What Is Weather Compensation?

[ReganAndCarter]

It looks like I will be funding a new combi for my daughter, and would like to get her a Broag like mine.

I have heard that these boilers can have weather compensation, but can't find an explanation of what this is, and its advantages.

Can anyone explain in layman's terms what it does?

Many thanks.

 

[kevplumb]

in basic terms it's an outside thermostat

tells the boiler what the temp is outside and compares it to the temp inside

then adjusts the load accordingly

i shall now wait for the thechnophobes to start shouting

 

[ColinJac]

in basic terms it's an outside thermostat

tells the boiler what the temp is outside and compares it to the temp inside

then adjusts the load accordingly

i shall now wait for the thechnophobes to start shouting

You are right, we will shout. It is not a thermostat, which is a thermally operated switch, switching on a predefined and user set temperature setpoint. A weather compensator uses a temperature sensor and always knows what the outside temperature is.

That I do know.

 

[ColinJac]

I did a search and it is here. It is a feed-forward controller anticipating the coming temperature drop or rise in the building, that ensures that the return temperature is as low as possible ensuring high condensing efficiency. It puts the radiator output temperature roughly in line with the heat demands of the building. I saves gas and makes the building more comfortable.

That is about it.

http://www.diynot.com/forums/viewtopic.php?t=120774

If it is available it is well worth getting then. They are standard in commercial installations and have been for over 50 years.

 

[kevplumb]

I did a search and it is here. It is a feed-forward controller

oh yeah laymans terms

 

[ChrisR]

There's a lot more to it than that.
"Weather Compensation" is an old name, which marketers have to use because it's become accepted as a "good thing". The simplest implementation of a weather compensated house control system is pretty hopeless, not desirable at all.
Strictly speaking you don't need to know the outside temperature to control your comfort any more than you need to know the angle of inclination of the road to control a car's speed. You need a speedo and a brain.
Boiler control systems come with a number of control elements, some of which an installer can choose from, and the outside temperature is usually in there. It's partly for historical or marketing reasons I'm sure, because starting from scratch with current techniques, a Control Engineer wouldn't need the outside temperature to make an optimised system. A good room sensor which the system can use to measure how the house responds, as it controls things, is just one essential element.

SO, if you want the current most efficient systems, you have a package. How much you actually save, is quoted as 2% upwards, but it depends exactly what you're comparing. Objectively derived figures from scientfic methods are very thin on the ground. Beware hobby-horse plumbers flogging you a glossy brochure promising the moon!

There is more to install, and quite quite a lot more to get right, where guesses are made about configuration. Then there's a big problem in my experience, of the user not understanding ( and mis-remembering ) what's going on with their heating system because it can seem to be doing the wrong thing sometimes. That means installers get called back because the user feels out of control. Sometimes of course it will be doing the wrong thing, and some expect perfection.
Quite often I've had to disable "clever" features, which a customer had paid (often over the odds) for, not long before.

For my own purposes I'd like the most sophisticated system, and would still moan about its shortcomings.
For my mother, I'd be very selective, and would be severely hampered by the boiler manufacturers' lack of detail about what they're selling, which isn't by any means optimal yet.

So is "weather comp" worth it? It depends.
Beware of short answers!

 

[ColinJac]

Strictly speaking you don't need to know the outside temperature to control your comfort any more than you need to know the angle of inclination of the road to control a car's speed.

I have dealt with them in commercial terms in some form or other for many years. Years before domestic boilers adopted them. Weather compensators anticipate the coming heat loss and start to heat up a building very slightly to prevent a cold spot. That is feed forward control. It does the reverse as well. This prevents having the heating on too high to catch up after the building has cooled using normal "feed back" control from the room temperature sensors or thermostats.

In your road analogy. Go to trains. The tilting trains had feedback control and jilted "after" running into a curve. The train would sense the curve and tilt and then go too far and pull back and forth a few times. That is "feed back" control. They now have "feed forward" control using sensors in the track telling the train a curve is ahead. The train tilts accordingly, nice and smooth and no one gets sick and the train runs around the curve faster and smoother.

Weather compensators tell the heating system that the temperature is falling outside, yet the temperature inside may be OK. It anticipates the heat loss of the building and adjusts to suit. The clever units "learn" the heat up times of the building, so there is no temperature overshoot or undershoot.

A decent weather compensator will have a "learning" function (not user adjustable) and room temperature trimming. I believe many domestic boilers have this. I saw a Glow Worm combi with this.

A good room sensor which the system can use to measure how the house responds, as it controls things, is just one essential element.

A good room sensor by itself cannot "measure how the house responds". The compensator needs two points of reference. The others is the outside temperature.

For my mother, I'd be very selective,

For my mother I put in an on-off switch which turned the heating on and off with the temperature set and she does not touch it. It is on 24 hours and she turns off the heating when going to bed.

So is "weather comp" worth it? It depends.
Beware of short answers!

It is worth it from what I have read. It keeps the return temperature as low as possible using less gas. It appears a perfect match for condensing boilers if the controls fully modulate to the dictates of the weather compensator and inside room sensor.

It can be setup and left with the user using simple controls like thermostat sensors with knobs on them. Simple switches on the wall (a light switch) to override the timers. The user side on most heating systems is too complicated.

 

[D_Hailsham]

"Weather Compensation" is an old name

The Yanks name for it is "outdoor reset"! They call the standard thermostat "bang bang"; presumably "bang", boiler on, "bang", boiler off??

 

[ChrisR]

A good room sensor by itself cannot "measure how the house responds". The compensator needs two points of reference. The others is the outside temperature.

Of course it can.
The system knows the time. If eg it's cooler in the house than it was yesterday just before the heating comes on, it knows it's going to need more power to heat up by the set time. The outside temperature is a derivable paramater not a principal one.
Remember the boiler's also already measuring the return temperature, or should be, too.
Outside temp also doesn't take account of sun wind or rain, opening windows, people in the house, the oven etc etc etc. Outside temp control is an open loop control which introduces all sorts of errors which have to be fudged over, or corrected.
If your train lurched the loop parameters were wrong. Loop gain, damping factor, loop delay and so on.
In a house, the temperature sensor is way more sensitive than a human - it knows there's a change well before you do.
A normal PID control system can predict very well how a system will respond - "learning" algorithms have been around a long time - well before I was writing my own in the 70's.
Feed forward control can't avoid producing an over/undershoot error, depending on the inertia in the system.

The grail isn't even internal room temperature, it's comfort. Some people expect the inside temp be lower in the winter and want it that way because they get used to it. Other houses have so many cold spots that the average temp has to be higher for sensitive people. Comfort can be made up from air temperature and radiation from a hot radiator.
This and more is all stuff which means the occupier is more likely to feel out of control with a "clever" system.

System needs a decent room sensor and decent software, that's all, with a knob on the front you can turn in stages, marked "For Simple People" at one end and "For SmartAsses" at the other!

Commercial requirements, btw, are different - for reasons I won't go into here.

When weather compensators came in, it was BEFORE the boss of ICL stated that there would never be a need for a computer in a house. Times have changed.

 

[Agile]

To the OP, Wc is able to improve comfort and save money but ONLY if the user will leave it alone to do its job.

About 30% of the WC installations members of this forum have installed have had to be disabled or severely curtailed because the user could not understand how they worked and thought that if the radiator was not too hot to touch then it was not working properly.

There is a lot of ignorance in the world.

And as well a lot of resistance to modern developments. I would not want to fit WC or even a programmable thermostat to someone who did not even have email!

We used to say if the time display on the VCR was flashing then dont bother about any clever controls.

Tony

 

[mehran]

beware of long answers!!

in its simplest form an outside sensor turns up the radiator temperature as it gets colder outside. then turn down the rad temp as it get warmer out side again.

the cooler the rads can run the more gas/money you can save over having them too hot/

even if it saves 1% off your gas bill it will save you the tiny cost of buying an outside sensor over the boilers life time.

the main problem is no one like been told what to do or how to use something. there is also more then one way to run/control a heating system.

 

[Agile]

When the landlord pays for the heating, tenants have evolved a very simple weather compensation!

If it gets too hot then just open the windows. Saves switching off the heating.

Tony

 

[Boilerman2]

To get back to the point Remeha make a fantastic opentherm control which simply wires to the Comms Bus on the boiler it has a option for an external sensor - BUT don't fit this on a South facing wall due to solar gain which is undesireable I didn't bother with the outside sensor so my compesator operates on room temperature only as the room temperature set point aproaches the gas rate of the boiler is modulated down to reduce flow temeprature and keep the boiler condensing the rsult is extremely stable room temperature the unit also acts as a optimiser to delay start up until the last moment to achieve room set point at occupancy time

 

[ColinJac]

A good room sensor by itself cannot "measure how the house responds". The compensator needs two points of reference. The others is the outside temperature.

Of course it can.
The system knows the time. If eg it's cooler in the house than it was yesterday just before the heating comes on, it knows it's going to need more power to heat up by the set time.

You are confusing a weather compensator with stop-start optimisation.

The outside temperature is a derivable paramater not a principal one.

The outside temperature is not derived from anything as it is always there.

Outside temp also doesn't take account of sun wind or rain, opening windows, people in the house, the oven etc etc etc. Outside temp control is an open loop control which introduces all sorts of errors which have to be fudged over, or corrected.

An outside temperature controller can have room temperature fine tuning. This is not a problem. Which is an open loop with a nested feedback loop. I have seen the outside sensor replaced by a room sensor, to good effect. The slope of the control has to be set to suit and usually tweaked after. (don't do this at home)

If your train lurched the loop parameters were wrong. Loop gain, damping factor, loop delay and so on.

It displayed the difficulties of feedback control. Which is control that reacts after an event has occurred. The feed forward control was much superior.

In a house, the temperature sensor is way more sensitive than a human - it knows there's a change well before you do.
A normal PID control system can predict very well how a system will respond - "learning" algorithms have been around a long time - well before I was writing my own in the 70's.

An ideal heating system would continually and instantaneously adjust its rate of heat delivery to match the heat loss of the building. The indoor air temperature would remain rock solid stable. There would be no difference in comfort regardless of outside conditions. Feedback control, PID or not, cannot do this.

Feedback control is reaction after an event. The event is it is getting cold in here. As I have explained feed forward control "anticipates the coming heat loss. There is such as thing in the USA as the "cold 70F". The are still in F. The room temperature maybe 70F, and people still feel cold. The building over cooled before the heating came on (feedback control). The heating came on but the fabric of the building is still absorbing the heat. Weather compensation avoids this (feed forward control). A good control system will finer tune the room temperature, but it will increase the room temp about 0.5C, when the outside temp is dropping to compensate for the heat being extracted from the builds fabric.

Outside reset was derived because of the cold 70F. Originally done with simple thermostats.

Feed forward control can't avoid producing an over/undershoot error, depending on the inertia in the system.

It can when combined with a nested feedback control.

Comfort can be made up from air temperature and radiation from a hot radiator.
This and more is all stuff which means the occupier is more likely to feel out of control with a "clever" system.

A clever system can only do so much if the house has cold drafts, poorly sized and positioned radiators and poor insulation.

Commercial requirements, btw, are different - for reasons I won't go into here.

They are in some cases, in others they are not, just being larger domestic systems.

In some they have weather compensated rads to give background heating only and an air system to top up the heat needed and the required fresh air. They generally operate as separate control systems.

When weather compensators came in, it was BEFORE the boss of ICL stated that there would never be a need for a computer in a house. Times have changed.

I don't know what you are on about here. One thing weather compensation gives, as some have noted on this thread, is that is lowers the return temperature on condensing boilers, saving gas, making the system cheaper to run. A perfect match. It also keeps radiator temperatures lower for the vast majority of run time.

 

[ColinJac]

To get back to the point Remeha make a fantastic opentherm control which simply wires to the Comms Bus on the boiler it has a option for an external sensor - BUT don't fit this on a South facing wall due to solar gain which is undesireable I didn't bother with the outside sensor so my compesator operates on room temperature only as the room temperature set point aproaches the gas rate of the boiler is modulated down to reduce flow temeprature and keep the boiler condensing the rsult is extremely stable room temperature the unit also acts as a optimiser to delay start up until the last moment to achieve room set point at occupancy time

I hear a lot of good about these boilers. With the outside sensor you do not have compensation. You still have feedback control which modulates the burners flames up and down.