Calculating chiller selection

An analysis on an office building in Milwaukee shows a dramatic difference in chiller operating costs for a building based on chiller selection.

09/16/2013


Figure 7: This comparison of chiller operating costs uses a load calculation program and NPLV for a 1,000-ton water-cooled centrifugal chiller plant for an office building. Courtesy: Ring & DuChateauTo display the variations in operating costs for chillers, an analysis was completed for a 300,000-sq-ft office building using an energy simulation calculation program with weather data from Milwaukee for a 1,000-ton water-cooled chilled water plant to determine the chiller with the lowest operational costs. 

Multiple chiller selections were made varying compressor types, chilled and condenser water temperature ranges, air-cooled versus water-cooled heat exchangers, and variable frequency drives to determine the best combination of variables. Chiller selections were made with two or four chillers in parallel, each sized at equal capacity in a variable primary flow configuration, which is common for a new building with multiple cooling coils and chillers. 

To focus on the variation in operating costs, each chiller was calculated with an unloading curve in 10% increments and used in the energy simulation program to determine the annualized operating costs. An analysis was also completed using a simplified approach to see if a quick analysis could be completed with a relatively small degree of error without using an energy simulation program. For the simplified method, IPLV was used for determining chiller operating costs by multiplying the IPLV kW/ton value, the chiller plant tonnage, the chiller plant operating hours provided by the load calculation program, and the electrical consumption rate. 

For all calculations a typical office building schedule was used with operation from 8 a.m. to 5 p.m., Monday through Friday. An electrical rate of $0.12/kWh was used for on-peak electrical consumption and $0.10/kWh for off-peak electrical consumption with an on-peak period from 9 a.m. to 9 p.m. 

The results of the analysis, as well as the chiller selection options, are shown in Figure 7. There is a dramatic difference in chiller operating costs for a building based on chiller selection. Furthermore, the figure shows the resulting error in the simplified method using IPLV for chiller energy consumption as a viable option to calculate operating costs, which ranges from 3 to 5 times the calculated operating cost based on an energy simulation program. The operating cost for each option is provided, with subtitle A for the simplified method and subtitle B for the energy simulation method. In all cases, the IPLV method is dramatically more expensive in determining chiller plant energy consumption. This error can be directly attributed to calculating operating costs from using actual weather data and a true building load profile in lieu of predetermined AHRI operating points. 


David Grassl is a mechanical engineer at Ring & DuChateau, and an adjunct professor in the Civil & Architectural Engineering & Construction Management Department at the Milwaukee School of Engineering. He has analyzed and designed approximately 10,000 tons of chilled water systems for plants ranging from small, individual systems for office buildings to large, complex central plants for universities.



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
2016 Product of the Year; Diagnose bearing failures; Asset performance management; Testing dust collector performance measures
Safety for 18 years, warehouse maintenance tips, Ethernet and the IIoT, GAMS 2016 recap
2016 Engineering Leaders Under 40; Future vision: Where is manufacturing headed?; Electrical distribution, redefined
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Safety at every angle, Big Data's impact on operations, bridging the skills gap
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Driving motor efficiency; Preventing arc flash in mission critical facilities; Integrating alternative power and existing electrical systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role of plant safety and offers advice on best practices.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me