01-06-2018, 10:34 AM
(This post was last modified: 01-06-2018, 10:57 AM by srv52761.
Edit Reason: added anecdote.
)
(01-06-2018, 08:50 AM)Cecil Wrote: William - The dehumidifier makes sense. That is easy to accomplish too.
Jim, it is 2*F here today. will be -20*F before the middle of Feb. Heating my shop to 68* would be much more than $30/mo. Besides, I am a hobbyist and I don't work in the shop every day. I do hear what you are saying about the leg. I have heard the same from many people.
Dehumidifiers work similar to air conditioners, a fluid removes heat from one place and blows it to another. For the sake of discussion we will dispense with the part where the heat goes and concentrate on the cooling part-the part that removes water.
A coil is cooled, air blows across the coil, the air is cooled. Any moisture above the holding capacity of the air at approximate temperature of the coil condenses and the resultant air has less water vapor than previous air.
Ok, let's look at this in more detail with some hypothetical numbers.
Let us say the coil gets to 40*F (not uncommon). The area near the coils will be 40-43 or so. As the room air is blown past the coil the coil will "give up some of its coldness" (actually the opposite, the room air will give up its heat, but the other makes explanation easier). So the coil and adjacent area will be about 45-50. So any moisture above a dewpoint of 45 or so will condense. The resultant air will be 100% relative humidity at 45 degress. This will mix with the warmer air in the room to produce some relative humidity based on the temperature of the room.
If the room temp is 65F, then we are looking at a RH of about 50%, if the room temp is 85F then we would be looking at a RH of maybe 35% or a little lower.
But what happens when the ambient temp is in the single digits, your 2F, for instance
To protect your equipment from water that will condense at 2F, you must remove enough water that condenses at maybe 1 or 0, as it will mix with the air that didn't pass through the coil.. So your coil must get down to a few degrees below zero.
But your coil can't get that low. The ambient air (say 25F during the day) has already condensed the water vapor in excess of the capacity of the coil.
Most dehumidifiers start to lose effectiveness at about 55F. They do make low temp dehumidifiers that work down to about 36F, but these are three or four times the cost of the regular residential models.
Dehumidification may not give you the results you want.
A tip I got from this forum a number of years ago has already been mentioned. A clamp light with a 100w or bigger incandescent bulb on the inside keeps my tablesaw top condensation free all winter long (it also helps in the summer, too).
If you want to play around with the numbers some here is a handy dew point, rh, temp calculator
http://www.calculator.net/dew-point-calc...&x=56&y=16
edit: as an example,
I mentioned in a different thread we had a hvac unit freeze up on us over the Christmas break and water dripped on and under our hardwood gym floor. A company specializng in remediating this problem set up blowers and dehumidifiers. Their dehumidifiers are the low temp, commercial models-big ones. Our gym is about 11,000 sq.ft. 30ft high.
Outside temp was 12F daytime to -11F overnight, inside temp we kept at 68-70. About 24 hrs of dehumidification produced almost no water...and we think this was water already in their equipment.
