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HVAC Resources for Professionals  

HVAC Charts

Idea!... print out and laminate two charts back to back for toolbag durability.

Charging and Temperature Difference Charts

Charging and Temperature Difference Chart 1


Charging and Temperature Difference Chart 2

Along with superheat and condenser temperatures, this chart allows you to check the evaporator airflow from the entering wetbulb temperature. Open Chart 1


Like the chart to the left, but allows you to determine the evaporator delta T range from the relative humidity. Open Chart 2


Other Charts

Superheat Graph

A superheat chart in graphical form. Open Chart 3   Rules and Rules of Thumb for heat pump duct systems. Updated for 4% flex duct compression!
Open Chart 4

Although the Manual D procedure all but guarantees a duct system that will provide each room with the correct amount of air comfortably, quietly and at a low energy cost, it's often not done. More common is the "rules of thumb" and "trial and error" method.

With a variable speed blower, the rules of thumb guide (above right) should at least allow 400 cfm/ton across the coil . Do not rely on this guide to provide rated performance, efficiency or comfort throughout the home. Without some luck, open floor plans, open doors, and a lot of practical experience with trial and error, it's not likely to happen. The assured method is to follow the manuals, measure and calculate everything and assume nothing. Incorporate transfer grilles and dampers for air balancing where necessary.

An often over looked aspect of duct design, epesially with air handling unit supply plenums, is the System Effect and Static Regain. This article from ACHR News Extra Edition is reccomened reading.
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