What the Heck?I question the following statement on page 18 of your October 30, 2000 issue: “When using the hot water coil, mini-duct systems also alleviate the problem of dry air that can come with traditional forced-air systems, as the medium for treating the heated air is water.”
What the heck has that got to do with anything? This looks like a sales pitch story, and I don’t buy it because everything I have been taught about humidity in air doesn’t explain how heating with a hot water coil makes any difference. After all, water from inside the coil doesn’t get into the air, or does it?
Heating air is a sensible heat process and the specific humidity will not change with different heat sources. A hot water coil does not automatically add moisture to the air being heated. Humidifiers add moisture to the air.
For example: When 75Â°F air containing 50 grains of water vapor (moisture) enters the hot water coil and is heated to 120Â°, the air will still contain the original 50 grains of moisture, even though the air is heated with a hot water coil.
To change the moisture content of air, moisture must be added or removed from the air.
Yes, I know that the slick wet salesperson will try to sell this and upon questioning will get out the psychrometric chart and show that the relative humidity will drop from approximately 40% to approximately 4% when heated to 160Â°, will only drop to approximately 10% when heated to 120Â°, but will fail to explain that this really means nothing.
Why do writers of articles such as this give readers questionable information? If their purpose is to make us think, I think Mr. Messmer is wrong on this one.
Wally W. Braatz
Propane ProponentI have long thought that propane would be an obvious replacement for both R-22 and R-502. While the capacity in a given compressor is about 10% less than with R-22 and 15% less than R-502, the discharge temperature is low, even at high compression ratios, and the head pressure is lower for a given condensing temperature. Further, the oil return is better with propane than with either R-22 or R-502, and much less charge is required because propane liquid has much lower density than either of these.
I am amazed about the horror that the U.S. safety agencies exhibit with respect to a few ounces or even a few pounds of propane in sealed refrigeration systems, compared with the European agencies. I can recall that for years I sprayed propane or isobutane on my face every morning along with my foamy shave cream. This stuff was contained in the cylinder by a flimsy press valve. Those same safety experts seem to have no problem either with me having 20 pounds of propane in the fuel tank for my gas grill or a pound of the stuff in the little cylinder with which I fuel my crêpe maker. Go figure. Could some commercial interests have a hand in those U.S. safety decisions?
At any rate, foreseeing some of the above advantages for propane as a refrigerant, back in 1991 I published an article in ASHRAE Journal that contained tables setting forth a complete set of line sizes for propane that I had calculated, employing the ASHRAE-approved formulæ. I have this four-page article in .tif format and would be happy to e-mail it to all who e-mail a request to me at DEK50@columbia.edu.
Dan Kramer, P.E.
Specialist Grade Member RSES
Publication date: 12/04/2000