Attachment 4 2020-06-12 USGS EROS Mech Narrative Bid Documents

Engineering, Inc.
18207 Edison Avenue
Chesterfield, MO 63005-3715

(636) 530-7770
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