Adoption of new energy efficiency codes have moved the industry toward the construction of super-insulated homes. In theory this should mean that a super-insulated home should require a smaller air conditioning unit when compared to a home of equivalent size that is not super-insulted. Right? Well, the answer is – maybe.
Industry air conditioning equipment selection follow the same basic principle as selecting a kitchen appliance. If a 750 watt microwave oven is just just a little too small for you, well, there’s not an 800 watt microwave oven on the shelf, available for purchase. You have no choice but to purchase that slightly over sized 1000 watt microwave oven to meet your needs, because that’s the way manufacturing of equipment is standardized – in incremental sizes. Matching air conditioning equipment for your needs, works very much the same way. But you need to match both your home’s cooling & heating capacity as well as air flow needs, and that can get tricky. A super-insulated home will have a reduced cooling and heating capacity requirement, but in many instances, not a proportionally reduced air flow requirement. Higher air flow circulation may still be needed to prevent “hot spots” or stratification of air from occurring, particularly in vaulted or high ceiling areas. Proper air flow then, in most homes, is primarily a function of the geometry or volume of the conditioned space, more so than the insulation properties of the home. Unfortunately, Florida energy compliance software (ACCA manual J) used for sizing a/c, will adequately size the cooling and heating capacity needed for your home, but is not intuitive in sizing the proper amount of air flow needed. To complicate matters further, once again, a/c air handlers, come in standard sizes like microwave ovens. So if you choose one with a smaller cooling & heating coil, your going to get a smaller supply fan in the unit too. There’s no choice in the matter because of ‘the law of incremental size manufacturing’. So be careful that your energy rater or equipment sizing guru knows what they’re doing and doesn’t overlook the required amount of air distribution in your home just because the Florida energy compliance software says that the home has ‘Passed’. Up-size the a/c unit to get the right size supply fan, if necessary, to ensure your home gets both adequate coil capacity and sufficient air flow from the unit.