Air-cooled ammonia refrigeration systems and methods

A method of providing refrigeration using an air-cooled ammonia refrigeration system, the method comprising:

• supplying a vaporous ammonia to a plurality of air-cooled condensers, each of the plurality of air-cooled condensers comprising a heat exchanger and at least one axial fan, and the plurality of air-cooled condensers having a plurality of valves coupled thereto, the plurality of valves having a first configuration corresponding to a first operating state of the plurality of air-cooled condensers in which the plurality of air-cooled condensers are capable of condensing vaporous ammonia to form liquid ammonia by heat transfer;
• condensing the vaporous ammonia in the plurality of air-cooled condensers to form liquid;
• flowing the liquid ammonia to an evaporator configured to evaporate the liquid ammonia to form vaporous ammonia;
• flowing the vaporous ammonia back to the plurality of air-cooled condensers in the first operating state;
• a control circuit coupled to the plurality of air-cooled condensers, the control circuit configured to:
• determine a head pressure of the plurality of air-cooled condensers;
• when the head pressure of the plurality of air-cooled condensers is lower than a predetermined lower value, converting one or more of the plurality of air-cooled condensers in the first operating state to a second operating state by reconfiguring the plurality of valves from the first configuration to a second configuration, the second configuration corresponding to the second operating state of the one or more of the plurality of air-cooled condensers in which the one or more of the plurality of air-cooled condensers functions as an evaporator capable of evaporating liquid ammonia to form vaporous ammonia by heat transfer, the plurality of valves in the second configuration being configured to:
• direct at least a portion of the liquid ammonia condensed by the plurality of air-cooled condensers in the first operating state to the one or more of the plurality of air-cooled condensers in the second operating state, and direct the vaporous ammonia evaporated from the one or more of the plurality of air-cooled condensers in the second operating state back to the plurality of air-cooled condensers in the first operating state;
• flowing a portion of the liquid ammonia condensed by the plurality of air-cooled condensers in the first operating state to the one or more of the plurality of air-cooled condensers in the second operating state to evaporate the liquid ammonia received from the plurality of air-cooled condensers in the first operating state to form vaporous ammonia;
• and flowing the vaporous ammonia evaporated from the one or more of the plurality of air-cooled condensers in the second operating state back to the plurality of air-cooled condensers in the first operating state.