Temperature Sensor Location
Where to fit and locate field devices.
If the valve is lift and lay type and the application is diverting, then the valve must be fitted in the return.
If the valve is lift and lay type and the application is mixing, then the valve must be fitted in the flow.
The rule of thumb for lift and lay valves is "2 ins and 1 out"
Rotary (shoe) valves can be fitted in either the flow or return for either mixing or diverting applications.
Use pipe unions, so that the valve can easily be removed.
Actuators on Valves:
If the heating medium is steam then the actuator/valve arrangement is not fitted vertically, tilt the valve/actuator to an angle so that heat can convect away vertically and the actuator is not subjected to as much heat.
In all cases, do not fit the actuator/valve arrangement so that the actuator is vertically under the valve. If the valve leaks, it will damage the actuator.
Temperature Sensor location, in both wet and air applications the sensor need to sense correctly the medium it is in. Where possible install in a location for easier maintenance e.g. at a height reachable from a fixed floor level.
Pipe Temperature Sensors:
The tip of the sensor needs to be in the core of the medium i.e. the centre.
The sensor needs to be fitted where stratification does not take place or is reduced. This can be achieved by fitting after a pump or after a bend where turbulence provides a good mix.
If the sensor is fitted on a bend, then the probe faces the flow of/oncoming water.
In CHW applications, fit the pocket just off horizontal, so that any condensation forming in the pocket can drain away. Adequate insulation will prevent condensation forming in the pocket. If fitting vertically in the top of the pipe is unavoidable see Lessons Learned Article #5148.
Duct Temperature Sensor:
Supply Air - If a probe type sensor is fitted, it needs to be ideally 3 meters downstream and in the centre of the duct from the supply fan and preferably after a bend fitted with turning vanes.
Return Air - The temperature sensor needs to be fitted before/upstream of the extract fan.
Frost Coils - Temperature sensor, due to the short distance available, probe sensors are difficult to locate, but try to be as far away from the coil e.g. on the other side of the pre-filter bank and in the centre of the duct/AHU. Even better is to use an averaging type temperature sensor.
Frost Coils - Fan Hold Off thermostat.
Allow sufficient capillary to cover the battery surface.
Lace the capillary across the frost battery on the downstream side using the correct clips.
If the thermostat body needs to be fitted on the external side of the AHU, then fit with the minimum of capillary on the external of the AHU. Use a grommet or stuffing gland to protect the capillary as it goes through the AHU skin.
If the AHU is fitted outside or is in an unheated space then the thermostat needs to fitted internal to the AHU.
Do not cut the capillary if it is too long. Tidy capillary ends so they do not flap in the airstream.
Outside Temperature Sensor:
Outside temperature sensors should be located correctly to the local region you are in and the application they are serving i.e. compensated outside sensor in the UK are fitted on a wall facing north.
The sensor should not be fitted on flues, chimneys, near opening windows. They should not be fitted near to compounds containing plant expelling heat e.g. chiller compounds.
The sensor should be fitted at a height that does not require the use of steps or ladders for maintenance.
Room Temperature Sensor:
Sensors should be fitted at an agreed height and not fitted on external walls, near opening windows and doors or above radiators. They need to be exposed to the area they are controlling and not be directly influenced by heat sources e.g. computers.
Sensors with exposed setpoint adjust or controls need to be fitted at a lower height so that people with disabilities can adjust them.
Sensors that are fitted onto partitioned walls or have a conduit need the hole plugging so that there are no draughts. Sensors that are fitted directly to concrete or steel beams should be packed out with a thermal insulating material.
Valves and Sensor Wiring:
Allow sufficient cable to allow removal of actuator or sensor without having to disconnect the device.
For the full Building Controls Group - Control Sensor Installation guide click here.