Features

How Does It Work? Why Should You Choose It?

There are many places one can go to get an outline on the pros and cons of different methods for enclosure cooling. Although we will briefly touch on them here, this is really an in-depth article on how to choose a Peltier (thermoelectric) air conditioner, once you have committed to the technology.

The Peltier Effect

Why Thermoelectric?

Opening an enclosure and blowing a fan on heat sensitive components may be a cheap and easy way to cool things down, but it is dirty and dangerous. Exposing components to ambient dirt and debris can damage said components. It also increases the risk of shock to those working around the area. It is best to have a cooling component in place as part of your system. Before going into a detailed look at thermoelectric cooling, a few other technologies are quickly outlined below.

Refrigerant air conditioners have their place but are a maintenance challenge when placed in hard-to-access, remote areas. Whether it is difficult installation, refrigerant leaks due to nearby vibrations, expensive compressor replacements or all of the above, endusers can find refrigerant-based cooling to be inconvenient and expensive to maintain in certain applications.

Heat exchangers and heat pipes are limited in performance due to ambient conditions. Certain applications will require more cooling than these technologies can provide. Finally, compressed air products will require the expense of maintaining a compressed air supply.

Thermoelectric technology has seen advances and improvements in recent years. An overview of the technology will outline benefits and drawbacks to the end user followed by discussion of the newest innovations.

(Note: Comparison chart is only an approximation.)

Thermoelectric air conditioners create a closed system. When installed properly there is no exchange of ambient air into the enclosure. The cooling is created via the Peltier effect, which is a solid-state method of heat transfer through dissimilar semiconductor materials. Two dissimilar conductors replace refrigerant in both liquid and vapor form. A cold sink (evaporator surface) becomes cold through absorption of energy by the electrons as they pass from one semiconductor to another. A DC power source pumps the electrons from one semiconductor to another and a heat sink (condenser) discharges the accumulated heat energy from the system.

Thermoelectric air conditioners are free of refrigerants or other chemicals. These are solid-state cooling products. There are no filters to change, no compressor, and the only moving part is the fan. This means there is virtually no maintenance required and a long life expectancy.

Thermoelectric air conditioners excel in high ambient temperatures. Performance ratings are higher than what was available in the past. It is now possible to get up to a half ton of cooling from a thermoelectric cooler. This allows for thermoelectric cooling to be used in larger enclosures. Applications vary, of course, and small enclosures such as camera housings can be cooled with as little as a 100 BTU/hr thermoelectric air conditioner.

Thermoelectric air conditioners are typically more expensive to purchase up front compared to a refrigerant based cooler or a simple heat exchanger. However, the reduced need for maintenance and replacement parts must be considered as part of the value added to using the technology.

Thermoelectric Cooler Mounting Styles

Recent Changes to Thermoelectric Technology

In recent years, there have been innovations and improved products in the thermoelectric market. New design features allow for energy savings, such as including a passive cooling mode when demand is lower. This will draw significantly less current than the active cooling mode used in times of higher demand.

In the past, thermoelectric air conditioners were limited in performance to about 2,000 BTU/hr. Now, increasingly efficient designs are allowing for air conditioners with up to a half-ton of cooling. This is partly design innovation but also due to higher quality, more robust materials that are now available to manufacturers, such as more efficient heat sinks and more reliable thermoelectric modules.

Modern thermoelectric modules are able to heat more efficiently as well as cool (via reversing the polarity of the module). This allows more thermoelectric products to offer both cooling and reliable heating as the demand exists. By using the thermoelectric modules for heating, efficiency is increased since electric heaters are not needed. For either cooling-only needs or heat-and-cool applications, there is a greater ability for tight temperature controls.

Choosing a System

Factors to consider:

Performance curve per Din 3168

1. How Much Cooling is Needed

The total load is created by the heat your equipment is generating as well as ambient conditions, delta-T, enclosure size, etc. How much cooling is required will be determined by many factors including the details of the enclosure and surrounding environment. There are many sizing tools available online, free, from thermoelectric air conditioning manufacturers and enclosure manufacturers.

2. Allowable Enclosure Temperatures

Thermoelectric air conditioners are often used to cool equipment below ambient. Most electronics are rated to 110°F or so. Therefore, cooling an enclosure to 95°F might strike you as warm, but it actually is more than cool enough to keep electronics happy and running. Using an air conditioner that is too large can mean less efficiency. Cooling significantly below ambient beyond what is needed can cause excessive condensation.

In other words, design for allowable conditions both inside and outside the enclosure. This includes basing maximum allowable internal temperature around the known operating limits of your equipment rather than an arbitrary temperature.

Know what the minimum enclosure temperature should be. If heat is needed in winter months, an air conditioner with heat function can be considered.