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7.3.3 Domestic Hot Water

Hot Water Plant

The Domestic Hot Water (DHW) Plant shall be located within the Boiler Room or within its own space. All new or replacement DHW Plants shall provide water at 140°F. A main temperature mixing valve shall be used to reduce the water temperature to 120°F for distribution throughout the building. The amount of DHW storage shall be kept to a minimum to reduce energy of the system in not reheating water to maintain temperature. 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.

Venting and combustion air for these systems shall be designed by the Mechanical Engineer and shown on the Mechanical plans.

Materials

Same as Domestic Cold Water. Refer to Chapter 7.32.

Sizing

Piping shall be properly sized to maintain proper water velocities within the piping of between 5 and 9 feet per second. The maximum allowable pressure drop in the system shall be 2 PSI per 100 feet of pipe run. Water velocity is extremely important for the DHW system design. Low water velocity results in pipe scaling, pipe capacity reduction, system capacity reduction, and eventually failure. All pipe sizing shall meet applicable Codes and standards. If considerations are being made for future demand, notes shall be provided on plans and estimates of future demand shall be added to the calculations for the entire system.

Distribution

Same as Domestic Cold Water. Refer to Chapter 7.32.

Valving

Same as Domestic Cold Water. Refer to Chapter 7.32.

DHW Supply Temperatures

DHW shall be distributed throughout the building at 120°F. At each fixture, a pointof-use temperature mixing valve shall be used to reduce the outlet temperature to the specified temperature. All lavatory and other handwashing sinks shall be set for 115°F and Showers at 110°F.

Kitchen Systems

DHW shall be supplied to the Kitchen spaces at 120°F for use in cooking needs and dishwashing (in Food Hall Kitchens only). Point-of-use temperature mixing valves shall be provided for fixtures requiring less than 120°F. A complete list of Kitchen fixtures, with associated flow and temperature requirements, shall be provided by CPS Nutrition Support Services. The EOR shall provide the proper piping to each point of connection and include isolation valves, unions and other elements required for final connection.

Hot Water Return Systems

Hot Water Return (HWR) systems are required shall be installed in all new and major renovation projects. The return system is connected near the end of the DHW supply piping main run. Branch piping shall be included so that hot water is circulated to within 25 feel of all usage points. When metering faucets are in use, recirculation shall be provided to within 2 feet of that faucet. The connection from the DHW system to the HWR system shall be made with a balancing valve to throttle the flow and a check valve to prevent flow reversal caused by fixtures discharging. The piping shall be sized at between 1 and 3 feet per second, well below the DHW system.

Each HWR system shall include a dedicated Recirculation Pump. The total flow of each pump shall be calculated based on system heat loss and each branch flow rate shall be determined based on the ration of that line compared to the total flow. Pumps shall be located within the same room as the DHW Plant.

Thermal Expansion

All DHW and HWR system shall take into account the need for thermal expansion compensation. The use of expansion loops, fittings and thermal expansion tanks shall be used as required.