Sensible Heat Ratio / Latent Split (ASHRAE)

Returns the sensible / latent split (1.08 / 4840 coefficients with altitude correction), SHR, and return / supply humidity ratios (grains/lb). Use the sensible-heat-ratio calculation instead if you already have both Q values. Per ASHRAE Fundamentals 2021 Ch. 1 / Ch. 18.

Q_sensible = 1.08 * CFM * (T_ra - T_sa) * (rho/rho_sea). Q_latent = Q_total - Q_sensible. SHR = Q_sensible / Q_total. W from dry-bulb / wet-bulb via ASHRAE Fund Ch.1 eq. 35: W = ((2501 - 2.326*T_wb_C)*W_s_wb - 1.006*(T_db_C - T_wb_C)) / (2501 + 1.86*T_db_C - 4.186*T_wb_C). dW = Q_latent / (4840 * CFM * rho_ratio). W_sa = W_ra - dW. Altitude correction P(z) = 101.325 * (1 - 2.25577e-5 * z_m)^5.2559.

ASHRAE Fundamentals 2021 Chapter 1 (psychrometrics) and Chapter 18 (nonresidential cooling and heating load calculations).

ashrae.org for TOC; full handbook is licensed.

Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.

Field names used by the API: total_capacity_btu_hr, return_db_F, return_wb_F, supply_db_F, cfm, Q_sensible_btu_hr, Q_latent_btu_hr, SHR

• Sensible coefficient 1.08 = 60 min/hr * 0.075 lb/ft^3 * 0.24 Btu/(lb F) at standard sea-level air densityASHRAE Handbook
• Latent coefficient 4840 = 60 min/hr * 0.075 lb/ft^3 * 1076 Btu/lb water at standard sea-level air density (lb-water / lb-dry-air form)ASHRAE Handbook
• Altitude correction rho / rho_sea = P(z) / P0 with P from standard-atmosphere formulaASHRAE Fundamentals 2021 Ch. 1 eq. 3
• Humidity ratio from wet-bulb ASHRAE Fundamentals 2021 Ch. 1 eq. 35 (psychrometric)ASHRAE Handbook
• Saturation pressure Magnus form e_s = 0.61094 * exp(17.625 * T / (T + 243.04)) kPa (adequate for the 32-120 F range)engineering practice; ASHRAE Fund Ch. 1 eq. 6 simplified
• Band labels SHR 0.65-0.80 typical residential cooling; 0.55-0.65 high-latent climate; >0.80 dry-climate; <0.55 dehumidification-dominantspec-v9 §B.1 context band