ALL ABOUT GEOTHERMAL AC AND HEAT IN TEXAS
GEOTHERMAL ENERGY, GEOTHERMAL HEATING, GEOTHERMAL HEAT PUMPS
GEOTHERMAL ENERGY, GEOTHERMAL HEATING, GEOTHERMAL HEAT PUMPS
Texas, along with a lot of other southern states, has been slow to embrace geothermal, or ground source heat pumps as a viable alternative to conventional ac and heat systems. There are valid reasons for this, and the arguments are melting away as geothermal systems are becoming increasingly popular in the South. I have prepared this argument based on my last 12 years since I became involved in the geothermal, or ground source heat pump business. First a bit about myself, so that you may gain some belief in what I have to say!
After studying engineering in college in the 1970’s (but failing to complete), I became a general contractor for years, and then worked in the electrical and HVAC ( Heating, Ventilating and Air Conditioning) trades as a serviceman. In 1994 I qualified for and earned my Texas State HVAC License. I have contracted HVAC since then, both residential and commercial, large and small, including public works projects. About 12 years ago, we were offered our first federal government geothermal project, and installed several systems in Galveston, Texas. I have since then been trained and certified in most major geothermal brands of units, as well as certified installer via testing by the IGSHPA (International Ground Source Heat Pump Association) presently considered the ruling authority on the business in the United States. I became entranced with the theory and economy of the systems, which at that time were quite popular in Europe and the Northern U.S., but not in the South. Despite the higher up front cost, the cost savings and “green” energy values appealed to me. I studied hard and have become a great believer in the value of geothermal, or ground source, HVAC systems. It is true that geothermal technology proves more valuable in heating based climates, but the technology has evolved to where it makes financial sense to us folks in the South as well. There are differences in how we do it, and I will explain later.
DEFINITION: LOOP SYSTEM: The geothermal, or ground source heat pump, has to have contact with the ground to transfer heat from your house in summer, and extract heat to warm your house in winter. The “loop” is the piping system that carries the water heated or cooled by your home, to the ground, one way or the other. It may be thru a series of vertical well loops, horizontal piping in trenches, via a water well, a series of coils in a pond, or even via your swimming pool.
BOTTOM LINE: Myself and others have installed thousands of successful geothermal AC and Heat systems in Texas, and the economy results have proved themselves. It works well, and usually makes financial sense. The only drawback, as I have always said, is the up front additional cost of the ground loop, which is the heart of the economy of the system.
WHAT IS GEOTHERMAL: The trade misuses the name “Geothermal AC and Heat” because true geothermal is the use of inner Earth heat to power steam plants and such. The true correct term should be ground source heat pumps, since we derive heat and cooling from the ground, not central earth magma. However, the term geothermal sounds good and has stuck, to the disdain of many engineers and scientists.
NUTS AND BOLTS: There have been lots of stories of geothermal installation failures in Texas, and they always are the result of untrained, or incorrect installations. Some are because of untrained “newbies” trying to plow into a new field, and some because “geo contractors” from other areas (up North) have moved here and tried to ply their trade the same way they did it up there. Both wrong. Ground source units in Texas are a special breed, and require very different engineering. Why? Two reasons. Ground temperature and heat imbalance. Ground temperature here (and most don’t know this) is a steady 71 degrees year round 25 feet below the surface. On the other hand, say around Illinois, the stable earth temp is about 52. It’s a little harder for us to cool our home with 71 degree earth temperature than 52 degrees. Some of the guys from up North don’t realize this and it takes a larger loop design to cover our summer ac load. We also have a lopsided heating and cooling season. Theoretically, if we used the same amount of energy to heat in winter as we dispelled in summer, the earth below us could be a bank to add and withdraw at an even rate. This would be very efficient. In South Texas, and much of the South, we generate 80% more heat removed from our homes than we withdraw in the winter. We have to consider that the ground has to dissipate extra heat we are injecting. Bottom line is, it’s all about loop design and it needs to be right.
FACTS AND FALLACIES ABOUT GEOTHERMAL AC AND HEAT IN TEXAS:
QUICK NOTE AND DISCLAIMER: Loop design should be based on a structure heat and cool load, not “per ton” of AC installed. That is, the ground loop has to dispel and retract the heat generated by the structure, regardless of the size of the AC unit. Thus said, I will continue based on a “per ton” basis for simplicity.
VERTICAL LOOPS: (The more the better: FALSE) Vertical loops are the most popular in Texas and for good reason. You can get lots of ground contact in a 250 or 300’ vertical well, in a small amount of surface area. Drilling down to 300’ in most of Texas is easy, and therefore, less expensive. On the other hand, it still costs foot by foot, and some contractors will want to sell you extra wells to 1) make more money and 2) protect their calculations. Problem is, excessive loops size generates installation costs that will not be offset by energy savings. A careful designer will review drilling records of nearby wells ( available on State records) and determine the underground soil conditions, which determine the correct and necessary loop lengths. Rule of thumb in the Houston area, if you drill into areas that reach water table 60-100’ deep, 250’ of loop bore per ton works well. If area is “dry” to 120’ deep, 300’ per ton bores per ton are probably necessary. Better yet, design for a maximum loop temperature of 100 degrees, which does mean that for a few days or a week your system will operate at a lowered efficiency, but not enough to justify the cost of a loop that will maximize at 95 degrees. Truth is, a system designed to maximize at 100 degrees rarely breaks 95 anyway, because of the built in safety margin in the design software. Its all about saving money.
HORIZONTAL LOOPS: (They don’t work in Texas: FALSE) Horizontal loops, in most areas work well, if properly sized and installed. I install them. I know. My favorite is a 4 pipe system 5’ to bottom for two pipes, and then two more at 3’ deep. Why? I’ve worked it all ways and this works the best in Texas. If soil is moist it takes about 220-250’ of trench per ton. If dry soil closer to 300’/ton. Trenches can be 20’ apart. Why horizontal? Install cost is about 60% of vertical bores. How much land does it take? 1/2 acre of clear field can carry 4 tons. Just food for thought.
POND LOOPS: ( You need a 1/2 acre or more: FALSE) You can use your pond to heat and cool your home, but again in Texas, the rules are different. Some rules of thumb are 3500 sq ft of pond/ton, and such, but these are numbers from designers dealing with icing and frozen ponds up north in winter and still trying to heat homes. Here we have a lot more leeway with ponds. Biggest issue is depth and drying up. The pond has to be deep enough to maintain at least 80 degree or cooler water in summer, which is 8-10’ deep, and cannot dry up. The size is not so important, but I will say that probably 1000 sq ft of surface/ton is minimal. Ponds depend on depth (ground contact) and evaporation to keep cool. Sometimes, a fountain may help keep temperatures in line. Ponds are a very economical way to “geo” your house and I install them often. Ponds also seem to vary in temperature with the seasons more than ground loops, and generally require antifreeze to get through the coldest days.
OPEN LOOPS: WELL WATER (Cheapest way to have geothermal : FALSE...Maybe) Although I have installed many open loop, or well water systems, that provide fresh well water to the unit an then dump it to another well, creek or pond, this is not the best way to operate on a geothermal ac system. Granted, it is less cost up front, especially if you already need a well if you have no city water. Also, constant temperature ground water generates better efficiencies than common loop systems, that do heat up and cool down over the season. On the other hand, you will be working your well system much harder, and your system is subject to the chemical effects of the ground water in your region, rather than the treated water in your closed loop. Pumping costs may be higher, but generally offset by better efficiency of ground water systems. Some people argue that is involves water waste, but I find this hard to swallow, since I think it goes back to where it came from, at least eventually. Truth is water well repairs seem more prevalent than geothermal repairs, and I’ve had several “open loop” customers who came back to me years later and converted to some version of closed loop.
USING YOUR POOL TO HEAT/COOL YOUR HOME: (Does it work? TRUE) I’ll try to be short on this one, because it has so many elements. Basically you can use your pool like a small pond, but it cannot really support the heating and cooling loads of your home on its own. On the other hand, you home can provide some free pool heating in early Spring and Fall, and extend your swimming season. You can add a pool cooling tower to maintain cool pool temperatures in summer, and have a few ground loops to provide the heat required for winter. Basically, with a pool you can save on your installation cost, heat your pool early spring an late fall for free, and get a 30% federal tax rebate on the installation of the geo system. Options are a geo heater for your hot tub, cooling your overheated pool in summer, and heating the tub when you want it. The list goes on.
HYBRID GEO SYSTEMS: (Can it save install costs? TRUE) Part of the problem in making geothermal AC systems cost effective in Texas is the fact that we have to install more pipe in the ground than up North to keep loop temperatures useful, especially during our hot summers. Or do we? Another concept is hybrid systems, that utilize a combination of ground source loops, and a small cooling tower to satisfy heating and cooling loads. The concept? We can install enough loop in the ground to satisfy our heat demands, which may only satisfy 40% of our cooling load, and then supplement with a small cooling tower to cover the additional excess summer heat. What is a cooling tower? It is a small fountain inside a fiberglass shell that basically cools by evaporating water. Evaporative coolers are popular in Arizona and Nevada desert areas, where their humidity is a low 15% or so, but in Houston where our humidity is already 50% or more, cooling by evaporation is not comfortable indoors, but still works outside. The whole deal is, a small cooling tower is less expensive to install and operate than what it replaces in ground loops. This is something that requires some design thought to consider.