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Cooling coil performance analysis for Canadian HVAC systems
A cooling coil removes both sensible heat (temperature) and latent heat (moisture) from air simultaneously. The split between these two effects, expressed as Sensible Heat Ratio (SHR), determines how effective the coil is at dehumidification versus simple temperature reduction. Getting this analysis right is essential for selecting the correct coil for any application, from a dry Calgary winter ventilation system to a humid Toronto summer comfort cooling system.
Total coil capacity (BTU/hr) = CFM × 4.5 × (h_entering − h_leaving). Sensible capacity = CFM × 1.08 × (T_entering − T_leaving). Latent capacity = Total − Sensible. SHR = Sensible / Total. At elevated sites like Calgary, the 4.5 and 1.08 factors need density correction — this calculator applies it automatically based on your elevation input.
Apparatus dew point and bypass factor explained
Apparatus dew point (ADP) is a theoretical concept: it's the point on the saturation curve where the straight-line coil process, when extended, would intersect 100% RH. A coil with many rows and tight fin spacing has a low bypass factor (closer to 0.05-0.10), meaning the leaving air condition is close to the ADP. A coil with fewer rows has a higher bypass factor (0.15-0.20), meaning a larger fraction of air bypasses the coil surface without full contact, leaving warmer and more humid air than the ADP would suggest.
Use bypass factor to evaluate whether an existing coil can achieve a target leaving air condition, or to select the right number of rows for a new coil design. A coil selection software tool will show BF directly, but this calculator lets you back-calculate it from measured or design entering and leaving conditions for verification.
SHR selection for different Canadian applications
Standard residential and commercial comfort cooling targets SHR of 0.75-0.85. Humid climates or high-latent-load spaces (gyms, pools, kitchens) need lower SHR coils (0.60-0.70) to manage moisture without overcooling. Dry climate ventilation-only systems in places like Calgary may see SHR above 0.90 since latent load is minimal. Always verify your coil selection's rated SHR matches your actual load profile — a coil with the right total capacity but wrong SHR will either overcool the space or fail to control humidity.
Frequently Asked Questions
SHR = Sensible capacity ÷ Total capacity. Sensible = 1.08 × CFM × (T_entering − T_leaving) in BTU/hr. Total = 4.5 × CFM × (h_entering − h_leaving). A typical comfort cooling coil has SHR of 0.75-0.85. Low-SHR coils (below 0.70) remove more moisture relative to temperature drop, used in humid climates or high-occupancy spaces. Use the enthalpy calculator to verify entering and leaving enthalpy values independently.
Apparatus dew point (ADP) is the theoretical saturation point where the coil's process line intersects 100% RH. Bypass factor (BF) is the fraction of air bypassing the coil surface: BF = (T_leaving − T_ADP) / (T_entering − T_ADP). Typical BF ranges from 0.05 (many rows, tight fins) to 0.20 (fewer rows). Lower BF means more effective air-to-coil contact. Use this calculator's results table to back-calculate ADP and BF from your entering and leaving design conditions.