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Useful Technical information


1 BTU (British Thermal Unit) is the amount of heat energy required to raise the temperature of 1 lb. of water 1 degree fahrenheit (F) (0.47 deg C).
1 therm of energy (TH) is equal to 25.2 kcal.
1 litre of Natural Gas is approximately equal to 35.3 BTU or 0.14 kcal.
1 litre of Butane Gas is approximately equal to 113 BTU or 0.448 kcal.
1 litre of No. 2 (diesel) fuel oil is equal to 36 460 BTU or 145 kcal.

Gas cost:
The cost of gas is usually stated as "Price per therm". In computing costs, the total charges billed in (1) period should be divided by the total number of therms used during the same period. This gives the average cost per therm, including any incentive rates used by local gas suppliers, such as "straight line rates", "block rates", etc. Average costs should be calculated showing the effects of usage-based rates. Additional charges such as "demand charge", "commodity charge" or "service charge" may also be part of the gas cost and should be included in all calculations.

Gas: Commercial dryer make-up air guide 


1 litre of water weighs 1 kg

Boiler Horsepower:
1 Boiler horsepower consumed by a laundry using steam-heated equipment, first determine all of the machinery that will require steam. Next, list steam consumption of each machine in BHP. Multiply each consumption factor by the quantity of that machine in the laundry. The sum of these will be the total steam consumed per hour of laundry operation under ideal conditions. To allow for losses and inefficiences, multiply this by 1.1 (to add 10% safety factor) and divide by 0.7 (efficiency factor). The result is the minimum boiler size for the laundry.

Metric equivelants and common conversion factors:

 1 U.S. gallon = 3.785 litres  1 litre = 0.264 U.S. gallon
 1 cubic foot = 0.028 cubic metres = 28.137 litres  1 metre = 39.37 inches = 3.28 = 3ft 3-3/8 inches
 1 litre = 0.035 cubic feet  1 foot = 0.3048 metres
 1 square foot = 929.03 square centimetres  1 square metre = 10.76 square feet
 1 pound = 0.4536 kilograms  1 kilogram = 2.20 pounds
 1 pound per square inch (psi) = 0.069 bar  1 bar = 14.5psi
 1 cubic metre per minute (CMM) = 35.3 cubic feet per minute (CFM) 

V=0.785 x D2 x P
Being: V: Drum volume dm3 (litres).
D: Drum diameter dm.
P: Drum depth dm.

Volume needed to hold 1 kg of dry linen.
Being: R: Load ratio kg/dm3. C: Load capacity kg.
V: Drum volume dm3.
Usual values: Washers: 1/10 to 1/12
Dryers: 1/23 to 1/28
Batch washers: 1/40 to 1/45

Indicative value of extraction force applied to the linen, in respect of the force of gravity.
G= 5.6 x N2. x D/1,000,000
Being: G: G Value
N: Drum revolutions r.p.m.
D: Drum diameter cm.
Usual extraction values:
Hand-mount washers: from 70 to 120.
Soft-mount washers: from 280 to 400.

H= Ph-Ps
Being: H: Humidity in litres.
Ph: Wet linen weight in kg.
Ps: Dry linen weight in kg.

% H= Ph-PsPs x 100
Being: % H: Humidity percentage.
Ph: Wet linen weight in kg.
Ps: Dry linen weight in kg.

dm3 (litres) of water that a dryer or an ironer can eliminate per time unit.
C= Hi-Hft x 60
Being: C: Evaporation capacity (l/h).
Hi: Initial humidity (litres).
Hf: Final humidity (litres).
t: Processing time (minutes).

- Fluid quantity admitted per hour.
- Used for the costing process.
- Fluid quantity admitted per fraction of hour during admission.
- Used for the calculation of pipe sections.
I.E.: During washing period a washer admits 50 l of hot water, the admission time is 1 minute and the complete cycle is about 1 hour.
Solution: The washer’s consumption of hot water is 50 l/hour and requires a flow of 50 l/minute = 3,000 litres/hour.

P = M · K · N · 7H · R
P = Production (kg/h.).
M = % occupation.
K = Weight of dirty linen per person and day (kg/pl. day).
N = Nr. of people (pl).
7 = Days week.
H = Working hours/week.
R = Efficiency.