Cooling air by running it through underground pipes

[Sultan of Hel]

An environmentalist friend of mine wants to cool a building on his property (something like a shed or workshop) not with AC, but by blowing air from outside into a pipe underground, running it underground for a distance, and then blowing that air straight up into the building.

I need to find the temperature of the air that comes into the building on a hot, humid day. I have the speed at which the fan pushes the air (can be converted to CFM), the outside air temperature and humidity, the pipe material and thickness, and the soil type and temperature.

I tried combining two equations:

$$h=\frac{x}{k}$$
$$h=\frac{k_w}{D_H}Nu, Nu=0.023\cdot Re^{0.8}\cdot Pr^{0.33}$$

...and got 21.81 W/(m^2*K)

I'm positive I'm doing something wrong, and even if I'm not, where do I go with that number?

 

[Chestermiller]

That's the heat transfer coefficient to the air inside the pipe. But you also need a value for the heat transfer coefficient from the ground outside the pipe.