Direct cooling and indirect cooling
Air-forced Cooling systems
Air-forced Cooling systems are compact evaporators operates by forced air circulation by a rotating fan, however by this way of cooling a perfect heat transmission occurs.
Air-forced cooling has been designed to keep a low temperature stabilised once it has been environmental cooled, however it often does not remove field heat rapidly enough to maintain the quality of highly perishable crops. Standard room cooling is very often inadequate for products stored in large area's like storage sheds, bulk boxes or pallet loads, and for products that requires immediate cooling indeed.
Normally area cooling process, heat is removed slowly from only that products near the outside of the area to cool. Near the center of this area, heat is often generated by natural respiration more rapidly than it can be removed, causing the temperature to rise. 
Some types of products, such as fish, must be cooled as quickly as possible after harvesting to preserve its fresh quality. Even a delay of several hours may be enough to reduce quality considerably. In such cases, room cooling is not fast enough to prevent serious damage.
To preserve quality, fresh products should be cooled to its lowest safe (optimum) storage temperature as quickly as is practical and economical. Forced-air cooling is much faster than room cooling and is being used increasingly in the area of Fish-holds, storage environments to cool those products quickly.
Advantages of Forced-air cooling
- It decreases the time the produce remains at elevated temperatures, thereby reducing deterioration;- It results in shorter cooling times and thus more efficient use of the cooling facility;
- Fish, food and products which requires cooling effectively in a variety of unopened storage area's without wetting or subjecting it to excessive handling;
- Forced-air cooling is often more energy efficient than standard room cooling when large volumes of products must be cooled;
- An available room-cooling facility with adequate cooling capacity can be converted to forced-air cooling with only a relatively small investment in fans
Forced-air cooling is likely to increase the overall energy cost slightly by increasing electrical demand, a measure of the rate at which electricity is consumed. To reduce demand cost, produce should not be cooled any faster than necessary.
Forced-air cooling can also increase cooling cost by increasing the cooling load per unit of time. Quicker cooling requires larger refrigeration units, the cost of which must be amortized over the life of the facility.
Forced-air cooling is a useful tool for preserving the quality of fresh produce like fish. It is most effective when the product demands quick cooling or when the amount of produce to be cooled per day or week is large enough to justify the increased equipment and electrical demand costs.
Forced-air cooling is accomplished by exposing packages of the product in a cooling room to higher air pressure on one side than on the other. This pressure difference forces the cool air through the packages and past the produce, where it picks up heat, greatly increasing the rate of heat transfer. Depending on the temperature, airflow rate, and type of produce being cooled, forced-air cooling can be from 4 to 10 times faster than standard room cooling.
Advantage by Air-forced cooling will be optimised by:
- Less piping's in fish-hold.
- Area room will been saved (more room for fish storage).
- No corrosion by the use of Stainless Steel SS 316).
- Automatic defrost to improve the nominal capacity to a maximum, however this procedure results in an superior ratio of wages to capacity.
Blast Freezers:
What is a blast freezer?
A blast freezer is a freezer which is extremely cold. It may also be known as a shock freezer. Such freezers are intended to rapidly bring the temperature of foods down, freezing them extremely quickly. These specialized freezers are used in the frozen food industry for everything from ice cream to television dinners, and they are also utilized in some commercial kitchens for specialty tasks. It is possible to obtain a blast freezer from a freezer manufacturer, with some manufacturers offering custom modifications for specific applications.
Scrimp-vessels ( Africa and America) are mostly standard equipped with Blast freezers indeed. Blast freezers consists of special produced tunnels with one directional strong forced air-flow. This air-flow proceeds through the product and evaporator.
The temperature air by – 35°C attend to a product temperature of – 28°C within 2,5 – 3 hours.
