High velocity cooling systems work the same as low velocity systems except they differ in the size of ducts, fan speeds and location of fan. One of the reasons why these systems cost more than most systems is installation.
Due to the duct design and fan speed, pressure and the velocity of the air mandate the ducts be sealed. One of the unique aspects of these systems is the supply ducts are usually only 3 inches in diameter. They can easily be slid down a wall cavity. Another one is due to the velocity of the air in the ducts; mufflers are installed just prior to the diffusers.
These systems work very well and are ideal in retrofits. The only real disadvantage to these systems are the cost and they are noticeable when they go on and off. If you home have steam, electric baseboard or hot water as your heating system and you wish to have central air conditioning installed in your home, you have several options.
This actually depends upon the type of home you have. These by the way are my recommendations. Even if you had a forced hot air heating system, I would recommend a separate cooling system. The reason for this is explained in Combination topic. If you have a single story home like a ranch or split-level with a full unfinished attic, the best choice here would be a low velocity cooling system.
If you have a two-story home with an unfinished attic, your choices are window/wall units, ductless split, low velocity and high velocity. High velocity is probably the best choice with a two-story ho
me with an unfinished attic. The way this system would be installed is by putting the air handler in the attic. If at all possible put it on the second floor and suspend it from the ceiling either in a closet or laundry room. A duct will attach at each end of the air handler usually about 18 inches in diameter. The supply main duct is usually laid in the attic along one side of it. Off the main duct come feed ducts to each room.
This feed duct is usually three inches in diameter. At the end of this duct just before the diffuser a muffler is installed to eliminate any noise that may be created from the velocity of the air.
The diffusers are usually no more than six inches in diameter and are not noticeable. The return ducting system does not necessarily have to be in each room. Most installations will use a single return located strategically in the ceiling of the upstairs hallway. This is based on the premise that hot air rises and you can take in more air through a duct than you can put through it.
The best way to illustrate this to you is drinking soda through a straw. If you were to take the soda into your mouth through the straw, you would see it is done easily and quickly. If you were to then try to push the soda in your mouth through the straw it would be difficult and slow. Another aspect of this is, if you made the container of the soda air tight except for the straw and attempted to draw soda from it, it would be very difficult if not impossible. It is not necessary for you to know the physics of pressurizing and depressurizing areas and its tendency to equalize but you do have to have an understanding of it. For this applies to all forced air systems.
Ideally a supply and return should be located in each room. In actual application, this is never done. The reasons for this are practicality and cost. In the case where several rooms are located and there are no doors that can impede the airflow, like the kitchen, family, living and dining rooms.
If a single return located in one of the rooms, the warm air at the ceiling would move easily to the return. This is not only practical but cost effective. On the other hand take a bedroom with the return located in the hallway that serves all the bedrooms. When the bedroom door is closed it impedes the flow of warm air to the return from that bedroom.
Hence it prohibits the amount of cool air that comes out of the supply. In other words you cannot blow air into a room without taking out the same volume of air. There are several options to correct this. Leave the bedroom doors open, put vents on the walls near the ceiling in the hallway for every bedroom or put a return in every bedroom.
What most people misunderstand is that the return system is a very important part of your distribution system. In other words the location of the returns and the configuration of your home determines the distribution of cooling in every room. Though you may be able to cool the entire home with the single return, the difference is how well it does it and how much it will cost to do it.