Document B5y9JZeEoK9LGLozRJjpxv2Qj

600 CHAPTER 29 1949 Guide principally to insure satisfactory and economical service to the consumer. There are certain fundamental principles that should be followed in the design of a building heating system which is to be supplied from street mains. Although some of these apply to any building, they have been demonstrated to be especially important when steam is purchased. .1. Provision should be made for conveniently shutting off the steam supply at night and at other times when heat is not needed. It has been thoroughly demonstrated that a considerable amount of heat can be saved by shutting off steam at night. Although there is, in some cases, an increased consumption.of heat when steam is again turned on in the morning, there is a large net saving which may be explained by the fact that the lower inside temperature maintained during the night obviously results in lower heat loss from the building, and less heat need therefore be supplied. . Steam can be entirely shut off at night in most buildings even in very cold weather without endangering plumbing. It is necessary, however, to have an ample amount District Heating . .> 60D ' Because of the lack of coincidence between the heating system load and the hot; water demand, a greater amount of heat can be extracted from the condensate if; storage capacity is provided for the. preheated water. Frequently a type of econ omizer is used in which the coils are submerged in a storage tank. ' 5. Heat supply should be graduated according to variations in the outside temperature. - The maximum in economical operation and satisfactory heating can only be ob tained by the use of some automatic temperature control system. ! . METERING The perfection of fluid meters has contributed as much to the advance ment of district heating as any other one thing. Meters are classified into two groups: Condensate Meters and Rale of Flow Meiers. Condensate Meters The one type of quantity meter used is the condensate meter, which may be of the tilting bucket or revolving drum type. The condensate meter is a popular type for use on small and medium Fig. 5. Method or Installing a Water Heater and Economizer in a Gravity Heatinq System of heating surface so that the building can be quickly warmed in the morning. Where . the hours of occupancy differ in various parts of the building, it is good practice to install separate supply pipes to the different parts. For example, in an office build ing with stores or restaurants on the first floor whi^h are open in the evening, a sepa- rate main supplying the first floor will permit the steam to be shut off from the remainder, of the building in the late afternoon. The division of the building into zones each with a separately controlled heat supply is sometimes desirable, as it permits the heat to be adjusted according to variations in sunshine and wind. S.. Residual heat in the condensate should be salvaged. Tins heat may be salvaged by means ,of a cooling coil, or as is more frequently done, by a water heating economizer (see Fig. 5) which preheats the hot water supply to the building. l ; The.condensate from the heating system, after leaving the trap, passes through the:economizer. The supply to the.hot water heater passes through.the economizer, absorbing heat-from.the condensate. If the hot water system in the building is of the recirculating type, the recirculating connection should be tied in between the economizer and the water heater proper, not at the economizer inlet, because the recirculated hot water is itself at a high temperature. Fig. 6. Gravity Installation for Condensation Meter Using Vented Receivers sized installations, where all the condensate can be brought to a common point for metering purposes. Its simplicity of design, ease in testing, ac curacy at all.loads, low cost, and adaptability to low pressure distribution has made it standard equipment with many heating companies. Condensate meters should not be operated under pressure; They .are-! made for either gravity or vacuum installations. Where bucket traps am used, a vented receiver is essential ahead of. the meter. Where continuous- flow traps are. used, a vented receiver, is not necessary, but is desirable.. Fig. 6 illustrates a gravity condensate.meter installation using a vented'; receiver. - Rate of Flow or Flow Meters Flow meters used for district heating work are of three types:. Area . Meters, Head Meters and Velocity Meters. (See Chapter 4,' Fluid Flow.);. Area.meters are those, in the operation of which, a variation in the cross-., section of stream under constant head is used as an indication of the rate: of flow. A tapered plug is suspended in an orifice and. moves axially with the flow, which is vertically upward. . The., weight of the plug provides, a definite pressure differential and the plug floats at such a height as will provide enough orifice area to pass the flow at the pressure difference. The.