Re: mold in a floor plenum due to condensation

[Guest guest]

Dear Colleagues:

Since %RH is a function of temperature, and temperatures vary within buildings,

I find it far less potentially confusing to deal entirely with just dew point

temperatures.

To prevent condensation then, one only needs to be concerned that the dew point

temperature of any surfaces shall not be below the dew point temperature of the

air, and vice versa.

Sincerely,

W. Bearg, PE, CIH

Building Scientist

-------------- Original message ----------------------

> :

>

> So what is the desirable RH range?

>

>

>

>

>

>

>

>

> > ,

> >

> > Unlike most indoor environments, computer rooms, server rooms or data

centers

> > have very specific needs (lower temps but higher %RH than other indoor

> > environments). Keeping the rooms humidified suppresses the static electric

> > discharges that could short out the computers/servers. Unfortunately what

it

> > appears to be in this case is that the Liebert units

> > (http://www.liebert.com/dynamic/catprodlist.asp?pid=4 & cycles=60HZ

> > <http://www.liebert.com/dynamic/catprodlist.asp?pid=4 & amp;cycles=60HZ> )

need

> > to be calibrated and set to the proper set points. If the unit is not set

or

> > calibrated properly, then the basics principle for this room will not be

> > within spec. The room should not be like a meat locker with high %RH.

> >

> > Normally Liebert units have a 4² pleated filter with a spot efficiency of

60%.

> > Dust counts (0.5µm) within the room would be kept to an extreme minimum.

Some

> > standards do exist for dust within these types of environments:

> >

> > FED STD 209/E (with drawn in 2001)

> >

> > http://www.set3.com/papers/209e.pdf

> >

> > ISO 14644

> >

> > http://www.iest.org/iso/iso.htm

> >

> > As far as cleaning computer rooms there are companies that specialize in

that

> > sort of work.

> >

> >

> >

> > Geyer wrote:

> >>

> >>

> >> Steve:

> >>

> >> Your point is very astute and well put. I think you are onto something

> >> here.

> >>

> >> Regarding static electricity....the dirtier the air (i.e., dust particles)

> >> the greater the potential static electrical capacity in aggressive airflow

> >> environments. The subject room being one containing computer servers is

> >> probably well filtered; to keep dust to a minimum. This said, I imagine

that

> >> a lower RH can be tolerated given the cleaner air ­ cleaner than outdoor

air.

> >> If I recall, the original post indicated that RH in the plenum was greater

> >> than 60% at 40F - this seems high to me given the clean-room like

> >> environment, and a lower RH may/could be tolerated. However, like you

> >> pointed out, if the plenum is 40F at 65%RH, then the RH will greatly

reduce

> >> as the air is heated by the servers above, and at the ceiling height the

air

> >> may be quite warm with a very low (and possibly undesirable) RH.

> >>

> >> I can see where this gets to be a challenging issue for this type of

> >> application. Moreover, I often find that these rooms rely on

re-circulation

> >> with minimal, if any, fresh air make-up; which compounds the problems of

> >> mitigating biological bloom. A delicate balance, with responsive controls,

> >> and good distribution uniformity is warranted.

> >>

> >> Again, assuming that sub-slab vapor intrusion is not significant, I

believe

> >> your observation has merit.

> >>

> >>

> >>

> >>

> >>

> >>

> >>

> >>>

> >>>

> >>>

> >>>

> >>> In a message dated 6/6/2007 1:07:04 PM Eastern Daylight Time,

> >>> mgeyer@... writes:

> >>>

> >>>> Don¹t forget about modifying the HVAC system too, and possibly installing

> >>>> additional dehumidification capacity.

> >>>>

> >>>

> >>>

> >>> Leibert systems typically ADD humidity for static control in computer

> >>> rooms. The floor plenum is a supply plenum. The return is at the top of

> >>> the AHU in the room which is warmer due the server heat sources. I wonder

> >>> if the problem isn't purely psychrometric due to wiring resting on the

cold

> >>> slab being able to achieve the dew point when humidified supply air enters

> >>> the cold floor space. The RH is regulated in the warmer computer room,

not

> >>> the supply plenum after the coils. Maybe the wires are cold because the

> >>> floor cold and there is no infiltration through the slab. The obvious

> >>> moisture source is the humidified air. There may be others.

> >>>

> >>> Steve Temes

> >>>

>

>