Installing High-Velocity HVAC

Continuously blowing outlets provide heating and cooling and can be installed high or low on the wall, as well as in the ceiling or floor.

Placement isn't as important as providing an accurate number of outlets per room and avoiding blockage.

The outlet grid design imposes laminar air flow, correcting noisy vents.

The system's air handler, or blower unit, can be installed in a horizontal, hi-boy, or counterflow attitude and located to maximize usable floor space. A conventional system isn't as lenient in its placement.

An operating temperature of 120° to 140°F permits use of a standard water heater to supply the fancoil unit. Slower passage of air over a larger than conventional coil surface enables higher coil-to-air heat transfer. Because of the lower temperatures, all ductwork must be completely insulated to retain operating efficiency.

A single-diameter, minimally sized plenum stores and distributes pressurized air to the branch ducts at an equal rate. A conventional system relies on progressive step-downs in the size of the main trunk to maintain a relatively equal volume of airflow at each vent, making installation far more labor intensive.

Airtight ductwork is absolutely essential to the function of a high-velocity system. The author seals every joint in the ductwork with a clear, SMACNA-rated tape. Careful and attentive application ensures an airtight joint and makes leak testing unnecessary.

Branch ducts must be no shorter than 10 feet long and no longer than 25 feet. The flexi-duct can be coiled back upon itself to provide the minimum duct length, with no reduction in performance.

The author uses a standard blast gate to regulate fresh, outdoor makeup air entering the return plenum at a rate of about 10% of the total volume. Return air is drawn through a HEPA filter and conditioned before being returned to the living space.

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