By combining solid-state cooling via a Peltier device with a photovoltaic (PV) solar panel, a zero emissions air conditioner module can be implemented for supplemental environmental temperature management. This design was modeled for integration in the place of a small-aperture “window unit” style air conditioner and operates within the parameters of a standard 45 Watt photovoltaic panel.
Peltier-style thermoelectric modules are sometimes termed “heat pumps” although their operation is not actually a pumping mechanism, but instead relies on a current passing through a juncture of dissimilar materials that can transfer thermal energy from one side to the other. Reversing the polarity of power through Peltier devices reverses the transfer of thermal energy, allowing the same module to be used to warm or cool an area based on the direction of current flow.
Peltier modules can draw heat even from otherwise frigid air, and can exhaust heat into hot air with the proper heat-sink and fan impeller to move air across the sink – so the solid-state air conditioning unit can be used to alternatively cool or warm an area regardless of the external temperature. Peltier modules can be stacked to provide increasing levels of thermal transfer as measured against the ambient temperature. This requires additional power which would require more efficient photovoltaic panels, but current single-panel designs can provide upwards of 250 Watts or more and multiple external panels can be aggregated to provide the necessary current.
This design was originally intended to maintain temperature regulation in enclosed automobile cabins using only solar power to avoid draining a vehicle’s batteries, and does not rely on ozone-depleting CFC coolants but operates solely through solid-state cooling. The experimental module was installed in a wooden box to provide support for the solar panels and the heat sink and the air conditioner requires a penetrating aperture to allow efficient thermal transfer through the Peltier module. By providing isolating thermal insulation around the Peltier module, water infiltration through the opening was avoided.
As with all air conditioners, during cooling the inside heat-sink accumulated atmospheric water condensate. A drain pan was added below the heat sinks to catch this water and two hoses allowed the accumulated water to be drained out either side of the simulated cabin. After the desired temperature level was reached, subsequent water accumulation was minimal and of measurable volume only in the mornings when the sun first rose and energized the photovoltaic panels. Condensate water could be collected through a filtration system for areas in need of clean water supplies.
The addition of larger panels and rechargeable batteries salvaged from a prior project allowed the air conditioner to continue operation in darkness, which reduced the water accumulation overnight but at the cost of additional weight that would be undesirable in vehicles. This additional weight could be acceptable in structural designs to retain more constant temperatures in extreme climates. Constant temperature regulation using renewable power and no CFC coolants provides greater efficiency over a full day’s time, avoiding the need for rapid thermal evacuation in the morning of each day using the limited capacity of individual Peltier modules. Multiple stand-alone units of this design could be installed in structures to supplement traditional forms of air conditioning to reduce grid load during peak periods, when solar power for the solid-state cooler’s PV panels will also be at peak potential.