Quck answer
Chiller efficiency is calculated by dividing the cooling capacity (in tons or kW) by the input power (in kW) of the chiller. The result is expressed as a percentage or a coefficient of performance (COP). A higher efficiency indicates a more energy-efficient chiller. To calculate chiller efficiency, follow these steps:
1. Determine the cooling capacity of the chiller in tons or kW.
2. Measure the input power of the chiller in kW.
3. Divide the cooling capacity by the input power to get the efficiency.
4. Multiply the result by 100 to get the efficiency percentage.
For example, if a chiller has a cooling capacity of 100 tons and an input power of 80 kW, the efficiency would be 125% or a COP of 1.25.
Cold water chillers are commonly used in large-scale applications for industrial, commercial, and architectural air conditioning. These systems operate using a heat pump mechanism similar to air conditioners, but instead use recirculating water to transfer heat during both the evaporator and condenser phases of their refrigeration cycles. Accurately calculating chiller efficiency requires careful consideration of various engineering units and conversion factors.
Chiller System for Cooling Food Manufacturing Areas
Step 1
Chiller water flowing through heat exchangers.
Define the chiller application. For instance, a chilled water system is used to maintain a temperature of approximately 40В°F in a food manufacturing area. The chiller system recirculates 40 gallons of water per minute, which is cooled by 24В°F and consumes 24.8 kW/hr of electricity to provide refrigeration. This information can be used to calculate the chiller efficiency in terms of the energy efficiency ratio (EER) and the coefficient of performance (COP) for chillers.
Step 2
Calculate the chiller capacity in tons of refrigeration. The formula for total heat removed in a chiller installation is h = 500 X q X dt, where h represents the total heat removed in Btu/hr, q represents the chilled water flow rate in gallons per minute, and dt represents the chilled water’s total temperature differential. Substituting these values, h = 500 X 40 gpm X 24В°F = 480,000 Btu/hr. If 1 Ton of refrigeration equals 12,000 Btu/hr, then the system has a cooling capacity of 40 Tons of refrigeration.
Step 3
Calculate the chiller system efficiency using the air conditioning efficiency formula EER = Btu/hr cooling/watts consumed. Substituting the actual values, 480,000 Btu/hr/24.8 kW/hr = 480,000 Btu/hr/24,800 watts/hr = 19.35. This represents very high cooling performance compared to the 2010 SEER standards of 13-14 for domestic air conditioning, reflecting the higher efficiency of the chilled water strategy. COP would be the EER (19.35) X 0.293 = 5.67.
Chilled Seawater for Preserving Seafood
Step 1
Live lobsters being chilled for transport to market.
Define the chilled water application. Seawater with a specific enthalpy of 0.94 Btu per pound per degree Fahrenheit is being chilled by 18В°F to preserve seafood freshness. If the system requires 69.06 kW-hr to chill 6,000 gallons per hour of this recirculating seawater, you can calculate the chiller efficiency.
Step 2
Refrigeration chillers require careful monitoring.
Calculate the total Btu/hr being removed by the chiller system. Since h = 500 X q X dt, and the heat capacity of seawater is only 0.94 Btu per pound, then the modified formula will be h = 500 X q X dt X 0.94 = 500 X 6,000 gallons per hour/100 gallons per minute X 18В°F X 0.94 = 846,000 Btu/hr/12,000 Btu/hr per Ton = 70.5 Tons of refrigeration.
Step 3
Calculate the chiller system efficiency by dividing the 846,000 Btu/hr by the 69.06 kW-hr consumed to yield an EER of 12.25 and a COP of 3.59.
FAQ
1. What is chiller efficiency and why is it important?
Chiller efficiency refers to how effectively a chiller system converts electrical energy into cooling output. It is an important metric because it determines the energy consumption and operating costs of the chiller. A highly efficient chiller can significantly reduce energy usage and save money for the user.
2. How is chiller efficiency measured?
Chiller efficiency is typically measured using the Coefficient of Performance (COP) or the Energy Efficiency Ratio (EER). COP is calculated by dividing the cooling output by the electrical power input, while EER is calculated by dividing the cooling output by the power input at a specific operating condition. Both values provide an indication of the chiller’s efficiency.
3. What factors affect chiller efficiency?
Several factors can affect chiller efficiency, including the type of refrigerant used, the chiller’s design and size, the operating conditions (such as temperature and humidity), and the maintenance and cleanliness of the chiller system. Proper installation, regular maintenance, and correct sizing of the chiller can help improve its efficiency.
4. How can chiller efficiency be improved?
To improve chiller efficiency, it is important to ensure proper chiller sizing for the cooling load, maintain clean heat transfer surfaces, regularly inspect and clean the condenser and evaporator coils, optimize the chiller’s control settings, and use high-efficiency components and technologies. Additionally, implementing a comprehensive energy management system and monitoring the chiller’s performance can help identify areas for improvement.
5. What are some benefits of using a highly efficient chiller?
Using a highly efficient chiller can result in several benefits, including reduced energy consumption and operating costs, lower carbon emissions, improved sustainability, enhanced reliability and longevity of the chiller, and compliance with energy efficiency regulations. It can also contribute to a more comfortable and productive indoor environment by providing consistent and reliable cooling.