Does any know at what point mold would become an issue with a space temperature of 92 degrees with a RH of 60%.
Wow... tough question. This can depend on a number of factors. Types of mold spores in the air is the main thing. Some molds form at varying temperature/humidity combinations. Molds require temperature and humidity to be in the range that fosters each type of mold's growth. Mold spores are the seeds, so it depends on what seeds are present; often changes with wind direction and seasons. Simply having the lawn crew cutting the grass can spike mold spore generation. The fourth element that molds require is bacteria. Mold needs bacteria as a food source; bacteria is omnipresent often found with organic matter (dead skin cells inside buildings for example). So if you are unable to keep mold spores out (extremely difficult), or manage temperature or humidity to eliminate condition for mold growth (unlikely) you can still kill the bacteria. You can use something like non-toxic hydroxyl radicals or if there are no health issues, ozone or other sanitizing substances. Best regards,
Tom
If conditions are right mold will grow. The paper back on drywall is a good area, moisture in the track of slider window openings, leaks under sinks, etc. One way to combat higher than wanted humidity is use an HRV (Heat Recovery Ventilation Unit) to provide proper air exchange and at the same time reduce humidity. Grasses and trees will hold all kinds of spores. When sampling for spores inside, a control sample is taken outside as well. It should be done during decent weather and if it rained recently one needs to wait a few days for it to dry out otherwise you will get inappropriate readings for your outdoor control sample. Hope this helps as well!
I would not only worry about mold in that type of environment, I would also worry about other forms of bacteria. Air exchange would be critical.
Harry Kohal www eaglecmms.com
If the RH is 60% and the air temp is about 90 degrees, condensation will form on a surface that has a temperature of 74 degrees. On the other hand, if all surfaces are at the normal air temp of 90 degrees, and air is still 60%, then condensation will form when air of 105 degrees hits it (due to convection, or workday temp cycles). Find a "dew point" chart through Google.
Air with a dry bulb of 92F and a RH of 60% has a dew point temperature of 80F. So, any surface with a temperature of 80F or below would condense this air and provide an environment suitable for the indoor amplification of mold.
David W. Bearg, PE, CIH
I follow arpoa re: conditions.
Keeping things in perspective, we're lucky to have the little fungi and bacteria with their appetites. We'd be 3 miles deep in undecomposed tree trunks etc. if it were not for them.
That said (and reflecting Tom Moriarty's comments) I found, in a building complex where much of the human occupied space was used only a few days per week, or even per month, in a part of the US (inland Mississippi) where the air can and does include a good bit of moisture, I eventually obtained essentially zero visible mold. Three basic measures worked quite well. (1) Thoroughgoing cleanliness - items and surfaces, obvious and obscure, were made is as free of dust, debris particles, grease and oils, etc. as practical. Books, rugs, fabrics - clean appropriately. Allow no leakage when it rains. The preceding make surfaces less hospitable to bacteria. (2) No sensible moisture - open up and ventilate or (even better) circulate air in a leisurely way everywhere; (3) within reason (your energy and equipment budgets, and discomfort or risk of valuable building contents determine "reason"), remove moisture from the atmosphere.
Once we had everything clean everywhere, I bought an inexpensive wick type psychrometer ($35) which measures relative humidity and air temperature, and left it here and there, wherever someone had sensed a moldy odor or coughed etc. , or we had previously removed mold. In some spaces, where the building envelope allowed ready exchange between inside and outside air, and with indoor temps approaching 90, relative humidity peaked out just under 80%. That's still non condensing. As long as air is circulating into all the nooks, crannies, closets, etc., those spaces, previously a constant problem, stayed free of sensible mold.
We reduced energy costs substantially and halted visible mold and condensation that had previously been a large problem all over the complex of historical and auxiliary buildings. A few children sensitive to air quality were much more comfortable.
Of course, there were still spores everywhere - more or fewer from time to time - as TM describes above. It's just that mold and bacteria found the whole facility less hospitable.
Sorry for the long note, but our experience shows that remarkable (albeit less than ideal) results are obtainable without large expenditure while you find a more engineered solution and set a capital budget item.
Concur too with David, Dan, and HarryK, emphasizing air exchange and surface temps.
chief51,
Any mold problem is really a moisture problem. Our organization deals with this exact question on a daily basis, as we work with thousands of water damage mitigation professionals on a yearly basis.
In the most basic and critical terms, mold will grow on any surface where organic materials are present (even just bio-film or dust) if there is ample moisture present IN THE AIR ON THE SURFACE OF THE MATERIAL. This moisture / humidity at the surface of the material is referred to as a 'water activity' (abbreviated as aW).
As mentioned above, different species of mold require different aW. However, if we take those species that (1) may commonly be found in indoor environments and (2) require the lowest aW, then we can set for you some simple goals to prevent mold problems.
The two most common fungi found indoors due to moisture related problems are Aspergillus an Penicillium. These molds are 'Xerophilic' and require a aW of .66-.70.
That may sound a bit confusing initially, but let me explain.
Water Activity is simply the humidity available right at the surface of the material, where '0' is none, and '1' is saturation. Translated to more common terminology, it is an expression of the 'relative humidity' (RH) in a slightly different language. '0' = 100% RH, and '1' = 100% RH. In other words, the Xerophilic fungi mentioned above require a RH of 66% - 70% at the surface of the material.
Your scenario had you with a 60% RH in the ambient air within your occupied space. This number is close to the required moisture load needed by Xerophilic fungi.
The more significan problem, however, is that your 60% RH was at a temperature of 92 degrees Fahrenheit. Relative Humidity is a very interesting quantification of moisture in air. Although you may have 60% RH in the ambient air, if the temperature changes - so will your RH. In very simple terms, RH is the amount of moisture in the air expressed as a percentage of what the energy (loosely, temperature) can support. Your temperature of 92 derees can 'support' a lot of water vapor.
As that temperature changes, the amount of water that it can support will also change. In other words, as the air is 'cooled' and losses energy, there is less energy available to support water vapor.
Some of the earlier posters referenced this by discussing condnesation and dew point temperature. Water vapor is a high energy state of water. As energy is removed from (released by) the water vapor, it tends to revert to a liquid (condense).
Here's my point: if any materials, environments, etc. are COLDER THAN 92 degrees, then your ambient air will not remain at that temperature. It will cool. As it does, the RH value WILL INCREASE.
To determine how much, you would need to look over a 'psychrometric chart.' I've done that from my end, and here's what it says:
If cooled to approximatly 86 degrees Fahrenheit, the RH of the air in your example would rise to 66% RH. This would result in a high enough aW to support the growth of Xerophilic fungi.
This must be prevented.
You can manage this a few ways.
Easiest way: Determine your coldest temperature that your indoor air will be exposed to, and utilize that temperature to set an indoor humidity goal. This is quite simple to achieve, and is the BEST wat to prevent indoor mold problems. I can supply you with this calculation easily, if you would post that data here for me to evaluate. Humidity can be managed and controlled by dehumidification (most reliable) or by ventilation (if you have acceptible outdoor conditions - again I can provide input here if you can share more about your situation).
More complicated way: Use the temperature I mentioned above (86 degrees Fahrenheit) to set material temperature goals. Ensure NO materials or other spaces within the structure that will receive this air are at or below this temperature.
Sorry for the long post, but wanted to make sure I hit all the bases.
If you're curious about learning more, I use two documents as authoratative sources on these issues:
IICRC/ANSI S500, 3rd edition, 2006 (www.iicrc.org)
New Guide to Restorative Drying, 2006 (www.dri-eaz.com)
Brandon Burton
Technical Education Manager
Restoration Sciences Academy
Correction to my post above:
Water Activity: '0' = 0% RH, and '1' = 100% RH.
Should have reviewed my post before posting it. Sorry for the typo.
The other issue to consider is whether this humid air is allowed to travel to other parts of the building where, if cooler surfaces are present, condensation could occur, thus contributing to either condensation, mold growth, or both
Excellent information from Brandon and the others. You may also want to consider the following three options.
1. Using very inexpensive temp/humidity data loggers that can be attached by velcro at various areas of the facility. With your computer and software you can download the data from these units to get important information about your environment. they are called HOBO dataloggers.
2. If there is an HVAC system present keep the blower on the 'On' setting not auto. This will help circulate air through the facility.
3. On at least a monthly basis treat the facility using an electrostatic sprayer with a broad spectrum disinfectant. It is extremely inexpensive and safe including for food contact surfaces. It is registered with the EPA as a category 4 product. It is NSF certified. It dries in minutes, requires no downtime, no wiping or rinsing after application and will not streak glass, windows etc. My company treats indoor environments as well as buses, homes, playgrounds, etc in the Northeast. If you want more info on any of the suggestions reply to this post with a contact point.
And as posted by other members none of the above three steps takes the place of routine housekeeping & cleaning.
Bill Haile
CEO & Chief Inspector
American Ecotech Corp.
Long Island NY
americanecotech@gmail.com