Manufacturers of these systems claim that dehumidification with high-velocity air distribution is better than with conventional forced-air systems. In the air conditioning season, lower humidity levels can allow occupants to feel comfortable with the thermostat set at higher temperature, resulting in reduced energy costs. In both heating and cooling seasons, delivering air at higher velocity through smaller supply lines mixes the room air more effectively, reducing temperature stratification, and eliminating the need to place duct outlets at windows or exterior walls to avoid hot/cold spots. However, these systems commonly require a greater number of outlets—about five outlets per ton of cooling, or one outlet for every 2,400 BTUs of heating—adding to material costs and installation time.
High velocity also probably means more fan HP and possible noise. DO NOT RUN AIR faster than 550 fpm across cooling coil or you will get moisture blow through into the ductwork. I would not use high velocity unless owner demanded it and signed a waiver.
Am I missing something here?
I thought the so called high velocity systems were simply done by increasing the static pressure in the duct to get more velocity only at the outlet nozzles.
Not by running the velocity up over the fan coils.
B.E.
These "high velocity" systems consist of a packaged air unit with a refrigerant section and cooling coil designed for low temperature air - typically 45F to 50F supply air temperature, hence the claims of the ability to lower the humidity in the home. The lower supply air temperatures also mean that they need to use the jet-type nozzle air supply terminals to mix and diffuse the colder supply air to avoid cool/cold drafts and insure full room air mixing. So the system works by using lower total air circulation volumes of lower temperature supply air with higher duct static/friction to accomplish the same thing that a standard air conditioning coil add-on to a gas fired furnace system does. Fan motor Hp would likely be higher in the high velocity system, even with the lower volume of supply air, and account for the additional energy consumed by the lower temperature cooling system. An astute designer will look at the "total package" energy and performance criteria to make a proper evaluation. Criteria like smaller ducts play into it, but more insulation on the ducts required due to lower SAT's.
