General OPL Laundry Calculations

All information below is based on industry standard guidelines and should only be used as a guide. All applicable local codes should be met and may vary at the actual installation site.

Cylinder Cubic Content
Cubic content measures the physical size of cylinder (or basket). It is the best way to compare rated capacity of competitive machines. The higher the cubic content, the more laundry the machine’s cylinder can hold.It is calculated as follows:

• (PI)R2 (radius of cylinder) x depth of cylinder / 1728 = cubic content of cylinder.

• The accepted capacity for washer-extractors is between 5 and 7 lb. per cubic foot.

• Accepted capacity for dryers is between 2.5 and 3.5 lb. per cubic foot.

Volume
Volume refers to the available area within the cylinder of the washer. Here are some relationships between cubic content, gallons and liters.

• 1.0 cubic foot = 7.48 gallons = 28.27 liters                                                 • 0.134 cubic foot = 1.0 gallons = 3.78 liters

G-Force
G-Force is a relative measurement used to compare a washer’s extraction capabilities (spin cycle). Comparatively, higher RPM’s relate to higher G-Force when the cylinder size is similar. However, larger diameter cylinders can spin slower, yet attain a higher G-Force than smaller diameter cylinders. Here’s the formula to calculate G-Force RPM2 x diameter (inches) / 70,500 = “G” Force

Water Data
Here’s some specific data on water:

• About 60% of water used in a typical laundry formula is hot (if a conventional water system is used).

• 1 cu. ft. of water = 62.425 lb. 1 cu. ft of water = 7.48 gallons

• Gallon(s) x 1336 = cubic feet gallon(s) x 231 = cubic inches

• 1 pound of water x .016 = cubic foot pound of water x .12 = gallons

• 1 gallon = 8.33 lb. @ 62 degrees Fahrenheit (oF)

• Boiling water = 212 Fahrenheit (oF) = 100 Celsius (oC)

• Freezing water = 32 Fahrenheit (oF) = 0 Celsius (oC)

• To convert to oF; multiply oC by 9, divide by 5, and add 32.

• To convert to oC; subtract oF by 32, multiply by 5, and divide by 9.

Moisture Retention
Moisture retention measures the water extracted from the load. The more water removed from the load, the less drying time required. Too much water removal, however, can damage fabrics. A certain amount of water retention is required for finishing procedures. To calculate moisture retention, use the following formula:

Weight after extraction - dry weight / dry weight = Moisture Retention (%)

Water Hardness
More tallow soap is required for washing in hard water than in soft water. A water softener may be required if grains/gallon of hardness exceed 3.

Water Hardness definitions: Grains/Gallon Parts/Million Description

• less than 1.0 less than 17.1 soft

• 1.0 to 3.5 17.2 to 60 slightly hard

• 3.6 to 7.0 61 to 120 moderately hard

• 7.1 to 10.5 121 to 180 hard

• 10.6 & over 181 & over very hard

Gas Data
A BTU is the amount of heat required to raise one pound of water approximately one degree Fahrenheit (oF):

• one Therm (TH) = 100,000 BTU

• one cubic foot = 1,000 BTU (approx..)

• one MCF (1,000 cubic feet) = 10 Therms (approx..)

• one cubic foot of Butane gas = 3,200 BTU

• one gallon No. 2 diesel fuel oil = 139,500 BTU (approx.)

• one gallon No. 6 fuel oil = 149,000 BTU (approx.)

• one kilowatt (kW) = 3,415 BTU

• one gallon propane = 92,000 BTU

• Gas cost : The cost of gas is usually stated in the price per therm or price per M or MCF (1,000 cubic feet). In computing costs, the actual total to the end user should be used, and divided by the number of therms used to find the cost per therm. Various rate structures are used by local gas suppliers. These include “ straight line” rates, and “block” rates in which the rate varies for various quantities. Additional charges such as “demand charge”, “commodity charge”, or “service charge” may also be part of the gas cost. Any charge the customer may pay to receive gas, including sales tax where applicable, should be included in the total gas cost from which the actual cost per therm is derived.

Boiler Horsepower
one BHP = the work of converting 34.5 lb. of water per hour from and at 212 oF to steam at 0 lb. gauge pressure.

• one BHP = 33,500 BTU/hr

• one BHP = 34.5 lb./steam

• one BHP = 9.803 kilowatts

How to size dryers
Dryer should be of larger capacity than corresponding washer-extractor. Estimate between 1.4 and 1.5 times washer-extractor capacity. (i.e.: a 50 lb. washer requires approximately a 75 lb. dryer).

Average loads per hour:         gas fired = 2         steam heated = 1.5         electric heated = 1

How to size gas water heaters
To determine the quantity of hot water requirements per hour: Figure about 2.5 gallons per pound washed. Figure about 60% of the water to be hot. Determine temperature of incoming water. Subtract this from the desired hot water level to arrive at the degree of rise. Formula: gallons hot/hr x 8.3 (lb./gal) x degree rise / 6 = BTU/hr

Example:
100 gal/hr x 8.3 (lb./gal) x 100 F rise / .6 = 138,333 BTU/hr

If heating with steam, divide by 33,500 BTU/BHP. Storage capacity should equal from 1/2 to 1 hour’s demand.

How to size water softener
Determine grain hardness (3 grains acceptable without softening). Determine total gallons of water to be used per hour. Multiply grains hardness x total gallons x hours of operation between regeneration (backwashing). Example: 20 grains x 1000 gallons x 24 hours = 480,000 grain softener
Check the flow rate of softener, and make sure it is adequate.

How to size air compressors
Add up CFM requirements on all air driven equipment. Add an additional 25% to CFM. Tank size should be 3 to 5 times the CFM output in gallons of storage.

Example:
Required 20 CFM + 25% = 25 CFM
Tank should be 75 - 125 gallon size.

How to size boilers
Find the BHP rating on each piece of equipment in the operation that requires steam. If pounds of steam consumption is known (in place of BHP), divide by 34.5 to get BHP.

To all BHP requirements, add 10% of the total for heat loss/radiation and divide by .7 (this allows for efficiency factor and keeps you from operating the boiler at full capacity, which is both costly and harmful to the boiler).

How to size drain troughs
Determine the total number of gallons to be dumped at one time by all present and future machines. Use high level rinse figures to get this total.

Divide total gallons by 7.48 gallons/cubic foot to get the total cubic feet required.

Example:
300 gallons / 7.48 = 40 cubic feet of trough area

The trough depth should usually be 12 inches, and the width 14 inches.
In the example above, assume a 12 inch deep and 14 inches wide trough:

14” x 12” = 168 sq. inches

168/144 (one sq. ft.) = 1.166 sq. feet (trough area)

40 (cubic feet required) / 1.166 = 34.3 feet (length of trough)

Drain trough should slope 1/4” per linear foot to the outlet drain. On long troughs, this can be decreased to 1/8” per linear foot to keep the depth from becoming too great.