How to Convert and Optimize Primary/Secondary Pumping Systems to Variable Flow Primary Systems Presented By: Hemant Mehta, P.E. 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) Oldest variable flow primary system 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 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. Louisville Medical Center CW Sump 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 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 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) 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 Duke CCWP-1 Before Duke CCWP-1 After • Dark blue pipe replaces old primary pumps Duke Levine Science Research Center CHW System Duke CIEMAS Building CHW System 90% closed Triple duty valves 50% closed Duke CIEMAS Building AHU-9 Balancing valve 50% closed 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 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 8 Pumps Removed 7 Pumps Removed 3 Pumps Removed Memorial Sloan-Kettering - Before Memorial Sloan-Kettering - After Bypass or removal of pumps Bypass or removal of pump Bypass or removal of pumps Pump Cemetery To date we have removed several hundred large pumps from our clients’ chilled water systems 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? 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? 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 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 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 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 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 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 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 Variable Volume Primary System Flow Diagram Variable Volume Primary System Flow Diagram Chillers Variable Volume Primary System Flow Diagram CHW Pumps Variable Volume Primary System Flow Diagram DP Bypass Variable Volume Primary System Flow Diagram Condensers Variable Volume Primary System Flow Diagram Control Valves Variable Volume Primary System Flow Diagram CW Pumps Variable Volume Primary System Flow Diagram Cooling Towers 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 Louisville Medical Center Chilled Water Operating Data Production 50 Cost 0.200 1985: $ 0.171/ton-hr 45 C H W Pro d u ctio n (m illio n to n -h o u rs) 35 0.150 30 2002: $0.096/ton-hr 25 0.125 20 0.100 15 10 0.075 5 0 0.050 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Year C o st ($/to n -h o u r) 0.175 40 Thank You Hemant Mehta, P.E. President (646) 827-6400 [email protected]