I – Introduction

1. Cooling of air inside insulated spaces (cold rooms or processing areas) is needed either for food/products holding/storage under controlled temperature and/or relative humidity or for processing areas where people works in operating conditions below ambient temperature.

2. Besides the temperature and/or relative humidity in storage cold rooms or in processing areas, there are several important factors that may optimise the operating conditions or even the “pay back” of the investment in terms of refrigeration equipment, as it follows:

2.1. Air velocity inside the controlled ambient (cold store or processing area)

a) In terms of unpacked products to be stored under controlled temperature, namely chilling conditions (-2ºC up to +8ºC), it may be required low turbulence / air velocity or low air circulation under small DT operating conditions. This is the situation of vegetables, fruits, alive trees or flowers, cheese cold rooms, for example.

b) In terms of “confort” and health requirements it is a fact that inside “spaces” where people work under temperatures between +2ºC and +16ºC,  noise and air circulation conditions (velocity and turbulence) over them must be as low as possible (meat or fish processing, corridors, loading / unloading areas for example),.   

2.2. Customer’s friendly design

There is another very important situation or requirement related to “consumer’s friendly” design in terms of “reach-in” or “walk-in” cabinets for beverages or products holding in supermarkets or convenience shops.

As a matter of fact customer’s reaction to high air velocities or noise when reaching the products inside the refrigerated cabinets or cold rooms may reduce selling’s! On the contrary, if the very same customers find a pleasant designed cabinet with a comfortable and kind access, for sure that he will feel invited to pick and buy the very same goods he rejected on the other situation (unpleasant usage).

2.3. Cost of [m2] of floor space in supermarkets or shops

a) The cost of used [m2] is obliging marketing and logistic technicians to create new concepts of layout and design of selling areas such as supermarkets and shops.

b) Manufacturers / contractors of refrigeration equipment are therefore obliged to redesign their equipment / plants to adapt them to this new concept – compact and customer’s friendly design.

c) The air cooler inside a cold room, a “reach-in” or “walk-in” cabinet is needed but:

• It reduces storage capacity
• It is very much related to the maximum outside dimensions of the cold room or cabinet.

3. These are real limitations for air coolers manufacturers that feel than obliged to follow the trend of HVAC (heating, ventilation and air conditioning) OEM’s in terms of “friendly, kind, smooth and compact design”, with low noise, high performance and reduced energy consumption operating conditions.

II – State of the Art

1. Nowadays coolers are mainly produced with forced convection air flow through a coil block produced with copper tubes expanded to the fin collars of the aluminium fins, being that:

• Copper tubes are called primary surface
• Aluminium fins are called secondary surface

2. Air coolers in terms of air circulation are produced under two concepts, as it follows:
“Blowing through arrangement”, where the air goes first through the fan and than through the coil.
“Sucking or draw through arrangement” where the air goes first through the coil and only than through the fan.

3.In terms of casing / coil arrangement in Refrigeration, the  casings of air coolers are rectangular by means of covering a rectangular coil block plus a space between the coil and the fans panels so called “plenum” or “cut off”. In low profile air coolers where height must be reduced, there is the so called double flow arrangement by means of two coaxial coils with fans in the middle. Apart from the reduced height these solutions reduces the air velocity inside the cold room / cabinet because the airflow is splitted in two air streams.

4.Coolers design in refrigeration application is quite different of HVAC field. As a matter of fact in Refrigeration designer deals with:

• very small DT when refereed to HVAC conditions
• very low air temperature, down to –35ºC
• very low refrigerant temperatures, down to –45ºC
• ice build up over the coil block and required efficient operations under frost conditions and optimal defrosting as well.
• Because of this operating conditions, Refrigeration coil blocks present:
• big heat exchange surfaces (primary and secondary ones) due to small DT.
• wide fins spacing due to ice build up
• integral fins whenever it is possible to optimise operating conditions on frost situation

III – Centauro “State of the Art” in terms of air coolers

1. In between the wide range of Centauro products many solutions can be found in terms of air coolers for the applications under analysis. Nevertheless the commitment of Centauro to full fill the customer’s expectations took Centauro to a situation of developing its own concept of “friendly, kind, smooth, efficient and reliable” air cooler for reduced internal volumes in terms of cold rooms / cabinets or small / medium processing rooms...

2. This new concept of refrigeration air cooler is the opposite to the conventional “rectangular air coolers” produced by Centauro and similar Companies by means of:

• smooth and round casing with round corner (kind and hygienic design)
• Circular coils instead of rectangular coil, from ¼ of circle, through ½ a circle up to 80% of a circle.
• Higher number of fans of smaller diameter enabling in “high tech” design to user not so expensive “DC” small fan motors.
• Optimal air distribution in 90º angle, 180º angle or almost 360º angle, enabling at the same time a maximal usage of the refrigeration space by means of location of the air cooler in a corner, in contact with a wall or even in the center of the cold room.
• Wide fins spacing 3.2 mm up  to 6.3 mm
• Corrugated fins, not louvered

3. This new concept of smooth and round cooler is quite different of special designed coils for air conditioners where OEM use:

• small fins spacing 1.4 up to 2.1 mm
• louvered fins
• Special design of the coils fitting the reduced spaces in the equipment by means of splitting the main coil into smaller coils (cutting into small coils in depth or in height) and brazing their circuits in between after they fit to the required geometry.
• Usage of non integral fins due to the constructive above mentioned solutions

• Usage of very small internal volume by means of tubes of 7.9 mm or even less outside diameter.

4. The heavy ice build up over the fins in the coil block is really the borderline between HVAC and Refrigeration air coolers. In low temperature applications, with frost conditions and required regular defrosting an integral fin  (not cutted into smaller fins either in depth or height) is required to allow an efficient and reliable operation.

IV – Round Centauro Coolers

1. It is under these concepts of “low temperature / refrigeration air cooler” that Centauro developed and designed its own machine to produce round coils with integral fins up to 4 rows depth.

2. Centauro is able to produce round condensers and coolers for refrigeration applications. In terms of air coolers is than able to produce:
¼ of circle coolers (EC) for mounting in corners, with air distribution in 90º angle.
½ of circle coolers (ML) to mount very near a wall with air distribution in 180º angle.
Round coolers (ER) to mount in the center of the roof with almost 360º angle in terms of air distribution

3. Special features of round coolers range ML / EC

3.1. Compact design suitable for low temperature application by means of:

a) Wide fins spacing up to 6.3 mm
b) Optimised internal volume by means of using 9.52 mm OD (outside diameter) tubes or, for big capacities, 12.7 mm OD
c) Integral fins either in depth (up to 4 rows) or in height.

3.2. Optimal and smooth air circulation by means of a distribution through an angle between 90º and 180º, with the advantage of blowing through arrangement (EC range and ML range).

3.3. Optimal face velocity in the coil (bigger face area) even in the tight conditions of low temperature air coolers – small working DT, higher air volumes.

3.4. Optimised conditions of the air leaving the coil in terms of:

a) air turbulence
b) air throw
c) air velocity
d) air temperature
e) air relative humidity

3.5. Reduced noise levels by means of being possible to use a bigger number of fans with smaller diameter and smaller motors enabling, in the limit to jump into DC main power supply to the motors.

3.6. Energy saving by means of the type of motors that can be used. It is a very big advantage to enable the use of small “DC” current fan motors, facing the future energy saving requirements.

3.7. Hygienic requirements are optimised by means of a casing without sharp corners! Any “detail” of it is round and smooth.

3.8. Available round coils for re-heating of the air (hot gas, hot water, and electric heating).

4. Special features of full round coolers “ER” range

a) Same as per EC and ML air coolers, except in some “sizes” where integral fin is not yet possible, reason why unless hot gas defrosting is used, “ER” coolers are recommended for air temperatures over +2ºC.
b) Round coolers “ER” can be used in cold rooms over +2ºC and mainly in small / medium processing rooms. For this last application drain correction can be scrapped by means of using a drain pump.

5. Capacities and features of round coolers

5.1. Fan diameters from 110 mm up to 630 mm, axial or radial / centrifugal type.

5.2. Fan motors with different power supply

• DC current
• AC current 230V / 50 H3 ~         (60 HZ M.P.S. available)
• AC current 400V / 50 H3 / 3~      (60 HZ M.P.S. available)

5.3. Several fan r.p.m. either fixed or under speed regulation concept

5.4. Operating with bi-phase or single-phase refrigeration flow (DX, pumped circulation, flooded coil or fluid cooler).

5.5. Duties from 0.10 kW up to 12.0 kW at SC1, according to ENV 328

5.6. Air volumes from 110 m3/h up to 5 000 m3/h.

5.7. Defrosting by means of :

• electrical heaters (only EC and ML)*
• hot gas
• For the moment

5.8. Available reheating coil by means of “round” coil block and usage of hot gas, hot water (glycol) or electrical heaters.

5.9. Usage of special copper tubes either smooth or inner grooved

5.10. Usage of corrugated fins in plain aluminium or coated aluminium.

6. Execution drawings and relevant photos of produced and tested round coolers (EC / ML) are joined.