EARTH ENERGY SOCIETY OF CANADA
Société canadienne de l'énergie du sol

 

TECHNOLOGY

An earth energy heat pump is one of the most efficient means available in Canada to provide space heating / cooling for homes and offices. It transfers the heat located immediately under the earth's surface (or in a body of water) into a building in winter, using the same principle as a refrigerator that extracts heat from food and rejects into a kitchen. A heat pump takes heat from its source at low temperature and discharges it at a higher temperature, allowing the unit to supply more heat than the equivalent energy supplied to the heat pump. 

    For a technical explanation of how an EE system works, click here.

    For questions to clarify with an installing contractor, click here.

    For a demo on how EE works, click here

    For four options on loop design, click here.

Many Canadians are familiar with air-to-air heat pumps, which use outdoor air as the source of heat. These units are well suited for moderate climates, but they do not operate efficiently when the outdoor temperature drops below -10oC and there is little "heat" left in the air to extract. 

In addition to heating and cooling the building interior, EE units can also heat domestic water. For details on the different methods, see the section on OPTIONS.


WHERE THE HEAT COMES FROM...

An EE system relies on the 51% of solar energy that is absorbed by the land and water.
 

(chart courtesy of NASA)


CO-EFFICIENT OF PERFORMANCE...

The major advantage of an EE system is that the heat obtained from the ground (via the condenser) is much greater than the electrical energy that is required to drive the various components of the system. The efficiency of a unit is the ratio of heat energy provided versus the electrical energy consumed to obtain that heat, and it is called its Coefficient Of Performance (COP). EE units sold in Canada must exceed 3.0 (ie: for every kilowatt of electricity needed to operate the system, the heat pump provides three kilowatts of heat energy).


COST BENEFITS...

With a COP of 3.0, the cost of heating would be one-third (ie. two-thirds less) of the cost to operate an electric resistance heating system, such as baseboards or electric furnace. With a COP of 4.0, the savings can be as much as three-quarters off the price of electric heating and cooling. As earth energy technology improves and the COP increases above 4.0, the operating savings also increase.


COMFORT ADVANTAGES...

An EE system warms air in smaller increases over a longer period of time, compared to the 'burst' of a combustion oil or gas furnace. As a result, homeowners notice a stable level of heat with no peaks or troughs, less drafts, etc.


ENVIRONMENTAL BENEFITS...

Governments and energy planners prefer EE technology because it is an environmentally benign technology, with no emissions or harmful exhaust. The EE industry was the first in Canada to move away from damaging CFCs (chlorofluorocarbons). Although EEunits require electricity to operate the components, a high COP means that EE systems provide a significant reduction in the level of CO2, SO2 and N0x emissions (all linked with the issue of greenhouse gas emissions and global warming).


OTHER APPLICATIONS FOR EARTH ENERGY...

EE units can be used for the dehumidification of indoor swimming pool areas, where the unit can dehumidify the air and provide condensation control with a minimum of ventilation air. The heat recovered from the condensed moisture is then used for heating domestic/pool water or for space heating. 

Efficient heating performance makes EE a good choice for the heating and cooling of commercial and institutional buildings, such as offices, stores, hospitals, hotels, apartment buildings, schools, restaurants and penitentiaries. 

EE systems can heat water or heat/cool the interior space by transferring heat from the ground outside, but they can also transfer heat within buildings with a heat-producing central core. The technology can move heat from the core to perimeter zones where it is required, thereby simultaneously cooling the core and heating the perimeter. 

EE systems are also used as heat recovery devices to recover heat from building exhaust air or from the waste water of an industrial process. The recovered heat is then supplied at a higher temperature at which it can be more readily used for heating air or water.


HOT WATER HEATERS...

EE water heaters (desuperheaters) are a popular option, usually adding less than $1,000 to the total installation, but reducing the 25% of heating cost that an average household will spend on heating water for domestic use. 

Desuperheaters can be "low" or "high" priority, depending on whether the homeowner wants the ground heat diverted to hot water first (thereby turning on the auxiliary electrical space heater) or to heat water only after the space heating requirement has been satisfied. 

There are a number of factors that will have a major influence on the installation and performance of an earth energy system. It is important for the potential customer to understand these issues.


HEAT LOSS...

The most important first step in the design of an EE installation is to determine how much heat is required to satisfy your comfort level. The national installation standard for residential earth energy units (CSA C445) states that the heat loss must be calculated in accordance with the F280 program. This method needs to know the insulation levels of all walls and windows, the number of occupants, your geographic location in Canada and soil type, and many other factors, to determine the total annual heat loss in British Thermal Units (BTU) or kilowatts (kW). It will also calculate the cooling load for summer (all units will provide sufficient cooling if the unit is large enough to provide sufficient heat) and for hot water heating, if included. With this final heat loss, the installed unit will match your demand.


TERMINOLOGY...

Due to the large demand for EE as cooling devices in the United States, the earth energy industry uses the term 'ton' to describe a unit that will provide approx 12,000 BTU of cooling capacity. On average, a typical 2,000 square-foot new residence would require a 4-ton unit for sufficient heat.


SIZING...

EE units do not need to meet 100% of the calculated heat loss of a building, as long as they have an auxiliary electric heating source for backup and for emergencies. Almost 90% of a home's heat load can be met by an EE unit that is sized to 70% of the heat loss, with the remaining 10% of load supplied by the auxiliary plenum heater. Over sizing can result in control and operational problems in cooling mode (especially if the unit has a single-speed compressor), and the installed cost will increase significantly for little operational savings. Conversely, undersizing will lower the installed cost, but the additional length of time that the unit will operate will place excessive demand on many components and may result in unacceptable chill. The governing CSA standard for installations (C448) says that 70% is the minimum, and the industry tends to accept 75% to 80% of heat loss as an optimal design size.


AIR FLOW...

EE units work efficiently because they provide a small temperature rise, but this means that the air coming through the register on your floor is not as hot as the air from a gas or oil furnace. A unit must heat more air to supply the same amount of heat to your house, and duct sizes must be larger than those used for combustion furnaces to accommodate the higher CFM (cubic feet per minute) air flow.


SOIL TYPE...

Loose dry soil traps air and is less effective for the heat transfer required in EE technology than moist packed soil. Each manufacturer provides specifications on the relative merits of soil type; low-conductive soil may require as much as 50% more loop than a quality high-conductive soil.


LOOP DEPTH...

EE technology relies on stable underground (or underwater) temperature to function efficiently. In most cases, the deeper the loop is buried, the more efficient it will be. A vertical borehole is the most efficient configuration, but this type of digging can be very expensive.


LOOP LENGTH...

The longer the amount of piping used in an outdoor loop, the more heat that can be extracted from the ground (or water) for transfer to the house. Installing less loop than specified by the manufacturer will result in lower indoor temperature, and more strain on the system as it operates longer to compensate for the demand. However, excessive piping can also create a different set of problems, as well as additional cost. Each manufacturer provides specifications for the amount of pipe required. As a broad rule of thumb, an EE system requires 400 feet of horizontal loop or 300 feet of vertical loop to provide heat for each ton of unit size.


LOOP CONFIGURATION...

Closed loops generally are installed either in a vertical or in a horizontal configuration, depending on the land available and a number of other factors.
              


LOOP SPACING...

The greater the distance between buried loops, the higher the efficiency. Industry guidelines suggest that there should be 3 m (10 feet) between sections of buried loop, in order to allow the pipe to collect heat from the surrounding earth without interference from the neighbouring loop. This spacing can be reduced under certain conditions.


TYPE OF LOOP...

Earth Energy ground pipe comes in two common diameters: 0.75" and 1.25". Two coiled loops (commonly called the Svec Spiral and the Slinkey) require less trenching than conventional straight pipe. As a result, the higher cost of the coiled pipe is offset by the lower trenching costs and the savings in property disruption.


WATER QUALITY...

Open water systems depend on a source of water that is adequate in temperature, flow rate and mineral content. EE units are rated under the national performance standard (CSA C446) based on their efficiency when the entering water temperature is 10oC (0oC for closed loop units), but this efficiency drops considerably if the temperature of water is lower when it comes from the lake or well. Each model has a specified flow rate of water that is required, and its efficiency drops if this rate is reduced. The CSA installation standard demands an official water well log to quantify a sustainable water yield. Water for open-loop systems must be free of many contaminants such as chlorides and metals, which can damage the heat exchanger of a unit.


WATER DISCHARGE...

There are environmental regulations which govern how the water used in an open-loop system can be returned to the ground. A return well is acceptable, as long as the water is returned to the same aquifer or level of water table. A discharge pit is also acceptable, as long as certain conditions are followed.
open


BALANCE POINT...

The outdoor temperature at which an EE system can fully satisfy the indoor heating requirement is referred to as the balance point, and is usually -10oC in most regions of Canada. At outdoor air temperatures above this balance point, the unit cycles on and off to satisfy the demand for heat indoors. At temperatures below this point, the unit runs almost continuously, and also turns on the auxiliary heater (called second stage heat) to meet the demand.


AUXILIARY HEAT...

When the outdoor air temperature drops below the design balance point, the EE unit cannot meet the full heating demand inside the house (for units sized to 100% of heat loss, this is not an issue). The difference in heat demand is provided by the supplementary or auxiliary heat source, usually an electric resistance element positioned in the unit's plenum. Like a baseboard heater, the COP of this auxiliary heater is 1.0, so excessive use of backup heat decreases the overall efficiency of the system and increases operating costs for the homeowner.


HEAT TRANSFER FLUIDS...

Closed-loop units can circulate any approved fluid inside the pipe, depending on the performance characteristics desired. Each manufacturer must specify which fluids are acceptable to any particular unit, with the most common being denatured ethanol or methanol (the latter is not approved for use in Ontario).
 




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