Air to Air Thermoelectric Coolers
Air Conditioners, Heat Pumps, Swamp Coolers, Cooling Towers are terms most of us have heard describing methods of cooling commercial buildings and homes. Especially if you live in a warm climate where cooling is almost a necessity. What about cooling electronic components, electrical enclosures, small spaces like cars and campers? It often isn’t practical to use water or freon based systems to produce cooling.
There is an alternative that has been around a long time to cool small areas with solid state electronics. Using the Peltier effect is one of the more practical methods. As a thermoelectric air conditioner, these devices can be used where conventional coolers can not.
What is the Peltier Effect and How Does It Cool?
Charles Peltier first discovered that current flowing between two junctions made of different conductive materials caused heating and cooling in 1834! Materials that he used then were bismuth and copper. Temperature raised in one direction and cooled in the other. Of course the phenomenon is called the Peltier Effect.
The advent of semiconductors made it possible to create very small Peltier coolers. Using P and N type semiconductors in a matrix between two sheets of thermally conductive plates create the same effect as the original experiments with copper and bismuth.
How are the Peltier Coolers Made?
It is possible to obtain the small usually ceramic coolers and construct your own Peltier Effect cooler. The thermally conductive plates will become hot and cold when DC current is applied to the assembly. Without a way to disperse the temperature created on either side the temperature produced could destroy the device. Additional components are needed.
Heat sinking is required to remove the heat from one side of the sandwiched components. The surface on the hot side rapidly heats up as the other side is cooled. In reverse ice can be created on the other surface in a short period of time. By adding heat sinks to both sides the transfer of heat and cooling effect has more practical applications.
On a small scale the devices can be used to draw heat away from electronic components like a CPU chip in a computer device. Larger physical spaces like an electrical enclosure need fans connected to one or both sides to be practical.
Whether large or small some type of control system needs to be in place to prevent overheating of the device and control temperature.
What are the Applications and Features of Peltier Coolers?
Typical Applications for the air-to-air thermoelectric coolers are:
- Control Panels/Outside Enclosures
- Analytical/Medical Instrumentation
- Industrial Instrumentation
- Food and Beverage Cooling
- Telecom Cabinets
- Water/wine Coolers
- Spacecraft and Satellites
- ATM Enclosures
Thermoelectric coolers are noted for:
- No Refrigerants
- Compact Design
- DC Operation
- Reliable Solid-State Construction
- ETL Recognized and RoHS Compliant
- Reduced Repairs & Downtime
- Off-the-shelf Availability
Controlling Temperatures Inside Outdoor Electronic Enclosures.
Outdoor enclosures installed where these types of conditions exist need thermal management systems to prevent the temperatures from falling below the dew point.
Where do these conditions exist? Many gas & oil facilities are in locations where the temperature and humidity vary considerably with the seasons. Texas, northern Africa, the Middle East, are a few. In southern Iraq and other oil fields in the middle east the temperature can vary from 125 F to 25 F. These temperatures included a wide range of humidity and dew points.
Heaters are often used to keep the humidity inside the cabinet lower than the dew point. These heaters are mounted at the bottom of the cabinet where nature convection carries the heat through the cabinet. Sometimes a fan is used to ensure the heat is evenly dispersed to all surfaces. Point surface conduction heaters can also be used on selected components that might be more susceptible to condensation forming on their surfaces.
In the summertime natural convection and forced air just aren’t sufficient to keep the operating temperatures of electronic equipment under their critical thresholds. Peltier air to air coolers coupled with fans can accomplish this in the more remote areas. No need for water or freon in the desert where one is scarce and the other difficult to maintain.
Temperature Control Systems are Needed for These Temperature Ranges.
Humidity creating moisture in the cabinets with the temperature change can be an issue. One solution is to include a sensor to detect the moisture in the air.
A humidity sensor (or hydrostat) senses the moisture in the air. The humidity sensor, hygrostat measures, and reports both moisture and air temperature. The ratio of moisture in the air to the highest amount of moisture at a particular air temperature is called relative humidity. Relative humidity becomes an important factor when combating condensation.
When the sensor senses the moisture is getting too high relative to the temperature it can turn on heating elements to raise the temperature. Raising the temperature decreases the relative humidity in the cabinet and reduces the chance for condensation. These types of control loops can be found in your household refrigerator preventing condensation from forming on the inside walls and food. Typical household freezers don’t have condensation protection due to the lower temperature and you will find ice (condensation) on the surfaces of the packages inside.
The same concept occurs inside outdoor electronic cabinets such as ATMs, kiosks, traffic light controls, industrial applications like oil & gas, windmills, and others installed in remote locations.
Overview of what controls and devices are available from DBK USA.
Temperature sensors and hydrostats in the same control loop can monitor the ambient temperature and dew point. Control devices for the thermoelectric cooler assembly and PTC fan heaters help maintain the ideal temperature for the equipment and prevent moisture in the cabinets.