Second Generation Integrated Combined Heat and Power Engine Generator and Liquid Desiccant System

Abstract

The Combined Heat and Power (CHP) concept is aptly suited to improve or eliminate some of the global and local issues concerning electric commercial buildings. CHP involves on-site or near-site generation of electricity by using gas-fired equipment along with utilization of thermal energy available from the power generation process. CHP has the potential of providing a 30% improvement over conventional power plant efficiency and a CO2 emissions reduction of 45% or more. In addition, an overall total system efficiency of 80% can be achieved because of the utilization of thermal energy, that would otherwise be wasted, and the reduction of transmission, distribution and energy conversion losses. CHP technology also makes cost savings possible by reducing high summertime electrical demand charges while at the same time providing necessary space heating and cooling. Savings are further increased in applications where waste heat can replace electric heating. Moreover, CHP has the ability to address indoor air quality issues when utilizing a desiccant dehumidifier by providing direct humidity control and consequently reducing the potential for mold and bacteria development. Because power generation is done on-site, CHP provides control in meeting a building’s electrical needs and also provides an increased level of reliability to ensure high employee productivity. The current research is being carried out in a four–story commercial office building that has been established as the CHP research and demonstration facility on the campus of the University of Maryland in College Park, MD, USA. The 52,700 square feet administrative building includes two heating, ventilating and air-conditioning (HVAC) zones of equal area where zone 1 includes the first and second floors and zone 2 includes the second and third floors. This has facilitated the installation of two different CHP systems for the two zones. The research in this paper discusses about the CHP system catering to zone 1. This paper describes a second generation CHP system involving the integration of a new 75 kW commercial engine generator with the existing liquid desiccant system. The engine generator is connected parallel to the grid for supplying 75 kW of electrical power to the building while the combined waste heat recovered from the exhaust gases as well as the jacket water from the engine is used to heat a 50:50 ethyl glycol–water loop through a packaged heat recovery system. This recovered heat is then used for the regeneration of the lithium chloride solution in a liquid desiccant system and the ethyl glycol–water solution is returned back to the engine. The liquid desiccant system reduces the latent load of the ventilation air entering the roof top unit. Technical challenges concerning electrical and control aspects that were related to modifications of the original CHP system are described and improvements to the original system design and performance are evaluated. The paper then discusses the experimental results obtained with first generation CHP system and its overall performance.