Determining Total Load of Cooling Coil

[lumbee]

I am trying to determine the total load that the cooling coil needs to handle. Below is the information I have.

1. Outside design conditions and quantity.
2. Room design condtions.
3. Room sensible loads.
4. Room latent loads.

I have plotted the outside and room design conditions on a psych chart. I can't find the mixed condition because I don't have the quantity of returned air. I also need to find the condition of air leaving the coil. This should be a function of coil. I know the equation for getting the total load across the coil, but I'm missing something.

 

[trashcanman]

Total coil load = room sensible + room latent + outside air load. If you know the quanity of outside air, return air = total supply air - outside air.
To determine the coil leaving conditions, computer the ESHF (Effective Sensible Heat Factor) = Room Effective Sensible Heat Gain/Room Effective Total Heat Gain. For example, say the ESHF = 0.8. Plot a line from the room condition (say 75db/62.5wb) at 0.8 slope (from psychrometric chart) to about 95% saturation curve (no coil is 100% efficient). Now you have the coil leaving db/wb. Let's say it is 55/54. For room design db=75, DT = 75-55 = 20 Deg.F. Now, the room SA cfm = Effective Room Sensible Heat/(DT*1.08).
= ERSH/(20*1.08)= SA CFM. Now computer the actual ent coil condition. Ent DB is approx.=(Room DB*return air CFM +outside air DB*outside air CFM)/Supply Air CFM. Not exactly equal, but close enough. Plot a line from outside air condition to room air condition. Where that line crosses the Ent DB, that is the Ent WB as well. Now you know the coil ent and lvg. conditions. Good ole' psychrometric chart!