1. The influence of condensation temperature on the performance of the chiller
The operating efficiency of the chiller is affected by the evaporation temperature and the condensation temperature. When the evaporation temperature is constant, the higher the condensation temperature, the lower the operation efficiency. The worse the efficiency.
The refrigeration coefficient of the reverse Carnot cycle is:
(1)
Where: - is the refrigeration coefficient of the reverse Carnot cycle
< p> - is the cooling capacity, W;- is the power consumption, W;
- is the evaporation temperature, K;
- is the condensation temperature, K .
According to the design parameters of the chiller under current air conditioning conditions, it is assumed that the low-temperature heat source (evaporation) temperature of the reverse Carnot cycle is 5.5°C and the condensation temperature is 36.5°C. The refrigeration coefficient at this time is 8.99. Table 1 shows the impact of condensation temperature on the refrigeration coefficient of the reverse Carnot cycle. When the condensation temperature increases by 1°C, the refrigeration coefficient decreases by 2.94% to 2.33%, and the lower the condensation temperature, the more significant the impact.
Table 1. Effect of condensation temperature on refrigeration coefficient of reverse Carnot cycle
Condensation temperature (℃)
36.5
37.5< /p>
38.5
39.5
40.5
41.5
42.5
Cooling coefficient
8.99
8.71
8.44
8.20
7.96
7.74
7.53
The cooling coefficient reduction percentage (%) when the relative condensation temperature is 36.5℃
3.13
6.06
8.83
11.43
13.89
16.22
The cooling coefficient decreases in percentage (%) when the condensing temperature increases by 1℃
2.94
2.76
2.60
2.46
2.33
For the vapor compression theory shown in Figure 1 Calculate the refrigeration cycle. The refrigerant is R 134a. According to the design parameters of the chiller under current air conditioning operating conditions, the evaporation temperature is 5.5°C, the condensation temperature is 36.5°C, the superheat of the refrigerant vapor before entering the compressor is 0°C, and the condensation temperature is 0°C. The subcooling degree of the refrigerant liquid at the outlet of the device is 0°C, and the isentropic adiabatic efficiency of the compression process is 0.9. The theoretical refrigeration coefficient at this time is 6.83. Table 2 shows the influence of the condensation temperature on the theoretical refrigeration cycle refrigeration coefficient. The condensation temperature If the temperature rises by 1°C, the refrigeration coefficient will decrease by 2.93% to 3.66%, and the lower the condensation temperature, the more significant the impact will be.
Table 2. Effect of condensation temperature on the refrigeration coefficient of the theoretical refrigeration cycle
Condensation temperature (℃)
36.5
37.5
p>38.5
39.5
40.5
41.5
42.5
Cooling coefficient
6.83
6.58
6.33
6.11
5.89
5.69
< p>5.49The cooling coefficient reduction percentage (%) when the relative condensation temperature is 36.5℃
3.66
7.32
10.54
p>13.76
16.69
19.62
The cooling coefficient decreases in percentage (%) when the condensing temperature increases by 1℃
3.66
3.22
3.22
2.93
2.93
Table 3 shows McQuay PFS330.3 Performance indicators of type single screw chiller. As the cooling water inlet and outlet temperature increases, the COP of the chiller decreases. When the cooling water inlet and outlet temperature increases by 1°C, the COP decreases by 3.24% to 3.35%, and the lower the cooling water inlet and outlet temperature, the more significant the impact.
Table 3 Performance indicators of McQuay PFS330.3 single-screw chiller
Cooling water inlet and outlet temperature
30 ~ 35 ℃
32 ～ 37 ℃
35 ～ 40 ℃
COP
5.52
5.15
4.65
The cooling coefficient decreases in percentage (%) when the condensing temperature increases by 1℃
3.35
3.24
Note: Refrigerant: HFC 134a; Chilled water inlet and outlet temperature: 12 ~ 7 ℃
Table 4 shows the performance indicators of Trane CVHG-780 centrifugal chiller. As the temperature of the cooling water inlet and outlet increases, the energy consumption coefficient of the chiller (electric power consumed per 1 ton of cooling capacity produced) increases. For every 1°C increase in the cooling water inlet and outlet temperature, the energy consumption coefficient increases by 3.14% ~ 3.46%.
Table 4 Performance indicators of TRANE RTHB 450L water-cooled screw chiller
Cooling water inlet and outlet temperature
25 ~ 30 ℃
28 ～ 33 ℃
30 ～ 35 ℃
32 ～ 37 ℃
35 ～ 40 ℃
Cooling capacity ton
402
398
393
387
379
Input power KW
216
234
246
259
279
Energy consumption coefficient y(kW/ton)
0.537
0.588
0.626
0.669
0.736
The energy consumption coefficient increases by 1°C when the cooling water inlet and outlet temperature increases (%)
3.14
3.23
3.46
< p>3.33Note: Refrigerant: HCFC22; Chilled water inlet and outlet temperature: 12 ~ 7 ℃
American Air-Conditioning and Refrigeration Institute (ARI) 1997 Guideline E (1997 GUILINE for Fouling Factors: A survey of their application in today 's air conditioning and refrigeration industry Guideline E) points out in Article 4.3: Fouling thermal resistance on the water side of the heat exchanger has a significant impact on the performance of air conditioning and refrigeration equipment, such as water-cooled chillers. When running at full load, the heat exchange tube wall is in a clean state, the outlet temperature of the chilled water is 7 ℃, the temperature of the cooling water outlet of the chiller is 35 ℃, the condensation temperature of the refrigerant of the chiller is 36 ℃, and the evaporation temperature is 6 ℃, its energy consumption coefficient is 0.60kW/ton. If the thermal resistance of dirt on the water side of the condenser and evaporator is both 4.4, then the condensation temperature of the refrigerant increases to 37°C, the evaporation temperature decreases to 5°C, and the energy consumption coefficient is 0.65kW/ton, that is, the operating cost increases 8.3%. The actual impact may be slightly different due to the different forms of condenser and evaporator heat exchange tubes. According to the performance calculation of the refrigeration cycle, it can be seen that if the evaporation temperature decreases by 1°C, the performance of the chiller will be reduced by 10% higher than if the condensation temperature increases by 1°C, the performance of the chiller will be reduced by 10%. Therefore, it can be considered that if the condensation temperature increases by 1°C, the efficiency of the chiller will decrease by approximately 4%.
According to the national standard GBJ19-87 (2001 edition) (China Planning Publishing House, 2001) "Heating, Ventilation and Air Conditioning Design Code - Article Explanation", Article 7.2.3: The lower the condensation temperature, the lower the refrigeration temperature. The larger the coefficient, the less power consumption of the compressor.
For example, when the evaporation temperature is constant, for every 1°C increase in the condensation temperature, the power consumption rate per unit cooling capacity of the compressor increases by approximately 3% to 4%.
In summary, the actual operating water-cooled chiller For every 1℃ increase in the condensation temperature, the power consumption rate of the compressor per unit cooling capacity increases by approximately 4%.
2. The impact of dirt thermal resistance on condenser heat transfer
The increase in cooling water temperature will increase the condensation temperature of the chiller. In addition, if the heat exchange conditions of the condenser deteriorate when the cooling water temperature remains unchanged, the condensing temperature of the chiller will also increase and the COP will decrease.
In the cooling water system, due to factors such as the quality of the supplementary water and mechanical impurities in the system, especially the large contact between the open cooling water system and the air, the water quality is unstable, and a large amount of scale, dirt, etc. are generated and accumulated. Microorganisms, etc., form dirt on the surface of the heat exchange tube of the condenser, which worsens the heat transfer and reduces the efficiency of the condenser. Dirt is generally a poor conductor of heat, and its thermal conductivity is only one-tenth of that of carbon steel, while it is not as hot as copper. Compared with good conductors, the difference in thermal conductivity is greater. And with the widespread application of enhanced heat transfer technology, the impact of fouling thermal resistance on the heat transfer process has become more obvious. As energy prices continue to rise, various heat transfer enhancement measures are commonly used to increase the heat transfer coefficient. At the same time, the impact of dirt on heat exchangers has become more significant.
What can be directly observed during actual operation of a water-cooled chiller is the difference between the condensation temperature of the refrigerant and the outlet temperature of the cooling water, that is, the condenser end difference. For water-cooled condensers:
(2)
Where: : is the heat release of the condenser, kW
: is the specific heat of the cooling water, kJ/kg. ℃
: is the flow rate of cooling water, kg/s
: is the temperature difference between the inlet and outlet of cooling water, ℃
From the above formula, It can be seen that when the unit is running at full load, the heat release of the condenser can be approximately unchanged, and the temperature difference between the inlet and outlet of the cooling water can be approximately unchanged. Considering that during the heat exchange process of the condenser, the exhaust gas of the compressor is cooled from the superheated steam to the saturation temperature section. The temperature difference is large, but the heat transfer coefficient is low. The heat exchange process in this section is similar to the condensation heat exchange section. That is, the temperature of the refrigerant in the condenser is approximately the condensation temperature. Since the specific heat of the cooling water is a constant value, the average temperature of the cooling water can be expressed as the outlet temperature of the cooling water minus half of the temperature difference between the inlet and outlet of the cooling water:
As can be seen from the above formula, in the unit When running at full load, the heat release of the condenser can be approximately unchanged, and the temperature difference between the inlet and outlet of the cooling water can be approximately unchanged. Considering that during the heat exchange process of the condenser, the exhaust gas of the compressor is cooled from the superheated steam to the saturation temperature section. The temperature difference is large, but the heat transfer coefficient is low. The heat exchange process in this section is similar to the condensation heat exchange section. That is, the temperature of the refrigerant in the condenser is approximately the condensation temperature. Since the specific heat of cooling water is a constant value, the average temperature of cooling water can be expressed as the outlet temperature of cooling water minus half of the temperature difference between the inlet and outlet of cooling water:
(3)
In the formula: : is the average temperature of the cooling water, ℃
: is the outlet temperature of the cooling water, ℃
The heat exchange temperature difference of the condenser is the condensation temperature of the refrigerant and Difference in average temperature of cooling water:
(4)
In the formula: : is the logarithmic average temperature difference of the condenser, ℃
: is the refrigerant The condensation temperature, ℃
: is the end difference of the condenser, that is, the difference between the condensation temperature of the refrigerant and the cooling water outlet temperature, ℃
Therefore, when the unit is running at full load, the condensation The change in the logarithmic average temperature difference of the condenser is equal to the change in the condenser end difference.
When dirt is formed on the surface of the heat exchanger, the total heat transfer thermal resistance of the heat exchanger increases, resulting in an increase in the logarithmic average heat transfer temperature difference, that is, an increase in the condensation temperature. Assume that the temperature difference between the inlet and outlet water of the condenser is 5°C, and the condenser end difference is 1°C, that is, the heat transfer temperature difference is 3.5°C. Figure 2 shows the effect of fouling thermal resistance on the end difference when the heat transfer coefficient is different. The larger the value, the more significant the impact of the dirt thermal resistance on the terminal difference. Figure 3 shows the effect of fouling thermal resistance on the heat transfer temperature difference at different times. The larger the value, the more significant the effect of fouling thermal resistance on the heat transfer temperature difference.
In addition, the load rate also affects the end difference of the condenser. When the unit is running at full load, the heat release of the condenser also reaches full load. When the condenser is in a clean state, the following formula is
(5)
In the formula: : The heat release amount of the condenser when the unit is running at full load, W
: The total heat transfer coefficient when the unit is running at full load and the condenser is in a clean state , W/m 2. ℃
F: Heat exchange area of ??the condenser, m 2
: Heat transfer temperature difference when the unit is operating at full load and the condenser is in a clean state, ℃< /p>
During actual operation, there is the following formula:
(6)
In the formula: : The heat release amount of the condenser during the actual operating condition of the unit, W
: The total heat transfer coefficient of the unit under actual operating conditions, W/m 2. ℃
: The heat transfer temperature difference of the unit under actual operating conditions, ℃
< p>From formulas (5) and (6):(7)
From formula (2):
(8)
It is deduced:
(9)
It can be seen from equation (9) that the condenser end difference is proportional to the load factor, that is, the lower the load factor, the condenser end difference The smaller the difference.
Therefore, during the actual operation of the chiller, we should pay close attention to the changes in the condenser end difference and take corresponding measures in a timely manner to maintain a high operating efficiency of the chiller.
3. Countermeasures against dirt
The current countermeasures against dirt on the cooling water side of the condenser of the chiller include chemical water treatment and rubber sponge ball cleaning methods
3.1 Chemical water treatment method
The traditional chemical water treatment method is to add three kinds of water treatment agents with different functions: corrosion inhibitors, scale inhibitors and bactericidal algaecides. Corrosion inhibitors can form a film on the metal surface to prevent corrosion; scale inhibitors act on the crystals of calcium carbonate and other components that form scale, causing them to twist, dislocate, and deform, thereby hindering the growth of scale; bactericidal and algaecide It has an inhibitory effect on bacteria and prevents their reproduction. Theoretically, chemical water treatment methods can achieve better results, provided they have effective water quality stabilizers and professional operators and management personnel. However, regular sewage discharge will cause certain pollution to the environment. Due to the above characteristics, the cost of chemical water treatment is relatively high, and the reality in the central air-conditioning industry is that Party A’s managers cannot judge and test the quality level of the water treatment company’s services due to their professional studies. Most of the competition is based on price, resulting in The industry cannot get reasonable profit returns, the industry has a serious brain drain, and the service quality is far from the theory. Therefore, even if most of the current air conditioning cooling water systems adopt chemical water treatment methods, they still need to use a brush to clean the condenser during shutdown maintenance every winter
3.2 Rubber sponge ball cleaning method
< p> is a set of comprehensive uses of fluids, hydraulic machinery, microcomputers and other technologies to achieve the simplest cleaning solution. Install a ball server and ball collector in the inlet and outlet pipe of the condenser cooling water of the chiller unit, using a special formula and structure The rubber sponge ball flows into a certain circulation program and wipes away bits and pieces of sediment on the tube wall through the condenser heat exchange tube under the action of hydraulic pressure. Since the circulation process is online and automatic without stopping, the time interval is short. , the deposits are wiped off in the early stages of formation, so that the tube wall remains clean forever, and the heat exchange efficiency of the condenser is always kept at the highest value. Overcome the decrease in cooling efficiency of the chiller due to the generation of dirt, thereby reducing energy consumption and saving energy. Eliminate the root causes of condenser tube corrosion, extend the service life of the tubes, reduce maintenance costs and the use of chemicals, reduce the discharge of cooling water concentrate, and reduce environmental pollution. This is by far the most effective method of keeping condenser tubes clean at all times.4. Conclusion
In summary, only traditional chemical water treatment methods can only solve part of the problems of the central air-conditioning cooling circulating water system, coupled with the rubber sponge ball cleaning method Only in this way can the problem of long-term efficient operation of the chiller be fundamentally solved.
Based on foreign advanced technology, we finally produced the most efficient and cost-saving automatic online cleaning system---FTC online cleaning system. The basic principle is to use the action of water flow to pass the cleaning ball with a wet diameter larger than the inner diameter of the cooling tube through the cooling tube to continuously clean the cooling tube and always keep the cooling tube in a clean state. Reduce the load of the compressor and enable the equipment to operate efficiently, thereby achieving energy saving.
This system can clean dirt and impurities in the cooling pipe online without shutting down the unit or reducing the load, thereby improving the cleanliness of the condenser pipe. And always maintain high heat transfer efficiency, improve the refrigeration efficiency of the air conditioning unit, and ensure the safe operation of the unit.
Product features:
1) Compact structure: The product adopts a unique structural design, which effectively prevents the mixing of cooling water supply and return water. Adopting modular frame design technology, the external dimensions of each functional segment are composed of a certain module, resulting in a compact structure.
2) Safe and reliable: Each piece of equipment has undergone strict quality inspection and testing to ensure that its quality meets the design requirements. Key components are all made of world-class brand-name products, such as Swiss BELIMO, Japanese EBARA, and German SIEMENS. Superior performance, safe and reliable.
3) Easy operation: The electronic control system adopts intelligent control technology, allowing the system to accurately control the cleaning cycle of the balls through the control valve. It provides automatic and manual operation modes and uses a touch screen for operation. The humanized design provides great convenience to the operator.
4) Good cleaning effect: Under normal circumstances, 15%--30% of power consumption can be saved, and automatic cleaning can be performed online, which can save costly equipment shutdown and cleaning costs, making the air conditioner host always Maintaining high heat conversion efficiency effectively solves the problem of low heat conversion rate of traditional central air conditioners due to scaling, minimizes energy waste in the air conditioning system, and achieves high efficiency and energy saving. It can also greatly save labor, achieve an effect that cannot be accomplished by manual cleaning, avoid corrosion of equipment pipelines, and extend the service life of equipment.
5) Short investment recovery cycle: The system can clean multiple chillers online at the same time, improving cleaning efficiency, saving investment costs, and naturally shortening the investment recovery cycle.
6) Good environmental protection effect: Use special pellets for physical cleaning, and concentrate the cleaned dirt into the sewage discharge device for regular discharge, which will not cause any harm to the surrounding environment.
7) Wide range of use: suitable for all water-cooled chillers, power plants and all cooling systems using shell and tube heat exchangers.
5. Cleaning effect
1) Effectively reduce usage costs
After the equipment is installed, remove dirt, keep the condenser in a clean state at all times, and improve the efficiency of the condenser. Improve heat exchange efficiency, reduce compressor load and reduce power consumption. Keep equipment running efficiently.
2) Protect equipment and extend service life
There is no need to use mechanical or chemical methods for cleaning, which extends the maintenance cycle and service life of equipment and avoids high-pressure operation and over-pressure shutdown. , improving the MTBF (Mean Time to Repair Between Failures) value of the equipment. And will not cause any harm to the environment.
3) Save a lot of maintenance costs and reduce accidents
Central air conditioners that have not been cleaned will cause equipment pipeline blockage, scaling, and overpressure shutdown settings to malfunction. For example, if the operating system leaks due to corrosion and causes solution contamination, the host needs to be repaired and the thermal device and solution need to be replaced. Generally, maintenance costs are extremely expensive. After installing this system, maintenance costs can be reduced and the service life of the equipment can be extended, providing benefits to the owners. Reduce losses of hundreds of thousands or even millions.
6. Benefit Analysis
The advantages of using the FTC energy-saving cleaning system are countless. Compared with the joy of saving huge operating costs, the initial investment in installing the system appears to be minimal. In fact, On the other hand, the installation cost can be included in the electricity bill and daily maintenance expenses saved by the entire cleaning machine. In some cases, the investment can be recouped in less than a year of use. Within 15 years after using FTC, there is no need to spend about 20,000 to 30,000 yuan every year on so-called manual "chemical cleaning" to damage your central air-conditioning host; 100% meets urban environmental protection requirements.
We promise: after using FTC, we are guaranteed to save energy starting from 10%, and some can reach up to 40%. After installing and using FTC, the investment cost can be fully recovered within one year of cumulative operation of the air conditioner, and the investment cost will be returned every year for more than ten years.
The basis is as follows:
A. If your central air conditioning condenser is in a clean state without any scale or dirt, its normal power consumption range after being turned on for 5,000 hours is as follows: Taking 1,000 refrigeration tons as an example,
1,000 refrigeration tons × 0.8KW / power consumption per refrigeration ton × 80% host load >B. Philip Kotz, an American refrigeration research institute, has proven that after your central air conditioner condenser is manually cleaned with chemicals, crystals and scale will appear on the wall of the condensation tube as long as it is turned on for 200 hours. As time goes by, the scale becomes thicker and the heat exchange efficiency becomes lower; the cooling capacity decreases, causing the compressor to increase its operating power and consume more electrical energy. Scientific proof: If there is a 0.3 mm thick film layer of scale in the condenser tube, it will consume 10% more power; 0.6 mm thick scale will consume 20% more power; 0.9 mm thick scale will consume 31% more power.
If the scale and dirt thickness of your central air conditioner is 0.3 mm, it will consume 10% more power.
2'560'000 yuan mm, it consumes 20% more power.
2'560'000 yuan mm, it consumes 31% more power.
2'560'000 yuan × 31% = 793'600 yuan (extra cost for 5,000 hours of startup)
Recommendation to owners: using FTC products is a short-term small investment , a project with long-term big returns. FTC can fully serve as the protector of central air-conditioning, achieving huge energy-saving benefits for you while completely solving the problem of central air-conditioning pollution emissions.
This patented technology product is for market promotion, and we are now looking for powerful companies to cooperate or transfer the patented technology.
Sincere companies please call: 15963368777
Mr. Qi