Direct Digital DBT, %RH, and Condensate Control for a DOAS-CRCP system

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Direct Digital DBT, RH, and Condensate Control
for a DOAS-CRCP system

• ASHRAE Winter Meeting Symp. 3, Orlando-Feb. 6,
  2005Stanley A. Mumma, Ph.D., P.E. Jae-Weon
  Jeong, Ph.D.Architectural Engineering
  DepartmentPenn State University, _at_ Univ. Park, PA

sam11_at_psu.edu jqj102_at_psu.eduhttp//
doas-radiant.psu.edu
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Presentation Outline

• First thoughts when considering DOAS-CRCP
  control.
• DOAS-CRCP design philosophy.
• Summary of the design issues you may wish to
  consider.
• Field experience with single zone controls.
• Extension to multi-zone applications designed
  with a DOAS supply air temperature equal to the
  required design SA DPT. Why you ask!

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First Thoughts about control?
Points list
Nyquist Plots
Stability and dynamic response
Schematics
Z and Laplace Transforms
Sequence of operation
Bodi Plots
BACnet
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DOAS-CRCP Design Concept
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Issues that impact Control

• Thermal comfort, temperature and humidity
  control.
• DOAS SAT, neutral or cold.
• Envelope, Internal generation (high or low occ.
  Density), Geo. Loc.
• Std. 62, and IAQ.
• ADPI with low to very low air flow.
• Condensation control.
• Instrumentation for control and monitoring.
• Controlled devices.
• Desire for BACnet compatibility Web Access.
• Control hardware and software.

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Schematic Control Points Single Zone
DOAS-CRCP System
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2. Occupied-Unoccupied Control
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3. Enthalpy Wheel Control
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4. Chiller Control
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5. Cooling Coil Control
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6. CRCP Control
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7. Thermodynamic Calculations
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Extension to Multi-Zone Facility

• Case 1, Low Occupancy Density Facilities such as
  Offices.
• Maintain low SAT, i.e. EW with CC.
• Modulate the panel inlet water Temperature rather
  than flow as in the single zone.
• Space DPT sensing not required, provided DOAS
  supply conditions maintained, but condensation
  sensing is still needed in some perimeter spaces.
• If movable sash facility, sash position sensing
  is required.

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Extension to Multi-Zone Facility

• Case 2, High Occupancy Density Facilities such as
  schools.
• Maintain low design SAT with capability of
  central free reheat, i.e. EW-CC-SW.
• A critical space reset control will be discussed
  next. The intent is to minimize terminal reheat
  energy use.

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Paper Figure 3
ReHt
EW--CC-- SW
CRCP
Is Terminal Reheat allowed? Yes!!! See ASHRAE
Std. 90.1- 2004 Sec. 6.5.2.1 If the air
reheated does not exceed that required to meet
ASHRAE Std. 62.1
Space 1 of nDBT, RH
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OA h
ReHt
RA h,
EW--CC-- SW
CRCP
Operate the EW whenOA h gt RA h, otherwise off
SpaceDBT, RH
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CC CV
ReHt
EW--CC-- SW
CRCP
Modulate the CC CV so no space RH gt 55orno
space DBT gt 75
SpaceDBT, RH
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CRCP CV
ReHt
EW--CC-- SW
CRCP
Modulate the SW speed to hold at least one
CRCPCV wide open
SpaceDBT, RH
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ReHt CV
CRCP CV
ReHt
EW--CC-- SW
CRCP
Modulate the CRCP CV the ReHt CV in sequence
to maintain the Space DBT _at_ 75F
SpaceDBT, RH
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Conclusions

• The single zone DOAS-CRCP system has been
  operating superbly now for over 3 years with the
  controls presented here.
• Without a single incidence of condensation.
• Maintenance free.
• Based upon that experience, the control was
  extended to a multi-zone building utilizing low
  SAT. A CRITICAL ZONE DBT AND DPT RESET SCHEME
• The many interacting local control loops in the
  reset control will require care (slow response)
  to avoid hunting.

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Questions