1. Compare and Select the chillers under the conditions they are most likely to experience
Normally Chillers are selected based on full load but typically the full load occurs only 1% to 2.5 % of the time and hence most systems operate at 50 % or less of their capacity.
Strategies for selecting and improving Chiller plant load efficiency
- Peak Load demand determines the overall capacity of the system.
- Part load requirement determine the number and size of chiller required. Cooling Load Profile will help to determine the type of chiller to use and if single or multiple chillers should be installed. Multiple chiller installation allow facilities professionals to stage their operation to match building loads while keeping the chillers operating at energy efficient loading.
- Standby Strategy– Adopt standby or (N+1) Strategy. The provision of 1 additional backup unit is known as N+1 Strategy. The application where cooling is required for critical service delivery, one back up unit would be required.
2. Condenser Water Temperature Adjustment
- Chiller energy consumption is a function of the condenser pressure and temperature.
- 1 to 2% energy saving can be achieved per degree of reduction in condenser water temperature.
3. Adjust Chilled Water Temperature
- Rising the chilled water temperature lowers the compressor load resulting in decreased energy consumption.
- In centrifugal chillers at constant speed 0.5% to 0.75% power consumption can decrease per degree increase in chilled water temperature.
4. Chilled Water Flow Isolation
- Effective water flow management of the chiller is a source of potential energy saving. Water Pumped through idle chillers consumes unnecessary energy by adding temperature to the water. This can be as much as 2-2.5 Deg.F
- Keep provision to isolate inactive chillers from the chilled water and condenser water loops when they are not in operation. The use of automatic shut-off valves is recommended.
5. Variable Speed Drive Chiller
- The use of variable speed drives greatly enhances energy efficiency. This enables the chiller to match the speed of the compressor to the load at the maximum efficiency.
- The availability of variable speed centrifugal chillers has improved in recent years, thus reduces the purchase cost. Most VSD chillers offer good part load efficiency even better than at full load.
6. Variable Pumping Flow Through Chillers
- It vary the volume of chilled water flow as per demand.
- It makes use of two loops of primary and secondary distribution, each equipped with variable speed pumps to deliver chilled water per demand.
- This type of chiller can save energy up to 5-10 %
7. Select the number and size of chiller based on anticipated operating conditions.
If only a portion of the building is functional during lean periods, it makes sense to install a smaller capacity chiller to serve that relatively small but constant cooling load.
8. Select unequally sized machines for multiple chiller installations
- When going for single chillers, varying chiller sizes can help meet intermediate loads more effectively.
- For example, splitting the chiller sizes 1/3 – 2/3 will help to meet the major load by 2/3 capacity chiller for most of the days. Thus making one chilled operates near its most efficient point.
9. Chiller Sequencing
- In case of multiple chillers, always load the one that has the best efficiency.
- When chillers are of different types. Consider operating the centrifugal chillers at full load and then with the screw chiller at part load.
- Always consider Efficiency vs. Load when starting and stopping of the Chillers.
10. Automatic Tube Cleaning System
- Fouling of condenser increase the condensing temperature, the head pressure and compressor energy use.
- Go for in-built automatic tube cleaning and flow revering arrangement.
- Fouling is critical with river water condensers, process evaporators and condensers on towers or systems.
- Energy savings commonly range from 15-20%
- Additional saving from reduced maintenance and less downtimes are possible.
11. Chiller Plant Automation, Reporting, Control
Well –designed automation package can greatly reduce the energy consumption of a chiller plant and provide an improved level of monitoring and reliability.
Advantages of using DDC
- Compatible with building energy management system
- Provide 24 hrs. electronic monitoring and control of chiller.
- Report information to a control center or cell phone.
- Report operational problems and even dispatch a service call.
- Early detection of problems and prevent equipment damage.
- Control functions include employment (on-off) demand limiting, chill water reset, pump employment water flow control.
- Automated systems can perform logging duties for operators.
12. Demand Limiters and Staggered Start
- Chiller draw maximum current or power during start-up.
- Most electric utilities base their demand charges 15 or 30 minute interval on monthly or manual basis.
- When starting multiple chillers, stagger the starts at least by one demand period. Start the second chiller after the first has loaded to save significant energy cost on utility bills in the category of demand charges.
13. When to use Chiller?
- Building of 20000 Sq. area or more
Advantages of Use Chiller Plant
- Lower operating Cost especially if used with cooling tower or an evaporative condenser. The COP of water cooled chiller is high compared to other options and the operating costs can be as low as 0.5 KW per ton.
- Centrifugal chillers are highly efficient both at full load and par load operation. Screw chillers are next best option.
- Chilled water systems are the engineering systems that are tailor made to suit the design requirements of high sensible and lantant load.
- The air delivery systems (AHU) can be custom designed to provide higher or lower CFM per ton suiting the specific requirements.
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