An outside air ventilation system that is separate from the central air handling and distribution system.
The conventional practice for designing variable-air-volume (VAV) systems is to have a single air handler supply both the conditioned air and outside air to the building. There will be spaces in a building needing only 5% outside air (OSA), and other spaces needing 50% outside air. To set the primary AHU at 50% would overventilate many spaces. Of course, an algorthym is available to utilize the 'unused' return air allowing for the typical 25% outside air setting on the primary AHU. But, as outside air is expensive to temper, being able to provide dedicated outside air to each zone has the potential to save energy.
A dedicated outdoor air system (DOAS) supplies outside air to the terminal units in the building separately from the main supply air. This strategy allows for better humidity control, more precise air delivery, and decreased energy consumption. Studies have shown that this approach saves 8-20% of heating or cooling energy.
The applications where this approach is most worthwhile is in humid climates or where humidity needs to be controlled tightly, such as a library or museum. (http://www.mge.com/business/saving/madison/pa_54.html#IDAA3R0D).
Status:
Baseline Description: Convential HVAC with Ventilation Air Mixed with Supply Air Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 Commercial Building Stock Assessment gives the actual electrical building energy use index (EUI) for various types of heating and cooling systems (Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding numbers are 19.9 and 9.4 kWh/sf/year, respectively for a heating and cooling use of 10.5 kWh/sf-year).
Since this technology can be applied to many types of commercial buildings, a baseline heating and cooling energy use of 10.5 kWh/sf-year is assumed (NEEA, 12/21/2009).
"Typical" Savings: 10%
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
S.A. Mumma, 02/15/2001. Dedicated Outdoor Air Systems Presentations Penn State University
S.A. Mumma, 02/15/2001. Dedicated Outdoor Air Systems Penn State University
Mike Wolfe, 12/01/2009. Optimizing Dedicated Outdoor-Air Systems Heating/Piping/Air Conditioning Engineering
NIBS, 01/01/2012. Dedicated Outside Air Systems (DOAS) and the hybrid HVAC system National Institute of Building Sciences
ASHRAE, 04/19/2012. Dedicated Outdoor Air Systems – A Path to Balancing Energy and IEQ ASHRAE
EERE, 10/29/2010. Strategies to Cut Energy Use by 50% in Commercial Buildings Building Technologies Program
Tiax Llc, 02/28/2006. Rooftop Unitary Air Conditioner with Integral Dedicated Outdoor Air System National Energy Technology Laboratory
COMNET, 01/01/2010. Commercial Buildings Energy Modeling Guidelines and Procedures Commercial Energy Services Network Special Notes: 7.2.3 Dedicated Outside Air Systems (DOAS)
Greenheck, 06/14/2007. Product Application Guide - Optimizing Dedicated Outdoor Air Systems Greenheck Fan Corp.
Technical Advisory Group: 2010 HVAC TAG (#3) TAG Ranking: 12 out of 36 Average TAG Rating: 3 out of 5 TAG Ranking Date: 06/29/2010 TAG Rating Commentary: Appropriate in many but not all applications. Can be coupled with indirect evaporative cooling as well as heat recovery. Not sure how this is emerging - proven technological approach to system design "Refer to #74, "Radiant Htg & Cooling with DOAS"I prefer the wording of this broader proposal. Radiant htg and cooling is only one of the various ways to do this. I believe the strategy is truly emerging, and needs experience with various approaches. By its nature, this would be a "custom" measure, and would require all parties to have a clear understanding of each project. It is most likely to be suitable as a technology or strategy used in New Construction, rather than retrofit, but if a retrofit opportunity is available, it could provide good before/after data. One approach to address DOAS would be to track projects being implemented around the Northwest; i.e. case studies."
Technical Advisory Group: 2009 HVAC TAG (#2) TAG Ranking: Average TAG Rating: TAG Ranking Date: TAG Rating Commentary: