PipeChat Digest #1494 - Thursday, July 6, 2000
Re: Tracker Question-KEYBOARDS
  by "Bob Scarborough" <desertbob@rglobal.net>

(back) Subject: Re: Tracker Question-KEYBOARDS From: "Bob Scarborough" <desertbob@rglobal.net> Date: Wed, 05 Jul 2000 23:56:50   At 11:12 AM 7/5/2000 -0500, you wrote: >Because, when the compressor goes off, the fans simply pump whatever = moisture >remains in the coils back into the room. I have seen actual rain falling = in >rooms from some systems. >If you can explain it better, have at it!!!<snip>   All coils, whether direct expansion or chilled water, are designed so that condensate drains into a pan plumbed to a drain. In the extreme climes of the South, this amount of water can be considerable, but nonetheless, drains quickly in a properly engineered and installed system. There is a period after refrigeration shutdown where some of the condensate = evaporates again into the airstream should the inside air fan continue to run. However, the amount of moisture introduced is confined to that amount of liquid left on the coils at time of shutdown. Some of it is again evaporated into the airstream quickly, and the rest drains off. This, of course, assumes at least an attempt at proper maintenance.   Most systems use a minimal filtration system for the intake to the air handler; 10% ASHRE-rated filters (the common, 1" "funace filter" found at hardware stores) are much too common. Many commericial system are = designed to use 2" pleated-medium 30% filters. Use of low-grade filters, or lack = of them entirely, can cause the coil to grow a "fur" of dirt which, after a period of time, is too great to be washed into the condensate drain by the precipitating condensate. In such cases, dehumidification (as well as sensible cooling capacity) will be materially decreased. Still, the = amount of moisture re-evaporated into the airsteam will be confined to that = amount that was present on the coil (and soaked into the dirt) when either the compressor was shut down or the chilled water supply was interrupted. You cannot get "something for nothing"; in this case, an air handler cannot = add more moisture to the conditioned space that wasn't there originally.   As for conditioned spaced "raining", this can occur in areas of extreme humidity, again such as the South, where outside air is allowed to enter the conditioned space in large quantities from outside the system, such as open door or windows. The unconditioned air is cooled by mixing with the interior air, and its moisture content will readily condense on any item that is at or below the mixed air's dew point. This is quite common on registers and diffusers, which are cooled by the conditioned air delivered through them. In large conditioned buildings, where the system has excess capacity, a problem can occur where the conditioned space is sensibly cooled without proper removal of the latent heat of water content. In = such cases, if the space's sensible air temperature reached the its dew point, spontaneous condensation can occur, causing "inside rain". This was a problem in the Houston AstroDome from the start, causing Carrier Corporation engineers to try various methods of reducing latent heat more efficiently within the air handlers.   Suffice it say that the total heat energy of a mass of air in any enclosed space contains both sensible heat and the latent heat of evaporation of water vapor. The only way to raise total heat content is to add sensible heat, through sun radiation, cooling of human occupants, and other = sources, or by evaporating water, which can come from a vareity of sources, also including occupants. You cannot add latent heat simply by circulating = air.   DeserTBoB