Low Velocity Cooling Systems
Low velocity cooling systems are the most common because they are easy to install and are quiet. These use a return and supply ducting distribution system and are usually located in attics. All the registers supply and return, are located in or near the ceilings of the home.
The way these systems work is the warmest air in the home is located at the ceilings where the registers are and the return register takes this air into the system. It is cleaned first through the use of a filter. The primary purpose of the filter is the fan and/or cooling coil were to get dirty, you would have problems with the unit.
Once this is done the warm air is then blown over a cooling coil where the heat is extracted from the air. Then the cooler air is distributed through the home via the supply ducts. Because hot air rises and cool airdrops, couple with the fact the registers location in the ceiling, the fan for these systems are usually 2,000 to 3,000 CFM.
The results are quietness and an unawareness when these systems go on and off. On top of all that, they cool the home extremely well. This system has a flawless design; it is the installation that has concerns. Attics can reach temperatures above 135 degrees F. and though these air handlers are insulated, that attic temperature will have an adverse affect on your cooling cost. The best location for the air handler is to suspend it from the ceiling inside the home in a closet or laundry room and feed the return and supply ducts into the attic. The next concern is leaky ductwork.
If flexible ductwork is used, without question, your ducts are leaky. After inspecting well over 10,000 homes with this type of system, not one was ever found not to be leaky. Some of the places you will find leaks are; the access panel for air handler, after a few times of opening and closing the weather stripping wears off, access ports for wires and hoses on air handler, they are poorly sealed or not at all. Others are the return and supply plenums, all couplings, flexible ducts attached to couplings and more. An example of duct sealing cooling systems is to remove the flexible duct from the main trunk.
The coupling will be exposed. Where the coupling joins with the trunk, take mastic with a putty knife and seal where the two meet. Then take the flexible duct and pull back the insulation exposing the duct. Slip the duct onto the coupling making sure it is kept one inch away from the trunk. Then take a strap clamp and secure the flexible duct to the coupling. Where you left that one inch gap between the duct and trunk, take a piece of saran wrap and wrap it around the flexible duct and coupling. Tape over that and slide the insulation up until it is snug against the trunk. Tape the insulation to the trunk and that joint is sealed.
This system must be sealed during the winter. The best way to do so is to take down the registers. Take a plastic bag and crumple some newspaper in it so the bag is fluffy. Stuff the bag into the duct and take a piece of saran wrap to cover the opening and then reinstall the register. If your return register has a filter in it, take it out and wrap it in a plastic bag and reinsert. If you do not do this, warm air will enter the system during the winter and condense. It will also lower your fuel bills if you seal the system during the winter.