Geothermal heat pump systems are probably the most important renewable heating and cooling technology for homes in NY. Geothermal heat pump systems function by using the constant temperature of soil below the frost line to provide heating in the winter or as a sink for cooling in the summer. NY has an excellent geothermal resource, and like solar, this resource is widely distributed.

The heat pump is familiar refrigeration technology, and it uses one unit of electricity to extract 3-5 units of heat from the ground. This ability gives these systems an effective efficiency of 300-500%, which is also referred to as a Coefficient of Performance (COP). For reference, this would be compared to a high-efficiency condensing boiler's efficiency of 96%. Geothermal systems can typically meet 70-100% of client's current building heating, cooling, and domestic hot water (DHW) needs.

Types

The types of geothermal heat pump systems differ by their earth loop type and/or medium of heat exchange. Presently, the most common forms of earth loops are horizontal, vertical, or diagonal, and the two primary mediums of exchange are water-based and direct exchange systems.

Horizontal loops have the advantage of ease and simplicity of installation. Because these loops are typically placed at 6-8' below grade, however, they are more subject to the temperature fluctuations the earth experiences at its surface. This variation in temperature causes a reduction in COP over the winter season. Also, because these loops are shallow, there length requires and disturbs more land, and thus requires a property with space for this excavation.

Vertical loops, on the other hand, are more compact in their footprint and because of their depth (typically 150' to 400' depending on the project), they do not experience a significant COP fluctuation over the heating season. These systems, however, require more skill to install and also require larger equipment, which depending on the geology can slightly increase the costs of installation.

Diagonal loops are typically at a 30 degree angle from the horizontal and are 65-75 ft in depth. These loops have the advantages of vertical loops, but are particularly used for urban and some suburban installations, where space is at a premium for excavation and bringing in large equipment is more difficult. The one restriction on diagonal loops is that they are less suitable for very wet soil with bedrock at a significant distance below grade because the casing of the boreholes is more difficult at an angle than it is vertically.

Water-Based systems use water and a non-toxic antifreeze in special plastic tubing as the heat transfer medium for the earth loops. These earth loops then bring the heat into the heat pump, where it is transferred to the refrigerant loop and extracted. This design is resilient and well-tested, but it also loses efficiency because the heat must be transferred to two mediums before it is extracted. More heat transfer medium is also typically required, which translates into additional ft of earth loops and more energy required for loop pumping.

Direct Exchange systems eliminate the water intermediary, and use the refrigerant directly in the earth loops. This significantly increases system efficiency, meaning a higher COP is usually attained and the loop size required is reduced.

Principle Components

• Earth or Ground Loops

• Heat Pump (Including compressor, condensor, and evaporator)

• Buffer Tank with Heat Exchanger or Air Handler

• Monitoring system including BTU meter (flow meter and temperature sensors), digital electrical meter, and integrating software/datalogger with web interface

Requirements

Heating Distribution Systems

Geothermal systems can heat to 120 degrees, and thus these systems can work well with both forced air and hydronic heating distribution systems. Generally, for new construction or significant renovation, we recommend hydronic systems because they require less energy to move the heat, and they are also generally more comfortable. This is especially true of radiant floor systems.

Please note that when using a baseboard or radiant floor system with a geothermal system, the baseboard or radiant floors must be designed to operate with water between 90 and 120 degrees. Most radiant floors are designed this way, but much existing conventional baseboard is sized often for water temperatures near 180 degrees. When this is the case, this baseboard must be replaced with low-temperature baseboard or modern flat radiators, like that from Runtal or Smith's Environmental.

Cooling Distribution Systems

Geothermal systems can also cool homes effectively, and this is possible through hydronic chilled beam or forced air distribution systems. Forced air systems, however, are much more common in the US at this time. If a house already has central air conditioning (AC), the existing compressor unit can be removed, and the existing air handler and ductwork can simply be connected to the heat pump system. If a home does not currently have a central AC system, there are several low-cost, quiet, small, and flexible duct systems designed for retrofit applications that can added to the home. These products include the Unico small duct high-velocity system, which we have had success using in many such applications.

Land area

As we discussed briefly above, land is required for the installation of the earth loops. Specifically, the exact amount of space will be determined by the system loop type and size being supported, but it typically ranges from 400 ft2 to 8000 ft2. This area must be relatively free of septic, well, gas, and electric systems etc, although obviously some of these can be identified easily and worked around.

Monitoring

At Halco, every geothermal system we do is monitored and production is guaranteed. We pay a high degree of attention to production and economic calculations, as well as system monitoring, because that's not always done in the industry and we think it essential for guaranteeing and demonstrating system performance.

Process

For most clients proceeding or considering a geothermal heat pump system, the first step is taking a look at their last year of heating bills. The next step is usually a free site visit to review the home and discuss the options in person. The next important initial part of the process is usually the home energy audit. For most clients considering geothermal systems, an home energy audit will determine the actual current conductive and convective losses of the building, and will allow us to both properly size a system and recommend energy efficiency and envelope improvements that are cost effective and often significantly lower the overall heat load requirements of the house and reduce the heating capacity required by the geothermal system. For more information on our home energy audit program (including types of audits and costs), please see the Home Energy Performance Division.

Characteristics

Geothermal systems have a life expectancy of 50 years plus for the earth loop field, and twenty years for the heat pump unit. The warranties on these two primary components are usually 25 years and 10 years, respectively.

Certification

We are members of the International Ground Source Heat Pump Association (IGSHPA), and presently have one IGSHPA Certified Designer/Installer and one IGSHPA Certified Vertical Earth Loop Installer/Driller. Several other staff members have participated in other professional trainings, and several will also be IGSHPA certified Designer/Installers in the coming months.

Costs and Economics