DX vs. Water-source

I've received a couple questions as to the differences in installation between a DX geothermal setup and a water-source geothermal system. Although this is, by no means, a complete discussion of the installation of either product, this should give you a general idea of what to expect.

Water-source geothermal systems come in two flavors: open loop and closed loop. For our purposes, let's ignore open loop water-source geothermal systems as they are becoming extremely difficult to install thanks to state and federal regulations dictating the collection and return of groundwater. Instead, we'll talk about closed-loop systems, the most common geothermal HVAC solution found in the United States.

Unlike a DX system, heat transfer in a closed loop water-source system occurs between the ground, water in underground loops, and the refrigerant. The heat pump unit itself contains a water to refrigerant heat exchanger which allows the refrigerant in the heat pump to trade heat with the water from the ground loops. On the other side of the heat pump, refrigerant trades heat with air in a refrigerant to air heat exchanger, much like a DX system.

The major difference in installation (and in operation, really) is the ground loops. Closed loop water-source systems use high-density polyethylene piping filled with a water and antifreeze solution instead of copper tubes filled with refrigerant. However, HDPE piping and water are less effective at transferring heat than refrigerant in copper piping, so substantially more piping must be installed to achieve the same tonnage rating for a heat pump. Thus, installation costs tend to be quite a bit higher with water-source systems than DX systems simply because drilling and excavation costs are greater. While there are advantages to having a water/antifreeze solution in the ground over refrigerant (it's generally preferable to leak water and antifreeze than refrigerant), the lower heat transfer coefficient of water combined with HDPE piping reduces system efficiency while requiring a water to refrigerant heat exchanger, further lowering the coefficient of performance.

3-ton closed loop water-source geothermal system HDPE ground loop installation

In short, a DX system requires less drilling and excavation while providing higher efficiencies and lower costs of operation when compared to closed loop water-source systems. This isn't to say water-source systems are a bad option...they, too, provide substantial environmental, financial, and efficiency benefits over traditional heating and cooling solutions.

5-ton DX geothermal system copper ground loop installation (panorama)

Note the differences in pit depth and overall ground loop size, even when comparing a 3-ton closed loop water-source system to a 5-ton DX system.


The Green Home

I completely forgot about one of the other solar-centric items Bill Nye discussed...stranger yet, it's an item I have in my own home, so it's particularly fitting that I should forget to discuss it.

Solar tube lighting. Imagine, instead of using lights during the day in your home, having a bright light provided by the sun, even in rooms without windows or with otherwise poor lighting. The concept is simple, but simplicity is elegance, particularly when it comes to reducing your carbon footprint.

Essentially, a small domed window installed on the roof is connected, via a mirrored tube, to a "light fixture" in the ceiling. Because the tube is mirrored and the dome on the roof is a Fresnel lens, large quantities of sunlight can be funneled into your home, easily lighting most rooms during the day and further reducing home energy needs. Plus, unlike typical skylights, solar tube lighting uses very small openings in your home, reducing energy loss through poorly insulated skylight windows and increasing the efficiency and effectiveness of your home's HVAC system.

The Science Guy Weighs In

" Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam. " - Carl Sagan

I had the pleasure of listening to Dr. William Nye of "Bill Nye the Science Guy" fame speak last night at Northeastern University. While he didn't demonstrate the effects of gravity or explain magnetism, he did discuss the supreme importance of science in the battle against climate change, including an explanation of the above photograph*. During his two-hour presentation, he mentioned several technologies which he utilizes in his own home as ways he helps minimize his carbon footprint and fight global warming.

His most interesting offerings were the "green switch" and solar water heaters. Nye's green switch is a simple on/off switch which turns off specified electrical outlets around his home using a wireless radio signal. Electronics in standby mode, including those with no visible lights such as phone and laptop chargers, account for 8% of the nation's energy use. That's 8% of our energy being used by devices just, as Nye said, "waiting to be turned on." This switch can be turned off at night, cutting off power to the "twin fangs" of power adapters and devices around the home and saving countless watts of energy from being turned into wasteful heat. Even if the switch is used only half the day, a 4% savings on your energy bill is easily reached.

And this switch only simplifies the process of energy savings. Simply unplugging devices which aren't in use can achieve the same effect, albeit with a little more work.

Nye also discussed the many benefits of solar energy, including solar water heaters seen across the globe. Simple in their operation and highly effective, even in the low winter sun, solar water heaters provide free (as in $0.00) hot water by harnessing the energy of the sun to boil a refrigerant, which in turn heats water. Natural convection currents carry cold water to the bottom of the heater and force hot water out the top and into the home, and the cycle continues all day until hot water is stored at night.

Much like these water heaters, direct exchange ground source heat pumps use the warmth of the sun, just in a different manner. The solar energy reserve of the Earth provides all the heat one needs to heat a home in even the coldest of climates at a fraction of the cost of traditional heating, and with a fraction of the environmental impact.

If you have a DX heat pump installed in your home, we'd love to hear about it. Feel free to leave a comment or send us an email and we'll be happy to share our passion for the fight against climate change.

-Marcus

* The photograph above was taken by Voyager 1 from well outside the solar system in 1990. The tiny, one-pixel blue dot along the right side inside the orange band is Earth. Named "Pale Blue Dot," it is considered one of the ten most important space photographs ever, and is largely viewed as the image which inspired modern conservationism.

Latent Heat and More on the Green Home

The question we most typically receive from customers and others interested in direct exchange geothermal heat pumps is "How do you heat a home to 70 degrees when the Earth is only 50 degrees?" Well, the answer is rooted in a physical principle called "latent heat." Unlike "sensible heat," what you think of when you say "It's hot outside," or "Man, Boston is cold," latent heat is related to material phase change.

In high school chemistry, a lot of time is spent on so-called "ice problems." The idea of an ice problem is that heating water from ice to vapor is an energy intensive process. Heating water from ice to steam is a complicated issue which touches on two different types of energy: The energy required to change temperature and the energy required to change state.

When solving an ice problem, most students learn to remember a graph that looks like this (click picture for larger version:

As you can see, the plot is not linear. Instead, at 0 degrees Celsius (32 degrees F) and at 100 degrees C (212 degrees F), the energy usage drastically increases while the temperature does not change. All of this energy is required to change the state of water from ice to liquid and from liquid to vapor. Refrigeration equipment, including EarthSource's DX heat pumps, utilize the large amount of energy released during a phase change to heat and cool your home.

Sure Marcus, but that looks complicated. What does it mean for me?

Well, what that means is that there's lots of energy to be harvested during a refrigerant phase change. Thus, even if you're only turning 32 degree liquid refrigerant into 32 degree vaporized refrigerant in the ground, compressing it and turning it from vapor into liquid converts all that latent heat energy into sensible heat energy, giving you a very hot fluid with which you can heat your house well above the temperature of the ground.

Simple, right? Yes, actually, and that's why heat pumps are so efficient and reliable. Our DX systems are warrantied for 10 years and the ground loops are warrantied for 50 years, guarantees we can make because the system uses so few moving parts.


The Green Home - Continued

Even the best, most efficient HVAC solution won't be effective with a poorly insulated home. The simplest way to save energy without changing a single piece of equipment is properly insulating the walls, floors, and ceilings of your home. Although adding insulation can be an intrusive process in older homes, there are several newer options available for homeowners who wish to improve their home's efficiency without tearing up walls.

The always inventive Bob Vila suggests blow-in insulation, where foam, fiberglass, or another particulate insulation material is blown in to walls through a small hole using an air pump. Nearly as effective as typical fiberglass insulation, blown-in foam can reduce energy bills 20-30%. Verifying the insulation's effectiveness can be achieved by converting a standard digital camera into a thermal infrared imager...instructions for this process are widely available online.

Beyond insulation, windows and doors are a huge energy drain. Even double-pane windows are considered energy-inefficient by modern standards, with triple-pane windows promising substantially reduced heat loss across the window and other benefits including increased security and reduced noise. Properly-fitted doors with a brush draft stopper can make a noticeable difference, particularly for homes where bare feet are common.

A welcome to our blog

Welcome to the Direct Exchange Geothermal weblog. Authored by members of the EarthSource Energy Solutions staff, this blog aims to illuminate new technology which can minimize the effects of civilization on the climate. We welcome any insight, questions, or general comments, either on a direct exchange heat pump installation at your home or any other topic relating to ecological sustainability.

We should be updating this blog fairly regularly with up-to-date information, so be sure to check frequently for new content.

To begin, I'll start with a brief discussion of direct exchange geothermal heat pumps while touching on the concept of a "green home" and a low-cost option to help decrease a home's impact on the environment.


Direct Exchange Geothermal Heat Pump Basics

Geothermal heat pumps are not what one might think of when the word "geothermal." Unlike the spectacular effects of geothermal energy in places like Yellowstone Park, DX heat pumps use the surprisingly stable year-round temperature of the Earth to heat and cool your home. Because the Earth is constantly collecting solar energy, the ground about 5 feet below the surface is usually around 50 degrees Fahrenheit. Any heat pump operates by extracting heat energy from one side of its operation and depositing it in the other. Unlike air-source heat pumps, which must extract heat from air which might be at a very low or very high temperature, DX heat pumps are always working with one side around 50 degrees. This makes them very efficient and very reliable, even in extreme weather.

The difference between direct exchange heat pumps and other geothermal heat pumps is that, with DX, copper loops are buried in the ground to provide direct heat transfer with the Earth using refrigerant. This requires very little digging (sometimes just a 10 foot diameter circle will do) because the heat transfer from refrigerant to copper pipe to soil is very efficient. So, any DX heat pump utilizes copper ground loops, a small heat pump unit which contains a compressor and a few other mechanical parts, and an air handler or other internal coil which is used to distribute conditioned air or water to the home.

Essentially, a direct exchange heat pump is a refrigerator. You know that hum coming from your fridge? Well, that's the compressor cycling refrigerant through two coils. One of those coils is the big coil on the back of the fridge. It gets hot while the refrigerator is in operation, while a second coil inside the refrigerator gets cold. When a direct exchange heat pump is in heating mode, the air handler inside the home functions as the warm coil. Heat energy is transferred from the ground and into the home through the refrigerant. In cooling mode, the cycle is reversed, and heat from the home is discharged to the ground through the refrigerant, making the indoor coil cold and cycling cool air through the house.

This entire process is very energy efficient. Instead of a large A/C unit and carbon-unfriendly heating oil, year-round heating and cooling needs are performed by a single unit drawing 30-70% less energy than typical HVAC units. With some other additions, heating and cooling your home can be a zero-carbon process, but we'll talk more about that later.


The Green Home

The concept of a green home has become particularly relevant as oil and energy costs rise. Although initial investment is usually much higher than the construction of a standard home, lower energy costs indicate reduced environmental impact while also reducing the load on the homeowner's wallet. As part of an ongoing series, I'll highlight some technologies and ideas which can be used both in new home construction as well as retrofits, with an emphasis on reducing energy use and carbon production.

One simple (and inexpensive) method to increase the efficiency of a home is to collect rainwater in large cisterns. Although rainwater is typically unsuitable for drinking, it can be used for tasks as simple as watering plants or as part of an advanced gray water system. A gray water system uses non-potable water, including rainwater, to operate toilets and water yards, among many other uses. Although the concept makes sense ecologically, it still poses legal questions, so be sure to check local laws and regulations. If you encounter obstacles, write your representatives!

-Marcus

Help us help you!

Direct exchange geothermal heat pumps are proven technology, but very little information exists on the tens of thousands of United States and international installations. Much of this data could be used to improve heat pump design and fashion a more need-dependent dealer base around the world while simultaneously helping customers find support. If you currently own a direct exchange heat pump system from any manufacturer, defunct or startup, we'd love to hear from you.

Please contact Marcus, our associate engineer, at marcus@earthsource-energy.com . Thanks!