HVAC TAB & Functional Testing Flashcards

During TAB of a variable flow hydronic system, the differential pressure setpoint at a remote pressure sensor is found to be set too high. What is the primary consequence?

Answer: Pump will operate at higher speed than needed, wasting energy

An excessively high DP setpoint forces the VFD to maintain unnecessary pump speed, consuming more energy than required to serve actual system demand.

What functional test verifies that a building automation system demand-controlled ventilation (DCV) strategy is operating correctly?

Answer: Simulate elevated CO2 levels and verify OA damper modulation increases airflow

DCV functional testing requires simulating high CO2 concentration and confirming the BAS responds by increasing outside air intake to dilute contaminants.

A fan coil unit in heating mode shows adequate airflow but insufficient heat output. Water flow and entering water temperature are verified correct. What should be checked next?

Answer: Control valve three-way bypass position and coil air venting

Air trapped in a hydronic coil or a three-way valve in bypass reduces effective heat transfer even when water temperature and system flow are correct.

During commissioning, which test confirms that a chiller's safety controls are properly configured and functional?

Answer: Simulate high condenser pressure, low evaporator pressure, and motor overtemperature trips

Functional testing of chiller safeties requires simulating fault conditions to confirm the chiller shuts down within specified parameters to protect equipment.

What is the purpose of recording motor nameplate data during TAB?

Answer: To calculate actual brake horsepower and verify motor is not overloaded

Motor nameplate data (voltage, FLA, service factor) allows TAB technicians to calculate actual brake horsepower and compare against measured amperage to detect overloading.

During functional testing of a smoke control system, what must be verified after the HVAC system is commanded to smoke control mode?

Answer: Designated fans pressurize egress paths and exhaust fans remove smoke from affected zones

Smoke control functional testing verifies that the system creates tenable conditions in egress paths by pressurizing stairwells and exhausting smoke from fire zones.

An exhaust air terminal in a laboratory fume hood measures 20% below design face velocity. After confirming exhaust fan operation is correct, what is the most likely cause?

Answer: Exhaust duct damper not fully open or supply-exhaust flow imbalance in the lab

Low fume hood face velocity despite correct fan operation usually indicates a partially closed exhaust damper or insufficient supply air delivery creating a negative pressure imbalance.