Conventional refrigerant dehumidifiers are effective in reducing high humidity to a normal level (approximately 40% relative humidity, or about 55 GPP) in room temperatures.

Their chief shortcoming is their inability to reduce the humidity to a level appropriate for supporting evaporation in sites that includes large amounts of bound water. They simply cannot get the air in the drying environment dry enough to “pull” enough moisture from saturated materials.

Low grain refrigerant (LGR) dehumidifiers, however, can continue to remove moisture from environments below 55 GPP. In fact, LGRs work better in most drying environments. They work well in high humidity and work efficiently in drier conditions.

LGRs will continue produce lower specific humidity – and therefore lower vapor pressures – in conditions that will render conventional refrigerant dehumidifiers ineffective.

An LGR achieves this higher efficiency by incorporating a pre-cooling system, which supplies the unit with cooler air to process. These systems do not require additional energy to operate, and allow the dehumidifier to remove more water in a broader range of conditions.

There are three types of pre-cooling systems used in LGRs:

The heat pipe is a looped system placed in front of and immediately behind the cold coil. A refrigerant sealed inside the pipe collects heat from the incoming air, and the refrigerant then heats and evaporates. The heated, evaporated refrigerant is transferred to the back side of the cold coil where it is cooled and condensed. This cooled refrigerant is then transferred to the front of the coil where it is once again heated and evaporated. This cycle repeats over and over, continually supplying cooled refrigerant to the front of the cold coil and pre-cooling the incoming air.

A thermal siphon operates similarly to the heat pipe, but utilizes a “stacked” hot and cold coil. It will fit into a much smaller dehumidifier chassis.

Instead of using liquid refrigerants to transfer heat, an air-to-air heat exchanger utilizes air. Warm incoming air is directed through the channels of a corrugated plastic or aluminum block. At the same time, cooled air from the cold coil is directed through a second set of corrugations in the block. This pre-cools the warm incoming air before it passes through the hot side of the refrigerant cycle. Air-to-air exchange systems are lightweight and less complex than either heat pipe or thermal siphon systems.

Because of their efficient use of energy and their ability to continue operating efficiently in low grain and high temperature environments, many restorers use only dehumidifiers equipped with LGR technology.

Brandon Burton is the technical education manager for the Restoration Sciences Academy, a part of Legend Brands. He has served the restoration community for more than 15 years as an IICRC instructor, ANSI/IICRC S500 chair, RIA restoration council member, and many other industry roles. You can contact Burton at brandonb@rsa-hq.com.