The effects of operation parameter on the performance of a solar-powered adsorption chiller

A solar-powered adsorption chiller with heat and mass recovery cycle was designed and constructed. It consists of a solar water heating unit, a silica gel-water adsorption chiller, a cooling tower and a fan coil unit. The adsorption chiller includes two identical adsorption units and a second stage evaporator with methanol working fluid. The effects of operation parameter on system performance were tested successfully. Test results indicated that the COP (coefficient of performance) and cooling power of the solar-powered adsorption chiller could be improved greatly by optimizing the key operation parameters, such as solar hot water temperature, heating/cooling time, mass recovery time, and chilled water temperature. Under the climatic conditions of daily solar radiation being about 16–21 MJ/m², this solar-powered adsorption chiller can produce a cooling capacity about 66–90 W per m² collector area, its daily solar cooling COP is about 0.1–0.13.     

A novel thermal water pump for circulating water in a solar water heating system

This research purpose was to perform a parametric study of a novel thermal water pump well fitted in a simulated solar water heating system (SWHS). The SWHS was composed of a heating tank (HT), a hot water storage tank (ST) and an overhead tank (OT). The HT together with a specially designed valve act as a novel thermal water pump that gets power from hot water vapor and air pressure produced by a built-in electric heater in order to transfer heat from the HT to ST. The general operation of this pump has four stages for each cycle: heating, water circulating, vapor circulating and water supplying. The discharge water heads were varied with an increment of 0.25 m from 0.75 to 3 m. According to the experiment, it was found that the pump could operate at an average HT temperature of about 80–95 °C leading to 70–80 °C ST temperatures and 20–35 pumping cycles and consumed 17 MJ energy input during 9-h period. The overall thermal efficiency of the SWHS was 33–42% and the mean pump efficiency was about 0.005–0.011% depending upon the discharge heads.     

Design and fabrication of a cost effective solar air heater for Bangladesh

In this research, a solar air heater is designed, fabricated and its performance is assessed in the perspective of an emerging/developing country with a huge energy demand like Bangladesh. The winter season (mid-November–mid-February) of the country characterizes by low temperatures, cool air blowing from the west or northwest, clear sky and meager rainfall. Minimum temperature in the extreme northwest in late December and early January sometimes reaches 3 °C and day length is about 10 h. The shortness of winter days can be compensated by reducing the heat loss during long nights. The solar air heater is constructed to prevent as much heat loss as possible. In other words, the heating of air is accomplished by maximizing light gain and minimizing heat loss. It is observed that the fabricated solar air heater is working efficiently. The maximum room temperature and the temperature difference from ambient are 45.5 °C and 12.25 °C for forced circulation and 41.75 °C and 8.5 °C for natural circulation respectively. The experimental outlet temperatures have been compared with that of theoretical values. Due to its low-cost and simple technology, it is affordable in all aspects, viz. of cost, operation and maintenance by the typical people of Bangladesh.     

A study on the performance enhancement of heat pump using electric heater under the frosting condition: Heat pump under frosting condition

The purpose of the present study is to enhance the heating capacity and increase COP under the frosting condition during heating operation of small capacity air-to-air heat pump. We applied an electric heater in front of outdoor unit of heat pump instead of indoor unit as usual. When the outdoor temperature is 2 °C/1 °C (DB/WB), the present heat pump turns on the electric heater in outdoor unit. The heating capacity increases 38.0% and COP increases 57.0% in comparison with those of conventional heat pump. When the outdoor temperature is 4 °C/2 °C (DB/WB), the electric heater is in ON/OFF mode according to the temperature of the evaporator. The heating capacity increases 9.1% and COP increases 71.1% in comparison with those of conventional heat pump.     

Experimental study and exergetic analysis of a CPC-type solar water heater system using higher-temperature circulation in winter

The common solar water heater system can meet low temperature requirements, but exhibits very low efficiency in attaining higher water temperatures (55–95 °C). In the current paper, a compound parabolic concentrator (CPC)-type solar water heater system experiment rig with a U-pipe was set up, and its performance in meeting higher temperature requirements was investigated. The experiments were conducted in December at Hefei (31°53′ N, 117°15′ E), in the eastern region of China. The system showed steady performance in winter, with overall thermal efficiency always above 43%. The water in the tank was heated from 26.9 °C to 55, 65, 75, 85, and 95 °C. Through the experimental study and exergetic analysis of the solar water heater system, results of the five experiments showed thermal efficiency of above 49.0% (attaining 95 °C water temperature) and exergetic efficiency of above 4.62% (attaining 55 °C water temperature). Based on these results, the CPC-type solar water heater system with a U-pipe shows superior thermal performance in attaining higher temperatures and has potential applications in space heating, heat-powered cooling, seawater desalination, industrial heating, and so on.     

Design and performance of a solar-powered heating and cooling system using silica gel/water adsorption chiller

In this paper, a solar-powered compound system for heating and cooling was designed and constructed in a golf course in Taiwan. An integrated, two-bed, closed-type adsorption chiller was developed in the Industrial Technology Research Institute in Taiwan. Plate fin and tube heat exchangers were adopted as an adsorber and evaporator/condenser. Some test runs have been conducted in the laboratory. Under the test conditions of 80 °C hot water, 30 °C cooling water, and 14 °C chilled water inlet temperatures, a cooling power of 9 kW and a COP (coefficient of performance for cooling) of 0.37 can be achieved. It has provided a SCP (specific cooling power) of about 72 W/(kg adsorbent). Some field tests have been performed from July to October 2006 for providing air-conditioning and hot water. The efficiency of the collector field lies in 18.5–32.4%, with an average value of 27.3%. The daily average COP of the adsorption chiller lies in 33.8–49.7%, with an average COP of 40.3% and an average cooling power of 7.79 kW. A typical daily operation shows that the efficiency of the solar heating system, the adsorption cooling and the entirely solar cooling system is 28.4%, 45.2%, and 12.8%, respectively.     

Year round test of a solar adsorption ice maker in Kunming,China

A solar adsorption ice maker with activated carbon–methanol adsorption pair was developed for a practical application. Its main features include utilization of a water cooled condenser and removing all valves in the refrigerant circuit except the one that is necessary for refrigerant charging. Year round performance tests of the solar ice maker were performed in Kunming, Yunnan Province, China. Test results show that the COP (coefficient of performance) of the solar ice maker is about 0.083–0.127, and its daily ice production varies within the range of 3.2–6.5 kg/m² under the climatic conditions of daily solar radiation on the surface of the adsorbent bed being about 15–23 MJ/m² and the daily average ambient temperature being within 7.7–21.1 °C. The suitable daily solar radiation under which the solar ice maker can run effectively in Kunming is above 16 MJ/m².     

Design of solar powered adsorption heat pump with ice storage

The design and performance of a solar (and/or natural gas) powered adsorption (desiccant-vapor) heat pump for residential cooling (and heating) is described. The entire system is modeled and analyzed: adsorption heat pump itself, ice thermal storage reservoir, and solar collectors. The adsorption heat pump embodies patent pending improvements to the state-of-the-art which elevate coefficient of performance for cooling from a maximum of 1.2 reported in the literature to a conservatively predicted minimum of 1.5. The adsorption device utilizes economical, robust configurations (shell-and-tube) and components (helical annular finned tubes, multi-lumen tubes) commonly employed in heat exchangers in a manner heretofore untried, as well as other enhancements (metal wool to diffuse heat throughout the adsorbent). The vessel is all aluminum and the adsorbent-refrigerant pair is carbon-ammonia. The ice reservoir provides 24 h cooling. Two types of solar collector are determined to be satisfactory at the selected operating temperature of 170 °C: (1) compound parabolic concentrator with high concentration ratio (10+) and automatic tilt adjustment, and (2) evacuated (0.001 atm) flat panel, similar to atmospheric pressure versions employed for domestic water heating.     

Energy analysis of heat surplus storage systems in plastic tunnels

This paper presents the findings of a theoretical analysis and experimental verification on the storing of heat excess in soil and liquid accumulators located in a foil tunnel. There was positive verification of the formulated macroscopic heat exchange model in both accumulators (maximum error 81%) and the quantity of heat stored in them was defined. During the experiments, under existing weather conditions, the amount of stored heat stood between 6 MJ and 45 MJ in the liquid accumulator and between 9 MJ and 130 MJ in the soil accumulator. The quantity of heat supplied from the accumulator to the interior of the tunnel during discharging, which stood between 0.6 MJ and 46 MJ, was also described. The COP was determined for the tested system both for the accumulator charging process and the discharging of the soil accumulator. Furthermore, the quantity of heat used for heating up heat originating from the discharging of the accumulator whilst heating the tunnel for favourable and unfavourable surrounding climate conditions was determined.     

Development and validation of static simulation model for CO2 heat pump

A simulation model for the CO₂ heat pump water heater was developed and validated in this study. Component models of the gas cooler, evaporator, compressor, and expansion valve were constructed with careful consideration for the heat transfer performances. To validate the simulation model, experiments were carried out using an actual CO₂ heat pump water heater (water heating capacity: 22.3 kW; hot-water temperature: 90 °C). In simulations and experiments, the effects of the inlet water temperature and outside air temperature on the system characteristics were discussed. As a result, the average difference in COP between the simulation results and experimental results is 1.5%.     

Solar hybrid air-conditioning system for high temperature cooling in subtropical city

Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5–7 °C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15–18 °C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city.     

Dynamic performance of a façade-based solar loop heat pipe water heating system

This paper reported a dedicated study of a novel façade-based solar loop heat pipe (LHP) water heating system using both theoretical and experimental methods. This system employs a modular panel incorporating a unique loop heat pipe that is able to serve as part of the building façade or a decoration layer of the façade, thus creating a façade integrated, low cost, highly efficient and aesthetically appealing solar water heating structure. Taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger and storage tank, a dedicated computer model was developed to investigate the dynamic performance of the system. An experimental rig was also established to evaluate the performance of such a prototype system through measurement of various operational parameters, e.g., solar radiation, temperatures and flow rates of the heat pipe fluid and water. Through comparison between the testing and modelling results, the model has been approved to be able to give a reasonable accuracy for predicting the performance of the LHP system. Two types of glass covers, i.e., double glazed/evacuated tubes and single-glazing plate, were applied to the prototype. It was found that for both covers, the heat pipe fluid temperature rose dramatically at the start-up operation and afterwards remained a slow but steady growth; while the water temperature remained a steadily growing trend throughout the operational day. The temperature rise of the circulated water at 1.6 l/min of flow rate was around 13.5 °C in the double-glazed/evacuated tubes based system and 10 °C in the single-glazing based system; correspondingly, their average solar conversion efficiencies were 48.8% and 36%, and the COPs were 14 and 10.5 respectively. In overall, the double-glazed/evacuated tubes based system presented a better performance than the single glazing based one.     

Thermal conduction between a heated microcantilever and a surrounding air environment

This paper investigates transient heat conduction between a heated microcantilever and its air environment. Continuum finite element simulations allow detailed analysis of heat flow within and from the resistively heated microcantilever. Heat generation of 8 mW excites the cantilever with heating that is either steady, pulse, sinusoidal, or pulse duty cycle. The time-averaged heat conduction from the cantilever leg to the nearby air is typically two to six times greater than the heat conduction from the heater to the air. The cooling time constant increases as the pulse heating time increases; for heating times of 1–1000 μs, the cooling time ranges 4.6–70 μs. The effective heat transfer coefficients around the heater and around the leg are considerably large; on the order of 1 kW/m² K. This study of heat transfer between a microcantilever and its surrounding air environment will aid the design and operation of microcantilever heaters.     

Residential air conditioning and heating by means of enhanced solar collectors coupled to an adsorption system

This work explores the possibility to perform heating and air-conditioning of state of the art building located near Paris in France. For air-conditioning, enhanced compound parabolic solar collectors are used as a heat source of an adsorption system (methanol/activated carbon), while during winter direct coupling with the building is performed.A model describing the adsorption unit, the solar collectors and the house was used to simulate the performances of such an installation.For air-conditioning, thermal comfort is achieved as indoor temperature is kept below 25 °C during five consecutive hot days (heat wave effect), contrarily to the case for which only free-cooling during nighttime is used. For heating, the indoor temperature remains below the comfort temperature value by 2 K. Nevertheless, the auxiliary heating need will remain limited so that savings on electricity or fossil fuel consumption will be possible.     

Transient analysis of modified cuboid solar integrated-collector-storage system

A novel solar water heating system, modified cuboid solar integrated-collector-storage (ICS) system with transparent insulation material (TIM) has been designed and developed, which combines collection and storage in a single unit and minimizes the nocturnal heat losses. A comprehensive study has been carried out to evaluate the heat transfer characteristics inside the enclosure of the system to enhance the collection and storage of solar energy. The transient behavior of the modified-cuboid solar integrated-collector-storage system is investigated numerically to evolve optimum configuration. The optimum design for the system is obtained by carrying out a numerical parametric study with different geometry parameters like the depth of the cuboid (d = 2, 5, 8, and 12 cm), and inclination angles (10°, 20°, 30°, and 50°). The inside heat transfer coefficient of the ICS system, stratification factor and water temperature distribution inside the enclosure have been predicted by numerical simulation. Average heat transfer coefficient at the bottom surface of absorber plate is 20% higher for depth of 12 cm as compared to the 2 cm depth of cuboid section, after 2 h of heating. The stratification factor also increases from 0.02 to 0.065 as depth of the system increases from 2 cm to 12 cm. There is a marginal effect of inclination angles of the system on the convection in the enclosure. As the inclination angle increases from 10° to 50°, the average heat transfer coefficient increases from 90 W/m² K to 115 W/m² K. But the stratification factor is comparatively high for lower inclination angles. With the optimum design parameters, a field experimental set-up was built and the numerical model was validated for efficient heat collection and storage in a modified cuboid ICS system. The model is in good agreement with the experimental results.     

Development of an economical model to determine an appropriate feed-in tariff for grid-connected solar PV electricity in all states of Australia

Australia is a country with a vast amount of natural resources including sun and wind. Australia lies between latitude of 10–45°S and longitude of 112–152°E, with a daily solar exposure of between less than 3 MJ/(m² day) in winter and more than 30 MJ/(m² day) in summer.Global solar radiation in Australia varies between minimum of 3285 MJ/(m² year) in Hobart to 8760 MJ/(m² year) in Northern Territory. As a result of this wide range of radiation level there will be a big difference between costs of solar PV electricity in different locations.A study we have recently conducted on the solar PV electricity price in all states of Australia. For this purpose we have developed an economical model and a computer simulation to determine the accurate unit price of grid-connected roof-top solar photovoltaic (PV) electricity in A$/kWh for all state of Australia. The benefit of this computer simulation is that we can accurately determine the most appropriate feed-in tariff of grid-connected solar PV energy system. The main objective of this paper is to present the results of this study.A further objective of this paper is to present the details of the unit price of solar PV electricity in the state of Victoria in each month and then to compare with electricity price from conventional power systems, which is currently applied to this state. The state Victoria is located south of Australia and in terms of sun radiation is second lowest compared with the other Australian states.The computer simulation developed for this study makes it possible to determine the cost of grid-connected solar PV electricity at any location in any country based on availability of average daily solar exposure of each month as well as economical factors of the country.     

Study on a re-heat two-stage adsorption chiller – The influence of thermal capacitance ratio,overall thermal conductance ratio and adsorbent mass on system performance

Silica gel/water based adsorption cycles have a distinct advantage in their ability to be driven by heat of near-ambient temperature so that waste heat below 100 °C can be recovered. One interesting feature of refrigeration cycles driven by waste heat is that they do not use primary energy as driving source. From this context, some researchers investigated the performance of multi-stage adsorption refrigeration cycles those can be operated by heat source of temperature 60 °C or lower which are usually purged to the environment, with a heat sink of temperature at 30 °C. However, the performances of multi-stage systems are low. To improve system performance, an analytic investigation on a re-heat two-stage chiller is performed to clarify the effect of thermal capacitance ratio of the adsorbent and inert material of sorption element, overall thermal conductance ratio of sorption element and evaporator along with silica gel mass on the chiller performance. Results show that cycle performance is strongly influenced by the sorption elements overall thermal conductance values due to their severe sensible heating and cooling requirements resulting from batched cycle operation. The effect of thermal capacitance ratio (C_s/C_m) becomes significant with relatively higher mass of silica gel. It is also found that the chiller performance increases significantly in the range of silica gel mass from 4 to 20 kg.     

A new type adsorber for adsorption ice maker on fishing boats

A new type of adsorber for an adsorption ice maker on fishing boats, which uses a compound adsorbent (activated carbon and CaCl₂) and ammonia working pair, is designed. This type of heat pipe adsorber solves the problem of incompatibility between ammonia, copper, seawater and steel. The heating/cooling power for the adsorption/desorption process of the adsorbent, which is required to be transferred by one heat pipe in the adsorber, is computed by the test results of the adsorbent, and the heat transfer performance of one heat pipe in the adsorber is simulated according to the theory of the two phase closed thermosyphon. The heat transfer performance of the heat pipe can meet the heat demands for adsorption/desorption of the adsorbent when the evaporating temperature is −15 °C and the cycle time is 10 min. A test unit is set up to test the heating/cooling performance of the heat pipe type adsorber, and the experimental results are coincident with the simulation. The performance of a two bed adsorption ice maker with heat pipe adsorbers is predicted, and the cooling power is about 17.1–17.8 kW at the evaporating temperature of −15 °C and cycle time of 10 min with mass recovery between two 29 kg compound adsorbent beds.     

An experimental study of heater size effect on micro bubble generation

An experimental study of the heater size effect on micro boiling is reported in detail. Using a 1.66-ms-wide heating pulse, boiling in subcooled water was investigated on a series of micron/submicron thin film Pt heaters with various feature sizes ranging from 0.5 μm to 70 μm. It was found that there existed a critical heater size (10 μm): single spherical bubble generation with heater’s feature size less than 10 μm; oblate vapor blanket on the heater surface with the size larger than 10 μm. The bubble dynamics was studied by the visualization of the bubble nucleation process with a high-speed CCD. The onset bubble nucleation temperature was measured by using each Pt heater as a resistive temperature sensor. The formation of the oblate vapor blanket was attributed to the condensation effect of the vapor outside the superheated zone. The analysis was further validated by generating spherical bubble on heater with size larger than 10 μm with a longer heating pulse.     

Efficiency of PET reactors in solar water disinfection for use in southeastern Brazil

Solar water disinfection using the solar water disinfection (SODIS) method is not a well-known technique in Brazil. The objective of the study was to investigate the effectiveness of a solar energy concentrator made of cardboard and covered with aluminium foil in heating water in transparent and black-backed PET reactors and to compare the efficiency of these reactors with those that are used on asbestos roofing. The efficiency of the method was evaluated for a year with monthly in loco readings and through analysis of the local weather where the study was performed. The black-backed PET reactors in the solar concentrator were better at heating water than any of the other treatments, both on strong and moderate weather days. On weak weather days, however, these reactors did not heat the water enough for solar disinfection to take place. Disinfection of polluted river water samples was evaluated in black-backed solar reactors. The most probable number (MPN) of thermotolerant coliform bacteria and Escherichia coli in water collected from the river were measured using the multiple tube fermentation technique before and after solar treatment. River water samples exposed to 3 h of solar radiation on moderate weather days had 99.9% inactivation of faecal coliforms (E. coli) when the water reached more than 50 °C (average 6 h peaks of radiation – 685.6 W/m²). However, inactivation of faecal coliforms was not observed in reactors exposed to solar radiation in the same weather conditions on asbestos roofing. A computer simulation of water heating was carried out using a dynamic fluid model based on the diffusion equation. The computational model produced temperature values similar to the experimental curves (r² = 0.99). The results suggest that using a specific radiation data set, the behaviour of water temperature in the PET reactors can be accurately predicted. Therefore, it may be possible to make predictions about water purification by the SODIS method in southeastern Brazil, where there are similar weather conditions.