This is a follow-up article in the Renewable Energy Series, the introductory article can be found here: Renewable Energy Technology Applications - Introduction

Source:NREL

This is the first part of three parts for Series 1 and it is on Solar Ventilation Air Pre-heating.

• Solar Thermal (Solar Ventilation Air Pre-heating & Solar Water Heating) and Concentrating Power Technologies (Series 1).
• Photovoltaics and Daylighting Technologies (Series 2).
• Wind Technologies (Series 3).
• Geothermal Energy Technologies (Series 4).
• Biomass Technologies (Series 5).
• Hydro-power and Ocean Technologies (Series 6).

Solar Ventilation air pre-heating

Uses the energy of solar radiation to pre-heat the air using passive solar energy before it’s circulated through the building’s ventilation system, especially in areas where heating loads are dominant and the best combination of available sun and high heating requirements for buildings.

The technology is best applicable to large industrial facilities that require a steady supply of ventilation air such as:

1. Vehicle maintenance facilities
2. Aircraft hangers.
3. Warehouses.
4. Large crop drying facilities.
5. Apartment Buildings
6. Process air heating

Solar air Pre-heating system and components

Transpired solar collector

This is a wall constructed of perforated metal sheets four feet wide and in any length. The collector is perforated with tiny holes and painted a dark colour to absorb maximum solar radiation.

Mounting Brackets

The transpired collector is secured to the south-facing wall by mounting brackets that stand the transpired collector away from the wall to create a space to retain the pre-heated ventilation air. This space is referred to as a plenum.

Perimeter flashing

Proper installation of flashing is required around the perimeter of the transpired collector to keep air from going around it and bypassing the tiny holes.

Ventilation fan

The ventilation air is drawn through the holes in the collector and into the plenum by the action of a ventilation fan, which typically already exists in a building.

Ducts and Ductwork

Existing ductwork can be used to distribute hot air from the solar ventilation preheating system directly into a space heated by unit heaters or other means.

Actuated Bypass Damper

The dampers would be controlled such that when the space is calling for heat, the outside air damper would be closed and the solar ventilation preheat damper would be open. If the space does not need the heat, the outside air damper would be open and the solar ventilation preheat damper would be closed.

Operating Principle of Transpired Solar Collector

The principle of the transpired solar collector is such that the thin boundary layer of solar heated air enters in through small holes before it has a chance to mix with surrounding air.

Winter Operation(Cold Season)	Summer Operation (Warm Season)
The bypass damper is closed (circled in red) and ventilation air is drawn in through the tiny holes of the transpired solar collector. The temperature might increase as much as -9 (15F) to -1 (30F) degrees Celcius on a sunny day .So instead of coming in at -17 Celcius (0F) the air is coming in at -1 (30F) degrees Celsius, and that saves a lot on the fuel required to heat the ventilation air.	The bypass damper opens (circled in red) and fresh ventilation air is brought in without passing through the solar collector.

Advantages

1. Low cost and high efficiency (up to 80%).
2. Very low maintenance as the ventilation fan is the only moving part.
3. No storage required, as air is being heated as it is used.
4. Operates near ambient temperature.

Disadvantages

1. Not suitable for equatorial and temperate areas as heating loads in these areas are minimal.

System Costs for Solar Ventilation pre-heating.

References

1. National Renewable Energy Laboratory
2. Federal Energy Management Program
3. Delft University, Solar Energy V1.1, p.349
   Images Source:NREL

Next Article: Solar Water Heating

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