Practice

At a site $5{,}000\,\text{ft}$ above sea level, a sensible recovery wheel preheats the outdoor air for an office air handler. The wheel handles $4{,}000\,\text{cfm}$ of outdoor air entering at $20\,°\text{F}$ and an equal $4{,}000\,\text{cfm}$ of exhaust air entering at $72\,°\text{F}$ (both airflows at site conditions), and its sensible effectiveness at this balanced flow is $70\%$. The recovered sensible heat rate (Btu/h) is most nearly:

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