Document zxJa1oKVG6QJ96moEL67Jd33

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 Flow meters using an orifice, Venturi tube, flow nozzle, or Pitot tube as the primary device are made by a number of manufacturers and can be obtained in either the mechanically or electrically operated type. The electric flow meter makes it possible to locate the instruments at some distance from the primary element. Flow meters employing the orifice, Venturi tube, flow nozzle or Pitot tube should be so selected as to keep the lower operating range of the load above 20 per cent of the capacity of the meter. This is desirable for accuracy as the differential pressure at light loads is too small to properly actuate the meter. A few general points to be considered in installing a meter of this type are: 1. It is desirable to place the differential medium in a horizontal pipe in preference to a vertical one, where either location is available. CHAPTER 16. DISTRICT HEATING by using a consumption of- 0.0025 lb per day per cubic foot of heated space for office buildings, and 0.0065 lb per day per cubic foot for apartment houses. Additional data on steam requirements of various types of buildings in a number of cities may be found in the Handbook of the National District Heating Association. RATES Fundamentally, district heating rates are based upon the same princi ples as those recognized in the electric light and power industry, the main object being a reasonable return on the investment. However, there are Fig. 8. Vacuum Condensation Meter Installation without Master Trap 2. Reservoirs should always be on the same level and installed in accordance with the instructions of the meter company. 3. The meter body should be placed at a lower level than that of the pressure differ ential medium. Special instructions are furnished where the meter body is above. 4. Meter piping should be kept free from leaks. 5. Sludge should not be permitted to collect in the meter body. 6. The meter body and meter piping should be kept above freezing temperatures. 7. It is best not to connect a meter body to more than one service. 8. Special instructions are furnished for metering a turbulent or pulsating flow. STEAM REQUIREMENTS Steam requirements for heating various types of buildings are given in Chapter TO. Steam requirements for water heating can be satisfactorily estimated ; Fig. 9. Orifice Meter Steam Supply Connection other requirements to be met; the rate for each class of service should be based upon the cost to the utility company of the service supplied and upon the value of the service to the consumer, and it must be between these two limits. District heating rates should be designed to produce a sufficient return on the investment regardless of weather conditions, although existing rate schedules do not conform with this principle. Lastly, the rate schedule must be reasonably easy for the intelligent lay man to comprehend. Depreciation should be based on a careful estimate of the life of various elements of the property. Appropriations to reserves should be made, with generosity in good years and with discretion in less favorable years. Glossary of Terms Load Factor. The ratio, in per cent, of the average hourly load to the t 319