Air-Side Economizer Free-Cooling Hours
Sensible free-cooling capacity (BTU/hr) and annual ton-hours of mechanical cooling offset from supply airflow and the mix-to-supply delta-T over the economizer-eligible hours.
Formula and source
Q_sens = 1.08 * CFM * dT (sensible heat, standard air); ton-hours = Q_sens * hours / 12,000. dT is the mix-to-supply delta-T.
ASHRAE sensible-heat relation Q = 1.08 * CFM * dT (public); air-side economizer changeover per ASHRAE Standard 90.1, by name.
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