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[en] This paper deals with the problem of energy efficiency evaluation and economic feasibility analysis of a small scale trigeneration system for combined cooling, heating and power generation (CCHP) with an available Stirling engine. Trigeneration systems have a large potential of energy saving and economical efficiency. The decisive values for energetic efficiency evaluation of such systems are the primary energy rate and comparative primary energy saving (Δq), while the economic feasibility analysis of such systems relates the avoided cost, the total annual saving and payback period. The investigation calculates and compares the energy saving and economic efficiency of trigeneration system with Stirling engine against contemporary conventional independent cooling, heating and power, showing that a CCHP system saves fuel resources and has the assurance of economic benefits
[en] A composite material was developed as sorbent for sorption thermal energy storage (TES) which was used to recycle the low-temperature heat in industry and life fields in this study. The composite sorbent was formed by strontium bromide (SrBr_2) and the additive of expanded natural graphite treated with sulfuric acid (ENG-TSA). Sorption characteristics, kinetic sorption performance, thermal conductivity and permeability of 15 samples were studied. The material test results indicated the following: (1) the composite SrBr_2 is of high energy density and good mass transfer performance; (2) it can be regenerated below 100 °C; (3) the additive of ENG-TSA greatly improves the heat transfer performance, while no degradation is observed on sorption water uptake; (4) the optimal composite sorbent is of 743 kg/m"3 and with 10 wt% ENG-TSA. An lab-scale sorption TES system with 1 kWh design capacity was established and investigated. Under the conditions in winter seasons: charging temperature T_c_h_a is 80 °C, discharging temperature T_d_i_s is 35 °C, condensing temperature T_c is 15 °C, evaporating temperature T_e is 15 °C, the heat storage capacity can reach 1.02 kWh. The heat storage density obtained is 242 Wh/kg composite sorbent and the heat discharging power is 67.4 kW/m"3 composite sorbent. - Highlights: • A new type of consolidated composite SrBr_2 sorbent was developed. • We tested the thermal properties and sorption performance of samples. • The optimal composite sorbent was chosen for thermal energy storage. • A 1 kWh sorption thermal energy prototype was investigated.
[en] Different adsorbents, such as physical, chemical and composite adsorbents are analyzed. Three types of working pairs, activated carbon-methanol, chemical adsorbent-ammonia and composite adsorbent-ammonia can be used for adsorption ice makers on fishing boats. The advantages, disadvantages and performances of three types of adsorption ice makers, with activated carbon-methanol, CaCl2-NH3 and compound adsorbent (made by CaCl2 and activated carbon)-NH3 as adsorption pairs, are compared at the condition of two bed systems. The activated carbon-methanol ice maker shows the advantage of reliable safety, and the composite adsorption ice maker shows the best adsorption performance. The cooling power of 20.32 kW can be obtained from the composite adsorption ice maker when the volume for each adsorber is 0.288 m3, which is about 10 times that of the physical adsorption ice maker and 1.38 times that of the chemical adsorption ice maker
[en] Based on the heat and mass transfer model validated by experiment, the performance of the plate solar ice-maker is analyzed systemically with the opinion of two-type characteristic parameters, which includes parametric effects of adsorbent bed of solar ice-maker and outer parameters referring to circumstance. A large number of simulations were undertaken to test the performance of the refrigerator for various collector design parameters and environmental parameters. These works are beneficial to further study the optimization design of a solar cooling system. (Author)
[en] In this study, a small scale hybrid solar heating, chilling and power generation system, including parabolic trough solar collector with cavity receiver, a helical screw expander and silica gel-water adsorption chiller, etc., was proposed and extensively investigated. The system has the merits of effecting the power generation cycle at lower temperature level with solar energy more efficiently and can provide both thermal energy and power for remote off-grid regions. A case study was carried out to evaluate an annual energy and exergy efficiency of the system under the climate of northwestern region of China. It is found that both the main energy and exergy loss take place at the parabolic trough collector, amount to 36.2% and 70.4%, respectively. Also found is that the studied system can have a higher solar energy conversion efficiency than the conventional solar thermal power generation system alone. The energy efficiency can be increased to 58.0% from 10.2%, and the exergy efficiency can be increased to 15.2% from 12.5%. Moreover, the economical analysis in terms of cost and payback period (PP) has been carried out. The study reveals that the proposed system the PP of the proposed system is about 18 years under present energy price conditions. The sensitivity analysis shows that if the interest rate decreases to 3% or energy price increase by 50%, PP will be less than 10 years. (author)
[en] Highlights: ► We develop one heat pipe type adsorption refrigerator. ► New compound adsorbent of CaCl2/activated carbon–ammonia can work more effectively. ► Combined mass recovery-heat pipe heat recovery can improve adsorption performance. ► Combined mass recovery-heat pipe heat recovery can reduce cycle time. - Abstract: A heat pipe type adsorption refrigerator system is proposed and investigated, which can be powered by solar energy or waste heat of engine. The study assesses the performance of compound adsorbent (CaCl2 and activated carbon)–ammonia adsorption refrigeration cycle with different orifice sets and different mass and heat recovery processes by experimental prototype machine. Specific cooling power (SCP) and coefficient of performance (COP) were calculated with experimental data to analyze the influences of operating condition. The results show that the jaw opening of the hand needle nozzle can influence the adsorption performance obviously and the thermostatic expansion valve (TEV) is effective in the intermediate cycle time in the adsorption refrigeration system. The SCP of the cycle with the mass-heat recovery together (combined recovery process) is superior to that of the conventional cycles with mass recovery or heat recovery independently.
[en] In this study, a small scale hybrid solar heating, chilling and power generation system, including parabolic trough solar collector with cavity receiver, a helical screw expander and silica gel-water adsorption chiller, etc., was proposed and extensively investigated. The system has the merits of effecting the power generation cycle at lower temperature level with solar energy more efficiently and can provide both thermal energy and power for remote off-grid regions. A case study was carried out to evaluate an annual energy and exergy efficiency of the system under the climate of northwestern region of China. It is found that both the main energy and exergy loss take place at the parabolic trough collector, amount to 36.2% and 70.4%, respectively. Also found is that the studied system can have a higher solar energy conversion efficiency than the conventional solar thermal power generation system alone. The energy efficiency can be increased to 58.0% from 10.2%, and the exergy efficiency can be increased to 15.2% from 12.5%. Moreover, the economical analysis in terms of cost and payback period (PP) has been carried out. The study reveals that the proposed system the PP of the proposed system is about 18 years under present energy price conditions. The sensitivity analysis shows that if the interest rate decreases to 3% or energy price increase by 50%, PP will be less than 10 years.
[en] Highlights: → Use two kinds of circulation media in the solar collector. → Air heating and pebble bed heat storage are applied with different operating modes. → Design parameters of the system are optimized by simulation program. → It is found that the system can meet 32.8% of the thermal energy demand in heating season. → Annual solar fraction aims to be 53.04%. -- Abstract: The application of solar air collectors for space heating has attracted extensive attention due to its unique advantages. In this study, a solar air heating system was modeled through TRNSYS for a 3319 m2 building area. This air heating system, which has the potential to be applied for space heating in the heating season (from November to March) and hot water supply all year around in North China, uses pebble bed and water storage tank as heat storage. Five different working modes were designed based on different working conditions: (1) heat storage mode, (2) heating by solar collector, (3) heating by storage bed, (4) heating at night and (5) heating by an auxiliary source. These modes can be operated through the on/off control of fan and auxiliary heater, and through the operation of air dampers manually. The design, optimization and modification of this system are described in this paper. The solar fraction of the system was used as the optimization parameter. Design parameters of the system were optimized by using the TRNSYS program, which include the solar collector area, installation angle of solar collector, mass flow rate through the system, volume of pebble bed, heat transfer coefficient of the insulation layer of the pebble bed and water storage tank, height and volume of the water storage tank. The TRNSYS model has been verified by data from the literature. Results showed that the designed solar system can meet 32.8% of the thermal energy demand in the heating season and 84.6% of the energy consumption in non-heating season, with a yearly average solar fraction of 53.04%.
[en] Highlights: ► A solar desiccant cooling/heating system is simulation studied. ► The mean deviation is about 10.5% for temperature and 9.6% for humidity ratio. ► The 51.7% of humidity load and 76% of the total cooling can be handled. ► About 49.0% of heating load can be handled by solar energy. ► An optimization of solar air collector has been investigated. - Abstract: To increase the fraction of solar energy might be used in supplying energy for the operation of a building, a solar desiccant cooling and heating system was modeled in Simulink. First, base case performance models were programmed according to the configuration of the installed solar desiccant system and verified by the experimental data. Then, the year-round performance about the system was simulated. Last, design parameters of solar air collectors were optimized that include collector area, air leakage and thermal insulation. Comparison between numerical and experimental results shows good agreement. During the simulation, the humidity load for 63 days (51.7%) can be totally handled by the two-stage desiccant cooling unit. For seasonal total heating load, about 49.0% can be handled by solar energy. Based on optimized results, the thermal energy subsystem functioned to its expected performance in solar energy collection and thermal storage
[en] Highlights: • A CCHP system integrated with biomass gasification was optimized. • The optimization was based on life-cycle assessment. • The optimization involved energetic, economic, and environmental aspects. • The overall-performance criterion was obtained with TOPSIS. - Abstract: A multi-criteria optimization for a biomass gasification-integrated combined cooling, heating, and power (CCHP) system based on life-cycle assessment is carried out. The criteria comprise primary energy saving ratio (PESR), total cost saving ratio (TCSR), and CO2 emission reduction ratio (CERR). The overall-performance criterion, Cl, is obtained with Technique for Order of Preference by Similarity to Ideal Solutions (TOPSIS). Results show that the Cl reaches its maximum when the nominal electric output is 1572.8 kW, the biomass feedstock type is wood pellet, and the operation strategy is following the electric load (FEL). The PESR, TCSR, CERR, and Cl are 0.101, 0.271, 0.498, and 0.867, respectively. By comparing with reference systems, it is found that in FEL mode, the system is improved because of higher energy utilization efficiency and better use of economic and environmental advantages of biomass. In following the thermal load (FTL) mode, economic performance is compromised for optimal overall performance. Sensitivity analysis is carried out to find out the effect of variation of various parameters on optimization results. It is found that the variation of a single-aspect parameter could affect the system performance on all aspects. The variation of primary energy consumption per unit electricity from the grid (pecen,g) has the greatest effect on optimization results. The corresponding variation ranges of PESR, TCSR, and CERR owing to its variation are from −0.063/0.231/0.473 to 0.284/0.295/0.624 and from −0.029/0.101/0.314 to 0.194/0.123/0.379 in FEL and FTL modes.