## Ground-Water Loops

The software allows for a ground-water loop to be used in association with a heat pump. Here temperature is calculated depending on depth. The following assumptions were made in this respect:

Soil temperature θ(x,t) depending on depth x (into the soil) and time t varies under the influence of the seasonal course of the outdoor temperature according to the following formula:

\(\theta(x,t) = \ \theta_{m} – \ \theta_{0} \cdot exp\left( – x\sqrt{\frac{\pi}{a \cdot T}} \right) \cdot cos\left( \frac{2\pi}{T}t – x \cdot \sqrt{\frac{\pi}{a \cdot T}} \right)\)

With a ground water depth of about 10-15 m and deeper it can be assumed with good accuracy that the ground water temperature remains constant over the year and matches the average annual outdoor temperature.

**Static Pressure**

Polysun enables users to correctly calculate both static and dynamic pressure. To correctly calculate the required height difference ∆H a distinction should be made whether or not the loop return line is immersed in the return water tank. A negative difference is also possible; this will result in the pump being relieved of pressure. The image below illustrates this correlation: