Keep in mind that the outlet temperature is very close to the actual load temperature, so this setting is the most critical.  It should also be understood that a wet load can handle higher temperatures than a dry load, since the H2O helps to protect the products from damage by keeping them cool.  However, this condition changes as the moisture is removed.

Assuming that you have a microprocessor or PLC that allows formula set- up, you should consider the following steps.

A. An initial high-heat cycle may be used to drive-off a high percentage of moisture.  This portion of the overall cycle is typically used in the first 3-5 minutes. Temperatures might be something like 600F inlet and 200F outlet.

B. After the initial heat, switch to a high, medium or low temperature cycle, depending upon the products being dried.

HEAT CYCLE EXAMPLES:

HIGH               

INLET TEMP: 600F (CONDITION: 600F)

OUTLET TEMP: 200F (CONDITION: 190F)

MEDIUM       

INLET TEMP: 550F (CONDITION: 550F)

OUTLET TEMP: 190F (CONDITION: 180F)

LOW                

INLET TEMP: 525F (CONDITION: 525F)

OUTLET TEMP: 170F (CONDITION: 170F)

  1. For "time and temperature", only, dryer controls, the temperatures are set and the dryer runs for a preset amount of time.  Precision is improved with the ability to control the heat cycle using both inlet and outlet temperatures.  Problems arise with changes in load weights and/or moisture retention.  For example, if you perfect a time formula for a 400-lb dry weight load of towels, but your next load is 440-lbs., the towels won't be dry and will require an expensive restart to finish them.

  2. An algorithm adds even more precise control by allowing the formula to regulate heat by the preset inlet temperature and then switching to the preset outlet temperature.  In this case, the temperature rises until it reaches the desired inlet temperature, then the regulation of the heat control is switched to the outlet temperature setting, which is crucial at the end of the cycle to prevent product damage.  Instead of using time to determine the proper point to end the cycle, the algorithm can be set-up to end the cycle when the inlet temperature drops to some temperature, or when it drops to a temperature for more than a certain amount of time.  In other words, once you start controlling the heat by the outlet temperature, the inlet temp. begins to drop.  You need less and less inlet temperature to maintain the outlet temperature.  Therefore, at some point in the inlet temperature's decent, the laundry becomes dry.  The problem with this method is accuracy... the "at some point" question that the programming must answer is often not very accurate.

  3. A humidity sensor can be used in place of, or in conjunction with, an algorithm.  In this case, the moisture content of the exhaust air is measured. The heat cycle can be terminated at a predetermined humidity level (typically determined by you through testing).  Problems with humidity sensors... it's difficult to keep the sensitive humidity probes clean, they lose calibration over time and, often, the cost to replace them means that the operator goes back to time & temperature formulas.  ** One note of interest, instead of using humidity probes in the airflow, commercial dryer manufacturer, UniMac, has developed something that they call "OPTidry™".  Moisture sensors are installed within the lifting ribs of the dryer basket and accuracy is claimed to be "unmatched".  It remains to be seen if the sensors will hold up in the tumbling environment, however. 

  4.  AutoDry™ is a new set of programming techniques used by CLM; whereby, cycle termination is determined by a heat value. This value is generated from the initial temperature rise to set-point.  The larger the load and the more moisture within it, the greater the energy used to bring the load to temperature.  This heat value along with temperature comparisons are formulated to calculate the heat cycle termination point.  AutoDry™ is claimed to be more precise than temperature  algorithms and more dependable than humidity sensing.

C. The moisture is now removed from the load; however, products with thick waist bands, cuffs or collars will require additional dry time.  An ending heat cycle can be run, typically for a period of 3 - 5 min. to aid with this issue.

D. Finally, a cool down cycle should be run to bring the load down to a safe hands-on temperature... say 135F.

Reversing may be required to prevent tangling of large pieces; such as, sheets, blanks and large towels.  However, you don't want to reverse unless it's absolutely necessary.  Reversing adds time and inefficiency to the cycle.  This is true for two main reasons. 

First of all, during reversing, the load drops to the bottom of the basket for several seconds each time the rotation direction is changed.  This drop to the bottom reduces the air-to-goods access, and subsequently increases dry time and reduces efficiency.  Secondly, the design of many dryers is such that performance drops when the rotation is reversed.