Abstract: The use of on-site or near-site distributed electric power generation (DG), as part of an integrated energy system (IES), brings available
waste heat closer to the end user's thermal loads. Heat-activated technologies such as desiccant dehumidification units are increasingly being viewed as an
important element to effectively apply in IES designs that increase system efficiency, reduce fuel costs and consumption, and provide both electrical and thermal load energy.
The purpose of this study is to investigate both the baseline performance of a commercially available direct-fired desiccant dehumidification unit and its performance
as one of the components of an IES. Desiccant dehumidification units, which are used to reduce the latent load (remove moisture) of the process (conditioned)
air, are specified on the basis of grain depression and/or latent capacity (LC). Several operating parameters, such as process and regeneration air conditions
(dry-bulb temperature and humidity), volumetric airflow rates, and desiccant loading affect the ability of the desiccant unit to remove moisture. This study
investigates the impact of varying process and regeneration conditions on LC and latent coefficient of performance (LCOP) of heat-activated desiccant dehumidification
units. The baseline performance of the desiccant unit with regeneration air heated by direct burning of natural gas is compared wth an IES case in which
the exhaust gas from a microturbine and its heat recovery unit are used as the regeneration energy source.
Baseline performance tests show that both LC and LCOP increased with inlet air dew point while keeping the otheer parameters (gas input and electric parasitics)
constant. The maximum baseline LCOP and LC were 0.58 and 103,246 Btuh/h (30 kW), respectively. Using residual microturbine exhaust gas (what remains of the
exhaust after going through an air-to-water heat recovery unit) as the regeneration heat source results in a 50% decrease in the latent cooling capacity
of the desiccant dehumidification unit unit as compared to its baseline performance. However, adding the desiccant dehumidification unit to a microturbine/heat recovery
unit in the IES increased system efficiency by 7% over the microturbine/heat recovery unit only. Emissions tests show that the most signficant pollutant is
carbon monoxide (CO). The average CO level in the regeneration outlet air (flue gas) was found to be about 13 ppm. In addition, the emissions tests did not show
an significant cross-contamination between the process and regeneration airstream sides of the desiccant dehumidification unit.
Keywords: desiccant dehumidification, microturbine, integrated energy system, IES, combined cooling heating and power, CHP, distributed generation, DG, TAT, thermally activated technology
American Society of Heating, Refrigerating, and Air-Conditioning Engineers
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ASHRAE Transactions 2003
Vol. 109, Pt. 2