Direct Digital DBT RH and Condensate Control for
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 sam 11@psu. edu; jqj 102@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? t s i qu Ny s t o Pl e s n o p s re c i m a n y y t i bil d d an Sta Z and t s i sl t n i Po s m or e c a pl f s n Tra La Bo s t o l P di m e h Sc f o e q e S c n ue s c i at n o i t ra e p o et n C A B
DOAS-CRCP Design Concept 20 -70% less OA, DOAS Unit W/ Energy Recovery Parallel Sen. Radiant Cooling System Cool/Dry Supply 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 Re. Ht EW--CC-- SW Is Terminal Reheat allowed? Yes!!! See ASHRAE Std. 90. 12004; Sec. 6. 5. 2. 1 “If the air reheated does not exceed that required to meet ASHRAE Std. 62. 1” CRCP Space 1 of n DBT, %RH
OA h RA h, EW--CC-- SW Re. Ht CRCP Operate the EW when OA h > RA h, otherwise off Space DBT, %RH
CC CV Re. Ht EW--CC-- SW CRCP Modulate the CC CV so no space %RH > 55% or no space DBT > 75 Space DBT, %RH
CRCP CV Re. Ht EW--CC-- SW CRCP Modulate the SW speed to hold at least one CRCP CV wide open Space DBT, %RH
EW--CC-- SW CRCP Modulate the CRCP CV & the Re. Ht CV in sequence to maintain the Space DBT @ 75 F Space DBT, %RH Re. Ht CV CRCP CV Re. Ht
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.
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