yup, a note of the time, and a sprint (creaky-knee'd) up t'stairs before bed, then back downstairs, and then remembering to turn it back off before sleep, and then pushing t'wife out of bed before get-up time to ditto.

Instead, it's all programmed, and it does this automatically.

I hate battery-powered devices, too, but my Hive ones last a couple of years, and I think only take two AAs. In reality, little cost for the huge convenience and energy saving. And, since it is programmed via the App, there is no extra setting up.

grumpy_codger

I think you oversimplify how other smart thermostats work compared to EasyControl.

E.g. my former Honeywell has some learning capabilities and "knows how long it takes to get your home to the right temperature without the guesswork, saving you money on your energy bill." I.e. it adapts to the house+CH combination and predicts the time needed to reach the set temperature. You set the time when you need the desired temperature, not the time when CH switches ON. I don't know for sure, but given that it would be stupid not to predict the switch OFF time as well and to switch the heating off a little before the the set temperature is reached.

Regarding the bedroom, in my old house I never heated it, but the door was always open. The first floor was always 2C-3C hotter than the ground floor despite all ground floor TVRs were set on maximum and all first floor rads, except the bathroom, were barely warm.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/82142577#Comment_82142577

Indeed, and that's why I said it was in 'basic terms'.

'Smart' programmers are smart, in that they work things out to provide a better level of control - as you say, they can figure out when to turn on the boiler so the house achieves the required temp at the wished-for time. As the weather cools, it'll turn on the boiler earlier. On mild nights, later.

What a non-compliant-protocol programmer won't do, tho', is directly control the boiler to modulate it - turn it up and down - to have it run as cool and gentle as possible, in order to maximise efficiency.

Condensing boilers rely on the cooler return water to condense out the flue gases, and extract that heat from it. The cooler, the better.

You don't need any smart TRVs.

All programmers can be made to work. I'm simply suggesting that the EMS model will ultimately save you energy costs and, likely, boiler wear.

grumpy_codger

https://forums.moneysavingexpert.com/discussion/comment/82142614#Comment_82142614

Thanks. So, is my understanding correct that modulation can make the water temperature lower if needed thus making condensing more efficient?

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/82142846#Comment_82142846

Yes.

Modern boilers like yours will modulate in any case - the burner will be controlled up and down to suit the demand, which is the temp set on the boiler display. But that's an internal control - instead of heating up at full blast and then going 'click' off when the water is hot, and then 'click' back on when it cools a bit, it'll heat up fast, but then back off the burner as the water approaches the required temp. It'll try and maintain the required temp by doing this, but that 'temperature' is still a high 'set' one. That's all internal, and independent of the external controls.

What the Smart Prog with correct protocol adds is that it'll adjust the actual water temp up and down to match the house's demand - the boiler's CH output temp is no longer 'set'. Once the house heats up to the required temp, then it just needs to be kept there. The Smart Prog will do this by telling the boiler to back off to a tickover, so the rads will be maintained at a cooler working temp, but steadily, and enough to hold the house at the called-for room temp. In effect, the external controls will override the internal ones to make the boiler actually turn down low, not to 'maintain' the water temp, but to let it run as cool as possible whilst still meeting the house demand.

I guess the most obvious indication of this will be that the rads will not go hot and then cold and then hot as the non-protocol controller tells it to meet the house demand, but will instead be held at the required 'warmth'.

Fewer on/offs, and a steady lower temp instead.

That's my understanding anyhoo.

FreeBear

https://forums.moneysavingexpert.com/discussion/comment/82142577#Comment_82142577

From data collected by my home automation system, I know my house heats up at a rate of 1°C per hour. Base temperature is set to 17°C (my nit time setback). Knowing that I want the house at 20°C at 09:00, from around 06:00, the target temperature is increased by 0.5°C increments every 30 minutes. Much of the time, the room temperature doesn't drop that much overnight, so the heating may not kick in until 08:00.

Another benefit from 0.5°C increments is that the boiler isn't running at full capacity, so sits in that sweet spot for good efficiency.

I've commented elsewher on the subject of TRVs - When a boiler modulates down by way of reducing the flow temperature, TRVs switching radiators off is likely to reduce the total amount of energy that can be dissipated. Should this total drop below the minimum that the boiler can produce, it will start to short cycle - Bad for efficiency and long term reliability.

I have manual TRVs on 7 of my radiators plus another 2 without - Just need single TRV to operate on one of the bigger radiators and the total heat load can drop below the ~3.2kW floor of my boiler. Not all boilers will go down to ~3.2kW. Some of the cheaper ones stop at 5kW or even 7kW - When your average house only need 6-7kW to heat, adding TRVs (smart or dumb) can easily result in the boiler constantly short cycling.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/82142994#Comment_82142994

I think there's a better way to explain myself. 😶

Your boiler, as it stands, has a CH temperature output control, yes? What do you have it set at? Ie, the CH flow temp from your boiler to your rads.

That is a 'set' temp, tho' you can adjust it.

For max boiler efficiency, you'd want that flow temp as low as possible so the 'return' is ditto - that cooler return is what extracts extra heat from the burner through better condensing.

For max boiler efficiency, you could (should) manually adjust that output as the ambient temps rise and fall - tweak it up for winter when it's needed, and down as spring arrives. You would be 'compensating for the weather' by doing this, but the actual flow temp is set each time to whatever you dialled it to.

Say it's 65oC - your boiler will fire up powerfully from cold to get up to that temp. As the rads heat up, and the return does the same, the boiler self-modulates to reduce the burner flame to just maintain that 65oC flow, but it's still 65oC, and the return will be commensurately hot too. So will your rads - when they are on, they'll be at 65oC (or 60, or whatever you've set the boiler flow to.) Always at that temp. The burner modulates up and down to keep that temp steady.

Ok, add a Smart controller with the correct comms protocol. This can adjust that actual output temp. Now, as the controller/room stat calls for heat, the boiler fires up to provide the required CH flow temp to get the rads - and room - heated up to the programmed temp, say a room temp of 20oC. But now, as that room temp is being reached, the Smart Prog tells the boiler to lower the CH flow output temp, and it monitors the room temp to get that flow just hot enough to maintain that temp. So, as your room approaches the required temp, the boiler's output temp, and therefore the rads' temps, are steadily tweaked down to land at the required room temp gently - and it's then held there by constant up and downs in the CH flow temp.

That means for most of the time, after the room temp has been achieved, the CH flow will be well below what it started at; the rads will be running steadily cooler to provide the right output to keep the room temp steady.

It in turn means that instead of the rads always being at 65oC when on, and then they go off, and then they come back on, it'll now run at a steady, say, 50oC, being tweaked up and down as needed. The boiler will run for longer periods at a time, but that means fewer on/offs, so less wear on the gas valve and ignition. And the cooler running will mean less stress on the components. As well as greater efficiency.

In short, I think it would be a wasted opportunity to not go 'correct' protocol. From what I read, savings of around 10% are achieved, so it would pay for itself in - what - a couple of years? As well as less wear on your boiler.

And it looks like a nice unit.