Starting in the spring thermal energy is absorbed by the ground. The rate of which this energy is absorbed is determined by the make up of the ground, the insulating properties of the topology and the amount of energy available. There are many variables which effectively dictate the performance of the ground as a thermal tank.The most obvious variable is the mean energy available supplied from the environment. Most notable being solar energy from the sun. Another source of energy may be from man in the form of waste heat. Assuming that a mean figure can be cited in approximate form there is still the challenge of determining the resistance of the topology. The topology in itself tends to become very complicated in that it can act as a source and a sink depending upon other environmental conditions such as rainfall and wind.
The ground itself tends to act like a thermal tank in that energy absorbed in the warmer months is also given up in the colder months. Though it can be argued, i suggest that this form of energy not be confused with geothermal energy. This particular energy is seasonal. This makes the energy sourcing and sinking a lead lag system. There is in fact a thermal wave which propagates through the ground starting in the summer (effectively recharging the thermal tank, if you will) as the tank accumulates energy. The opposite holds true for colder months where the thermal tank gives up the thermal energy. At this point the wave begins the travel back to the surface. A balance is generally reached between geothermal and seasonal energy. At some point the two thermal waves intercept canceling the gradient.
If the nulling point can be found it should be possible to construct a device which could tap into this seasonal energy for heating purposes. This should not be confused with geothermal heating which uses the inner heat of the earth. The seasonal energy tank is likely to be very near the surface for a geological area that under goes all four seasons. Being a seasonal tank, there is finite capacity. This is classically considered to be an adverse property in terms of heating potential. Without carefully considering the tank characteristics it is very likely either saturate the tank or deplete it of thermal energy. Once either state is reached the tank is no longer available for the given mode. In the abstract this looks very much like a standard LCR circuit in electronics. Where the thermal wave in itself is L. The heat capacity of the ground being C and the coefficient of ground being R. And the sinking or sourcing medium being the dimensioned variable F.
Initially i thought the topology may be R, but since i plan charge this tank internally the ground itself becomes R. Since the charging is internal the topologies now becomes r which is the leakage resistance. In the warmer months r is a positive number. In the colder months r becomes negative. Another aspect here is that in the warmer months r gradually decreases and in the colder months r gradually increases.
As can be seen this becomes a rather difficult model to approximate. One may wonder why i would suggest using a thermal tanking circuit as this in place of geothermal energy. If correctly analyzed a thermal tank can be tuned to capture a great deal of solar energy in the warmer months. A very high thermal gradient would be present allow more energy to be moved from solar collectors to the ground. This potential difference not only moves more heat, but the potential may be tapped with machines that exploit the Carnot cycle. Of course this all needs to be studied.
In order to substitute LCR with real numbers i need to know several characteristics of the ground. That being the plasticity limit and the liquid limit of the ground. Knowing this i can approximate the Btu content of the tank in a given area. A few core samples will be needed in order to properly determine this. Before i acquire a core sample i need to get an approximation of the thermal gradient's propagation speed. I also need to know where this thermal wave intercepts with the geothermal wave.
This will be a rather long project being that i must sample a complete season. In order to do this i will need a thermal probe which penetrates at least 4 feet into the ground.
The next post will cover the thermal prove in more detail.
