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Sensible heat ratio in HVAC coil selection and psychrometric analysis
Sensible heat ratio (SHR) is the fraction of total heat transfer that is sensible, expressed as a decimal from 0 to 1. SHR = Qsensible / Qtotal = Qs / (Qs + Ql). A value of 1.0 means all heat transfer is sensible (temperature change only, no moisture change). A value of 0.5 means half the coil capacity goes to cooling and condensing moisture. From psychrometric entering and leaving conditions, SHR equals the ratio of the sensible enthalpy change to the total enthalpy change: SHR = Δhs / Δh, where Δhs = cpm × (T1 − T2) and Δh = h1 − h2 using the same water thermophysical reference data NIST maintains at both state points.
SHR is one of the three interdependent parameters that fully define a cooling coil process, alongside the apparatus dew point and the bypass factor. Knowing any two determines the third. Most coil selection software asks for entering conditions and either the leaving dry-bulb plus leaving RH (which gives SHR implicitly) or the total and sensible loads (which gives SHR directly). This calculator works from measured or designed state points, making it useful for verifying coil performance during commissioning (log the reading on an HVAC commissioning checklist) or troubleshooting a coil that isn't meeting its latent duty.
Typical SHR values for Canadian HVAC applications
SHR depends on climate, ventilation rate, occupancy, and the ratio of sensible to latent internal gains. In dry Canadian cities like Calgary and Edmonton, typical office SHR runs 0.82 to 0.90 because dry outdoor air contributes little latent load. In Toronto, Ottawa, and Windsor, the same office drops to 0.70 to 0.78 due to high summer outdoor humidity. High-ventilation spaces like classrooms, restaurants, and assembly halls run lower SHR (0.60 to 0.72) across all climates because occupant and ventilation latent loads dominate. Indoor pools and food preparation areas, where makeup air volumes are set with the kitchen exhaust calculator, can see SHR below 0.50. When measured SHR from this calculator differs significantly from the design SHR, it often indicates a ventilation override, coil fouling, or a refrigerant problem. Use the cooling coil calculator to translate SHR into the coil selection parameters needed for equipment specification.
SHR, apparatus dew point, and the psychrometric chart
On the psychrometric chart, the SHR defines the slope of the coil process line. That line, extended to the saturation curve (100% RH), intersects at the apparatus dew point (ADP). The ADP is the effective coil surface temperature for psychrometric purposes, and it's exactly this SHR-to-ADP relationship that AHRI Standard 410 uses to define standardized coil rating procedures. A lower SHR (more latent removal) means a steeper process line and a lower ADP, requiring a colder coil and often a higher refrigerant temperature drop. A high SHR (mostly sensible) produces a nearly horizontal process line with a high ADP, achievable with a warm coil or chilled water at a modest differential. The apparatus dew point calculator computes ADP directly from entering conditions, leaving conditions, and the process line defined by this tool's SHR output. From ADP and the required leaving condition, the bypass factor calculator then determines the coil contact efficiency needed to match that leaving state.
Frequently Asked Questions
SHR varies by climate and application. In dry Calgary and Edmonton, typical office SHR runs 0.82 to 0.90. In humid Toronto and Ottawa, the same building drops to 0.70 to 0.78. High-ventilation spaces like classrooms and restaurants run 0.60 to 0.72 across all Canadian climates. Indoor pools fall below 0.50. Measured SHR significantly different from design usually indicates a ventilation override, coil fouling, or a refrigerant charge problem. Use the enthalpy calculator to verify the h1 and h2 values before running this analysis, and the apparatus dew point calculator to link SHR to coil ADP for equipment selection.
Calculate total cooling load (sensible plus latent) and use SHR to split it: Qs = SHR × Qt and Ql = (1−SHR) × Qt. The SHR also defines the process line slope on the psychrometric chart, which intersects the saturation curve at the apparatus dew point. A coil with the correct ADP and bypass factor delivers the target leaving air condition that satisfies both loads simultaneously. Selecting a coil for sensible load only will leave too much moisture in the air and cause high indoor humidity. Use the bypass factor calculator to convert SHR and leaving conditions into a coil contact efficiency specification, then verify the coil with the cooling coil calculator.