What's Behind Geothermal

One of the most neglected areas of Energy is Geothermal.  We hear far too little about it.  We hear lots about Atomic Energy, Solar, Coal and Wind Energy, but seldom about Geothermal.

Geothermal is in part the most natural of things in that it comes from the words geo meaning earth and 'therme' meaning heat.  Behind it is the Sun.

Natural Hot Spring in Japan

In another way Geothermal is far more subtle than the other forms of energy in that it uses the earth on which we stand to heat in the winter and cool in the summer.  We often conjure up images of hot springs as above, when the word Geothermal is mentioned, but that's just a small part of the spectrum of thermal heating alternatives. What we are talking about is the Earth as a heat sink with the Sun as the source

Sunlight is the source of energy for the Earth's oceans, atmosphere, land, and biosphere. This energy serves to heat the Earth to temperatures far above the minus 454 degrees Fahrenheit (3 degrees Kelvin) of deep space. 

Averaged over an entire year and the entire Earth, the Sun deposits 342 Watts of energy into every square meter of the Earth. This is a very large amount of heat—1.7 x 1017 watts of power that the Sun sends to the Earth and atmosphere system. For comparison, a large electric power plant would produce 100 million watts of power, or 108 watts. It would take 1.7 billion such power plants to equal the energy coming to the Earth from the Sun

How the Heat Energy is Used

This energy is absorbed into the atmosphere, oceans, rock and soil of the earth. About 48% of it is absorbed by the earth.  The mantel of the earth is heated and this is the source of Geothermal Energy that we can tap.  Why?  At a depth of approximately 15 feet the ground temperature remains fairly constant, with an average temperature  near 55F year-round, depending on the local climate, terrain and soil type.

If it is hot out we can use this temperature differential to cool ourselves.  If it is cold, we can use it to help us warm ourselves.

How Geothermal Works

Everywhere in the world, just below frost depth, the earth maintains a constant average temperature

To generate heat in the winter and cold in the summer, geothermal systems use a loop of copper or plastic piping buried in the earth, hence the origin of the term ground-source geothermal. The loop contains ecologically friendly refrigerant, which is circulated through the loop under pressure.

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In the winter as shown in the schematic the loop collects the relative warmth from the ground and delivers it to the home’s traditional forced-hot-air system through a pressure-reduction and heat-exchange system. In the summer, the refrigerant collects heat from the house and emits it through the same loop back into the earth, while distributing cooler air like a conventional air-conditioning system (see cooling cycle below). The compressor and heat exchanger needed to run a typical system require electricity, which can be supplied through solar, wind or from traditional AC power. Geothermal systems emit no gases, so they can be located indoors, even in a closet. They are also notoriously quiet.
 

The Cooling Cycle

In this cycle the relatively constant temperature of the earth is used to cool our house or any building.  A solution is circulated to gather the heat energy emitted by the sun and stored at a modest depth by absorption.  If we go below frost line, we are at or near a constant temperature. 

These systems run at good efficiency if they are properly matched with the size of the building they are serving.

The Heating Cycle

The heating Cycle is the reverse.  When it's cold out, we can use the warmth of the earth as compared to the surface to circulate and distribute the heat to the building.

The Heat Transfer Miracle

We are really quite used to heat transfer applications.  Our refrigerators use it all the time with refrigerant and circulating tubes powered by a pump to compress gas.  It's not the same  cycle as geothermal, but the idea is similar.  The Earth in the case of Geothermal is our 'battery' for storage and use in a heat differential manner..

For local information go to South-Port Mechanical Ltd.