CMD Group is a ConstructConnect™ company. Learn more

An Overview of Solar Ventilation Air Heating

10/19/2007 by Andy Walker, PhD PE

Share

Solar ventilation air preheating is a cost-effective application of solar energy thanks to an innovative transpired collector that is both inexpensive and high-performance.

Heating of ventilation air accounts for about 15% of the total heating load in an average commercial building, much more in buildings that require a lot of ventilation, like factories and laboratories. Preheating the air with solar energy before it is drawn into the space can save much of this energy.

Solar ventilation air preheating technology is simple, low-cost, extremely reliable (no moving parts except the fan), very low in maintenance requirements, and high in efficiency (up to 80%). There are no problems with freezing or fluid leaks, but there is also no practical way to store the heated ventilation air for nighttime use. Well over two million square feet of transpired collectors have been installed since 1990.

Transpired Collector Principle

The key to low cost and high performance is an elegant solar technology known as the transpired collector. A painted metal plate is perforated with small holes about 1 mm (0.04 in) in diameter and 3 mm (0.12 inch) apart. At this small scale, within 1 mm of the surface of the plate, flow within the laminar boundary layer is dominated by viscosity of the air, and heat transfer is dominated by conduction. This is in contrast to the air flow even a few more mm away from the plate where the flow is dominated by the momentum of the wind, and the heat transfer is dominated by convection. These two differences between the boundary layer of air within 1 mm of the plate and the air farther away are key to the operating principle of the transpired collector.

Sunlight strikes the black surface of the plate and is absorbed. Solar heat conducts from the surface to the thermal boundary layer of air 1 mm thick next to the plate. This boundary layer of air is drawn into a nearby hole before the heat can escape by convection, virtually eliminating heat loss off the surface of the plate. Since the plate operates at less than 20°C warmer than ambient air, heat loss by radiation is not overly consequential. There is no cover glass to reflect or absorb radiation.

To operate effectively, the fan-induced flow through the wall must be sufficient to continuously draw in the boundary layer. Consequently, efforts to increase the temperature of delivered air by reducing the flow rate will adversely affect performance. Don’t get greedy. They don’t call it ventilation preheating for nothing. On cold winter days, supplemental heating by gas or electricity will be required to ensure comfortable conditions.

The transpired collector is mounted about six inches away from the south wall of a building, forming a plenum between the wall and the collector. The collector is fastened to the wall, and the edges are sealed using standard metal building flashing techniques. A fan is installed in the wall to draw air from the plenum into the supply ductwork. The solar preheated air can be delivered to the air handler for the heater or directly into the space to be ventilated. The bypass damper could be thermostatically controlled, and fan operation will depend on the ventilation needs of the space.

The transpired collector makes an efficient sunlight-to-air heat exchanger that tempers the incoming fresh air. It is not possible to recirculate the room air back to the collector for reheating because the fact that it pulls air into the face of the wall is necessary to the operating principle. The amount of temperature increase that the air experiences coming through the collector depends on the air flow rate and on the incident solar radiation. The recommended air flow rate is about 4 CFM per square foot of collector area. At flow rates less than 2 CFM/SF, the boundary layer can blow away before it is sucked through a hole, and at flow rates higher than 8 CFM/SF, the required additional fan power begins to erode the cost savings.

Typical Applications for Solar Ventilation Air Preheating

The transpired collector technology is appropriate for preheating ventilation air in industrial and maintenance buildings, school and institutional buildings, apartment buildings, commercial buildings, and penthouse fans. Examples include factories, aircraft hangers, chemical storage buildings, and other facilities that require ventilation air. Industrial process uses for heated air, such as crop drying, can also be addressed with this technology.

Due to its metal construction, the transpired collector matches well with other metal construction, which is most common in industrial applications. The design of a new building is the best time to consider solar ventilation preheating, but it can be used in retrofit applications as well. It can even improve the appearance of a dilapidated façade. There must be sufficient south-facing vertical wall to mount the collector, and the wall must be largely unshaded by surrounding buildings, trees, hills, or other objects.

Design considerations for solar ventilation air preheating include some flexibility with wall orientation and color. A south-facing wall is best, but not absolutely necessary: +/- 20° of south gives 96%–100%, of heat delivery, while +/- 45° of south gives 80%–100% of the heat delivery of a south-facing wall. Black is best for absorbing solar radiation, but a wide choice of dark to medium colors may be used with efficiency loss of less than 10%, and about 20 colors are available standard from the supplier, with custom colors possible.

Related Articles

Recent Comments




Article Archive

Date Article
11/17/14 Top 10 largest construction project starts in the U.S. - October 2014
11/14/14 Non-residential Construction Starts Rose Gently in October
07/10/14 The Importance of Matching Volume to Contractor Capacity in JOC Procurement Strategy
07/10/14 Consider a Seed Project as Part of Your JOC Procurement Strategy
07/10/14 The Best Unit Price Book for Your Job Order Contract
07/02/14 ECONOMIC NUGGETS – July 1, 2014
10/23/14 Twenty major upcoming Water Treatment Plants and Manufacturing & Warehousing construction projects - U.S. - October 2014
10/23/14 Twenty major upcoming Alberta and British Columbia construction projects - Canada - October 2014
10/15/14 Trend lines of construction starts in Canada - September 2014
10/15/14 Top 10 largest construction project starts in Canada - September 2014
09/17/14 Twenty major upcoming midwest and northwest construction projects - U.S. - September 2014
09/17/14 Twenty major upcoming medical and educational construction projects - Canada - September 2014
09/17/14 Trend lines of construction starts in Canada - August 2014
09/17/14 Top 10 largest construction project starts in Canada - August 2014
08/15/14 Twenty major upcoming medical and educational construction projects - U.S. - August 2014
08/15/14 Twenty major upcoming industrial and water treatment construction projects - Canada - July 2014
08/15/14 Trend lines of construction starts in Canada - July 2014
08/15/14 Top 10 largest construction project starts in Canada - July 2014
07/24/14 Twenty major upcoming entertainment facility and stadium/arena construction projects - U.S. - July 2014
07/24/14 Twenty major upcoming Ontario and Quebec construction projects - Canada - July 2014
07/24/14 Trend lines of construction starts in Canada - June 2014
07/24/14 Top 10 largest construction project starts in Canada - June 2014
07/16/14
07/14/14 Top 10 largest construction project starts in the U.S. - June 2014
02/03/14 Infographic: Where Can You Use Project Leads in the Construction Process?
07/25/13 The Canadian Economy’s Two Great Blessings
02/15/13 Construction Economic Notes – February, 2013
11/05/12 Recycled-Content Tile
10/05/12 Fiber-Cement Siding
09/18/12 Return on Your Green Home Improvement Investment
08/09/12 Green Building Solutions to Stormwater Runoff
08/07/12 An “Aha” Moment Solves Challenge of Cost Estimating Local Circus Roof
07/19/12 Estimate Types
06/20/12 Ground-Source Heat Pump
05/14/12 Universal Design for Outdoor Living
04/23/12 What Is Universal Design?
04/09/12 Natural Landscaping
03/14/12 Green Material Alternatives for Plumbing Fixtures
03/02/12 Budgeting & Financing Green Construction
02/22/12 Greening Your Firm
02/10/12 Roofing Defects
02/06/12 Roofs: energy efficiency strategies
01/18/12 Commercial Real Estate and Green Construction
12/14/11 Renewable Energy & Distributed Generation Technologies
11/04/11 Tubular Skylights
10/04/11 Are Online Ads An Endangered Species?
09/27/11 Performance Bonds Guarantee Clients Receive Exceptional Service
09/15/11 Deconstruction for Green and Economic Benefit
09/01/11 4 Ways for Businesses to Create a Good First Impression on Twitter
08/11/11 Building Information Modeling (BIM) for Green Building
07/21/11 Green Alternatives for Concrete
07/12/11 Evaluating Products Over Their Life Cycle
06/30/11 Low-Cost Green Strategies
06/28/11 Bricks are from Venus, Clicks are from Mars
06/17/11 Zombie Avoidance Techniques for Building Product Manufacturers
06/08/11 Blogs & Websites: The 5 Signs of Website Wellness
06/06/11 Building Product Manufacturers & Green Products
06/01/11 Is Fear of Sharing Information Costing Your Company Sales?
05/26/11 What Are Green Products?
05/20/11 The Building Envelope
05/16/11 Blogging: Website Heal Thyself
05/03/11 Metals Compared to Wood for Sustainable Construction
04/12/11 Storm Water Collection & Infiltration
03/23/11 Commissioning the Green Building
02/23/11 Building Program for Green Design
01/21/11 Building Deconstruction Process
05/02/11 Why Building Product Manufacturers and Social Media Are a Marriage Made in Heaven
05/06/11 Building Product Manufacturers: How Understanding Architects Can Help Your Business
10/21/09 Distributors & Manufacturer Representatives
07/15/10 Estimating Doors: Tips from the Experts
07/06/10 How to Handle Construction Materials to Prevent Mold
06/21/10 How to Maximize the Benefits of Exterior Security Lighting
06/04/10 SmartBuilding Index
06/01/10 Regional Housing Construction Tracking and Forecast Information
05/28/10 How to Find Regional Construction Tracking and Forecast Information
05/24/10 Building Product Manufacturers
05/18/10 Practicing the Art of Sustainability - Why Atlanta's Current Building Codes Need Updating Now
02/23/10 Learning to use EE
01/11/10 Earn AIA CEU Credit Attending RCD Webcasts
07/17/09 Cost Estimators Winning Work With BIM
07/16/09 Becoming an Invited Bidder - More Tips
07/16/09 Becoming an Invited Bidder - Tips
07/16/09 Becoming an Invited Bidder
07/16/09 SmartBIM Object Modeling Guidelines for Revit
07/15/09 Interference Check and BIM
06/26/09 A Look at Contractor Failure: Part 2
06/19/09 RicciGreene Associates
06/19/09 Doug Thornton AIA, LEED A.P. of AERC, PLLC
06/18/09 A Look at Contractor Failure: Part 1
06/12/09 Owners and SmartBIM Objects – What You Need To Do
06/10/09 Dealing with the IRS
06/05/09 Getting Paid on Construction Contracts
06/02/09 BIM Coordination and Collaboration
05/28/09 Marketing Your Construction Firm on the Cheap
05/20/09 Little Habits with Big Payoffs for Contractors
05/12/09 SmartBIM Spaces
05/07/09 AIA Show Recap as Seen by the SmartBIM Solutions Team
04/27/09 Business Case Study - Survey Of Spending Patterns In Educational Facilities
04/23/09 Taking Advantage of the Recession: Hiring the Right People
04/20/09 Cork as a Green Flooring Option
04/08/09 Owners - It's Time to Substantially Increase Your Architect's and Engineer's Fees
03/05/09 There's a Solution to Performing Time Consuming Quantity Take-Offs
02/20/09 SmartBIM Library is Half-Off for a Limited Time Only
02/09/09 You are Wasting Your Money
01/20/09 Obama: 'Dramatic Action' On Economy Needed
01/14/09 Use of BIM Jumps Dramatically Over Last 12 Months
12/10/08 Minimizing the Size of Family Files (Revit Objects)
11/11/08 Maximize Online Advertising Dollars
11/07/08 Architects and Engineers, WE NEED YOU
10/29/08 Why Do You Need SmartBIM Objects
10/28/08 Why Building Information Modeling?
10/29/08 10 Questions To Ask About BIM Objects
10/08/08 The Object Mess
10/07/08 Implementing BIM to Your Office
10/06/08 Meeting the Needs for Governmental BIM Compliance while Avoiding Current Liability Obstacles
09/15/08 The BIM Transformation is Manageable with the NEW SmartBIM Library v3
09/14/08 KOLBE Windows and Doors vs. Building Information Modeling
09/12/08 The Evolution of Building Information Modeling: BIM 1-2-3
08/11/08 BIM 101 Overview - From Hand Drawings, CAD and now BIM
08/12/08 Draper, Inc. on BIM Object Developments
07/08/08 IFD Library Partners work to establish standards for creators of BIM software
06/23/08 Architectural Education
06/17/08 Parametric Revit Objects – Part I - Fundamentals
06/17/08 Window Glazing Coefficients
06/01/08 Frequently Asked Questions About Building Codes
06/05/08 Calling All Current and Prospective Revit Users - This Blog Is For You
05/06/08 System Requirements for SmartBIM Library
05/06/08 SmartBIM Library 2.0 Release Notes
05/05/08 Building Information Modeling Moves into AEC Mainstream, Adding Value to Project Delivery Process
04/08/08 Flooring: Cost Considerations
02/08/10 General Contractors & Trade Contractors
01/24/08 Building Element Models (BEM)
12/21/07 LEED Certification Primer
12/13/07 Building Integrated Photovoltaics (BIPV)
09/24/07 Mixed-mode Building Design Combines Old and New Ideas
10/15/07 Checklists Identify Potential Envelope Design Improvements
10/24/07 Greenroofs as High Performance Design
10/21/07 What Makes a Building Product Green
10/24/07 Lighting Considerations in Green Building
10/24/07 Water Conservation in Green Buildings
10/24/07 Rainwater Collection Systems
10/24/07 Efficient Cooling Methods for Green Buildings
10/24/07 Controlling Heat Transfer in Green Buildings
10/24/07 Limiting Heat Loss Through Windows
10/23/07 Formaldehyde Use in Building Construction
10/23/07 Using Plants to Improve Indoor Air Quality
11/05/07 Greening Healthcare
10/19/07 Daylighting Controls
10/19/07 Use of Windows, Skylights and Light Pipes in Daylighting
10/19/07 An Overview of Daylighting
10/19/07 An Overview of Solar Ventilation Air Heating
10/19/07 Types of Collectors for Solar Water Heating
10/19/07 An Overview of Solar Water Heating
10/19/07 Cooling Load Advoidance
10/19/07 Components of Passive Solar Heating Designs
10/19/07 An Overview of Passive Solar Heating
10/23/07 Improving Indoor Air Quality
10/19/07 An Overview of The LEED Rating System
10/19/07 Cost Considerations in Building Deconstruction
10/17/07 Building Deconstruction
10/25/07 Roofing Considerations in Green Building
10/19/07 Green Site Selection and Development
10/24/07 Reducing Energy Use in Buildings
10/17/07 Green Demolition
10/18/07 Integrating Solar Power Generation into Buildings using Thin Film PV
09/10/07 Compost Company Promotes Green Environment
03/31/06 Green Roof Sets An Example For Minneapolis Sustainable Design

CMD Group- construction industry news-image” title=