How does the calibration offset work in an HR92?

[Old_Codger]

Our installer seems to have programmed many of our valves with a calibration value of -3, but some have -1.

Why would he have done this? What is the likely consequence of the different figures?

What does this value mean? I’m guessing it has something to do with the fact that the sensor is right next to the radiator and not in the middle of the room or near where we sit? So, it will inevitably be hotter than the room if the rad is on.

If that’s the case once the room comes to temperature eventually I guess some sort of equilibrium will be reached ? If so how do Honeywell prevent that offset becoming a “deadband” i.e. the valve can’t reopen until the temp drops by at least the calibration offset?

[DBMandrake]

The calibration offset is quite simple to understand.

As you say, the sensor is right beside the radiator so will tend to read higher than the true room temperature due to the proximity of the heat from the radiator. Convective airflow past the radiator will counteract this to some degree by drawing cool air from along the floor past the sensor but typically the sensed temperature will still be at least 1C hotter than actual room temperature.

So if you set the set point to 20C your room would only end up at a true temperature of 19C as measured by an independent thermostat.

Calibrate applies an offset to the temperature sensed by the HR92 before it is sent back to the controller and before it is used to decide whether the room is too hot or too cold.

So if set to -1C and it senses 21C it will be reported at 20C. This affects both displayed temperature as well as affecting the temperature that the room eventually settles on. So a negative calibrate setting will cause the actual room temperature to be hotter, as measured by an independent thermostat.

-1C is typical for many radiators/rooms, but in one of my rooms I need -2C in summer and -3C in winter because convection is poor in that room and the radiator is a bit undersized.

If you need more than -1C for calibrate for a given room the room may be better off with a remotely situated wall thermostat instead, and one day I will get around to fitting one in that particular room. (I already have a wall mounted DTS92 in the living room and both bedrooms)

Calibration doesn't introduce any deadband so you don't need to worry about that. It's purely a numeric offset to the sensed temperature before it is used by the system.

[Old_Codger]

Thank you. The installer set the offset to -3 with no knowledge of how the system would actually perform. Should I drop them all to -1 and see if things are better?

[DBMandrake]

Thank you. The installer set the offset to -3 with no knowledge of how the system would actually perform. Should I drop them all to -1 and see if things are better?

If you're fussy about the calibration of the system I would start with -1C and use a standalone thermometer sitting on a desk or coffee table to sample the room temperature away from the radiators - choose a time when the set point is constant for many hours and the room has had time to reach that set point and settle properly, (a few hours) then compare the temperature reported by the HR92 with your standalone thermometer.

If -3C is really needed it suggests convection from the radiator is not very good or the room has heat loss at one end of the room - for example a room that is permanently open to a hallway, in which case there will be a larger difference between average room temperature and temperature sensed by the radiator.

[Old_Codger]

I think the problem may be the rooms we use most (kitchen and living room) often have the doors open. They end up to hot if they don’t.