4/23/2020 11:19:59 AM
Comment: In the definitions under "Pressure Termination" it says;
Pressure termination is accomplished by a pressure controller that senses the rise in evaporator pressure. The rise in suction pressure in the evaporator indicates the evaporator temperature has increased and the frost disappeared.
It also provides redundant control of the defrost termination on the failure of temperature or pressure termination.
This last line needs to be removed. "It also provides redundant control of the defrost termination on the failure of temperature or pressure termination."
It is inaccurate and seems like a "copy and paste" from the proper definition of "Time Termination".
4/16/2020 10:27:53 AM
Comment: On page 13, step 2 says the ORD forces gas from the top of the receiver through SV-A or SV-B.
Problem 1, the outlet of the receiver going toward the ORD valve isn't at the top of the reciver, small detail but still important for visually understanding where the vapour is coming from.
Secondly, SV-A and SV-B are not connected onto ORD from which the desbription claims the intermediate gas would come from, they are instead still connected to the discharge line where hot gas would come from, not intermediate gas.
Sv-A and SV- B are in the wrong location and ORD ins't capable to accomplish it's described job.
4/16/2020 10:18:51 AM
Comment: This should be called "Three pipe hot gas defrost with conventional flow"
Conventional flow means the direction the refrigerant flows within the evaporator is the same in cooling mode or defrost.
The first paragraph is ok.
The paragraph below figure 3 and the step-by-step description on page 11 contain mistake.
Page 10; this type of system usually consists of 1 evaporator for 1 condensing unit. Which causes it to run out of heat quickly.
Page 10 paragraph below figure 3 says; "Only one evaporator can be defrosted at any given time", which is true. Because it
should be the only one.
Page 11 step 3 says; "evaporator B continues to operate in refrigeration mode" If evap. B was to operate in cooling mode, evap. A would not run out of heat, now with the way this system is piped, evaporator B would not be able to see refrigerant flow since the higher pressure coming out of evap.a would block it.
A single evaporator system would be simpler, and more accurate.
Or simply say that the evaporator not in defrost is now on "Stand by".
4/16/2020 9:53:19 AM
Comment: Figure 2 drawing does not work.
SV-A and SV-B are attached to the wrong evaporators.
Also, this should be called "Two pipe Hot gas defrost reverse flow".
Using a more complex diagram with a liquid line header, hot gas header and showing a "DDRV" Defrost Differential Regulating Valve
and its operation would be more useful and more challenging to this level of students.