Chapter 7 – Maintenance
Page 7-4
TestEquity TEC1 Thermoelectric Temperature Chamber
Theory of Operation
Thermoelectric Cooling and Heating
Air-to-air exchangers utilize the Peltier effect, whereby the heat is transferred via the flow of
current through thermoelectric modules. One part absorbs the heat and, as a consequence,
reduces the temperature (cold side) and the other part dissipates the heat to ambient (hot side).
Fans are used to move air over heat sinks attached to both the hot and cold sides of the
thermoelectric modules. If the polarity is reversed, the hot and cold sides are also reversed.
There are no moving mechanical parts (except fans) so thermoelectric air-to-air exchangers are
extremely reliable with an almost unlimited life span and require no maintenance (except
possible fan replacement). A thermoelectric air-to-air exchanger does not contain any polluting
substances such as CFC or other gases, has a more compact and simple structure than a
conventional refrigeration system.
Temperature Control
Refer to the electrical schematic to identify the items referenced below. Three thermoelectric
modules (TE1, 2, 3) provide cooling and heating. The air is circulated by a fan which is mounted
to each thermoelectric module. A DC power supply (PS1) provides 12 VDC to power the fans
and thermoelectric modules. A temperature controller (TCR1) measures the air temperature
using at RTD temperature sensor (RTD) and cycles an array of solid state relays on/off as
required to modulate DC power to the thermoelectric modules. The solid state relays are
arranged in an H-bridge configuration to provide switching with polarity reversal for cooling and
heating.
When cooling is required, TCR1 output 2 (cool) turns on. This energizes SSR1 and SSR2. This
applies power to TE1, 2, 3 with (+) on the red wires and (–) on the black wires.
When heating is required, TCR1 output 1 (heat) turns on. This energizes SSR3 and SSR3. This
applies power to TE1, 2, 3 with (–) on the red wires and (+) on the black wires.
