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Q: I read with interest the information last month on how many air movers to use on a job. But what about dehumidifiers? These are expensive pieces of equipment and I only want to purchase what I need.
A: Deciding how many dehumidifiers you need is important. It’s something you need to determine exactly, as wasted equipment does you no good.
Last month we listed the four types or classes of water loss, and how to use that information to determine air movers. That same information is important here.
You can refer to the January issue of CM/Cleanfax magazine, page 18, for that information.
The following chart is used in the industry as a guide for the first day in determining the type of dehumidifier you need.
Then on the second day, we use our moisture detecting instruments to determine if more dehumidification and/or invasive procedures are needed
How to calculate and use this chart — Day 1
- It is imperative that the restorer identify the color of the water loss (not just source) to determine how to properly proceed. (What goes and what stays).
- The restorer then needs to identify the classification of this water loss based upon the definitions (Class 1, 2, 3, or 4).
- Calculate the cubic footage of the room or area to be dried. This area should be minimized to the affected areas only by creating a "drying chamber". To calculate cubic feet you must multiply the length of the area by the width. This total gives you the square feet of the surface. Take the square foot total and multiply by the height of the room. This total is the cubic volume (foot) of airspace.
- Take the cubic feet of air in the drying chamber and divide it by the factor in the chart matching the dehumidifier type and classification of the water damage. For example: 12,000 cubic feet in a Class 3 loss when using an LGR dehumidifier means: 12,000 ÷ 40 pints = dehumidification needs of 300 pints removal at Association of Home Appliance Manufacturers (AHAM) specifications.
- Divide the pints available/cubic feet by the AHAM rating of pints of your dehumidifier and place that number in the "drying chamber" on day one. Example: The LGR you own is rated at 150 pints removed at AHAM (80 degrees Fahrenheit at 60 percent relative humidity in 24 hours) means two (2) of these units are placed in the drying chamber to take care of the 300 pints.
- Psychrometric monitoring, including grain depression readings, should be taken often. Grain depression is calculated by taking thermo-hygrometer readings of ''air in'' and ''air immediately out'' of the dehumidifier. Calculate the grains in and out, then subtract the out going grains from the incoming grains. This is grain depression. A grain depression of 10 or below is the cut-off point for refrigerants. Constantly record your findings!
With "in place drying", the air movers are placed every 10 to 14 linear feet at a 45 degree angle — against the wall — in the same direction.
This system allows for an eventual balance between evaporation and dehumidification.
For the first five to eight hours (approximately), you will note a "spike" in relative humidity and specific humidity.
After approximately five to eight hours, you will note that the grains begin to travel on a downward path.Evaluating your efforts — Day 2
Re-evaluate the structure using moisture meters and the thermo hygrometer along with psychrometry and make the necessary adjustments.
Craig Jasper is president of the Cleaning Restoration Institute (CRI). He is an Institute of Inspection, Cleaning and restoration Certification (IICRC)-approved instructor and the author of many articles appearing in numerous trade publications. He has worked with many mills and franchises putting together courses and projects to improve the cleaning and restoration industry.