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

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Presentation on theme: "How to Convert and Optimize Primary/Secondary Pumping Systems to Variable Flow Primary Systems WM Group Engineers, P.C. Presented By: Hemant Mehta, P.E."— Presentation transcript:

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

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 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 Duke University Background

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 Balancing valve 50% closed Duke CIEMAS Building AHU-9

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 3 Pumps Removed 7 Pumps Removed 8 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

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 dont 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 dont 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 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 Hemant Mehta, P.E. President WM Group Engineers, P.C. (646)


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