ERV/HRV Sensible Effectiveness and Recovered Load
What the recovery core gives back: a balanced ERV/HRV at a rated sensible effectiveness pre-tempers the incoming outdoor air off the leaving exhaust, so the air reaches the coil at T_oa + eps x (T_ra - T_oa) and the plant is relieved of Q = 1.08 x CFM x eps x dT. A 200 cfm unit at 75 percent on a 10 F design day delivers 55 F air and recovers 9,720 Btu/h - three quarters of the ventilation heating load, the number a designer subtracts before selecting equipment. Sensible only, balanced flow, rated (not frosting-derated) effectiveness. A design aid, not the manufacturer's certified data.
Formula and source
dT_F = t_ra_F - t_oa_F; t_leave_F = t_oa_F + eps_s x dT_F; Q_s_btuh = 1.08 x cfm x eps_s x dT_F; Q_noerv_btuh = 1.08 x cfm x dT_F; Q_resid_btuh = Q_noerv_btuh - Q_s_btuh.
The ASHRAE Standard 84 / AHRI Standard 1060 sensible-effectiveness definition (eps_s = (T_leaving - T_oa) / (T_ra - T_oa)) and the recovered sensible load Q_s = 1.08 x CFM x eps_s x (T_ra - T_oa), by name; the sea-level sensible constant 1.08 = 60 x 0.075 x 0.24 is a named constant.
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