The potential role of trans-critical CO2 heat pumps within a solar cooling system for building services: The hybridised system energy analysis by a dynamic simulation model.

The rotary desiccant wheels application in the air conditioning systems are used for the air dehumidification by means of hygroscopic layers for water vapor adsorption. Nevertheless, external heat sources are required for water desorption to close the air treatment cycle. This paper investigates on the possibility to integrate in that cycle a new component, such as the trans-critical CO2 heat pump, to reduce the contribution of external thermal sources. In so doing, the high temperature waste heat discharged by the heat pump hot sink can be fruitfully exploited. Additionally, a PV array has been added to the typical layout based on the solar collectors, in order to assure the heat pump electrical driving. The energy analysis is carried out by calculating the energy performance indicators of the whole cooling system, simulating it by a dynamic model built in the MATLAB SIMULINK environment. Specifically, an air handling unit has been properly sized to supply cooling load to a reference conference hall of 1200 m3, with changes in boundary conditions (i.e. solar radiation, daily temperature and relative humidity variations). Indeed, three different cities representing the most typical Italian climatic zones, have been considered for assessing the proposed technical option suitability.

Thermo-Economic Evaluation of Aqua-Ammonia Solar Absorption Air Conditioning System Integrated with Various Collector Types.

The main objective of this paper is to simulate solar absorption cooling systems that use ammonia mixture as a working fluid to produce cooling. In this study, we have considered different configurations based on the ammonia-water (NH3-H2O) cooling cycle depending on the solar thermal technology: Evacuated tube collectors (ETC) and parabolic trough (PTC) solar collectors. To compare the configurations we have performed the energy, exergy, and economic analysis. The effect of heat source temperature on the critical parameters such as coefficient of performance (COP) and exegetic efficiency has been investigated for each configuration. Furthermore, the required optimum area and associated cost for each collector type have been determined. The methodology is applied in a specific case study for a sports arena with a 700~800 kW total cooling load. Results reveal that (PTC/NH3-H2O)configuration gives lower design aspects and minimum rates of hourly costs (USD 11.3/h) while (ETC/NH3-H2O) configuration (USD 12.16/h). (ETC/NH3-H2O) gives lower thermo-economic product cost (USD 0.14/GJ). The cycle coefficient of performance (COP) (of 0.5).

Exergoeconomic Assessment of Solar Absorption and Absorption-Compression Hybrid Refrigeration in Building Cooling.

The paper mainly deals with the match of solar refrigeration, i.e., solar/natural gas-driven absorption chiller (SNGDAC), solar vapor compression-absorption integrated refrigeration system with parallel configuration (SVCAIRSPC), and solar absorption-subcooled compression hybrid cooling system (SASCHCS), and building cooling based on the exergoeconomics. Three types of building cooling are considered: Type 1 is the single-story building, type 2 includes the two-story and three-story buildings, and type 3 is the multi-story buildings. Besides this, two Chinese cities, Guangzhou and Turpan, are taken into account as well. The product cost flow rate is employed as the primary decision variable. The result exhibits that SNGDAC is considered as a suitable solution for type 1 buildings in Turpan, owing to its negligible natural gas consumption and lowest product cost flow rate. SVCAIRSPC is more applicable for type 2 buildings in Turpan because of its higher actual cooling capacity of absorption subsystem and lower fuel and product cost flow rate. Additionally, SASCHCS shows the most extensive cost-effectiveness, namely, its exergy destruction and product cost flow rate are both the lowest when used in all types of buildings in Guangzhou or type 3 buildings in Turpan. This paper is helpful to promote the application of solar cooling.

Cooling supply with a new type of evacuated solar collectors: a techno-economic optimization and analysis.

Renewable cooling via absorption chillers being supplied by various green heat technologies such as solar collectors has been widely studied in the literature, but it is still challenging to get positive economic outcomes from such systems due to the large expenses of solar thermal systems. This study offers the use of a new generation of solar collectors, so-called eccentric reflective solar collectors, for driving single-effect absorption chillers and thereby reducing the levelized cost of cooling. This article develops the most optimal design of this system (based on several different scenarios) using multi-objective optimization techniques and employs them for a case study in Brazil to assess its proficiency compared to conventional solar-driven cooling methods. For making the benchmarking analyses fair, the conventional system is also rigorously optimized in terms of design and operation features. The results show that the eccentric solar collector would enhance the cost-effectiveness by 29%. In addition, using optimally sized storage units would be necessary to get acceptable economic performance from the system, no matter which collector type is used. For the case study, at the optimal sizing and operating conditions, the levelized cost of cooling will be 124 USD/MWh and an emission level of 18.97 kgCO2/MWh.

Analytical modelling of food storage cooling with solar ammonia-water absorption system, powered by parabolic trough collectors. Method.

The study presents a new analytical model capable to reveal the thermal behaviour of all the components of the solar ammonia-water absorption system, powered by parabolic trough collectors, serving different types of food storages: refrigeration chamber, refrigerated food storage, freezing chamber and frozen food storage. The heat inputs, that determine the total cooling load, for each food storage spaces consist of: heat gains through walls, heat gains through ventilation (fresh air), heat that must be dissipated from the stored products (technological cooling load required to cool down the products) and heat gains through operation. The influence of the number of solar parabolic trough collectors and of the storage tank size on different parameters of the refrigeration plant are investigated under low and high storage temperatures.•Food cooling with solar absorption refrigeration system.•Hourly based variation of NH3-H2O solar absorption system performances.•Long term simulation of solar absorption cooling for refrigeration and cooling.

Performance analysis of sustainable solar energy operated ejector refrigeration system with the combined effect of Scheffler and parabolic trough collectors to lower greenhouse gases.

The work aims to analyse an ejector refrigeration system powered with solar energy through serially connected collectors to lower greenhouse gases. The collectors chosen for the work are Scheffler and parabolic collectors with an area of 2.5 m2 and 6 m2, respectively. The steam generated by the collectors is stored temporarily in a 15-l storage tank. The thermic fluid transfers heat between the steam storage tank and refrigerant, and thus the generator temperature increases. This design was intended as an alternate for a traditional 3.5 kW room air conditioner with substantially lower energy consumption. This modified system consumed lesser energy input of about 20-30% than conventional air conditioners. Further, for the same specification, the ejector system has consumed less power of about 2.475 kW than the traditional refrigeration system.

Energy and exergy simulation analysis and comparative study of solar ejector cooling system using TRNSYS for two climates of Iran.

This paper addresses hourly simulation of 3.5 kW Solar Ejector Cooling System (SECS) using R600a and R290 hydrocarbon refrigerants for application in two office buildings in semi-arid and hot-humid climates of Iran. During the period of the study, thermodynamics energy and exergy of the cooling systems when charged with the two refrigerants are fully assessed by simulation at the two study sites. The simulation studies of the entire cooling system indicate that the most irreversible process and hence the prime exergy destruction is related to the solar collector system followed by the ejector component in the cooling cycle. The ejector is a constant-area mixing (CAM) type which is mathematically modeled in Engineering Equation Solver (EES) software. Generator of the cooling cycle is modeled in EES using ε - N T U method and a simulation program is developed on TRNSYS-EES co-simulator for dynamic study of the cooling cycle. For comparison of efficiency of the two refrigerants, working conditions are set to be the same. The systems are equipped with auxiliary heaters to provide constant inlet temperature of 85 C ∘ for the generator when solar radiation is partially in phase with the building sites. The hourly and monthly simulation of both SECS in June, July, August and September 2019 demonstrate that R290 is more efficient for increasing the overall C O P ( = 0.2844 ) of the system than R600a ( C O P = 0.2797 ) of the building office in the semi-arid region where the generator receives most of its thermal energy from solar radiation in July 17, 2019. Although, the same refrigerant is also more efficient than R600a in the hot-humid region system in the same day, but the system compensates shortage of its necessary solar thermal energy mostly from the auxiliary heater.

Experimental investigation on solar-powered ejector refrigeration system integrated with different concentrators.

The objective of the work is to analyse and to improve the efficiency of solar-powered ejector refrigeration system integrated with flat-plate collector and Scheffler concentrator. The Scheffler concentrator of 2.7 m2 and flat-plate collector of 5 m2 collecting area are coupled with the storage tank of 15 l capacity. The developed system was designed for a potential replacement of conventional 1-ton room air conditioner with much reduced electrical energy consumption. The system was built based on two key subsystems namely 'Scheffler concentrator-based vapour system' and 'ejector-based cooling system'. The pilot effort showed promising results with the probability of energy-saving potential as near 70 to 80% over conventional air conditioners.

Hybrid Zeolite SAPO-34 Fibres Made by Electrospinning.

A new generation of compressor-free heat pumps based on adsorption technology and driven by solar energy is available. Performance and costs are, however, the main obstacles to their commercial diffusion, and more material and system developments are required. In this work, a new coating made of microfibres produced by the electrospinning of polymer/zeolite mixtures is presented. Three different polymer carriers, polyvinyl acetate, polyethylene oxide and polystyrene, have been used together with zeolite SAPO-34 as an adsorbing material. Electrospun microfibres showed a mean diameter ranging from 0.75 µm to 2.16 µm depending on the polymer carrier, with a zeolite content from 60 wt.% to 87 wt.%. Thermal analysis (TGA-DSC) results showed that water desorption from microfibres at T = 150 °C was close to 17 wt.%, a value in agreement with the adsorption capacity of pure SAPO-34. The morphology characterization of coatings demonstrated that the microfibre layers are highly porous and have an elevated surface area.