(4) The installation by the same manufacturer estimated to cost 15% more than a brine system.
(5) There would be no stored energy in the ammonia pipes as in brine pipes should the refrigerating plant suspend operation temporarily.
(6) The compressor hazard from returning liquid and possible machine wrecking with line breaks, ammonia losses, and danger to life.
(7) In case of extension or modification of piping, the difficulty with ammonia pipes over brine is marked.
(8) In direct expansion plants the cooling effect is stopped immediately when the compressor is stopped. It is required to operate incessantly, or if speed be reduced the current is chiefly wasted in resistance grids if electrically driven. Whereas in a brine plant the compressors can be stopped several hours, the brine being circulated rises in temperature but not sufficiently to vary room temperatures. This is a great advantage, permitting keeping “off peaks” on commercial electric lines and consequently earning lower rates.
(9) With an electrically driven compressor, speed control is fixed within quite limited bounds and if direct expansion system is used more power is purchased than needed for reasons already mentioned.
(10) The total cost for operating pumps and calcium taken collectively will be far less than the uncontrollable ammonia leakage. The coil attendants can be less skilled.
(11) Brine temperature 25 degrees below zero, Fahr., can be carried, sufficiently low for all purposes. Rooms can not be controlled at as exact temperatures with direct expansion as with brine, owing to its sensitiveness.
(12) Lastly and very important, the complicated piping system to carry several back pressures to produce varying temperatures and the necessity of operating several compressor “ends” makes a complicated installation of small units as against a simple system carrying one temperature brine.
Plants of the character described usually operate on direct expansion, require three sets of temperatures, three sets of suction pressures and three sets of suction mains with various cross connections and intricate pump-out arrangements. This necessitates multiplicity of machines and connections to various cylinder ends.