Alexander Bell , who goes by Andy, is our design wizard, and I've been getting involved with the process again lately. When I talk to potential clients, a lot of them tell me their contractor wants to size their air conditioner using a rule of thumb. The rule is usually something like this: Install one ton of air conditioning capacity for every or square feet of conditioned floor area. How far off are they? Let's take a look.
HVAC: Equations, Data, and Rules of Thumb, Second Edition
Hvac Design Thumb Rules | Air Conditioning | Hvac
For instance, instead of a proper duct underneath the furnace, it consisted of some sheet metal and cardboard in the dirt beneath the garage pad, the plenum was a swiss cheese of holes with miles of bent flex duct, a duct off the end of the trunk, a supply takeoff facing into the blower, leaks you couldn't believe and improper sealing, insulation and hangers to name a few. I had to remove it all anyway since the plumbing wasn't much better and the so-called supply system was in the way. Fast forward to this past month, I have just completed the new supply side ducting and now need to fix the return side. The return system was not much better. They had chopped two large rafter bays open in the ceiling of an end room and had a small return on the second floor inside a bedroom. I extended and enlarged as much as I could the second floor return to the hall 6 supply vents on second floor so some air will be returned down the stairwell.
Air Conditioner Sizing Rules of Thumb Must Die
Bell Jr. The heating, ventilation, and air conditioning HVAC equations, data, rules of thumb, and other information contained within this reference manual were assembled to aid the beginning engineer and designer in the design of HVAC systems. In addition, the experienced engineer or designer may find this manual useful as a quick design reference guide and teaching tool.
The figures above indicative only. It is recommended to always generate a detailed heating and cooling load calculation such as using Manual J for the building or space in question. Room air conditioner - Capacity ranges 0.