Down in the hole
Lord, it's deep and the sides are steep
And the nights are long and cold
Down in the hole
Light and love and the world above
Mean nothing to the mole
Down in the hole
James Taylor
What would the answer be if this question were asked of a group of four-year-old children: “What do you think you would find if you dug a hole at the beach that was 200 feet deep?” In my experience, the answers would range from the fantastic, “an underground sand creature that has a secret passage to the ocean”, the whimsical, “a special land where fairies had a magical kingdom,” to the mundane, “worms and dirt and maybe some dead stuff.” In truth, after watching the guys drill the holes for the ground loops, I think the answer is really just “more sand.” How about this one: “How deep is 200 feet?” Since the average American four-year-old child is about 3.3 feet tall, it would take 60.6 children standing on top of each other to make a tower 200 feet tall, even if the boys were standing on tip-toe. Put them down instead of up, and that’s a really deep hole!
On Valentine’s Day, Steve Van Horn and his Chesapeake Wells crew began the installation of the vertical loops for the geothermal heat pump. Vince and I took the dogs up to the house and sat on the walkover to watch the process. As Steve had told me earlier, his is one of the world’s dirtiest jobs. I would add the adjectives “cold”, “wet”, and maybe “tedious” to that description. Digging a deep well hole is definitely hard work!
At the beach, a geothermal heat pump requires a closed loop system, meaning that the fluid, in this case water, circulates through the loop fields’ pipes and does not pull in water from a water source. (Open loops would be subject to salt water intrusion.) The pipes run through the ground, but there is no direct interaction between the fluid in the pipes and the earth other than the heat transfer across the pipe. There are four choices for the shape of the ground loop system: Vertical, horizontal, and slinky (coiled), and pond. Because the beach environment is sandy and subject to erosion and overwash, vertical loops offered the best opportunity for damage control, and they obviously take up less horizontal space, so that was our choice. The length of loop required is determined by the ground formation, the ground temperature, the heating and cooling power needed for the house and the balance between the amount of heat rejected to and absorbed from the ground during the year. This determination was done our mechanical engineer. Steve dug eight wells that are about 200 feet deep, so there are about 1600 feet of pipe. (A well in this definition is a deep hole, rather than a place to fill your water bucket.) Although the tubing can be made from various metals, these pipes are polyethylene, also a common material for this use and more appropriate in the corrosive environment of the coast. The pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. Oh, wait! That makes it 3200 feet of pipe!
On Valentine’s Day, Steve Van Horn and his Chesapeake Wells crew began the installation of the vertical loops for the geothermal heat pump. Vince and I took the dogs up to the house and sat on the walkover to watch the process. As Steve had told me earlier, his is one of the world’s dirtiest jobs. I would add the adjectives “cold”, “wet”, and maybe “tedious” to that description. Digging a deep well hole is definitely hard work!
At the beach, a geothermal heat pump requires a closed loop system, meaning that the fluid, in this case water, circulates through the loop fields’ pipes and does not pull in water from a water source. (Open loops would be subject to salt water intrusion.) The pipes run through the ground, but there is no direct interaction between the fluid in the pipes and the earth other than the heat transfer across the pipe. There are four choices for the shape of the ground loop system: Vertical, horizontal, and slinky (coiled), and pond. Because the beach environment is sandy and subject to erosion and overwash, vertical loops offered the best opportunity for damage control, and they obviously take up less horizontal space, so that was our choice. The length of loop required is determined by the ground formation, the ground temperature, the heating and cooling power needed for the house and the balance between the amount of heat rejected to and absorbed from the ground during the year. This determination was done our mechanical engineer. Steve dug eight wells that are about 200 feet deep, so there are about 1600 feet of pipe. (A well in this definition is a deep hole, rather than a place to fill your water bucket.) Although the tubing can be made from various metals, these pipes are polyethylene, also a common material for this use and more appropriate in the corrosive environment of the coast. The pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. Oh, wait! That makes it 3200 feet of pipe!
Anyone who has tried to build a sandcastle knows how hard it is to create any kind of hole in the sand that will stay open, and the idea of a 200 foot deep hole seemed laughingly impossible, though I knew better than to say so. As it turns out, the borehole is commonly filled with drilling mud, a sodium bentonite clay that does a multitude of jobs in the drilling process. In the end, the clay surrounds the pipe both keeping the borehole intact and providing a good thermal connection to the surrounding sand for maximum heat transfer. Steve uses a product called Quik-gel, a sodium bentonite clay found in Wyoming. This is really neat stuff, and it can be used in outside stock ponds or lagoons, to prevent leaching in land fills, for waterproofing, on and on. Steve adds soda ash to the mixture when digging in a saltwater environment.
So, what happens, exactly, to make this possible? The well drilling rig uses a diesel engine to power an hydraulic pump. The hydraulic pump spins the drill string, a column of drill pipe that transmits the drilling fluid (via the mud pumps) and rotational power (via the top drive) to the drill bit. The drill string is hollow so that the drilling fluid can be pumped down through it and circulated back up the annulus (the void between the drill string and the formation). The drill bit has holes in it to allow the drilling mud to be at the site of the scour. As the hole is dug deeper and deeper, the clay coats the walls of the borehole. The bentonite clay is also a viscosifier, keeping the bits of shell and debris in suspension until they can be pumped out into the mud pit. The mud pit, in this case a horse trough, works as a settling tank for the debris, which is shoveled out before it can be re-circulated through the system. Thus, the mixture of clay and water is continually pumped down into the hole and the debris brought back out of the hole until the proper depth is achieved.
Finally, the ground loop pipes are fed down into the hole along with the same length of rigid CPVC pipe, which acts as a sort of guide for the flexible pipe. The CPVC pipe is then pulled back out, leaving the loop in place. After all the loops are installed, the loops are connected together in the form of a manifold, and the loop field is established. Finally, the loops are trenched in and fed into the house where they will be connected to the Water Furnace heat pump system. Voila! Oh, if it were only that easy…
Take a look at the guys in action:
