||09-04-2007 04:34 PM
Originally Posted by rjordan392
I used to have sling psychrometer but found I had to be quick at reading the wet bulb reading as it would start to rise as soon as I stopped rotating it. The problem was the instruments degree numbers were too small to try to focus on, causing a delay in reading it. I keep an eye out for a used larger one. In the meantime, I'll use the Mason's. I read online that A mason's needs 600 fpm of air directed at it for best accuracy and I have a small fan about 6 feet away delivering a decent flow of air and I am only guessing that its enough. I usually wait about 15 minutes before taken my dry & wet bulb readings.
I jerry rigged a wet/dry thermometer for the same purpose and it worked pretty good. I got two outdoor thermometers from Lowe's. I took about half dozen of them and set them on the shelf side by side and picked two that read the closest to the same number near the center of all the readings. I took and tied them together back-to-back and mounted them on the end of short piece of 1 1/2" plastic pipe with the bulbs about in the center of the pipe. I put a small sock on the inner bulb and mounted a small computer processor cooling fan at the other end, which I powered with a 12 volt battery. The fan sucked the air through the tube, passing over the dry bulb first. To use it I wet the sock, set the unit on a shelf, table, whatever, and turned on the fan. After a minute or so the wet bulb would stabilize and then I read both thermometers. Worked good. Not necessarily 100% accurate, but close enough to get a measure of how well my a/c system was working. I used the numbers to size my replacement a/c unit. Gave me good data.
You quite possibly have an oversized a/c for your house. What happens is the air gets cooled to set point before the moisture gets removed. Go to http://www.centralcityair.com/index2.htm
and read David Debian's diatribes about sizing a/c systems for the humid south. Because of his arguments about sizing a/c I put in a 3 ton condenser and 2 1/2 ton evaporator when I replaced the system in the house I used to own in Hammond, LA. Worked great.