HVAC Systems
Efficiency metrics and conversions
COP = EER / 3.412, and 1 kW/ton equals COP 3.517 and EER 12.0. EER is a full-load rating, SEER is seasonal for small unitary equipment, and IEER or IPLV captures part-load behavior, which is the honest number for a chiller running most hours at 30 to 60% load. Boilers report combustion efficiency, thermal efficiency, and AFUE; AFUE is annualized for small equipment and based on higher heating value, so it is not directly comparable to steady-state combustion efficiency.
Air-side and water-side fundamentals
Q-sensible (Btu/h) = 1.08 x cfm x delta-T; Q-total = 4.5 x cfm x delta-h. VAV with static pressure reset, supply air temperature reset, and a functioning air-side economizer is the standard efficient configuration. Simultaneous heating and cooling, such as terminal reheat fighting a cold supply, is a classic audit finding. Fan and pump laws: flow varies with speed, head with speed squared, power with speed cubed.
Traps
Watch for economizer high-limit setpoints that lock out free cooling, minimum outdoor air set from 62.1 rather than a fixed percentage, and part-load ratings quoted at AHRI conditions that do not match actual entering condenser water temperature. Do not mix tons (12,000 Btu/h) with MBH, and remember that chiller kW/ton includes compressor, condenser, and auxiliary power.
Rule of thumb
A chilled water plant averaging 0.60 kW/ton including towers and pumps is well run; 0.80 or above signals trouble. A 0.1 to 0.2 in. w.c. duct static reset often yields 5 to 10% fan savings.