Laundry-Calculations. How to do Laundry and calculate the number of machines required for a given job

Use the Laundry-Calculations page to work out how many and what size of machine you will require for a given laundry load .

The total weight in Kilograms of the laundry is the first task.

The size of the room is important especially when the number of machines become large. Take a look at my laundry room design page for guidelines at Laundry Room Design Or you can pop and have a look at my quick guide on how to avoid the disasters that have littered the laundry world at Laundry-Room.

The Laundry list is the first port of call to find the total amount of work to be processed.

The laundry List is the best way forward if you can get one.

If it is a hotel with different seasons and occupancy rates, you can either work out an average or work for the busiest time. It may be possible to work overtime during the peak and build the laundry for the normal week.

With a modern calculator you can try several ways of coming to the final figure for a weeks/days/hours load required.

2. We then use the material Load Ratio figure in Laundry-Calculations for the particular fabric being used, which has to be washed.

3. Then we need the Drum Volume of the washing machines available for the site. With this figure we can work out how many kg of laundry per machine for the given fabric and level of soiling.

The load ratio is the drum volume required to properly wash, rinse and mechanically agitate the soiled laundry to a satisfactory level of cleanliness in the given time.

Most commercial and domestic washing machines are sized using the Din standard (fixed weight in grams per centimetre squared of Turkish cotton towels), which is a 1:10 ratio.

This means that using Laundry-Calculations 'theoretically' for every 1kg of cotton 10 litres of drum volume is required to wash the load correctly.

However - Load Ratio (LR) can only be used as a rough guide.In reality it is dependent upon the material weight, mass, construction and type of soiling.

Laundry-Calculations helps you steer clear of the pitfalls, with insider knowledge on how to avoid the mistakes which could be very costly.

If you go back to the sinners diagram in how to (Take a look at the sinners diagram again) and look at the mechanical action being dependent on the drop height of the drum if the machine is overloaded the drop is reduced eventually to nil.

Where mixed loads of cotton a 1:12 Load Ratio is used to provide enough room inside the drum, which means 1kg of mixed cottons will require 12 litres of drum volume per Kilogram of Laundry.

Poly-cotton being lighter and less absorbent with a higher mass we require a LR of 1:15 which means 15 litres of drum space for each 1kg of polycotton laundry to clean a normally soiled load.

This may be increased to 1:18 for heavily soiled polycotton materials.

Typical Load ratios for a range of materials.

Cottons (towelling/linen) light soiling is -1:12.

Cottons (linen) heavy soil -1:12.5.

Poly-cotton (Linen) (Light Soil) –1:15

Poly-cotton (Linen) (Heavy soil) –1:17

Woollens –1:20/25

Duvet quilts (Internal) –1:20/22

Mops –1:9.5 special low ratio to reduce knotting.

So you see it is not quite as straight forward as you may have thought in the beginning, but it is logical and can be worked out if you know all the questions to ask to get the right answers.

What about Drum Volume?

Example – one week’s hotel bed linen 200kg of poly-cotton sheets to process. Say we knew the wash drum volume was 73 litres, which is the size of a typical 7.5kg washing machine currently on the market.

If we were to work out the through-put on the weight alone and the size of the machine in the brochure (7.5Kg) that would be 200/7.5 = 27 cycles (assume that a polycotton cycle takes 40 minutes)

This equates to 18 hours of work per week for one machine.

HOWEVER - this is based on the DIN capacity of the washing machine, which is specific to Turkish Cotton standard.

We know that the correct Load Ratio for Poly-cotton is 1:15.

This means that for every 1kg of poly-cotton we require 15 litres of drum volume not 10.

We know our washing machine has a drum volume of 73 litres –therefore-

If we calculate 200 x 15 = 3000 drum litres are required.

3000 divided by 73 is 41.09 or rounded up to 42 cycles at 40mins per cycle equals nearly 28 hours of work or an extra 11 hours more work than if you used the Din standard.

This is a much more realistic figure for our Laundry-Calculations than using the weight capacity of the machine from the back plate and the simple Din standard.

Laundry-Calculations for a Nursing Home.

From our experience, we assume that for the normal up and about ambulant resident they will produce 10kg of laundry per week.

Again, from experience we assume an incontinent resident will produce 25kg of laundry per week.

For sever cases such as Althziemers patients and where there may be a lot of mopping up of food during meals with severely handicapped persons this may go up to 32Kg per week per resident!!

20 x 10kg + 20 x 25kg = 700kg per week to process for the home, this will be a mixed load of all types of fibre, including wool, cotton, poly-cotton, so we would use a Load Ratio (LR) of 12 X 700 = 8400 drum litres per week required to process the Nursing Home laundry.

If we were to take two typical 10kg commercial washing machines with a drum volume of 100 litres this would give us a capacity of 200 litre per load.

So we can calculate that for 8400/200 = 42 cycles per week or a full week of 8 hour days work to complete the process.Using two 10kg machines a full weeks work of 42 hours just for the washing process.

This would mean that that there would be spare capacity using overtime should it be required. Laundry-Calculations helps you make the right decisions so no money is wasted, buy the right machines once not the wrong machines several times. I have produced some spreadsheet on google docs which your are invited to use by following the licks below and I will email permission to edit them.

You can now go and look at my spreadsheets on a google file sharing site

It is probably best to copy them to your computer either by high lighting the full sheet and copying to your clipboard, or by downloading them. Cheers Brian
Hospital and Hotel Laundry calculation Spreadsheet
OPH and Nursing Home Laundry Calculation spreadsheet.
Laundry Weights calculation worksheet

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And I hope my Laundry-Calculations page was of use to you when working out which size of laundry machines and how many you needed to do the task, and that you will come back for more laundry and dishwasher information at a later date. Please put it on your favourites then you can get here in one hop. Hotel/Hospital Laundry calculations spreadsheet site at Google docs

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