Document Lp75MN5pdXorQOKkJXDXQL6d7

HEATINC VENTILATING AIR CONDITIONING GUIDE 1941 tion of the day switch and entirely cut off the supply of steam to the radiation at night during certain hours which are selected by the operating engineer. The maximum in economical operation and satisfactory heating can only be obtained by the use of some automatic temperature control system. FLUID METERS The perfection of fluid meters has contributed more to the advance ment of district heating than any other one thing. These meters may be classified as follows: 1. Positive Meters: The fluid passes in successive isolated quantities--either weights or volumes. These quantities are separated from the steam and isolated by alternately filling and emptying containers of known capacity. 2. Differential Meters: In the differential meter, the quantity of flow is not determined by simple counting, as with the positive meter, but is determined from the action of the steam on the primary element. Additional sub-divisions of these two general classifications can be made as follows: Fluid Metem Positive - Quantity Weighing Volumetric Quantity - Current - Turbine Weighers Tilting trap Rotary Bellows Differential Rate of flow Head (Kinetic) Area (Geometric) Venturi Flow nozzle Orifice Pitot tube Orifice and plug Cylinder and piston Head area (Weir) V-notch Special notch In selecting a meter for a particular installation, the number of different makes and types of meters suitable for the job is usually limited by one or more of the following considerations: 1. Its use in a new or an old installation. 2. Method to be used in charging for the service. 3. Location of the meter. 4. Large or small quantity to be measured. 5. Temporary or permanent installation. 6. Cleanliness of the fluid to be measured. 7. Temperature of the fluid to be measured. 8. Accuracy expected. 9. Nature of flow: turbulent, pulsating, or steady. 10. Cost. (o) Purchase price. (b) Installation cost. (z) Calibration cost. (d) Maintenance cost. 11. Servicing facilities of the manufacturer. 12. Pressure at which fluid is to be metered. 13. Type of record desired as to indicating, recording or totalizing. 14. Stocking of repair parts. 316 CHAPTER 16. DISTRICT HEATINC 15. Use of- open jets where steam is to be metered. 16. Metering to be done by one meter or by a combination of meters. 17. Use as a check meter. 18. Its facilities for determining or recording information other than flow. ' Condensation Meters The majority of the meters used by district heating companies in the sale of steam to their customers are condensation meters. The condensation meter is a popular type for use on small and medium sized installations, where all of the condensate can be brought to a com mon point for metering purposes. Its simplicity of design, ease in testing, accuracy at all loads, low cost, and adaptability to low pressure distri bution has made it standard equipment with many heating companies. Two types of condensation meters are in general use: the tilting bucket meter and the revolving drum or rotor meter of which there are several makes on the market. Condensation meters should not be operated under Fig. 7. Gravity Installation for Condensation Meter Using Vented Receivers pressure; they are made for either gravity or vacuum installation. Con tinuous flow traps are necessary ahead of the meter if a vented receiver is not used. Where bucket traps are used, a vented receiver before the meter is essential. If desirable a receiver may be used with a continuous flow trap, but this is not necessary. Fig. 7 illustrates a gravity installation using a vented receiver ahead of the meter, while Fig. 8 shows a vacuum installation without a master trap. Flow Meters Steam flow meters are available in many types and combinations. The orifice and plug meter is one in which the steam flow varies directly as the area of the orifice. The vertical lift of the plug, which is proportional to the flow, is transmitted by means of a lever to an indicator and to a pencil. arm which records the flow on a strip chart. The total flow over a given period is obtained by measuring the area by using a planimeter on the chart and applying the meter constant. Fig. 9 shows a typical-orifice-type meter connection and indicates typical requirements in the installation of this type of meter. 317