Variable Time Retention Freezer VRT

The variable retention time freezer (VRT) is used to cool or freeze products in boxes, cartons, or trays.  Its major advantage is that it can freeze several different products, each with different freezing times and different size package using a programmable computer that controls its operation.  Our VRT  has a series of independent trays that can be loaded into any tray guide at any level.  A programmable computer controls the VRT.

Variable Time Retention Freezer VRT

The machine cycle begins when new product is sent from the processing area to the VRT.   An accumulating conveyor system receives and holds the boxed product until a sufficient number of boxes are received to fill one freezer tray.

When a full load is ready, the boxes are automatically transferred to the infeed conveyor and loaded onto an empty tray. The vertical loading elevators raise the loaded tray to the designated level. The tray, is then inserted into the tray guides.  As a new tray is moved into position, It advances all of the trays ahead. The last tray on the loaded level is transferred onto the rear elevator and is lowered. Once the frozen tray Ii reaches the bottom, the product is unloaded and removed by the exit conveyor. Empty trays are returned to the front of the freezer to receive new product.

New trays entering into the freezer are electronically stamped with an entry time.   As trays advance through the freezer,. their elapsed dwell time is traced.   Periodically, the dwell time of each tray as updated and displayed on the VRT status screen. Through this method, elapsed dwell time of each tray can be reviewed at a glance.

If frozen product needs to be removed from the freezer but no new product needs to be loaded, the unload process is used.  Empty trays are returned from the unloaded area and inserted into levels selected for unloading. This cycles empty trays through the freezer and transfers trays with frozen product to the rear elevator for unloading.   In the automatic mode, the computer is used to make the unloading decision.   All trays with product meeting or exceeding the required dwell time are automatically cycled out of the freezer.  Our VRT can be operated in a semi-automatic or manual control mode. Typical industry applications include freezing meat, precooked foods, and fruit/fruit juices in cartons or trays, and freezing ice cream in trays or overwraps.

Our VRT freezer is designed for counterflow heat exchange. Directing the coldest air against the coldest product ensures thorough product freezing.   Packages are arranged with minimal spacing to allow for efficient heat rejection from both sides. The perforated trays are designed to allow uniform heat rejection from the package bottom.  Packages are loaded on the trays so that the long side is aligned with the airflow.  This, along with the perforated trays, exposes the maximum area of the carton to the cold air, thus minimizing freezing time.

After passing over the product, the refrigerated air is returned down the sides of the tunnel and across the evaporators. Careful attention is placed on creating efficient turbulent airflow across the product, while minimizing fan horsepower.  This design reduces air quantities by as much as 50% compared to conventional systems using an air-distribution system that distributes air from the sides of the VRT. 

VRT freezers have controlled air- flow with freezing times of 20% to 40% less than blast freezers