Engineering notes
Humidity: room or duct — a combo head is not always two points
Room humidity is not duct humidity. A temp-RH combo is cheaper than two heads — only if the file allows one location. Range and signal must match the DDC.
The file lists two points: meeting-room temperature, meeting-room humidity. Stores issue a combo because “same place”. Fine if the consultant accepts one mounting. Wrong if humidity sits on the AHU return — a wall head reads mixed room air and the AHU humidify loop looks at the wrong spot.
Usual range 0–100 %RH, 0–10 V or 4–20 mA, or a bus. Clean rooms and cold stores: ask accuracy and condensation on the element — an office head on a cold soffit reads 100% and dies. Outdoors needs a rain shield, not a room head.
Write wall or duct, the signal, and whether temperature shares the head. Choosing a sensor