There are plenty of energy savings in clean rooms, such as heating, ventilation and air conditioning (HVAC), process cooling, compressed air, and other facilities. Here are 10 tips for new and existing plants to address energy efficiency.

01 Low section wind speed design
Section wind speed is the speed at which air in an air handling component passes through a filter or heating/cooling coil. Low Profile Wind Velocity (LFV) designs use larger air processors and smaller fans to reduce air flow rates and reduce energy consumption and equipment lifetime costs. Most engineers based on "experience" design air processors to 500 inches per minute. Such a design saves time, but increases operating costs. In low profile wind velocity (LFV) designs, larger air processors and smaller fans are used to reduce air flow rates, reduce energy consumption and set life costs.
The pressure drop determines the energy loss of the fan. The "square rule" shows that the pressure drop is proportional to the square of the velocity drop. If the cross-section wind speed is reduced by 20%, the pressure drop will be reduced by 36%. If the cross-section wind speed is reduced by 50%, the pressure drop will be reduced by three-quarters. According to the "cubic rule", the change in energy consumption of the fan is proportional to the cube of the change in flow rate. If the air flow is reduced by 50%, the energy consumption of the fan will be reduced by 88%.
As a result, larger air processors, larger filters, and coil areas consume less fan energy and can be used with smaller fans and motors. The small fan adds less heat to the air, reducing the difficulty of cooling. Small thickness coils are easier to clean and more efficient, so the temperature of the frozen water can be higher. The filter works better and has a longer life at low cross section wind speed.
The LFV design reduces the pressure drop of air and water and reduces the amount of water carried by the cooling coils. A streamlined design with few sharp corners reduces pressure drop by 10% to 15%.
The LFV design can also reduce the pressure drop by a quarter. The goal is to reduce energy loss by at least 25% and reduce the size of the variable speed fan. The optimal cross-section wind speed range is 250-450 ft/min, depending on usage and energy consumption.
02 Number of air changes
The clean room maintains a certain air flow to maintain cleanliness and particle count. The flow rate is determined by the number of air changes per hour, which also determines the fan size, building configuration and energy consumption. The reduction in air flow rate can reduce construction and energy costs while maintaining cleanliness. Reducing the number of air changes by 20% can reduce the size of the fan by 50%. Air cleanliness is more important than energy savings, but recent research has shown a documented reduction in cleaning costs.
There is no consensus on the optimal number of air changes. Many of the principles are outdated, based on old ideas and inefficient air filters. The survey showed that the recommended number of air changes for clean rooms under ISO Level 5 standards ranged from 250 to more than 700.
A national laboratory in the United States is in the process of defining ISO Level 5 standards for clean rooms. Studies have shown that the actual air changes range from 90 to 250 - much lower than operating procedure standards and without affecting production or cleanliness. Therefore, the recommended number of air changes for ISO Level 5 clean rooms is about 200, with a conservative upper limit of 300.
03 Motor Efficiency
The motor consumes most of the electricity in the clean room. A continuously running motor consumes a large amount of electricity every month. If the efficiency is properly improved and the size is properly adjusted, the economic effect is mostly good after renovation. A few percentage points increase in efficiency can increase profits.
Using a high-quality and efficient motor doesn't have to cost too much. High efficiency means minimum, minimizing the load before changing the size of the motor. Variable speed drive (VSD) can improve the efficiency of operation when the output changes.
04 Variable speed drive freezer
Variable speed drive chillers can save a lot of energy and money. Many clean room designers and operators believe that it is not necessary to use variable speed drive freezers, because the load is usually constant, and the multistage freezers are usually controlled for high load operation. However, freezers with constant load usually work below full load. Variable speed drive freezers usually operate at 90%-95% of full load to save energy. A 1000-ton refrigerator works steadily at 70% of its full load, and if a variable speed drive is used, it can save $20,000 to $30,000 a year. According to the manufacturer's data, the price of electricity is $0.05 / KWH, so that the cost can be recouped in about a year.
Multistage chiller chiller units rarely operate at high load. In general, the field load usually does not exactly match the energy level change of the unit. Many operators run extra chillers to be reliable, and if one fails, the others can be replaced immediately to take over its full load, so chiller units often run the chillers at 60 to 80 percent of their cooling capacity.
When buying a new refrigerator, it is cost-effective to specify the purchase of a variable speed drive refrigerator. Using variable speed to drive the chiller reduces energy consumption while allowing other chiller to operate reliably. There are many studies and experiments to prove that the effect of variable speed drive freezer is very good. For more than 20 years, variable speed drive chiller manufacturers have created more reliable products for use in new and upgraded clean plants.
05 Double temperature freezing cycle
Refrigeration systems are usually designed to withstand maximum loads, whether or not the maximum loads occur frequently. The temperature of the chilled water in the freezing cycle of the process is determined by the extreme heat load, which is only a small fraction of the total load, and this is only one or two of many cases. This creates excess freezing capacity, which is inefficient in the case of insufficient load. When the temperature of the supplied frozen water is low, the working efficiency of the freezer will be very low. On average, for every one degree Fahrenheit increase in the chilled water supply temperature, the freezer efficiency increases by more than one percentage point. If the load is divided and two different temperatures of chilled water are provided, then the work efficiency will be higher. Designers can use parallel circulation lines to divide them into two subsystems, so that when the maximum cooling capacity is required, the freezer can work under relatively less harsh conditions.
Designers can use parallel circulation lines to divide them into two subsystems, so that when the maximum cooling capacity is required, the freezer can operate under relatively less harsh conditions. Moderate temperature cycles (e.g., 55 ° F to 65 ° F) are performed with specialized chillers whose operation is optimized for the temperature of chilled water and can meet most of the plant's needs. Another smaller, high-efficiency freezer provides lower temperature cycles (e.g. 39 ° F to 43 ° F) to meet the demanding portion of the load.
This program can quickly increase the efficiency of the entire chiller unit by 25 percent or more. For the same capacity of the refrigerator, high temperature work is much less expensive than low temperature work.
06 Cooling tower optimization
The high efficiency cooling tower improves the efficiency of the freezer by reducing the supply temperature of the condensate water. All cooling towers should work in parallel, and the effect is optimal when the surface area is increased by evaporation.
For every ton of chilled water output from the chiller, a typical cooling tower requires 100 watts of energy. Efficiency improvements of up to ten times can be achieved, such as closer access, outlet temperature differences, more efficient airflow design, high-quality and efficient fans with variable speed drive motors, reduced height to limit pump head, and increased filling area (select large size towers).
The temperature difference is different between the humidity temperature of the outside air and the supply temperature of the cooling water, and should be controlled between 3℉ and 5℉.
All cooling towers should work in parallel so that evaporative cooling is optimal with increased surface area. Many mission plants use multistage towers, which use single - or two-speed fans and divide the towers into different stages. One tower operates at full speed until the load exceeds its capacity, and then the other tower opens, which operates at a lower or higher power state. This solution can lead to large and increasing changes in the cooling tower load, frequently falling below or exceeding the required rating, resulting in a zigzags of energy consumption, reducing the efficiency of the freezer.
Therefore, all cooling towers should work in parallel, and the evaporative cooling is optimal when the surface area is increased. If more towers work at low speeds, use variable speed drive to adjust the speed of the fan, adjust as the load changes, according to the "cube law", at lower speeds the fan can save energy.
The plant usually uses a special cooling tower to supply condensate water to each refrigerator. This concept does not allow the chiller to operate in parallel with the cooling tower. Only the addition of ordinary headers to the condensate system allows the cooling towers to run in parallel, regardless of cooling requirements.
07 Free cooling
The use of outside air for cooling is economical and widely adopted in commercial buildings. Another "free cooling" solution is suitable for systems that require a constant supply of chilled water and fan coils, such as clean rooms.
Free cooling technology directly uses cooling towers in low-temperature or low-humidity environments to produce chilled water, reducing or replacing the use of freezers. Depending on the weather, the use of the free cooling system can reduce the energy consumption of the cooling system to one-tenth (from 0.5 kW/cold ton to 0.05 kW/cold ton).
Direct heat exchange with the process load allows the free cooling technology to take advantage of the warmer atmosphere outside for several hours longer than heat exchange in a secondary or tertiary heat exchange system. The temperature difference between the cooling water and the condensate separated by the plate heat exchanger is very close (e.g., only 2 ° F). When the temperature and humidity are quite low, the cooling tower can operate independently without a fan. According to the thermo-humidity map, many places can be free cooling for many hours each year.
08 Heat recovery
Many mission plants consume large amounts of energy to produce heat, and even more energy to remove "waste" heat from the process, without combining the two processes. The recovered heat can be used to preheat fresh air, supply air for reheating, and other purposes. AHU preheat coils can preheat external air with waste water (or precool in hot weather).
Reheat coils can recover waste heat from the air compressor or the cooler's condenser return water, while saving freezer energy and boiler fuel. Heat exchangers can exchange heat between different media that cannot be mixed or in direct contact.
09 Variable frequency pump
In the past, equipment equipped with variable frequency drives often failed, and the control was complex, so many engineers and managers were reluctant to use variable frequency drives. Reliability is more important than energy saving, and the old variable frequency drive has poor reliability. In the last decade, the reliability of variable frequency drives has improved and the price has decreased. Many critical systems are now using variable frequency drives.
We believe it is safe and cost-effective to use variable frequency drives on many systems and all types of pumps in the clean room. In fact, it can be proved irresponsible to consider the return on investment without using the variable frequency drive, because the payback period is less than one year.
The pump flow of chilled water and condensate water varies greatly, and the chilled water and condensate water system has a minimum flow requirement, which is basically between 50% and 75%. According to the "cube rule", a small reduction in flow will result in significant energy savings. A 20% reduction in flow produces an almost 50% reduction in pump power.
Most known chilled water systems use a primary pump constant flow/secondary pump variable flow design, and the secondary pump is driven by frequency conversion. When using variable frequency drive, all chilled water should use double channel valve, otherwise it will lose the meaning of using variable frequency pump.
When the new plant is built, the variable flow primary pump system is used, and the secondary pump is no longer needed, saving the engineering cost. Properly run, this simple and reliable system can save significant amounts of energy through changes in chilled water flow in the freezer.
10 Centrifugal compressor
Improvements in air compressors have saved a lot of energy. Centrifugal compressors are oil-free and much more efficient than screw compressors. However, centrifugal compressors cannot be idled, that is, low load conditions are extremely unfavorable to centrifuge operation (>30%), which makes them very inefficient under low load conditions. The most effective and economical way is to use a combination of centrifugal and screw compressors. Select centrifugal units to meet the base load, and then use smaller screw units to meet the peak load. The compressor unit should be equipped with a heat recovery system.
Another option is to use a high-efficiency centrifugal compressor as a large compressed air unit for the entire site, with enlarged gas tanks and connecting pipes as buffers. This ensures that a constant load is maintained throughout the plant, reducing the loss of equipment during loading and unloading, and reducing energy waste.