Commercial Sizing for AC

fast5frog

Just curious guys I dont do much commercial work, if you size an area for a 5 ton unit, being a commercial application, someone told me you need to double that size to compensate for the room at capacity. Is this true or just one guys way of using his "general rule of thumb"?

S Ebels

No substitute for a heat gain calc................

In commercial you can run into loads that vary tremendously. Take a resturant with 10 customers in it at 10:30 AM and now figure the load when it's filled to capacity with 120 people and the buffet table loaded at 6:PM. Huge difference.

One of the first jobs I did when I apprenticed (with a guy that taught me a lot about what not to do) was a resturant. It was about 2,100 sq ft in the dining area and he said "7 tons 'll do it". I asked him how he arrived at that and he said 400 sq ft / ton of cooling for commercial plus some for the people. That was 10 years ago and despite the resturant owner adding an additional 3 tons of window shakers, the place is still an oven when it's full. My old boss found out that rules of thumb are not rules to live by. I found out that there is no better way to size any HVAC equipment than by doing a calc on the building. Don't shortcut this step. It'll bite you hard!

GMcD

What SEbels said plus

Sizing a restauramt AC system also has to acccount for how the make-up air for the kitchen exhaust gets heated and cooled too. If there is a separate MUA for the kitchen, no problem, ignore that, but you still need to size the AC system for the peak loads and have some way of controlling it for the 80% of the time the loads will be low-medium. Gotta do the basic building heating/cooling loads, plus people at 300 btuh a person, plus ventilation for those folks at 20 cfm per person adds up pretty quick, plus the increased latent loads due to the increased ambient humidity in the space too. With such high variation on "people loads" the mixing dampers should track from a CO2 sensor to minimize heating/cooling outdoor air during occupied periods. There is no rule of thumb for commercial spaces. The only rule of thumb is get a professional to do the calcs and system design.

fast5frog

Thanks

Thanks alot guys. I appreciate your input on this. I at least have a better understanding now. Thanks again!

Mike T., Swampeast MO

And in Retail

Make certain you include the lighting in your calculations! 1000s of watts are common when incandescent is used.