Hot water heating system

The use of hot water heating systems can be seen in many types of buildings and facilities, especially for single-family houses and low rise multiple-dwelling buildings. Many HVAC systems use hot water systems as the primary source for heating the distribution air. The alternate chilled water cooling systems (hydronic cooling) are popular in certain large residential buildings, hospitals, and office buildings. The main components of a hydronic system are:

  1. Boiler (heating source) or Chiller (cooling source)

  2. Circulating pump(s)

  3. Expansion tank(s)

  4. Heating load (radiators, convectors, HVAC units, etc.) or cooling load (terminal units, fan-coil units, HVAC units, etc.)

  5. Air separator

  6. Connected piping system

  7. Make-up and fill water system

  8. Control system.

    The hydronic system consists of

  • Operating temperature;

  • Pumping and piping arrangement

  • Operating pressure.

Depending on the particular application and the type of the facility, the proper selection of the boiler(s) or chiller(s), pumping systems, piping arrangement, and control system are essential for an effective and economical hydronic system. Temperature Classifications.—the temperature classifications of the hydronic systems
can be categorized as

1) Low-temperature water (LTW) system
2) Medium temperature water (MTW) system
3) High-temperature water (HTW) system
4) Chilled water (CW) system
5) Dual temperature water (DTW) system.

Low-Temperature Water (LWT) System: The maximum temperature limitation, in this case, is 250°F, The maximum allowable working pressure is 160 PSIG. The maximum working pressure depends on the static head of the building (height of the building) and the location of the system pump(s). It is recommended for working pressure of higher than 60 psi to use steam to water or water to water heat exchanger(s) so that the heating boiler and its closed piping loop can be separated and to operate at lower operating pressure without being affected by the high system working pressure. Separating the boiler by using heat exchanger(s) from the rest of the system minimizes boiler leaks and prolong the life of the boiler. Medium Temperature Water (MTW) System: In this case, the working temperature is ranged between 250°F and 350°F with an operating pressure of 300 PSIG. The maximum temperature is 400°F. Chilled Water (CW) System: In this case, the chiller(s) operates to provide a supply water temperature of 40 to 55° F, and a pressure of up to 120 PSIG. For temperatures below 40°F, mostly in process applications, antifreeze of brine solution may be used. Dual Temperature Water (DTW) System: In this case, both boiler(s) and chiller(s) are used with the common piping system to provide hot water heating and chilled water cooling. The maximum operating temperature of the heating water is limited to 180°F and
minimum 40°F for the chilled water.

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