Article: Multi Air stream Technology
12Pages

By R. Schomaker Director Export Biddle bv Җ P.O.Box 15 - NL - 9288ZG Kootstertille tel. +31 512 335554 export@biddle.nl www.biddle.info >

The right way to an open doorway in cold stores offering many advantagesFog and icing are problems in cold stores. These come about when cold air from the cold store meets ambient air in the front hall. A solid separation between the cold store and the front hall is not achievable since there is traffic in and out. Manufacturer of climate separation and climate control equipment Biddle in Kootstertille The Netherlands has fount the solution: the cold store air curtain. Whilst the cold store door is open all day, ambient and cold air remain strictly separated. Problems caused by convection...

Picture 1: The effect of fog in a cold store. Ice on walls and ceiling, snow and ice on the floor. To minimize the loss of cold air and penetration of warm air in the doorway of a cold room, often plastic flaps are used. They create a flexible, transparent barrier between warm and cold side. However, every time a fork lift truck with pallets or personnel passes the doorway, these flaps are pushed away with force and as a result these flaps damage very quickly and openings appear. Due to the high convection forces the flaps are also pushed aside and this also creates openings which cause at...

A different solution which is frequently chosen to minimize losses of cold air with all negative things coming as a result is to apply so called fast moving doors. These doors are operated by pulling a cord and open only when people or pallets are moving through the doorway. Besides a quite high investment they have more disadvantages; every time they open, huge volumes of cold and warm air mix and the same problems as described above occur. In addition these doors are very sensitive and small collisions and the extreme temperature conditions often cause damage or failures and repair costs...

Picture 7 - 8: The Biddle solution with a MAT air curtain The pictures above show a solution to create a fully open doorway with a special MAT air curtain. MAT stands for Multi Air Stream, a patented technology that uses three individual air flows to minimize the exchange of energy between a cold room and loading area and to take away any risk of fog and ice build-up. The result is a completely un-interrupted doorway with clear visibility, no ice on floor, walls, ceiling, products or on the refrigeration equipment, no possibility for bacteria growth, no energy losses or strong increasing...

MAT Figure 2: The principle of operation of the MAT air curtain Prevention of turbulence and condensation The MAT air curtain is a unit creating three individually controlled flows of air. These air streams are generated by powerful fans and pass a rectifying grill before they leave the unit. The unit is mounted in a frame and corridor in front of the cold room door opening. The rectifying grill makes sure that the air streams are nearly laminar and that they will reach the floor with minimum turbulence. The primary task of the air curtain is to create a barrier for cold air leaking from...

Figure 3: The Mollier diagram which shows the functioning of the MAT Energy saving because of intelligent control To control the three flows of air and to provide always the correct amount of heating for the middle stream, the MAT is equipped with several intelligent digital controllers. The MAT is also equipped with sensors for measuring the loading hall temperature and humidity level. Based on the readings of these sensors the controllers set the heating level such that there is just enough drying capacity. With varying conditions for the loading hall the controller will always find a new...

Maintenance Depending on use and the humidity levels in the loading hall the unit needs to de-frost. This is done automatically when the cold store door is closing. Under normal conditions this should be done every 24 hours but at least once per 5 days of continuous operation of the MAT. After about 15 minutes of de-frosting the unit is ready for use again. The maintenance of the MAT unit is limited to a regular check if all fans are working properly. Depending on the location of use, an annual or bi-annual cleaning of the fans with high pressure air is all you have to do. The advanced...

Figure 6: An example for the mounting of the MAT For a good functioning of the MAT it is important to avoid draft close to the cold room doorway. This means in practice that there should not be any doors within a few meters from the MAT to the outdoor space. In case of a door to a neighboring loading hall close to the installed MAT, great care should be taken again to avoid draft. A MAT installed on a doorway from a cold room directly to outdoor space is strongly advised against! In case of a situation where there are several doorways to one cold room at different height levels, there...