Dry knowledge of relevant chillers in HVAC engineering
When it comes to chillers, here are some dry things to know about it:
Basic principle of chiller: A chiller is a kind of equipment used for refrigeration, which absorbs heat from the room or fluid by circulating the refrigerant, and then releases it into the external environment, thereby reducing the temperature of the room or fluid.
Refrigeration cycle process: The refrigeration cycle of a chiller usually consists of a compressor, condenser, expansion valve, and evaporator. In this cycle, the refrigerant is compressed into a high-pressure and high-temperature gas, and then dissipates heat through the condenser to become a high-pressure and low-temperature liquid, and then depressurizes through the expansion valve to become a low-pressure and low-temperature evaporator, and finally absorbs heat in the evaporator and evaporates to complete the cycle.
Refrigerant selection: Common refrigerants include chlorofluorocarbons (e.g., R-22, R-134A), hydrofluorocarbons (e.g., R-410A), and ammonia (NH3). In recent years, many countries have phased out the use of chlorofluorocarbons (CFCs) in favor of more environmentally friendly refrigerants such as HFCs due to the destruction of the ozone layer by HCFCs.
Chiller type: Chillers can be divided into two types: air cooling and water cooling. Air-cooled units use outside air for condensation and are suitable for locations where installation space is limited or where sufficient cooling water cannot be supplied. Water coolers, on the other hand, require ** cooling water and heat dissipation through a cooling tower or chiller.
Application of chillers: Chillers are widely used in air conditioning systems, industrial cooling and refrigeration. They can be used in a variety of places such as office buildings, commercial centers, hotels, hospitals, electronics plants, chemical plants, etc., to provide a comfortable indoor environment or to meet specific process needs.
Energy-saving and control strategies: Energy-saving measures for chillers include the selection of high-efficiency compressors, the optimal design of heat exchangers, the application of frequency conversion speed regulation technology, and the use of intelligent control systems. With proper energy management and system optimization, the energy efficiency of chillers can be significantly improved.
Evaporation pressure and evaporation temperature
In the operation of the chiller, the evaporation temperature and evaporation pressure are closely related to the heat brought by the cold water into the evaporator. When the heat load is large, the return water temperature of the cold water of the evaporator increases, causing the temperature of the evaporator to rise, and the corresponding evaporation pressure also increases. Conversely, when the heat load is reduced, the cold water return temperature decreases, and its evaporation temperature and evaporation pressure decrease. When the heat load of the air-conditioned room is reduced in actual operation, the cold water return temperature decreases, and the evaporation temperature and evaporation pressure decrease.
In operation, the temperature of the cold water outlet should be increased as much as possible under the condition of meeting the requirements of air conditioning. In general, the evaporation temperature is lower than the cold water outlet temperature2 4 . The evaporation temperature is usually controlled in the range of 3 5. Too high evaporation temperature is often difficult to achieve the required air conditioning effect, and too low evaporation temperature not only increases the energy consumption of the unit, but also easily causes the evaporation pipe to freeze and crack.
Condensing pressure and condensing temperature.
In chillers, the pressure indicated by the high pressure gauge is called the condensing pressure, and the temperature corresponding to this pressure is called the condensing temperature. The level of condensation temperature, under the condition that the evaporation temperature remains unchanged, is of decisive significance for the power consumption of the unit. The increase in condensing temperature and power consumption increases, and the increase in condensing pressure of centrifugal refrigeration units will cause the main engine to surge. Conversely, the condensing temperature decreases, and the power consumption decreases.
During the operation of the chiller, attention should be paid to ensuring that the cooling water temperature, water quantity, water quality and other indicators are within the qualified range. When the air exists in the condenser, the temperature difference between the condensation temperature and the cooling water outlet increases, while the temperature difference between the cooling water inlet and outlet decreases, and the heat transfer effect of the condenser is not good, and the condenser outside the condenser has a hot feeling. In addition to this, the influence of scaling and sludge on the water side of the condenser tube on heat transfer also plays a considerable role.
Pressure and temperature of cold water.
The chiller for air conditioning is generally operated under the conditions of cold water return temperature 12, water supply temperature 7 and temperature difference 5 specified in the standard working conditions.
The cold water flow rate of the evaporator is inversely proportional to the temperature difference between the supply and return water, that is, the larger the cold water flow, the smaller the temperature differenceConversely, the smaller the flow rate, the greater the temperature difference. Therefore, the working condition of the chiller stipulates that the temperature difference between the cold water supply and return water is 5, which actually stipulates the cold water flow rate of the unit. Under standard operating conditions, the pressure drop of cold water supply and return on the evaporator is set to 05kgf/cm2。The pressure drop adjustment method is to adjust the opening of the outlet valve of the cold pump, and the opening of the water supply and return valves of the evaporator.
The pressure and temperature of the cooling water.
The chiller operates under standard operating conditions, and its condenser return temperature is 30 and the outlet temperature is 35. For a chiller in operation, environmental conditions, loads, and cooling capacity have all become constant. At this time, the condensation heat load is undoubtedly also a fixed value. The standard stipulates that the temperature difference between the inlet and outlet water is 5, and the cooling water flow must also be a certain value. And this flow rate is inversely proportional to the temperature difference between the inlet and outlet water. Therefore, the chiller operates under standard working conditions, as long as the temperature difference between the inlet and outlet of the cooling water is specified. This flow rate is usually controlled by the cooling water pressure drop in the inlet and outlet condensers. Under standard operating conditions, the pressure drop of the condenser effluent is set to 0About 75kgf cm2. The pressure drop adjustment method is also to adjust the opening of the outlet valve of the cooling water pump and the opening of the inlet and outlet valves of the condenser. In order to reduce the power consumption of the chiller, the condenser temperature should be reduced as much as possible. There are two desirable measures: one is to reduce the return temperature of the condenser, and the other is to increase the amount of cooling water.
For centrifugal chillers, either too high or too low condensation pressure can cause surge. When the centrifugal chiller encounters this situation, it should be noted that the difference between the condensation pressure and the evaporation pressure should not be too small, and the requirements for preventing surge should be met, otherwise surge will occur. In the autumn when the temperature is lower, it is more advantageous to run a reciprocating chiller, because the condensing pressure is lower and the power consumption is much lower.
The suction temperature of the compressor.
The suction temperature of a compressor refers to the temperature of the gas or vapor entering the compressor. Suction temperature is critical to the operation and performance of a compressor. In general, a lower suction temperature can improve the efficiency and performance of the compressor, while a higher suction temperature may cause the compressor to overheat and reduce efficiency.
The exact value of the suction temperature depends on the specific application and compressor type. Different types of compressors have different operating temperature ranges and requirements. For example, the common suction temperature range for air compressors is between room temperature and 50 degrees Celsius, while the suction temperature used in refrigeration cycles in refrigeration compressors is typically lower and can be close to or below zero degrees Celsius.
In order to ensure good compressor performance and life, the following points need to be noted:
1. Keep the air circulation around the compressor good and avoid overheating.
2. Clean and replace the compressor filter regularly to prevent dust and dirt from clogging the suction port.
3. Ensure that the inlet pipe and connection part of the compressor are well sealed to avoid gas leakage and reduce the suction temperature.
Compressor discharge temperature.
The discharge temperature of a compressor refers to the temperature of the gas or vapor that is discharged from the compressor. The exhaust temperature is an important indicator during the operation of the compressor, which plays a key role in judging the working state and performance of the compressor.
The discharge temperature of a compressor usually depends on several factors, including the type of compressor, operating pressure, ambient temperature, and compressed medium, among others. Different types of compressors have different discharge temperature ranges and requirements. Generally speaking, the upper limit of the compressor discharge temperature is determined by the characteristics of the compressed medium and the withstand temperature, beyond which it may lead to heat loss of the medium, deterioration of oil lubrication performance, and aging of seals.
In practice, it is usually necessary for refrigeration compressors to control the discharge temperature within a safe range to avoid exceeding the maximum tolerance temperature of the medium. Generally speaking, the discharge temperature of the refrigeration compressor should be below 50 degrees Celsius to ensure the normal operation and long life of the compressor.
In order to control the discharge temperature of the compressor, the following measures can be taken:
1. Ensure a good cooling system, including a cooling fan or cooling water circulation system, to effectively reduce the temperature of the compressor.
2. Check and clean the cooler or condenser to ensure that its surface is clean and the heat exchange effect is good.
3. Monitor and adjust the operating parameters of the compressor, such as working pressure and cooling medium flow, to control the exhaust temperature within a safe range.
Intermediate pressure and temperature of a chiller.
1. Intermediate pressure: The chiller usually includes a compressor, which is responsible for compressing the low-pressure refrigerant gas into high-pressure gas. Intermediate pressure refers to the pressure of the high-pressure refrigerant gas at the outlet of the compressor. The exact value of the intermediate pressure depends on the design and requirements of the refrigeration system, as well as the type of compressor used. In general, the intermediate pressure can be between 2 and 25 bar.
2. Intermediate temperature: Intermediate temperature refers to the temperature of the high-pressure refrigerant gas at the outlet of the compressor in the chiller. The intermediate temperature is closely related to the intermediate pressure and is also affected by the type of compressor and the operating conditions. In general, the intermediate temperature can be between 60 and 150 degrees Celsius.
It is important to note that the specific intermediate pressure and temperature are also affected by the choice of refrigerant and the conditions under which it will be used. Different refrigerants have different properties and operating ranges, which can have an impact on intermediate pressures and temperatures. In addition, the chiller's design, load requirements, environmental conditions, etc., can also have an impact on the intermediate pressure and temperature.
The pressure in the energy saver is the middle pressure of the unit, and the corresponding refrigerant temperature is the middle temperature of the middle temperature, and the principle of determining the middle pressure is to make the total power consumption of the low-pressure and high-pressure compressors of the two-stage centrifugal refrigeration compressor as small as possible, and the refrigeration system of circulation is as large as possible.