Abstract: A cascade refrigeration system using a first refrigerant or a high stage and a second, R-744, refrigerant for low stage refrigeration has a defrost system including a defrost compressor, a defrost inlet heat exchanger and defrost outlet heat exchanger. The defrost inlet heat exchanger receives a defrost portion of second refrigerant and adds an additional defrost heat load thereto from first refrigerant, thus evaporating defrost portion. Defrost portion is then compressed into high pressure defrost vapor portion in the defrost compressor. The defrost vapor portion is then circulated through a selected evaporator, where a defrost heat, augmented by additional defrost heat load, defrosts selected evaporator, defrost vapor being at least partially condensed into defrost condensed portion which is liquefied in defrost outlet heat exchanger.

Abstract: A dual refrigerant refrigerating system provides a refrigeration cycle in which a primary refrigerant cools a secondary refrigerant in a primary evaporator into a partially frozen state, in which a fusion portion thereof is frozen. The primary refrigerant thus absorbs a secondary latent heat from secondary refrigerant, including a latent heat of fusion required for freezing the fusion portion. Secondary refrigerant is subsequently at least partially thawed, in a secondary evaporator, by re-absorption thereby of secondary latent heat from material proximal to secondary evaporator. Evaporation in secondary evaporator requires at least partial thawing of fusion portion, and thus latent heat of fusion is at least partially re-absorbed by secondary refrigerant, thus increasing secondary heat absorbed from material and facilitating refrigeration thereof. The system also provides defrost and heat reclaim capabilities.