Weather Compensation and Outdoor Temperatures

[D_Hailsham]

Weather compensation depends on a temperature sensor on the outside of the building. The recommended location is on the North or West wall of the house.
For the last few months I have monitored the outside temperature using a thermometer which measures inside and outside temperatures and stores the minimum and maximum since last reset.

The front of the house faces due North and the outdoor sensor is located on an upstairs windowsill in the middle of the house.

I have recorded the Max and Min temperatures, inside and out, every day at about 11pm each day and then reset the thermometer. So I have the data for the previous 24 hours.

Most of the data is self explanatory, but there have been some outside Max temperatures for which I can't find an explanation. For example, on 29 April the Maximum outside temperature was 32.6C. The maximum, so far today is 26.7C.

How can the north side of a house reach these temperatures? They would really mess up a WC system.

View media item 77632

 

[ALEC1]

there are two approaches, one that includes indoor room sensing and one that does not.

only two manufacturers have the latter, viessmann and vailant they can work on the out door sensor only averaging the temperature on a rolling basis.

I have my outdoor sensor on a south facing wall..as that is the orientation of my property...

it works fine... as the flat gets excess sun so the sensor Temperature rises and the flow temp decreases

WC involves judgement, which I guess why the likes of BG don't use it...power to the skilled worker is not always appreciated...

 

[indus]

Hi

Could you kindly explain what weather compensation actually does?

Thank you

 

[Dan Robinson]

Dynamically adjusts the heating flow temperature based on the temperature outside and a pre determined program in the boiler.

For example.... my heating is on on the ground floor. But as it is 13 degrees outside, the boiler has got a running temp of 34.5 degrees.

The system is sized (from scratch) to run at 55 degrees when it is minus 3 outside and gradually reduce the running temperature to a minimum of 25 degrees when the outside hits 20.

I have sized my UFH and rads accordingly.

Where the system pre-exist and you are putting WC on afterwards, you set the programming accordingly.

The system runs for much longer than without WC, but the theory is you run it at a lower level. Much like doing 50 instead of 80 in your car.

Certain members here are obsessed with it, but it is not for every property or PERSON. Women tend to be the ones who don't get on with it the most due to the incessant need for the rads to be glowing.

My missus actually asked me why our ground FLOOR wasn't hot

I'm not being chauvinist. It is a plain fact.

But then we know all women are mental.

 

[mogget]

Some of us understand heat Dan.

Doesn't stop me being mental though

 

[Onetap]

How can the north side of a house reach these temperatures? They would really mess up a WC system.

It has to be a defective sensor or a heat source of some sort; reflected sunlight, a warm air discharge (extract fan, outdoor AC unit, car parked below sensor, etc..). The sensor is meant to be measuring air temperature; in reality it measures its own temperature and the assumption is that the air temperature will be identical. A radiant heat source will mess that up quite spectacularly. The air temperature in the shade could not reach that temperature in April without some heat source.

 

[Onetap]

The system runs for much longer than without WC, but the theory is you run it at a lower level. Much like doing 50 instead of 80 in your car.

More like doing a steady 50, instead of having an on/off engine that accelerates to 80, switches off and coasts to 20 and then accelerates to 80 again.

 

[ALEC1]

weather compensation in Germany has been mandatory since 1985, so the technology that Comes with boilers developed there tends to be very good.

There are several by-products: comfort, with stable room temperatures when programmed to be on, reliability, less cycling, heating up from cold puts less strain on everything, and economy... a lot of the time the flow temperature is well below 55c the dew point of the flue gases.

One manufacturer (vokera) claims that the condensing effect will save 4-7% of a gas bill! Danfoss reckon stabilising room temperatures saves about 10-12%, and Viessman reckon you can save around 20%..with their advanced controls.

 

[Onetap]

I have my outdoor sensor on a south facing wall..as that is the orientation of my property...

it works fine... as the flat gets excess sun so the sensor Temperature rises and the flow temp decreases.

It won't work fine, unless the sensor is shrouded to keep sunlight off it.
The sensor is meant to measure air temperature and it won't do that if it is in direct sunlight. Put your hand on a car that has been standing in sunlight and see whether it feels warmer than the air temperature.

It may work adequately for your purposes, the sensor may be shrouded or you may think it works fine. That's another matter.

I had that problem with a BMS sensor mounted on (ISTR) the west side of a building. On some afternoons it was in direct sunlight for short periods, the indicated temperature went to 35 or 40 degC and the WC heating system shut down. I imported another value of the outside air temperature from another BMS outstation over the LAN until the sensor was moved.

 

[D_Hailsham]

How can the north side of a house reach these temperatures? They would really mess up a WC system.

It has to be a defective sensor or a heat source of some sort; reflected sunlight, a warm air discharge (extract fan, outdoor AC unit, car parked below sensor, etc..). The sensor is meant to be measuring air temperature; in reality it measures its own temperature and the assumption is that the air temperature will be identical. A radiant heat source will mess that up quite spectacularly. The air temperature in the shade could not reach that temperature in April without some heat source.

It was the Sun!

I happened to wake up about 6am the other morning, so I checked the thermometer - External Max was over 30C. I then opened the window and looked out to the East. The sun was in full view, so its heat was striking directly on to the sensor.

So that's why they tell you to put a WC sensor in a shaded location!

Does any one know how to do 3-dimensional geometry to calculate when the sun will be shining onto the north side of my house?

 

[ALEC1]

I Germany you can buy special shade boxes...

I think also NW is more acceptable... the heating will have been on for lomger...

 

[Richardthe3rd]

My understanding is that the outdoor sensor should always be sited in a shaded area facing due North.

I think there's a few of the learned(?) members have a problem understanding that the Sun rises in the East & sets in the West, also how the earth moves in relation to the Sun on a seasonal basis.......

Yes, trust Onetwat to post long winded drivel, when in most cases an outdoor sensor is a simple thermistor sensing ambient temperature.....

Ah Dan, you should follow my lead when it comes to the fairer sex, two room thermostats, a tamper proof one doing the business & the one for the Ladies - the dummy one......

 

[Dan Robinson]

More than once i have left old timers powered but otherwise disconnected at the request of the warmer blooded bill payer.

I also have many customers with the offset parameter of their programmable thermostats set to give a warmer reading.

Not a single person has realised - much to the joy of the aforementioned warmer blooded bill payer.

 

[indus]

Thanks for the explanation.

How difficult/expensive is WC to retrofit to an existing system? Can it be used with all boilers ie system, combi etc?

Thanks

 

[mogget]

Ah Dan, you should follow my lead when it comes to the fairer sex, two room thermostats, one to turn the heating on and one to turn it up further

There - corrected that for you