Thermoelectric temperature control

Thermoelectric temperature control is the use of the thermoelectric effect, specifically the Peltier effect, to heat or cool materials by applying an electrical current across them.^[1] A typical Peltier cell absorbs heat on one side and produces heat on the other.^[1] Because of this, Peltier cells can be used for temperature control.^[1] However, the currently use of this effect for air conditioning on a large scale (for homes or commercial buildings) is rare due to its low efficiency and high cost relative to other options.^[1]

Figure 1. Energy balance of a Peltier cell based heat pump

Peltier cell heat pump

A typical Peltier cell based heat pump can be used by coupling the thermoelectric generators with photovoltaic air cooled panels as defined in the PhD thesis of Alexandra Thedeby.^[2] Considering the system with an air plant that ensures the possibility of heating on one side and cooling on the other.^[3] By changing the configuration it allows both winter and summer acclimatization.^[4] These elements are expected to be an effective element for zero-energy buildings, if coupled with solar thermal energy and photovoltaic^[5] with particular reference to create radiant heat pumps on the walls of a building.^[6]

It must be remarked that this acclimatization method ensures the ideal efficiency during summer cooling if coupled with a photovoltaic generator. The air circulation could be also used for cooling the temperature of PV modules.

The most important engineering requirement is the accurate design of heat sinks^[7] to optimize the heat exchange and minimize the fluiddynamic losses.

Thermodynamic parameters

The efficiency can be determined by the following relation:

${\displaystyle \eta ={\frac {T_{C}-T_{H}}{T_{C}}}}$

where ${\displaystyle T_{C}}$ is the temperature of the cooling surface and ${\displaystyle T_{H}}$ is the temperature of the heating surface.

The key energy phenomena and the reason of defining a specific use of thermoelectric elements (Figure 1) as heat pump resides in the energy fluxes that those elements allow realizing:^[8][9]

• Conductive power ${\displaystyle {\dot {Q}}_{L}}$: ${\displaystyle {\dot {Q}}_{L}={\frac {L}{d}}S(T_{H}-T_{C})}$
• Heat flux on the cold side ${\displaystyle {\dot {Q}}_{C}}$: ${\displaystyle {\dot {Q}}_{C}=\alpha IT_{C}-{\frac {I^{2}R}{2}}-{\frac {k}{d}}A\Delta T}$
• Heat flux on the hot side ${\displaystyle {\dot {Q}}_{H}}$: ${\displaystyle {\dot {Q}}_{H}=\alpha IT_{C}+{\frac {I^{2}R}{2}}-{\frac {k}{d}}S\Delta T}$
• Electric power ${\displaystyle {\dot {E}}_{EL}}$: ${\displaystyle {\dot {E}}_{EL}=\alpha IT_{C}+I^{2}R}$

Where the following terms are used: ${\displaystyle \Delta T=T_{H}-T_{C}}$, ${\displaystyle I}$electric current; α Seebeck coefficient; R electric resistance, S surface area, d cell thickness, and k thermal conductivity.

The efficiencies of the system are:

1. Cooling efficiency: ${\displaystyle \eta _{C}={\frac {\dot {Q_{C}}}{{\dot {E}}_{EL}}}}$
2. Heating efficiency: ${\displaystyle \eta _{H}={\frac {\dot {Q_{H}}}{{\dot {E}}_{EL}}}}$

COP can be calculated according to Cannistraro.^[10]

Final uses

Thermoelectric heat pumps can be easily used for both local acclimatization for removing local discomfort situations.^[11] For example, thermoelectric ceilings are today in an advanced research stage^[12] with the aim of increasing indoor comfort conditions according to Fanger,^[13] such as the ones that may appear in presence of large glassed surfaces, and for small building acclimatization if coupled with solar systems.^[14][15]

Those systems have the key importance in the direction of new zero emissions passive building because of a very high COP value^[16] and the following high performances by an accurate exergy optimization of the system.^[17]

At industrial level thermoelectric acclimatization appliances are actually under development^[18]