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re: r: r: we are looking for agents world wide
5 jul 2004
greetings andrea,

i suggest you ignore paul's angry outbursts. he doesn't own this group.

>...anyhow if someone except you may have some problems in dealing with
>air distribution and air diffusion , laminar and turbolent cross flows,
>and the fanger pmv or ppd can write me...i can reply and try to solve
>the problems...

that's generous and on-topic. i have a couple of questions:

1. if you put some water inside a perfectly-insulated cup, would it find
itself close to the dew point temp, as water evaporates from the surface
and water vapor molecules diffuse to the top of the cup, while the air
above the water acts as a good insulator (about r5 per inch for downward
heatflow)?

which water depth will keep it coolest in an r5 3" diameter x 6" tall cup?  
as we fill the cup, the air layer insulates less, but more water evaporates,
according to fick's law, because the concentration gradient increases as the
air layer thins, no?

2. ashrae-standard 55-2004 ("thermal environmental conditions for human
occupancy") defines two "comfort zones," winter (with a clo = 1 clothing
thermal resistance) and summer (clo = 0.5.) its basic program estimates
the predicted mean vote (pmv: +3 hot, +2 warm, +1 slightly warm, 0 neutral,
-1 slightly cool, -2 cool, and -3 cold) and the predicted percentage
dissatisfied (ppd) based on clothing, activity, metabolic rate, external
work, air temp, mean radiant temp, air velocity, and rh...

50 clo = 1'clothing insulation (clo)
60 met=1.1'metabolic rate (met)
70 wme=0'external work (met)
80 ta=19.6'air temp (c)
90 tr=19.6'mean radiant temp (c)
100 vel=.1'air velocity (m/s)
120 rh=86'relative humidity (%) make one of rh or pa non-zero...
130 pa=0'water vapor pressure
140 def fnps(t)=exp(16.6536-4030.183/(ta+235))'sat vapor pressure, kpa
150 if pa=0 then pa=rh*10*fnps(ta)'water vapor pressure, pa
160 icl=.155*clo'clothing resistance (m^2k/w)
170 m=met*58.15'metabolic rate (w/m^2)
180 w=wme*58.15'external work in (w/m^2)
190 mw=m-w'internal heat production
200 if icl<.078 then fcl=1+1.29*icl else fcl=1.05+.645*icl'clothing factor
210 hcf=12.1*sqr(vel)'forced convection conductance
220 taa=ta+273'air temp (k)
230 tra=tr+273'mean radiant temp (k)
250 tcla=taa+(35.5-ta)/(3.5*(6.45*icl+.1))'est clothing temp
260 p1=icl*fcl:p2=p1*3.96:p3=p1*100:p4=p1*taa'intermediate values
300 p5=308.7-.028*mw+p2*(tra/100)^4
310 xn=tcla/100
320 xf=xn
330 n=0'number of iterations
340 eps=.00015'stop iteration when met
350 xf=(xf+xn)/2'natural convection conductance
360 hcn=2.38*abs(100*xf-taa)^.25
370 if hcf>hcn then hc=hcf else hc=hcn
380 xn=(p5+p4*hc-p2*xf^4)/(100+p3*hc)

what's going on in lines 350-380?

390 n=n+1
400 if n>150 goto 550
410 if abs(xn-xf)>eps goto 350
420 tcl=100*xn-273'clothing surface temp (c)
440 hl1=.00305*(5733-6.99*mw-pa)'heat loss diff through skin
450 if mw>58.15 then hl2=.42*(mw-58.15) else hl2=0'heat loss by sweating
460 hl3=.000017*m*(5867-pa)'latent respiration heat loss
470 hl4=.0014*m*(34-ta)'dry respiration heat loss
480 hl5=3.96*fcl*(xn^4-(tra/100)^4)'heat loss by radiation
490 hl6=fcl*hc*(tcl-ta)'heat loss by convection
510 ts=.303*exp(-.036*m)+.028'thermal sensation transfer coefficient

why does line 510 use m instead of mw?

520 pmv=ts*(mw-hl1-hl2-hl3-hl4-hl5-hl6)'predicted mean vote

what's going on in line 520?

530 ppd=100-95*exp(-.03353*pmv^4-.2179*pmv^2)'predicted % dissatisfied
540 goto 580
550 pmv=99999!:ppd=100
580 print ta,rh,clo,pmv,ppd

t (c)   rh   clo   pmv            ppd

19.6    86   1     -.4778556      9.769089
23.9    66   1      .4732535      9.676994
25.7    15   1      .5239881      10.74283
21.2    20   1     -.4779105      9.770202
23.6    67   .5    -.4747404      9.706658
26.8    56   .5     .5145492      10.53611
27.9    13   .5     .5003051      10.23146
24.7    16   .5    -.4883473      9.982468

the first 4 lines are the winter comfort zone corners.
the second 4 lines are the summer comfort zone corners.

nick




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