Transpired collectors

Transpired collectors use solar energy to preheat ventilation (outdoor) air as it is drawn into a building. The technology is ideally suited for buildings with at least moderate ventilation requirements in sunny locations with long heating seasons. Transpired collector technology is remarkably simple. A dark, perforated metal wall is  installed on the south-facing side of a building, creating approximately a 6-inch (15-cm) gap between it and the building’s structural wall. The dark colored wall acts as a large solar collector that converts solar radiation to heat. Fans associated with the building’s ventilation system mounted at the top of the wall draw outside air through the transpired collector’s perforations, and the thermal energy collected by the wall is transferred to the

air passing through the holes. The fans then distribute the heated air into the building through ducts mounted from the ceiling. By preheating outdoor air with solar energy, the technology removes a substantial load from

a building’s conventional heating system, saving energy and money.

A transpired collector is installed on all or part of a building’s south-facing wall, where it will receive the  maximum exposure to direct sunlight during the fall, winter, and spring. The size of the wall varies depending on heating and airflow requirements and climate, but in many applications, the transpired collector will cover the maximum south-facing area available. The amount of energy and money saved by a transpired collector depends on the type of conventional fuel being displaced, occupant use patterns, building design, length of heating season, and the availability of sunlight during the heating season. In general, each square foot of transpired collector will raise the temperature of 4 cubic feet per minute (cfm) by as much as 40°F, delivering as

much as 240,000 Btu annually per square foot of installed collector.

In addition to the metal sheeting that captures solar energy, the transpired collector heating system includes air-handling and control components that supply the solar heated air. The ventilation system, which operates independently of a building’s existing heating system, includes a constant-speed fan to draw air through the

transpired collector and into the distribution duct. Engineers typically use a 3-horsepower, 32-inch blade fan with about 10,000-cfm capacity.

Source: CED Engineering

 Where to Apply

The following are the most common transpired collector applications:

• Manufacturing plants

• Vehicle maintenance facilities

• Hazardous waste storage buildings

• Gymnasiums

• Airplane hangars

• Schools

• Warehouses requiring ventilation

 

What to Avoid

The following is a list of general applications and conditions that preclude the cost effective use of transpired collector technology:

• Outdoor air not required

• Shaded or insufficient south-facing wall area

• Buildings with existing heat recovery systems

• Locations with short heating seasons

• Multiple-story buildings (because of possible problems with fire codes).