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.