—The cycle, therefore, is a gas in the expansion tank at low pressure and temperature, admitted to the pump or compressor under this condition, compressed to a small volume and increased in pressure, discharged in this condition to the condenser where it becomes a liquid and in a condensed form at a lowered temperature and ready to return to the expansion tank to be used over again.
Ammonia gas is the heat carrier. If it be used in packing house service, either it absorbs the heat directly from the rooms in which the animals are suspended or the brine in the tank is circulated through the rooms to absorb the heat and carry it back to the cooler or expansion tank.
Condensing Water.
—In Chapter II reference was made to the condensing water for refrigerating system. This is important because the lower its temperature, the less the pressure will be created which means the less the power must be exerted in the production of the mechanical refrigerating effect. The water flowing over the condenser carries the heat to the sewer. Thus the heat from the carcasses, the sun heat on the walls of the building, the actinic rays through the windows, the heat from the men employed within, that from the electric lights within, and that absorbed from the earth upon which the building stands must all be collected and eventually passed into the sewer.
Absorption Equipment.
—Absorption refrigeration equipment is used to some extent in packing house work, but its complexity makes unnecessary an attempt of its description in this work.
Unit Basis.
—The unit basis of refrigeration commonly used in expressing quantity is tons of refrigeration, meaning the tons of refrigerating duty that can be performed per day of twenty-four hours. The standard measurement per ton as adopted by the American Society of Refrigerating Engineers, is a cooling effect equal to 288,000 B.t.u., being equivalent to the extraction of this quantity of heat from any substance.
It has been established by the Bureau of Standards that in freezing one pound of water at 32° F., to ice at 32° F., 143.5 British thermal units of heat must be withdrawn from the water. For convenience in practice the fractional part is ignored, and 144 B.t.u. per pound of water is accepted as standard in calculations.