Economic Considerations

   Dedicated Outdoor Air
   Systems (DOAS)
   Environmental Safety
   Radiant Ceiling Panels
   Economic
   Considerations
   Proof of Concept
   Technical Papers
   PPT Presentations @
    ASHRAE Meetings
    Links
   LEED Green Building
              Email:    Dr. Stanley A. Mumma,
   Ph.D., P.E




   Since February 15, 2001

Economic Considerations: DOAS/Radiant vs. VAV

The DOAS/Radiant cooling approach provides superior indoor air quality (IAQ), humidity control and thermal comfort. How significant is this superior IAQ, humidity control and thermal comfort? It is estimated by Lawrence Berkeley National Laboratory that US companies currently loose as much as $48 billion annually in medical expenses due to biological contaminants that lead to sick building illnesses and $160 billion annually in lost productivity due to inadequate ventilation. The DOAS/Radiant cooling approach, by virtually eliminating these problems, offers a huge and largely overlooked economic benefit. Financial benefits of that magnitude alone should be sufficient incentive for every engineer/architect/owner to use the DOAS/Radiant cooling system. However, it is a well-recognized fact that these issues are not always sufficiently compelling to motivate prospective investors. They generally expect to realize at least a first cost benefit. Operating cost savings are just an added benefit, but rarely a major factor in the decision making process. Therefore, a careful first cost analysis is necessary to justify this design approach.

The major factors that impact the first cost reduction of the DOAS/radiant system compared to a conventional all air VAV system are:

Chiller size reduction due to need for less OA and total heat recovery in the DOAS.

Pump size reduction due to chiller size reduction.

Ductwork reduction due to the small (only about 15 to 20%) DOAS air flow rate when
    compared to an all air VAV system.

Plenum depth reduction, and the associated savings in building enclosure/interior
    partition/ structural/plumbing/ fire protection/and vertical transportation materials due
    to the smaller ducts and elimination of terminal VAV boxes.

Air handling unit size reduction.

Electrical services reduction for the mechanical equipment due to smaller chiller, fans
    and pumps.

Piping reduction due to functional integration of the thermal and fire suppression
    transport systems.

Acoustical ceiling panels reduction where replaced with the radiant system.

Mechanical shaft reduction due to the much lower air volumes.

The major factor contributing to the first cost of the DOAS/radiant system is:

The radiant panels.

A first cost analysis (using representative pricing data extracted from Means Cost Data Manuals) for a 6 story, 31,000 sq ft per floor, office building (in compliance with the ASHRAE energy conservation std. 90.1-2004) located in Philadelphia, PA is presented in the table below.

Cost item	Unit cost	Units VAV	Units DOAS/radiant	Cost savings
Chiller	$1,000/ton	506 ton	306 ton	$200,000
Chilled water pump	$25/gpm	1215 gpm	737 gpm	$11,950
Ductwork	$1/sq-ft DOAS, $4/sq-ft VAV	186,000 ft²	186,000 ft²	$558,000
AHU	$2/cfm VAV $4/cfm DOAS	135,000 cfm	25,000 cfm, 100% Ventilation air	$170,000
Electrical Serv.	$50/kW	630 kW	372 kW	$12,400
Facade/partitions	$35/ft²of facade	No depth reduction	1 ft plenum depth/floor or 4308 ft²	$150,780
Integrated thermal and fire suppression piping.	$0.65/ft² savings	NA	186,000 ft²	$120,900
Drop ceiling	$1.50/ ft²	NA	79,200 ft²	$118,800
Mechanical shaft impact on lost rentable space	$125/ ft²	NA	500 ft² saved	$62,500
Savings Subtotal				*$1,405,300*
Radiant Panel	$13/ ft²of panel	NA	79,200	$(1,029,600)
*Net savings*				$375,700 or $2/ft²

The operating cost figures also favor the DOAS/Radiant system. An hourly energy analysis for 12 hours a day 5 days per week provides the following op cost data. The utility rate for this project was:

Energy Charges:     Demand block 1: 200 kWh/kW, $0.065/kWh
                               Demand block 2: 200 kWh/kW, $0.052/kWh
                               Demand block 3: remaining kWh, $0.05/kWh

Demand Charge:     $6.94/kW

System	Annual Mechanical	Annual Total Mech, Illum, and Equip	PW annual Total, 3yr, 8% interest	Total present worth = � PW annual - Net savings
VAV	$77,350	$299,914	$772,900	$772,900
DOAS/radiant	$59,730	$273,565	$705,000	$329,300

These cost considerations are extremely encouraging. However the structure of professional fees may discourage crediting items outside ones own discipline (i.e. Mechanical in this case). For example, reductions in the first cost of the building enclosure, mechanical shaft floor area reduction, and dual use of fire suppression piping could be perceived as having an adverse impact on the Architects fees. If actual practice supports these estimates, there can be no impediment to rapid implementation, short of defending the status quo!

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

l Home l Dedicated Outdoor Air Systems (DOAS) l Environmental Safety l Radiant Panels l Economic Considerations l
l Proof of Concept l Technical Papers l ASHRAE Presentations l Links l LEED Green Building l Email l

Dedicated Outdoor Air Systems & Radiant Ceiling Panels
This site maintained by S. A. Mumma ©2001
All Rights Reserved. All material on this site are trademarks or registered trademarks of their respective companies or mark holders and remains their property.
Copyright �2001 Bob Hedman.