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-   -   Mason's Dry & Wet Bulb Hygrometer (http://www.diychatroom.com/f17/masons-dry-wet-bulb-hygrometer-11169/)

rjordan392 09-01-2007 07:37 AM

Mason's Dry & Wet Bulb Hygrometer
 
Hello,
I purchased one of these to calibrate the humidity level on my thermostat and also to monitor the performance of my central air conditioning as the thermostat is too slow to record changes. Based on my readings, the indoor wet bulb temperature is too high even though the house is cooled down to the desired temperature. This leaves me with higher humidity then I expected from my cooling system.
Is the Mason's hygrometer more accurate then other types of hygrometers?

hvactech 09-02-2007 10:23 AM

No!! the masons is merely a toy, use a sling or digital pschrometers in order to get acurate readings

rjordan392 09-03-2007 04:50 PM

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.

dmaceld 09-04-2007 04:34 PM

Quote:

Originally Posted by rjordan392 (Post 61118)
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.

rjordan392 09-04-2007 06:05 PM

I live in the northeast, so its not as humid as the South. The folks in my area all have either 2 or 2-1/2 ton units. I just had a 2-1/2 ton replaced with a 2 ton unit. Even though the humidity setting is programed for 52%, there is very low moisture removal for the amount of cooling I am getting. For some reason, the first stage of my compressor is not doing the job and the differance in the before and after air temperatures at the indoor coil is only 14 degrees, sometimes 16. I believe this is the problem. I been told that I should have at least 20 degrees differance. The only way that I can get that is to force into second stage by lowering the temperature 5 degrees from its setting. The second stage will not kick in automatically like it should. I am now trying to get some cooperation between the installing dealer and the regional manager to both come to my house to resolve my problem. If I don't get this fixed; it means I come home to a cool house with too much humidity.


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