Controls and Thermostats Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Controls and Thermostats flashcards as text
What communication protocol, standardized by ASHRAE, was specifically designed for building automation systems?
Answer: BACnet
BACnet (Building Automation and Control Networks) is the ASHRAE standard 135 communication protocol designed specifically for HVAC and building automation interoperability.
What does PID stand for in HVAC control systems?
Answer: Proportional-Integral-Derivative
PID control combines Proportional, Integral, and Derivative actions to minimize error, eliminate steady-state offset, and dampen rapid oscillations.
What is the primary function of an economizer in an HVAC control system?
Answer: To use outdoor air for free cooling when outdoor conditions are favorable
An economizer uses outdoor air for cooling when outdoor temperature and/or enthalpy is suitable, reducing or eliminating mechanical cooling energy consumption.
In a zone control system, what device modulates airflow to individual zones based on each zone's thermostat demand?
Answer: Zone damper or VAV box
Zone dampers (in simpler systems) or VAV (Variable Air Volume) boxes modulate airflow to each zone individually based on that zone's thermostat signal.
What is 'hunting' in an HVAC control system?
Answer: Continuous oscillation of the controlled variable above and below setpoint due to overcorrection
Hunting occurs when a control system repeatedly overcorrects, causing the controlled variable to swing continuously above and below the setpoint without stabilizing.
What is the primary energy-saving feature of a programmable thermostat?
Answer: Automatic temperature setback during unoccupied periods
Programmable thermostats save energy by automatically reducing heating or cooling demand during unoccupied hours (setback), lowering energy consumption when conditioning is not needed.
What does an enthalpy controller measure to determine if economizer free-cooling is beneficial?
Answer: Both outdoor air temperature and humidity to calculate total heat content
An enthalpy controller measures both outdoor dry-bulb temperature and wet-bulb temperature (or relative humidity) to calculate total heat content (enthalpy) and enable economizer mode only when outdoor air is truly beneficial.