Document B8RodzgKxN6JQdQ0ek0EDJd6w

1078 CHAPTER 49 1954 GuidT any house or apartment. Table 8 gives estimates of the maximum hot' water requirements in 24 hr in various types of buildings. In estimating the size of hot water storage tank required, and the heating capacity to be provided, either from the boiler or from an independent domestic hot water heater, it is necessary to know the total quantity of water to be heated per day, and the maximum amount which will be used in any one hour, as well as the duration, of the peak load. In cases where the requirements for hot water are reasonably uniform, as in residences, apartment buildings, hotels, and the like, smaller storage capacity is required than in the case of factories, schools and office build ings, where practically the entire day's usage of hot water occurs during a very short period. Correspondingly, the heating capacity must be pro portionately greater with uniform usage of hot water than with inter mittent usage, where there may be several horns between peak demands during which the water in the storage tank can be brought up to tempera- Table 9. Estimated Hot Water Demand Characteristics for Various Types of Buildings Type of Building Hot Water Required Max. Hourly Demand in Relation to Day's Use Duration of Peak Load Hours Storage Capacity in Relation to Day's Use Heating Capacity in Relation to Day's Use Residences, apartments, hotels, etc. Office buildings Factory buildings 40 gal per person per day* 2 gal per person per day4 5 gal per person per day* 1/7 1/5 1/3 4 V5 2 1/5 2/5 1/7 1/6 1/8 Restaurants Restaurants 3 meals per day Restaurants 1 meal per day 1/10 1/10 1/10 8 1/5 1/10 1/5 2 2/5 1/6 At noF ture. As a general rule, it is desirable to have a large storage capacity in order that the heating capacity, and consequently the size of the heater, or the load on the heating boiler, may be as small as possible. In estimating the hot water which can be drawn from a storage tank, it should be borne in mind that only about 75 percent of the volume of the tank is available, since, by the time this quantity has been drawn off, the incoming cold water has cooled the remainder down to a point where it can no longer be considered hot water. Where steam from the heating boiler is used to heat domestic hot water, the computed load on the boiler should be increased by 4 sq ft BDR (equiva lent direct radiation) for every gallon of water per hour heated through a 100 deg rise. The actual requirement is (100 X 8.33)/240 = 3.48 sq ft pr gal heated 100 deg. The value of 4 allows for transmission losses. There are two methods in common use for estimating the hot watei requirements of a building: (1) by the number of people, and (2) by the number of plumbing fixtures installed. Where the number of people to be served can be reasonably estimated, the data in Table 9 may be used. Example S: Determine the heater size and storage tank capacity for a residence housing five people. Solution: From Table 9, a residence housing five people would have a daily re" Water Services 1079 quirement of 5 X 40 = 200 gal. per day, and a maximum hourly demand of 200 X 1/7 = 28.5 gal. The heater should have a storage capacity of 200 X 1/5 = 40 gal, and a heating capacity of 200 X 1/7 = 28.5 gal per hr. The conditions given in Example 8 may be cited as average. It is pos sible to vary the storage and heating capacity by increasing and decreasing one over the other. Such a' condition is illustrated in Example 4- Example 4: Determine the required heater capacity for an apartment housing 200 people, if the storage tank has a capacity of 1000 gal. What heater capacity will be required if the storage tank is changed to 2500 gal capacity? Solution: Assume an apartment house housing 200 people. From the data in Table 9: Daily requirements = 200 X 40 = 8000 gal. Maximum hours demand = 8000 X 1/7 = 1140 gal. Duration of peak load = 4 hr. Water required for 4-hr peak = 4 X 1140 = 4560. If a 1000 gal storage tank is used, hot water available from the tank =- 1000 X 0.75 = 750. W ater to be heated in *1 hr -- 4560 -- 750 = 3710 gal. Heating capacity per hour = 3710/4 = 930 gal. If instead of a 1000 gal tank, a 2500 gal tank had been installed, the required heatmg capacity per hour wou,ld, ,be4--5-6--0-'-------(-2--50--0---X----0-.-7--5-)- = 671 ga,l. Table 10 may be used to determine the size of water heating equipment from the number of fixtures. To obtain the probable maximum demand, multiply the total quantity for the fixtures by the demand factor in line 11. The heater or coil should have a water heating capacity equal to this probable maximum demand. The storage tank should have a capacity equal to the probable maximum demand multiplied by the storage capacity factor in line 12. Example 5 will illustrate the procedure. Example S: Determination of heater and storage tank size for an apartment build ing from number of fixtures. 60 lavatories ....................................................................... X 2= 120 gal per hr 30 bathtubs........................................................................ X 20 = 600 gal per hr 30 showers........................................................... X 75=2250 gal per hr 60 kitchen sinks................................................................ X 10 = 600 gal per hr 15 laundry tubs.................................................... X 20=300 gal per hr Possible maximum demand.......................................... = 3870 gal per hr Probable maximum demand....................... = 3870 X 0.30 = 1161 gal per hr Heater or coil capacity.................................................. = 1161 gal per hr Storage tank capacity.................................. = 1161 X 1.25 = 1450 gal Although, in private dwellings a water temperature of 140 F is reason able for dishwashing, in public places sanitation regulations call for 180 F water. Most of the dishwashing machines now available on the market require 180 F water. Tbe amount of 180 F water needed in restaurants per day may be determined according to the method outlined by the American Gas Association,3 in the following paragraphs: 1- Multiply the number of meals per day by the number of dishes per meal (6 for low-price restaurants, 8 for medium-price restaurants, and 10 for high-price restau rants) to determine the total number of dishes per day. 2. Divide the total number of dishes per day, as determined by method in para graph l( by the average number of dishes per rack to find the number of racks per day. 3. Multiply the number of racks per day by the gallons of 180 F water (using 1.5 for single tank machines and 0.75 for two tank machines). This product will give the gallons of 180 F water per day for rinse sprays. 4. Multiply the number of meal periods per day (one, two or three) by the dish-