Effect of Refrigerant Flow Control on the Heating Performance of a Variable-Speed Heat Pump Operating at Low Outdoor Temperature

2005 ◽  
Vol 127 (2) ◽  
pp. 277-286 ◽  
Author(s):  
Bong H. Kim ◽  
Dennis L. O’Neal
Keyword(s):  
Flow Control ◽  
Heat Pump ◽  
Performance Enhancement ◽  
Capillary Tube ◽  
Opening Angle ◽  
Variable Speed ◽  
Outdoor Temperature ◽  
Heating Performance ◽  
Heating Capacity ◽  
Expansion Valve

An experimental study was conducted to investigate the effect of electronic flow control on the performance of a variable-speed heat pump. A heat pump with two different expansion devices (capillary tube and electronic expansion valve) was tested in a psychrometric calorimeter over a range of outdoor temperatures from −15 to 7°C. Heat pump performance was first optimized with respect to charge for each expansion device through cycle-matching tests. Parametric tests also were conducted by changing compressor speed and opening angle for the electronic expansion valve at each outdoor temperature. The refrigeration cycle characteristics of the electronic valve were illustrated using pressure-enthalpy diagrams. Performance enhancement was also analyzed in terms of superheat, heating capacity, and energy efficiency ratio (EER). Comparison of the capillary tube and electronic valve indicated that the superheat significantly improved when using the electronic valve. Also, unit showed larger heating capacity and EER with the electronic valve than with the capillary tube except when the compressor speed was above 95 Hz. Enhancement of heating performance became larger as outdoor temperature decreased.

An Empirical Model for a Variable Speed Refrigeration System

2011 ◽  
Vol 383-390 ◽  
pp. 7563-7568
Author(s):  
Hua Li ◽  
Ji You Fei
Keyword(s):  
Decoupling Control ◽  
Opening Angle ◽  
Model Parameters ◽  
Variable Speed ◽  
Refrigeration System ◽  
Order Model ◽  
Indoor Temperature ◽  
First Order ◽  
Proposed Model ◽  
Expansion Valve

This paper deals with an empirical dynamic model for decoupling control of the variable speed refrigeration system (VSRS). To cope with inherent complexity and nonlinearity in system dynamics, the model parameters are first obtained based on experimental data. In the study, the dynamic characteristics of indoor temperature and superheat are assumed to be first-order model with time delay. While the compressor frequency and opening angle of electronic expansion valve are varying, the indoor temperature and the superheat exhibit interfering characteristics each other in the VSRS. Thus, each decoupling model has been proposed to eliminate such interference. Finally, the experiment and simulation results indicate that the proposed model offers more tractable means for describing the actual VSRS comparing to other models currently available.

Capillary Tube as an Expansion Device in a CO2 (R744) Transcritical Heat Pump System

2015 ◽  
pp. 360-377
Author(s):  
Neeraj Agrawal ◽  
Souvik Bhattacharyya
Keyword(s):  
Critical Temperature ◽  
Heat Pump ◽  
Capillary Tube ◽  
Optimum Operating ◽  
Optimal Length ◽  
Pump System ◽  
Optimum Operating Condition ◽  
Heat Pump System ◽  
Expansion Valve ◽  
Vapour Compression

Natural refrigerants which are ecologically safe and were in use extensively in the pre-CFC era are witnessing a revival of CO2 (R744). Inherently being a low critical temperature (31.2 ?C) refrigerant, the CO2 cycle based system operates in transcritical mode offers an opportunity to obtain an optimum operating condition. Capillary tubes which are extensively used in small size vapour compression systems work very differently in a CO2 transcritical heat pump system. In this chapter it is described that installation of a capillary tube having an appropriately designed length replacing an expansion valve will result in a natural adjustment of the gas cooler pressure, so that the system balance always shifts to a favourable COP direction; this is contrary to the scepticism that exists on the capability of a capillary tube to attain the optimal pressure operation. There is an optimal length of capillary tube for a given diameter at which the heat pump runs optimally.

ANALYTICAL STUDY ON THE HEATING PERFORMANCE OF A MULTI-TYPE HEAT PUMP SYSTEM WITH n-INDOOR UNITS

2011 ◽  
Vol 19 (01) ◽  
pp. 25-36 ◽  
Author(s):  
JONG WON CHOI ◽  
IL HWAN LEE ◽  
MIN SOO KIM
Keyword(s):  
Heat Pump ◽  
Heat Exchangers ◽  
Lumped Parameter Model ◽  
Distributed Model ◽  
Experimental Conditions ◽  
Pump System ◽  
Heat Pump System ◽  
Heating Performance ◽  
Lumped Parameter ◽  
Expansion Valve

This paper presents the steady-state heating performance of a multi-type heat pump system. The compressor and expansion valves are described by a lumped parameter model for its rapid and prompt response to the disturbances compared to those of the heat exchangers. Fully distributed model (or spatially dependent model) is used for the evaporator and condenser since the lumped method does not guarantee enough accuracy in estimating the performance of heat exchangers with phase change. Most researches on the numerical simulation in heat pump system focuses on the precise modeling for the steady or transient states while few researches on the simulations consider the relationships among several indoor units, expansion valve openings and compressor speed in multi-type heat pump system. In this study, the heating performance of a multi-type heat pump system using R410A with three indoor units is simulated for the investigation of system characteristics and the simulation results are verified for several experimental conditions. Finally, the simulation technique is extended to the system with n-indoor units.

Experimental Study of a Solar Assisted Air Source Heat Pump in Heating Condition

2011 ◽  
Vol 243-249 ◽  
pp. 4909-4912
Author(s):  
Yin Liu ◽  
Guang Hui Zhou ◽  
Jing Ma
Keyword(s):  
Experimental Study ◽  
Low Temperature ◽  
Heat Pump ◽  
Outdoor Environment ◽  
Heating Condition ◽  
Heating Performance ◽  
Temperature Conditions ◽  
Air Source Heat Pump ◽  
Heating Capacity ◽  
Environment Temperature

In order to improve the performance of air source heat pump in low temperature conditions, designed a solar assisted air source heat pump with the gas-liquid bio-sources heat exchanger. The heat pump can work with solar heat water and air as a heat source at same time. The heating performance of the heat pump in low temperature conditions was tested. The results show that, in comparison to the single air source heat pump, the heating performance of the solar assisted air source heat pump is improved remarkably. When the solar water flow is at 0.6m3/h and the outdoor environment temperature is -7°C, the heating capacity raised about 38% and the COP raised about 30%. When the outdoor environment temperature is -15°C, the heating capacity and the COP all raised more than 50%.

scholarly journals Energy Saving Potential of Radiant Floor Heating Assisted by an Air Source Heat Pump in Residential Buildings

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1321
Author(s):  
Yu-Jin Hwang ◽  
Jae-Weon Jeong
Keyword(s):  
Energy Saving ◽  
Heat Pump ◽  
Residential Buildings ◽  
Heating Systems ◽  
Air Source Heat Pump ◽  
Heating Capacity ◽  
Heating Loads ◽  
Radiant Floor Heating ◽  
Floor Heating ◽  
Floor Temperature

The objective of this research is to establish an appropriate operating strategy for a radiant floor heating system that additionally has an air source heat pump for providing convective air heating separately, leading to heating energy saving and thermal comfort in residential buildings. To determine the appropriate optimal operating ratio of each system taking charge of combined heating systems, the energy consumption of the entire system was drawn, and the adaptive floor surface temperature was reviewed based on international standards and literature on thermal comfort. For processing heating loads with radiant floor heating and air source heating systems, the heating capacity of radiant floor heating by 1 °C variation in floor temperature was calculated, and the remaining heating load was handled by the heating capacity of the convective air heating heat pump. Consequently, when the floor temperature was 25 °C, all heating loads were removed by radiant floor heating only. When handling all heating loads with the heat pump, 59.2% less energy was used compared with radiant floor heating only. Considering the local discomfort of the soles of the feet, the floor temperature is expected to be suitable at 22–23 °C, and 31.5–37.6% energy saving compared with those of radiant floor heating alone were confirmed.

Experimental Investigation on Flow Characteristic of Stepped Capillary Tube for Heat Pump Type Air Conditioner with R410A

2014 ◽  
Vol 960-961 ◽  
pp. 643-647
Author(s):  
Yan Sheng Xu
Keyword(s):  
Mass Flow Rate ◽  
Heat Pump ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Coefficient Of Performance ◽  
Tube Length ◽  
Air Conditioner ◽  
Capillary Tubes ◽  
Tube Assembly

A stepped capillary tube consisting of two serially connected capillary tubes with different diameters is invented to replace the conventional expansion device. The mass flow rate of refrigerant R410A in stepped capillary tubes with different size were tested. The model of stepped capillary tube is proposed, and its numerical algorithm for tube length and mass flow rate is developed. The experimental results show that the performance comparing between stepped capillary tube system and capillary tube assembly system, the cooling capacity is reduced by 0.3%, the energy efficiency ratio (EER) is equal to each other, the heating capacity is increased by 0.3%, the coefficient of performance (COP) is decreased by 0.3%. That is to say, the performance index of the two kinds of throttle mechanism is almost identical. It indicates that the stepped capillary tube can replace the capillary tube assembly in the R410A heat pump type air conditioner absolutely. The model is validated with experimental data, and the results show that the model can be used for sizing and rating stepped capillary tube.

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