Domestic Hot Water System, What is domestic hot water system

Domestic hot water speaks to what is domestic hot water and how does a domestic hot water system work in a building.

To explain the DHW system it is required to understand that the system heats cold water to produce domestic hot water for building use. It is suggested that the domestic hot water temperature be maintained at a minimum of 120 F, to satisfy health code requirements.

Ensure the temperature of the domestic hot water is not controlled too high, as scalding could occur.

Theory of Operation

The boilers heat water to 140F and provide it to the storage tanks. This 140 water is provided to one of the inlets of the low and high capacity mixing valves. City water is provided to the other side of the mixing valves.

The mixing valves set points are adjusted to 120F.

If the low capacity mixing valve can't supply enough system water the system pressure begins to drop. The pressure regulating valve at the outlet of the high capacity mixing valve starts to open and maintains capacity.

Explain Domestic Hot Water Components

The domestic hot water system may consist of:

  • Boilers

  • gas fired.
  • electric.

  • Heaters

  • gas fired.
  • electric.

  • Pumps.

  • Boiler to storage tank to system.
  • Hot water return from system.

  • Storage tank or tanks.

  • Mixing valves.

  • High capacity.
  • Low capacity

  • City makeup water system through mixing valves.

  • High capacity makeup pressure regulating valve.

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