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Published: 2008

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The Need and the Opportunity Codes such as ASHRAE 90.2 and IECC, and programs such as Energy Star and Builders Challenge, are causing new homes to be built to higher performance standards. As a result sensible cooling loads in new homes are going down, but indoor air quality prerogatives are causing ventilation rates and moisture loads to increase in humid climates. Conventional air conditioners are unable to provide the low sensible heat ratios that are needed to efficiently cool and dehumidify homes since dehumidification potential is strongly correlated with cooling system operating hours. The project team saw an opportunity to develop a system that is at least as effective as a conventional air conditioner plus dehumidifier, removes moisture without increasing the sensible load, reduces equipment cost by integrating components, and simplifies installation. Project Overview Prime contractor Davis Energy Group led a team in developing an Integrated Heating, Ventilation, Cooling, and Dehumidification (I-HVCD) system under the DOE SBIR program. Phase I and II SBIR project activities ran from July 2003 through December 2007. Tasks included: (1) Mechanical Design and Prototyping; (2) Controls Development; (3) Laboratory and Field Testing; and (4) Commercialization Activities Technology Description. Key components of the prototype I-HVCD system include an evaporator coil assembly, return and outdoor air damper, and controls. These are used in conjunction with conventional components that include a variable speed air handler or furnace, and a two-stage condensing unit. I-HVCD controls enable the system to operate in three distinct cooling modes to respond to indoor temperature and relative humidity (RH) levels. When sensible cooling loads are high, the system operates similar to a conventional system but varies supply airflow in response to indoor RH. In the second mode airflow is further reduced, and the reheat coil adds heat to the supply air. In the third mode, the reheat coil adds additional heat to maintain the supply air temperature close to the return air temperature (100% latent cooling). Project Outcomes Key Phase II objectives were to develop a pre-production version of the system and to demonstrate its performance in an actual house. The system was first tested in the laboratory and subsequently underwent field-testing at a new house in Gainesville, Florida. Field testing began in 2006 with monitoring of a 'conventional best practices' system that included a two stage air conditioner and Energy Star dehumidifier. In September 2007, the I-HVCD components were installed for testing. Both systems maintained uniform indoor temperatures, but indoor RH control was considerably better with the I-HVCD system. The daily variation from average indoor humidity conditions was less than 2% for the I-HVCD vs. 5-7% for the base case system. Data showed that the energy use of the two systems was comparable. Preliminary installed cost estimates suggest that production costs for the current I-HVCD integrated design would likely be lower than for competing systems that include a high efficiency air conditioner, dehumidifier, and fresh air ventilation system. Project Benefits This project verified that the I-HVCD refrigeration compacts are compact (for easy installation and retrofit) and can be installed with air conditioning equipment from a variety of manufacturers. Project results confirmed that the system can provide precise indoor temperature and RH control under a variety of climate conditions. The I-HVCD integrated approach offers numerous benefits including integrated control, easier installation, and reduced equipment maintenance needs. Work completed under this project represents a significant step towards product commercialization. Improved indoor RH control and fresh air ventilation are system attributes that will become increasingly important in the years ahead as building envelopes improve and sensible cooling loads continue to fall. Technologies like I-HVCD will be instrumental in meeting goals set by Building America and other programs to reduce energy use while improving the indoor environment. Next Steps The following steps are needed to bring the product to commercialization: (1) Value engineering to reduce costs; (2) Addition of zoning capability to improve marketability; (3) Fabrication and testing of additional prototypes; and (4) Identification of a manufacturer. Initial efforts to interest large air conditioner manufacturers has shown some interest, but the preferred path to market may be to employ a boutique manufacturer that markets to HVAC contractors. Distribution of the results of this work will improve opportunities for attracting manufacturers. Additional funding is needed to prepare the product for this final step.