Load Calculation

[wb]

Load Calculation Question.........

Observed a load calculation with software and it recommends a 1-ton system for a heat gain up to 15,000 btu's.

Recommends 1 1/2- ton system for heat gain up 21,000.

Why a 12,000 btu system for 15,000 Btu heat load?
Why a 18,000 btu system for 21,000 Btu heat load?
etc. etc.

Thanks for any feedback?

[md master]

Because you've done a load calc on a "peak degree day". Whatever that value is for your area (say 95*f), you'll actually see many more "normal" non-peak days (possibly 80*-85*),where that maximum value (load rating)is not needed, during those times a slightly smaller unit will cycle regularly and still have enough run time to effectively reduce indoor humidity. During those few "peak" days the unit will run longer, but the longer run times during hot whether are better for the equipment than short cycling terribly during "normal" ambient temperature ranges causing higher than normal indoor humidity. That's why it is better to slightly undersize than to oversize a unit.

[wb]

Thanks MD...........
Completely understood...