Quote Originally Posted by US Iceman View Post
No argument from me on those points. I fully concur.

For a hot gas defrost system to work well at these lower pressures the ability to provide an adequate supply of hot gas is determined by the hot gas supply pipe capacity. If this pipe cannot supply enough hot gas at a low pressure loss then you can have some problems.

The next big issue is being able to drain the condensate from the coils during defrost as fast as it forms. This is dependent on the coil design (the coil circuits have to be free draining) and the method of controlling the defrost. Defrost relief valves work only on pressure and do not know the difference between liquid or vapor, only pressure. This is where drainers work very well, if properly applied.

The last point is pressure. If you try to defrost at low pressures (just high enough for defrost to occur) you cannot have high pressure losses in the hot gas supply piping.
Unfortunatly, many coils don't have free condensate draining.