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we're gonna cover total heat transfer this is how to calculate the total heat transfer from a cooling coil so the formula basically is BTUs per hour total equals the amount of CFM going over the coil times 4.5 which is a constant times the Delta amp thil P is the change in total heat content of the supply air so you've got that entering total heat - the leaving total heat so what we're going to do is measure our field conditions in this example we're gonna say we have 2,000 CFM entering the coil with a 76 degree dry bulb in a 64 degree wet bulb then we measure our leaving conditions we got the same 2,000 CFM but now that air has been cooled down to 56 degrees dry bulb and 53 degrees wet bulb so I'm going to show you how to put that on psychometric chart but you don't have to worry about that the calculation will do these numbers here you go entering conditions 76 so as you can see our dry bulb temperature runs along the bottom of this psychometric chart so there's 70 here's 80 so here's 76 the line runs straight up so we had 76 dry bulb and we have 64 wet bulb the wet bulb numbers run along this curve here's 65 one back is 64 there's the 64 wet bulb line and here's where they intersect so what we're going to do from there entering conditions is we're going to extend that wet bulb line up into this area these charts here is the BTUs per pound of dry air and what that gives us is twenty nine point three one BTUs for every pound of dry air entering the coil now we're going to plot the leaving conditions so we had 56 dry ball so once again here's the dry ball here's 50 years 60 here's 56 now we're going to plot the wet ball of the leaving so this is leaving the coil it's 53 wet bulb here's 55 here's 50 51 52 53 now we're gonna find that intersection and we're gonna extend that line and right on to the enthalpy chart it shows us that we've got 20 2.02 BTUs per pound of dry air so you can see right away this is our delta enthalpy entering condition enthalpy leaving condition enthalpy so that's the Delta T in the equation so the calculation again BTUs per hour total equals the CFM times the constant times the Delta enthalpy so here we go we had 2,000 CFM we had entering enthalpy total leaving enthalpy total so the difference between this is the Delta enthalpy basically it's just math at this point there you got it sixty five thousand six hundred and ten BTUs per hour very simple equation instead of the psychometric chart they make just charts where you can just look up the wet-bulb and get this value so look for enthalpy charts that...