Search

In order to design the vertical falling film evaporators applied in the sewage source heat pump systems, a numerical study employing the VOF (Volume of Fluid) method has been carried out to determine the thickness and the wave behavior of falling liquid film outside a vertical tube. The effects of the annular gap, tube diameter, tube length, spray density, viscosity and surface tension are discussed. The simulation results demonstrate that spray density and the fluid viscosity are the two most influential factors affecting the film thickness. Besides, when spray density is larger than 0.100 kg/(m∙s), the film thickness decreases slightly with the increase of the flow distance. So the influence of tube length on film thickness cannot be ignored and it also should be considered in the film thickness prediction model. On the other hand, the tube diameter and the surface tension have little effect on the film thickness. It mainly have a significant impact on the wave amplitude of the liquid film at low flowrate. Besides, the annular gap provides a limited effect on the outlet section of the falling film. On the basis of the simulation results, a new correlation incorporating the tube length is developed to effectively predict the falling film thickness. Compared with the experimental data, it is found that the prediction accuracy of the correlation can be controlled within ±15%. The present research provides a theoretical basis for designing falling film evaporators.

Systematic and random errors for working sensors in building systems can seriously affect the operation performance and have a significant negative impact on energy efficiency and indoor comfort. H...

The temperature of domestic drain water is relatively high, but its flux is sometimes insufficient as a heating source. Thus, the conventional wastewater source heat pump water heater is incapable of meeting user heating demand given the limited sensible heat temperature difference in many situations. To address this problem, a novel in–house heat pump water heater with a freezing latent heat evaporator and assisted by domestic drain water was proposed. A prototype of the system was first constructed to determine the performance of the system. An experiment was then conducted, in which a parallel helical coil tube evaporator was designed and developed to extract freezing latent heat from domestic drain water. Experimental data was obtained in different experimental conditions. Results of the investigation show that the heat pump water heater with a freezing latent evaporator recovers 3.4 times more energy than the conventional wastewater source heat pump water heater, and saves 60% energy compared with the traditional electric water heater. Furthermore, an interesting result is that the heat transfer coefficient increased significantly at the moment the wastewater was just frozen. This paper provides a reference for the wastewater source heat pump water heater to extract freezing latent heat from domestic drain water.

Among sub-items of energy consumption in public buildings, lighting sockets play an important role in energy-saving analysis. So, the energy consumption data quality of lighting sockets is important. However, limited by the initial cost of energy monitoring platform, it is difficult to install electricity meters covering all branches and to retrofit the incompact classification electricity branches, which results in a mixture of the lighting socket energy consumption and other components. In this study, a separation methodology is proposed. First, the abnormal data in the energy monitoring platform are cleaned and screened using a clustering algorithm. Second, the average outdoor air temperature partitioning model (OATPM) method and the k-nearest neighbor (KNN) clustering algorithm method are proposed for identifying and separating the abnormal data. These two methods have complementary advantages in the best applicable scenarios, including calculation accuracy and other aspects. The verification results for three buildings show that the relative error of this separation methodology is less than 15%. Finally, this paper presents the optimization parameters of the KNN method. Through this methodology, building managers need only historical data in an energy monitoring platform to separate the combined power consumption of the lighting sockets and air-conditioning online, independent of detailed information statistics.

An intensive study on the heating temperature aimed to create a satisfying indoor condition that should meet the residents’ thermal requirements in accordance to their daily behavior pattern. Unlike urban residents who stay indoors for a long time, rural residents constantly live in a dynamic environment: they often leave their residences and get busy with numerous labor activities. Therefore, the thermal sensation questionnaire survey performed in a steady environment is not suitable for them. To study the rural heating temperature in a dynamic environment, a three-years field investigation was performed in South Liaoning province. During the investigation, a continuous tracking method was adopted to record the residents’ behavior; objective environmental parameters test and subjective thermal sensation surveys were rigorously recorded. The results indicate that the residents behavior pattern exerts an influence on the heating temperature by influencing the residents’ clothing insulation. Heating temperature in auxiliary rooms can be directly determined by the residents’ thermal sensation, with the reasonable value of 11 °C. The influence of residents’ behavior on clothing should be considered when determining heating temperature in the master bedroom, the reported value of which is 13 °C. The heating temperature obtained by the thermal sensation fuzzy comprehensive evaluation model in paper reflects the rural residents’ real-life requirements on thermal environment, and it provides a reference for designing rural residences.

Electricity consumption in university dormitories deserves more attention owing to its constituting a large proportion of total electricity consumption in university buildings and the enormous electricity conservation potential. This research proposes a methodology comprising aggregated and segmented analyses to provide an in-depth understanding of electricity consumption in university dormitories from multiple perspectives. Aggregated analysis provides global perspectives for electricity consumption by resolving a novel and practical problem of setting free electricity consumption quotas for student dormitories. Segmented analysis provides partial perspectives for electricity consumption by discovering electricity consumption patterns according to the academic calendar. The actual daily electricity consumption data of 2434 undergraduate dormitories, 542 graduate-MS dormitories, and 583 graduate-PhD dormitories collected by smart meters from a Chinese university are analyzed to demonstrate the application of the proposed methodology. The main results of the research include the following: (1) different modes of setting free electricity consumption quotas have different effects on electricity conservation, and the monthly mode seems to be a more efficient alternative to stimulate energy-saving behaviors than the annual mode; (2) there is no significant linear correlation between outside temperature and electricity consumption against the background of limited electric power and nonusage of air conditioning systems; and (3) the representative electricity consumption patterns in the three types of dormitories are explored according to the academic calendar. The university administrators can devise good electricity use policies and implement electricity network planning and operations according to the patterns. The implications of the results and several recommendations for promoting energy conservation are provided simultaneously

Saving energy in rural residences is of great importance. In this paper, a field investigation of the basic physics information and thermal environment of rural residences was carried out, using a rural residence in Dalian as an example. Based on the analysis of this investigation, we find that the thermal performance of the building envelope, the living habits of the occupiers and the household economy have a close relationship with unsatisfactory residential thermal environment. Therefore a new perspective regarding optimization of rural residences is provided in terms of building plan layout, shape and properties of the building envelope. This paper presents rural residential optimization methods in which orthogonal numerical test and rules for integrated balancing methods are combined. Through numerical simulation with TRNSYS, the significance of different factors influencing indoor temperature has been given, and the optimal thermal parameters of the building envelope and plan layout of a rural residence are determined. The results show that south window-to-wall ratio is the most significant factor influencing indoor temperature and therefor this is the primary parameter requiring optimization. The south window-to-wall ratio of a rural residence in a cold region should be 45%. In addition, it is demonstrated that the optimal rural residence, when compared to traditional rural residences, has a satisfactory social benefit in terms of improving the indoor thermal environment and protecting the atmospheric environment during a heating season. This paper will offer a theoretical reference for the construction of modern rural residences.

Generally, the temperature of domestic waste water is high above 30℃. However, when dealt with by common sewage-source heat pump system, temperature difference between inlet side and outlet side is small as 5℃. It leads to manifold cycles and energy waste. To acquire a unit of heat pump water heater of sewage dealing with large temperature difference with high energy utilization rate, through which the cold water (about 5℃) can be heated once to hot water (about 45℃) to reach the temperature for daily use and waste water (about 30℃) can be rapidly dropped to cold water (about 6℃) to satisfy the standard of waste water emissions. In this paper, two staged series of heat pump water heater dealing with large temperature difference is proposed. And performance factor of system is analyzed through simulation by MATLAB so as to find the optimum middle operating point. This method ensures pattern operating in large temperature difference but in small flow at both the hot and cold sides. At the same time, it avoids the lasting elevation of condensing temperature and the constant reduction of temperature in evaporation, which helps to facilitate the stability and optimal performance of the operating unit.

In this paper, a heat pump hot water unit with the dual-source evaporator using air or water as the heat source is proposed. The idea is firstly to use the heat from the bath wastewater to heat the domestic hot water. If the stored wastewater is insufficient, the ambient air will be applied for assisting the heat pump. The structure of the dual-source evaporator is simpler and compacter compared with the traditional form of two evaporators arranged in parallel. For testing it, the heat pump hot water unit with the evaporator is established. The performance of the unit and the dual-source evaporator are investigated experimentally when the bath wastewater is used as the heat source. Experimental results show that the coefficient of performance (COP) of the heat pump can reach 5.02 when the wastewater temperature is 32℃, and the heat transfer coefficient of the evaporator can reach to 1003.56 W/m2 K. And the temperature of wastewater can be decreased to 8℃ by cyclical utilization. So the effect of heat recovery is remarkable for the heat pump hot water unit with the dual-source evaporator. When air is used as the only heat source, the performance of the heat pump is about the same as that of a conventional air-source heat pump, and this paper does not research on it.

Heat pumps are a part of the environmentally friendly technologies using renewable energy and have been utilized in HVAC systems. A heat pump water heater unit with frozen type evaporator was designed and developed. And a test bed was constructed to determine the performance of the unit. In the experiment, a parallel helical coil type evaporator was used in the unit to extract latent heat from the sewage. The data (dynamic COP and other parameters) was obtained in three processes(including the first freezing, melting, and the second freezing) at different water temperatures (8.2℃ and 13.8℃). Results show that compare with traditional water source heat pumps, the newly designed unit with the frozen evaporator can reduce the required water amounts as a heat source by more than 90%. The higher initial temperature of hot water and sewage, the higher temperature of sewage after melting. Meanwhile, with the increase of the initial temperature of hot water and sewage, the comprehensive COP was greater. This paper will provide a reference for the sewage source heat pump system to extract the latent heat from the sewage.

The public bath is the emphasis target of energy-saving renovation of existing public buildings in China. In that case, the integration of the hot water supply system according to the characteristics of heat sources should be studied and optimized to improve the comprehensive energy efficiency and the hot water production of the system. This paper analyzed and remedied the deficiencies of several common hot water supply systems with multi-heat-source, introduced a novel hot water supply system with multi-heat-source based on PVT (photovoltaic and thermal) heat pump and water source heat pump, and then carried out the integrated optimization research of this new system. The main studies include: (1) Established the novel hot water supply system with multi-heat-source and the calculation model of system heating characteristic. (2) Introduced the evaluation method of the comprehensive energy efficiency and economic performance for the hot water supply system with multi-heat-source. (3) Aiming at reducing the total cost of hot water supplying, the integration optimization ideas of system were proposed. By above methods, the integrated optimization of the existing North Mountain Public Bath in Dalian University of Technology was conducted. On one hand the daily production of the existing hot water supply system in the public bath is increased from 80 t to 146 t, the supply capacity of hot water is significantly promoted. On the other the total cost of hot water supplying decreases from 9.6 RMB/(t year) to 4.9 RMB/(t year), the comprehensive energy efficiency and the economic performance of system is improved.

Although the integration of photovoltaic-thermal (PV/T) heat pump systems on buildings can assist in reducing the electricity demand of high-energy consuming buildings, the large occupation area of PV/T modules hinders its popularization. To overcome this problem, a novel PV/T evaporation roof coupled with a heat pump system composed of electronic expansion valves, a condenser and a compressor is proposed, which serves as an electric generator, evaporator for the heat pump system and the external surface of a building roof. This paper investigates the actual operating performance of the direct-expansion roof-PV/T heat pump system under different seasonal conditions. The structure and design of PV/T evaporation roof and the whole system are first presented, followed by the construction of an experimental platform and finally the operation of the system is analyzed through performance evaluation indices and field-testing. The experimental results indicated that the system performed better in the summer than in the winter, with the electrical efficiency, thermal efficiency and overall efficiency averaging at 11.23%, 64.25% and 83.32%, respectively. The average COP was 5.9, with a maximum value of 8.9. Additionally, it took 2 h to heat the water within a 1.5 m3 heat storage tank from 25 °C to 60 °C, which was twice as fast as under winter conditions. Meanwhile, a significant decrease in system performance resulting from changes in environmental parameters in the winter was observed. The average electrical efficiency, thermal efficiency, and overall efficiency were 11.67%, 60.17% and 78.84%, respectively, while the average and maximum COP were 3.7 and 5.24 respectively.

Through the integrated modeling of gas turbine and tunnel kiln combined system, a thermodynamic calculation method of combined system is put forward, and the combined system operation parameters are obtained. By this method, the optimization of the combined system is analyzed and the optimal configuration of the gas turbine is calculated. At the same time, the thermal efficiency of the combined system is analyzed, and the heat distribution and thermal efficiency of the system before and after the improvement are explained. Taking the 1500 kg/h ceramic production as an example, pointed out that if the tunnel kiln has a gas turbine with a power of 342 kw. The amount of electricity of the combined system that produced per unit volume of the fuel which consumes more than it used to will be 7.19 kwh, the system thermal efficiency will reach 57.49%, which higher than the individual gas turbine's cycle thermal efficiency 20% at least.