auditorium load calc

[swoosh172]

I have an auditorium with 20 foot ceilings and exterior walls. I can run the ductwork in the walls and have the supply and return diffusers located in the walls. Should I model the room as only having 10 foot walls, approximate occupied area, or should I model the full 20 foot walls and place the diffusers 10 feet above the floor since I don't really care about the temperature above the occupied floor level. If I model the full 20 feet I am worried that the cfm's will be way oversized.

 

[DrRTU]

The people load and OA numbers that will drive the load. Run the load with the larger walls and note the wall gain as a percent to the total load. I bet the walls will be a small percent of the total. You can ratio the output (big wall vs. small wall) it's only a sensible gain. I would review the load at various people quantities on your design day. 10% people quantity on a less than design day will drive the RH up from an oversized system.

 

[GMcD]

It'll also depend on the air delivery configuration - low level displacement ventilation supplied in the seat steps can allow discounting a significant % of the people cooling load, and discount all of the lighting, as a lot of the heat gain goes into the high level extracted air. The air unit cooling coil will still see a lot of that load, but you'll find that there is a big reduction in the overall amount of air required for cooling in a DV system vs a fully mixed air system (overhead supply air for cooling).

 

[Waramanga]

I agree with GMcD, if you are pushing heaps of air around the room (rather than low level low velocity) then you will need to model the whole room, but you can rely on a degree of stratification. My apologies, I have no idea how you would quantify this! If you have a transient loading (i guess you do, auditorium) then you have to look out for the thermal lag in the volume of air. I have done some calcs for similar halls and cold start up with such a large mass of air inside the building keeping the reaction time of the system down. I have sized most systems for these jobs based on recovery time rather than fabric losses, which are usually pretty small (no glass!!!)

 

[swoosh172]

Let's say it's not an auditorium but a large 2 story entrance atrium and people will just be walking through it so really no outside air load is required. Would I then just try to condition the first 10 feet or so and not even model the upper 10 feet, since this is the only area where people will notice the temperature? We have a local mall here that has a large 2 story glass atrium and skylight, but all the HVAC diffusers are down low near the occupied space which seems to tell me that they aren't conditioning the air above.

 

[imok2]

A lot of information can be had at this web site:

http://www.ishrae.in/journals/2003jan/article01.html

 

[sridhar1312]

For any auditorium the refrigeration load is calculated based on Fresh air per person and air distribution ideally is through side wall grills at 8 feet from the seating or 10 feet with zero degree deflection for grill so that it will reach the far end of the hall .
it is better supply is staggerd on both sides for good air distribution.
Height above 10 feet is of no concern but it will be at room temperature or return air temperature.