Controls and Thermostats Flashcards

What type of thermostat uses a bimetallic strip as its primary sensing element?

Answer: Mechanical thermostat

Mechanical thermostats use a bimetallic strip that physically bends with temperature changes to make or break electrical contacts.

What is the 'deadband' in thermostat operation?

Answer: The temperature range between heating and cooling setpoints where neither system operates

The deadband is the neutral zone between heating and cooling setpoints that prevents simultaneous heating and cooling operation.

What does DDC stand for in building automation and HVAC controls?

Answer: Direct Digital Control

DDC (Direct Digital Control) uses microprocessors to directly monitor and control HVAC equipment using digital signals and algorithms.

Which control type continuously modulates output between 0% and 100% in proportion to the deviation from setpoint?

Answer: Proportional control

Proportional control continuously varies output based on how far the controlled variable deviates from setpoint, unlike simple on/off control.

What is the primary purpose of a heat anticipator in a mechanical thermostat?

Answer: To prevent temperature overshoot by shutting off the furnace slightly early

The heat anticipator pre-heats the thermostat's sensing element to signal the furnace to shut off before the setpoint is fully reached, preventing overshoot.

In HVAC controls, what does the term 'setpoint' refer to?

Answer: The desired target value that the control system works to maintain

A setpoint is the target value — usually temperature — that the control system continuously works to achieve and maintain in the conditioned space.

What type of sensor is most commonly used in modern electronic thermostats to measure temperature?

Answer: Thermistor or RTD

Modern electronic thermostats use thermistors (NTC/PTC) or RTDs (Resistance Temperature Detectors) because their electrical resistance changes predictably with temperature.