proper system charging

[crsh124]

By no means am I trying to tell you guys how to do a/c work as I am a tin knocker. But learning as much as I can in the service part. Tell me if I am wrong, inorder for a unit to be most eff. It must be sized properly in order to remove the heat from the structure. It must not only change the temp of the air in the room but change the temp of the walls and furniture in the room. Remove air temp to fast is not efficient as the unit will cycle on and off to much because the heat has been removed from the air and reached the t-stat causing it to cycle off with leather furniture still giving off the same heat that has not been removed. If a system was sized right we would not need t-stats on the wall they would be placed in the return next to the unit and be auto. Why is there a chart for charging a system by the manufactor on a 12 seer if it doesn't mean anything? With a 10 year warranty I think it does mean something. I except all comments as I said I am a tin knocker and from reading some of these post going to school may be a bad idea.

[ct2]

How much good do those sight glasses do when using a blended refrigerant

[Shophound]

Originally posted by bornriding
Heat removal, both sensible and latent, is accomplished at the evaporator coil, nowhere else. 'end quote'

So, the air entering the room ( from the supply register )at a temperature of 55 'f' 90+% humidity, is not? exchanging heat with the warmer room air. It is just pushing the warmer air back to the return ????. Is that what yur saying? I consider the cooler air blown into the room as a heat exchange between the warmer air and the cooler air, with the relsultant air ( at some temp in between ) being then drawn into the return air system. This heat exchange, also produces a reduced humidity level in the room as the cooler air absorbs heat from the warmer air. And therefore, the return air will be at a lower humidity level as well.

The air removed from the room by the return air ductwork or path is passed over the evaporator coil, where it gives up both latent and sensible heat. From that point it becomes supply air, cooled and dehumidified, and is returned to the room to replace the air removed by the return air path.

The cooling and dehumidification of air is accomplished at the evaporator coil. The undesirable levels of heat in the room was transferred to the evap coil. Air was returned to the room at a lower temperature. This was a result of the air removed from the room having given up its heat to the refrigeration circuit.

In essence you are replacing warmer air with cooler air. But the warmer air must be removed first, have its unwanted heat removed, then returned to the space as conditioned air.

Yes, you can cool a room by placing flat plate evaporators on the walls, and the room will lose heat to the colder plates, without an exchange of air in the room. You can also cool a room by placing a huge chunk of ice in the room, so the heat within the room flows into the ice, thereby leaving the room colder. This also would require no air exchange.

But we are speaking about forced air refrigeration, not static air cooling. For this you must remove/return or recirculate the air to be cooled to accomplish the desired temperature level.

The air leaving the evaporator coil is at the highest cooled and conditioned state. As it leaves the supply register and mixes with the air in the room, the warmer air in the room will move toward the cooler air and attempt to equalize with the supply air temperature. The warmer air will lose some heat in this fashion, but the first cause of the supply air being colder to begin with is due to the evaporator having already extracted heat from the room from the return air.

So, yes, you could say that the supply air is accomplishing a measure of direct cooling of the room air by merely flowing into the room, just as sticking a hose flowing out cold water into a tank of hot water will cause the tank of heated (let's say it is continually heated by a burner) water to cool.
However, to maintain the cooler temperature of the tank against the constant addition of heat from the burner, the water hose must remain in the tank, emitting the same colder water. Eventually the tank would overflow unless some measure of recirculation was established that would remove a portion of water, pass it over a cooling medium, then return it to the tank at a cooler temperature.

Same goes for a room. If you just kept pumping cold air into a room without providing an escape or return air path, it would "overflow" with air and reduce the volume of air entering the room due to back pressure (if the room was fairly airtight). A reduction of volume would reduce the amount of cold air entering the room, which would in turn reduce the amount of cooling available.
So, it's recirculated.