1. How to Convert and Optimize Primary/Secondary Pumping Systems
to Variable Flow Primary Systems
Presented By: Hemant Mehta, P.E.
WMGroup Engineers, P.C.

2. History of Variable Primary Flow Projects
King Saud University - Riyadh (1977)
Louisville Medical Center (1984)
Yale University(1988)
Harvard University (1990)
MIT(1993)
Amgen (2001)
New York-Presbyterian Hospital (2002)
Pennsylvania State Capitol Complex (2005)
Duke University (2006)
NYU Medical Center (2007)
Memorial Sloan-Kettering Cancer Center (2007)

3. King Saud University – Riyadh (1977)
60,000 ton capacity with 30,000 tons for first phase
Six 5,000 ton Carrier DA chillers
Seven 10,000 GPM 240 TDH constant speed pumps
Major Problem: Too much head on chilled water pumps
Lesson Learned: Be realistic in predicting growth

4. Louisville Medical Center (1984)
Existing system (1984)
Primary/Secondary/Tertiary with 13,000 ton capacity
Current System (2007)
120 feet TDH constant speed primary pumps with building booster pumps – 30,000 ton capacity
Changed the heads on some of the evaporator shells to change number of passes
Primary pumps are turned OFF during winter, Early Spring and Late Fall. Building booster pumps are operated to maintain flow.

5. Yale University (1988) Existing system (1988)
Primary/Secondary/Tertiary with 10,500 ton capacity
Current System (2007)
180 feet TDH VFD / Steam Turbine driven variable flow primary pumps – 25,000 ton capacity
Changed the heads on some of the evaporator shells to change number of passes

6. Amgen (2001)
Creation of a computerized hydraulic model of the existing chilled water plant and distribution system
Identification of bottlenecks in system flow
Evaluation of existing capacity for present and future loads
Two plants interconnected: Single plant operation for most of the year, second plant used for peaking
Annual Energy Cost Savings: $500,000

7. Additional Variable Primary Flow Projects
Harvard University (1990)
MIT(1993)
New York-Presbyterian Hospital (2002)
Pennsylvania State Capitol Complex (2005)
Duke University (2006)
NYU Medical Center (2007)
Memorial Sloan-Kettering Cancer Center (2007)

8. Duke University Background
CCWP-1 plant was built four years ago
CCWP-2 design was 90% complete (Primary/Secondary pumping)
We were retained by Duke to peer review the design
Peer review was time sensitive
Plant design for CCWP-2 was modified to Variable Primary pumping based on our recommendations

9. Duke CCWP-1 Before

10. Duke CCWP-1 After
Dark blue pipe replaces old primary pumps

11. Duke Levine Science Research Center CHW System

12. Duke CIEMAS Building CHW System
90% closed
Triple duty valves
50% closed

13. Duke CIEMAS Building AHU-9
Balancing valve
50% closed

14. NYU Medical Center (2007)
Plant survey and hydraulic model indicated unnecessary pumps
1,300 horsepower of pumps are being removed, including 11 pumps in two brand new chiller plants
$300,000 implementation cost
$460,000 annual energy savings

15. NYU Medical Center (2007)
Plant survey and hydraulic model indicated unnecessary pumps
1,300 horsepower of pumps are being removed, including 11 pumps in two brand new chiller plants
$300,000 implementation cost
$460,000 annual energy savings
8 Pumps Removed
3 Pumps Removed
7 Pumps Removed
3 Pumps Removed

16. Memorial Sloan-Kettering - Before

17. Memorial Sloan-Kettering - After
Bypass or removal of pumps
Bypass or removal of pump
Bypass or removal of pumps

18. Pump Cemetery
To date we have removed several hundred large pumps from our clients’ chilled water systems

19. Good Engineers Always Ask “Why?”
Why does the industry keep installing Primary/Secondary systems?
Why don’t we get the desired system ΔT?
Why does the industry allow mixing of supply and return water?

20. Good Engineers Always Ask “Why?”
Why does the industry keep installing Primary/Secondary systems?
Why don’t we get the desired system ΔT?
Why does the industry allow mixing of supply and return water?
Answer: To keep consultants like us busy!
Why change?

21. Reasons to Change
Chiller manufacturing industry supports the concepts of Variable Primary Flow
Evaporator flow can vary over a large range
Less space is required for fewer pumps
Lower first cost and operating costs

22. Change is Starting Around the World
Most of the large district cooling plants in Dubai currently use Primary/Secondary pumping
By educating the client we were able to convince them that this is not necessary
We are now currently designing three 40,000 ton chiller plants in Abu Dhabi using Variable Primary Flow as part of a $6.9 billion development project

23. Design Guidelines of A Primary Variable Flow System
Main Equipment
Minimize amount of installed equipment
Estimate maximum chiller capacity required with full build-out of your campus
Use 350 SF/Ton as a guideline for most building types
Multiple Plants/ Virtual Central System
Review your existing system and decide your needs for ultimate build-out

24. Design Guidelines of A Primary Variable Flow System
Chillers
Renegotiate with manufacturer to provide maximum capacity based on the chiller selection.
Keep flow velocity around 6.5 ft/sec at peak
Chilled Water Pumps
Variable Frequency Drive
Review feasibility of oversizing pumps in lieu of providing a standby pump

25. Design Guidelines of A Primary Variable Flow System
Condenser Water Pumps
Variable Speed Condenser Water Pumps?
Cooling Towers
Design for at least 2°F higher wet bulb temperature than normal design wet bulb
Specify full flow coverage at 50% of peak flow
Pressurization Tank
City water pressure may be adequate
Tank May not be required for large system
Air Separators
Not required

26. Design Guidelines of A Primary Variable Flow System
Controls
Flow control valves on CHWR and CWR lines to each chiller
Chilled water differential pressure bypass valve at the plant
Differential pressure sensors at the hydraulically most remote buildings
Flow meters on CHWR and CWR lines to each chiller
Outside air weather station
Temperature and humidity sensors for cooling tower controls
Learn the behavior of your system
Remember
You can not manage what you do not measure

27. Design Guidelines of A Primary Variable Flow System
Chilled water flow controls and site differential pressure
Master Control
CHWP VFD is controlled to maintain required differential pressure at remote buildings
Sub Master Control
Provide to maintain individual chiller minimum flow

28. Variable Volume Primary System Flow Diagram

29. Variable Volume Primary System Flow Diagram
Chillers

30. Variable Volume Primary System Flow Diagram
CHW Pumps

31. Variable Volume Primary System Flow Diagram
DP Bypass

32. Variable Volume Primary System Flow Diagram
Condensers

33. Variable Volume Primary System Flow Diagram
Control Valves

34. Variable Volume Primary System Flow Diagram
CW Pumps

35. Variable Volume Primary System Flow Diagram
Cooling Towers

36. Summary
There are many chilled water plants with significant opportunities for improvement
WM Group has a proven record of providing smart solutions that work
We will be happy to review your plant logs with no obligation
1985: $ 0.171/ton-hr
2002: $0.096/ton-hr

37. Thank You WMGroup Engineers, P.C. Hemant Mehta, P.E. President
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