Sensible vs Latent Heat: Psychrometrics, Phase Change & HVAC Enthalpy
Sensible heat causes a measurable change in dry-bulb temperature without changing physical state, whereas latent heat represents the hidden thermal energy absorbed or released during moisture phase changes (evaporation and condensation) at constant temperature. In air conditioning psychrometrics, the Sensible Heat Ratio (SHR) determines how equipment capacity splits between cooling air and dehumidification.
Technical Comparison & Conversion Matrix
| Thermodynamic Property | Sensible Heat (Q_sensible) | Latent Heat (Q_latent) |
|---|---|---|
| Physical Effect on Fluid | Changes dry-bulb thermometer temperature with no change in physical state | Causes phase transformation (liquid to vapor or vapor to liquid) at constant temperature |
| Measurement Instrument | Standard dry-bulb thermometer or electronic thermistor probe | Psychrometer, hygrometer, dew point meter, or humidity ratio chart |
| Standard Airflow Equation (Sea Level) | Q_s = 1.08 × CFM × (T_entering - T_leaving) | Q_l = 4840 × CFM × (W_entering - W_leaving) = 0.68 × CFM × Δgrains |
| HVAC Equipment Role | Drops indoor air temperature from 75°F down to desired thermostat setpoint | Condenses moisture out of humid air onto evaporator coil drain pan |
| Typical Residential Split | 70% to 80% of total cooling capacity in dry climates (SHR = 0.75–0.85) | 30% to 40% of total cooling capacity in humid humid climates (SHR = 0.60–0.70) |
| Human Thermal Comfort Impact | Affects dry skin convective and radiative heat exchange with room surfaces | Affects skin sweat evaporation efficiency; high latent heat causes sticky, muggy discomfort |
| Dehumidifier Specific Operation | Net sensible neutral or slight heating (compressor heat rejected into space) | 100% focused on latent heat extraction via vapor condensation |
Live Calculator: BTU to CFM Airflow Calculator
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Computed Output
Interactive Online Calculators
Instantly compute exact values using our deterministic edge calculation tools:
BTU to CFM Airflow Calculator
Convert sensible heating and cooling BTU/hr to required CFM airflow and tonnage for HVAC design.
Residential & Commercial Heat Load (Manual J) Tonnage Calculator
Estimate residential cooling and heating heat loss/gain in BTU/hr and required HVAC air conditioning tonnage.
Humidity, Dew Point & Comfort Calculator
Calculate dew point temperature, grains of moisture, and indoor comfort index.
Frequently Asked Questions
What is the Sensible Heat Ratio (SHR) and why is it critical for air conditioner sizing?
SHR is sensible cooling capacity divided by total cooling capacity: SHR = Q_s / (Q_s + Q_l). An air conditioner with an SHR of 0.75 devotes 75% of its power to lowering air temperature and 25% to removing humidity. Oversized units satisfy sensible temperature too fast and shut off before removing latent moisture, creating cold, clammy indoor air.
Where does the factor 4840 in the latent heat formula originate?
4840 equals air density (0.075 lb/cu ft) multiplied by the latent heat of vaporization of water (approx. 1061 BTU/lb) multiplied by 60 minutes per hour: 0.075 * 1061 * 60 = 4774.5, adjusted for standard air psychrometric properties to 4840.