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Calculating BTU/HR RequirementBTU is the abbreviation for British Thermal Unit. It is the amount of heat requiredto raise the temperature of 1pound of water, 1F. At different temperaturestheoretically the amount of heat required to raise the temperature of 1pound ofwater may be slightly higher or lower, but the variation is so small that it is nottaken into account. The weight of 1U.S. gallon of water at 62F. is 8.3391 pounds.The amount of BTU/HR required can be calculated by multiplying themaximumwater flow rate in pounds/hour desired times themaximum water temperature risein degrees Fahrenheit desired.Example: The customer's peak water usage is 200 gallon per minute. Thecustomer has worse case (lowest temperature) incoming water at 60F. and wantsto heat it to 160F.First, youmust convert the 200 gallons per minute to pounds per hour. Multiplythe 200 GPM by the weight of one gallon of water or 8.33 LBS/GAL to get poundsper minute. Therefore, 200 GPM multiplied by 8.33 LBS/GAL equals 1,666LBS/MIN. There are60minutes in anhour, somultiply the 1,666 LBS/MIN by 60minutes to get pounds per hour. Therefore, 1,666 x 60=99,960 LBSIHR of waterbeing heated.Secondly, you must determine the temperature rise by subtracting the incomingwater temperature from the desired final temperature. Therefore, 160-60 equals a100F. temperature rise.Finally, you multiply the pounds per hour of water being heated times thetemperature rise time's IBTU/LB - F to get the required BTU/HR. Therefore,99,960 x 100x 1=9,996,000 BTU/HR requirement.A shortened method for calculating BTU/HR required, ismultiplying GPM by 500by the temperature rise desired.

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Calculating Fuel SavingsGiven the customer's BTU/HR output requirement, it is amatter oflooking at thedifferences in efficiency between the direct contact water heater and the boiler.Example, a99% efficient direct contact hot water heater requires afuel input of10,096,969 BTU/HR to produce a9,996,000 BTU/HR output. Where as a70%efficient boiler requires afuel input of 14,280,000 BTU/HR. Theboiler requiresan additional 4,183,031 BTU/HR. In other words, you will save this amount ofenergy per hour by using adirect contact hot water heater instead of aboiler.Knowing the BTU/HR saved and the hours per year operated, afuel savings can bedetermined. Gas is sold either by the therm, which is 100,000 BTU's or by thecubic foot. If sold by the cubic foot, you must determine how many BTU's are ineach cubic foot of gas. This BTU value per cubic foot varies depending on the gastype and gas supplier. Roughly, natural gas has avalve of 1,000 BTU/CU FT andcost $10.00 per 1,000 cubic foot.4,183,031 BTU/HR of energy saved divided by 1,000BTU/CU FT equals 4,183CU FT/HR of gas saved. If acustomer ran 8hours per day, 5days aweek, 52weeks ayear, his annual gas savings would be (4,183 CD FT/HR x 8HRS/DA Y x5DAYS/WEEK x 52WEEKSIYEAR) 8,700,640 CU FT/YR of gas at $10.00 per1,000 CD FT equals an annual dollar savings of $87,006.40.