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Heat drying: Practical applications that work |
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From Volume 23, Issue 13 - March 2008 |
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Heat drying is not a new concept.
Restorer’s have used heat knowingly or not to help dry faster or in hard-to-dry areas.
Most restorers, when drying a small room — such as a bathroom — place a dehumidifier and closed the door. They come back two days later and the bathroom is hot and dry.
What caused the drying? Was it the removal of moisture from the air by the dehumidifier, or was it the heat created by the dehumidifier?
I’ve had restorers tell me that they place two dehumidifiers with fans in one room and close the door so the room heats up and dries everything faster.
Sounds like heat drying to me.
We know that heat speeds drying, such as with hair dryers, hand drying machines, clothes dryers, etc. All are examples of adding heat to expedite the drying process. Note that all of the above also use air movement as part of their process.
Would putting a dehumidifier in the clothes dryer speed up the drying process? Likely the answer is “yes”, but not nearly as effectively as heat.
We have been taught that heat is acceptable, within limits. Limits on heat have been placed because dehumidifiers didn’t work well above 90 degrees Fahrenheit degrees and typical dehumidifiers cannot reasonably keep up with the high evaporation rates created by the additional heat in many water loss scenarios.
Heat and air movement/exchange
Heat provides the main source of energy to create evaporation.
Adding air movement creates a synergistic effect which results in faster evaporation.
Air exchange is a well-known method for removing large quantities of moisture-laden air fast and efficiently.
You can take an air mover, connect ducting, vent the tube outside and remove moisture laden air much faster than you can remove the water from the air with a dehumidifier.
A modest 2,000 cubic square foot heat drying system can exchange the air volume in a 2,500 square foot building with 9 foot ceilings once every 11.25 minutes.
Air exchange is an integral part of most heat drying systems and air exchange can keep up with the fast evaporation rates heat drying produces.
One type of heat drying system sits outside of the structure, takes outside air, heats it up and blows it into the structure.
Air movers are placed and distribute the heated air like a blender mixing your favorite drink. Air is then moved from inside to outside the structure.
Many systems now come with digital thermostats that are inside the structure. This allows you to set any temperature (70, 90, 135 degrees Fahrenheit etc.) you like and the system cycles to maintain the desired temperature.
Simple comparisons
Heat drying structures is similar in concept to how a clothes dryer works.
Fresh air is brought into the dryer, heated up, circulated and then vented out of the dryer and out of the house through a hose.
This process continues until the clothes are dry.
Does our clothes dryer care about relative humidity? Not really. Can the clothes dryer dry clothes when it is raining? Not only is the answer yes, but with seemingly little effect to the drying time.
In one hour a clothes dryer can dry our clothes.
We water damage professionals are proud when we dry a house in three days and just fine if it takes four or five days.
I shake my head every time I think of this. Are we not drying professionals?
Oversaturation?
Let’s say the air is 80 degrees Fahrenheit with 100 percent relative humidity.
If you put a pan of water on the stove, will any of the water evaporate as you are heating it up? Yes.
Basic theory is: Heat up the water and it will evaporate.
Heat energy also penetrates building materials and causes evaporation beyond the surface of the material.
This additional heat (energy) means you can typically dry a structure in 1-3 days without demolition.
How much heat?
I have measured the temperature of the hose on the back of my clothes dryer at the wall and it was 126 degrees Fahrenheit.
It doesn’t seem to damage anything I’m aware of. Does that mean 126 degrees Fahrenheit is an acceptable temperature to dry with?
I live in Arizona. 125 degrees Fahrenheit in a structure is nothing to us.
In the summer I take thermal image readings on exterior walls that register more than 140 degrees Fahrenheit at 9 a.m. It registers 150 degrees Fahrenheit and more in the attic, and 160 degrees Fahrenheit and more in the car.
In June, we can blow hot dry air from outside into the structure with an air mover and dry if we want. But we can’t make any money that way… retract statement.
Pull out your psychrometric calculator. If you take 80 degrees Fahrenheit air at 75 percent relative humidity, then heat the air to 125 degrees Fahrenheit, now you have 125 degrees Fahrenheit air at 19 percent relative humidity (approximately.)
Not only are these great conditions to dry the structure, but you would take days, if at all possible, to duplicate conditions with typical dehumidifiers.
Knowing when you are dry is as important as knowing when you are not.
Conditions in the structure change quicker when heat drying.
Over drying can be a problem in some scenarios, so monitor diligently; twice a day would be best.
No one likes to grossly over dry their clothes. The same thought should apply to drying structures.
Ken Horvath is a cleaning and restoration veteran of more than 26 years experience with thousands of successfully completed drying projects. He is a representative of Thermobile heat drying systems and founder of K & J Representatives, LLC., a company with the goal of advancing the structural drying industry through innovation. |
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Narrated Step By Step Examples of How the Eliminator/ELE 6400 |
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As Seen in Cleanfax |
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