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              Email:    Dr. Stanley A. Mumma,
   Ph.D., P.E
   

      

   Since February 15, 2001 		Note:  To view the system operation in real time, request login instructions from Dr. Mumma via e-mail at:  sam11@psu.edu.

Control Overview
  


 Simplified Control Description:


Since this proof of concept project is a single zone-cooling only application, the controls are very simple. Fundamentally, the DOAS system and the parallel radiant cooling system operate in stages. The constant volume DOAS unit is the first stage used to meet the space DBT setpoint with a variable supply air temperature. As the cooling load increases, and the DOAS supply air temperature drops to 52F (or a programmable low limit), the supply air is sufficiently dry to maintain a space design DPT of 55F. If the space thermostat is still not satisfied when the first stage is at full capacity, the second stage, radiant cooling is enabled. Note, the radiant panel capacity is limited until the space DPT has been brought under control by the low supply air temperature. The temperature of the panel supply water is modulated to accommodate the balance of the space sensible load. The space DPT is used to establish a low limit for the radiant panel supply water temperature. The low limit is the space DPT plus 0-3F. Since the space has exterior movable-sash fenestration, and access doors that open to unconditioned spaces, there could be concern about condensation if the windows are open.  The ASHRAE IAQ column "Chilled Ceiling Condensation Control" addresses that concern.  The schematic diagram illustrates the humidity, temperature, flow, and CO2 points used for control and performance monitoring.

Fail Safe Condensation Control:


A prime objective of this proof of concept project is to demonstrate that the issue of condensation control can be reliably achieved. As noted in the ES article "Dedicated Outdoor Air in Parallel with Chilled Ceiling System", some believe that damaging condensation is not a question of “if” but “when”. The normal operating control overview was discussed above. In a step to guarantee that damaging condensation can not form, the simple and inexpensive fail safe approach used in the project will be discussed. As demonstrated in the ASHRAE Journal article "Ceiling Panel Cooling Systems", condensation takes a very long time to form on a horizontal surface, and even after 8.5 hours with the panel surface temperature held 14F below the space dew point temperature it did not release a drop of condensation. Vertical surfaces are quite a different case. Gravity will cause the moisture beads formed on the supply water piping to the panel to run downward. A condensate sensor is placed at the bottom of a vertical section of the supply piping to receive the water droplets--view it from the virtual tour site. By placing the condensate sensor switch in series with the power to the panel temperature control modulating valve, the power is lost when condensation is detected. The modulating panel temperature control valve has a spring return, with the port to the primary loop normally closed. Therefore when condensed water droplets are detected, the control valve closes immediately while the panel pump is allowed to operate for 15 minutes more to warm the cool water.  Water damage from condensation need not and will not be tolerated!

Real Time Web Based Performance Data and Control Logic


The proof of concept project is being controlled with Automated Logic hardware and their operating system software--WebCTRL.  This enables authorized individuals to view both the operating data in real time as well as view the control logic developed for the project by Dr. Mumma and
Ph.D. Candidate Jeong.  The system and controls are so stable that the data is quite tranquil.  A sample of the data is available at: click here.  However if you wish to view the site in real time, request login instructions from Dr. Mumma via e-mail at:  sam11@psu.edu.


Please visit the Papers section of this site for more information on
      Dedicated Outdoor Air Systems and Radiant Ceiling Panels.



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Dedicated Outdoor Air Systems & Radiant Ceiling Panels
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Copyright ©2001 Bob Hedman.