Direct Exchange

Basic Description and Operation

One system, multiple uses
Whether you live in Sidney Australia, Sitka Alaska, or Siauliai Lithuania, the EarthLinked ™ system is the simple solution to a comfortable environment throughout your home. A single unit can provide space heating and cooling, and water heating, no matter the climate conditions. Because of its small size and mechanical simplicity the system is convenient, reliable and easy to maintain.

Space heating and cooling

Thousands of families around the world use EarthLinked to heat or cool homes of all sizes and styles. The system enables you to maintain comfortable and stable temperatures that you select year-round.

Air handling and radiant floor heat

EarthLinked is designed for easy integration with various air distribution systems installed in your home to circulate hot or cool air depending on the season. Alternatively, you can connect to a radiant floor heating option to distribute heat evenly and efficiently throughout your home. With this configuration, heat is distributed through hot water circulated in a piping system in your floor. The radiant floor option provides up to 40% additional energy savings added to those already delivered by the EarthLinked system.

Hot water

You can use the EarthLinked system to heat water up to 120_F (49_C), optimizing your energy consumption and saving money. The system uses waste heat given off in the air-conditioning mode in summer or natural heat stored in the ground and harvested by the heating mode in winter. Either way, you can reduce your water-heating costs by as much as 75% compared to electric resistance heating.

Swimming pool heating

No matter the size of your pool, you can use the EarthLinked system to quietly heat the water to a comfortable temperature without harmful combustion byproducts—all with the highest efficiency.

The EarthLinked ™ system has three major components:

An earth loop system that circulates a heat transfer refrigerant to exchange heat with the earth.
A heat pump that moves heat or cool between the building and the earth via the earth loops.
A distribution system to distribute comfort throughout the building.

And two options for water heating:

A desuperheater to capture waste heat from the air conditioning cycle and move it to the water heater.
A full-demand water heater, where the EarthLinked system supplies all of your hot water needs year-around.

Earth Loop System - engineered for efficiency and flexibility

The earth loops are like arteries in a human body. The loops are connected to the heat pump to circulate refrigerant and directly exchange thermal energy with the earth. EarthLinked ground loops have the smallest size and smallest footprint in the market. They have the highest temperature differential with the earth, which means they can use the least amount of earth contact to work effectively. The loops can be installed in three different configurations—horizontal, vertical or diagonal—for maximum design flexibility and cost-effectiveness.

The long-lasting earth loops are made of copper, one of the few metals that exist naturally as an element in the earth. A noble metal, copper resists corrosion because of the protective film that forms naturally on its surface. In rare exceptions where pH readings exceed safe levels, we offer the proprietary Cathodic Protection System for the in-ground copper to preclude corrosion in harsh conditions. With installations dating back to 1980, we have never experienced a field failure of a production earth loop due to corrosion.
The earth loops are pre-assembled and pressure-tested for maximum convenience, quality, and easy installation. Depending upon underground conditions, loops using vertical or diagonal configurations are typically installed in less than two days, whereas horizontal loops can be installed in a single day.

Heat Pump - the heart of the system

Like a pulsing heart, the heat pump circulates the refrigerant through the earth loops to exchange thermal energy with the earth. No complex digital or mechanical equipment is required. Just three mechanically simple devices (a compressor, a condenser and an evaporator) enclosed in a small indoor unit and integrated to work seamlessly, leveraging the natural laws of physics. The heat pump is engineered for easy integration with the building’s heat distribution system. Because the unit is fully enclosed, it can be installed indoors and does not have to withstand the stress of extreme temperature changes and inclement weather.

Refrigerant Flow Controls

A uniquely innovative, patented technique enables control of the flow and stability of the refrigerant without any electronic devices, thereby further improving the efficiency and reliability of the EarthLinked system. The refrigerant is efficiently managed by two simple proprietary flow control devices: the Active Charge Control and Liquid Flow Control.
These two mechanical controls respond directly to the temperature and velocity of refrigerant flow through the system. They modulate the amount of refrigerant in circulation to assure optimum efficiency at all times. By eliminating subcooling in the condenser, the system operates at lower refrigerant "head" pressures with increased mass flow, which reduces energy consumption, increases heat transfer, system reliability and useful life.

Steps to a Proper Installation

Once the appropriate system capacity is identified by calculation the building loads with a Manual J load calculation, the following steps are taken:
Choosing the appropriate loop configuration. Earth loops can be installed in vertical, diagonal or horizontal configurations to provide the lowest cost method, depending upon space availability. The design options are flexible to adapt to site conditions and available space.
Drilling for space efficiency. Depending on the loop configurations chosen, holes are drilled in the ground or installed horizontally in the excavated space.
The copper loops. After the holes are drilled or excavated, the earth-loops are inserted. These loops circulate the refrigerant continuously from the earth loop field to the heat pump and distribution equipment in the building. Once the loops are installed, the holes are grouted to assure good earth contact and no voids.
Connecting the earth loops to the manifold. All of the loops are joined either to the supply or return manifold where the earth loops converge, channeling refrigerant through the lines that are connected to the compressor.
The role of the compressor. The refrigerant lines are connected to the compressor, which increases the pressure and temperature of the refrigerant. Heat energy released by the pressurized refrigerant may be channeled either to the building if heat is needed or to the earth if cooling is needed. The process is controlled by a thermostat and a reversing-valve.
Connecting an air handler. The refrigerant line may then be run from the compressor to an air handler. The air handler is used to transfer heat from the refrigerant to the air and circulate the heated air in the building, or to remove it from the building in summer by exchanging it from the circulating air into the refrigerant line for transport to the earth.
Connecting a radiant hydronic system. In the alternative, the refrigerant line may be run from the compressor to a refrigerant-to-water heat exchanger that is used to transfer heat into a hot water circulating system to heat the building.

Heating Mode Specifics

In the heating mode, the refrigerant enters the earth loops as a cold liquid (blue in the graphic) and comes out as a cool vapor (green in the graphic). When a refrigerant evaporates it absorbs a large quantity of heat from any surrounding material.
Therefore as the refrigerant flows through the loops, it absorbs heat from the earth and stores it in vapor form for later release. The cool (green) vapor that is heat-charged after leaving the earth loops then enters the compressor where its temperature is raised from about 40_F to about 160_F.
During this compression stage, the temperature of the vapor increases because of the intense compression and the vapor leaves the compressor (red in the graphic) hotter than the air in the building being heated. Because the vapor leaving the compressor that is hotter than the inside air, heat transfers into the air flow as the air passes the fan coil in the air handler. This warms your home.

As the heat is removed while the hot vapor passes through the condenser, the vapor condenses and exits the condenser as a liquid. This warm liquid (yellow in the graphic) enters the flow control unit, which monitors the amount of vapor arriving at the liquid flow control (LFC), and meters liquid only through the device for its return to the earth loop field.

Cooling Mode Specifics

In the cooling mode, cool vapor (green in the graphic) arrives at the compressor after absorbing heat from the air in the building. The compressor compresses the cool vapor into a smaller volume, increasing its heat density.
The refrigerant exits the compressor as a hot vapor (red in the graphic) which then goes into the earth loop field. The loops act as a condenser condensing the vapor until it is virtually all liquid. The refrigerant leaves the earth loops as a warm liquid (yellow in the graphic).

The flow control regulates the flow from the condenser so that only liquid refrigerant passes through the control. The refrigerant expands as it exits the flow control and becomes a cold liquid (blue in the graphic). Because the liquid evaporates as it passes through the cooling coil located in the air handler, it absorbs heat from the air blowing over the coil surface and thus cools your home.

Copper Tubing in Soils

Copper tubing buried in the earth is used for the refrigerant-to-earth heat exchanger in the EarthLinked ™ (direct geoexchange geothermal) heat pump system of EarthLinked Technologies, Inc. (ETI). Copper was chosen for the buried earth loop heat exchangers for several reasons.
Copper tubing is strong, ductile, resistant to corrosion, has a very high thermal conductivity, and is available in many different diameters and in long coil lengths. Copper connections can be brazed, the tubing may be bent, and copper tubing is economically available. In addition, copper has a long history of use in air conditioning and refrigeration, and is the material of choice for potable water for water lines buried underground and in buildings.
In 2001, ETI retained the services of Dr. T. D. Burleigh (a university professor with a Ph.D. in Metallurgy from the Massachusetts Institute of Technology, who is a NACE certified Corrosion Specialist and a registered Professional Engineer) to analyze the system and recommend the best methods to assure that the copper loops would never corrode. A comprehensive study was conducted in cooperation with Robert W. Cochran, a Professional Engineer with ETI. Following is a summary of the results of that proprietary study and the description of the protective system developed by ETI.
Copper metal has a very long and indefinite lifetime in most soils. Copper buried in the earth is naturally corrosion resistant because it generally requires an oxidizing environment to corrode, and most soils are reducing, thus they contribute electrons to the copper and protect it against corrosion. In those areas where corrosive conditions may exist, corrosion can be prevented with a small amount of "impressed electrical current" applied to the copper loop via an insulated cable.
For long life and reliability, ETI chose the Impressed Current method of Cathodic Protection. ETI developed an electronic control system, known as the Cathodic Protection System (CPS) to deliver a steady flow of electric current to the earth loops, manifolds, and line sets, without regard to weather, changing soil conditions, and other subsurface conditions. The copper loop is connected to the negative terminal of a rectifier, and a buried inert metal or graphite anode is connected to the positive terminal. The earth completes the electric loop. The amount of current is pre-set at the factory to match the amount of copper in the system to be protected.
Corrosion of metals is an electrochemical process of deterioration that results from a loss of electrons as they react with water and oxygen. As the current flows from the CPS, the metal surface to be protected is given a uniform negative electrical potential that precludes corrosion.
The CPS was designed by ETI in consultation with Dr. Burleigh in 2001 to preclude corrosion of Earth loops in hostile environments.