7.2.3 System Sizing | Chicago Public Schools

Domestic Hot Water Plant

Provide a minimum of two tank type centralized, self-contained, gas fired domestic water heaters (high efficiency condensing type preferred), sized at 75% of system capacity each in Boiler Room to serve building hot water. Heaters shall operate at 140°F to minimize growth of legionella. On projects where gas boosters are provided (for heating hot water systems), include a set of dry contacts on each water heater to engage the booster upon a call for heat. Do not provide gas boosters solely for domestic water heating. Water heaters shall be sized according to the methods developed by ASHRAE and ASPE. Provide each heater with an ASME constructed expansion tank.

General building distribution shall be served with master high-low thermostatic mixing valve assembly to maintain building distribution system at 115°F supply and return having a dedicated building circulating pump. Hot water shall be circulated to within 25 feet of all usage points, however if metering faucets are used, recirculation shall be provided within two feet of the fixture. The on/off operation of the 120°F water recirculation pumps shall be controlled by an aquastat or programmable time clock. Provide point-of-use temperature mixing valves at all faucets and shower heads to achieve code allowable temperatures at all fixtures.

As an option to centralized hot water heating, a system utilizing point-of-use water heating at remote locations may be utilized if all codes, standards and end-use requirements are met. Use of these systems shall be approved by the Design Manager during design. If used for supply to an Emergency Shower or Eyewash, the system shall have the ability to provide the proper temperature for the total duration required per Code.

Domestic Booster Pump Systems

Provide a constant or variable speed duplex domestic booster pump package with a bladder-type compression tank to meet the flow and building water pressure requirements. Each pump shall be sized for 65% of total system capacity. Overall pump system capacity shall be sized for 75% of maximum flow rate as determined using the fixture unit method outlined in the Chicago Building Code. The pump shall include a protocol interface to the building automation system. Minimum mapped points shall include enable/disable, suction/discharge pressure, discharge pressure setpoint, each pump status/speed and general alarm. Coordinate with mechanical/BAS.

Sump Pumps

Sump pumps systems shall be used for all buildings drains and drain tile systems that cannot flow directly to the sewer by gravity alone. A duplex system shall be used to provide redundancy in the system. Each pump shall be sized for 70% of the maximum calculated flow rate and 100% of the required dynamic head. The system controls shall include a lead/lag option to alternate the pump operation at every 50 hours of operation. The sump basin shall be vented to eliminate the presence of hydrogen sulfide gas, which may damage drain piping. A sump system shall have a submerged pump, with the motor located above the pit cover and be operated by a series of float switches.

If the building includes an elevator, an elevator pit pump shall be provided with all related controls and systems. If hydraulic elevators are being utilized on the project, the elevator sump pump system shall be equipped with an alarm and oil minder system. The discharge from this system shall be routed to the nearest indirect sanitary discharge location capable of receiving sump pump’s design flow rate. Discharge shall not drain into another sump type system; it shall discharge to a gravity drain location.

If applicable, Sump systems shall be added to any emergency power system serving the building.

Coordinate with temperature controls to provide a separate set of floats for high water alarm on the building automation system. Locations of all pump controllers shall be shown on plans and coordinated with all trades.

Ejector Pumps

An ejector pump is designed to transport sanitary waste and larger solids suspended in the effluent. An ejector basin shall be of airtight construction and shall be vented. It is airtight to prevent the escape of foul odors generated by sanitary waste from the sub-drainage system. Because it is airtight, a vent is required to relieve the air in the basin as wastes discharge into it and also to supply air to the basin while the contents are being discharged to the sanitary gravity drainage system. This vent shall never be capped due to odors because it is imperative to vent the hydrogen sulfide gases from the basin.

A duplex system shall be used to provide redundancy in the system. Each pump shall be sized for 70% of the maximum calculated flow rate and 100% of the required dynamic head. The system controls shall include a lead/ lag option to alternate the pump operation at every 50 hours of operation.

An ejector system shall feature full submerged pump and motor assemblies and shall be operated by a float switch.

Collection Basins and Tanks

Basins are shall be steel or cast iron. Sump pits shall be cast-in-place concrete. All sidewall pipe connections shall be factory made or field fabricated for concrete pits. Covers shall be fabricated with all required openings for mechanical systems, pipe connections, power and controls. Gaskets, seals and bushings shall be included.