What is a BTU?
BTU which stands for British Thermal Unit is just another example of the British trying to confuse everyone. While the metric system has gained a stronghold in science and engineering, it seems like heating and cooling are stalwarts against the tide of the metric system.
The British thermal unit (symbol BTU or Btu) is a traditional unit of energy equal to about 1,055 joules. It is approximately the amount of energy needed to heat 1 pound (0.454 kg) of water (i.e. exactly one tenth of a UK gallon, or around 0.1198 US gallons) from 39 to 40 ° F (3.8 to 4.4° C).[wikipedia]
Latent vs Sensible & Dry vs Wet Bulb Temperature
The Engineering Toolbox has the specifics including formulas, but the basics are:
Latent load = Wet bulb
Sensible load = Dry bulb
Links for more info from The Engineering Toolbox:
Cooling Loads – Latent and Sensible Heat