Research On Thermodynamic Characteristics Of New Distributed Energy Resources

Due to the increasing stress of state grid and the progressive using of natural gas, Distributed Energy Resources (DER) has drawn extensive attention by now. This paper studies a new Distributed Energy Resources (NDER). The electric power generated by the prime mover is not used for lighting as usual, but drive electrical air conditioning system to produces cooling/heating capacity to meet the cooling/heating demands, together with the cooling/heating capacity generated from the absorption chiller/heater that is driven by the heat from the prime mover. So the NDER can perform heating or cooling independent of the state grid.The most distinct characteristic of this NDER is to combine the cogeneration (combined heat and power) and the single provision (heating or cooling). Consequently, it has the following advantages:1) having a high primary energy ratio,2) avoiding the mutual dependance among different products,3) having far less natural gas consumption than in the cogeneration,4) avoiding the problem of interconnecting with public power grid,5) relieving the stress of inadequate natural gas supply in winter and relatively redundant gas supply in summer,6) substantially reducing the power supply for air-conditioning system in summer, thereby to shift peak load, optimize the structure of energy consumption, and increase the reliability of the energy network.This paper studies the thermodynamic characteristics of the NDER.The NDER's components and their applicability are studied. The assembly of the NDER can be different, so that different system performance can be gained, and each component corresponds to a specific application.The coefficients of cooling and heating supply of NDER are obtained from the First Law of Thermodynamics, and the sensitivity analysis of NDER shows that these coefficients are affected remarkably by the generating efficiency and the COP of heat pump. For comparison, the NDER's energy efficiency is higher than the ground source heat pump and the direct-fired lithium bromide water chiller/heater.The exergy transfer characteristics of NDER are obtained from the specific consumption analysis based on the Second Law of Thermodynamics. To achieve the average exergetic efficiency in multi-operation condition, we firstly developed two methods to calculate the average exergetic efficiency for the heating and cooling system one is the heat-weighed-temperature method and the other is the fuel-weighed method. As a result, the exergy analysis can be extended from design condition to all conditions. And the second method is applicable to any process.We also analyzed the thermodynamic process of strong water/lithium-bromide solution absorbing water vapor, in the absorption refrigeration cycle. It seems that Fick law is not applicable for this process, so the chemical potential is introduced for the first time to explain this mass transfer process. The analysis shows that in the absorption process, although the temperature of the water vapor from the evaporator is lower than that of the sprinkling solution, its chemical potential is higher than that of the water in the solution. As a result, the solution absorbs the water vapor. The higher the solution temperature is, the easier the water vapor is absorbed. The introduction of chemical potential helps to explain the absorption process essentially from thermodynamics.This paper also presents the mathematical models established for the NDER's main components. The off-design characteristics of NDER are simulated basing on different prime movers. Because internal combustion engine has high power efficiency and good off-design performance, the internal combustion engine-NDER has a better partial load performance than the ground source heat pump and the direct-fired lithium bromide water chiller/heater. Moreover, this system is an energy-saving system with a yearly energy saving rate of 24.1% compared to the ground source heat pump, and 37.5% compared to the direct-fired lithium bromide water chiller/heater. However, because the gas turbine's power efficiency is low and its off-design performance isn't good, even if the gas turbine-NDER is energy saving at design condition, its energy saving effect slowly disappears as load decreases. Nevertheless, if the gas turbine-NDER is used in large public buildings with designated cooling/heating time and small load fluctuations, it can shift peak load and be energy-saving.Finally, various NDERs are designed for typical buildings (e.g. hotel, office building, tower block, apartment building, building complex) with different loads. From these case studies, NDER is shown to be energy-saving, and therefore is a worthy and remarkable system.