B08_Attachment_4_2020-06-12_USGS_EROS_Mech_Narrative_Bid_Documents.pdf
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- Solicitation number
- 140G0126Q0288
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This is a 100% Design Submittal for the EROS Condenser Water System project located in Sioux Falls, South Dakota, prepared by SSC Engineering, Inc. under Contract Number 140G0118D0013, dated June 12, 2020.
The project involves redesigning the condenser water system to accommodate a 600-ton peak cooling load. The mechanical design includes three 300-ton chillers configured to provide N+1 redundancy at peak load, with chillers capable of increasing condenser leaving water temperature above 100 degrees to enhance AHU preheat coil capacities. The design addresses existing operational issues by upgrading suction and feed piping from 8 inches to 10 inches through a new pipe chase to improve net positive suction head and balance condenser water distribution across the chiller array. New piping serving AHUs and CRACs has been increased by one pipe size to accommodate future capacity changes. CRAC unit taps and runouts are sized at 3 inches to support approximately 50-ton CRAC units at each tap. The project eliminates the open cooling tower heat exchanger loop to reduce maintenance, cost, and complexity while increasing system efficiency, consolidating tower water and condenser water onto a single piping loop with proper water treatment to prevent corrosion. Four Baltimore VTL-209 cooling towers will replace existing VTL-185 towers in the penthouse, utilizing the same physical space and operating with variable frequency drive (VFD) fans at 70% speed to draw 40% total peak power while allowing year-round operation with basin heaters. This approach provides the least installation complexity and highest operational efficiency compared to alternative configurations involving air-cooled chillers.
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Engineering, Inc.
18207 Edison Avenue (636) 530-7770 Chesterfield, MO 63005-3715 www.sscengineering.com
EROS Condenser Water System Sioux Falls, SD
Contract Number: 140G0118D0013
June 12, 2020
100% Design Submittal
Mechanical System Design Criteria:
This project was designed around a 600 peak load. Piping and equipment is sized to accommodate a 600 Ton load.
(3) 300 ton chillers will allow for (1) chiller to be redundant at peak load. The new chiller is intended to match the existing and provide N+1 redundancy. The Condenser leaving water temperature of these chillers is able to be increased to more than 100 degrees as desired to increase the AHU preheat coils capacities.
The condenser water pumps are gravity feed from the open penthouse tower. Currently there is a net positive suction head issue with an 8” suction feed and operating 2 pumps concurrently. By utilizing a 10” pipe through the pipe chase, the return water velocity with 2 pumps operating will be equal to that of 1 pump operating with an 8” suction pipe.
Currently there is also an issue balancing the condenser water feed to the chillers. By installing a new 10” feed pipe that supplies condenser water to the far end of the chiller array first, the chillers will have an equal pressure drop to all condenser coils, allowing for easier balancing.
This project replaces the chilled and condenser water pipe that serves AHUs, CRACs, etc. New piping serving the equipment taps and control valves to AHUs have been increased by one pipe size over the existing AHU capacity. This allows for future space capacity changes in the system. The details of these expansions/changes are unknown at this time.
The new condenser water and chilled water piping will be routed through a new pipe chase.
This chase runs through office 1414. This office will need to be re-arranged to allow for the new chase.
Taps and runouts for CRAC units are all sized at 3”. This allows for a ~ 50 ton CRAC unit to be installed at each tap.
An air-cooled chiller was investigated to be used for operation during the heating season. This chiller would have been placed on the roof and used to trim the remaining heat from the condenser water loop after the AHU pre-heat coils were used. This would also allow for all of the towers to be drained down during the winter months. This air-cooled chiller would replace a cooling tower and operate during summer months to cool condenser water.
Adding an air-cooled chiller in place of an open tower and an additional chiller will add complexity to the system. The Air-cooled chiller would be low maintenance, but it would still need to work in conjunction with the open towers, so that advantage would be diminished. The initial cost of an air-cooled chiller and associated additional piping, structure on the roof and heat exchanger would be much higher than an
EROS Data Center, Sioux Falls, SD Contract Number 140G0118D0013 DD Submittal additional water to water chiller and open tower. An air-cooled chiller operates at ~ half the total efficiency across the operating temperature profile.
Because of the 85 degree condenser water being used for AHU re-heat in the winter months, there isn’t a way to provide a “free cool” mode, where the chiller can be shut down and bypassed to allow the chill water to pass directly to the tower heat exchanger. The chiller is required to “heat” the condenser water to a temperature usable for the AHU preheat coils.
There is a desire to increase the condenser water temperatures in order to provide more heat capacity to the AHU preheat coils. Currently there is a current limit issue on the chillers that doesn’t allow for elevated condenser water temperatures. According to York this current limit is adjustable. If this current limit is reset to match the breaker, elevated condenser water temps maybe achieved during heating season to provide more capacity to the preheat coils.
The decision was made to eliminate the open cooling tower heat exchanger loop, which will reduce maintenance, cost, complexity and increase efficiency. This puts the tower water and the condenser water on the same piping loop. With proper water treatment, this should not cause corrosion problems.
The larger capacity Baltimore VTL-209 fits within the constraints of the penthouse, and has the same physical dimensions of the VTL-185 tower it replaces. Using the existing cooling tower locations reduces cost and complexity. Most ducted towers are tall, and fluid coolers are typically twice the size of an open towers. utilizing open towers with VFD fans, is optimal for efficiency can operate year-round.
The new open towers can be drained during winter months, if not in use, but with basin heaters and VFD fan control, these towers can operate year-round along with providing higher efficiency. Using (4) towers will meet the capacity demands of the system while allowing the fans to run at 70% speed and draw 40% total peak power. Having (4) towers allows for 1 to run at higher capacity during winter months which increases efficiency during colder months.
Utilizing open towers in the existing tower locations provides the least complexity, installation cost, and highest efficiency.
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