Mold is Back, Why?

[madhat]

The unit is VFD Racan with Chilled water only, has minimum position on O.A. for ventilation and econimizer cooling regulated by temperature only. set to 50F start. The unit was run with high chilled water temperatures and a chilled water valve that wouldn't open all the way. Also with clogged drains and dirty coils for god only knows for how long. Unit was power washed including coil from both sides, with Evap. cleaner. The only things not power washed were the bearings and motor which were shrink wrapped after degreasing and wiped down with Calgon CD. Chilled water valve actuator was replaced, chilled water temperatures corrected. Unit was allowed to dry and put back in service for several weeks. Then motor and bearing blocks were reteated with CD, and wrapped. Entire unit was fogged till dripping with CD, allowed to dry. Now the mold is back on the steel structure for the fan and on the fan itself.

[HVACJOEK]

McQuay Makes for their Swt and Swp self contained units an untraviolet light option that does work on killing mold and such... here is a quote from their "Catalog 860-7".

"The ultraviolet lamps irradiate the coil and drain
pan surfaces with light in the 245 nanometer wavelength of the
light spectrum (UV-C). UV-C light has proven effective in
killing most bacteria, molds, and viruses in both laboratory and
practical application."

I have seen them work in Hospital and treatment centers units. I hope this helps you with your quest for a better IAQ :cool:

[tex~n~oz]

Hey Hatter.. I've had the same trouble and it never goes away living in the tropics.. The UV-C lights do a fairly good job of keeping mold off surfaces that are 1) close enough to the light source to get a good dose. 2) not shielded from the light source. The UV-C does NOTHING for the hidden areas of the coil fins, drain pans, fans, etc..

The source of your mold isn't the issue, the nutrients that it feeds on are. Mold loves low nitrogen, high cellulose material to grow on, that's why Stachybotris Chartrum (toxic black mold) is such a problem in sheet rock, white pine woods and dust.

Because the mold spores live for 200 years, once established, it's almost impossible to get rid of. They re-introduce themselves through the filters once the unit comes back online. So you are limited to 1) removing the source of nutrients or 2) chemically combating the mold in it's problem spots.

Getting rid of the source of it's nutrients are almost impossible and it only takes one microscopic spore to re-infest.
Chemically treating the air handler is the best and easiest way. Here we buy cylinders of inert gas mixed with Benzalkonium Chloride and every couple of hours the AHU shuts down, and a whiff of gase is injected into the AHU. The unit stays offline for another couple of minutes to allow the gas infuse into the coil and hidden spaces. Because the chemical is hygroscopic, it tends to attach itself to the water molecules and self rinses. I've not had one complaint of odour or allergy and the coils and chambers are perfectly clean year round.

Good luck with your mold issue mate.. It's a real buggar to get a handle on.

[retired1]

If it is in the airhandler , the spores are in the building (drywall, ceiling tiles, carpet, etc.) and in the ducts. Just cleaning the airhandler will not get the job done.

Another method of combat is to once a month at the end of the business's day (best done on a Friday evening, letting the airhandler run all weekend), go up and spray the inside of the air handler with pool chlorine and let the air handler run all night. Next morning you will hear how clean the building smells and the current batch of mold in the air handler and ductwork should be dead.

Every third month use bromide (pool baqucil) to keep the mold from becoming resistive to chlorine.

ONE LAST THOUGHT: Using bromide all of the time is more expensive upfront, but is less corrosive than chlorine and will allow the airhandler to last longer.