How to improve chiller plant efficiency?

Jun. 10, 2024

Maximizing chiller efficiency: some key strategies - ARANER

Chiller efficiency represents a critical factor in assessing a cooling system&#;s performance as well as every chiller plant&#;s overall sustainability in both environmental and economic terms.

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The choice of chiller system plays a critical role in cooling large buildings and infrastructures. As such, achieving chiller efficiency is able to not only minimize operating costs but also generate energy efficiency, thus accessing environmental benefits and guaranteeing compliance with current environmental regulations. Let&#;s look at some key strategies to achieve it.

What is chiller efficiency

Chiller efficiency can be defined as the effectiveness of this type of system in generating cooling while cutting back on energy consumption.

The path towards achieving chiller efficiency is better understood in the current context of sustainability and rising energy costs. As such, the projects to accomplish chiller efficiency are often paired up with other environmental and cost-efficiency actions, such as achieving savings in water consumption in chillers.

As we&#;ll see below, there are various factors that can have an influence on chiller efficiency. These include the choice of chiller technology, the actual operating conditions, the maintenance practices and protocols, and the chiller plant&#;s load variability.

Measuring chiller efficiency

Chiller efficiency is typically measured using the following two parameters that relate the cooling output to the electrical energy input.

Coefficient of Performance (COP): it measures the ratio of the heat removed (cooling capacity) to the electrical power consumed by the chiller. Mathematically, it's expressed as: COP = Cooling Capacity (watts) / Electrical Power Input (watts). A higher COP indicates better efficiency, so that more cooling is provided per unit of electricity consumed.
Energy Efficiency Ratio (EER): EER is a similar measurement to COP but is often used in the United States (while also present in other regions). It measures the ratio of cooling capacity (in BTUs or British Thermal Units) to the electrical power input (in watts), so that EER = Cooling Capacity (in BTUs) / Electrical Power Input (in watts). Again, a higher EER signifies better chiller efficiency.

How to achieve chiller efficiency

Proper chiller selection

Operators must ensure they choose the most efficient chiller type and size for their specific cooling needs. Factors such as the load profile, climate, and system requirements must all be considered in the choice between air-cooled chillers, water-cooled chillers or absorption chillers, among others.

Operators must pay close attention to choose a chiller plant that is properly sized for the building, so that it operates at its most-efficient capacity. This is because some chiller systems typically present better performance at 40% and 60% of their peak capacity, while some may peak at approximately 70-75% load. This means they use less energy per unit of cooling capacity when operating at part-load conditions.

Additionally, the chiller plant must be designed with efficiency in mind. This includes properly sizing pipes, pumps, and controls to minimize energy losses and optimize system performance.

Regular maintenance

A comprehensive maintenance program must be implemented so that it includes cleaning and inspecting key components like coils, tubes, and heat exchangers. Otherwise, dirty or malfunctioning components can significantly reduce efficiency.

As part of regular maintenance operations, conduct periodic energy audits and efficiency assessments to identify areas for improvement and track chiller efficiency over time.

Optimal water treatment

Water quality in the chiller system must be monitored and maintained in order to prevent scale, corrosion, and biological growth. Microbes, scale or iron deposits (among other problems) that are not properly controlled can reduce chiller efficiency significantly. On the contrary, an appropriate water treatment chemicals and practices to ensure clean and efficient heat transfer.

Match output to actual cooling load

Operators must ensure chiller operating parameters (such as temperature and flow rates) are adjusted to match the actual cooling load. This is because overcooling or excessive flow rates can waste energy.

Implementing advanced chiller controls and monitoring systems will also be a winning strategy, as they allow to continuously optimize chiller operation based on real-time conditions and load variations.

Additionally, these operations can be automated to operate based on set temperatures, which can help reduce energy consumption.

Implement smart load management strategies

Implementing load-shedding strategies during partial load conditions can be beneficial for maximizing chiller efficiency. If a chiller system presents multiple chillers, this can be achieved by running them at partial capacity. As such, running multiple parallel devices will optimize energy and economic savings, allowing equipment to run at lower speeds.

Similarly, the implementation of adequate Energy Management Systems (EMS) can help operators monitor and control your chiller system in real-time, while also optimizing operations based on factors like outdoor temperature and building occupancy.

h3. Guarantee consistent, reliable data

Additionally, operators must establish a strategy to document operational data, so that efficiency and performance values can be recorded in chiller logs. It&#;s preferable if this is an automatic process, guaranteeing values are consistently recorded.

Chiller performance values should be recorded both at full and partial loads, thus effectively calculating chiller efficiency and being able to measure and diagnose the potential causes of inefficiency.

This is particularly important considering how a chiller plant represents an extremely dynamic piece of equipment. Chiller flows are not constant or rigid. In fact, chillers expand and contract from their original design, and are subjected to processes such as wear, tear and age. As such, accurate, continuous verification of their performance is crucial when striving for chiller efficiency.

Heat recovery systems

Current opportunities for chiller heat recovery are crucial for achieving chiller efficiency. Recovered heat can be used for space heating, domestic hot water, or other purposes, reducing the need for additional heating systems.

At the same time, Thermal Storage Tanks (TES tanks) can significantly improve chiller efficiency by allowing you to shift the cooling load to off-peak hours, reduce chiller cycling, and take advantage of lower electricity rates during non-peak times.

If you want to learn more, please visit our website Custom Chiller System.

As such, during periods of low electricity demand or lower electricity rates (usually at night), the chiller system can produce chilled water and freeze it in the thermal storage tank. This chilled water is then used to cool the building during peak demand periods, reducing the load on the chiller during the day when electricity rates are higher.

Upgrading or Retrofitting

Modern chillers often have improved efficiency and control capabilities, compared to old and inefficient chiller systems. This is why it&#;s often important to consider upgrading or retrofitting older chillers with newer, more energy-efficient models.

In such scenarios, it&#;s worth exploring innovative chiller technologies, such as magnetic-bearing chillers or absorption chillers, which can offer higher efficiency under specific conditions.

Modern, high-efficiency chillers typically have a higher COP, indicating better energy efficiency. Additionally, they incorporate improvements such as variable speed compressors or advanced control systems, which can adapt to varying operating conditions and optimize the chiller's performance in real-time. They are also designed to perform exceptionally well at partial load conditions, resulting in significant energy savings in real-world applications where loads vary.

This is precisely where, at Araner, we can help. As part of our commitment to develop cutting-edge heating and cooling engineering, we&#;re able to design custom solutions to achieve maximum energy savings and chiller efficiency.

Take a look at our district cooling initiatives, designed with cost-efficiency and sustainability as principles, or get in touch with our team to learn more about how we can help you achieve maximum chiller efficiency.

3 Ways To Increase Chiller Efficiency

VFDs, parallel devices, and increasing supply temperatures all contribute to energy savings for chiller plants.

By Thomas Squillo, Contributing Writer HVAC

1. Consider variable speed retrofits

Most components within a chilled water system will benefit from variable speed drives. In fact, most current energy codes require VFDs for these components in new systems and major retrofits. VFD costs have also decreased dramatically in the last several years.

As shown by the constant- and variable-speed chiller efficiency charts on page 38, there is a huge benefit to VFDs for chillers, but only if condenser water temperature relief is also implemented.

Cooling tower fans are another opportunity to save energy with VFDs. As loading and outdoor wet-bulb temperature decrease, variable speed fan motors not only save fan energy due to fan law benefits (a fan at 50 percent speed draws 12.5 percent of the power of a fan operating at 100 percent), but also provide more stable temperature control.

Variable speed pumping can provide an energy savings opportunity, but requires a close look at other parts of the system. On the chilled water side, a constant to variable flow retrofit may involve major and costly renovations of control valves and control sequences. Also, variable flow capabilities of existing chillers need to be reviewed. Low flow limits of the chiller may reduce the economic feasibility of variable chilled water pumping. On the condenser water side, variable flow control may be limited by chiller flow requirements or cooling tower fouling/freezing concerns. However, if pumps are oversized on a constant flow system, balancing pump flow by lowering speed versus flow restriction using a balancing value may provide good payback, even without adding variable flow during system operation.

2. More is less: Running multiple parallel devices optimizes savings

Chiller plant equipment generally runs more efficiently at part-load. Chillers, for example, can run at optimum efficiency somewhere between 40 percent and 60 percent of peak capacity. Cooling tower fans and system pumps that are piped in parallel may also benefit from a control scheme that operates more pieces of equipment at lower speeds, versus a staging scheme which allows operating equipment to increase to full capacity before staging on the next unit. For cooling towers and chillers, running more equipment maximizes heat transfer surface area at all operating points, which increases efficiency and reduces pressure drops. For pumps, taking advantage of pump law savings and running at optimum pump efficiency points is key. The pump law is similar to the fan law: When pump speed is reduced, energy consumption is cut by the cube of the reduction in speed. However, any control scheme change needs to consider minimum chiller and cooling tower flow limits.

3. Increase supply temperatures

Most commercial systems are designed with a chilled water supply temperature in the range of 40 F to 45 F. This generally allows for proper dehumidification and an acceptable supply air temperature for occupant spaces during peak times. However, these peak weather and load conditions are rarely seen.

Implementing supply air temperature reset control can save energy in several ways. First, when cold supply air temperatures are not required (acceptable humidity levels and no zones at peak load), raising supply temperatures can help prevent over-dehumidification of spaces and unneeded latent cooling. More importantly, higher supply air setpoints can allow chilled water supply temperature to be increased, substantially improving chiller efficiency. In general, chiller efficiencies improve approximately 2 percent for every degree that chilled water supply temperature is increased.

Other design and control features should also be investigated to optimize energy savings. As noted earlier, VFDs on all or some components should be considered. Also, a close look at setpoints, temperature reset, and other simple control sequence changes are usually effective and have minimal cost.

Of course, these methods are not right for every system. Depending on budget and financial requirements, climate, expected load profile, and existing equipment limitations, your optimal solution will be unique and will likely require an engineering analysis and annual energy use calculations.

Thomas Squillo serves as technical director, mechanical, for Environmental Systems Design.

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