Ted Cushman

High-performance buildings present a special problem to HVAC designers—not because the numbers are big, but because they’re small. In a superinsulated home with very low heat gain or heat loss, it can be a finicky puzzle to match the equipment to the loads. Too much capacity, and systems won’t run efficiently; too little capacity, and rooms may be too hot or too cold. Too much or too little dehumidification, and rooms could be over-dry, or damp and clammy, even when the room temperature is on the money. The balancing act is trickiest in the “swing” or “shoulder” seasons of spring and fall, when calls for heating or cooling are small and intermittent, but the house still needs continual fresh air.

Airtight and superinsulated buildings, of course, require mechanical ventilation. In warm climates, the humidity brought in by the code-required in-flows of fresh air can apply a “latent load” that challenges air conditioners—a load that looms relatively larger in the calculations for a building with superinsulated walls and roof, advanced...

or Register to continue reading