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!