Air Compressors for Geothermal Drilling
The main question is always what sort of ground do I need to drill? You might be able to rotary mud drill, in which case this is not too difficult. But what happens when we meet rock, hard rock and lots of it. That is the realm of down the hole hammers and air compressors.
Let’s take a look at some of the givens. A smaller hole requires less expensive drilling equipment. There is less spoil to remove from the hole and therefore less bit wear. There is less grout needed to fill the hole. So small is good, but how small do we need to go? Sizes between 6” and 4” are common but the smart guys are drilling with 4” hammers. Is a 4” hammer as fast as a 6” when it comes to drilling? With the right amount of air, yes. What is the right amount? For 4”geothermal system you will need to drill not just to the water table but well through it, so pressure to lift the water is important. Thirty foot of water needs about 15 psi to lift it. So 100 foot requires an extra 50 psi, 200 foot 100 psi and so on. So some contractors are using up to 500psi systems. Wow! A good flow would be 400 to 500cfm with a capability of increasing the pressure up to 500psi. Normal drilling would only need about 350psi but to clear the water that extra 150 psi really helps.
Make sure the hammer you are using is a high pressure unit and capable of handling that amount of air. Also remember that the hammer works on a pressure differential. So on the surface, a hammer rated for 300psi must not have more that that pass through it. When it is under 100 foot of water an extra 50 psi can be used. This is because of the pressure differential at the hammer not the surface. A new hammer 4” will be available this fall from NUMA www.numahammers.com . It is specifically designed with the geothermal market in mind. It is a fast drilling unit with ability to cope with water. For air compressors talk to Sullair www.sullair.com and Atlas Copco www.atlascopco.com So there you have it all I know about compressor selection for geothermal