Here's another update.
My gas bill for December: 166 Units without weather compensation
My gas bill for January: 170 Units, with weather compensation.
(1 unit = 100 cuft)
Am I disheartened? No, not at all. The last week of January was way below zero and the boiler ramped up accordingly. When spring eventually arrives that's when I expect to see significant savings.
Watch this space !!!!
Here's this months update. Units are 100's cuft
December 166 units (no weather compensation 5.21 units/day average)
January 170 units (1st month with weather compensation. 5.19 units/day average)
February 163 units (short month so 5.28 units/day average)
The first week or so of February was cold and the boiler ramped up, while the second half was unseasonably warm and the boiler throttled back accordingly. Roll on summer.
Interesting indeed. How does this compare to last year?
Can't really compare with last year as the house renovations were a long way from being completed. Having floorboards up, ceilings down and walls missing is not conducive to saving energy.
Thanks to Oakbank for starting this thread. I am not as familiar with weather compensation solutions as smart thermostats. In the UK at least they seem to be relatively rare/unknown/unpromoted.
However based on my knowledge and use of smart thermostats I thought it maybe helpful to detail how they relate to this issue.
The traditional boiler control method is/was a simple on/off control achieved by sending to the boiler a 'call for heat' signal. This causes the boiler to run at full power whilst the call for heat signal is present and then to fully turn off when it is not. This overall is a less efficient method than the newer approach which is referred to as modulated control. With modulated control the output of the boiler is varied depending on the demand and closeness to the desired heat level. Modulated control not only should achieve energy savings but help ensure a more stable temperature is achieved with less over and under shooting of the desired temperature.
It seems the weather compensation kit is causing a suitable boiler to operate in modulated mode even with a 'dumb' thermostat.
Since it is possible and arguably more common to achieve modulated control with a suitable smart thermostat this could be considered as an alternative way of achieving this and arguably has additional benefits.
In my case my boiler is located on a south facing wall with its exhaust also on that south facing wall. It would be harder to correctly fit a weather compensator since it would need shading from sunlight to avoid the temperature sensor reading being distorted. (You could fit a shield to prevent sunlight hitting it.)
A smart thermostat typically is able to obtain outdoor temperatures via an Internet service by looking up a local weather station and hence will not need to rely on your own outdoor sensor. This will therefore solve my problem.
A smart thermostat also adds the benefit of advanced scheduling and the ability to monitor the presence of occupants and therefore achieve additional energy savings. It can also link to a thermostat or even multiple thermostats and matching smart TRV valves and report to the boiler if any room needs heat. (If all rooms are reaching their desired temperature the boiler can then reduce its output.)
So whilst a weather compensator would and should be a definite improvement over the traditional call for heat method I would say a smart thermostat would be even better.
Note: There are two different but similar digital protocols which a smart thermostat can use to control a boiler to enable modulated control. There is eBUS and OpenTherm. OpenTherm was original developed by Honeywell and as its name suggests is now an open standard. eBUS is a proprietary standard - each manufacturer has their own flavour.
According to Tado a manufacturer of a smart thermostat and TRV system which supports both OpenTherm and eBUS they say eBUS is superior - mainly I believe in the area of fault monitoring of boilers.
Vaillant and Worcester Bosch only sell boilers in the UK with eBUS support.
Nest only has OpenTherm support.
Drayton Wiser only has OpenTherm support.
Most of Honeywells better smart products are US only but logically they also will only support OpenTherm.
As far as I can tell Hive and Netatmo do not support OpenTherm or eBUS.
As mentioned Tado supports both OpenTherm and eBUS - with the problem mentioned below for the newer Vaillant VR66 controller.
Due to local requirements in the Netherlands, both Vaillant and Worcester Bosch sell boilers fitted with eBUS to OpenTherm conversion modules _made by Vaillant or Worcester Bosch themselves_. However Vaillant at least will invalidate your warranty if you get and fit this genuine module in the UK.
Apparently Vaillant have also more recently changed/updated their eBUS protocol in the newer VR66 controller and not released the specs and Tado have not yet been able to reverse engineer this. The VR65 is supported by Tado.
There are some lesser known boiler brands which do have built-in OpenTherm support. See - https://myboiler.com/opentherm-capable-boilers/
The belief is that Vaillant and Worcester Bosch are using eBUS to mainly force customers in to buying their own matching compatible (semi) smart thermostats.
08-05-19, 17:32Oakbank"So whilst a weather compensator would and should be a definite improvement over the traditional call for heat method I would say a smart thermostat would be even better."Couldn't agree more. Thanks for your detailed explanation re. boiler controls. I acknowledge weather compensation is a 'half-way house' when it comes to boiler control and a smart thermostat offering modulating control based around a room temperature setpoint is the way forward. My boiler, a Logic Heat, is one of those listed as being OpenTherm capable. I just need to get the right smart thermostat and get it all to work.
Excellent post, thank you.
I assume that in all cases the modulation is gas valve mark-space rather than analogue burner modulation?
I don't know the answer to this. All I can say is they will vary the output of the boiler i.e. the amount of flame to match the required heat output. What method is involved I don't know. As someone who is an IT person rather than a boiler engineer I would have thought this would involve the gas valve being opened to varying levels to pass varying amounts of gas to the burner. The smart thermostat is merely sending commands to the boiler it would be the boiler then varying the output accordingly.
I would suggest you consider Tado as this is the most compatible solution and has the option for multiple thermostats i.e. zoning, and the option of smart TRV valves.
Note: Google owners of Nest have recently announced the discontinuation of the 'Works with Nest' API making the Nest less useful potentially. The v3 Nest will still support OpenTherm but not eBus and still does not offer matching smart TRV valves.
I have not listed Ecobee as a smart thermostat option incase anyone was wondering because their international support is pitiful.
I strongly suspect mark/space, I just can't see gas valves operating reliably in a progressive mode (if such valves even exist).
This means that there will always be some stepping of output (i.e. less integration of output) especially if the boiler is low capacity. The larger the heat exchanger capacity the more the steps will be smoothed.
I could be talking complete b*ll*x but seems to make engineering sense.
I suppose it all depends on how small the hysterisis is - too small and valve will operate too frequently, too large and the overshoot will be worse.
Hysteresis is how much it over or undershoots before it switches off or on.
So for example if you have a room stat with a hysteresis of for example one degree either way and you set it to 20 deg. it would switch the heating off when it reached 21 and on when it fell to 19.
The smaller the hysterisis the more frequently it will switch on and off and the more even the output temperature will be, but it will hammer the boiler if too frequent.
I'm guessing that the recommended setting will be as large as possible with an acceptable evenness of output temp.
I suspect there is a manufacturers recommended setting, but if you find it's either switching on and off too frequently, or the output temp is fluctuating too much (for example it's cooling down too much before it fires again, or getting too hot before it stops) you'd have to tweak it one way or the other.