HomeMy WebLinkAboutB14-0479 Hot water calcs.pdf
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APPENDIX C - Worksheets for Calculating Minimum Hot Water
Requirements
The following worksheet is provided to assist operators in calculating hot water usage and sizing of the
water heater system required for the operation.
What is the distance between the water heating system(s) and the fixture that is farthest from the heating
system?
Fixture: _______ Feet from water heating system: ________
Standard Tank Type Systems:
I. Calculate Total Water Required By All Fixtures:
A. Three compartment sink calculation of water usage:
1. Measure dimensions, in inches, of each compartment, if compartments are not
the same dimensions see note below.
Length = __________ Width = __________ Depth = __________
2. Insert measurements into equation:
( ________ x ________ x ________ x 3 x 0.375 ) ÷ 231 = _________ GPH
length width depth water usage
Note: If all the compartment sizes of the sink are not the same, then 3 is taken out of the equation,
and the above calculation is done for each compartment. The volumes are added to obtain the
total gallons per hour of hot water used in the sink.
Enter number into the attached “Table to Calculate Total Water Required By All Fixtures,” found
on page C-4 .
B. Utensil soak sink
1. Measure dimensions, in inches, of the sink
Length = __________ Width = __________ Depth = __________ GPH
Mop Sink 85 feet
n/a
n/a
12/18/14
Crespelle Pop-up Restaurant, Vail, CO
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2. Insert measurements into equation:
( __________ x __________ x __________ x .375 ) ÷ 231 = __________
length width depth water usage
Enter number into the attached “Table to Calculate Total Water Required By All Fixtures,” found
on page C-4.
C. Dishmachine and conveyor pre-rinse water usage:
1. Use manufacturer’s rating in gallons per hour. Enter number into attached
“Table to Calculate Total Water Required By All Fixtures,” found on page C-4.
2. Clothes washer water usage.
• Use manufacturer’s rating: _________, or
• 32 GPH for 9-12 pound washer, or
• 42 GPH for 16 pound washer.
Enter number into the attached “Table to Calculate Total Water Required By All Fixtures,” found
on page C-4 .
D. “Calculate Total Water Required By All Fixtures” and the number of fixtures in the
operation to determine maximum hourly usage for each type of fixture in the operation.
Total water (GPH) required by all fixtures: _________ GPH.
II. Calculate Maximum Hourly Hot Water Usage
If gas water heater is used go to Step A; if electric, Step B.
A. Gas Water Heater: If a gas water heater is to be used, calculate the maximum hourly hot
water usage for the facility by adjusting the total water required by all fixtures for
altitude. The altitude adjustment is 4% per 1000 feet of elevation, or 20% at 5000 feet.
Use the following equations to determine the maximum hourly hot water usage when a gas
powered water heater is to be used:
(0.04 x ______________ ÷ 1000 ) + 1 = ______________
` elevation of facility adjustment factor
_______________ x _______________ = _______________ GPH
adjustment factor total water required maximum hourly
by all fixtures hot water usage
n/a
17
8150 1.326
1.326 17 22.5
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Example, if the total gallon per hour usage for an establishment at an elevation of 5000 feet is 100
GPH, the adjustment factor is 1.2. Therefore, a water heater with 120 GPH recovery rate would
be required.
Use this value in the equation to calculate the minimum BTU rating of the water heater.
B. Electric Water Heater: If an electric water heater is to be used, the maximum hourly
usage for the operation is the same as the total water required by all fixtures. Use this
value in the equation to calculate the minimum Kilowatt (KW) rating of the water heater.
C. The value determined in Step A or B the minimum recovery rate of the water heater
which should be provided for the facility.
III. Calculate the minimum BTU or Kilowatt rating of water heater:
A. For gas water heater, calculate the minimum BTU rating:
(max hourly usage as calculated above) x (100˚F*) x (8.33) = minimum BTU rating
.80 or use manufacturer’s thermal efficiency
B. For electric water heater, calculate the minimum Kilowatt rating :
(max hourly usage as calculated above) x (100˚F*) x (8.33) = minimum KW rating
3412
*If there is no high temperature dishwashing machine or other fixtures requiring input water
temperature of 140°F (100°F rise) or more, then 80°F rise can be used.
C. Select water heater based upon BTU or Kilowatt rating.
Make: _________________ ; Model #: __________________
BTU or Kilowatt Rating: ______________________________
Recovery rate: _____________ gallons per hour at 100°F rise at sea level.
D. Heat reclaim systems:
Make: _________________ ; Model #: __________________
BTU Rating: ______________________________
Recovery rate: _____________ gallons per hour at 100°F rise at sea level.
(22.5) * (100) * (8.33) / 0.95 = 19,728
Qty. 2 Lochinvar WHN 399 boilers
399,000 each x 2 = 798,000 btu/h combined
Qty. 1 Lochinvar SIT 030 side-arm water heater
160
The domestic hot water is provided by the building's central heating plant, which has a
total input rating of 798,000 btu/h. Per this Appendix C calculation, the restaurant
requires 19,728 btu/h, which is only 2.5% of the plant's capacity. The central plant has
more than adequate capacity to serve the domestic hot water needs of the restaurant.
-Bryan J. Houle, P.E.
Rader Engineering, Inc.
12/18/14
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Table to Calculate Total Water Required For All Fixtures.
Plumbing Fixture Water Usage
(gallons per hour)
Number of
Fixtures
Maximum Hourly
Water Usage Per
Type of Fixture
(gallon per hour)
example: dishwashing
machine 50 1 50
example: handsink(s) 5 4 (5 x 4 = ) 20
3-compartment sink
3-compartment sink (bar)
Utensil soak sink
Dishmachine
Dishwashing machine
conveyor pre-rinse
Clothes washer
Hand operated pre-rinse
sprayer* 32
Hand washing sinks
(including restrooms)* 5
Mop/utility sinks 7
Garbage can washer 35
Showers* 14
Hose bib used for cleaning 35
Total water (GPH) required by all fixtures:
*A hot water use reduction can be calculated for water saving devices used on hand operated pre-rinse
sprayers, hand washing sinks and showers by doing the following calculations.
1 7
2 10
17