Document Z8yZeqgvY35p1y8VZoD331JGZ

118 CHAPTER 7 1962 Guide And Data Book United States because of practical and economic difficulties. The use of high-pressure, high-temperature water distribu tion at 275 to 400 F has found favor in Europe, where fuel is scarce and is finding some application in the United States* High-pressure water distribution has some practical economic advantages over steam (see Chapter 29 High Tem perature Water Systems). Higher thermal efficiencies better daily and annual system load factors, lower water treat ment costs, smaller pipe sizes,- fewer piping accessories, and feasibility of installing pipe to follow contour of ground are given as a few. On the other hand hot water requires a two-pipe distribution system which increases the capital in vestment in some cases. System maintenance is enmplifgfavJ by thenecessity to drain at least a portion of the system when connections are made or leaks repaired. The advantages of hot water have exceeded the disadvan tages in some industrial applications and in Air Force bays in this country. As the cost of fuel increases, additional ap plications will probably become practicable, especially in new installations serving buildings designed for hot water heat ing.1 REFERENCES *P. L. Geiringer: Recent developments in high temperature water for area beat distribution in the United States '{National District Heating Association Proceedings, 1956). * Steam requirements for processes, maximum demand and load factor (District Heating Handbook, National District Heating Association, 3rd ed, p. 346). 'Influence of pressure (District Heating Handbook, National District Woai.'ng Association, 3rd ed, p. 147). 4 Effect of looping (.District Heating Handbook, National District Heating Association, 3rd ed, p. 155). 4 American Standard Code for Pressure Piping (American Standards Association, B 31J, 1955, p. 66). 4 Steam pressure boosters (District Heating Handbook, Na tional District Heating Association, 3rd ed, p. 329). 'Graphical. Solution of Vntoin's Formula (chart published by the National District Heating Association). For explana- tun of chart see District Heating Handbook (National D. trict Heating Association, 3rd ed, p. 194). 4 Gordon Carlson: ' Improved method of supporting steata pipes in tunnels (National District Heating Association Pro. ceedingt, 1955, p. 125). 'District heating piping systems, and Fabrication detail (American Standard (7ode for Pressure Piping, American Standards .Association, B 31.1, 1955, Sections 4 and 6). "Piping, valves, fittings and accesories (District Heating Handbook, National District Heating Association, 3rd ei. d 169). . "Steam traps and drain pockets (District Heating Hand book, National District Heating Association, 3rd ed, p. 175) "Control of steam flow (District Heating Handbook, Na tional District Heating Asodation, 3rd ed, p. 211). "The reinsulation of underground cteam (National District Heating Association Proceedings, 1945, p. 21). M Underground insulation specifications. Thermal conductiv ity, Steam pipe'insulation. Soil temperature surrounding a buried steam line, and Heat loss from insulated buried steam line (District Heating Handbook, National District Association, 3rd ed, p. 162, p. ISO, p. 1S4, p. 188, and p. 189, respectively). "Sabin Crocker: Heat loss (Piping Handbook, McGraw-Hill Book Co, 1955, 4th ed, p. 1016). "Return of condensate (District Heating Handbook,- Na tional District Heating Association, 3rd ed, p. 15S). " Reducing and relief valves on consumers' premises (Ameri- can Standard. Code for Pressure Piping, American Standards Association, B 3U, 1955, p. 66). "Temperature control (Principles of Economical Heating, National District Heating Association, 5th ed, p. 25). "Hours of heating (Principle* of Economical Heating, Na tional District Heating Association, 5th ed, p. 22). "H. T. Kucera: New developments in programming build ing heating (National District Heating Association Proceed ings, 1956). " Utilization of heat in condensate (Principles of Economical Hearing, National District Heating Association, 5th ed, p. "Metering (District Heating Handbook, National District Heating Association, 3rd ed, p. 221). "Hot water for district heating (District Heating Handbook, National District Heating Association, 3rd ed, p. 423). CHAPTER 8 HOT WATER HEATING SYSTEMS ("eafvrcx and Design of low Temperature Hot Wafer Systems; Two-Pipe, One-Pipe, and Series-loop System^ Piping Principles} Circulating Pumps; Expansion Tanks; Boiler Room Piping; Use of Sfeam; Temperofure Control; System Adjustment; Cleaning Systems AHOT WATER heating system is one in which water is useti to convey heat by flowing through pipes connect 4. The system may generally be designed with a minimum of mechanical specialties thereby favonng economical mainte nance. ing a boiler or water heater with radiators, convectors, or 5. Due to practical elimination of air, corrosion within the other suitable heat distributing means. The systems discussed system is minimized. in this chapter have supply water temperatures less than 250 F and are classified as Low Temperature Systems. Sys tems having supply water temperatures above 250 F are classified`as High Temperature Systems and are discussed in Chapter 9. Classified according to the means of generating flow, hot water heating systems are of two types: the Grav ity-System in which circulation of the water is due to the difference in weight between the supply and return water ^himns of any circuit or system, and the Forced System in which a pump, usually driven by an electric motor, maintains the necessary flow. ffipiy the available bead or force producing circulation in a gravity system is limited, the piping must be of such size that the friction loss at the desired flow is not in excess of the available head. Gravity circulation heads which can be obtained with vari ous supply and return temperatures are shown in Fig. 1. The 6. Where extended glass exposures occur, the heating ele ments, which are relatively large because they operate at low temperature, may be well distributed under such exposures to counteract downdrafts. 7. Quiet operation may be expected in a properly designed and installed system. In the design and operation of forced circulation systems, it is necessary to take precautions against any condition that would permit the water 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 neces sary 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. harif principles which determine design in gravity and forced systems are the same but since the former has less total head available to produce flow, greater precautions are necessary DESIGN OF LOW TEMPERATURE HEATING SYSTEMS in design to secure even distribution of heat with gravity sys tems. Complete details on the design of gravity type systems are contained in editions of the Heating Ventilating Am Conditioning Guide issued before 1957. Fig. 1 is also useful in determining effects due to temperature difference in forced The significant factors affecting the design of low tem perature hot water heating systems are discussed in the sec tions that follow. Heat Loss Calculations systems when large elevation or temperature differentials occur. This chapter is devoted to the design of forced hot water systems using supply water temperatures below 250 F. The selection of type of distribution system for heating-a particular building should be based upon an objective analy' sis of the characteristics of the building, the comfort and temperature conditions required, the system operating and The adequacy as well as the proper distribution of the heat m a building served by a hot water system depends primarily' on the proper calculation of the heat loss for the individual spaces and the accurate sizing of the heating units to offset those heat losses. Heat loss should be determined in accord ance with the principles discussed in Chapter 25 of the 1961 Guide And Data Book. maintenance characteristics, the space available for piping Selection and Location of Heating Units and equipment, and the economics involved. Information on the types1 of room heating units available FEATURES OF HOT WATER SYSTEMS ' for hot water systems will be found in Chapters 45 and 46 of Advantageous features of forced low temperature hot wa ter systems are: the 1961 Guide And Data Book and Chapter 10 of this volume. While the style or type of unit selected for a given space may depend on personal preferences of the purchaser, 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 ap proximate control of capacity and indoor temperature by instruments sensitive to outdoor temperature changes. the designer should make certain that the heat output atTthe water temperature available is equivalent to the calculated heat loss from the space. The heating units within each separately controlled cir cuit should be of similar types, for example: either all castiron or all fin-tube convector-type units. Fan units should not be included in a controlled direct radiation zone. The U9