Transient analysis of parallel plate forced circulation solar water heating system

In this paper, a transient analysis of a forced circulation solar water heating system with and without heat exchangers in the collector loop and storage tank has been presented for a parallel flat plate collector. The effect of various water heating system parameters on its performance have been studied. Numerical calculations have been made for a typical cold day viz. 26 January 1980 in Delhi.     

Transient analysis of forced circulation solar water heating system

This paper presents a transient analysis of a solar water heating system with forced circulation. Two modes of hot water retrieval have been taken into account viz direct from the tank and through a heat exchanger placed in the tank. Analysis has been presented both for constant flow and constant collection temperature modes. Effects of heat exchanger length and time of starting hot water retrieval on the system performance have also been studied. Numerical calculations have been made for a typical cold day (26 January, 1980) at Delhi.     

Experimental investigation of a solar energy heating system under the climatic conditions of Edirne

Seasonal storage of solar energy to supply the heat requirement of buildings in Edirne (41°39′54″N) has been examined experimentally. Solar energy has been stored in a cylindrical underground storage unit. Measurement values have been recorded per hour by means of a computerized recorder between July 2005 and May 2006. Monthly average temperature values of the heat storage unit and the surrounding ground have been calculated through the measurement results. The transient heat transfer which takes place between the heat storage unit and the surrounding ground has been calculated by means of the QuickField finite-element analysis program. It has been determined that the most significant deviations between the theoretical and the experimental temperature values turn out to be in question during the heating period. The annual solar fraction of the solar energy heating system has been determined as 53% for space heating and 85% for domestic water heating.     

热泵工艺在油田注水站的应用分析

热泵系统也称余热回收系统,是使用部分驱动能源(如燃气、蒸汽、燃气或热水),将余热形式为地热水、冷却水、洗涤水或伴油污水,温度在20~70℃的低品位能量取出,转移到45~100℃的中高温热媒中的系统。热泵系统在利用低品位热能的同时,仅消耗少量电能,节能效果显著。我国直到20世纪90年代,开始大面积应用热泵技术。目前,在热泵制造、安装和运行规模上,已走到了国际前例。现在,不管是压缩式热泵,还是吸收式热泵,也不论是设备还是系统,其技术已经成熟,热泵机组制热温度达到45~100℃,COP值(能量与热量之间的转换比率,简称能效比)也达到相当高的水平,机组的超小型化和超大型化技术得到长足发展,被广泛应用到建筑、烘干、石油化工、医药、筑路等领域。以热泵工艺在油田注水站的应用为分析对象,针对热泵的起源、发展、工作原理及在注水站的应用展开论述,着重从初期投资、运行费用、人工费用、社会效益、节约清水及10年费用现值方面,对注水站采用热泵冷却工艺与常规冷却工艺进行对比分析,提出了注水站采用热泵工艺有利于提高注水站系统的热能效率,降低运行成本,减少加热炉加热过程中产生的废气和余热排放,实现节能减排,对于热泵工艺在大庆油田注水站的应用具有借鉴意义。     

Transient analysis of closed loop solar water heating system

This paper presents a simplified transient analysis of a forced-circulation solar water heating system with a heat exchanger in the collector loop. Besides two modes of hot water withdrawal viz constant flow and constant collection temperature; the paper also studies the effectiveness of the flow through the heat exchanger and its length. The system performance has been further studied by considering different timings of starting hot water withdrawal. Calculations have been made for a typical cold day (26 January 1980) in New Delhi.     

Experimental investigation of a multi-function heat pump under various operating modes

Heat pumps have been spotlighted as efficient building energy systems because they have great potentials for energy reduction in building air conditioning and reducing CO₂ emission. In this study, a multi-function heat pump which has the functions of heating, cooling, and hot water supply was designed and its performance was investigated according to operating modes. In the cooling-hot water mode, the capacity and COP were enhanced as compared to other modes because the waste heat from the outdoor heat exchanger was utilized as useful heat in the indoor heat exchanger. In the heating and hot water supply mode, the compressor speed should be increased to get appropriate heating and hot water capacities. For all operating modes, the system could be optimized by adjusting the superheat.     

洗浴废水源热泵供暖的节能分析

运用DEST软件分析了山西省太原市某洗浴中心采用洗浴废水源热泵系统供暖的逐时负荷的情况,得出,采用洗浴废水源热泵供暖比常规地下水源热泵系统供暖具有明显的节能优势。     

Evaluation and optimization of water source heat pump for district heating: A case study in steel plant

Using high-temperature heat pump technology to recover waste heat of circulating cooling water in a steel plant for central heating system not can only reduce the temperature of circulating cooling water to meet the needs of smelting process but also can save energy and protect environment as well as bring great economic benefits to steel plant that can sell heat to the heat users. The energy consumption equation of heat pump central heating system was established based on the energy consumption of heat pump, energy consumption of water pump, and heat loss. The optimal inlet water temperature, inlet flow rate, and the number of operating heat pump modules at different outdoor temperatures were calculated by genetic algorithm. The superiority and operating control strategy of heat pump central heating system were discussed. The results show that with the increase of outdoor temperature, the optimal inlet flow rate and the number of operating heat pump module decrease. However, the inlet water temperature almost does not change. It is more suitable for the heat pump central heating system to change the inlet flow and the number of operating heat pump modules. The operating control strategy equation was established by linear fitting, which provides guidance for the engineering application of heat pump central heating system.     

Upgrading heat by a reversed absorption heat pump

Analysis of a reversed absorption heat pump's performance for upgrading low temperature waste-heat from industrial processes and solar heat from a flat-plate solar collector has been carried out. In the case of upgrading waste-heat, the ratio of output to input heat decreases as the temperature at which the output heat is needed increases. For water heating, the performance of the conventional solar water heating system is better than that of the heat pump system because in the latter case, heat is rejected from the condenser.     

Performance equations for air- and water-heating systems

Expressions for the performance parameters F′, U_L and F_R of various collector configurations have been documented previously. For a system which consists of an air-heating collector connected to a compact air/water heat exchanger, these performance parameters derivations have not been documented. In this paper, the derivation of performance parameters has been accomplished for an air/water heating system. The utility of these performance parameters in finding the rating parameters of an air/water heating system and mutual comparisons of various of these parameters for other systems are made.     

Long-term (18 years) performance of a residential solar heating system

The long-term performance of a residential solar heating system has been determined for a system which has been operating continuously since 1957 with no maintenance. This residential solar heating system is the Colorado Solar House located in Denver, Colorado, designed and operated by George O. G. Löf.The performance of this system was determined during the 1959–1960 heating season, and the results were publised. The performance of this system was redetermined during the 1974–1975 heating season so that changes in performance occurring over a period of 15 yr could be determined.The collector is an Overlapped-Glass Plate Solar-Air Heater. The system is completely automatic with provision for water heating in addition to space heating. Solar heat is stored in a rock bed of primarily granitic rock approximately 1.3–2.5 cm in diameter.The ratio of useful collected solar heat divided by the total solar radiation on the collector dropped to 71.8 per cent of its original value in 15 yr. For both seasons, the useful collected solar heat was correlated with the ratio of degree days per month divided by the total solar radiation on the collector. For the same value of this ratio, less useful collected solar heat was delivered during the latter season.Additional work that will be published at a later date includes the detailed performance of the hot water heating system.     

Properties optimization for phase-change energy storage in air-based solar heating systems

A parametric study has been conducted to determine the optimum physical properties of phase-change energy storage materials for solar air-heating systems. Simulation techniques are used to determine the system performance over the entire heating season. Variations of the solar fraction of the load with melting temperature, latent heat, load characteristics, and control strategy have been determined. Air-heating systems with a wide range of hot water and space heating loads have been examined. The effect of semicongruent melting of the phase change material on system performance has also been investigated.     

Thermal performance of a solar-aided latent heat store used for space heating by heat pump

In this study, the cylindrical phase change storage tank linked to a solar powered heat pump system is investigated experimentally and theoretically. A simulation model defining the transient behaviour of the phase change unit was used. In the tank, the phase change material (PCM) is inside cylindrical tubes and the heat transfer fluid (HTF) flows parallel to it. The heat transfer problem of the model (treated as two-dimensional) was solved numerically by an enthalpy-based finite differences method and validated against experimental data. The experiments were performed from November to May in the heating seasons of 1992–1993 and 1993–1994 to measure both the mean temperature of water within the tank and the inlet and outlet water temperature of the tank. The experimentally obtained inlet water temperatures are also taken as inlet water temperature of the simulated model. Thus, theoretical temperature and stored heat energy distribution within the tank have been determined. Solar radiation and space heating loads for the heating seasons mentioned above are also presented.     

Design and performance of direct heat exchange geothermal district heating schemes

A variety of geothermal district heating scheme designs have been studied, differences of configuration have been identified and the design principles used to obtain maximum geothermal heat supply have been defined. The main principle is that return temperatures to the heat exchange must be as low as possible and to achieve this the network must be operated with variable temperature and flow in response to fluctuating demands. The location of back-up boilers, the type of sub-station and the inclusion of domestic water heating normally have small effects on performance. However, in some cases, water heating can have a detrimental effect.     

A review on the energy and exergy analysis of solar assisted heat pump systems

During the last decade, a number of studies have been conducted by various investigators in the design, modeling and testing of solar assisted heat pump systems (SAHPSs). This paper reviews the studies conducted on the energy and exergy analysis of SAHPS systems in Turkey and around the world as of the end of December 2004. The studies undertaken on the SAHPS systems are categorized into four groups as follows: (i) SAHPSs for water heating, (ii) SAHPSs with storage (conventional type) for space heating, (iii) SAHPSs with direct expansion for space heating, and (iv) Solar-assisted ground source heat pump greenhouse heating system (SAGSHPGHS). This paper investigates the studies on SAGSHPs, especially ground-source heat pumps, also known geothermal heat pumps, at the Turkish universities in more detail, by giving Turkey's solar energy potential.     

Modelling and analysis of the dynamic behavior of a forced circulation solar water heating system with storage tanks in series

A generalized model for a forced circulation solar water heating system with storage tanks in series is presented in which the loss of heat through an insulation lagging is considered, and the periodic time variation of the intensity of solar radiation, as well as both the ambient air temperature and the temperature of cold water entering the first main tank, is taken into account. Using the Laplace transformation, an exact solution is presented which, under certain conditions, reduces to an approximate solution. The conditions for convergence to the approximate solution are discussed, and figures are presented comparing it with the exact solution for several different sets of conditions. In this communication, the effect of the number of storage tanks on the outlet temperature of the hot water and the effect of various water heating system parameters on its performance have been analytically investigated. Numerical calculations have been made for a typical cold day.     

The performance of an open-loop lake water heat pump system in south China

A district heating and cooling (DHC) system that utilizes lake water as heat source–sink of heat pumps has been constructed in Xiangtan, a city in Hunan province in south China. An initial analytical study had been carried out before the construction. In this paper, a simplified two-dimensional model is developed to simulate the steady lake water temperature (LWT) distribution during continuous operation. The simulation results indicate that the impacts of the discharge on entering water temperatures (EWT) and the ecological environment of lake are acceptable. Field test results showed that the COP values of the system were, respectively, 0.7–0.85 higher in cooling season and about 0.46 higher in heating season than those of the air-source heat pump (ASHP) units at the same sink and source temperatures. An acceptable payback period of 5.6 years was found through an economic analysis based on the comparison between the initial and operating costs of the system and those of the distributed ASHP units that would have been installed according to initial scheme.     

Energy consumption of a residential building: comparison of conventional and RES-based systems

The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved.     

Hydrogen release from a metal hydride tank with phase change material jacket and coiled-tube heat exchanger

Hydrogen fuel cells are received increasingly wide attention in order to develop green ships and reduce greenhouse gas emissions in the field of waterway transportation. Metal hydrides (MHs) can be used to store hydrogen for green ships due to their high volumetric storage capacity and safety. Various measures should be considered in the design and manufacture process of the MH reactor to strengthen its performance of heat and mass transfer and obtain an acceptable hydrogen storage capacity. In this work, LaNi₅ hydride is used as the hydrogen storage material and packed in the reactor. A basic axisymmetric numerical model for the hydrogen storage system without a heat exchanger has been developed and proved to be effective through the comparison between its simulation results and the published data during dehydriding. A hybrid heat exchanger, which is consisted of a phase change material (PCM) jacket and a coiled-tube, has been applied into the hydrogen storage system to relieve the thermal effect of MH in the dehydriding process on system performance. Effects of the heat transfer coefficient between the circulating heating water in the coil-tube and the MH bed, the temperature of circulating heating water and the pressure at the outlet on the dehydriding performance have been investigated. Based on parametric study, the relationships among the average dehydriding rate, the heat transfer coefficient, the heating water temperature and the outlet pressure have been found and fitted as simple equations. These fitted equations can be considered as a reference, which provides an important method to effectively control the dehydriding rate in order to satisfy the fuel requirement of the power unit and ensure the safe navigation of green ships in the future.