Cleaning & Restoration Association News

Is It Hot or is It Not?

September 8, 2005
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Change is inevitable. I remember the first air mover I ever saw. It consisted of an old furnace blower and motor with some sheet metal, all screwed together.

When I first started doing water-damage restoration 30 years ago - flood sucking in those days - the only tools we used to ascertain the level of damage were our tennis shoes. If the socks inside our shoes got wet, we knew it was a pretty wet flood.

One of the big new changes we see today is the application of heat as it pertains to drying. I solicited the help of Jeremy Reets, owner of Champion Cleaning Systems in Sharpsburg, Ga. Jeremy has worked with, studied and tested heat-drying systems over the past couple of years, and he is responsible for much of this article.

Does heat dry?
Remarkably, almost all other drying devices we use are heat based. Clothes dryer? Heat. Hair dryer? Heat. Food dehydrator? Heat. So, does heat dry? Well...yes and no. Heat, or energy, is one of the factors that creates evaporation (Image 1). The amount of energy in water molecules determines what phase those molecules will be in: solid, liquid or gas. In a water-damage environment there is a lot of liquid that needs to be changed into gas (evaporated) and removed from the structure through evacuation. Heat, while effective for evaporation, does not remove moisture from the environment.

What is the slowest part of the drying process - evaporation or evacuation?
Evaporation. We have the dehumidification technology to draw moisture down to almost non-existent levels, but we still have to wait on evaporation to take place. Therefore, we must speed up evaporation. Heat can help if you understand what it does.

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When doesn't heat work well? If it is misapplied, will it create problems?
It would be incorrect to conclude that just adding heat to a drying job will increase the rate of evaporation during water removal. The evaporation pie (Image 2) illustrates the four factors affecting the rate of evaporation:
  • Energy available to the water
  • Airflow to the water
  • Vapor saturation levels
  • Time

    Adding heat only affects one part of the evaporation pie, and only if the energy is readily available to the water. If heat is not available in abundance to the water, the results will be negative.

    The process of applying heat is different from standard air mover/dehumidifier setups, and proper processing is necessary for heat to dry effectively. Effectively directing and concentrating heat energy on the water in a structure results in quicker evaporation (Image 1).

    How can heat drying possibly work when it is 90 degrees outside, with 90 percent humidity?
    In order to be able to use heat to create evaporation at an ultra-high rate of speed, you must understand and be able to measure the relationship between water and energy (psychrometry). There are several factors involved in measuring this relationship:

  • Specific humidity
  • Temperature
  • Relative humidity
  • Vapor pressure
  • Dew point

    Since water is in a constant state of cyclic phase change - between solid, liquid and gas - based on available energy, restorative drying depends on creating conditions that keep more water in the gaseous state and allow less moisture to return to the liquid state. This is called net evaporation (Image 3).

    Net evaporation can be accomplished, regardless of the temperature and humidity that Mother Nature throws at you, if you are able to control evaporation factors and saturation levels in the drying environment. The only way to do this is through evacuation, which consists of dehumidification, ventilation, or, even better, a combination of the two.

    When does heat drying work well? How can you use it to maximum effect?
    Heat drying can be very effective in both the middle of winter and on the hottest day of summer. It is the control and application of the heat that will lead to either success or failure.

    Can heat-based evaporation equipment be used in low humidity regions of the country?
    Absolutely. Return to Image 2 again for a minute: Energy, Airflow, Saturation and Time. In low-humidity regions you must still provide energy and airflow, or you will increase time. You can't get around the evaporation pie.

    How does heat drying work in concert with dehumidification?
    When properly applied, heat drying will create significant water vapor. This gaseous water must be removed either through some form of dehumidification or by evacuation. How vapor-saturation levels affect evaporation is a discussion for another time, but in short, the higher the saturation of vapor in the drying environment (relative humidity), the more energy required to achieve net evaporation (more water molecules changing to gas than returning to liquid).

    When you are working at higher temperatures (90-100 F), how do you dehumidify, since dehus are not as effective at high temps?
    Either use high-temp dehus or use the air conditioning. Yes, an air conditioner is a true high-temperature evaporation unit. It may blow your mind that we would consider using heat and the air conditioning at the same time. How could that possibly make sense? Your grandmother may even call you up and give you what for. While this may seem counterproductive, it actually speeds drying in many situations.

    Is there evolution in drying science?
    Yes. At the Connections Convention and Trade Show 2005 in Las Vegas, Sept. 23-25, dozens of systems and programs built around drying technologies will be on display. Wouldn't it be nice to find a system that uses all of the pieces of the evaporation pie at their most effective levels?

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