Black gold
Texas tea
Limestone, huh?
Insertion of the geothermal heat transfer tubing into the wells.
We didn't hit oil like Mr. Clampett, but limestone we've got plenty of. Sorry to any neighbors who were bothered by dust during drilling. If it ever rains the dust should wash away. Our problem is a bit more dramatic since we have 4 piles of soggy rock dust, mostly limestone.
All of this activity is for the geothermal HVAC system. The next stage is for a trench to be built that will accommodate the geothermal tubes and allow them to be linked together in a big loop. This trench will be filled with the limestone dust and then soil removed to dig the trench. Geothermal heating and cooling is one of the most important aspects of this project. With this system not only do we get a very efficient system, but it is almost completely pollution free. The only energy required is for pumps and fans. We don't need to burn anything. And the energy for the pumps and fans will be coming from solar panels! All of this reduces our carbon footprint pretty close to zero. And did I mention it's pollution free?
Our system is based on the fact that the Earth is a constant temperature (of about 55°F) at 200 feet down. We drilled 4 wells, each to that depth. This gives us a 5 ton system for cooling and a large heating capability. Into each well is inserted a loop of tubing which is then surrounded by a type of grout. This puts the tubes in contact with the Earth where heat can be exchanged. We either release heat to the ground in hot weather or we take heat from the ground during winter. Inside the tubes is a fluid based on a glycol compound (a safe version of the anti-freeze in your car). This fluid warms up or cools down, depending upon the season, as it passes 200 feet down the tubes. The tubes are connected in a loop to allow the fluid to circulate back up to the house. The whole system is ridiculously simple and trouble free.
When the fluid circulates back to the house it will go into a heat pump which will extract heat from the fluid during winter and release heat to the fluid during summer. Explaining that process reminds me of physics lectures, but you can look it up on the web at Wikipedia: Heat pump physics. Suffice it to say that you have a heat pump in your kitchen, most people just call it the refrigerator.
In our whole house geothermal heat pump, the fluid itself never leaves the tubing, it stays within the system to be circulated back down the wells. But before it goes back outside it passes through a set of tubes contained in a giant water tank. The heat the glycol fluid contains is transferred to the water in this tank when we're heating the house (or for cooling, heat in the water tank is transferred to the circulating glycol fluid). Then the warm water in the tank is pumped to the radiant floor system in the house and we are thus warmed. For cooling the cooled water contained in tubes will pass by a fan that will blow air across the tubes. This cooled air then goes into the house and we are thus cooled. The system is known as a water-to-water system (really it's glycol fluid-to-water) because the fluids are used as the medium for energy exchange. Here's a diagram that takes me a bit of effort to digest:
Our system is so efficient that as a side benefit it will also make all of our domestic hot water and store that in another tank, separate from the one used for heating and cooling.
Combine all of that with zoned heating/cooling, a solar panel system, and we should have an HVAC system that doesn't compromise comfort while being energy wise.
What about the "V"? The industry term we've gotten used to is HVAC which stands for "heating, ventilation, air conditioning". One of the things that comes up when building an energy efficient home is indoor air quality (IAQ). A big component of IAQ is ventilation, the "V" of HVAC. Our house is so heavily insulated and sealed that we need to be careful to maintain good IAQ. We aren't burning anything (except a wee bit of gas during cooking when we're not just microwaving leftovers), but the air can still become spoiled. So we have an energy recovery ventilator (ERV) as part of our HVAC system.
Even animals have sort of a biological energy recovery system. Take a snowshoe hare for example:
This little guy has huge ears to listen for hungry foxes and wolves. The blood going to warm those ears would lose all of its heat to the air without a biological energy recovery mechanism. The animal would then get too cold to survive up North. So the blood going to the ears in arteries passes very close to blood returning from the ears in veins. The warm blood gives up some of its heat to the cool returning blood and thus doesn't lose it to the air.
Our house ERV works in a similar fashion. Air is brought in from outside (cold air in winter, warm in summer) through ductwork which runs very close by the ductwork for the stale air being exhausted. The different air streams will transfer heat between themselves. Thus in summer the cool, but stale air being exhausted will pass by warm, but fresh air. The fresh air will thus be pre-cooled by the stale air (and the stale air will be warmed by the fresh air). The reverse would happen in winter. In this fashion we are able to recover at least 70% of the energy that would be lost by this ventilation of stale air. Pretty slick, huh? And we learned that from a bunny rabbit!
Onward and upward,
Mark, Mark and Isabel
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