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Earth Thermal Storage

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Maintenance free home heating/cooling systems may rely more on the constant temperature of the earth for storing energy.

Are we heading for a new energy crisis, like the one that we experienced in the seventies? It might have been that event which caused me to become concerned with ways of reducing energy costs and alternative energies that can be used in our daily lives. I do not see any one energy source becoming what petroleum has been to our society; I do see many different forms of energy being used for different tasks. If you have read some of my blog posts over the past few months, you will have seen a theme of looking at the possibilities of these technologies for the home. Specifically, I admit to being curious as to how these innovations may be used in Houston. It has been said that my city is the most heavily air conditioned place in the world, which requires a good deal of power; and this may be why Houston is looking more closely at green power technologies. Consider this week in weather here. At the beginning of this week, we are experiencing temperatures in the eighties (degrees Fahrenheit), but by the Thursday we will be in the fifties. Heating and cooling needed in one week. Include the humidity, you will see dealing with a home’s HVAC system in Houston a great testing ground for creating a robust green technology solution.

One technology that uses natural heat for the home is a heat pump. The concept is simple in its science: the only point where there is no heat is the temperature known as absolute zero. Since there is always heat in the atmosphere, you can take that heat for your home during colder weather. If it is warm, take the heat in the home to pump it out of the house. The problem arises that our technology only allows this air conditioning unit to effectively work above certain temperatures. One way to resolve this is to change the system to a geo-thermal one. Whereas outside air can experience large shifts, the temperature within the earth stays at a constant range at specific depths. Great idea, but it can be expensive to install. Expensive equals not going to be commonly used. Reduce the cost to find that such a system could reduce energy usage. Improving the efficiency and cost of green technologies would mean that they would be more commonly used.

How efficient is solar power for the home? Actually, it is not that great. The panels do not convert all of the energy which the capture from the sun into electricity. Once you do have the electricity, you find that we have batteries that are not the best at storing this green power. These last lines sound negative for solar. I am pro solar technology though, and I am positive that these problems will be resolved. Anytime I see a mention that solar can be made more efficient, I pay special attention. That is what lead me to examine the idea of a earth thermal storage as a means for improving solar power. The concept here is also simple science. If you warm a thermal mass, that mass will retain that heat (energy) for awhile. It will radiate that heat back to its surroundings. The best example of this concept being used for home heating is the fireplace known as a European fireplace. The heated air is forced through a passage lined with bricks to create a thermal mass. These bricks radiate the heat out to the home for some time after the fire has expired. Even having the sun shine through a window down onto a tile or cement floor will create this effect. The earth can also store this type of energy (heat). You may use this concept if you have a compost pile. Water heating systems that use compost piles play off of this heat.

The green energy produced by a solar panel can then heat your home using earth thermal storage. The Romans invented a radiant heating system which passed heated air through tubes that ran through the floors and walls. Current radiant heating systems mainly rely upon tubing which carries a heated liquid (usually water) underneath your floor covering. Heat rises, so the heat from radiant heating can be very comfortable for a room. Do you remember those old bathroom heaters which relied on a wire being energized? We could take the green electricity from a solar panel passed through wires that are in a thermal mass, which then radiates that heat back into a building. This idea originated in 1978 in a paper written by Lilleleht, Beard, and Fafarman. By heating the ground beneath a foundation, that heat can be used to heat the home, even after nightfall. Electricity in the batteries would not have to be used. Like the Romans, we could install these wires in the walls. I mention this, because it may be the best solution for existing homes. We might not be able to dig underneath a completed home, but we could access the walls and ceilings. This version of the system could be installed in a ceiling. Alright heat rises, so it would take more energy to heat a room, but that is more acceptable than tearing down a house.

Would I need solar panels to use such a earth thermal storage? It is my belief that most homeowners will not be obtaining their green energy from equipment on their own home. I feel that service providers (the utility companies) will be the main supplier of green power to the average homeowner. There are two methods that the concept of earth thermal storage could be used by a homeowner. I started this post with an explanation of a heat pump, and we could improve this device. In a paper written in 1982 by Ternes, a study conducted in Knoxville was detailed about improving a heat pump on a house which sat on pier and beams. Instead of taking the air from the general exterior, the air could pass over the earth (remember it is at a constant temperature) before going into the pump. The earth becomes a heat exchanger in this scenario. This is a brilliant idea, but I am not sure if any manufacturer is using this technology for their heat pumps. The second method is the same concept mentioned in the previous paragraph. The wires heating the walls, ceilings, or foundation would receive their power off of the grid. In this method, the wires would be heated at night. Activating it at night uses power when it is at its cheapest during a non-peak time. At least one firm is providing such a system.

I have not heard many people discuss this technology. I was wondering if such a technology would work in Houston. Radiant heating is more firmly established in the northern parts of the United States, but there is no reason it could not be used here. As mentioned, the real problem in this region is that we have to constantly switch between heating and cooling systems, this makes our forced air systems so easy to sue. Heat pumps would be the logical substitute for them, but many homes do not have pier and beam foundations. It would be nice to have toasty feet in the morning though.

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2 Responses to “Earth Thermal Storage”

  1. Max Holland Says:


    I quite enjoyed your blog, and would love to investigate more how these technologies could be used (economically) in Houston. The weather and humidity are at least quite predictable here. I am at the very least looking to force the 150F air out of my attic by solar (low expertise, expense, etc.), and hopefully feed any remainder back into my existing power to qualify for the (30%?) tax incentive.

    I calculated ambient temperature 10-40 feet below ground as about 69F, year-round. To your knowlege, could this differential sustain efficient year-round climate control? (Summer:Mar-Nov Winter: Dec-Feb, alternating weeks only) Is this temperature right at all? How high is the water table?

    Homes aren’t my area of expertise , but I would like to find cost-cutting/green measures to make Houston more bearable (and I LIKE the heat!). These slab-fixed homes must have some advantage, other than cost, but alas, they will do little for your cold feet.

    On the less green side of things, I’m looking for an efficient way to dehumidify besides the thermostat when my house feels like a warm, wet cave. Ceiling fans (and computer use….sigh) just wreak havoc on my allergies and dry eyes (essentially my area of expertise).

    Any ideas out there for any of these questions?

    Please pardon any duplications of other posts, as I have no experience with this blog format, and have not seen the other responses yet.

    Max Holland

  2. Thank you for dropping in Max. Solar fans can be quite effective, and they range in price from $70 to $250 per unit for residential applications (this is the price without installation costs). The most knowledgeable people on what systems are being included in the tax rebate when it comes to HVAC will be a reputable company, who can evaluate your set up to suggest best options.

    People frequently comment that Houston was built on a swamp. Not all of Houston was built on such terrain, but for most of the area the water table is pretty high. That is why we do not have many basements in this city. A geo-thermal heating/cooling system is possible here, but it is expensive. They drill the tubes down to a further depth where they can obtain a temperature around 55F. Such systems are very energy efficient compared to the standard forced air systems in most of our homes.

    Slab foundations are not the most green solution for our city. That is why some green builders are considering pier and beam foundations again.

    There are additional systems which can be added to your HVAC system to dehumidify your home. With what seems our ever present humidity, I decided against going such a route in my own home. I cannot recall the price off the top of my head, but adding a component is not so bad. Units for particular rooms has been my solution for family members. Those can be easily found in home improvement centers. I place them in the bedrooms or other room where my relatives spend the most time. They have been fairly helpful.

    If you look in the categories section to the right, you will find a subsection called “green home conversion”. That is where most of my articles on looking at green fixes for the home are located. The Google search option to the right searches sites that I trust outside of this one, so you may find help there too.

    Let me know if this helps. Thanks.

© Frank Schulte-Ladbeck Professional Home Inspector Houston, Texas
Frank Theodor Schulte-Ladbeck
home inspector, TREC# 9073
Houston , Texas , 77063 United States

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