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Humidity Controlled Dryer

Dryer uses humidity gauge to detect when clothes are dry
 
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As indicated above, this dryer will have a humidity gauge. Note that what such a device actually detects is RELATIVE humidity, the amount of moisture in the air compared to the amount of moisture that the air could actually hold. Warmer air can hold more moisture than cooler air.

When this dryer is activated, the first thing it does is take a reading from its humidity sensor. The onboard processor (every dryer nowadays has one, right?) converts that into the equivalent humidity percentage at the dryer's programmed operating temperature. Now it has a basis for comparison.

When the dryer starts turning its drum and warming the damp fabric inside it, some of the moisture in the fabric will evaporate, and the humidity inside the dryer will go up. This will be monitored by the humidity sensor, of course.

The onboard processor can constantly compare the currently-measured humidity inside the dryer to the computed level, equivalent to warm air with no wet fabric present. When the measured amount drops to become about the same as the computed amount, the dryer shuts off. It never wastes electricity by continuing to run after the fabric is dry.

Vernon, Aug 31 2009

prior art http://www.freepate....com/EP1744152.html
One of many? [csea, Aug 31 2009]

Smeg dryer with humidity sensor http://www.debenham...-1?CMP=OTC-GOOGLEPS
seems such a sensible idea that it's already been done, though I hadn't heard of it either. [TheLightsAreOnBut, Aug 31 2009]

And I found Hotpoint, Miele, and more. http://www.johnlewi...e/Feature.aspx?Id=8
Check out the section marked "Energy efficiency and the environment" [TheLightsAreOnBut, Aug 31 2009]

[link]






       I thought all modern dryers used humidity sensors. e.g. [link]. My own fairly ancient drier has a setting which uses a 2-conductor high impedance sensor with a long time constant to detect the moisture content of the clothing.   

       Not clear how this differs from standard practice.
csea, Aug 31 2009
  

       All the old dryers that I'm familiar with have a simple timer, plus a simple way to set the amount of heat. The user is expected to guess how much of them it takes to dry the fabrics. I was not aware that this Idea might already be in use; I did do a Search here to see if the Idea had already been posted, though....   

       I see that that "prior art" link doesn't mention any need to do computations on the humidity reading. In this paricular Idea, it is quite important to know the ambient humidity BEFORE the dryer is started. If no conversion-for-temperature calculation is done, a high ambient humdity would always be detected by the sensor, and could keep the dryer from ever shutting off, because the machine could assume the moisture it detects is still coming from the fabrics in the dryer.
Vernon, Aug 31 2009
  

       A [Vernon] idea at approximately 200 words? Gets my vote. Humidity is practically non-existent right now, and my laundry yesterday dried so fast that the dryer company actually made money on me for a change.
normzone, Aug 31 2009
  

       I like the idea, though I don't know how widely humidity sensors are already used in tumble dryers.   

       But the computation business is probably not needed. During the cycle, the humidity must rise initially, then stay level and high, then fall once the clothes are dry, then stay level again - just wait for a drop in humidity followed by a plateau, shirley?
MaxwellBuchanan, Aug 31 2009
  
      
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