Integration of trigeneration system and thermal storage under demand uncertainties

In a commercial building, a large portion of electricity is usually consumed in air conditioning to control indoor-air temperature and humidity. Energy savings or efficient production in air conditioning system is, therefore, crucial. In recent years, trigeneration systems, which provide electricity, heating and cooling, and thermal storage systems, which temporarily store cooling energy to smooth its production pattern, are attracting more attentions. These systems with different operating principles are usually designed based on nominal or peak loadings. With altering seasonal or day/night cooling demands, the performance and overall economics of the design may deprive. This work focuses on the design of a flexible and economical thermal energy production system by integrating trigeneration and cold storage techniques. The capacity determination of the main equipment units, their interconnections and operating conditions during different demand periods and electricity costs are discussed. A case study is used to demonstrate the system's merits to improve the air conditioning efficiency with overall investment and operating cost reductions under demand uncertainties. As demonstrated, the economic attractiveness of a thermal energy production system is sensitive to the electricity tariff used. Although a high degree of flexibility in meeting demand changes is usually introduced with a trigeneration system, its expensive investment cost makes it less economically attractive under the discounted electricity tariff. A hybrid system which produces thermal energy via both electricity and town gas is introduced. This hybrid allows operation mode switching according to the energy cost variations and ensures the best economic return. The sole dependence on network electricity can also be avoided and the process's operability can be enhanced. (C) 2009 Elsevier Ltd. All rights reserved.