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 Univ. Park, PA 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 Plots Z and Laplace Transforms Stability and dynamic response Schematics Points list 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 n DBT, %RH EW--CC-- SW CRCP ReHt Is Terminal Reheat allowed? Yes!!! See ASHRAE Std ; Sec “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 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.