Question

A balanced-flow ERV is used to ventilate a warehouse at a rate of 1,000 L/s. The air conditions within the warehousearequitecoolanddry,Tdb=10°CandRH=50%.Ataparticularmoment,theoutsideairenters theERVatTdb=38°CandRH=40%.Duringthistime,theairconditionsleavingtheERVontheexhaustside are measured to be Tdb= 31°Cand RH =35%.a)Estimate the Sensible-Effectiveness (%) of theERV.b)Estimate the Latent-Effectiveness (%) of theERV.c)Estimate the drybulb temperature (°C) and relative humidity (%) leaving the ERV on the fresh-airside.d)Plot the conditions of all four air-streams (i.e.,fresh-air, entering and leaving; exhaust-air, entering and leaving) on a psychrometricchart.

Answer 1

$\begin{aligned} rate &= 1000\ L/s\\ \\ T_{f_i} &= 10°C\\ ω_{f_i} &= 50\%\\ \\ T_{f_o} &= 38°C\\ ω_{f_i} &= 40\%\\\\ T_{s_i} &= 31°C\\ ω_{s_i} &= 35\end{aligned}$

$∆t = |t_{f i }− t_{f o}|=| 10°C- 38°C| = 28°C$

$∆t_{tot } = |t_{f i }− t_{si}|=| 10°C- 35°C| = 25°C$

$εS = \dfrac{∆t }{∆t_{tot}}= \dfrac{28°C}{25°C}= 1.12$

$∆ω = |ω_{f i }− ω_{f o}|=| 50\% - 40\%| =10\%$

$∆ω_{tot } = |ω_{f i }− ω_{si}|=| 50\% - 35\% | = 15\%$

$εL = \dfrac{∆ω}{ ∆ω_{tot}}= \dfrac{10\%}{15\% } = 0.33$