RS Electricals & HVAC Engineering Tools Portal
AHU Manufacturing Get Quote
Portal Home > HVAC & Cleanroom > Psychrometric Coil & SHR
Tool 16: Psychrometrics & Coil Thermodynamics

Psychrometric Mixed Air & Coil Sensible Heat Ratio (SHR)

Calculates mixed air dry-bulb temperature and humidity ratio, total AHU cooling coil capacity (kW & TR), sensible-to-total heat ratio (SHR), and moisture condensate drainage per ASHRAE Handbook of Fundamentals.

✔ 1. Formula Verified → ⚡ 2. Engineering Screening → 📐 3. Standards Referenced (ASHRAE Fundamentals) → ⚖ 4. Engineer Review Required
⚙ Psychrometric Air State Inputs
CFM
Design air delivery through the cooling coil.
°C
Room design return air temperature (typically 23–25°C for conditioned spaces).
%
Conditioned space target relative humidity (typically 50% ± 5%).
°C
Summer peak outdoor dry-bulb design temperature.
%
Coincident ambient relative humidity during peak summer/monsoon.
%
Fresh air percentage per ASHRAE 62.1 indoor air quality standards (10–20% for office; 100% for TFA/hospital OTs).
°C
Air discharge temperature leaving the cooling coil (typically 11.5–13.5°C for comfort AC).
📊 Coil Psychrometric Sizing Sheet
Preliminary Screening
Total Cooling Coil Capacity Required
34.5 TR
Total Heat Transfer: 121.3 kW (Sensible + Latent)
Mixed Air Dry-Bulb
26.9 °C
Mixed Air Humidity Ratio
11.23 g/kg
Sensible Heat Ratio (SHR)
0.70
Condensate Drain Rate
50.1 L/hour
Coil Dehumidification Load Breakdown
70% Sensible Cooling | 30% Latent Dehumidification
💬 Consult AHU Coil Engineers on WhatsApp

Governing Engineering Standards & Calculation Model

Governing Standards & References

  • ASHRAE Handbook of Fundamentals: Chapter 1 (Psychrometrics and Moist Air Thermodynamic Properties).
  • ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality.
  • AHRI Standard 410: Forced-Circulation Air-Cooling and Air-Heating Coils.

Engineering Equations & Derivations

T_mix = (T_ra × (1 - FA%)) + (T_oa × FA%)
W_mix = (W_ra × (1 - FA%)) + (W_oa × FA%) [kg_w / kg_da]
m_dot_da = CFM × 0.0004719 × 1.204 [kg/s]
Q_total = m_dot_da × (h_mix - h_off) [kW]
SHR = (m_dot_da × 1.006 × (T_mix - T_off)) / Q_total
Condensate = m_dot_da × (W_mix - W_off) × 3600 [L/h]

Standard saturation vapor pressures computed via Magnus-Tetens approximation. Off-coil air assumed at 95% relative humidity for typical wet-coil cooling and dehumidification regimes.

⚖ Statutory Notice & Engineering Disclaimer (Tier D Integration)

Psychrometric calculations provide preliminary thermodynamic screening and coil sizing. Actual coil performance depends on coil bypass factor (BF typically 0.05 to 0.15 for 4-row / 6-row / 8-row chilled water or DX coils), fin spacing (FPI), water entering/leaving temperatures (typically 7°C/12°C), and internal tube turbulence. Manufacturer certified coil selection software (e.g. Carrier, Trane, Dunham-Bush) must verify selection prior to coil fabrication.