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The choice of an appropriate HVAC actuator is dependent on three factors, which include torque rating, the voltage, and the control signal types. The error in any of these three factors will ensure malfunctioning or failure of the actuator even if the choice was seemingly good.

CO2 sensor is an instrument that measures the level of carbon dioxide in the atmosphere and is a vital component of demand controlled ventilation, which means the building will provide just the right amount of fresh air as needed by the actual occupancy and not on a pre-set schedule.

Humidity sensors detect the amount of water vapour in the air and return the value to the building management system or humidifier, thereby enabling buildings to maintain an optimal level of humidity. It is equally important to select the proper sensor and location for accurate readings.

Choose an immersion sensor for the most accurate pipe fluid temperature reading, a strap on sensor when speed of installation matters more than absolute accuracy, and a duct sensor when you need to measure air temperature rather than fluid temperature. Each type suits a different point in the system, and the right choice depends on what you are actually trying to measure.

A flow switch is designed to detect if there is any flow through the pipe and give an indication based on that. It is normally used to prevent the operation of the pump or the boiler without proper flow. Problems are likely to be due to either faulty no flow detection or being jammed.

A DDC controller, short for direct digital control, is the device that reads sensor inputs, runs programmed control logic in software, and drives outputs to actuators and valves, replacing older pneumatic or electromechanical control methods. DDC controllers are the physical building blocks that make up a wider BMS.

These protocols are BACnet, Modbus and KNX, and the selection of each one depends upon the size of the project and manufacturers of the various components. BACnet is suitable for almost all contemporary commercial BMS systems, while Modbus is commonly used in small and less expensive BMS systems. KNX is employed for lighting and room automation purposes.

A variable frequency drive, or VFD, adjusts a motor's speed by varying the frequency of its electrical supply, rather than running the motor at a single fixed speed. In HVAC, VFDs are most commonly used on pumps and fans to save energy and reduce mechanical wear compared with fixed speed operation.

The EC fan has an electronically commutated motor which features a built-in speed controller, which makes it more efficient compared to the normal AC fan while providing more speed control. The cost effectiveness of the extra expenditure, however, is dependent on the operating time and required speed variability.

The steam humidifier helps humidify the indoor air by heating up water to produce steam and then distributing the steam through the ductwork or into the room, solving the problem of a lack of humidity during winter. Sizing and controlling one correctly means matching its output to the actual moisture demand of the building.