Geothermal is not a new technology or method of using the earth’s energy to fulfill heating and cooling needs. It is, however, an evolving concept and one that has advanced dramatically over the past two decades, even within the past few years. Advances have occurred in four general areas:

1. Heat pump technology,
2. Well drilling methodology,
3. Geothermal system design, and
4. Professional training and certifications.

In this article, we will explore the current state of geothermal as an energy alternative and how these advancements make this a very viable and serious alternative.

Overview
Geothermal offers benefits unmatched by any other conventional or alternative energy solution. Simply stated, geothermal eliminates dependency on oil, propane, and natural gas as fuel sources while maximizing energy efficiencies. When compared to conventional air conditioning equipment, variable speed geothermal heat pumps are rated at 35 SEER[1] versus a 15 SEER high efficiency conventional air conditioning condenser unit.

The earth stores 47% of incoming solar energy making it a natural source for heat. A geothermal heating and cooling system moves the heat from the ground into the building’s interior using a high efficiency heat pump. During hot summer months, the system simply reverses and moves hot air from the building back to the earth to provide cooling. This process works more than twice as efficient as traditional air conditioning systems.

The temperature below the surface (20 feet and more) remains a constant 50-52 degrees throughout the year. This factor alone makes geothermal the most efficient form of heating and cooling. With the overall high efficiency of the system, fewer moving parts within the equipment, and the absence of open flames and vibrations, geothermal systems operate at substantially lower life cycle costs than conventional building heating and cooling systems. Geothermal systems create cleaner interior environments because there is no soot from combustion, and increased airflow means increased filtration. Another benefit is that the heat pump only needs to slightly bump up the air temperature during the winter, after the water-to-air heat exchange. That means no loss in moisture and no dry air during the winter months. A humidifier is not necessary.

Well Drilling Methodology
There are four approaches to installing geothermal wells. In my opinion, there is only one reliable method for the majority of states that provides the most consistent results with the least amount of maintenance requirements. That method is the vertical closed-loop well system. More about that later.

First, I don’t suggest any system that involves an “open loop” well system in which one well draws water in and another dumps it out. This is known as a “pump and dump system”.  With an open well system, you run the risk of introducing contamination and sediment into the equipment. These methods also tend to waste a lot of water. The drawing or pump well often dries out, requiring additional wells to be drilled. Moreover, the capacity of the drawing well (gallons/min. and pressure) has a direct impact on the geothermal system’s ability to handle heating and cooling loads. Lastly, open loop well systems require far more maintenance than a closed loop system.

In warmer climates, horizontal closed loop systems are used in which the well lines run horizontally (versus vertically) at about 8 feet below the surface. The problem with this method is that you’ll need four times the length of well piping in order to ensure consistent well line temperatures before the water/glycol mix reaches the heat pump for the water-to-air exchange. Installation of horizontal closed loop systems is also more expensive because of the excavation and trenching costs, in addition to the extra labor and materials for installation of the water lines. Besides that, subsurface temperatures do not remain consistent until at least 20 feet below the surface. You therefore run the risk of the geothermal system not running efficiently when higher demand exists.

The most reliable well drilling installation method is the vertical closed loop system. This is a completely contained loop with no possibility of air or contaminants entering the system. Installed properly, this system could easily achieve a 50-year lifespan. Everything is subsurface and vertical wells can be drilled just about anywhere. For example, we’ve installed them under the driveway adjacent to newly constructed homes.

I recommend well depths of 150 linear feet for each one-ton of the heat pump size, plus the length of piping needed to go to-and-from the building structure to the wells and between the wells. The wells should be located at least 10’-15’ from the foundation and separated by a distance of 20’- 25’ between wells when there are more than one for the same application.  The separation distance is important because wells that are drilled too close together may impact the heat transfer between the ground source and the water lines if there are more than one well competing for the same ground source heat. When drilling more than one well for the same application, the well depths must remain equal to ensure proper pressure. The boreholes should be 6" with 6 5/8" steel casing. Piping should be 1 1/4" HDPE geo-loop piping. Boreholes are grouted using a bentonite based thermal grout from the bottom up to the top. No mechanical joints should be used under ground. All foundation wall penetrations should be smooth bored and sealed. All geo-loops and lines after installation must be pressure tested to assure that there are no leaks.

Heat Pump Technology
Heat pumps are now available as a two-stage system. Couple that with a desuperheater for generating hot water and you have the most efficient heating and cooling system available today, with EERs as high as 29.1 and COPS as high as 4.8. A two-stage heat pump allows the unit to run at only 67% capacity most of the time to maintain a consistent temperature and humidity level. When there's demand for greater heating or cooling, such as during hot and cold temperature extremes, the unit automatically changes to function at 100% capacity. This part load/full load capacity significantly lowers annual operating costs while maintaining ideal comfort levels. In addition to the full load/part load operation, a variable speed blower motor adds to the efficiency with a multitude of operational modes. The blower motor automatically adapts to all applications. The desuperheater provides efficient production of domestic hot water. When you combine the 2-stage heat pump, the variable speed blower, and the desuperheater for domestic hot water, nothing comes close to matching the energy efficiency.

Geothermal System Design
There are several options for installing a ground source heat pump. Factors that determine the design specifications include the size and layout of the property, local energy costs, size of the building, energy load requirements, and underground conditions. Soil conditions dictate the amount of energy that can be stored in the ground and influence the system. A qualified engineer, certified in geothermal system design, should be the only one to determine specifications.

Geothermal systems are meant to exploit the earth’s free and continuous subsurface temperatures. To accomplish this, the systems must be sized properly. Oftentimes, systems are sized improperly and are too small to handle the environmental requirements of the conditioned space.  Some believe it’s a way to save money, relying instead on higher design temperatures and supplemental backup, such as an electrical backup component. The problem is there are no efficient forms of backup systems and relying too much on backup defeats the purpose of a geothermal system.

A practical approach to the use of supplementary electric heaters should be taken. The geothermal system must be properly sized so as to require minimal reliance on electric or any other auxiliary backup. This approach not only ensures maximum efficiency of the system, but also lowest cost of operation. Our goal is for the heat pump to require only 5% of supplementary backup  and only for those times when (1) the heating load exceeds the capacity of the heat pump, (2) there is an emergency situation, or (3) when this system requires a quick recovery from setback temperatures. Geothermal systems should be designed for 0^o temperatures. The less the geothermal system relies on electric backup, the lower the monthly operating costs. The goal is to utilize the “renewable” energy from the earth’s heat source, and not rely on the national electric grid and the associated costs.

Supplementary heating can also be achieved at a lower cost with the use of duct heaters located in the heat pump supply plenum for heating or subzone reheat.  Duct heaters are UL listed for zero clearance, meet all requirements of the National Electric Code, and are serviceable without removing the heater. The duct heat packages include a hinged control panel covering fusing, magnetic contactors, and a blower relay and range in size from 5 to 10 kW depending on the size of the heat pump.

Professional Training and Certification
Professional training and certification should be a basic requirement for any HVAC contractor who intends to install geothermal systems. A geothermal system is just another form of heating, cooling and ventilation so a licensed HVAC contractor is the best-qualified professional to handle geothermal installations. There are several training and certification programs available.

Certified GeoExchange Designer (CGD). This program was developed and is delivered through the combined efforts of the International Ground Source Heat Pump Association (IGSHPA), the Geothermal Heat Pump Consortium (GHPC), and the Association of Energy Engineers (AEE).

Accredited Geothermal Installer Certification. This program is offered through the International Ground Source Heat Pump Association (IGSHPA). Those who pass the exam become IGSHPA Accredited Geothermal Installers.

Geothermal Designer Boot Camp. This is a hands-on, real-world course that was designed for geothermal installers and designers. It is an advanced course that allows professional students to explore individual questions, what-if scenarios, and heating/cooling alternatives. The authors of the IGSHPA Residential and Light Commercial Design and Installation Manual created the program as a continuing education opportunity. Students are provided with advanced learning of proper system design, in addition to hands-on practice sessions alongside the program’s developers.

Standing Column Well (SCW) Geothermal Systems. Professional installers learn about standing column wells and the number of SCW design applications. They review the key thermal and hydro-geological bases for good performance and what makes the Standing Column Well (SCW) different and compelling as a geothermal HVAC solution.

[1] The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute in its standard ARI 210=240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. [1] The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is the Btu of cooling output during a typical cooling-season divided by the total electric energy input in watt-hours during the same period.

About the Author
Jeff Lefkovich is President of JBC, Inc. (www.jbcbuilding.com) and Legacy Homes of New England, LLC (www.legacyhomesofne.com). He can be reached at jlefkovich@yahoo.com or 203-994-4522.