True, peltier devices are about 4 times less efficient than compressor-based systems for cooling, however they are actually more efficient than standard resistive heaters for heating! Granted, cooling is generally more important than heating to most brewers, but take sake for example. When making kome-koji (moldy rice), I need to maintain 86 degrees. This device does that quite nicely and efficiently.
People are very quick to discount peltier devices because of their low cooling efficiency, but we must consider some other factors:
- They're very small.
- The are very inexpensive
- They're silent
- They require low voltage
- They do not require any refrigerants or high pressure tubing.
If I wanted a dual mode heat pump (compressor-based) to do what this project can do, I would have to spend a couple grand and it would be much much larger and heaver.
Then here's the final thing to consider about electric efficiency: I live in the American Midwest where the majority of our climate control expense is due to heating, not cooling. I also tend to do most of my brewing in the winter. So even if I only get 10-15% efficiency out of this system for cooling, the extra heat simply offsets my furnace's heating load. So in reality, the energy used is nearly free. It's all about moving heat to where it's needed...and away from where it's not.