%RH, and Condensate

bustlingdivisionElectronics - Devices

Nov 15, 2013 (3 years and 10 months ago)

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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 Department

Penn State University, @ Univ. Park, PA

sam11@psu.edu; jqj102@psu.edu

http:// 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?

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
n

DBT, %RH

EW
--
CC
--

SW

CRCP

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”

Space

DBT, %RH

EW
--
CC
--

SW

CRCP

ReHt


Operate the EW
when

OA h > RA h,
otherwise off

OA h

RA h,

Space

DBT, %RH

EW
--
CC
--

SW

CRCP

ReHt


Modulate the CC CV
so

no space %RH > 55%

or

no space DBT > 75

CC CV

Space

DBT, %RH

EW
--
CC
--

SW

CRCP

ReHt

Modulate the SW
speed to hold at
least one CRCP

CV wide open

CRCP CV

Space

DBT, %RH

EW
--
CC
--

SW

CRCP

ReHt

Modulate the

CRCP CV &

the ReHt CV

in sequence to
maintain the Space
DBT @ 75F

CRCP CV

ReHt CV

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.