Calculating infiltration through open external doors

[Netter1]

I could sure do with some help here.
I am a little fish in this big pond, so if you can go into detail that would be greatly appreciated.
Anyway, here is my problem...
I often deal with HVAC designs on commercial building that quite often have a Lobby. Well, here is the deal. We often take a guess and hope for the best, but on a recent job we had this guessing process bite us on the butt. We under specified a unit and we now need to put in a larger unit to deal with a door that is constantly opening.
Is there a simple way to calculate infiltration on a Lobby door? I have spent a couple of hours searching the net now and have come up with nothing! All they talk about is cracks around windows and doors. We could really do with some help on this.
Thanks in advance...

 

[quark]

Dehumidification Handbook by Munters suggests 50fpm inward flow(backed by experimental data) through the opening area eventhough you may have positive pressure in the room. You can do moisture and heat load calculations based on this figure.

PS: Don't be too generous in assuming no. of door openings and the duration of each opening.

Regards,


Believe it or not : A cobweb with it's strands a pencil width, can catch hold of a concord. All questions directed to Discovery Channel.

 

[Netter1]

Hi Quark,
I sure do appreciate your reply! I am a little embarrassed to say this though, but could you explain in a little more simplier way. I am quite new to this profession and boy do I have a lot to learn.
For example, is that 50 fpm multiplied by the door area? How do I get an answer in btuh for cold and heat requirements to compensate? On a previous job, we specified a unit and didn't allow for a door in a Lobby that is constantly opening and closing. In Summer, we are constantly loosing all our cooling out the door.
Thanks again,

 

[quark]

50fpm x Door opening area x no. of door openings over the working period x duration for which door is opened each time(in minutes). So you get total volume of infiltration. Distribute it over the working period and you will get volume flow rate. You know the conditions of ambient air and conditioned. Do the enthalpy balance as you do generally. That is all.

Regards,



Believe it or not : A cobweb with it's strands a pencil width, can catch hold of a concord. All questions directed to Discovery Channel.

 

[Netter1]

Thanks again Quark...
Do you know how to convert that into btuh?

 

[quark]

Sensible heat load Q (btu/hr) = 1.08 x cfm x (DB temp. of ambient air - DB temp. of conditioned air)

Total load Q (btu/hr) = 4.5 x cfm x (enthalpy of ambient air(btu/lb) - enthalpy of conditioned air(btu/lb))

Regards,


Believe it or not : A cobweb with it's strands a pencil width, can catch hold of a concord. All questions directed to Discovery Channel.

 

[Netter1]

Hi again Quark,
I again want to say thanks for all your help with this.
I did a fair amount of searching and just couldn't find anything on it. Maybe this is because I am not 100% sure of what I am looking for??
I have a long way to go heh?
Just for curiosity, what do you think of air curtains? I have seen them used and believe they are effective. What do you think? Do you think they are worth the initial expence of supplying and installing?