Definition
Heat energy that causes temperature change. Measurable by thermometer. In HVAC systems, cooling coils and heaters control sensible heat. Dehumidifiers do not directly control sensible heat, but silica gel rotor reactivation raises process outlet temperature.
Detailed Explanation
Sensible heat is the heat energy that raises or lowers the temperature of a substance without changing its phase. It gets its name from being "perceptible/sensible by a thermometer". In HVAC context, heating or cooling air (above the dew point) is pure sensible heat transfer.
Sensible heat is the complement of latent heat (heat consumed by phase change). When an AHU goes from the mixed air point to the supply air point, it carries both sensible and latent loads; the sum of these gives the total load (enthalpy difference). The cooling coil's Sensible Heat Ratio (SHR) is the ratio of this division:
SHR = Qsen / Qtotal
Typical SHR values: office comfort applications 70–80%, restaurant/cinema 55–65%, lithium battery dry rooms 20–30% (latent load dominates). In low-SHR applications, a chiller alone is insufficient; a dehumidifier is required.
Calculation
Sensible heat load for an air stream:
Qsen = mda × cp,ma × ΔT = ṁ × 1.012 × ΔT (approximate formula)
With volumetric flow: Qsen = V̇ × ρ × 1.012 × ΔT ≈ V̇ × 1.213 × ΔT (at standard conditions)
Qsen: sensible heat load (kW) V̇: volumetric air flow (m³/s) ρ: air density (≈ 1.2 kg/m³) cp,ma: specific heat of moist air (≈ 1.012 kJ/kg·K) ΔT: temperature difference (K or °C)
Quick rule: heating/cooling 1 m³/s of air by 1°C requires ≈ 1.2 kW of sensible heat.
Practical Example
We are designing the HVAC for an indoor swimming pool. Supply air 28°C, 50% RH; ambient room conditions 30°C, 60% RH. Volume: 4,000 m³/h air circulation.
Sensible load (room heating — heat transfer from water surface to air): ΔT = 30 − 28 = 2°C Qsen = 4,000 / 3,600 × 1.213 × 2 ≈ 2.7 kW
Latent load (pool surface evaporation, approximately 80 kg/h moisture entering the room): Qlat = 80 × 2,450 / 3,600 ≈ 54.4 kW
SHR = 2.7 / (2.7 + 54.4) = 0.047 → only 5% sensible, 95% latent load!
This extremely low SHR is the signature of swimming pool applications. A standard chiller cannot economically meet this load; pool-type dehumidifiers (NKT CDP series, Microwell Dry Wave, etc.) are therefore designed for the latent load and recover the heat of vaporization.
Engineering Note
The sensible/latent separation directly affects design decisions:
• SHR > 0.80: standard DX/chiller is sufficient; humidity control often happens as a byproduct. • SHR 0.60–0.80: an independent humidity control strategy is required; reheat or a separate dehumidifier should be considered. • SHR < 0.60: the chiller is only an auxiliary; the main job is done by a silica gel rotor or condensation-type dehumidifier. Swimming pools, food plants with moisture loads, and ice cream factories fall into this category. • Reheat energy penalty: in very low SHR applications, the cooling coil drops the air below the dew point, then reheats it back to setpoint. This is "paying twice" for energy; rotor-based dehumidifier alternatives eliminate reheat and save 30–50% energy.
The NKT energy comparison tool (araclar/enerji-karsilastirma) performs these economic analyses: it shows side-by-side consumption of classical DX, DX with condenser heat recovery, and silica gel rotor systems for the same load.