ACCA Manual D
Verifying ACCA Manual D Procedures
Why are duct design calculations important?
Achieving occupant satisfaction is the principal goal of any HVAC design. For residential air duct designs ACCA’s Manual D is the procedure recognized by the American National Standards Institute (ANSI) and is specifically required by residential building codes. Air is the first work in air conditioning. If the network of ducts carrying the air is not properly designed then the health and safety of the occupant are at risk, the equipment could fail more quickly, the energy costs could rise, and occupant comfort might be
sacrificed.
What problems come from wrong sized ducts?
In order for home owners to be comfortable a duct system must be designed to carry the right amount of air at the right speed, into the right room. If the ducts are the wrong size then the wrong amount of air will enter the room and may cause:
- The room to be too warm or too cool
- The air to be too drafty
- The air to be too noisy
- The air to be too slow. This will affect comfort
- The fan to work harder, possibly fail sooner
- Pressure differentials in rooms can reduce comfort and increase energy costs.
ACCA’s Manual D Residential Duct Design Checklist
Key Items:
Information from load calculation
- CFM for each room: Does each room have a heating and cooling CFM assigned proportioned air based on Manual J8 room by room load calculations?
Manufacturer’s data:
- Total external static pressure and accessory pressure losses. Did the contractor submit this data?
Manual D friction worksheet
- Available static pressure (ASP): Are the outlets, return grills listed at standard .03”
- Total Effective Length (TEL): Did the contractor calculate the TEL correctly?
- Friction Rate design value: Did the contractor use the correct friction rate calculator?
Air distribution system design
- Branch lead size
- Trunk size
- Return trunk duct velocities
- Return air path
Manual T
- Register and grille face velocities are correct.
- Are the registers and grills in the correct location
Example Drawing
