Site Survey, Load Calculation, and Equipment Selection
This domain tests whether you can survey a site, calculate a room-by-room load, and select equipment that matches both sensible and latent loads. The exam emphasizes Manual J, Manual S, and Manual D logic, design conditions, envelope details, and matched-system requirements.
Core rules and concepts
- Manual J is a room-by-room load calculation using local design conditions, orientation, window U-factor and SHGC, insulation, infiltration, duct losses, and internal gains.
- Manual S selects equipment using the manufacturer’s expanded performance data at design conditions, not nominal tonnage.
- Manual D sizes ducts for the available static pressure and required room airflow.
- A matched AHRI system pairs indoor and outdoor units; mismatched coils can change capacity and charging behavior.
- Check line-set length and elevation limits, electrical availability, clearances, condensate routing, and structural support during the survey.
- Oversizing causes short cycling, poor dehumidification, and higher humidity; undersizing cannot meet design load.
Worked example
A room has a sensible load of 24,000 Btu/h and a latent load of 6,000 Btu/h, so total load is 30,000 Btu/h. At the design indoor condition of 75°F dry bulb and 63°F wet bulb, a nominal 3-ton unit is rated 30,000 Btu/h total but only 22,000 Btu/h sensible. Because sensible capacity is below the 24,000 Btu/h sensible load, that selection is inadequate even though total capacity matches. Select a unit with at least 24,000 Btu/h sensible at design conditions, then verify airflow: 24,000 ÷ (1.08 × 20) ≈ 1,111 cfm for a 20°F temperature difference.
Traps that cost marks
Using square-footage rules of thumb; selecting by nominal tons; ignoring latent load and humidity; forgetting duct load or altitude corrections; and pairing a coil that is not listed with the outdoor unit.