Document M4vvLg9Lp8veaZkKdQ9dXzKEL

556 CHAPTER 21 1958 Guide FEATURES OF HOT WATER SYSTEMS Advantageous features of forced low temperature hot water systems are: 1. The piping need not be run at a definite level or pitch but may change up and down as required by architectural and structural elements of the building. High points should be vented and low points be provided with drain connections. 2. Heat distribution when warming up is uniform. 3. Hot water systems are readily adaptable to simple approximate control of ca Hot Water Heating Systems 557 temperature to fall below.freezing, particularly where coils are used to heat incoming outdoor air or where the heating plant may be shut down for more than 24 hours in cold weather. If the static pressure in the system is high, it may be necessary to use boilers built for operating pressures above 30 psig unless a steam boiler with heat exchanger is used to heat the water. See discussion in this chapter in section Expansion Tanks-and System Pressure Control. DESIGN OF LOW TEMPERATURE HEATING SYSTEM The significant factors affecting the design of low temperature hot water heating systems.are discussed in the sections that follow. pacity and indoor temperature by instruments sensitive to outdoor temperature >" changes. . 4. The system may generally be designed with a minimum of mechanical speci- V.' alties thereby favoring economical maintenance. . 5. Due to practical elimination of air, corrosion within the system is minimized; .- 6. Where extended glass exposures occur, the heating elements, which are relajf^j- tively large because they operate at low temperature, may be well distributed 'under: V such exposures^ to counteract downdrafts. " ;V'; ' 7. Quiet operation may be expected in a properly designed and installed system.^ In the design and operation of forced circulation systems, it is necessary1 to take precautions against any condition that would permit the water Fig. 2. Mass Flow and Specific Heat of Water (Specific heat is for pressure at saturated liquid temperature) loasic data for calculation and construction of curves from Keenan and Keyes)1 . Heat Loss Calculations adequacy as well as the proper distribution of the heat in a building SfI+b a water system depends primarily on the proper .calculation pi the heafcloss for the individual spaces and the accurate sizing Of the heat- 'j^ts to;offset those heat losses. Heat loss should be determined in accordance with the principles discussed in Chapter 12, Heating Load. Selection and Location of Heating Units s^0rmation on the types of room heating units available for hot water ystems will be found in: Chapter 22,.Radiators and Convectors;.Chapter Whilfh Seating; and Chapter 24, Unit Heaters and Unit Ventilators. ...nue the style or type of unit selected for a given space may depend on