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

sam11@psu.edu; jqj102@psu.eduhttp:// 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.