6. Find the mix point M by measuring the length of the line O-R
and multiply this by the mixing ratio.
On a full size CIBSE psychrometric chart this measures 110mm.
The ratio of recirculated air is 0. therefore; 110mm x 0.8 = 88mm
Measure up the O-R line from point O by 88mm.
This determines point M .
If there is more recirculated air than outside air at the mix point, then point M will be closer to point R than point O.
7. Find the room ratio.
This is the sensible to total heat ratio.
Neglect signs ie. the total heat for the room will be Sensible loss plus Latent gain.
Total heat = 18 kW sensible + 4.5 kW latent = 22.5 kW total.
Heat ratio = 18 / 22.5 = 0.8
Plot this ratio on the protractor, top segment, on the psychrometric chart and transfer this line onto the chart so that it passes through point R.