HVAC systems and equipment
Domain 2 tests equipment families, capacity ratings, efficiency metrics, and selection logic for HVAC systems.
Equipment families
DX split systems pair an outdoor condenser with an indoor coil and air handler. Packaged units place all components in one cabinet. Heat pumps add a reversing valve to provide heating and cooling. Gas furnaces, electric resistance, hydronic boilers, chillers, VRF systems, and ductless mini-splits each have different applications and control needs. Indoor and outdoor components must be listed as a matched system, or the manufacturer's expanded performance data must be used.
Capacity and efficiency
One ton of cooling equals 12,000 Btu/h. Cooling efficiency is rated by SEER2 and EER2; heat pumps use HSPF2; furnaces use AFUE; chillers use COP or kW/ton. Nominal capacity is not design capacity: a 3-ton unit at 95°F may deliver less than 36,000 Btu/h, and a heat pump's heating capacity falls as outdoor temperature drops. Gas furnace capacity must be derated for altitude per manufacturer data.
Worked example
A nominal 3-ton heat pump has published capacity of 34,000 Btu/h at 95°F cooling and 22,000 Btu/h at 17°F heating. The calculated heating load is 28,000 Btu/h. The unit needs 6,000 Btu/h of auxiliary heat at design conditions, plus staged controls and a balance point. Selecting by the 3-ton nominal label alone would undersize heating and could oversize cooling if the sensible load is lower.
Traps that cost marks
Do not replace like-for-like without a load calculation, mismatch coils, ignore latent capacity, forget electric heat strips and blower heat, or select equipment without checking static pressure and altitude.