Geothermal and standard HVAC equipment distribute air through out a home by a system called "duct work". When the system is properly designed, air distribution is even and a uniform temperature is maintained. The efficiency of duct work systems has been found to be as much as 60% less than it could be in most homes. Comfortworks proper duct design and installation allows for correct sizing of systems, and increased savings.
Leaking ducts cause increased utility bills and reduces the equipment's capable capacity. Homes with unbalanced air temperatures may be caused from poorly sealed ducts. Duct leakage also contributes to increased humidity, dirty air coils, and contaminants that may enter the air stream of the living space.
Ductwork can also be oversized or undersized. Oversized ducts can cause low air flow, reduced equipment efficiency, and uneven air temperature throughout the home. Undersized ducts may lead to low air flow, increased air noises, and reduced efficiency.
The objectives of good duct work design lead to each room receiving supply conditioned air, sized for the correct pressure drop across the equipment's air coil, sealed to provide maximum air flow and stop leakage, have a balanced return and supply to reduce air noise, and reduce losses by temperature gain from surrounding conditions (high attic temperatures).
Trunk and Branch Duct System
This system is made up of a large main supply trunk that is connected to the equipment and is constructed with rectangular metal ducting. The smaller branch runs are connected to the main trunk supply and are constructed with either metal round ducting or flex ducting.
The trunk is reduced in size as the branch runs are connected. This accommodates the loss of air volume, air velocity and pressure. Additionally, volume air dampers are installed on all the smaller branch runs from the trunk duct. These are used in balancing the air for the home rather than using the registers damper, which creates excessive air noise in the room.
A trunk and branch system creates a back pressure in the main trunk that allows air flow to distribute evenly through the smaller branch runs. This type of duct system is highly recommended for its performance and efficiency.
Radial Duct System
A radial duct system is a variation of the trunk and branch system and is by far the most common type of duct system installed by heat and air dealers. A large supply box plenum connects directly to the equipment and is constructed of rectangular metal. This supply plenum is used to connect large supply duct runs that run to the homes registers and is typically constructed with flex duct. The large supply ducts reduce in size as they connect to the homes registers and utilize wyes in the system to branch off to room registers.
Return Air Systems
Multiple room return air is the ultimate return duct system. This system ensures air flow is returned from all rooms even when the door is closed.
Central return air is the most common system used in homes, but is not necessarily the best. It is a system that consists of one or more large grilles located in central areas of the house and often close to the equipment. Undercutting of doors on rooms that can be closed off has been normal, but this is usually not a sufficient amount of clearance. Using transfer grills or jump ducts can avoid this problem.
The return duct removes air from the room and delivers it back to the equipment for filtering and reconditioning. Two return air systems are generally used in residences, central return air, and multiple room return air.
Location of Ductwork
Ducts are recommended to be located within conditioned spaces, a furred down chase, between floors of a two-story home, or in a encapsulated attic. Any duct losses will return to inside the house envelope and allows for reduced sizing of the equipment and lower operating costs.
Supply registers should be located so the ceiling diffuser discharges the air parallel to the ceiling. Using an adjustable register with curved or angled blades is preferred. These types avoid the air flow stream from blowing directly on occupants.
The location of the return air has only a secondary effect on air motion in the room. The location can improve stratification and mixing of room air. Returns are always best located high in the rooms. This is true if the duct system is located overhead or from the floor. Locating a return high will draw the heat off the top of the room and provide excellent stratification of the air.