Cycling Refrigerated Air Dryers
Hope Air Systems distributes compressed air dryers manufactured by Kaeser and other manufacturers designed to meet the critical operational specifications for its industrial customers. Among the most popular types of dryers are "refrigerated" dryers. They are available as cycling or non-cycling, each with particular advantages.
The Kaeser "Secotec" model of cycling refrigerated air dryers, available from 20 – 520 cfm @ 100 psig, provides maximum efficiency by operating the refrigerant compressor only when necessary. This is achieved by utilizing a thermal storage medium. The refrigerant system cools the medium to a certain temperature, cuts off, and then stands by until the temperature rises to a predetermined level before switching on again. In this way, the dryer is not wasting energy when the demand is low. A non-cycling dryer would continue to operate even during low demand periods.
Why do we need dry air?
As atmospheric air is drawn into a compressor, water vapor is introduced as well. During compression, air heats up and is able to hold more water vapor. Mechanical separators and filters are used to remove liquid water, yet air remains saturated with water vapor. As air travels through the piping, the vapor cools, condenses and may pass into production tools and equipment. Using a refrigerated dryer eliminates vapor before it condenses and affects the system.
Operations characteristics of cycling air dryers
Warm compressed air entering the dryer is initially cooled in the air-to-air heat exchanges by the cold compressed air leaving the dryer. This allows for greater efficiency by reducing the heat load on the refrigeration system. The air is cooled to the dew point temperature in the lower part of the heat exchanger by a refrigerant circuit with a thermal storage medium. The condensate formed by the cooling action is separated from the compressed air by a multi-stage, stainless steel, maintenance-free separating system. The automatic condensate drain drains the water without wasting valuable compressed air. The dried air leaving the dryer is reheated in the upper part of the heat exchanger before exiting the outlet. Reheating the compressed air eliminates pipe sweating downstream.
Energy savings advantage
The cycling control of the Secotec design provides the greatest savings during low demand periods, such as, evening and night shifts. The chart shows significant savings are possible on a daily basis. During breaks, low demand periods, and shut down, the dryer saves energy because the refrigerant system has shut off.
Energy savings specifics
Let's look at a hypothetical situation to understand potential energy savings. If a 240 cfm non-cycling dryer operated 24 hours a day, 365 days a year (never shutting off) it would operate over 8,000 hours. Using estimated costs for electricity (for comparison) the costs would look like this:
8,000 x 1.5kW x $0.08/kWh = $ 992
If the cycling dryer only runs when needed, which would be about 1,000 hours, instead of 8,000 hours, the costs would look like this:
1,000 x 1.5kW x $0.08/kWh = $ 120.
That's a savings of 88 percent or about $ 872 compared to $ 992. That's a lot of savings.
Important features and advantages
All components in the Kaeser Secotec dryer such as heat exchangers, refrigerant circuit, condensate separator and drain are conveniently accessible from above when the panels are removed. Service connections are provided at the suction and discharge lines to check the refrigerant circuit. The dryer construction and component arrangement minimize the required floor space. Among the important features are:
- efficient cycling control
- high thermal storage capacity
- minimal pressure drop
- no prefilter required
- stainless steel condensate separator
- no-loss electronic condensate drain
- quick access to components
- durable control cabinet
- easy to read control panel
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