Thermoelectric Plate Cooler ATP040 12VDC With Temperature
Controller And Relay
Thermoelectric Air To Plate Cooler ATP040 - 12VDC
Passive Load
In designing a thermoelectric (TE) cooling system, one of the most
important processes is reaching an understanding of your thermal
load. Without this vital information, you cannot wisely choose the
best TE device or heat exchangers for the job. Each thermoelectric
system has a unique capacity for moving heat. While it is possible
to simply build up a system and then see what it will do, it is
usually far more prudent to optimize your system for the desired
outcomes. There is no better place to start, than with a good,
solid estimate of how much heat must be removed from your thermal
load to achieve the performance objectives.
There are two components to thermal load in TE systems: active and
passive. Active load is found whenever part of the load actually
produces heat. An example would be an electronic circuit in an
enclosure; the circuitry would dissipate wattage based on its
voltage and current requirements. Many TE applications don’t have
an active load (e.g., a food and beverage cooler) and this term can
be entirely discounted in these cases. Nearly all TE systems,
however, must cope with the passive portion. To maintain a
temperature difference between a thermal load and the ambient
environment, a certain amount of energy must be continually moved
into (for heating) or out of (for cooling) the load. The rate at
which this energy is moved (usually expressed in watts), is the
passive load.
One way to conceptualize passive load, is to look at it like a
leaky boat. Water is continually streaming into the boat through
all of the various leaks (e.g., holes, faulty seals, etc.). The
more leakage there is, the faster the water will come into the
boat. Faced with this situation, if you wanted to maintain the boat
at a certain level in the water (and you couldn’t repair the
leaks), you would have to bale out the water at a certain rate. If
you bale too slowly, the boat will sink lower; if you dump the
water too quickly, you may rise above the desired level (which may
or may not be a problem). Ideally, of course, you would repair the
boat at the first opportunity so you could minimize your future
rate of baling.
With a TE system, you are trying to keep your thermal load colder
or hotter than the ambient temperature. Unfortunately, no matter
how well you design your system, there will be some leaks. There is
no type of insulation with an infinite thermal resistance, so some
heat will pass right through your primary line of defense.
Furthermore, seals used to cope with the inevitable holes (e.g.,
doors, TE engine pass-through, etc.), will also be imperfect. Thus,
in a cooling application, some heat is going to leak into the
thermal load from the ambient environment. To paraphrase a popular
sports expression, “You can’t stop it, you can only try to contain
it.” So you bale, only this time you are baling out heat, and
you’re not using a bucket or a water pump, but a thermoelectric
system—one which is steadily pumping watts out of (or into for
heating) the thermal load.
