Wang Haitao, Wang Zaoqi
(1. School of Environmental Engineering, Anhui Institute of Architecture and Technology, Hefei, Anhui 230027; 2. Department of Thermal Energy and Energy Engineering, China University of Science and Technology, Hefei, Anhui 230022)
Abstract: Under the same compressor frequency, condensate temperature and electronic expansion valve opening, the dynamic performance of PV/ T- SAH P system is analyzed.
Experiments and analysis were carried out, and the effects of different solar irradiance and ambient temperature on the performance of PV/ T- SAH P system were compared.
This paper introduces the stability principle of solar heat pump (PV/ T- SAH P) system, and points out some problems that need to be solved in PV/ T- SAH P system.
Key words: PV/ T- SAH P system; Minimum overheating; stability
China Library Classification Number: TK5 19 Document Identification Number: A Document Number:1003-5060 (2008) 07-1008-04.
In the solar heat pump system, most of the heat energy absorbed by the evaporator comes from solar energy, and the solar irradiance changes with the season and the time difference between morning and evening, and the capacity of the compressor is rated, so the document [1] points out that under certain other conditions [1- 6], whether the capacity of the collector matches the capacity of the compressor directly affects the working performance of the system. Because the system usually operates under off-design conditions, the area of the collector determined according to the design conditions often does not match the capacity of the compressor. Therefore, a new direct expansion solar heat pump system with comprehensive utilization of light, heat and electricity is proposed. The system integrates photovoltaic module with evaporator of heat pump device, and adopts variable frequency compressor and electronic expansion valve (EXV) in the system design, and solves the mismatch problem under off-design conditions by changing the capacity of compressor. But in the experiment, the system is unstable, or oscillating, that is, the system parameters such as compressor power, refrigerant pressure and temperature are periodically oscillating under certain working conditions. System oscillation is not conducive to its economy and security, so ensuring stability is a necessary condition for system configuration and control.
1 experimental device and electronic expansion valve
The PV/ T-SAHP solar heat pump system is shown in figure 1.
As shown in Figure 2, the experimental platform mainly includes temperature measurement and pressure measurement.
Quantity, power measurement, flow measurement, irradiation intensity measurement and wind speed measurement.
Quantity and so on. * * * There are 53 measuring points except working fluid flow.
At home, the software comes with it to measure separately, and other measuring points are data acquisition.
Real-time instrument acquisition and recording.
(1) data acquisition data acquisition instrument Agilent34970A,
Equipped with 3 HP 3490 1A acquisition modules and *** 54 voltage acquisition modules.
Collection channels, 6 current collection channels, and the experimental process is generally 30 s.
Collect data once. Figure 1 PV/ T-SAHP solar heat pump system
(2) Temperature measurement. Use 01.2mm copper-constantan thermoelectric.
Even; Evaporator inlet, evaporator outlet, condenser inlet, condenser
Outlet, water storage tank, compressor inlet, compressor outlet and shutter box.
Wait * * * 20; There are 23 photovoltaic evaporators in it.
(3) Pressure measurement. Special sensor for refrigeration pressure (Huba506, Sw eden), 0~ 30 @ 10.
2
KPa, accuracy? 1 1 0%,
The response time is less than 5 ms, and the load frequency is less than 50hz；; Quantity 4
a； Located at the evaporator inlet, evaporator outlet, condenser inlet and
The condenser outlet is used to observe the compressor, condenser, expansion valve and
Pressure change at inlet and outlet of evaporator.
(4) sunshine radiometer. TBQ-2 (Jinzhou, Sunshine) Day
1 radiation table; The installation position is parallel to the photovoltaic evaporator and the workbench.
Based on the principle of thermoelectric effect, the induction element is multi-connected by winding electroplating.
Light the thermopile.
(5) Power sensor. WBP 1 12S9 1 and WBI022S
(Weibo, Sichuan), 2 in number; Test the input power of the compressor respectively.
(AC) and photovoltaic modules output photovoltaic current (DC).
The system adopts the electronic extension of Zhejiang Sanhua DFP (L)116-12.
Expansion valve, four-phase stepping motor drive, valve opening pulse 32? 20, the whole process
Pulse 500, using the medium R22, the valve opening is controlled by research and development.
Controller control.
2 experimental results and analysis
2 1 1 experimental conditions
June 65438+1October 65438+April 2006, June 65438+20061October 6 and
65438+February 2, 2006, in Hefei (3 1b53. North latitude, east.
1 17b 15. ), so is PV/ T-SAHP system.
Opening of electronic expansion valve (opening pulse 400), the condensate water is the same.
Performance test at 30 e.
The instantaneous meteorological parameters and condensate temperature during the test are shown in the figure.
3. As shown in Figures 4 and 5. During the test, the valves 1, 2, 5,
The valve 6 is closed, the valves 3, 4, 7 and 8 are opened, and the working medium flows.
As shown in figure 2. The compressor operates at a constant frequency (50 Hz) and is controlled by the public.
Power supply from the grid. After inverter inversion, PV current from outside is output.
Boundary load consumption. During the test, the water tank stores 80 kilograms of water, and the water cooling plate
The water side velocity of the heat exchanger is 01217 kg/s.
2.2 Test results and analysis
2 1 2 1 1 Description of test results
Due to the cloudy weather in autumn morning, in order to be better
Observe and compare, first heat the water to 30 e in the morning of 3 d,
Then keep the temperature of condensate unchanged, and formally record it from 1 1: 2 1.
Record data.
As can be seen from Figure 3 and Figure 4, the amount of sun exposure in the afternoon of three days
The degree changes obviously and is easy to compare.
From Figure 6, we can see the change of compressor power in the system.
During the test period of June 5438+10/October 65438+April 2006, the average ambient temperature was high.
(27 1 56 e), under the condition of constant condensate temperature, the compressor runs stably.
1test time on October 6th 165438+ average ambient temperature (20 1 7 1 e) ratio.
No.7 Wang Haitao et al.: Stability of solar heat pump system10091kloc-0/October 14 The daily average ambient temperature drops by 6185 E, and the sun.
Compared with 10+04, the irradiance has little change, but the compressor's
Power supply fluctuates during the test.
On February 2nd, 65438, the average ambient temperature (8 1.85 E) was higher than the previous two times.
Lower, at this time, the power oscillation of the compressor is more intense.
As shown in fig. 7, the system under different solar irradiation is shown.
Changes of photoelectric efficiency gel of the system at temperature and ambient temperature. photoelectricity
The lower the ambient temperature, the higher the efficiency and the lower the ambient temperature.
When (65438+February 2, 2006, the average ambient temperature during the test.
7 1 4 e), and the highest photoelectric efficiency reaches 13 1 4%.
Compared with ordinary photovoltaic module (12%), the photoelectric conversion efficiency is improved.
Obviously improved, with little fluctuation.
This is mainly due to the cooling effect of refrigerant evaporation on photovoltaic modules.
Using high irradiance to manufacture photovoltaic cells of PV/ T-SAHP system.
In this case, it can also be kept at a lower working temperature, thus ensuring a lower working temperature.
The photoelectric conversion efficiency is high. OPS in the figure shows the operation of the evaporator.
Overheating.
Fig. 7 changes in photoelectric efficiency during testing.
Analysis of 212 test results. 2
When the geometric dimensions and thermal parameters of the evaporator are determined, the evaporator will be installed in
There is a minimum stable signal line in operation (referred to as minimum stable signal line).
[ 8] 。 Mi Sanshun went left, steaming hot.
The generator belongs to unstable area; The right side of M SS line is a stable working area;
On the MSS line, it is the critical value. Fig. 8 shows an evaporator.
MSS line and expansion valve characteristic line under different static superheat, when
When the evaporator load is Q, the refrigeration system works at point A..
The critical stable state is theoretically the best stable working point. such as
If the static superheat of the expansion valve decreases, the operating point will be unstable.
Area, the system will produce oscillation.
Fig. 8 Matching relationship between expansion valve and evaporator
The above phenomenon can be easily explained by MSS line theory, when the environment
When the temperature is very high (June 65438 +654381October+April 2006), the collector/evaporator
The superheat degree of outlet refrigerant is very high, and the system works in MSS line at this time.
On the right side of, in a stable workspace. When the ambient temperature is very low
(65438+February 2, 2006), the outlet refrigerant of the heat collector/evaporator passed through.
The heat is small. At this time, the system works on the left side of the MSS line.
In the unstable working area, the compressor oscillates violently.
The oscillation of PV/ T-SAHP system affects the operation of the system.
Both economy and security are very unfavorable because the system lacks stability.
Lack of theoretical and quantitative research, in order to ensure the stability of operation, is often one-sided
Effectively increase the operating superheat of the evaporator, thereby reducing the evaporator.
Because the heat release coefficient of the refrigerant in the superheated region is less than.
0/ 5 of the maximum heat release coefficient in 65438+ two-phase region
[ 8]
. Reduce the evaporator appropriately.
Overheated operation can achieve certain energy-saving benefits, but it can't.
10 10 Journal of Hefei University of Technology (Natural Science Edition) Volume 3 1 blindly reduces superheat, pursues operation economy, and leads to system failure.
Produce oscillation. Only for the dynamic characteristics of evaporator and expansion valve itself
Quantitative analysis is carried out to find out the critical stable region of the system.
Line) and conditions, find out all kinds of factors that affect the stability of the system, right
This quantitative relationship can ensure the stability of the system, and the most
Make full use of the effective heat transfer area of evaporator to obtain the highest
The economy. 3 Problems to be solved in this system
PV/ T-SAHP system is equipped with variable frequency compressor and electronic equipment.
The key problem of expansion valve is to ensure the stability and variable volume of the system.
The optimal operation state of the system within the range of quantity is the goal and reasonable.
Control scheme and control algorithm. In the process of system development
There are still many theoretical and practical problems to be solved.
Static and dynamic characteristics of 3 1 system
Understanding the characteristics of the controlled object is to seek reasonable control.
The basis of scheme and control algorithm. Static of each component in the system
Its dynamic characteristics are analyzed theoretically and studied experimentally.
The static model and dynamic model of each component are obtained by modular method.
Then, according to the relationship between the parameters of each component, the system static state is established.
State and dynamic models. According to the results of simulation calculation and experimental study
As a result, the static and dynamic characteristics of the system are analyzed.
Stability principle of 312 system
Because the system has two variable frequency compressors and an electronic expansion valve.
Flow regulating device, so there is also a problem of system stability.
Based on the static and dynamic research of the above system, this paper analyzes
Meets the characteristic requirements of the electronic expansion valve under the condition of stable system,
The stable region of the system is obtained.
3 1 3 control scheme and control algorithm
In order to reduce the response of flow regulation of electronic expansion valve to overheating
The electronic expansion valve causes the refrigerant at the outlet end of evaporator to lag and overheat.
Detection can be done by thermistor or pressure signal. Use 2 thermal sensors.
During resistance detection, one measures evaporation temperature and the other measures evaporation.
Outlet temperature; Using pressure signal to measure the pressure at the outlet end of evaporator
Measured and converted into evaporation temperature by physical program.
Because the pressure in the evaporator changes faster than the temperature, the pressure in the evaporator changes faster than the temperature.
The controller can respond to the change of superheat in time.
The response lag of flow regulation of electronic expansion valve to overheating
This problem can also be solved by the compound adjustment method of feedforward and feedback.
If the compressor speed is used as a feedforward signal, it can be adjusted according to the speed change.
The liquid supply of electronic expansion valve is omitted, and then combined with feedback for compound adjustment.
Because of the nonlinear characteristics of the system, there is a fuzzy algorithm.
Set the advantage. PID control algorithm and fuzzy control calculation can also be considered.
Methods, give full play to the advantages of various algorithms to achieve better control.
Control effect.
4 Conclusion theory
(1) The PV/ TSA high-voltage system composed of variable frequency compressor and electronic expansion valve has the problem of system oscillation.
(2) PV/ TSA high-pressure system composed of variable frequency compressor and electronic expansion valve is one of the most promising system configurations.
The development direction of solar heat pump system is pointed out.
It is necessary to have a deep understanding of the static and dynamic characteristics of the system.
Determine the reasonable control scheme and control algorithm to ensure the stability of the system.
Optimal operation of the system in qualitative and variable capacity range.
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