Receiver.
—From the condenser the liquid ammonia is collected in the receiver so as to have a quantity stored for use and in reserve for the fluctuating requirements.
Expansion Valve.
—A small but important item in the system is the expansion valve which is a valve with a controllable opening and comparatively small. This is interposed in the line between the liquid receiver and the cooler or expansion tank.
Cooler or Expansion Tank.
—The next element is the cooler in whatever form it may exist, whether it be ammonia coils submerged in brine tank, shell and tube cooler built like a boiler in which the ammonia surrounds the tube through which the brine solution is pumped, or ammonia “direct” expansion coils in the air within a room, it matters not. At this point the heat given off by the substance to be cooled is absorbed by the ammonia and taken up for discharge to the water flowing over the condenser.
No substance will change from a liquid to a gaseous form unless heat be supplied to perform the work of making this change. At the outset it was stated ammonia will boil or evaporate at 28¹⁄₂° below zero Fahr. when under no pressure or in the open air. Further, if ammonia be contained in a vessel and the pressure be reduced below atmosphere, the boiling point is lowered still further. For example at 10.6 vacuum gauge pressure the boiling point will be 40° below zero.
Imagine a brine cooler such as a tank with coil submerged and surrounded by a brine solution: This brine is circulated through the building and by common knowledge we know it absorbs heat and is returned warmer than it was sent out. It is supplying the heat for boiling the ammonia gas.
Reverting to the expansion valves: Assume there is a pressure of 180 pounds in the condenser and a liquid temperature of perhaps 85 to 90 degrees; the same conditions existing in the receiver; also assume a pressure of 15 pounds on the ammonia coils which will produce a temperature condition of zero. In the diagram, the coil in the tank is attached to the expansion valve while on the other end of the coil is made the connection to the pump or compressor. This by its action is withdrawing the ammonia gas as rapidly as it is generated, due to the tightness of the piston, which if it is properly fitted will pump a vacuum upwards of 22 to 25 inches upon the system attached to it, unless gas be supplied to fill the space. In operation, the expansion valve is opened slightly, the liquid is freed into a space where the pressure is lowered, a condition created for expanding the ammonia to a gas and the heat contributed by the surrounding brine is absorbed by the ammonia changing from a liquid to a gaseous form.