Air Conditioning, Refrigeration and Cooling Systems
Air Conditioning
Equipment and drainage
Air-conditioning equipment must be listed, installed per instructions, supported, and accessible. Outdoor units need clearance for airflow and service. Indoor coils produce condensate, and drainage is heavily tested: the primary drain must slope at least 1/8 inch per foot toward a suitable disposal point, must be trapped where the coil is on the negative-pressure side of the fan, and must not discharge where it causes damage.
Secondary protection
Where overflow could damage the building, a secondary drain, auxiliary drain pan, or float switch is required. The pan must be at least 3 inches larger than the unit in length and width and at least 1.5 inches deep, with its own drain. Pans must be corrosion-resistant. Condensate pumps are permitted where gravity drainage is not possible.
Air handling and plenums
Duct connections must be sealed, filter access must be provided, and return-air plenums are limited to materials the code allows. Refrigerant lines must be protected and supported.
Exam traps
- Omitting the trap on negative-pressure coils.
- Sizing an auxiliary pan to the unit exactly instead of 3 inches larger.
- Forgetting secondary protection when the unit is above a ceiling.
- Sloping drains the wrong way or mishandling traps.
Worked example
An attic air handler with a cooling coil sits above a bedroom ceiling. A trapped primary drain, an auxiliary pan at least 3 inches larger than the unit, and a secondary drain or float switch are all required before the ceiling is closed.
Refrigeration and Cooling Systems
System classification
Refrigeration requirements hinge on refrigerant classification and charge. Group A1 refrigerants are low toxicity and nonflammable; A2L refrigerants are mildly flammable; A3 refrigerants are highly flammable. High-probability systems are those where a leak can enter an occupied space; low-probability systems are arranged so leaks are unlikely to enter the space.
Quantity limits and machinery rooms
The code sets a refrigerant concentration limit (RCL) for each refrigerant. If the quantity of refrigerant in a space, divided by the volume, exceeds the RCL, mitigation is required: a refrigeration machinery room, ventilation, or refrigerant detection. Machinery rooms have specific construction, ventilation, detection, and occupancy restrictions, including limits on ignition sources and open flames.
Piping and components
Refrigerant piping must be approved material, supported, protected from damage, and tested for leaks. Pressure relief devices must be piped to a safe location. Access for service is required.
Exam traps
- Applying A1 rules to an A2L or A3 system.
- Calculating volume incorrectly, such as ignoring adjoining spaces connected by permanent openings.
- Forgetting that detection and ventilation are triggered by calculated quantity, not equipment size alone.
- Assuming any equipment room is automatically a machinery room.
Worked example (method)
Divide the room volume in cubic feet by 1,000, then multiply by the RCL from the code table for the specific refrigerant. If the system charge exceeds that result, the space needs mitigation under the adopted edition. Never substitute a generic number for the table value.