CFD Solution and Experimental Testing of Buoyancy-Driven Convection Caused by Condensers Immersed in a Water Tank of HPWH

2003 ◽  
Author(s):  
Zhiming Gao ◽  
Viung C. Mei ◽  
Fang C. Chen
Keyword(s):  
Water Temperature ◽  
Heat Pump ◽  
Cfd Simulation ◽  
Experimental Testing ◽  
Electricity Consumption ◽  
Water Tank ◽  
Water Heater ◽  
Water Heaters ◽  
C 30 ◽  
Tube Condenser

Heat pump water heaters can cut electricity consumption, comparing with the conventional electric resistant water heating tanks by half. A conventional heat pump water heater (HPWH) requires a water circulating pump to sample water temperature every 15 minutes in the tank and to draw water to a condenser-water heat exchanger outside the tank, if water temperature is below the set point. The pump would be on at least once every 15 minutes, 24 hours a day. The novel design presented in this study was to insert the condenser coil through the opening on the top of the water tank. This design eliminated the need of the water circulating pumps, and thus greatly improved the reliability of the HPWH systems. Two types of condenser coil designs were considered; one was a bayonet tube (tube-in-tube) and one was the “U” tube. Previous test data indicated that “U” tube design performed better than the bayonet tube condenser coil, and thus only “U” tube condenser coil was considered in the study. With straight “U” tubes inserted into the tank, it was found that the convective heat transfer was not strong enough to break water temperature stratification in the tank, which resulted in a temperature differential of 16°C (30°F) from top to bottom. However, when the coil was built in “L” shape, the water stratification disappeared. A computational fluid dynamics code, CFD, was used to study the straight and L shaped condenser coils. Results from CFD simulation were compared with the experimental data and found they were close to each other.

scholarly journals Characterization of Wrapped Coil Tank Water Heater During Charging/Discharging

2017 ◽  
Author(s):  
Ahmed Elatar ◽  
Kashif Nawaz ◽  
Bo Shen ◽  
Van Baxter ◽  
Omar Abdelaziz
Keyword(s):  
Water Temperature ◽  
Heat Pump ◽  
Thermal Stratification ◽  
Water Tank ◽  
Water Heater ◽  
Water Heaters ◽  
Discharge Flow Rate ◽  
Circulation Patterns ◽  
The Impact ◽  
Supply Water

Heat pump water heaters (HPWH) are an energy efficient method for water heating compared to conventional electric water heaters. A wrapped coil around the water tank is often used as the condenser for the heat pump for such applications. Thermal stratification, caused by varying heat transfer rate from the condenser to the water depending on the phase of the refrigerant and the wrap configuration, is often observed inside the tank, especially for HPWHs using CO2 as the refrigerant. The current study investigates the impact of the charging/discharging process on thermal stratification. A series of simulations were conducted based on the draw patterns recommended by the DOE method of test for rating water heater performance. We also analyzed the water circulation patterns during charging/discharging process. The thermal stratification was adversely affected because of the circulation even when the Heat Pump (HP) was operational. It was observed that a relatively higher charge/discharge flow rate disrupts the thermal stratification quickly and thus lowers the supply water temperature. Furthermore, the duration of charging/discharging also plays an important role. It was noticed that the back flow has insignificant effect on the supply water temperature if charging/discharging time is relatively small. However, the effect was obvious for larger water draw flow rates that last for longer time.

A New Performance Estimate Method for Design of Storage-Type Domestic Electrical Water-Heaters Based on the CFD Simulation

2010 ◽  
Vol 129-131 ◽  
pp. 463-466
Author(s):  
Li Li Zhao ◽  
Zhi Jun Zhang ◽  
Shi Wei Zhang
Keyword(s):  
Water Temperature ◽  
Cfd Simulation ◽  
Cold Water ◽  
Discharge Rate ◽  
Water Discharge ◽  
Hot Water ◽  
New Method ◽  
Dynamics Simulation ◽  
Water Heater ◽  
Water Heaters

The 3D physical model of the electrical water heater was built. The water-heater performance was resolved by computer fluid dynamics simulation (CFD). The heater performance is characterized by a new method rather than that the discharge efficiency, extraction efficiency and fraction of heat recoverable. The new method is based on the constant discharge water temperature and rate for end user, 5L/min and 43°C that include the hot water from EWH and cold water from outside EWH. But the water discharge rate from EWH was variable as the water temperature discharge from EWH was variable. Compared with the traditional method, it is more close to the user using reality condition.

Performance Study of Structure Improvement Design for Storage-Type Domestic Electrical Water-Heaters Based on the CFD Simulation

2010 ◽  
Vol 129-131 ◽  
pp. 602-606
Author(s):  
Zhi Jun Zhang ◽  
Shi Wei Zhang ◽  
Cheng Hai Xu
Keyword(s):  
Cfd Simulation ◽  
Discharge Rate ◽  
Hot Water ◽  
Dynamics Simulation ◽  
Water Tank ◽  
Performance Study ◽  
Water Heater ◽  
Water Heaters ◽  
Traditional Structure ◽  
Structure Improvement

The 3D physical model with two different structure of the electrical water heater was built. The performance of water heater was studied by computer fluid dynamics simulation (CFD). The heater performance is characterized the discharge efficiency, extraction efficiency and fraction of heat recoverable. It was 73.7%, 45% and 49.8% respectively with conventional structure, and it was 81.1%, 54.1% and 59.6% respectively of improved structure with discharge rate was 5L/min when all initial hot water temperature was 90°C. The temperature distribution of different discharged stage was also disclosure. The water inner the water tank of improved structure has the better thermal stratification than traditional structure. It was also agreed with the water heat performance.

Performance Study for Storage-Type Domestic Electrical Water-Heaters with Double Tank Based on the CFD Simulation

2010 ◽  
Vol 29-32 ◽  
pp. 1701-1705
Author(s):  
De Xi Wang ◽  
Zhi Jun Zhang
Keyword(s):  
Cfd Simulation ◽  
Discharge Rate ◽  
Hot Water ◽  
Dynamics Simulation ◽  
Water Tank ◽  
Performance Study ◽  
Water Heater ◽  
Water Heaters ◽  
Computer Fluid Dynamics ◽  
The Mathematical Model

The 3D physical model of the electrical water heater was built. The mathematical model of hot flow was resolved by computer fluid dynamics simulation (CFD). The effects of the rate of water draw on the heater performance have been investigated. The heater performance is characterized the discharge efficiency, extraction efficiency and fraction of heat recoverable. It was 85.9%, 66.0% and 70.9% respectively, and it was 74.0%, 27.3% and 39.9% respectively with discharge rate was 10L/min when all initial hot water temperature was 70°C. The water inner the water tank of draw rate 5L/min was well thermal stratification. It was also expatiated by the distribution temperature of CFD simulation.

Evaluation of Passive Anti-Fouling Technology Applied to CO2 Heat Pump Water Heaters

2014 ◽  
Author(s):  
Portia Murray ◽  
Stephen J. Harrison ◽  
Ben Stinson
Keyword(s):  
Heat Transfer ◽  
Water Supply ◽  
Heat Pump ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Reverse Direction ◽  
Water Tank ◽  
Flow Rates ◽  
Water Heaters

Heat pump water heaters are increasing in popularity due to their increased energy efficiency and low environmental impact. This paper describes the experimental testing of a transcritical CO2 heat pump water heater at Queen’s University. A modified 4.5 kW Eco-Cute unit was studied. It sourced heat from a constant temperature water supply and rejected the heat to a 273 litre hot water tank through a gas-cooler. The high temperatures that occur in the gas-cooler of this unit make it ideally suited for natural convection, (i.e., thermosyphon) circulation on the potable water side. This has the potential to reduce pumping power, simplify system operation and design, and increase thermal stratification in the hot water storage tank. This configuration, however, is susceptible to the accumulation of sediments, scale and mineral deposits (i.e., fouling) in geographic regions where high mineral deposits may be present in the water supply. To counteract fouling in these cases, a passive back-flushing system was proposed to prevent the accumulation of deposits on the heat transfer surfaces of the gas-cooler. As hot water is drawn from the system, the cold “mains” supply water is directed through the gas-cooler in the reverse direction of normal operation, scouring the heat transfer surfaces and dissolving deposits of inverse-soluble salts which are a major contributor to fouling on hot heat transfer surfaces. The gas-cooler used was a specially designed unit that, although offering high performance in a compact unit, may be susceptible to the fouling and blockage of the heat transfer passages when used at thermosyphon flow rates. Experiments were conducted to evaluate the effects of the back-flush operation on heat pump performance (i.e., COP) and operation. These were conducted under controlled laboratory conditions, at a range of draw flow rates and temperatures, and are summarized in this paper.

scholarly journals Comparison of Transcritical CO2 and Conventional Refrigerant Heat Pump Water Heaters for Domestic Applications

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 479
Author(s):  
Ignacio Paniagua ◽  
Ángel Álvaro ◽  
Javier Martín ◽  
Celina Fernández ◽  
Rafael Carlier
Keyword(s):  
Heat Pump ◽  
Thermodynamic Cycle ◽  
Heat Pumps ◽  
Design Tool ◽  
Operating Conditions ◽  
Hot Water ◽  
Coefficient Of Performance ◽  
Ambient Conditions ◽  
Water Heater ◽  
Water Heaters

Although CO 2 as refrigerant is well known for having the lowest global warming potential (GWP), and commercial domestic heat pump water heater systems exist, its long expected wide spread use has not fully unfolded. Indeed, CO 2 poses some technological difficulties with respect to conventional refrigerants, but currently, these difficulties have been largely overcome. Numerous studies show that CO 2 heat pump water heaters can improve the coefficient of performance (COP) of conventional ones in the given conditions. In this study, the performances of transcritical CO 2 and R410A heat pump water heaters were compared for an integrated nearly zero-energy building (NZEB) application. The thermodynamic cycle of two commercial systems were modelled integrating experimental data, and these models were then used to analyse both heat pumps receiving and producing hot water at equal temperatures, operating at the same ambient temperature. Within the range of operation of the system, it is unclear which would achieve the better COP, as it depends critically on the conditions of operation, which in turn depend on the ambient conditions and especially on the actual use of the water. Technology changes on each side of the line of equal performance conditions of operation (EPOC), a useful design tool developed in the study. The transcritical CO 2 is more sensitive to operating conditions, and thus offers greater flexibility to the designer, as it allows improving performance by optimising the global system design.

Statistical Analyses on Usage of Water Heater in Urban Residential Buildings

2014 ◽  
Vol 521 ◽  
pp. 748-751
Author(s):  
Zhao Xia Zhou
Keyword(s):  
Energy Consumption ◽  
Heat Pump ◽  
Residential Buildings ◽  
Water Heater ◽  
Water Heaters ◽  
Heat Pump Water Heater ◽  
Initial Cost ◽  
The Common ◽  
The Cost ◽  
Residential Water

A survey for water heater in urban residential buildings is carried in Wuhan. The results show that more than 40% subjects use solar energy water heat. More than 20% subjects point out the energy consumption of water heater should be decreased. There are about 24.8% subjects take initial cost as the first place when they chose water heater. 44.2% subjects know about heat pump water heater, but they could not buy it if the initial cost is too high. There are 84% subjects could select heat pump water heater when the cost is no more 20% high than the average price of the common water heaters. Moreover, the energy consumptions of residential water heaters are also investigated. The energy consumption characteristics of water heater in Wuhan are analyzed.

Efficient Heat Pump Water Heater Regulated by the Superheat of Compress Suction Tube

2011 ◽  
Vol 322 ◽  
pp. 129-133
Author(s):  
Cong Zhuo Jin ◽  
Qiao Li Chou ◽  
Huan Xin Chen
Keyword(s):  
Heat Pump ◽  
Industrial Development ◽  
National Standards ◽  
Water Heater ◽  
Suction Tube ◽  
Water Heaters ◽  
Technical Requirements ◽  
Regulation Method ◽  
Definition Of ◽  
Application Fields

This paper starts with a brief introduction to the industrial development background such as general technical principles and application fields of heat pump water heaters (HPWHs), and puts forward for the first time the definition of superheat of compress suction tube ΔTsuperheat-st aiming at special technical requirements of HPWHs and the new concept of PID regulation of ΔTsuperheat-st with an electronic expansion valve. An HPWH with this regulation method has been made, and has been tested in line with national standards and EU standards. Its results show that this HPWH is qualified in energy-saving grade as required in national standards.

Study of Different Types of Water Heating Systems - Under Living Lab Conditions

2019 ◽  
Author(s):  
Swapnil Dubey
Keyword(s):  
Energy Saving ◽  
Heat Pump ◽  
Heating System ◽  
Heat Pumps ◽  
Electrical Heating ◽  
Water Heating ◽  
Water Heater ◽  
Water Heaters ◽  
Living Lab ◽  
Almost All

Abstract In Singapore, roughly 20% of the energy consumed by households is used for water heating and almost all the energy consumed by conventional electric water heaters. One of the significant potential energy saving opportunities lies in using energy-efficient water heating appliances. Recently, there has been a move towards energy-saving design and the use of natural refrigerants over fluorocarbons. Unlike conventional electric storage water heaters, which use electricity to heat water directly, heat pump storage water heaters use electricity only to operate a pump that circulates refrigerants around the system. This refrigerant collects heat from the surrounding atmosphere and transfers it to the water. CO2 heat pumps have low global warming potential when compared to other refrigerants based heat pumps, has zero ozone depletion potential, inexpensive, non-flammable, generate high temperature. In this project, a comparative analysis of three different water heater types has been presented based on real-time usage and living-lab conditions under the tropical climate of Singapore. These three types are: 1. Electrical heater storage type 2. Hybrid heat pump with auxiliary electrical heating water heater 3. CO2 heat pump water heater without auxiliary heating Study found significant energy saving using CO2 heat pump compared to other water heating system and also better for environment.

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