Often called “heat and dump” dryers, because these constantly introduce heated fresh air, with this displacing an equivalent amount of moist air that is dumped. Most of the drying room air constantly circulates through the product, while a controller determines the percentage of fresh air to be introduced for maximum efficiency, given the stage of the drying cycle.
A heat pump may be used as the heat source. Yet a lower-cost alternative with higher running cost may simply involve the use of electric elements. This is viable for short seasonal applications.
Agridry Systems make use of a heat exchanger to capture the heat leaving with the moist air, using this to pre-warm the incoming ambient air.
This system is satisfactory for most products, but the lowest humidity achievable is limited by the geographic location and the season. Coastal or tropical locations during high humidity periods are the most problematic situations as the lowest humidity achievable may not suit some products.
Closed cycle heat pump dryers
Agridry Systems leads the industry with the efficiency and performance of their closed cycle heat pump dryers.
A very useful unit is the 500 kg model. The complete unit is constructed as an insert that is positioned in a 1800mm wide opening in the customers drying room. It can be transported by truck or within a shipping container and moved into position using a forklift. All it then requires is a three phase electrical connection and a drain.
The unit may accessible remotely, for checking the progress of a product batch, the logged data, or amending the program.
Advanced technical features:
For the technical-minded, the following design features allow for industry-leading performance figures to be obtained:
- Electronic metering control of refrigerant
- Computer-controlled bypass airflow rate through an efficient and deep evaporator coil to extract water from the airflow.
- Pre-cooling of the bypassed air entering the evaporator, by heat exchange with the leaving air.
- Sub-cooling of the refrigerant before it enters the evaporator coil.