High temperature heat energy is not always necessary for house heating and other household needs
Country house needs is not only water at boiling point.
Energy for home needs and it`s satisfaction via heat-storage battery of heat accumulators.
Not for all home devices is necessary heat energy with working liquid temperature up to 65 degrees C. In winter the temperature of entering into the house water is about +3 °C. For the kitchen, household needs or getting hot water, this very cold water would be well to warm up at least to +15 °C. Fresh winter air, after heat exchanger in the ventilation system, is making sense to warm to +30 °C.
The low-temperature heat requirements are not insignificant needs, as it seems to be. In most cases, for the house needs, we use hot water with the temperature up to +50 °C. That mean, that more than half of heat energy, needed to obtain hot water in winter, is possible to take from the low-temperature heat source. Preheating of fresh winter air in the ventilation system can be 1/3 of energy expenditures for the house heating.
Low-temperature heat source can be also used as a heat source for heat pump. And at the suitable moment, when there is wind, which produces energy for the heat pump compressor, to heat high-temperature heat-storage tank (heat accumulator).
Thus, we need two heat accumulators: first - low-temperature, +30... +75 °C, and the second - high-temperature, +60... +100 °C.
In some situations air or water or ground heat pump can give (as "wastes") cold with low temperature. It is good to have the third accumulator of heat energy*, the storage tank of "cold" with temperature -20... -10 °C. Cold from this accumulator can be used to provide refrigerating chest (as an alternative to refrigerator and low-temperature freezer), to cool air in rooms (instead of electrical air-condition). And for... electricity generating, by thermoelectric power generators - via Peltier modules.
Heat energy is a temperature difference.
Peltier modules also known as thermoelectric modules or semiconductor or solid heat pump, based on the Peltier–Seebeck effect.
From the online free encyclopedia Wikipedia, article Thermoelectric effect:
The Peltier–Seebeck effect, or thermoelectric effect, is the direct conversion of thermal differentials to electric voltage and vice versa. Related effects are the Thomson effect and Joule heating. The Peltier–Seebeck and Thomson effects are reversible (in fact, the Peltier and Seebeck effects are reversals of one another); Joule heating cannot be reversible under the laws of thermodynamics.
The Peltier effect is the reverse of the Seebeck effect; a creation of a heat difference from an electric voltage.
A Peltier cooler/heater or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other. Peltier coolers are also called thermo-electric coolers (TEC).
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