Is Geothermal Right for You?

Perhaps the first question to be asked is precisely this: While geothermal heating and cooling has a range of advantages and is clearly good for our planet and the environment, is a geothermal system the right thing/best thing for your home? 

To answer that question, here are a few basic questions in turn:

Can you afford a geothermal system? Depending on the loop application selected, a geothermal system can cost between $25,000 and $30,000. Most of the cost of the system centers on the need to excavate and prepare the geothermal piping loop: this upfront cost can amount to as much as $20,000 of the total cost, depending on the region of the country you live in, the prevalent soil conditions or water access, and the concentration of established geothermal business in your area. The inescapable fact is that a geothermal system costs more than a conventional HVAC system, although the payback on the system occurs much faster due to the energy savings achieved with a geo system. Plus, with at least up 30% coming back to you in the form of federal and possibly more from state tax credits and possibly utility rebates, the actual cost is about 40% lower than its first price.

Some residential developers have chosen to install the underground geothermal loops in advance, and new homeowners can tap into the loop while paying a modest monthly fee, much like a utility cost. This can save significantly over the cost of drilling your own geothermal loop.

Is your home properly insulated? If not, are you willing to pay for insulation? For a successful geothermal or any high efficiency HVAC system experience, a tight building envelope, achieved through effective insulation, is essential. Otherwise electricity costs won’t come anywhere near what you’ve been promised. Homeowners whose geothermal-equipped homes don’t have a tight envelope will blame the geo system for their high electricity bills when the lack of good insulation is the real culprit.

Is the soil composition in your area well suited for geothermal? Not all areas of the U.S. are as well suited to geothermal as other areas. For example, in Florida closed-loop geothermal is impractical because of the cooling dominant nature of the Sunshine State. Rather, placement of properly designed loops or exchangers in an adjacent body of water or pond is a great alternative as is what’s called a Class V Thermal Exchange method

F5.jpgDo you have enough property (ground space) for siting the underground loopIt is well understood that a geothermal ground loop must have sufficient space for the system to function optimally and its length should be matched to the anticipated demands made by the system in either its heating or cooling mode. (For more information on types of geothermal loops, see the discussion Types of Geothermal Loop Systems). A shorter ground loop can be subject to what’s called “thermal degradation” or “glide” over time. Conversely, an oversized ground loop (or heat pump) can be just as problematical. For efficient operations the ground loop must be properly sized to meet the expected heating-cooling demand (load) that the house will require, especially during what are known as “peak times.” Determining the load of a house is therefore a critical system design task. To determine the load requirements, there are analytic tools that need be used by your system designer/contractor:

ACCA Manual J Heat Loss and Heat Gain Analysis This peak heating and cooling load calculation tool analyzes the amount of heat loss and gain to and from the outdoor environment at outdoor-indoor design conditions that must be made up by the HVAC system to maintain occupant comfort.

Closed Loop/Geothermal Heat Pump Design Standards This ASHRAE-IGSHPA document is a source of precise standards and guidelines to be used with Manual J load calculations for the design and installation of closed loop geothermal heat pump systems.

Will you need additional equipment? Oftentimes a single heat pump will do the job for all the heating-cooling required. Heat pumps can also be used for heating domestic water in conjunction with what’s called a desuperheater or a “hot water generator.” A desuperheater, an optional feature, is a secondary heat exchanger installed at the compressor discharge that uses excess heat from the heat pump and superheats the hot gas excess for the purpose of producing hot water. The excess heat energy is available in both heat pump’s heating and cooling mode and only when the heat pump is in operation. Desuperheaters are not able to provide all the water heating a home may require, so a water heater is still needed. However, they can definitely reduce a home’s water heating bill. The addition of a properly installed buffer tank can provide impressive peak hot water availability.   

Distributing your geothermal heat & cooling: forced air or radiant? Heating or cooling your home with a geothermal heat pump requires a distribution system to move the heat from the heat pump throughout the home. This can be accomplished by either a forced air (with ducting) system or with a “hydronic” system using radiant panels or under-the-floor radiant. Both types work well with different types of geothermal pumps: for forced air with a water-to-air type of pump and a water-to-water pump with radiant. Homeowners should discuss the pros/cons of each type of distribution system with their contractor for a new home. For retrofits, where a geothermal system is replacing a boiler/furnace and conventional A/C system, the contractor needs to explain what changes, and at what cost, will be required to accommodate the geo system.