Direct Digital DBT, %RH, and Condensate
Control for a DOAS-CRCP system
ASHRAE Winter Meeting Symp. 3, Orlando-Feb. 6, 2005
Stanley A. Mumma, Ph.D., P.E. &Jae-Weon Jeong, Ph.D.
Architectural Engineering DepartmentPenn State University, @ Univ. Park, PA
[email protected]; [email protected]:// doas-radiant.psu.edu
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!
First Thoughts about control?
Nyquist Plots
Bodi PlotsZ and Laplace Transforms
Stability and dynamic response
SchematicsPoints li
st
Sequence of operation
BACnet
DOAS-CRCP Design Concept
20-70% less OA,
DOAS Unit W/ Energy Recovery
Cool/Dry Supply
Parallel Sen. Radiant Cooling
System
High Induction Diffuser
Building With
Sensible and Latent
cooling decoupled
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.
Schematic & Control Points: Single Zone DOAS-CRCP System
2. Occupied-Unoccupied Control
3. Enthalpy Wheel Control
4. Chiller Control
5. Cooling Coil Control
6. CRCP Control
7. Thermodynamic Calculations
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.
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.
Paper Figure 3
Space 1 of nDBT, %RH
EW--CC-- SWCRCP
ReHt
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”
SpaceDBT, %RH
EW--CC-- SWCRCP
ReHt
Operate the EW when
OA h > RA h, otherwise off
OA
h
RA h,
SpaceDBT, %RH
EW--CC-- SWCRCP
ReHt
Modulate the CC CV so
no space %RH > 55%or
no space DBT > 75
CC CV
SpaceDBT, %RH
EW--CC-- SWCRCP
ReHt
Modulate the SW speed to hold at least one CRCPCV wide open
CR
CP
CV
SpaceDBT, %RH
EW--CC-- SWCRCP
ReHt
Modulate the CRCP CV & the ReHt CV in sequence to
maintain the Space DBT @ 75F
CR
CP
CV
ReH
t C
V
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.
