Geothermal Energy Basics

How Geothermal Energy Works

“What is geothermal?” Has become a common question for us here at Cullen Construction, and most often it is followed by the comment “what will that cost me?” or “that sounds expensive”. In this, our first blog post, we hope to shed some light onto the common questions and misconceptions that come with a geothermal heating and cooling system.

Imagine a home in which the temperature is always comfortable, yet there is no visible equipment outside and not a sound to be heard; A system that performs efficiently but doesn’t require extensive maintenance or knowledge on the part of the homeowners. Sounds great right?

Here is a basic break downA geothermal system is a heating and cooling system that uses the earth as a source for heat in the winter or cooling in the summer. This eliminates the use of oil or gas as a primary energy source for heating and cooling one’s house or building.

Outdoor temperatures vary with the changing seasons but underground temperatures remain steady thanks to the insulating properties of the earth. Four to six feet below ground, temperatures remain relatively stable year-round. A geothermal system, which typically consists of an indoor handling unit and a buried system of pipes, called a loop, and/or a pump to reinjection well, utilizes these constant temperatures to provide “free” energy. This is the point where most clients walk away, because let’s face it, the energy to run the system may be free, but getting there, well, not so much. While the energy to run the geothermal system is free, there is definitely an initial cost involved. That is really the hardest part to digest, and the main reason most people jump ship on geothermal; they don’t look at it as an investment opportunity. Will putting in a geothermal system make you money? Well, no, but it will save you money in the future.

Unlike ordinary heating and cooling systems, geothermal HVAC systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth. Typically, for most systems, electric power is used only to operate the unit’s fan, compressor, and pump.

A geothermal cooling and heating system has three main components: the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork) and/or radiant heating (in the floor or elsewhere).

The pipes that make up an earth loop are usually made of polyethylene and can be buried under the ground horizontally or vertically, depending on the uniqueness of the site. If an aquifer is available, engineers may prefer to design an “open loop” system, in which a well is drilled into the underground water. Water is pumped up, run past a heat exchanger, and then the water is returned to the same aquifer, through “reinjection.” The most common is a closed loop system where a series of wells are vertically drilled into the ground.

A pipe is pulled through the ground, which contains a heat transfer liquid. The fluid is pumped through the pipe where it is heated or cooled, (dependent upon the home owners need), by the consistent year round temperature of the Earth. The liquid passes through a heat pump (small, usually located in ones mechanical room) which creates the necessary temperatures to run either a forced air system or a radiant system.

There are many advantages to a geothermal system. Obviously reducing ones dependence on fossil fuels is both economical and environmentally attractive. The initial installation cost is more than traditional HVAC systems. However, a one-time tax credit of 30% of the total investment is available for homeowners and 10% for commercial installations (H.R.1424). This tax credit expires on December 31, 2016. The payback of one’s investment can be between 3 and 10 years (on the longer side if it is retrofit). Much depends on the seasonal climates and energy envelope of one’s house.

Geothermal Mechanical Room

Geothermal Mechanical Room

This translates to gigantic 15 percent annual return on investment simply by installing a geothermal system, which is really a number from which many other energy sources are still far off.

The logic in this whole story is quite simple; namely homeowners pay back the investment with the money they would have paid to the oil or gas company. After payback, the savings continue with an average return of more than 65 percent – a percentage that is likely to become higher as fossil fuel prices increase.

Another advantage and long term benefit is the low maintenance requirements for a geothermal system; when installed properly, (Call Cullen!) which is critical, the buried loop can last for generations. The unit’s fan, compressor, and pump are housed indoors, protected from the ruthless weather conditions we can experience, so they tend to last for many years, often decades more than traditionally outside units. Usually, periodic checks and filter changes and annual coil cleaning are the only required maintenance.

Within the past year Cullen Construction has managed the installation of four major geothermal systems.

The systems were installed in Willistown, Bryn Mawr, Downingtown and Nantucket. Each system was designed unique to its site and climate zone. All of the systems are operating smoothly and comfortably and have greatly reduced the client’s monthly oil/gas bills. One was even installed under a pond!

Three of the houses were built using the geothermal system to heat radiant floors throughout the houses. They have all proven to be very quiet and comfortable. A huge architectural benefit is the elimination of unsightly and noisy air conditioning condensing units.

Whether you are thinking of building a new house or addition, or are just thinking of converting from fossil fuels to geo-thermal, give us a call. We can help walk you through the process from initial evaluation, design, and pricing, to complete installation.

Frequently Asked Questions:

Does geothermal still use electric?
Yes, geothermal will use electric, however, the systems use only one unit of electricity to move up to five units of cooling or heating from the earth to a building.
Do I have to have a big yard for all of the piping?
Depending on the characteristics of your site, the earth loop may be buried vertically, so you don’t need a lot of above-ground surface. Some areas even have an aquifer that can be tapped into, only a few square feet of real estate are needed. Also, the water is returned to the aquifer from which it came after passing over a heat exchanger, so it is kept clean of impurities. All of this can be determined by a visit from an experienced contractor, like Cullen Construction.
Will my geothermal systems eventually “wear out”?
Yes, I guess you could say it will eventually wear out, like anything else it in life. However, the loops can last for generations and the heat-exchange equipment typically lasts for decades, since it is protected indoors. If you are around to see it needing to be replaced, the expense is much less since the bulk of the work has been completed through the original installation, so the cost will be less since the loop or well is the priciest component to install.

Below are a few pictures from a Cullen Construction job completed in 2013