ASHRAE-Standard-55 - Page 028

Extracted Content

(This is a normative appendix and is part of this standard.)

NORMATIVE APPENDIX B COMPUTER PROGRAM FOR CALCULATION OF PREDICTED MEAN VOTE (PMV)

The following code is one implementation of the PMV calculation using JavaScript in SI units. This calculation does not include discomfort risk due to local discomfort factors. The input variable “clo” in the PMV function shall be calculated using the following equation:

clo = Icl × (0.6 + 0.4/ M ) for M  1.2

clo = Icl for M < 1.2

where M is the metabolic rate in met units and Icl is the clothing insulation.

The input variable Vel in the PMV function is the sum of the average air speed ( V ) plus the activitygenerated air speed ( Vag ) caused by motion of individual body parts (m/s). It is a function of metabolic rate and is added to the average air speed to determine convective cooling of the body. Vag is assumed to be 0 for metabolic rates equal and lower than 1 met and otherwise equal to

for M - 1 met.

pmv = function(ta, tr, vel, rh, met, clo, wme) { /*

returns [pmv, ppd] ta, air temperature (°C) tr, mean radiant temperature (°C) vel, average air speed (Va)+ activity-generated air speed (Vag)(m/s) rh, relative humidity (%) Used only this way to input humidity level met, metabolic rate (met) clo, clothing (clo) wme, external work, normally around 0 (met) */ var pa, icl, m, w, mw, fcl, hcf, taa, tra, tcla, p1, p2, p3, p4, p5, xn, xf, eps, hcn, hc, tcl, hl1, hl2, hl3, hl4, hl5, hl6, ts, pmv, ppd, n;

pa = rh * 10 * exp(16.6536 – 4030.183 / (ta + 235)); icl = 0.155 * clo; //Thermal insulation of the clothing in M2K/W m = met * 58.15; //Metabolic rate in W/M2 w = wme * 58.15; //External work in W/M2 mw = m – w; //Internal heat production in the human body

if (icl <= 0.078) fcl = 1 + (1.29 * icl); else fcl = 1.05 + (0.645 * icl);

//Heat transf. coeff. by forced convection hcf = 12.1 * sqrt(vel); taa = ta + 273; tra = tr + 273; tcla = taa + (35.5 – ta) / (3.5 * icl + 0.1); p1 = icl * fcl; p2 = p1 * 3.96; p3 = p1 * 100; p4 = p1 * taa; p5 = 308.7 – 0.028 * mw + p2 * pow(tra / 100, 4); xn = tcla / 100; xf = tcla / 50; eps = 0.00015; n = 0;

while (abs(xn – xf) > eps) {

xf = (xf + xn) / 2;

26 ANSI/ASHRAE Standard 55-2023