Example

The design specifications for an air conditioning system in a building on the North coast of KwaZuluNatal are:

Ambient conditions

$\backslash ($ : $35^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ at $\backslash (70\backslash \%\backslash )$ relative humidity

Conditions inside the air$-$conditioned space : $\backslash (25^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ at $\backslash (50\backslash \%\backslash )$ relative humidity

Total cooling load

Latent heat load

$\backslash [$

$\backslash$begin$\{$array$\}\{$l$\}$

: $45\backslash$mathrm$\{$~kW$\}\backslash \backslash$

: $8\backslash$mathrm$\{$~kW$\}$

$\backslash$end$\{$array$\}$

$\backslash ]$

Air recirculation

: $\backslash (80\backslash \%\backslash )-$ i$.$e$.$ After leaving the air$-$conditioned spaces $\backslash (80\backslash \%\backslash )$ of the air is mixed with outside air. The mixture then passes over a cooling coil, then it goes back into the air$-$conditioned spaces.

Relative humidity of the air at exit from the cooling coils

Draw the process on the psychrometric chart, write your name and student number on it and hand it in with your script. Then, calculate or determine:

a$)$ All properties of the air after mixing.

b$)$ Dry bulb temperature of the air at exit from the cooling coil and the by$-$pass factor for the cooling coil.

c$)$ Volume flow rate of dry air into the air$-$conditioned space. Why does this need to be calculated?

d$)$ Refrigeration capacity. Why is this not the same as the total cooling load?

e$)$ Volume flow rate of water from the cooling coil. What normally happens to this water?