How to Reduce the Energy Consumption of Central Air - Conditioning System through System Integration?

2024-12-17

Ideas for Central Air Conditioning Energy Consumption Control
To control the energy consumption of central air conditioning, it is necessary to consider it as a whole and conduct meticulous supervision and services throughout the entire process from design, construction to operation and maintenance:

Meticulous design of super-efficient central air conditioning systems;
BIM-based meticulous drawing and construction supervision;
Meticulous monitoring of the M-BMS multi-agent adaptive energy-saving control system;
Detailed discussion on the meticulous operation debugging and optimization of the HVAC and automatic control systems.
Here, we particularly need to point out that:
In the central air conditioning systems of most public buildings, the main reason for high energy consumption is problems in the design scheme. For example:
(1) Improper selection of the cold and heat source methods; (2) Over-sized capacity selection for chillers, water pumps, etc.;
(3) Inadequate precision in control.
The above problems also have significant drawbacks: Once completed and put into use, it is very difficult to adjust, renovate and optimize them in the later stage.

Meticulous Design of the System
2.1 Annual Load Simulation
Before the design of the scheme, we recommend calculating the building load hour by hour, day by day and month by month through simulation software according to the building data and the requirements of HVAC specifications to obtain accurate annual data, such as the total cooling load, the minimum cooling load, and the detailed daily and annual load variation laws of the building.
2.2 Annual Energy Efficiency Calculation under Variable Load Conditions
The central air conditioning system is a huge and complex system project, and the various system equipment are interrelated and influence each other.
The change of the building environment is a complex process determined by multiple factors, which is determined by outdoor weather conditions, indoor and outdoor ventilation conditions, the heat generation status of various indoor heat sources and other factors.
Therefore, the operation of the building environment control system must also continuously respond and adjust with the change of the building environment. We recommend calculating the annual energy efficiency of the building through computer simulation methods.
2.3 Optimization Design of the Air Conditioning Water System
2.3.1 Host Optimization
Based on the design load provided by the design institute and the equipment usage rules provided by the owner, analyze the model according to the hourly cooling load demand throughout the year, and combine the operation strategy of the air conditioning system group control equipment to select the host form and combination with the best comprehensive energy efficiency. Usually, a dual first-level energy efficiency variable frequency direct-drive host with a large temperature difference and a three-pass evaporator will be selected, and a two-pass condenser with a self-contained rubber ball cleaning end cover will be selected to ensure perennial self-cleaning and maintain the energy efficiency throughout the whole cycle.
Figure 1 High-Energy-Efficiency Variable Frequency Direct-Drive Centrifugal Unit
2.3.2 Optimization of the Large Temperature Difference of Chilled Water and the Terminal Unit
Currently, the conventional air conditioning chilled water system adopts a 5 °C temperature difference design, while high-energy-efficiency machine rooms generally adopt a large temperature difference design of not less than 7 °C, which can reduce the operation cost of water pumps. To adapt to the large temperature difference working conditions, the terminal unit selection is enlarged to be able to adapt to a wider range of output capacity requirements. It can easily adapt to the load even when the load becomes higher or even exceeds the maximum design load. At the same time, since it can handle both large and small loads with ease, it can truly save energy by increasing the outlet water temperature and reducing the air volume of the fan.
2.3.3 Optimization and Selection of the Air Conditioning Pipe Network
Firstly, the terminals with the same usage time and the same load usage rules should be connected by the same group of pipe networks to minimize the mutual influence between different pipes. On this basis, since the power of the water pump is directly proportional to the head, reducing the resistance of the water system is an effective way to reduce the power for water transportation. The following main measures are recommended.
First, Select Low-Resistance Valves and Fittings

Filter: The Y-type water filter supplied on the market has a small filtration area and relatively large resistance, generally 1 - 3 m. The basket-type filter with a water resistance less than 0.3 m should be preferentially selected. A right-angle filter can also be selected and installed at the inlet of the water pump, which can connect horizontal pipes and vertical pipes, saving an elbow and its resistance loss.
Check Valve: The commonly used butterfly check valve on the market currently has relatively large resistance, generally 1 - 2 m. The silent check valve with a water resistance less than 0.3 m should be preferentially selected.
Second, Optimization of Low Resistance of the Pipe Network
By leveling the height of the water inlet and outlet of the water pump with the inlet and outlet of the host, the elbows of the pipeline can be reduced. By horizontally connecting the host and the water pump in a straight-in and straight-out manner, the elbows can be reduced. For example, if the elbow at the inlet of the water pump is changed to a right-angle filter or the floor-standing header and manifold are cancelled in the design, the elbows can be further reduced. When setting elbows for the water pipes in the machine room, the flow-following elbows should be set as much as possible, and the resistance can be reduced by 50%.
Third, Simulation Modeling of the Air Conditioning Water System
The HVAC system is generally composed of many pipelines, equipment and other components combined together through various connection methods to form a network. In the entire network, each part is independent and yet influences each other, and their respective physical parameters cannot be solved separately. It is necessary to solve all the physical quantities in the entire network simultaneously. Through the pipe network modeling and simulation software, for more complex systems, accurate system models can be quickly and effectively established and comprehensive analyses can be carried out. By setting the pipeline parameters, resistance elements, and the dynamic water resistance curves of the host and terminal equipment, under the given design flow rate, the total pressure drop of the system under this flow rate can be simulated to provide a basis for the selection of water pumps. Under variable flow conditions, calculate the pump head under 10% - 100% working conditions respectively and output the simulation parameters of all equipment in the system, including flow rate, flow velocity, pressure drop, etc.
Figure 2 Simulation Modeling of the Air Conditioning Water System in a Certain Machine Room
2.3.4 Optimization of the Cooling Tower Performance
According to calculations, for every 1 °C increase in the condensation temperature, the power consumption per unit of cooling capacity will increase by about 2% - 3%. Therefore, reducing the supply and return water temperature of the cooling system can significantly improve the COP value of the water chiller. However, to achieve this goal, the following measures need to be taken:
Increase the heat transfer coefficient on the cooling water side of the condenser: An effective way to increase the heat transfer coefficient is to reduce the fouling thermal resistance on the water side and conduct effective treatment on the make-up water of the cooling water.
Increase the size of the cooling tower: Considering a certain margin factor, appropriately increase the size of the cooling tower according to the most unfavorable local conditions of the project, and strive to reduce the design condition approach temperature of the cooling tower to below 3 °C.
2.3.5 Optimization of Water Pumps
The energy consumption for transporting power in the air conditioning water system accounts for about 20% of the energy consumption of the air conditioning system, so there is relatively large room for optimization. The main measures are as follows:
Optimize the selection of the pump head: The sum of the resistance of the most unfavorable loop in the air conditioning water system and the resistance of each equipment in the machine room is used as the basis for determining the pump head. Therefore, by every means to shorten the length of the most unfavorable loop, selecting low-resistance valve parts or increasing the pipe diameter can reduce the pump head.
Reduce the head of the cooling tower body: The difference in height between the water inlet pipe at the top of the cooling tower and the liquid level of the water collection pan, that is, the size of the tower body head, directly affects the head of the water pump. Therefore, try to select products with a small tower body head as much as possible.

BIM-based Meticulous Drawing and Construction Supervision
Because the pipelines in the machine rooms of super-efficient cold source systems are often quite complex, a lot of energy and attention are required for construction, and many construction hidden dangers are likely to be caused during this process. Therefore, in this process, many units and teams have now started to use BIM technology.
BIM technology actually uses tools to better facilitate construction communication and collaboration. Its advantages are as follows:

Three-dimensional Visualization and Precise Positioning:
Traditional machine rooms use CAD software to express the routing of pipelines. While the BIM model can express in three dimensions, clearly showing the routing of pipelines with inclined angles in the super-efficient machine room system, and promptly finding problems in the construction design.
Recalculation of Equipment Parameters:
During the installation process of the super-efficient central air conditioning system, due to the in-depth design and route adjustment of pipelines, the length of some pipelines and the number of elbows will be increased or decreased during this process, which will have a certain impact on the resistance parameters of the original system. BIM technology can avoid this problem.
Positioning of Sensors:
Using BIM technology can precisely position sensors on the drawings, and it can be judged in advance whether the installation space and position can meet the requirements. If not, the pipeline system can be adjusted in time to ensure the smooth installation of automatic control sensors, providing a guarantee for the subsequent accurate data collection and avoiding the problem that the installation space and position of sensors do not meet the specification requirements and there are relatively large errors in the data collected during the subsequent operation.

Meticulous Monitoring of the M-BMS Multi-agent Adaptive Energy-saving Control System
Let's first understand what M-BMS multi-agents are.
M-BMS multi-agents are a certain number of autonomous individuals that cooperate and self-organize with each other. In this system, all units (subsystems) are independent and equal, and can independently complete their respective tasks without the intervention of other units. At the same time, each unit can also coordinate work to realize the operation of the entire system.
It is formed into a unified whole through self-coordination in the form of multi-agents by modules such as the host comprehensive energy-saving control system, the water pump intelligent energy-saving control system, the cooling tower intelligent energy-saving control system, and the terminal intelligent energy-saving control system.
The hardware form can be applicable to different forms of machine room systems according to different types and numbers of module combinations. Meanwhile, it is also applicable to integrated solutions for strong and weak electricity and solutions for weak electricity + strong electricity. In addition, it can conduct real-time interaction, detection and analysis with the cloud. If a certain device fails, it can also intelligently identify and prohibit the start-up of the faulty device and use other devices to compensate for its operation.
Figure 3 Architecture Diagram of the M-BMS Multi-agent Adaptive Energy-saving Control System
Functions of the M-BMS Multi-agent Adaptive Energy-saving Control System:
(1) The host comprehensive energy-saving control system module will make the air conditioning host automatically adjust the air conditioning combination and output load according to the real-time changes of the building load, thereby controlling the quality/quantity of the cooling and heating of the air conditioning water system, enabling the air conditioning host to operate in a high-energy-efficiency state, while ensuring that the chilled water pumps and cooling water pumps are in a low-energy-consumption state and ensuring that the system performance coefficient is the highest (that is, the overall energy consumption of the system is the lowest).
(2) The water pump intelligent energy-saving control system module starts the water pump softly through the frequency converter.
After the water pump starts, it realizes the optimal efficiency loading and unloading according to the control parameter values output by the controller and adjusts the output frequency of each water pump frequency converter to control the rotation speed of the water pump. The chilled water pump group will enable the system to achieve the maximum energy saving while ensuring the comfort of the terminal air conditioning users. The cooling water pump group will make the cooling transfer coefficient reach the optimal value.
(3) The cooling tower intelligent energy-saving control system module calculates the optimal cooling water temperature based on the collected real-time meteorological data and the historical operation data of the system, compares it with the detected actual parameters, and controls the start-stop and variable speed operation of the cooling fan according to the deviation value, thereby changing the heat dissipation of the cooling tower and making the return water temperature of the cooling water system tend to the optimal value.
(4) The terminal intelligent energy-saving control system can adjust the supply air temperature, the opening degree of the water valve and the frequency of the fan inside the module through the indoor temperature and humidity, match the cooling capacity with the demand under the premise of ensuring the terminal comfort, and minimize the energy consumption of the fan.
Meticulous Operation Debugging and Optimization of the HVAC and Automatic Control Systems
5.1 Meticulous Debugging of Air Conditioning Equipment
5.1.1 Meticulous Debugging of the Host
Complete the operation debugging work of the chilled water host, provide the debugging report, the spreadsheet or curve of the best part-load rate, the host energy efficiency status under the working conditions of the maximum and minimum chilled and cooling water flow rates, and the highest and lowest inlet water temperature of the cooling water and the outlet water temperature of the chilled water, and determine the best efficiency operation load section of each host. And issue the diagnosis and analysis report of the chilled water host.
5.1.2 Meticulous Debugging of the Chilled and Cooling Water Pumps
According to the optimized layout plan of the machine room and the design drawings of the pipe network, as well as the technical parameters of the purchased equipment, conduct accurate calculation and comparison, test and determine the best operation technical parameters of all water pumps. And issue the diagnosis and analysis report of the water pumps.
5.1.3 Meticulous Debugging of the Cooling Tower
According to the spreadsheet or curve of the best part-load rate of the chilled water host, test the number of cooling towers in operation and the cooling effect in different load sections. And issue the diagnosis and analysis report of the cooling tower.
5.1.
4 Meticulous Debugging of the Cold Source Machine Room System
After all the equipment in the machine room system has completed the single-equipment meticulous debugging work, start up the entire cold source machine room system, test the coordinated operation performance parameters of each equipment in each load section at the optimal efficiency point. And issue the diagnosis and analysis report of the cold source machine room system.
5.1.5 Diagnosis and Analysis of the Terminal System
When the meticulous debugging of the cold source system in the machine room is completed, under the condition that the supply water temperature of the chilled water reaches the design value ± 0.5 °C and the terminal system operates at full load and part load, and the temperature difference between the supply and return of the main chilled water pipe is ≥ the design temperature difference ~ 0.5 °C, determine that the terminal system can reach ≥ the design temperature difference ~ 0.5 °C for the temperature difference between the supply and return of the chilled water in different load sections, and issue the diagnosis and analysis report of the terminal system.
5.2 Debugging of the Energy-saving Control System
5.2.1 Sensor Calibration
Calibrate the temperature, flow and other sensors in the system according to the data required by the sensor technical specifications, aiming to meet the requirements of the technical documents.
5.2.2 Semi-automatic Mode Debugging
In the automatic operation mode of a single unit, start the unit with one key, and the cooling and chilled water pumps, electric valves and cooling towers in the unit will operate in an automatic interlocking manner. The automatic control system will automatically adjust the flow rates of the chilled and cooling water pumps to realize the efficient operation of a single unit.
5.2.3 Full-automatic Mode Debugging
(1) Optimal Control of the Host
Determine the best load value of the unit according to the set values of the inlet water temperature of the cooling water and the outlet water temperature of the chilled water corresponding to the spreadsheet or curve of the best part-load rate. Calculate the specifications and number of units that need to be put into operation according to the actual measured demand of the terminal load to realize the optimal number control.
(2) Variable Frequency Control of the Chilled Water Pump
According to the actual measured demand for the flow rate of the chilled water at the terminal, the pressure difference change of the most unfavorable loop and the temperature difference change between the inlet and outlet of the chilled water, precisely control the flow distribution and the operation frequency of the water pump to ensure that the temperature difference between the supply and return of the chilled water is greater than or equal to the design value and eliminate the energy-wasting phenomenon of large flow and small temperature difference.
(3) Variable Frequency Control of the Cooling Water Pump
According to the actual measured water flow demand and the temperature difference change between the inlet and outlet of the cooling water, precisely control the dynamic pressure balance of the parallel loops of the chilled water host and the operation frequency of the water pump to ensure that the temperature difference between the supply and return of the cooling water is not less than the design value, eliminate the energy-wasting phenomenon of large flow and small temperature difference, and ensure that the chilled water host operates in the highest efficiency interval.
(4) Debugging of the Cooling Tower Automatic Control System
Automatically control the number of cooling towers put into operation according to the actual measured flow rate of the cooling water; control the operation frequency of the fan according to the change in the difference between the outlet water temperature and the outdoor wet bulb temperature to ensure that the approach temperature is at a reasonable level.