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

1. 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, @ Univ. Park, PA sam11@psu.edu; jqj102@psu.eduhttp:// doas-radiant.psu.edu

2. 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!

3. First Thoughts about control? Points list Nyquist Plots Stability and dynamic response Schematics Z and Laplace Transforms Sequence of operation Bodi Plots BACnet

4. High Induction Diffuser 20-70% less OA, Cool/Dry Supply DOAS Unit W/ Energy Recovery Building With Sensible and Latent cooling decoupled Parallel Sen. Radiant Cooling System DOAS-CRCP Design Concept

5. 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.

6. Schematic & Control Points: Single Zone DOAS-CRCP System

7. 2. Occupied-Unoccupied Control

8. 3. Enthalpy Wheel Control

9. 4. Chiller Control

10. 5. Cooling Coil Control

11. 6. CRCP Control

12. 7. Thermodynamic Calculations

13. 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.

14. 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.

15. 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

16. OA h ReHt RA h, EW--CC-- SW CRCP Operate the EW whenOA h > RA h, otherwise off SpaceDBT, %RH

17. CC CV ReHt EW--CC-- SW CRCP Modulate the CC CV so no space %RH > 55%orno space DBT > 75 SpaceDBT, %RH

19. CRCP CV ReHt EW--CC-- SW CRCP Modulate the SW speed to hold at least one CRCPCV wide open SpaceDBT, %RH

21. ReHt CV CRCP CV ReHt EW--CC-- SW CRCP Modulate the CRCP CV & the ReHt CV in sequence to maintain the Space DBT @ 75F SpaceDBT, %RH

23. 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.

24. Questions