Few hotel laundries achieve their optimum efficiency and most miss out by a significant margin and offer major opportunities for useful improvements and significant cost savings.
The definition of optimum efficiency varies; it could involve minimum operating cost, maximum utilisation of a small space, minimum energy consumption, maximising labour productivity to compensate for under-staffing, maximising machine productivity to postpone capital investment and so on. For most, it is a combination of all these factors.
This month we look at where the initial opportunities lie as regards energy and water management and how you might tackle them in your setup. In a future blog, we shall be looking at the machine and labour productivity and how you can get more out of pint pot than you are at present!
Setting your target
You first need to state as accurately as possible what you are aiming for, or which current problems you want to eliminate. Consider the following improvements which you could address:
- Overall cleanliness: judged either by numerical measurement of whiteness (or simply by reference to a white handkerchief or napkin kept in the manager’s drawer).
- Stain removal: less than say 1% of items still stained after a normal wash, without reducing textile life.
- Water efficiency: most washer-extractors struggle to average less than 20 litres/kg dry textiles, although some machine designs can now get nearer to 10 litres/kg!
- Energy efficiency and cost: the best hotel laundries are now targeting under 1.5 kWh/kg textiles, but many still consume over 2.5 kWh/kg!! Again, some machines are much better than others!
Process design (if you are happy with your present quality you can skip this section for now)
Optimising your wash process is a vital first step, even though you will probably come back and revisit this again and again. Use your detergent supplier’s expertise to the full and identify each classification which you need to process. Remember that pillowcases usually need a more searching process than hotel sheets and spa towels are much more of a challenge than guest room towels.
For each classification you need to fix:
- Number of stages
- Duration and temperature of each stage
- Chemicals dosage for each stage
- Water level for each stage
- Final extract time.
Your chemicals supplier should be able to tabulate all of the above details for each classification to form your process manual. Don’t forget to include rewash processes in this. There is no point in just washing still-stained items in the same process again and again because you have just shown that the normal process does not work for these stains. You need dedicated rewash processes which will yield a high percentage of recovered and usable items from a single rewash, not the same items going round and round the system in the same wash with the same result – stains!
Now you are ready to start with your efficiency improvements.
It is usually worth getting the water consumption minimised first, because this affects wash heat energy, fill times, chemicals consumption and wash quality as well as water cost. In the following paragraphs, all water levels are measured as ‘running dips’, the average dip with the cage rotating normally.
The optimum pre-wash dip for a 23kg washer-extractor should be around 125mm (5”) if you need to remove food or other debris. If there is unlikely to be many solids soiling, then you can employ a lower dip for the pre-wash (down to say 75mm (3”)) and skip the drain after the pre-wash, taking the same water forward for the main wash. This is termed a ‘stepped wash’ and it saves water, time, heat energy and wash chemicals. The pre-wash should run for at least 4 min at below 40C (38C is ideal) in order to soften skin sebum and anything else which is protein-based (such as food, blood and other body fluids).
The optimum main wash dip should be around 75mm (3”) for a 23kg machine, in order to give a good ‘lift and drop’ action to remove soiling and staining effectively. The main wash time can vary from 7 – 8 min. for one-night hotel sheets up to 15 min. for heavily soiled kitchen cloths. There is no point in exceeding 15 min. because the suspending agents which keep in suspension the soiling and staining that has been removed, only work for a limited period. Longer stage times result in progressively heavier greying.
Optimising the rinse dips usually offers major opportunities, because factory settings on most washers are geared to coping with the poorest local water quality in the country. The minimum safe wash dip is that which yields final rinse water to drain with alkalinity of less than 2% above the alkalinity of the incoming softened water. Obviously, most water supplies are better than the poorest in the country, so nearly every rinse dip can be safely reduced. Reduce the dips by 1 cm at a time, keeping each rinse dip the same for maximum economy. When you have determined the safe minimum, you can then adjust your detergent dosages in proportion, in order to maintain the concentrations in the wash liquor unchanged. This s the key to your other benefits in dip management, which are reduced process time and reduced chemical cost.
Once you have got the water right, you can turn your attention to energy consumption (and cost!). Of course, you will already have made savings in wash energy by tuning the wash dips. Now you can extend this by tuning the final extract speed and time. Cotton flatwork can usually be spun at the highest extract speed because any creases can be ironed out or removed in the tumble dryer. Cotton garments require more care unless they are going to be steam pressed (for example on a rotary press or steam-air former). Controlling residual creasing on cotton garments that are to be tumbled dry or tunnel finished requires a skilful combination of washing technology and final spin speed and is a topic to be covered in a future edition of the Hydrofinity Blog.
The duration of the final extract is key to minimising energy in drying and finishing. It takes about fifteen times as much energy to dry one litre of moisture in a tumble dryer as it does in the final spin in a washer extractor (yes, fifteen times!!). Even an efficient ironer requires five times as much energy! The first step in capitalising on this is to set the duration of the final spin such that continuing the spin for another half minute yields no further reduction in final moisture content. This is particularly important for towelling because it also minimises the drying time and can make a very significant difference to the machine productivity of the tumble dryers over the working day.
Having got the spin times set up correctly, the next (and equally important) step is to use the dryers only for full-dried work, such as towels and bathrobes. Sheets and pillowcases should be finally finished on the ironer, with no intermediate ‘conditioning’ in the tumbler. Make the ironer do the entire work of drying because its thermal efficiency is two to three times that of the dryer. It is more effective to run the ironer slightly slower, with maximum coverage over the heated bed, than it is to load wet textiles into and out of the tumbler for a pre-dry of just a few minutes.
This logic applies equally to the practice of feeding pillowcases into an ironer twice, if the double thickness does not dry completely the first time. If you run the ironer at half speed, one operative can feed two lanes and produce a perfect finish at the lower speed without any reduction in the number of pillowcases produced per hour.
There are small differences in water, energy and chemicals consumption between most different models of washer-extractor, but one design does stand out from the crowd.
Xeros-enabled washing machines displace around half of the water required in both washes, giving it a world-class economy of both water and energy. Because this innovative design only has half the water requirement of others, it also needs only half the chemicals to achieve the necessary concentrations. This might go some way to explaining why some laundries operating washer-extractors are operating at over 25 litres water/kg textiles, whilst others can manage with half this! It could also explain why some laundries purchase over 2.5kWh of energy/kg textiles, whilst others are now targeting as little as 1.0 kWh/kg!
Big improvements in water and energy consumption can come from the sum of many little changes, of the type outlined here. It is still not widely recognised how much difference this makes to operating cost and carbon footprint. Every laundry has something to gain from the adoption of the simple principles described in this month’s blog, and the least efficient has the most to gain. This requires management effort, but, in most cases, it needs little or no investment. Good hunting!