established the maximum dry weight of articles to be processed per hour, a
choice has to be made regarding the washing machines to be used.
choice of washing machine(s) will, to a large extent, determine the size and
layout of the laundry.
choice of washing machine(s) will depend upon:
- The dry weight of
articles to be processed per hour
The total cost,
both capital and running, of the equipment, energy (electricity & steam),
water, and building
and cost of labour.
the three generic types, side loaders are popular in rural areas for a number of
reasons (see para 5.1.1), one being that they are locally manufactured. In urban
areas the choice would generally be between washer-extractors (some of which are
locally manufactured) and CBW machines which are all imported. (see para 5.1)
developed countries washer-extractors or CBW machines are exclusively used
because they are more cost efficient in terms of labour, water and energy. As
stated previously when the load exceeds 600 kg/hour CBW machines should be
seriously considered. It must be remembered that this is an arbitrary figure and
cost comparisons must be made taking into account all the factors mentioned
selecting equipment the following basic guidelines are considered important:
There should be
generally be at least two of each type of equipment to allow for maintenance and
breakdown. This may be difficult in a large production laundry with a CBW
machine and a multi roller ironer.
capacity washer-extractors are better for smaller laundries than one large
A smaller machine
will take less time to accumulate a full load and small odd lots of laundry can
be handled more efficiently.
Two machines give
the flexibility to wash different types of items simultaneously
Small machines will
impose less of a peak load on hot water and electrical systems.
should have a 20-25% large drum capacity than the corresponding washers.
methods for determining the number and size of washers and other related
equipment are described below. CBW machines are not discussed in detail as this
requires input from an experienced
launderer to specify the wash process required within
the machine to determine the number of sections, and engineering input
regarding energy, water and maintenance factors. However, some guidance is given
in Appendix C.
key factors in determining the number and/or size of washing machines are the
Peak load expressed
Loading factor of
the machine influenced by the fabric to be laundered and degree of soiling
Number of loads
completed per hour
pressure and temperature.
The methods for determining the peak
load in kg/hour are discussed in Chapter 4. Note that many overseas
equipment manufacturers refer to their model sizes in lb
capacities. For example 35, 50 and 85 model machines refer to lb
capacities and must be multiplied by 0,4536 to express the capacity in kg.
sizes are the following:
available side loading machines are available in 20, 30, 50, 90 and 140 kg
The loading factor or degree
of load (D.O.L.) relates the weight of fabric to the cubic capacity of the
washing cylinder (cage) and strongly influences washing quality, mechanical
action and mechanical damage if the machine is overloaded. This loading factor
is also discussed in detail in Chapters 11-13 on the laundering process but is
discussed here in terms of the sizing of the equipment.
the past, the loading factor has been expressed as lbs/ft³. This is being superseded
by either kg/m³
or gm/l (most commonly
used in the UK) or a ratio expressed as kg/ l, for example 1:18. The reverse
ratio l/kg is also used and may become the future standard. The loading factor
equivalents are the following:
The actual equivalent of lb/ft³ is often shown as an inverse ratio i.e. 1:62
means 1 kg per 62 litres cage volume. For the purpose of this report the loading
factor will be expressed as l/kg (litres per kilogram).
often relate their machine size to the load in kg it can take over a one hour
period. Two presumptions could be made. Firstly, that the loading factor is 10
or 11 l/kg and secondly, that two loads would be processed in one hour. On these
assumptions a 100/kg machine would produce 2 x 50kg loads in one hour. In
reality both the loading factor and the throughput could be grossly exaggerated.
In determining machine size the cage volume must be calculated on the basis of
an accepted loading factor for the fabric to be laundered and the degree of
soiling. For medium soiled cotton work, the most satisfactory loading factor is
18 litres of cage volume to 1kg of cotton work. For woollens and polyester/cottons, loading factors of 25 and 22 l/kg respectively should be used. If
machines having a large cage diameter in excess of one metre are envisaged,
mechanical action on the washing would be greater thus allowing higher degree of
loading and a loading factor for cotton fabrics of 11 to 12 l/kg could be used.
machine cage volume should be specified by all manufacturers.
maximum loading capacities should never be exceeded. Under loading on the other
hand is wasteful in energy, water and chemicals and will result in a lower
productivity. Another important aspect of under loading is that it can cause an
imbalance in the washing machine with potential mechanical damage.
stated previously, most hospital laundry is cotton and for planning
purposes a loading factor of 18l/kg can be presumed. However, if poly-cotton
sheets or heavy soiling of cotton fabrics is envisaged, the loading factor
must be reduced to 22l/kg and therefore greater machine capacity is required.
The next important factor is to
determine the number of loads per hour
that can be achieved by the machine and the operator. Very lightly soiled linen
will require a shorter total washing cycle than heavily soiled and /or infected
linen. Manufacturers sometimes claim up to 2 loads per hour but these claims are
often not obtainable in practice. For planning
purposes rules of thumb have to be used. From
discussions with the industry it appears that the loads per hour will vary from
1 to 1.4 per hour. The higher turnover can be achieved where the linen is
lightly soiled such as in a hotel (in some instances there is no pre-wash of the
sheets). If this is the case then up to 1.4 loads per hour can be achieved
especially with small washer-extractor machines where the operator can load and
unload rapidly. For hospitals and frail care units a complete cycle time between
1 and 1.3 loads/ hour should be used for washer-extractors. For side loaders
requiring the removal of wet washing a cycle time of 1 hour per load should be
factors required to determine the number of sections for a CBW machine are only
briefly described in Appendix C of this report. The total process time for each
batch of say 35kg of washing may take from 30 minutes to 45 minutes but this
does not determine the production. The production of a CBW machine is determined
by the cycle time which could be as rapid as a 35 kg batch every 2 minutes! CBW
machines vary in their batch capacity from 20-60 kg/ batch.
In order to achieve a desired production time or throughput of washing,
the water pressure must be adequate in order to fill the washer within a given
period of time and similarly the ambient water temperature must be brought up to
the desired wash temperature in a given period of time. Where the water is
electrically heated in the washing machines this will generally require the
installation and supply of a hot water storage system of supplying hot water in
quantities suitable to the workload. The water can sometimes be heated at night
using lower electricity rates and stored in insulated tanks for use during
working hours. Where steam is used, the direct introduction of steam into the
machines provides a rapid rise in the temperature of the water. Techniques to
speed up this process, if necessary, should be discussed with the suppliers of
equipment and the mechanical and electrical engineer.
In Table 6, three hypothetical examples of on-site laundries are shown,
each producing the same dry weight of laundry per hour, but differing in the
type and soiling of the laundry items from heavily soiled cotton overalls to
lightly soiled poly-cotton sheets. This table shows the influence of the loading
factor on the machine cage volume.
Three hypothetical examples showing the influence of the loading factor
on machine cage volume.
same peak load
x B = C
proportions of heavily soiled cotton overalls
cotton items with 70% cotton flat work - light to medium soiling
proportion of lightly soiled poly/cotton sheets etc. not requiring a
above it can be seen that for the same dry weight turnover of laundry per hour
for the three examples the machine cage volumes vary from 1800 litres to 2500
Percentage breakdown of articles to be processed through equipment other
70% of all cotton items laundered for a hospital require flat ironing. The
capital cost of flat ironers and the running and labour costs may force
hospitals and budget hotels to use poly-cotton sheets etc. and do no flat
ironing. The matron of one frail care unit, where cotton sheets are used, is of the opinion that with the high turnover of sheets in frail care per day and
the cost of ironing the sheets, they will have to consider not ironing the
percentage breakdown of articles requiring flat ironing, pressing and tumble
drying is important in establishing the need and size of equipment other than
the washer (see also para 1.5). The type of washer will also determine the need
and size of hydro extractors and tumble dryers.
side loaders are used, all the washing must pass through hydro extractors. If
high spin washer-extractors are used, hydro extractors are generally not
required (see para 5.2)
to four loads per hour can be processed through the hydro extractors which spin
at 1400 rpm and with a DC injection current to break them. Machines that do not
have these features have to be sized according to the manufacture's
normal or medium spin washer-extractors are used for 150kg weight of washing
then it would be prudent to install at least one 16kg hydro extractor or
preferably two smaller models. They would be used essentially for items tumble
drying (see paras 5.1.2 and 5.2).
dryers are generally manufactured with 25% more drum capacity than washers for
the same dry weight of laundry. The provision of a larger cylinder allows for a
better tumbling, airflow and drying operation. Over-sizing the tumble dryer is
especially important in processing towels, poly-cottons and other non-press
The percentage of items requiring
tumble-drying could vary considerably depending upon the type of washer used and
the fabric to be laundered. For example, where all flatwork has to be
preconditioned prior to ironing, all items could pass through the tumble dryer
for partial or complete drying. In other instances, all flat work could go
directly from high spin washer extractors to the ironers and only towels etc.
would be tumble dried. If CBW machines are used then all items are tumble dried
prior to ironing or folding. The number and size of the tumble driers required
must be established by the launderer and the equipment supplier.
The rate of processing laundry items
through flat ironers depends to an extent upon the skill of the operator
and other aspects discussed in para 5.5. If washer-extractors are used for
small to medium sized laundries, particularly on-site laundries, the
choice generally is for single heated roll ironers. Where large output are
required, irrespective of the type of washers used, multi-roller heated
bed (chest) ironers are generally used. For a large production in
association with CBW machines, automatic feeders and folders could also be
Both single and multi-roller ironers
are available with automatic folding devices. As stated in para 6.2, in
general 70% of all cotton items laundered for a hospital require flat
ironing but this percentage may decrease as discussed previously.
After estimating the percentage of
laundered items to be flat-ironed, choose the most appropriate type of
machine(s) for the output required. Manufacturers specify the output of
their machines in kg per hour. This is normally for a 100% ironer bed
usage factor but a factor of 80% should be used for planning purposes.
The rate of processing items through
presses depends very much on the skill of the operator. Throughput of these
machines must be discussed with the suppliers and the launderer.
In hospital laundries, the number of items
requiring pressing is decreasing and wash and wear items (including cotton
items) are being used (see para 5.6)
This information courtesy of Division of
Building Technology, CSIR.