Dedicated Outdoor Air
   Systems (DOAS)

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   Radiant Ceiling Panels

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



   Since February 15, 2001

Project Description


This project is a "proof of concept" of an exciting new method of providing a healthy working environment at reduced first and operating costs over conventional all-air systems. The concept was undertaken to help the University Community experience the healthy working environment that the system can provide. The project, which went into operation August 16, 2002, is also providing a real life learning environment for the students in the Departments of Architecture, Landscape Architecture, and Architectural Engineering as well as important operational information and experience for the personnel of the Penn State Office of Physical Plant (OPP).

The Concept:

A dedicated outdoor air system (DOAS) is used to place the required and conditioned ventilation air directly into the space without first mixing it with used return building air as is the current practice with all air systems such as VAV, thus always meeting the requirements of ASHRAE Standard 62 “Ventilation for acceptable Indoor Air Quality” with 100% fresh outside air. This cannot be achieved with confidence in multi-space all-air systems as documented in the Engineered Systems Article “Fresh Thinking: Dedicated Outdoor Air Systems”. Energy recovery is utilized by the 100% outdoor air (OA) system, as required by ASHRAE Std. 90, reducing the energy utilized to condition the OA by 70-80% over conventional systems. The OA is then mechanically cooled so that it can be used to remove all of the space generated latent (moisture) loads, thus decoupling the space sensible (temperature) and latent (moisture) loads. Once these loads have been decoupled, the remaining space sensible loads can be accommodated with any one of many parallel sensible cooling technologies. In this "proof of concept" project, ceiling radiant cooling is used to remove the remaining sensible cooling loads. By decoupling the sensible and latent loads, building moisture problems and the associated IAQ problems disappear.

Radiant cooling offers further energy savings. First, the pump operating costs to remove the space sensible load are far less than the fan operating costs to remove the same sensible load with an all-air system. And second, with ceiling radiant cooling the energy balance on the occupants is much different, so the space temperature can be elevated with a perception of thermal comfort equivalent to a lower dry bulb temperature.  To realize this in the project, the operative temperature (the average of the space dry bulb temperature and the space mean radiant temperature) is used for space temperature control

Finally, since the airflow rate with the DOAS system is typically only 20% that of a conventional all-air system, high induction diffusers (causing a large secondary flow of room air) are used to assure that the room does not feel stagnant to the occupants with ADPI values >95. The high induction diffusers also increase the chilled ceiling heat removal performance by about 15%. For an overview of the concept, please refer to the ASHRAE Journal Article “Dedicated Outdoor Air Systems”.

"Proof Of Concept" Location:

A 3,200
ft2 senior level Architecture studio was selected as the test site. It is on the 2nd floor of Engineering Unit B, and houses 40 students and their computers around the clock-7 days per week. The space is currently not cooled. It has one glazed exterior exposure, and 3 interior partitions adjacent to non-conditioned spaces. The floor and ceiling are also adjacent to unconditioned spaces. The ceiling height is 14 feet, with pendent illumination at the 9-foot plane.

Assessment of the DOAS Rating Point Potential against the LEED Green Building rating Std.:

The DOAS/Radiant mechanical system has the potential to generate rating points in 5 of the major categories: i.e. Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality, and LEED Innovation Credits. The DOAS approach has the potential to generate up to 21 Green Building Rating points, or up to 80% of the minimum points needed for Certification.

First and Operating Cost Implications:

This approach has the potential to reduce the first cost of the building by $2/
ft2 over buildings using conventional all-air VAV systems. It also has the potential to reduce the mechanical system operating costs when compared to an all-air VAV system by at least $0.10/ft2/year (or 29% less than a conventional all-air VAV system). Because of the demand savings, it also impacts the overall system operating costs, resulting in at least $0.15/ft2/year.

Health and Productivity Cost Implications:

Researchers at the Lawrence Berkeley National Laboratory estimate that U.S. companies could save as much as $58 billion annually by preventing sick-building illnesses and could benefit from $200 billion in productivity increases each year. The proposed DOAS/radiant system will deliver superior IAQ and thermal comfort, thus reducing or eliminating sick building illnesses and related workplace productivity loss.

The proof of concept project description:

The project consists of the following major components and capacities:

Component   Capacity
Air cooled chiller   10 ton
Cooling coil   < 6 ton, sensible plus latent
Fresh Air Ventilator unit (FAVU) with enthalpy
  wheel, fans, filters, and dampers
  1200 cfm, enthalpy wheel
  effectiveness >70%
8-2'X40' free hanging radiant panels   < 4 ton, sensible only
8-2'X2' high induction diffusers   150 cfm each
2-in line circulating pumps   22 gpm each
Instrumentation and controls   Capable of Web access

The dedicated OA system, consisting of the fresh air ventilator unit (DOAS), lower right hand corner of the schematic, and the cooling coil shown just to the left of the DOAS, provides constant volume-variable temperature ventilation air to the conditioned space. The DOAS cools and dehumidifies the ventilation air efficiently by using the 70% effective enthalpy wheel. When the conditioned ventilation air passes through the conditioned space it is capable of removing the entire space latent load, and up to approximately 3 tons of space sensible load. The ventilation air is introduced into the conditioned space via high induction (HI) diffusers installed at the 9' elevation adjacent to the radiant panels. The HI diffusers have a two-way throw, parallel to the long dimension of the radiant panels. The HI diffusers entrain about 20 cfm of space air for each cfm of discharge air, increasing the convective heat transfer on both the bottom and top sides of the free hanging radiant panels. The increased air movement is also intended to prevent a feeling of deadness in the conditioned space that might result from the low supply air flow rates compared to conventional all air designs.

Because of the leaky building site for this proof of concept project, great care was exercised in balancing the supply and return flows, via the fans in the DOAS, to assure that the conditioned space was at a near neutral pressure relative to its surroundings (around +0.01 in. W.G.). If the space is allowed to go negative, unwanted infiltration and latent load occurs. If the space is allowed to go positive, the energy recovery benefits afforded by the enthalpy wheel begin to diminish.

An air cooled chiller, top center of the schematic, is used to produce the chilled water needed first by the primary DOAS cooling coil loop, and secondarily by the radiant cooling panel loop. Modulating control valve V1 is used in the primary chiller loop to provide the required flow of chilled water to the cooling coil. Spring return-straight through normally closed modulating control valve V2 is used in the secondary radiant panel loop to vary the panel cooling water temperature. V2 is also a part of the condensation fail safe control. The pumps in both the primary and secondary loops provide a constant volume flow.

The 8 free hanging radiant panels are plumbed in parallel, and shown schematically on the far left of the schematic, span the complete 40' depth of the conditioned space, and are equally spaced over the 80' width of the conditioned space. The panels donated to this proof of concept project are manufactured using aluminum extruded fins and 8 parallel-header copper water ways per 2' wide panel. The cooling water to the panels enters on the fenestration end of the panels, and leaves on the end adjacent to the interior partition.

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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