space pressure and infiltration
space pressure and infiltration
(OP)
if a conditioned space has positive pressure how much of door infiltration is applicable (1 story building with automatic door and no vestibule)
Initially looking at supply/exhaust
Process exhaust and Mua
Bathroom exhaust
Ventilation
space was slightly negitive . so i can introduce more mua through Rtu to make positive ( say 1000 cfm)
when i look at infiltration from an automatic door using ashrae eq Q= Ca*A*Rp the infiltration is about 2000 cfm
can i neglect the 2000 cfm since space is positive ?
Initially looking at supply/exhaust
Process exhaust and Mua
Bathroom exhaust
Ventilation
space was slightly negitive . so i can introduce more mua through Rtu to make positive ( say 1000 cfm)
when i look at infiltration from an automatic door using ashrae eq Q= Ca*A*Rp the infiltration is about 2000 cfm
can i neglect the 2000 cfm since space is positive ?





RE: space pressure and infiltration
An air curtain can mitigate a lot of what will sneak in. A vestibule or revolving door even better.
In my area, the folks in the small markets just have to dress warmly and wear double socks in the winter.
Here's another good paper for you to supplement the ones I posted in your other thread:
http://www.sciencedirect.com/science/article/pii/S...
If you're determined not to do any reading, just consider this: If you can maintain even a (very high) 0.10" WC positive pressure in your building, how much pressure will be exerted on the area of your door by a 20 mph breeze? I'll leave that calculation to you.
Best to you,
Goober Dave
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RE: space pressure and infiltration
don't quote me on the numbers, I'm too lazy to actually calculate it now.
RE: space pressure and infiltration
i see ashrae formula Ps=CpPv and Pv=rhoUh^2/2gc then Uh=Umet(delta met/Hmet)^alpha met(H/delta)^(a)
i'm having finding cofficients to plug in
i found another formula in(MODERN HVAC) Pw=0.000482Vw^2
Pw = VELOCITY PRESSURE HD in inwg
Vw= wind speed mph
for 20 mph = 0.1928 inwg
so, if space is at .1 in wg there will be infiltration with door openings
i looked at other posts on pressurization and found alot of opinions . someone said they they add extra supply at .5 cfm/sf to pressurize to 0.04in wg
i am working on hvac plan for 5000 sf (1) story market with two automatic doors
i calculated my heat and cooling loads and thought the infiltration rate from automatic door was too high . the heat load is getting to 60 btu/sf with refrigeration effect.
some other books use air change factors based on building tightness . that may be the result of study. i don't know how reliable it is
RE: space pressure and infiltration
RE: space pressure and infiltration
Best to you,
Goober Dave
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RE: space pressure and infiltration