What's 44 degrees? Is that the outlet temp of the chiller? Is this essentially a 3 ton chiller? Do they make them that small?
What would be at 80 degrees in the second scenario?
Isn't the BTUH the BTUH no matter what? At 54 degree entering and 44 degree leaving water temps (ie, a 10 degree dT) you use Q = 500 x (dT) x gpm. You would use the same formula to get the desired info no matter what temp you are talking, just the dT and the gpm can change, right?
Maybe I'm confused or don't understand the question.
Checonbill, You seem to be confusing the outlet temp of the unit (44degF) with the ambient operating temperature of 80degF.
Like HVACctrl says, 3rt (36000 BTUH) is a pretty small chiller, and I'm guessing you mean a packaged or split air/air unit.
Manufacturer performance datasheets will provide tables indicating the actual capacity of the unit for different ambient and on-coil conditions - dry bulb, wet bulb, airflow. You can typically expect the actual capacity to be close (+/- 1000BTUH) to the nominal capacity around 80degF ambient, with other conditions typical.
Capacity is based on a nominal leaving water temperature from the chiller (44F in checonbill's case). A standard approximation for different temperatures is 2% per degree from nominal (above increases capacity, below decreases capacity). That works within about 15 degrees of the nominal temperature in each direction. Beyond that you have to look at several other factors along with manufacturers data to determine capacity.
And for random information, 36000 BTUH is somewhat small but we make them down to about 1/2 ton (6000BTUH) here.
