Eric Kozubal

A ZERO CARRYOVER LIQUID-DESICCANT AIR CONDITIONER FOR SOLAR APPLICATIONS

A novel liquid-desiccant air conditioner that dries and cools building supply air has been successfully designed, built, and tested. The new air conditioner will transform the use of directcontact liquid-desiccant systems in HVAC applications, improving comfort and indoor air quality, as well as providing energy-efficient humidity control Liquid-desiccant conditioners and regenerators are traditionally implemented as adiabatic beds of contact media that are highly flooded with desiccant. The possibility of droplet carryover into the supply air has limited the sale of these systems in most HVAC applications. The characteristic of the new conditioner and regenerator that distinguishes them from conventional ones is their very low flows of liquid desiccant. Whereas a conventional conditioner operates typically at between 10 and 15 gpm (630 and 946 ml/s) of desiccant per 1000 cfm (0.47 m 3 /s) of process air, the new conditioner operates at 0.5 gpm (32 ml/s) per 1000 cfm (0.47 m 3 /s). At these low flooding rates, the supply air will not entrain droplets of liquid desiccant. This brings performance and maintenance for the new liquid-desiccant technology in line with HVAC market expectations. Low flooding rates are practical only if the liquid desiccant is continually cooled in the conditioner or continually heated in the regenerator as the mass exchange of water occurs. This simultaneous heat and mass exchange is accomplished by using the walls of a parallel-plate plastic heat exchanger as the air/desiccant contact surface. Compared to existing solid- and liquid-desiccant systems, the low-flow technology is more compact, has significantly lower pressure drops and does not “dump” heat back onto the building’s central air conditioner. Tests confirm the high sensible and latent effectiveness of the conditioner, the high COP of the regenerator, and the operation of both components without carryover.

Development and Analysis of Desiccant Enhanced Evaporative Air Conditioner Prototype

This report documents the design of a desiccant enhanced evaporative air conditioner (DEVAP AC) prototype and the testing to prove its performance. Previous numerical modeling and building energy simulations indicate a DEVAP AC can save significant energy compared to a conventional vapor compression AC (Kozubal et al. 2011). The purposes of this research were to build DEVAP prototypes, test them to validate the numerical model, and identify potential commercialization barriers.

The Volatile Organic Compound (VOC) Removal Performance of Desiccant-Based Dehumidification Systems: Testing at Sub-ppm VOC Concentrations

We investigated the ability of a typical desiccant wheel to remove two common volatile organic compounds (VOCs), toluene and n-hexane, from an airstream at concentrations in the range 50–150 ppb. The effects of wheel speed, regeneration temperature, relative humidity, and VOC challenge concentration were examined. The desiccant wheel was able to transfer ~70% of the toluene and ~20% of the n-hexane from the process inlet stream to the regeneration outlet stream for the default process parameter settings. These removal efficiencies varied only slightly over the range of process parameters studied.

Combining liquid desiccant dehumidification with a dew-point evaporative cooler: A design analysis

This article uses a numerical model to analyze a concept combining a liquid desiccant dehumidifier with a dew-point indirect evaporative cooler. Each of these components, or stages, consists of an array of channel pairs, where a channel pair is two air channels separated by a thin plastic plate. In the first stage, a liquid desiccant film lining one side of the plates removes moisture from the process (supply-side) air through a membrane. An evaporatively cooled exhaust airstream on the other side of the plastic plate cools the desiccant. The second stage sensibly cools the dried process air with a dew-point evaporative cooler. This article uses a parametric analysis to illustrate the key design tradeoff for this concept: device size (a surrogate for cost) versus energy efficiency. The analysis finds the design parameters with the largest effect on this tradeoff and finds the combinations of design parameters giving near-optimal designs, which are designs with the highest efficiency for a given device size. The results indicate that there are two key parameters contributing to this tradeoff: the supply-side air channel thickness and the exhaust-air flow rate in the evaporative cooler.

Combined Cooling, Heating, and Power (CCHP) System: Cooperative Research and Development Final Report, CRADA Number CRD-14-570

of CRADA Work: NREL and Be Power Tech, Inc. (Be Power) will jointly develop a new combined cooling, heating, and power (CCHP) system that uses desiccants in combination with evaporative cooling and fuel cells. The combined system will have better economics and business case than a separate desiccant enhanced air conditioner and fuel cell system. The overall system is expected to become a net revenue generator by delivering power and air conditioning to a building while inputting natural gas and water. This development effort will revolve around adapting NREL’s desiccant cooling technology to work with Be Power’s proprietary system integration design for CCHP systems. The objective of the CRADA is to develop, then commercialize this CCHP system by jointly developing the system integration design, testing methods, and hardware for this system. The commercial name given to the CCHP system is BeCoolTM. Summary of Research Results: This report contains protected CRADA information, which was produced under CRADA No. CRD-16-570 and is not to be further disclosed for a period of five (5) years from the date it was produced except as expressly provided for in the CRADA. NREL provided expert consultation and design assistance to implement NREL’s desiccant cooling technology into the CCHP system. The tasks were to co-develop a CCHP system using NREL’s design tools and expertise. The project was structured into four project areas based on NREL areas of support for Be Power Tech:

Low-Flow Liquid Desiccant Air Conditioning: General Guidance and Site Considerations

Dehumidification or latent cooling in buildings is an area of growing interest that has been identified as needing more research and improved technologies for higher performance. Heating, ventilating, and air-conditioning (HVAC) systems typically expend excessive energy by using overcool-and-reheat strategies to dehumidify buildings. These systems first overcool ventilation air to remove moisture and then reheat the air to meet comfort requirements. Another common strategy incorporates solid desiccant rotors that remove moisture from the air more efficiently; however, these systems increase fan energy consumption because of the high airside pressure drop of solid desiccant rotors and can add heat of absorption to the ventilation air. Alternatively, liquid desiccant air-conditioning (LDAC) technology provides an innovative dehumidification solution that: (1) eliminates the need for overcooling and reheating from traditional cooling systems; and (2) avoids the increased fan energy and air heating from solid desiccant rotor systems.