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airhandler (Mechanical)
19 Jan 04 8:58
I have a project where I need to heat a single story enclosed parking garage below an upscale apartment building. I plan on using a roof mounted, utility set fan to meet the 1.5 cfm/ft2 of exhaust per 2000 IMC. This results in approximately 25,000 cfm of exhaust air. Question: Should I heat the make-up air with an air handler(s) or draw untreated air through louvers and mount unit heaters throughout the garage? What arrangement is typical for a heated parking garage?
wilg (Mechanical)
19 Jan 04 10:11
It depends on many variables,
 Initial cost vs operating costs,
 Architectual Geometric building constriants for
equipment, louvers, ductwork, ect.
Proper air distribution.
Maintenance considerations :
accessability to equipment, will the building have it's own
maintenance crew or depend on out sourcing.
Availability of utilities hot water, steam or are you planning on using electric unit heaters ?,
 Energy costs vs return on investment.
  Location of building...geographical environmenatal ambient  
conditions...( for building thermal storage) are we talking about
 a parking garage in Atlanta, Ga, or Bismark North Dakota ?
 You will end up with a lot of subjective answers instead of logical ones without detailed information.
stevenw (Mechanical)
19 Jan 04 10:28
The make-up air unit could cause pressurization problems if the exhaust fan is not balanced.
The units heaters sould not caused pressurizarion problems because they are inside the space just heating the air.
Accystan (Mechanical)
19 Jan 04 11:25
Depending upon the Code in your neck of the woods unit heaters and exhaust fan/s (and intake dampers) controlled by CO sensors may be the best way to go. Certainly the cheapest first cost, especially on gas. You then have the option of heating when the exhaust fan is off. Sorry I'm not familiar with the phrase, "2000 IMC". Is that your local/governing code. Does it require 1.5 cfm/ft^2 continuously? Some areas permit the exhaust fans to be automatically controlled (cycled) i.e. by CO sensors. I'm a bit out of touch with the latest detector technology but my recollection is that CO detectors do not respond well to diesel exhaust - you could check if there's an expectation of much diesel traffic in the parkade. You also may require the sensors to respond to propane or gasoline fumes from leaks.
ChasBean1 (Mechanical)
19 Jan 04 12:26
I would say take your pick. Heating the make-up air will probably be more uniformly comfortable in the garage in the end. Maintaining some average temp. (say 60°F) with either system should be comparable in energy use.
airhandler (Mechanical)
19 Jan 04 13:15
Thanks for the posts. Let me describe my building a little better.  The building is an upscale, 4 story wood frame condominium in New Jesey that the owner is marketing with 60F heated garage. There is little or no room to run ducts vertically within the building.  I will have to use areaways with grating to introduce the supply air. My concern is that several cars will be parked directly in front of the louvers where 10F air will freeze some persons Lexus.  I do not want the complaints of cold air rushing in. Does anyone have any high rise design experience where underground parking is common? Unfortunately I don't have any. I do not want to reinvent the wheel with this project. thanks.
Helpful Member!  khatra (Mechanical)
19 Jan 04 21:00
I would use combination: make up air handler to temper supply air (may be set for 60 F) and  exhaust fan for air pressure control.
Also I will provide CO detection system for automatic ventilation control.  

Under normal mode: Outside air for ventilation can be reduced to .75cfm/SF and under emergency mode outside air could be even graeter that 1.5 cfm/ SF.

Outside air for Make up air unit can be controlled throgh VFD or combination of outside and return damoer.   

1969grad (Mechanical)
19 Jan 04 23:52
Have you considered radiant heaters?

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