Measurement and adjustment of tumble dryers and ironers

Optimisation of continuous batch washers is highlighted very often. No wonder, since continuous batch washers are a dominating water consumer and a major energy consumer, too. Although continuous batch washers seem to be a big energy consumer, they are not the biggest. In most laundries, the dominating energy eater are tumble dryers and ironers. This is the reason why the company Procter&Gamble Professional (in cooperation with the Technical University in Brno (VUT Brno), Faculty of Machine Engineering) has analysed them thoroughly.

How to evaluate tumble dryer and ironer? While evaluating dryers and ironers, two basic parameters are essential. The first parameter is the energy efficiency, i.e. the energy consumed by the single machine in order to evaporate one litre of water from the linen. The second parameter is the drying performance, i.e. how many litres are evaporated per minute. The documentation supplied with tumble dryers and ironers usually presents these two parameters but the reality in the laundry is very different. The most frequent cause why the real parameters are considerably worse is wrong configuration or wrong settings, poor maintenance, or simply too optimistic data in the documentation. 

In practice, the most frequent problems related to tumble dryers:

• Wrong position of the recirculation valve in tumble dryer with air recirculation (most frequent case). 
• Wrong time setting (recirculation time, time without the recirculation).
• Polluted air filters in the tumble dryers (in certain types of tumble dryers, the drying performance is lowered even by two thirds).
• Extremely long drying time (sometimes even more than twice as long as it should normally be).

In ironers, the most frequent problems are related to:

• Wrong settings in throttling valves installed at cylinder draw off (most of the cases).
• Too slow drying (often the quality of the steam fluctuates, which means that the ironing speed must be lowered but after the steam quality is improved the speed is not increased).
• Useless operation of the fans during pause.

The tumble dryers and especially the ironers are significantly affected by the quality of the fill. In practice, the average fill in the tumble dryers is over 70 %. However, the utilisation of the area available in the ironers is - in some cases - some 10 % only.

How to measure the energy efficiency and the drying performance? It is possible to apply direct measurement: you just install a steam flowmeter before the tumble dryer or ironer, which produces data about consumed energy. At the same time, you need to weight the linen before the machine and after it, in order to have data about the evaporated water. Through these data, you get to know about the drying performance and the energy consumption. However, there is a big disadvantage, and that the time and the finances consumed (you need the steam flowmeter with a separator for each machine separately). Another disadvantage is, for example, that it is impossible to adjust the position of the recirculation valve properly, either. 

Another option, offered by the company Procter&Gamble Professional, is the indirect method: the air flow leaving the tumble dryer or ironer is subjected to analysing (refer to a detailed report of real measurement: measurement with the tumble dryers and measurement with the ironers). The measured quantities are: the flow, the humidity and the temperature. By means of these parameters, not only you are able to analyse the operation of the machine (to find out about the energy efficiency and the drying performance): you can adjust the machine (recirculation valve, drying time, etc.) as well. 

The course of measured quantities (tumble dryer)

The course of measured parameters (above). The green curve is the speed (flow rate) for the air leaving the tumble dryer; the violet curve is the absolute air humidity; and the red curve is the air temperature.

The evaluation of the energy efficiency (steam consumption per one litre of evaporated water) and drying performance (litres of evaporated water per minute) is shown at the bottom.

For the purposes of the energy consumption evaluation, the total consumption is divided into:

• Plain evaporation - the energy spent purposefully (since the water evaporation is the aim of the drying process).
• Heat loss (just an expert estimation). Anyway, one cannot influence this item in any way. 
• Warming up of the air used for drying - purposelessly spent energy: this is what we can minimise.

Evaluation of the energy efficiency and drying performance

There is a big difference in the energy efficiency and drying capacity in specific machines (refer to measurement in the tumble dryers and measurement in the ironers). However, there is a big difference between the machines that are adjusted properly or less properly. A laundry that washes 200 tonnes of linen every month and its tumble dryers and ironers are not in good condition may consume the energy used for drying and ironing equal to 160 000 EUR/year. Correct adjustments and proper operation of tumble dryers and ironers may bring saving in tens of percent out of this sum. This is the main objective of the service offered by company Procter&Gamble Professional to the customers.