Codes, Safety, and Load Calculations
What this domain covers
This domain tests load calculation, equipment selection, code principles, refrigerant safety, and jobsite safety. The exam expects you to know that sizing starts with a calculated load, not a rule of thumb, and that code compliance depends on the adopted edition and local amendments.
Core rules
- Load calculation. ACCA Manual J calculates heating and cooling loads from envelope, windows, orientation, infiltration, internal gains, and duct gains. Manual S selects equipment using the calculated sensible and latent loads, not total tonnage alone.
- Design conditions. Use the approved outdoor design temperature and indoor design temperature. In Hawaii, cooling loads dominate and latent load is significant; heating loads are small except at higher elevation.
- Codes and standards. Model codes include the IECC, ASHRAE 90.1, NEC Article 440 for refrigeration equipment, and EPA Section 608 for refrigerant handling. Local amendments govern.
- Safety. Use lockout/tagout, PPE, and proper refrigerant recovery. Never weld or braze near flammable refrigerant without following the equipment label and safety standard.
- Oversizing. Excess capacity causes short cycling, poor dehumidification, and higher energy use.
Worked example
A Manual J load shows 30,000 Btu/h sensible and 8,000 Btu/h latent, for 38,000 Btu/h total. Divide by 12,000: 38,000 ÷ 12,000 = 3.17 tons. A 3.5-ton nominal unit (42,000 Btu/h) is about 10.5% above the calculated total load, which is reasonable if its sensible capacity at design conditions meets the 30,000 Btu/h sensible load. A 5-ton “rule of thumb” unit would be badly oversized.
Traps that cost marks
- Sizing by square footage alone instead of Manual J.
- Selecting on total capacity while ignoring sensible and latent split.
- Forgetting duct gains and ventilation load.
- Assuming the same code edition applies everywhere; check the AHJ amendment.
- Treating refrigerant recovery and flammable-refrigerant rules as optional.