Noelle --

The amount of humidification capacity needed will depend on the climate and
on the construction of the building and storage room.  A good mechanical
engineer would be able to advise you on the size and type of mechanical
equipment needed and on the level of humidification achievable without
damaging an existing building.  If you tell me more about the project and
its location, I may be able to recommend someone.

If your collection and your building are valuable, I would seek professional
help.  Also, if the current environment of the art is different than the new
one, you may need a conservation expert's advice to avoid damage from a too
rapid change in T or H.

If you are working in an existing building that does not have a vapor
barrier (as is the case with the majority of older buildings and more recent
buildings constructed for general purposes), you may not be able to increase
the humidity to 40-50% without damaging the building itself -- especially in
a climate with relatively cold and dry winters like New York's .

Without a vapor barrier to contain the humidified air inside the rooms, the
point of condensation where moist, warm indoor air meets colder dryer
outdoor air will likely occur inside the exterior walls and roof structure
of the building on cold winter days (an architect or mechanical engineer can
calculate this).  If the walls are masonry, you may see evidence of this in
spalling of brick or stone (chipping off from condensed water freezing and
expanding inside the masonry).  Many types of insulation lose their
effectiveness if wet.  If the condensed water rusts masonry anchors or rots
structural elements, you may be creating a hazardous situation as well.

You may be able to build a humidified room within a larger unhumidified
building and avoid the problem -- or live with somewhat lower RH as many
museums and libraries in older historic buildings do.

Ann Trowbridge, AIA


----- Original Message -----
From: "Randi Sue Smith" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, November 07, 2001 5:07 PM
Subject: Re: Relative Humidity Question


> I believe some kinds of engineers (ASHRAE? America Society of Heating,
> Refrigeration, and Airconditioning Engineers?) and some HVAC system people
> can calculate this for room size spaces/whole buildings.  They calculate
> heating and cooling loads, and figure in local climate conditions, and
> maybe building structure, insulation, etc.  Do you need to humidify and
> dehumidify?  I have seen figures for amounts of silica gel needed to
> stabilize a storage case (probably in the catalogs selling selica gel, as
> well as other references).  Portable humidifier and dehumidifier sales
> literature includes output information in various forms.
>
> Good luck!
>
> Randi Sue Smith
> Curator
> D.C. Booth Historic National Fish Hatchery
> 423 Hatchery Circle
> Spearfish, SD  57783
> 605-642-7730
> 605-642-2336 fax
> [log in to unmask]
>
>
>
>                     Oliver Hirsch
>                     <archivalframing@JUN        To:
[log in to unmask]
>                     O.COM>                      cc:
>                     Sent by: Museum             Subject:     Relative
Humidity Question
>                     discussion list
>                     <[log in to unmask]
>                     LSOFT.COM>
>
>
>                     11/06/2001 03:51 PM
>                     Please respond to
>                     Museum discussion
>                     list
>
>
>
>
>
>
> We are involved in an art storage project for a client, and have a
question
> regarding stabilizing the relative humidity of our space.  We aim to
> maintain a RH of 40%, and are writing the List to ask if anyone might be
> familiar with a formula or a rule-of-thumb that allows one to calculate
the
> size of humidification unit required to stabilize RHat 40-50% in relation
> to a specified cubic footage?  Thank you in advance for any help.
>
> Best,
> Noelle Roberts
> Hirsch and Associates Fine Arts Services
> New York
>
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