Further to another thread, I've been looking into having my new boiler fitted with weather compensation controls.
I'm still waiting for the engineer's quote for this but am confident it's going to be very expensive. My question is, to which I'm unable to find an answer, is what sort of fuel savings is this likely to make? Although our gas bills in this old and poorly insulated property are sky-high, I'm sure it won't make economic sense to fit this gizmo unless it makes a reasonably substantial saving. All th blurb I can find is very cagey on this point.
(I'm going for a W-B 30CDi system boiler, and this is the weather compensation device:
Secondly, the engineer's pointed out that if I have this fitted, I need to be aware that the boiler will always prioritise HW over CH, so it can take quite some time for the CH to kick in if the HW is sold. (I think this is due the tio the diverter valve it needs? not sure). How much of a real problem is this?; but anyway I thought that was how all/most systems operate?
I doubt it'll make much difference, heat loss is heat loss. I can't make out from the .pdf you linked to if it (or the boiler) has connections for tank and room stats, it wibbles about running the DHW pump so many times/hour Why does it need to do that? If there is a tank stat that will be telling the system if the DHW is hot or not, does it need to run the pump to extract heat (and waste it...) from the cylinder to know if the DHW is still hot?
Personally well a insulated tank with tank stat and programable room stat with some TRVs will give a pretty effcient system. I doubt adding weather compenstation would add very much saving.
Upping the insulation and/or draft proofing will be far better so you don't lose the heat you have put into the place.
If the boiler is designed for this, the only additional expense is the outside sensor and wiring. Make sure it goes in a shaded north facing position.
I have a Viessmann with weather compensation. Sadly can't give any real figures over the old system as the gas price went up so much round about the time I fitted it. Suppose I could look at actual gas usage if I could be bothered. ;-)
Not noticed it with mine - but then the old system was designed for hot water priority too.
I would say setting up the software for weather compensation is pretty complicated and needed several goes to get right. That would be expensive if paying someone to do it.
Indeed. Look, in an older property, there are usually far more effective things to do first.
All a very excellent control system can do is to minimise *overheating*.
Basically that means getting a more even heat, and especially at floor level - UFH can run a room a couple of degrees cooler and it still feels as warm.and also with poorly insulated walls, the 'rad' is well away from the walls..making sure rooms don't overshoot, by turning down the boiler BEFORE the rooms are quite warm..that's very useful if you have a lot of masonry and want to run on a timer,
BUT if my experience is anything to go by, all that means is that maybe you get to run a couple of degrees colder overall - so say 18C instead of 20C. Since the majority of the heat is needed when its down around zero outside, that, at best, means a gain of 10%.
Draughtproofing and proper insulation can net you a 300% gain.
not really. I have twin valves, so I can run HW and CH together.
OK the boiler isn't entirely up to that, so it tends to slog for an hour doing both, in very cold weather, but it does DO both together.
I think if you are looking for best return in reduced heating bills, you had best tell us what you have now, in terms of room sizes and construction, and what its costing you.
I've spent nearly a grand tanking up the oil for the winter. I hope it lasts. I am not running any central heating beyond an 800W 24x7 Aga, which is so far enough.
That will change soon. December January and February will empty a 2500 liter tank of oil.
And the insulation is good, but its a big house.
Insulation, insulation, insulation.
For a detached rural house, I think a target for heating should be about £1 per sq ft per annum.
If you are significantly above that, then time to think insulation.
My ownn rule of thumb for cost benefit in decsinding value for money is...
0/. learn to wear a jumper and thick socks..
1/. draught proof.
2/. loft/pipe insulate
3/. wall insulate
4/. double glaze
5/. floor insulate
6/. upgrade heating system
7/. go fancy on boilers and thermostats and zones.
Of course, if you have draughty rotten crumbling window frames, then you might do 4 as part of 1 at not much extra cost.
The basic thrust of your question is sound - as you have probably realised a modern condenser is already >90% efficient (seasonally adjusted) when driving the rads and providing hot water. In fact the boiler efficiency can push 96% efficiency in an ideal environment if you have a boiler that condenses all the time at its maximum rate (note some combis don't condense at all in HW mode).
Historically, weather compensation minimised overheating, kept more stable temperatures and improved comfort. These days it still does that, but it also allows the boiler to operate with greater condensing efficiency. So the energy savings come into two categories; firstly it pushes the boiler to operate closer to its theoretical maximum condensing efficiency by matching flow temperatures to what is actually required (so lower average return temperatures) at any given time, rather than defaulting to what would be required on really cold days, and secondly it slightly reduces the total energy input by eliminating the overshoots you would normally get.
Putting numbers to this is harder. However, basic arithmetic tells you the first number will be less than 6%. So in reality a guestimate of say half to two thirds of that may be realistic 3% - 4%. The second one is a harder call, since it will be more dependent on nature of the building. Historically, manufacturers made claims of reductions in fuel use of up to 15%. That is probably not a realistic realistic gain when measured against a modern boiler with a modern electronic prog stat, but perhaps half that is[1]. So if you assumed something like 10% overall from reclaiming the last easily accessible vestiges of efficiency from the boiler itself, and eliminating unnecessary heating you would be in the right ball park.
[1] You might get more in a particularly leaky building, since it will tend to have more heating / cooling cycles in a given time.
If the choice were money spent on extras or extra insulation, then the insulation would be first choice probably. Unless you were installing the stuff yourself, in which case the parts alone are not that expensive (although the need for the diversion kit does make it more expensive).
(as you are probably aware, I am in a similar boat myself. With some of the boilers I have been looking at, the weather compensation is needed to allow split temperature operation, and to interface to multiple zones etc - so it was a pre-requisite. Also in many cases the cost difference is marginal say £90 for the compensator, vs £50 for a more mundane control, so the capital recovery time would be minimum at my current gas usage).
That's only partly true - the FW100 acts as a programmer for the HW - and you can dictate at what times the HW is allowed to heat. Only during those times should it then take priority.
Its probably not an issue in reality if you chose your times and settings carefully. Also if you HW recovers fairly quickly, it will not amount to much interruption time wise.
These were tested quite a lot and found not suitable for domestic install .... to compensate they have to react to external weather sensor ... so as it's getting cold outside it fires up boiler earlier. OK .. so where do you put sensor ? ... on South side ,,, in which case sun could turn off heating too early, or North facing and it could remain in shade & cold blissfully turning heating on in the house.
You would need multiple sensors and averaging circuitry to give good compensation control on house.
OK in commercial install ... where you might put a sensor on each corner of a larger building ... but overkill for a house.
Far better to well insulate, design with multiple zones and have digital stats on each zone .... I have 14 zones, no on/off, just different temp at different times of the day ... result a very high level of comfort.
Purchased a new Combi Atmos boiler ,the weather compensation extra was an externally mounted (North Wall) temperature sensor. No extra programming, just connect in the appropriate terminals and all it does is to alter the water temperature according to external air temperature. In practice a very comfortable even temp in the house. The compensation control is done by the separate Danfoss timer/ thermostat and fires up the boiler earlier on cold mornings, it claims to self learn by monitoring the inside temp. I've no idea what difference it makes to energy consumption. Don
Sorry, slight inaccuracy re the Danfoss 5000 :-[ , I was mixing up with the AQ6000 in the previous house. Re the 5000, It does not claim to self learn, the user has to set the warm up time to match the building energy characteristics. Don
Certainly I realise that any savings I make on gas will be secondary to whatever I could make by improving the insulation to the property, which is something I'm doing when and where possible. Not easy though as it's all solid walls and dormer roofs here and it's major upheaval to do anything much. I just felt that if I was installing a new CH system to last X years I don't want to fit something I regret Y years down the line though.
I reckon it will be fairly costly to install the weather compensation system particularly as apparently it (well, my choice does) needs this built-in divertor valve which takes the place of existing valves in the airing cupboard (a long way from the boiler location, with stairs intervening), so there's a reasonable amount of carpet/floor lifting/aggro to install new pipework. Getting thoroughly cold and hacked off with my plumber's inability to provide a quote for fitting this kit any time soon, so have decided to forget it and stick with conventional controls!
Yup, same here. I concluded I am going to have to insulate the outside rather than the inside - it will be less hassle and mess and also will place the bulk of the thermal mass inside the insulated envelope.
Much depends on how much you are paying for gas, and also what you are replacing. On my place I estimate the payback period in gas savings alone will be about 4 years worst case, (annual has bill probably £1300
- £1500). The current setup is unlikely to push 70% efficiency - probably closet to 65%. So being conservative, that is £300/year in gas if I moved to something about 90% efficient.
Do you have to go for that boiler? Many of the others I have looked at can drive a conventional zone valve[1] near the cylinder - and hence re-use the existing flow and return pipework - it would not be much cheaper in terms of parts, but would save lots of extra pipework.
[1] Although to be fair some like the Vaillant need an interface box of tricks at about £60 to do so.
That is called feed-forward control. It anticipates the coming heat loss.
North side out of the sun.
Weather compensation works brilliantly with condensing boilers as it lowers the temperature of the boiler promoting efficiency. Especially one which is linked to the boilers control system and modulates the burner to suit the flow setpoint which is automatically raised and lowered by the outside temperature sensor. Some room temperature influence. This means that, say the flow temp is determined to be 50C by the outside sensor, and the temp inside the house climb up to the house setpoint of say 21C. The control system will drop the flow temperature even lower, to say, 45C, then, 40C and so on until setpoint is reached and then off. It keeps lowering the flow temp to keep a constant low temp injection of heat to maintain room setpoint. This really increases comfort levels and promotes gas efficiency.
Weather compensation on domestic boilers is cheap. The Avantaplus boilers are very good at this. The W-B 2-way valve converts the boiler into a "dual-temperature" boiler, as is the Avantaplus. The Avantaplus boilers are better and cheaper. Remeha (Dutch) who make the Avantaplus have just brought out Baxi.
Use an OpenTherm compatible controller with OpenTherm controlled boiler. Atmos, Avantaplus, Keston, etc have it. Well worth it as it seamlessly notches into your boiler control system. OpenTherm protocol is standard on the Continent. UK makers tend to ignore it. I don't know why.
I had a Vaillant weather compensating system fitted in October; too early to report on savings yet.
I fitted everything myself, except the boiler because I need the Gas Safe certificate to get a completion certificate from Building Control. Be warned that the average installer is clueless about electronic controls. The man who put the boiler in only does Vaillant installs, yet he'd never seen the Vaillant WC kit I installed.
Secondly, the Vaillant controls were plug & play type in the ease of installation. However the weather compensation seems to simply sets the flow temperature as a function of the outdoor temperature. This is OK when the building is at operating temperature. It is not OK when the building is warming up. I'll have to study the manual more. Vaillant seem to 'lock you in' to their control system; an industry standard 0-10V control options isn't offered.
Third, the system it replaced was self built from individual components with a motorized valve keeping PIR control of the one room with the temperature sensor. I've got to say, the old system was far more comfortable. The house feels colder, but I still have a couple of radiators to connect so it may be down to that.
The comfort obtained from a reduced-temperature continuous heating is a major advantage, rather than just savings.
They all do that to provide an increased temperature to the hot water cylinder. You'd otherwise need an additional mixing valve within the boiler (Viesmann offer such a boiler) . No great problem that I've noticed. The heating goes off but the house doesn't instantly get cold. The HW cylinder has never got totally cold. It may make a difference if you have a huge HW demand.
I had a Vaillant weather compensating system fitted in October; too early to report on savings yet.
I fitted everything myself, except the boiler because I need the Gas Safe certificate to get a completion certificate from Building Control. Be warned that the average installer is clueless about electronic controls. The man who put the boiler in only does Vaillant installs, yet he'd never seen the Vaillant WC kit I installed.
They tend to have a boost which is on full, or above what the outside temp dictates and then when up to temp it will fall back to weather compensator control.
That is why OpenTherm control protocol is better. You can use any maker that complies with OpenTherm and it works on the boilers control system. The Avantplus is OpenTherm as is Keston and Atmos and few others. They tend to be Continental makes. Vaillant is German but do not offer OpenThem in the UK.
On my system (an ATAG boiler) the weather compensation links the boiler flow termperature to the outside temperature. the colder it is outside, the hotter it makes the radiators. You can choose one out of a family of curves and you also choose a 'ceiling' flow tempertaure beyond which the compensation will not raise it. You can see the curves on page 27 of the E series installation manual linked from here:
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ATAG also does something clever with the data from the room stats. it knows not only whether the room is up to temperature or not, but how far below temp it is. I then adjusts the "bursts" of heat so it comes up to temp and stop rather than overshooting. it seems to work well.
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