Answer to Question 1
Adaptive defrost systems initiate the defrost system based upon measured parameters rather than a timed cycle. As an example, if the registered air flow through the coil is reduced due to ice build-up then a defrost cycle will be initiated. The case controller does not necessarily require an actual air flow measurement. Electronically controlled expansion valves can act as mass flow meters. This can be accomplished by comparing the energy admission on the refrigerant side of the valve to the energy admission on the air side of the valve.
Answer to Question 2
The primary refrigerant is used for cooling the glycol in the chiller and is not delivered to the individual cases. This eliminates the need for long pipe runs of refrigerant as required in multiplex direct expansion systems that considerably reduces the amount of charge required. Long refrigerant runs of multiplex systems incur large pressure drops and result in high suction gas superheat. These conditions reduce the mass flow rate of the compressors that results in loss of refrigeration capacity for multiplex systems.
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