Document ppNv6ZbX1vxR0rxeDxkLvx1KE

HEATING VENTILATINC AIR CONDITIONING GUIDE 1940 maximum hourly load. This is usually based on a one year period but may be applied to any specified period. Demand Factor. The relation between the connected radiator surface or required radiator surface and the demand of the particular installation. It varies from 0.25 to 0.3 lb per hour per square foot of surface. Diversity Factor. The ratio of the sum of the individual demands of a number of buildings to the actual composite demand of the group. Types of Rates A. Flat Rates. 1. Radiator surface charge. Obsolescent. B. Meter Rates. 1. Straight-line. 2. Step. Obsolescent, 3. Block. (a) Class rates. C. Demand Rates. 1. Flat demand. 2. Wright. 3. Hopkinson. 4. Doherty (or Three charge) Straight-Line Meter Rate. The price charged per unit is constant, and the consumer pays in direct proportion to his consumption without regard to the difference in costs of supplying the individual customers. Block Meter Rate. The pounds of steam consumed by a customer are divided into blocks of thousands of pounds each, and lower rates are charged for each successive block consumed. This type of charge predominates in steam heating rate schedules for it has the advantage of proportioning the bill according to the consumption and the cost of service. It has the disadvantage of not discriminating between customers having a high load factor (relatively low demand) and those having a low load factor (relatively high demand). The utility company must maintain sufficient capacity to serve the high demand customers and the cost of the increased plant investment is divided equally among the users, so the high demand customers are benefitted at the expense of the others. Demand Rates. These refer to any method of charge based on a measured maximum load during a specified period of time. The flat demand rate is usually expressed in dollars per M lb of demand per month or per annum. It is based on the size of a customer's installation, and is seldom used except where a flow meter is not practicable. The Wright demand rale is similar in calculation to the block rate except that it is expressed in terms of hours' use of the maximum demand. It is seldom used but forms the basis for other forms of rates. The Hopkinson demand rate is divided into two elements: () A charge based upon the demand, either estimated or measured. () A charge based upon the amount of steam consumed. This rate may be modified by dividing the quantities of steam demanded and consumed into blocks charged for at different rates. The Doherty rate is divided into three elements: (a) A charge based upon demand. (b) A charge based upon steam consumed. (e) A customer charge. In the Hopkinson rate, the last two elements are combined into one element. Demand rates are comparatively new and are not yet widely used; though they are equitable and competitive they are difficult for the average layman to understand. 738 CHAPTER 43. DISTRICT HEATING They are of benefit to utility companies and to consumers because the investment and operating costs can be divided to suit the particular circumstances into demand, cus tomer, and consumption groups through the use of some modification of the Hopkinson rate. Demand rates are an advantage to the customer in that the use of such a rate reduces the rate per thousand pounds to the long-hour user. Fuel Price Surcharge. It is usually desirable to establish a rate upon a specified basic cost of fuel to the utility company. Where there are wide variations in the price of fuel, it is also desirable to add a definite charge per M lb of steam sold for each increment of increase in the price of fuel. This surcharge automatically compensates for the variations without necessitating frequent changing of the whole rate structure. UTILIZATION Considerable savings can be made by the proper and intelligent oper ation of heating systems. It should be borne in mind that a heating system is designed to heat a building to 70 F inside when the outside temperature is at its lowest point for that particular locality. There is a tendency to overheat the building at any time the outside temperature is above the design temperature unless some method of regulation is used, either automatic or manual. The general rules for economical operation are as follows: 1. Weatherstrip all windows, and calk all window frames. 2. Provide revolving or vestibule doors on all entrances. Separate shipping and receiving rooms by partitions so that the ever-open large doors will not ventilate the entire building. 3. Keep the radiation near the outside walls, under the windows, if possible. 4. Eliminate all unnecessary ventilation. Ventilating equipment is sized to meet extreme requirements. Do not supply ventilation to a theater or auditorium adequate for an audience of 2000 when there are only 200 present. 5. Determine the hours that heating is required during the day and see that the steam is shut off for the maximum time at night, on Sundays, and holidays. 6. Shut steam off entirely in unoccupied sections of the building, taking care to avoid freezing the water in the plumbing system. 7. Shut off steam during the day whenever possible. During the year steam can be shut off about 55 per cent of the total daytime, the saving is proportional. An automatic control will do it, but it can be done by hand with amazingly good results. 8. Determine the temperature required for the occupancy of the building. Do not heat a storage garage or a furniture warehouse to the temperature required in a hospital ward. 9. Provide some good means of temperature control. 10. In a hot water heating system keep the temperature of the water down to corre spond with existing outdoor temperatures. 11. In a vacuum system maintain a high vacuum. If this is not possible, locate and eliminate all leaks. 12. Install separate lines for those parts of the building that require long-hour or all-night heating. It is much cheaper than heating the entire building all night. 13. See that the entire system responds rapidly when steam is turned on. Locate and eliminate the cause of any sluggish circulation. Balance the radiation, provide adequate air elimination, and correct any trapped run-outs to provide quick system drainage. 14. Keep the system in good repair. Worn, damaged, or defective valves and traps will not function properly. 15. Insulate all steam pipes not used as heating surface. 16. Do not obstruct radiators or prevent the free circulation of air around them; to do so seriously reduces the heating capacity of a radiator. 17. Extract the heat in the condensate for hot water or some other useful purpose. 18. Provide thermometers and recording pressure gages so that the engineer can operate the system with full knowledge of what he is accomplishing. 739