Experiments of a solar flat plate hybrid system with heating and cooling

Based upon the prior research of the solar hybrid water heater and refrigerator, a new flat plate solar hybrid system with heating and cooling was proposed and experimental prototype device was constructed. With this new hybrid system, the heat and mass transfer can be improved effectively both in desorption process and adsorption process. The conventional flat plate solar water heater collector absorber is immersed inside adsorbent bed in the new hybrid system. The experimental results show that not only the cooling effect can be obtained, but also both the sensible heat of the adsorbent bed and the adsorption heat can be recovered effectively to produce hot water for domestic use. The COP of this new flat plate hybrid system can reach 0.11 and the heat efficiency is about 0.45, this achievement has demonstrated an efficient way of the application of solar energy.     

带饮水机的多功能电冰箱设计

在传统电冰箱的基础上,另独立设置2个保温箱贮存冷热饮用水。冷水制取是在冷水箱中设置蒸发器,将冷水箱中的水制冷。热水制取是在热水箱中设置逆流套管式冷凝器,利用制冷系统的排热量将饮水机中的水加热到一定温度,如温度不够则再通过电加热器,可将饮用水加热至沸腾,冷凝管通热水箱后可采用风冷式和水冷却两种方式相结合。根据设计和理论计算,多功能电冰箱的冷凝器可将饮用水加热到65℃左右,再用电加热器,可将饮用水加热至沸腾,比市场上纯粹用电加热的饮水机可节电22.31W;利用制冷系统将冷水箱中的水制冷,每产生4℃冷饮用水2L比市场上一般的压缩式制冷饮水机可节约大约2.3×105J的能量。     

变容量家庭能源中心单独制热水模式的实验研究

提出了可全年供应空调和热水需要的变容量家庭能源中心系统,并提出单独制热水模式下的性能系数计算方法。通过对该模式瞬时动态特性的研究,指出变容量压缩机可以有效地保证机组的安全可靠运行。实验研究了单独制热水模式在不同环境温度、不同压缩机负荷条件下的性能。结果表明,在同一压缩机负荷条件下,热水性能系数均随环境温度的升高而升高,与传统热泵热水器的变化趋势相同。而压缩机负荷变化对机组热水性能系数的影响在不同的环境温度下呈现不同的规律,因此,可根据不同的环境温度优化控制压缩机负荷,以提高制热水效率,节约能源。     

A run-around heat exchanger system to improve the energy efficiency of a home appliance using hot water

A significant portion of the energy consumed by many home appliances using hot water is used to heat cold supply water. Such home appliances generally are supplied water at a temperature lower than the ambient temperature, and the supply water is normally heated to its maximum operating temperature, often using natural gas or an electrical heater. In some cases, it is possible to pre-heat the supply water and save energy that would normally be consumed by the natural gas or electrical heater. In order to save the energy consumed by an appliance using water heater, a run-around heat exchanger system is used to transfer heat from the ambient to the water before an electrical heater is energized. A simple model to predict the performance of this system is developed and validated, and the model is used to explore design and operating issues relevant to the run-around heat exchanger system. Despite the additional power consumption by the fan and pump of the run-around heat exchanger system, the experimental data and analysis show that for some systems the overall energy efficiency of the appliance can be improved, saving about 6% of the energy used by the baseline machine.     

基于能量梯级利用的太阳能冷热联供系统

从能量梯级利用的角度出发，提出了一种新型太阳能冷热联供复合系统。该复合系统可根据太阳辐射强度在不同的季节分别用作单一的太阳能热水器、热泵热水器或太阳能吸附式冷热联供复合系统。建立了相应的数学模型，计算了该系统在不同季节各种典型工况下的性能指标。计算结果表明，该系统不仅可实现冷热联供的双重功能，而且具有较大的节能潜力。     

A study on the new separate heat pipe refrigerator and heat pump

A new separate heat pipe refrigerator and heat pump is suggested based on the general three temperature thermal jet refrigerator and heat pump cycle. Sub-cooled hot water or other appropriate liquid heated by low grade heat sources forms the hot end and another heat pipe containing evaporator and condenser ends, adiabatic section of two-phase ejector and throttling tube is as the cold end of the separate heat pipe system. Performance relations for the thermal jet refrigerator and heat pump of such system is analyzed and a method of thermodynamic performance analysis is recommended. Primary prediction shows the feasibility of such heat pipe system for cold and warm water supply.     

Performance of a prototype Stirling domestic refrigerator

The V-type integral Stirling refrigerator (VISR) consisting of an expansion cylinder, a compression cylinder and a heat exchanger in-between was developed and tested in this research. The expansion and compression pistons are V-shaped and driven by a crank-shift mechanism. A cold head connected to the expansion piston provides the cooling capacity. The refrigerator has a semi-hermetic configuration. The parameters such as the power consumption and the coefficient of performance (COP) are investigated under various rotating speeds and charged pressures. The results would help us for the optimal design and operation of the V-type integral Stirling refrigerator, when it is applied to the domestic refrigeration system. The characteristics curves of the prototype VISR could be applied to other usages.     

Refrigerator COP with thermal storage

Due to the extreme necessity to diversify renewable energy sources, the search for energy recycling methods through the utilization of thermal losses from equipment has become fundamental. Thus, these losses can be used as a new source of energy for water heating and storage in domestic hot water storage tanks (DHWST). For this reason, the construction of an experimental apparatus with a cylindrical thermal storage tank is proposed, in which the objective of the study will be a survey of the coefficient of performance concerning conventional and modified refrigerators, as well as to perform an analysis of hot water, through the thermal stratification technique using a refrigerator with a modified condenser. The collected thermal loss, as per the thermosyphon principle, will be stored as thermal energy. The results showed the full operation of the modified refrigeration system, which did not reveal significant alterations in thermodynamic behavior after the modifications made on the condenser. The dynamic behavior of the thermal distribution was observed through the thermal stratification effect and temperature evolution in terms of time, showing greater variability of the modified refrigerator generating more thermal comfort to users in addition to providing domestic hot water.     

Analysis and performance of a low-cost solar heater

One of the alternatives to reduce the consumption of electricity for heating water is by popularizing the use of solar energy. This work contributes with studies on a Low-Cost Solar Heater (LCSH), a new concept of solar water heater made entirely of polymeric materials, which requires a relatively low investment and is user-assembled. The solar collector, which absorbs solar energy and transfers it to water in the form of heat, is composed of uncovered flat panels of rigid PVC. The storage tank that holds the water heated during the day is made of polyethylene coated with polystyrene. The results of the LCSH were compared with those of a conventional solar heater composed of a glass-covered copper collector and a stainless steel storage tank. The efficiency of the systems was evaluated by measuring the incident solar radiation and water temperature with the systems operating naturally (thermosiphon). The heat loss in the hot water storage tanks was measured to estimate the thermal performance of the solar heaters. Considering that the target temperature for the heated water is slightly above the ambient temperature, the results indicated that the LCSH showed a satisfactory global heat transfer coefficient for storage tanks and that it attained an excellent thermal performance, although it is not as efficient as the conventional heater.     

An experimental study on a modified air conditioner with a domestic hot water supply (ACDHWS)

The recovery of condenser heat in air conditioners is attractive because of its great economy and environmental value. This work experimentally studies a modified air conditioner with a domestic hot water supply (ACDHWS) that operates in the space-cooling and water-heating mode. The working principles and the basic features of the ACDHWS are introduced in this paper. This is followed by an experimental study on dynamic operation characteristics, hot water supply performance, energy efficiency and the temperature distribution of hot water in the storage tank of the unit. The results show that the ACDHWS can reliably be used to heat domestic hot water without losing its cooling capacity when it is controlled well in different operation conditions. Comparatively, the coefficient of comprehensive energy performance (COP₂) of the ACDHWS is about 38.6% higher than that of the original unit. Furthermore, it is proved that the ACDHWS can continuously supply hot water for householders if a suitable hot water storage tank is installed. All these may be much helpful to develop a perfect ACDHWS product.     

Techno-economic analysis of a novel hybrid heat pump system to recover waste heat and condensate from the low-temperature boiler exhaust gas

This paper is based on the proposal of a new waste heat recovery (WHR) system, which can be utilized to heat the boiler return water, boiler supply air, and building heating air. The system is the combination of an indirect contact condensing unit (IDCCU), a mechanical compression heat pump, and two air preheaters. The system is modeled on the basis of mass and energy balance and then thermodynamically analyzed. Improved performance results were obtained in the form of an increase in the boiler's energy efficiency of about 10.47%, with 4.87% increase in exergy efficiency. The coefficient of performance (COP) of the heat pump was increased from 1.23 to 1.45 by the addition of an air heater in the conventional heat pump. The exergy destruction in each component is calculated. Sensitivity analysis was performed to check the influence of different operating parameters on the performance of the WHR system and boiler. It can be observed from the results that for a specific refrigerant temperature and a calculated amount of mass, flow rate can maximize the condensation efficiency of IDCCU by decreasing the flue gas temperature, while the use of the air heater can further reduce the flue gas temperature, and a stream of hot air can be utilized for space heating. A comparison is made with the other system on a performance basis. The results shows a clear difference in efficiencies and profit earned.     

烟气冷却器的节能效果评价

通过烟气冷却器充分利用电站锅炉的排烟余热加热凝结水能够替代部分回热抽汽,减少了回热系统对低压缸的抽汽,使汽轮机做功量增加,机组煤耗降低。烟气冷却器按照不同的联结方式与回热系统的加热器集成后,随着机组负荷的降低,所带来的节煤效果的差别逐渐变大。并且,不同的集成方式对加热器内部附加单耗的影响差异较大。另外,腐蚀问题仍然是限制低温烟气余热深度利用的瓶颈。若能在材料上有所突破,就能得到更低的排烟温度,使机组的热经济性进一步提高。     

Experimental results of a sensible heat storage system for residential and light commercial application

This paper presents the performance results for a sensible heat storage system. The system under study operates as an air source heat pump which stores the compressor heat of rejection as domestic hot water or hot water in a storage tank that can be used as a heat source for providing building heating. Although measurements were made to quantify space cooling, space heating, and domestic water heating, this paper emphasizes the space heating performance of the unit. The heat storage system was tested for different indoor and outdoor conditions to determine parameters such as heating charge rate, compressor power, and coefficient of performance (COP). The thermal storage tank was able to store a full charge of heat. The rate of increase of storage tank temperature increased with outdoor temperature. The heating rate during a charge test, best shown by the normalized rate plots, increased with evaporating temperature due to the increasing mass flow rate and refrigerant density. At higher indoor temperature during the discharge tests, the rate of decrease of storage tank temperature was slower. Also, the discharge heating rate decreased with time since the thermal storage tank temperature decreased as less thermal energy became available for use. Copyright © 1999 John Wiley & Sons, Ltd.     

Experimental investigation of effect of variation of mass flow rate on performance of parabolic dish water heater with non-coated receiver

Concentrated solar collectors have high efficiency. Therefore, when concentrating collectors are used for water heating application, the system yields higher efficiency. From a hot climate perspective, there is a huge potential available for low-cost solar water heating systems. With the system described in this paper, the needs of hot water in the domestic sector can be fulfilled instantly. Authors used the parabolic dish collector for instant water heating. This paper describes the effect of variation of mass flow rate on performance of the parabolic dish water heater prototype. Design of the solar parabolic dish collector consists of a novel truncated cone-shaped helical coiled receiver made up of copper at focal point. This prototype was evaluated for its performance during the month of April and May 2010.     

Analysis of thermal response of a food self-heating system

This paper presents a distributed model of heat transfer in a self-heating unit for group meals and its numerical simulation. A magnesium alloy and water exothermic reaction provides the necessary energy. The resulting governing equations of chemical reaction and heat conduction that depicts the heater performance were solved to develop an approximate analytical solution, to which experimental data found from literature were compared and curve fitted. Then, a model of a complete food-heating unit for group meals, which include a stack of four sets of food tray, heating tray, and heater sandwiched between them, as well as the cardboard container, was developed. The governing equations for heat conduction in the complete model were solved. The response in thermal performance of the heating system to the parameters that influence heating profiles of the heater such as decay constant and heat generation capacity were studied. The results show that the system thermal performance is most significantly affected by heat generation and a proper combination of heaters with different heat generation capacity can improve temperature uniformity between food trays. The results are useful for designing and optimizing self-heating multi-food tray units.     

Year round performance studies on a built-in storage type solar water heater at Jodhpur, India

An improved solar water heater (capacity 901) made up of a 112×80×10 cm rectangular tank which performs the dual function of absorbing heat and storing the heated water has been designed and a prototype tested in Jodhpur. The performance tests carried out at the Central Arid Zone Research Institute, Jodhpur, indicate an efficiency factor reaching as high as 70 per cent. The year-round performance tests show that this heater can supply 901 of water at a mean temperature of 50 to 60°C in winter and 60 to 75°C in summer (measured at 4:00 p.m.). The performance tests also indicate that sufficient hot water can be obtained in the early morning if the heater is covered with an insulation blanket overnight or if the hot water is stored in an insulated tank.A performance equation for this type of heater, where the inputs are the solar intensity, ambient air temperature and geometry and material specifications of the heater, has also been developed. With this performance equation the optimum gap depth, i.e. the distance between upper and lower plate of the heater, has been found to be 10·0 cm.     

Performance of solar water heaters with narrow mantle heat exchangers

This paper evaluates the performance of narrow-gap vertical mantle heat exchangers with a two-pass arrangement for use in pumped-circulation solar water heaters. Both measured mantle side and tank side heat transfer correlations have been developed and implemented in a TRNSYS model of a complete solar water heater incorporating this type of heat exchanger. Predictions of the annual solar contribution for mantle-tank systems are compared to direct-coupled systems. The direct-coupled systems are found to provide slightly higher annual energy saving than mantle-tank systems for standard domestic hot water demand in Australia. However, the reduction in performance is outweighed by the benefit of freeze protection provided by incorporating a collector loop heat exchanger in the system.     

Development of a beta-type Stirling heat pump with rhombic drive mechanism by a modified non-ideal adiabatic model

In this paper, a thermodynamic model is developed for predicting the performance of a beta-type Stirling heat pump with rhombic drive mechanism for water heater and the model is validated by a 1-kW class prototype Stirling heat pump. In the present model, the working space is divided into expansion space, heat absorber, regenerator, heat rejecter and compression space. The pressure, mass and temperature variations of working fluid in each working space are predicted. The temperature variation of wall boundary is also taken into consideration. The temperature of working fluid in each working space and the temperature of wall boundary are obtained by solving energy equations simultaneously. Eventually, the pressure of working fluid in each working space can be corrected by using empirical formula of pressure drop. All the thermal properties of working fluid and wall boundary in each working space at each time step can be obtained by repeating the above process. Then, the performance of heat pump such as absorbing heat, rejecting heat, indicated power and COP can be calculated. A series of experimental measurements and comparisons are also conducted for validating present model. The results show that the prototype heat pump can produce 904 W heating power and 38°C hot water under 1 LPM water flow rate with 5 bar helium at 1000 rpm.     

Thermal performance analysis of a direct-expansion solar-assisted heat pump water heater

A direct-expansion solar-assisted heat pump water heater (DX-SAHPWH) is described, which can supply hot water for domestic use during the whole year. The system mainly employs a bare flat-plate collector/evaporator with a surface area of 4.2 m², an electrical rotary-type hermetic compressor, a hot water tank with the volume of 150 L and a thermostatic expansion valve. R-22 is used as working fluid in the system. A simulation model based on lumped and distributed parameter approach is developed to predict the thermal performance of the system. Given the structure parameters, meteorological parameters, time step and final water temperature, the numerical model can output operational parameters, such as heat capacity, system COP and collector efficiency. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The effect of various parameters, including solar radiation, ambient temperature, wind speed and compressor speed, has been analyzed on the thermal performance of the system.     

Simulation analysis for the active solar heating system of a passive house

The active solar heating system consists of the following sub-systems: (1) a solar thermal collector area, (2) a water storage tank, (3) a secondary water circuit, (4) a domestic hot water (DHW) preparation system and (5) an air ventilation/heating system. An improved model for the secondary water circuit is proposed and two interconnection schemes for sub-systems (4) and (5) are analyzed. The integrated model was implemented to Pirmasens passive house (Rhineland Palatinate, Germany). Both interconnection schemes show that (almost all) the solar energy collected is not used for space heating but for domestic hot water preparation. The classical water heater operates all over the year and the classical air heater operates mainly during the nights from November to April. The yearly amount of heat required by the DHW preparation system is about 77% of the yearly total heat demand of the passive house and the classical water heater provides about 20% of the yearly heat required by the DHW preparation system. The solar fraction lies between 0.247 in January and 0.930 in August, with a yearly average of 0.597.