Short #2 - Delta T - HVAC School

Short #2 – Delta T

March 7, 2018

Delta T (Evaporator air temperature split) what it is, what it means and how to avoid some common pitfalls

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this short Q&A podcast, Bryan answers a listener-submitted question about apps for doing proper loads. Fred specifically asks about apps or charts that can help an HVAC contractor determine the insulation value of a home without assuming numbers or drilling into walls during load calculations.

Load calculations account for all the ways that BTUs can enter or leave a home: conduction, convection, and radiation. Insulation prevents heat transfer via conduction, so it’s important to the load calculation process. High-end HVAC design software like Wrightsoft and Kwik Model 3D will have these features built into them (based on the age and location of the home). ASHRAE’s handbook also has tables and data with R-values and U-factors to help you out with Manual J load calculations.

RED Calc is an app that allows you to calculate a wall’s R-value with measurements, including surface and air temperatures indoors and outdoors. This RED Calc software is available through the U.S. Department of Energy, as is REScheck. The DOE insulation fact sheet is also quite valuable, as are The Engineering Toolbox and materials straight from the insulation manufacturers.

The best way to get a comprehensive load calculation is to have a lot of tribal knowledge about how houses are built in your area, analyze energy bills, and combine tools like RED Calc with building performance tests.

RED Calc is available through the U.S. DOE at https://basc.pnnl.gov/redcalc. REScheck is available at https://www.energycodes.gov/rescheck.

ASHRAE’s resources are available at https://ashrae.org/technical-resources.

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