Transcript Condensation Control Experiences in a Building with

Condensation Control
Experiences in an “historic”
Building with Movable Sash
ASHRAE Anaheim Seminar 53, 1/28/04
Stanley A. Mumma, Ph.D., P.E.
Professor, Architectural Engineering
Penn State University
email: [email protected]
Web: http://doas-radiant.psu.edu
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What are your first thoughts when
you consider ceiling radiant cooling
panels?
$
Capacity
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Requirement for Ceiling Radiant
Cooling Panel Application
20-70%
less OA,
DOAS Unit
W/ Energy
Recovery
Parallel
Sensible
Cooling System
Cool/Dry
Supply
High
Induction
Diffuser
Building
With
Sensible
and Latent
cooling
decoupled
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Site for the condensation control
experiences: 1900’s Engineering Units
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3 of 12 36” X 96”single glazed movable
sash serving the 40’ x 80’ lab
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The Space as
seen from
inside
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System Schematic
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Size and extent of the major
components in the system
Radiant panels
8 @ 2’ x 40’—640 ft2: <4 ton
Chiller
2 @ 5 ton each
High Induction diffusers
8 @ 2’ x2’—150 scfm each
Air handling unit with EW, MS
Operated at 1200 scfm
Extensive instrumentation
T, flow—air & water, RH, CO2
DDC Controls
BACnet, web accessible
Pumps
Two circuits at 22 gpm.
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Condensate control method
1. Maintain the panel
inlet water
temperature above
the space DPT
2. Condensate sensor
is hard wired into
the power supply of
the panel spring
return control
valve.
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Field experience, student co-op?
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The lab is used by a new (but just one) group
of students per year
Near the beginning of the semester, I will
address them on the system—and make just
a few points.
• Leave the doors or windows open and radiant
cooling will be lost—not recommended
• Piling things on top of the panels will cause the
cooling to be reduced—not recommended
• Slicing the exterior duct insulation not a good
idea, condensate may drip on you and your
work.
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Student’s response?
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They never opened the windows or
propped the doors open. The condensation
control was unchallenged
An instantaneous open door and window
tests on a hot humid summer day thus
ensued.
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The data:
OA DPT
Windows opened
CHWT exceeds
room DPT after
22 min
2.5F
CHWT to panels
Room DPT
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Extreme Condensation, after 8.5 hr.
on a chilled panel intentionally
held 14oF below the space DPT
Fin
Isothermal
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Control response:
Windows
opened
Valve begins
to modulate
again to
maintain
CHWT at the
space DPT
Valve
responds
Valve
closed
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No Condensation on the panel
after the test:
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Very Slight Condensation on the
chilled water supply pipe to the panel
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What about the controls cost in a
large movable sash building with
many zones
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Panel capacity control: CV, VT or VV, CT
Our building used ~CV, VT
A large multi zone building would likely
use VV, CT to each zone
What happens then in large building if the
windows go open?
• Monitor the window position
• If OA DPT exceeds space design close the
modulating control valve.
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Conclusion:
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In the historic building with a large area
of movable sash, condensation control
was achieved easily, even when the space
DPT was suddenly elevated by opening all
of the doors and windows. The test was
repeated many times, with the same
outcome.
The passive fail safe sensor has yet to be
activated under automatic control—
consequently no condensation problems
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Oh, about capacity concerns
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Rules of thumb:
• 400 ft2/ton, or 30 Btu/hr-ft2
• Panel capacity, 20-30 Btu/hr-ft2
• Conclusion, entire ceiling and perhaps some of the
wall must be covered with panels.
What’s the problem here?
• A large percentage of the design chiller load is OA
• DOAS can take part of the space sensible and
100% of the space latent load
• Generally for low density occupancy spaces <50%
ceiling need be in panels
VAV reality check:
• 1 cfm/ft2 at 55F can do about 20 Btu/hr-ft2.
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First cost must be higher?
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Reductions in first cost with
DOAS/radiant
• Large reduction in chiller size, and associated
cooling towers, pumps etc.
• Ductwork is significantly reduced and VAV
boxes eliminated.
• AHU is much smaller.
• More rentable space.
• Floor to floor dimension—cost savings in
construction
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And OP cost is reduced by 30 to 40 percent
compared to VAV.
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Finally,
Terror resistance.
The system would look schematically look like:
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OA
Outdoor air unit with TER
Radiant
Panel
Space 3,
DOAS in
parallel w/
CRCP
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