There was a time when energy efficiency was not a criterion for designing critical environments. From data centers to museum exhibit spaces, critical environments required tight temperature and relative humidity control at all costs.
To meet the stringent space condition requirements while still mitigating risk, professional engineers have traditionally used precision cooling units that control humidity by cooling the air below the dew point (vapor condensation) and then reheating it to meet the desired space conditions. While this method is tried and true, it is also energy-intensive. Alternatively, engineers have employed solid desiccant systems to achieve the same results. Solid desiccant systems are typically made of silica gel or activated alumina and use a physical process called adsorption, where moisture is condensed and held on the surface of the material. Although they may require less energy than the vapor condensation systems (assuming a recovered source of heat), engineers have been challenged by the fact that solid desiccant systems are still often more expensive to install and maintain.