Heat transfer for R404A big evaporators

[luisarce]

Hey Fellows!
We are a company that since 50 years ago are working in *****, we had done very big supermarkets and a big quantity of walk in coolers using ever ***** (see our page www (dot) arceyasociados (dot) com (dot) ar)
At the present time we are involved in a contract of one big Ice cream storage for -25ºC in Buenos Aires Argentina
Dimensions are around 60 meters length, 14 meters with and 11 meters (Volume 10000 m3 equivalent of 350000 cuffs)
Due that in the state where will be placed ammonia is forbidden, the customer want do them using ***** 404A and we are planning use 8 tandem Copeland, each one has two Discuss compressor model 6DT3F11ME TSK 304 that are the biggest discus compressor, that a -35ºC in suction and 45ºC in discharge, has a capacity of 11 TR ( 33000 Kcal/hour) and we no consider sub cooling for the liquid , Pipes will be very short because compressor unit will be placed along de 60 meters length, justly over the evaporator
Remember electrical energy in Argentina is supplied as a 3x380 Volts, 50 cycles,
When we start to consider the evaporators our argentine habitual good supplier offer a evaporator of 310m2 of heat transfer surface with a middle differential temperature of 6ºC between air and refrigerant, with a K total of 24/25 Kcal/hour ºC m2, which is the habitual K, with smaller capacities, that we had measured in our installations and give a good performance.
As we had time for delivery we investigate in Europe and USA for a supplier that had more experience in this big evaporators and the selections of quotations obtained from Europe of supplier as LUVE or Eco from Italy show a less surface ( 200 m2 instead of 310) that are meaning that K is 34 Kcal /m2 ºc hour Monday I expect a information of Heat craft of USA
Can be this possible?

[US Iceman]

I would not be surprised to see various k factors for evaporators. This is comprised of several other details such as fin spacing (variable or constant), tube pitch, primary and secondary heat transfer surface (tube or fins), face velocity, etc. Freezer units can have much higher face velocities than evaporators for plus 0°F (32°F) applications. You just need to evaluate the specific details of each and see which provides the desired benefits you would like to provide to your client.

I would suggest R-507 for the freezer rather than R-404a. R-507 is an azeotrope so you do not have the issues related to the use of R-404a.

I might also suggest the use of balanced port TXV's. These respond much better to changing operating conditions like ambient temperatures.