Heat pump water heaters can increase the energy efficiency in sanitary hot water production, which is a relevant share of the final energy consumption in multiresidential and tertiary buildings. Refrigerants for these heat pumps are changing due to the F-Gas Regulation which bans high-GWP fluids. While CO2 is an established solution, propane is a promising low-GWP alternative for heat pump water heaters serving large users in the tertiary sector, where refrigerant charge limits (due to propane's flammability) can be bypassed by installing the heat pump outdoors. Here, the components of a CO2 and a propane air-water heat pump systems of 40 kW are sized and their COPs are compared in different climates; then, the two heat pumps are coupled to a storage tank and a user demand profile (hospital and school). For three different locations, tank size necessary to maintain users' comfort and seasonal performance factor are evaluated through simulation. 相似文献
In this review, flat plate and concentrate-type solar collectors, integrated collector–storage systems, and solar water heaters combined with photovoltaic–thermal modules, solar-assisted heat pump solar water heaters, and solar water heaters using phase change materials are studied based on their thermal performance, cost, energy, and exergy efficiencies. The maximum water temperature and thermal efficiencies are enlisted to evaluate the thermal performance of the different solar water heaters. It is found that the solar water heaters’ performance is considerably improved by boosting water flow rate and tilt angle, modification of the shape and number of collectors, using wavy diffuse and electrodepositioned reflector coating, application of the corrugated absorber surface and coated absorber, use of turbulent enhancers, using thermal conductive working fluid and nanofluid, the inclusion of the water storage tank, and tank insulation. These items increase the heat transfer area and coefficient, thermal conductivity, the Reynolds and Nusselt numbers, heat transfer rate, and energy and exergy efficiencies. The evacuated tube heaters have a higher temperature compared to the collectors with a plane surface. Their thermal performance increases by using all-glass active circulation and heat pipe integration. The concentrative type of solar water heaters is superior to other solar heaters, particularly in achieving higher water temperatures. Their performance improves by using a rotating mirror concentrator. The integration of the system with energy storage components, phase change materials, or a heat pump provides a satisfactory performance over conventional solar water heaters.
The total storage of full containment LNG storage tanks is very huge. Once the tank rupture or leakage,the consequence will be unimaginable. Therefore it is necessary to perform the risk-based inspection( RBI) and evaluation on LNG storage tanks,and the analysis on LNG storage tanks failure possibility is especially important in the RBI. Recently,Risk-based inspection( RBI) technology based on API 581 is gradually adopted and has become a new technology to determine economic feasibility and safety of equipment in petrochemical plants.However,there are limitations of applying API 581 to LNG equipment because of the unique structure of LNG storage tank( the metal inner tank and concrete outer tank). Therefore,a failure probability calculation model suitable for full containment LNG storage tanks is proposed. The domestic inner tank is usually made of 9% Ni,and its failure possibility can be calculate based on API581; the outer tank is usually made of pre-stressed concrete,and the failure possibility of structure durability can be calculated by the method of fuzzy mathematics;Then the failure possibility of the inner tank and the outer tank will be comprehensive considered by using cellulose model. Finally,by citing a real example,it also detailedly introduces the application of this proposed calculation model in the failure possibility analysis of full containment LNG storage tanks. This study provides a new approach for the evaluation of failure possibility on full containment LNG storage tanks. 相似文献
An investigation of a direct gas-fired single-effect ammonia–water absorption heat pump water heater for residential applications is presented. Combustion of natural gas provides heat to the desorber where refrigerant is generated. The absorber and condenser are hydronically coupled in parallel to a hot water storage tank, while the evaporator is hydronically coupled to an ambient air heat exchanger that extracts ambient heat. A thermodynamic model is developed and the system configuration is optimized to provide a baseline heating capacity of 2.79 kW at a coefficient of performance of 1.74. A detailed parametric study over a range of water and ambient temperatures is used to understand the variation in system performance as the water is heated from 14.5 to a minimum of 57.0 °C. The performance of the heat pump coupled to a 227-liter storage tank is also modeled for three different scenarios, a cold start response to a 76-liter draw, and response to stand-by losses. The absorption heat pump water heater is found to achieve coefficients of performance better than those of commercially available gas fired heaters and electric heat pump units. 相似文献
