Psychrometrics: sensible heat factor for cooling and dehumidification For a process over a cooling coil, with h1 = enthalpy of entering air, h2 = enthalpy of leaving air, and hA = enthalpy at the end of dehumidification (apparatus dew point), choose the correct expression for the sensible heat factor (SHF).
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Medium
Choose an option
-
ASHF = (h1 − hA) / (h1 − h2)
-
BSHF = (h2 − hA) / (h1 − h2)
-
CSHF = (h1 − h2) / (h1 − hA)
-
DSHF = (hA − h2) / (h1 − h2)
Answer
Correct Answer: SHF = (h1 − hA) / (h1 − h2)
Explanation
Given data
- h1: enthalpy of entering air
- h2: enthalpy of leaving air
- hA: enthalpy at apparatus dew-point (end of dehumidification line)
Concept/ApproachFor cooling and dehumidification, the sensible heat factor is the ratio of sensible heat to total heat for the 1→2 process and, in terms of psychrometric geometry, is given by the segment ratio along the process line.
Derivation (sketch-based reasoning)Total heat removed = (h1 − h2); sensible component corresponds to (h1 − hA).SHF = (h1 − hA) / (h1 − h2).
Sanity checkIf there is no dehumidification, hA → h2 and SHF → 1, as expected for purely sensible cooling.
Final AnswerSHF = (h1 − hA) / (h1 − h2)