DOE EERE Research Reports

Thermally Activated Heat Pumps

Desiccant Dehumidification Systems

Integrated Desiccant-Compression Ventilation System Development

Desiccant Dehumidification Enhancement of Electric Air Conditioning Units Final Report
October 1993

Bruce G. Nimmo
Kannan Rengarajan

Florida Solar Energy Center
300 State Road 401
Cape Canaveral, Florida 32920

Abstract: There is a growing recognition of the need to address humidity control for buildings in hot and humid climates. Some of the tangible benefits from improved indoor humidity control are: healthier environments, energy savings, demand reduction, and improved productivity. The increase in ventilation rates to meet ASHRAE standard 62-89 for commercial buildings, and the potential for high humidity problems have further motivated the electric and gas industries to develop advanced dehumidification technologies.

A new concept, the desiccant enhanced air conditioner (DEAC) dehumidification option, appears to offer improved humidity control at lower costs. Based on the results of this study, an energy saving potential of 3.25 to 6.5 x 106 MWatt hours per year exists for the estimated primary area of residential DEAC users. A comparative analysis of the DEAC system and its performance form the basis of this study.

The Desiccant Enhanced Air Conditioning (DEAC) concept was conceived and patented by C. Cromer of the Florida Solar Energy Center (FSEC). The DEAC uses a desiccant wheel or liquid desiccant to pre-cool and humidify return air before it enters a cooling coil. It then heats and dehumidifies the supply air after it leaves the coil. A unique feature of this process is that regeneration of the desiccant component is accomplished by the return air rather than by an external heat source. The result of the DEAC psychrometric process is increased dehumidification of the supply air.

One advantage of the desiccant approach over a sensible heat exchanger (e.g. heat pipes) is the relatively high wet bulb temperature of air entering the evaporator coil. This helps maintain high efficiency of the air conditioner while improving dehumidification.

Other air-conditioning (AC) systems currently available for improved dehumidification and considered in the study include: a. Heat pipe-assisted air conditioners, b. Air-reheat systems (e.g. electric reheat), c. Variable-speed air conditioners (VSAC), and d. Gas-fired solid and liquid desiccant systems.

The goals of this study were to:

  • Compare DEAC EER to alternative electric systems over a range of sensible heat ratios
  • Compare DEAC performance to that of electric and gas dehumidification systems when operating in three building types (residence, office, and fast food restaurant) in three climates (Miami, St. Louis, and Washington DC)
  • Identify the DEAC primary geographical region of applicability
  • Estimate for the primary region of applicability, the potential residential energy saving of the DEAC relative to the current high-efficiency air conditioner for the case when both meet the same standard of comfort
  • Provide an analysis of the run-around belt option as an alternative to the desiccant wheel for use in the DEAC
This report summarizes the basis and results of the computer simulation studies performed to achieve the above goals.

Keywords: desiccant, dehumidification, Cromer cycle, DEAC, desiccant enhanced air conditioner

Florida Solar Energy Center
300 State Road 401
Cape Canaveral, Florida 32920

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