Air Conditioning Installation
The successful installation of a new or upgraded residential air conditioning system requires careful attention to three critical factors: your home’s cooling requirements, the design of the ductwork system, and the proper selection of equipment. In the HVAC industry, there are three authoritative reference works that provide the technical guidance and procedures for addressing these factors. Installation professionals and HVAC experts should use the Air Conditioning Contractors of America (ACCA) Manual J and Manual D, along with Manual S, to achieve the most effective and most efficient air conditioning installation possible.
Manual J Load Calculations
ACCA’s Manual J is the first step in the design process of a new HVAC system. By following the Manual J methodology, HVAC designers are able to accurately determine the total amount of heat that is lost through the exterior of a home during the cooler months, and the total amount of heat that is gained through the exterior of a home during the warmer months. Through a complex series of calculations and inputs, the HVAC designer is able to analyze all aspects of thermal characteristics of every wall, floor, ceiling, door and window. In addition, an HVAC load calculation also takes into consideration other factors such as the home’s geographic location, orientation to the sun, envelope tightness, duct leakage, lights and appliances. ACCA’s Manual J even calculates the amount of heat and humidity that each occupant of the house will add to the interior of the home.
There are two types of Manual J load calculations:
- Whole House (Block) HVAC Load Calculations
- Whole House or Block HVAC Load Calculations provide the heating and cooling loads for the entire home. This type of load calculation is used when there is no need to design or modify an existing duct system. Whole house load calculations are commonly used to determine the correct HVAC equipment size and match-up that is required when replacing the HVAC system in an existing home.
- Room-by-Room Load Calculations
- Room-by-Room Load Calculations provide the heating and cooling loads for each individual room within the home. In addition to the information produced by a block load calculation, the Room-by-Room method also determines the amount of air that is required to heat and cool each individual room. This information is critical when determining the individual duct sizes as well as the size and overall layout of the duct system.
Manual S Equipment Selections
Once a Manual J HVAC load calculation has been completed, the HVAC designer will have the fundamental information required to accurately select the proper HVAC equipment based not its size, but on other performance traits such as the equipment’s total capacity to remove heat and moisture from the air as well as how much total air, and at what pressure, the system can produce. This is important to note because one 3 ton HVAC system can perform significantly different than another 3 ton HVAC system.
Manual D Duct Designs
Manual D is the ACCA method used to determine the overall duct lay-out including the individual duct sizes. To design a duct system, the HVAC system designer must have completed a Room-by-Room Manual J load calculation as well as a Manual S equipment selection. All to often, duct systems are created using rule-of-thumb methods in lieu of using Manual J, Manual S and Manual D. This practice is the predominant reason for complaints of temperature differentials throughout a home as well as complaints of excessive noise caused by air velocity that exceeds the maximum allowed by Manual D.