Over load or Under load?
Laundry Manager, Shangri-la’s-Eros Hotel
Interestingly, machines carry the tag: ‘Maximum Allowed Load’. Now, would this mean to run at lesser load so that machine will perform better and live longer or vice versa? Similarly, in the case of the dryer, if under loaded, clothes dry faster. But how much should the dryer be under loaded? I am trying to ascertain what optimal load is for a washer and for a dryer individually.”Halilur Rahman Service Manager – Laundry Equipment at Electrolux Professional
Do not under load machine than the recommended capacity as under loading more than 15-20% may cause imbalance of hard mount washers resulting damage of shaft seal and shaft. Same with soft mount which may unbalance the load. As the machine is on suspension, this unbalance does not damage shaft & seal much.
The dryer on the other hand, can run under load, but a lot of heat energy will be lost in the process. Dryer uses a combination of steam pressure of 7-10 bar, supply air and exhaust. For example, an exhaust of 200mm diameter will need five times bigger fresh air opening or ambient temperature fresh air duct behind the machine or connected with steam battery.
A dryer is generally connected with an exhaust duct, but one can seldom see a hotel providing fresh air five times more than the exhaust duct for the dryer. In case of low pressure, drying time will be increased.
The fresh air intake starts from the laundry area and follows through steam battery and circulates the hot air and exhausts through the outlet. If there is air conditioner in the laundry area, all the air gets sucked by the dryer and exhausted at outlet. This will make the laundry area very hot.
The ‘Maximum Allowed Load’ capacity is based on the analogy of a car with a maximum seating capacity of four, five or seven people with a specific mileage under standard test conditions.
Maximum load is not same as “Maximum Allowed Load”. There is a difference with respect to DOL. In order to set certain loading factors, some experiments with wash loads need to be done. Note down the records and analyse them. This will help determine which washer can be loaded with how much of a particular textile for a particular wash requirement. This experience can serve as a good reference in any other laundry, but may not be 100% applicable.
In dryers, the only way to know the load capacity is to install a steam meter and experiment by under loading maximum 5 to 10%. Conceptually, energy might be lost but when you calculate total loads and divide the steam consumed, it can be determined as to how much steam it consumed per kg of load with steam pressure remaining constant. If by under loading 10%, you are saving time, then you are saving energy for that time saved.
Steam pressure is directly related to temperature and steam flow. Low pressure implies low temperature & low flow and high pressure means high temperature & high flow, but this alone does not affect drying time or energy consumption. It is about heat transfer and steam pressure, air flow, drum perforation, drum size, MEP like duct size and ambient air temperature, which contribute together to determine dryer performance.
When one says under loading leads to unbalance, it does not happen with 10-15% under loading factors. For smaller machines, the effect will be lesser. Major under loading leads to excessive vibrations and unbalancing with large open pocket machines only.
Soied cotton towels can be loaded 110% of load capacity, as they are already wet after use when it comes to laundry. This can be misleading, as in 110% of dry weight there is 10% or 15%, 20% or 25% moisture? Towels should be loaded 85% on dry weight basis.
The Laundry Machine Capacity is always based on the total dry weight of the average washable textile. The commercial bigger capacity machines cater to sectors like Hospitality, Healthcare, Military establishments, Tourism and Transport. So considering the requirement, the average textile washed would be always be some blends of Cotton, Polyester, Viscose or Acrylic to get the strength and durability of the fabric or pure cotton like the requirement for room and bath linen of a Star-rated hotel. So we should stick to some average weight of the above textiles.
The machines are not calibrated on wet weight of the wash load as the load may contain varying levels of water percentage, which may mislead the actual loading capacity of the machine. The machine is to be loaded to the optimum capacity taking a variation of plus/minus 10%, if needed. This loading factor would optimise the cost of HLP, chemical, manpower, and machine maintenance. Considerable under loading or overloading is not at all advisable for efficiency and cost factor. Machines are manufactured after a detailed study by the manufacturer and cater to an average mixed wash load type. So, the loading capacity would mean the mentioned capacity irrespective of a hard or soft mount machine.
The washer has a maximum capacity and a smaller load can cause an out of balance situation and create vibration. It is good if you load the washer to its capacity and the quality of the goods also meets standards.
Kiran Raj Singh
- Cotton linen can be loaded to full capacity into washer extractor to obtain higher productivity, to prevent unbalancing of drum and hence to prevent vibration of machine. Soiled cotton bed sheets, duvet covers and pillow cases may be loaded up to exact load capacity (100% load capacity utilisation and soil cotton towels may be loaded 110% of load capacity as it is already wet after use, when it comes to laundry.
- Soiled cotton F&B linen could be loaded 80-90% of load capacity as it is heavy soiled and need more space. Pure synthetic will load lesser as they are lighter than poly-cotton @ 70% of load capacity or lesser.Cotton being heavier, can be loaded to full capacity, whereas polyester being lighter cannot be loaded fully because of higher productivity. 10-15% under loading of cotton linen may not result in unbalancing of drum, hence may not cause vibration of machine.
- Light soil bed sheets & duvet covers can be washed full load. Pillow covers can be washed at 90% load as it is relatively more soiled. As far as degree of soil is concerned, if the fabric is more soiled, more space is required to beating of fabric in the machine for proper cleaning. Hence, more the soil, lesser the load of fabric. You may change the formula or add up more chemicals for more soil load.
In the final analysis the loading calculations depend much on the fabric, soil conditions and also the capacity of the machine.