Solar Air Drying and Cooling

Solar Air-Heating Has Many Agricultural Uses

Solar-heated air can be used for drying most crops that require warm air. Solar heated-air is ideal for drying delicate foods since it will not burn or risk potential damage from high-temperature steam heat. Solar heat is non-polluting and best of all, it incurs no fuel costs.

Existing commercial drying operations can be converted to utilize solar heat by installing our system to pull heat from the building’s metal roof or wall. We pull heat from under the metal panels, add some ducting, and connect the ducts to the intake of the dryer fans. The system then pulls heated air from the underside of the panels and passes the air to the drying chamber.

We install simple sensors in the air flow and use thermostatic controls to turn off the incoming airflow when the temperature is not high enough for solar heating. The existing system then operates, as it always has, burning high-cost fuel but serving the drying process.

For some in-field applications, we can use a ground-mounted polymer system that is low-cost and very transportable.

In new buildings, our metal roofs and walls are integrated into the building’s structure. We can retrofit a system over almost any existing exterior wall or roof.

Solar-heated air can be used to dry:

  • Crops, timber, distillers grains, and textiles
  • Tea, coffee, beans, tobacco, etc.
  • Food for dehydration or processing
  • Sludge, manure, and compost

Solar-drying systems can realize Internal Rates of Return of 10-30% with a simple payback of as little as 5 years.

Pay back will depend on the cost of the fuel being offset, application, climate, design, and scale. Tax credits can lower payback periods for most commercial solar drying systems

Solar-Cooling. it’s not the Heat it’s the Humidity

The most energy-efficient cooling system uses the evaporation of water to lower temperatures for building cooling and industrial processes. However, thermal comfort in summer means more than keeping the air temperature below 75° degrees F. High temperatures, high humidity, or both can lead to excessive discomfort.

Water can be used to cool air to comfortable levels until the humidity levels get too high. When water evaporates it absorbs a large amount of heat from its surroundings (about 1000 Btu per pound of water evaporated). The most familiar example is the cooling effect of evaporating perspiration on the human skin.

In hot, dry climates, body temperature is partially controlled by the rapid evaporation of perspiration from the surface of the skin. In hot climates with high humidity, the cooling effect is minimal because the high moisture content of the air prevents further evaporation. In those humid climates, the most energy-efficient way to achieve a cool environment is often to lower humidity.

Traditional air conditioning systems must cool incoming air to a very low temperature to remove humidity. The air then is so cold the system must “re-heat” the air to send 60F air into the building’s space. The deep cooling and reheating use more energy than simply drying, then cooling the air. But most drying processes rely on expensive energy sources such as natural gas, and electricity.

Our solar cooling systems dry air using low-cost solar heat. We pass air through desiccants to create dry air that supports the evaporative cooling process. After leaving the desiccant, the hot dry air is cooled in one side of a heat exchanger. The warm, dry air is split into two air streams. The first stream supports an indirect evaporative cooling of the second stream. This cools the second stream without adding any humidity. We regenerate the desiccants with low-cost solar heat or a combination of solar and other waste heat source so they can be reused continuously.

This system uses less electricity to produce cool, dry air than a conventional air conditioning system. It is typically used in conjunction with a conventional air conditioning system. When solar or waste heat is applied, the conventional system can operate at lower capacity, saving electricity. During summer months, when excess solar heat is available, the systems provide maximum savings during the hottest part of the day. This is when the conventional system would be drawing the most power and the electric rates are highest.