QUESTION $2$

A$)$ It is required to maintain the air in a building at $22C$ dry bulb and $55\%$ relative humidity when the outside conditions are $26C$ dry bulb and $70\%$ relative humidity.

The total heat gains to the room $($sensible plus latent$)$ are $25$ kW and the latent heat gains are $10$ kW $.$

There is no re$-$circulation and the fresh air passes over a cooling coil to dehumidify it$,$ and then a re$-$heater, before entering the room.

The cooling coil contact factor is $0\mathrm{.}8,$ the volume flow of fresh air is $7\frac{m^3}{s}.$

Calculate, using a psychometric chart where applicable:

$($i$)$ The temperature of the air leaving the cooling coil

$[8$ marks$]$

$($ii$)$ The cooling coil load

$[4$ marks$]$

$($iii$)$ The re$-$heater coil load

$[4$ marks$]$

Data:

$c_{\text{p}\text{m}\text{a}}=1\mathrm{.}02k\frac{J}{k}gK$

$h_g=2540k\frac{J}{k}g$

${}_{\text{a}\text{i}\text{r}}=1\mathrm{.}2k\frac{g}{m^3}$