The compressor sucks in saturated and dry ammonia vapor at design evaporating temperature and pressure and compresses the vapor into a pre-determined higher pressure, called the condensing pressure with corresponding temperature. The actual temperature at the condensing pressure is considerably higher due to superheating it the compression process.

The vapor is then pumped to the condenser pipes, where it is cooled and liquefied using water sprays. The liquefied ammonia at high pressure is collected in a receiver and then pumped under pressure to the expansion valve, where the pressure is reduced by throttling and the low pressure liquid flows to the evaporator or bunker coils located inside the insulated warehouse.

The low pressure liquid ammonia inside the bunker coils evaporates into vapor being sucked by the compressor and in the process cools down, absorbing heat from the surroundings, thus lowering the temperature of the store. The evaporator coils are kept flooded with low pressure and low temperature liquid ammonia with the help of an accumulator vessel inside which boiling or evaporation of liquid takes place. The evaporating ammonia is sucked by the compressor and the cycle is established.

If the performance of the refrigeration system is to be optimized, it is necessary to ensure that pipes of right dimensions and quality are used across the system. Apart from the intricate pipe network in condensers and evaporators, designated as 'heat exchangers', the vapor compression refrigeration system has to include interconnecting pipes for these heat exchangers.

Given below are brief descriptions about the design & application of pipes at various stages of the refrigeration process, along with their sizes & specifications.

Pipe size normally used : 50mm NB Black Heavy Plain Ended (BHPE) Steel Pipes

Length of Pipes : 48 rft per ton refrigeration of the plant (TR as commonly known) with appropriate recalculated cooling water.

Basis of pipe selection : For a Refrigerating plant of 10TR duty, pipe lengths of an atmospheric type condenser will be approximately 20' 10" long including short U-bends (4" or 4 1/2" centres), 24 pipes high (8'7" is the centre distance between bottom and top pipes providing approximately 300 sq ft condensing surface.

Note : By providing a clearance of 4' to 6' between the lowermost pipe and water basin surface, water leaving condenser tubes gets cooled as in an atmospheric cooling tower. Without this clearance, or with North-South natural air flow restricted, condenser pipe lengths must be increased by 15 - 25%

The pipe surface is a function of the cooling to be achieved in the warehouse, and the heat transfer coefficient of pipes. For instance every 1 TR heat load for the flooded evaporator and a temperature difference of 30°F during the peak loading period, approx 240 rft of 40mm NB BHPE evaporator coils would be required under air agitation of ceiling fans.

Basis of pipe selection : Each set of bunker cooling coils normally comprises 40mm NB black heavy pipes and are usually between 50 to 60' long x 8 rows x 6 pipes high, using 40mm NB U-bend from 2 ft. long pipe with 5 ½" tube centers. The clearance between consecutive rows is kept about 6" to 8".

Storage Specifications : Fruits and vegetables other than potatoes are more susceptible to temperature and humidity, which must be closely controlled for freshness. However, we have appended a generic chart for vegetables and fruits.