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Variable speed drive refrigerant air dryer

Air compressors Refrigerant dryers Air and gas treatment

Most production operations have a fluctuating need for compressed air, but a traditional air compressor has just one speed: full capacity. If less air is needed, a lot of energy is consumed and wasted. But an air compressor equipped with Variable Speed Drive (VSD) provides significant energy savings by automatically adjusting motor speed to match air demand. Now a complementary technology applies energy saving Variable Speed Drive to refrigerant air dryers to deliver high quality air dried to a low and stable dew point while saving energy.

How a refrigerant air dryer works

Dryer
A refrigerant air dryer is a crucial air system component for operations that require compressed air dried to a low dew point. In the first stage, compressed air enters the dryer and passes through an air to air heat exchanger, which precools the incoming air.

In the second stage, compressed air passes through an air to refrigerant heat exchanger to reduce the compressed air dewpoint to 3°C / + 37°F. Water vapor that was in the air condenses into liquid, which is trapped and removed.

The dry air is then warmed up in the air to air heat exchanger to reduce the relative humidity in the air to prevent condensate from forming in downstream piping.

How a VSD refrigerant air dryer works

A refrigerant air dryer has a compressor of its own that compresses the refrigerant gas to liquid form. Conventional refrigerant air dryers typically employ a reciprocating (piston) compressor operating at one fixed speed. In terms of energy efficiency, this results in the same “on or off” shortcoming present in a fixed speed air compressor. In contrast, a VSD refrigerant air dryer uses a scroll compressor with one spiral element orbiting around second, fixed element. It’s compact and quiet, and the inverter that drives the scroll element can vary speed to match demand.

VSD system sync

Like a VSD air compressor, a VSD refrigerant air dryer automatically adjusts its output to meet fluctuating demand for dry compressed air. This is possible because the dryer’s control system works in the same manner as the compressor’s, adjusting speed by means of an inverter. As demand for air changes, the air compressor’s drive motor speeds up or slows down to match demand, and the refrigerant air dryer’s  refrigerant compressor simultaneously speeds up or slows down in sync with the air compressor.

More efficient than thermal mass (cycling)

An older technology known as thermal mass or cycling provides a degree of energy efficiency for refrigerant air dryers. A thermal mass air dryer cycles between running at full load and relying on a thermal mass for cooling. This represents an improvement over dryers that simply operate at a fixed speed (full capacity or off). However, cycling dryers must consume energy to cool down their thermal mass, which reduces their overall energy savings.

Dew point stability

An important advantage of a VSD refrigerant air dryer is a reliable supply of outstanding quality air at a stable, low dew point, regardless of ambient air temperature. With a thermal mass dryer, the compressed air dew point is the indicator for its fixed speed refrigerant compressor to start or stop. As a result, air dew point rises and falls. This fluctuation can compromise air quality by up to two purity classes. In contrast, a VSD refrigerant air dryer consistently delivers air that has been dried to a stable dew point.

Dew Point purity chart