HVAC - Heating and Cooling System
Goal
- Provide enhanced temperature and humidity control while minimizing energy consumption.
How It's Done:
Oversizing A/C systems is a chronic problem throughout Texas. Most A/C systems are sized by rule-of-thumb based on the number of square feet in the house, usually about 1 ton of cooling for every 300-500ft2, often with an extra ton or two thrown in for good measure. The problem with this method is that every house is different. A house with low E windows, natural shading, a low rate of infiltration, and better insulation may require only 50% as much tonnage to cool as one without those features. More importantly, an oversized A/C system will not be as effective at removing humidity from the air, resulting in a less comfortable home.
Our 3073 ft 2 two story floor plan, if insulated in the traditional way with R13 fiberglass batts in the walls, and R30 blown fiberglass in the ceiling, called for 7 tons of total cooling (4 ton unit downstairs, 3 ton upstairs). By moving the thermal envelope boundary from the ceiling to the roof deck, and treating the attic as conditioned space, we eliminate the losses that are normally figured in due to leakage in the duct system. These losses can be anywhere from 10-30%.
We have also changed the summer time air temperature around the ductwork from as much as 150 degrees to 75-80 degrees. The A/C system simply does not have to work as hard. The result -- we installed a single 4 ton unit for the entire house. This was a 43% reduction in cooling tonnage over what would have been required for a fiberglass insulated house.
This Adobe PDF document contains the information necessary for your HVAC professional to properly size and design an HVAC system for a full Icynene envelope.
The Icynene Thermal Envelope is a design technique that uses Icynene spray-in-place, expanding foam insulation. Icynene insulation will be applied to all exterior walls and directly to the underside of the roof deck, creating a completely sealed, unvented, conditioned attic space. This is an extremely effective and energy efficient design that has successfully been used in thousands of residential and commercial projects all over the United States.
