G eothermal. S ystems. The Earth Connection

Transcription

1 G eothermal S ystems The Earth Connection

2 T he Earth Connection Geothermal Systems in Southern Maryland Why Use a Geothermal System?... 3 Types of Geothermal Systems...4 Open Loop Systems...4 Closed Loop Systems...5 An Added Bonus... 8 Purchase and Installation Costs... 8 Energy Savings...9 Estimated Costs of Operation How Geothermal Systems Are Rated Annual Performance/Safety Maintenance Costs Energy Efficiency Ratings Fuel Costs Overall Benefits For More Information SMECO Office Information Southern Maryland Electric Cooperative May 1996 Printed on recycled paper

3 W hy Use a Geothermal System? T he earth--it absorbs heat from the sun and maintains a relatively constant temperature of 52 to 57 degrees Fahrenheit (F) in Southern Maryland. A geothermal system makes efficient use of the earth's stable temperature by heating and cooling your home through pipes buried in the ground. The constant temperature of the earth makes it easier to maintain a comfortable setting in your home. To date, there have been two basic ways to heat and cool your home: either by a standard air-to-air heat pump or by a fossil fuel furnace with a central air conditioner. Air source heat pumps are efficient, but must contend with fluctuating air temperatures in the summer and winter. Fossil fuel systems rely on the combustion of fuel to release heat which is then distributed throughout the house mechanically. Geothermal systems are designed to be environmentally safe and efficient. If you are comfortable setting your thermostat at 70 degrees F, it is much easier to heat a home with a geothermal system, with the earth's temperature starting at 52 degrees F, than it is for a standard heat pump using the outdoor air registering 35 degrees F. As a result, homes and businesses can be heated and cooled at maximum efficiency regardless of the outdoor air temperature and free from the combustion of fossil fuels. 3

4 A T ypes of Geothermal Systems ll geothermal systems use a compressor, a refrigerant, and an indoor heat exchanger with a fan. This unit is connected to a duct system. The one aspect of the geothermal system that may vary is the method by which the earth s energy is absorbed and released. Following are descriptions of the different types of geothermal systems. 4 The Open Loop System T he open loop system uses pumped ground water to absorb available heat energy from the earth or transfer heat energy to the earth. This system is used when an ample supply of ground water is available and there is limited cleared land. Ground water is pumped to the geothermal unit where it enters a coaxial (tube within a tube) heat exchanger. The refrigerant within this heat exchanger either absorbs or releases heat energy via the ground water, depending on the season. Upon leaving the coaxial heat exchanger, the ground water must be returned to the aquifer from which it came by way of a recharge well. Although open loop systems offer tremendous efficiencies in heating and cooling, they do draw large amounts of water. Recharge wells are required in order to diminish the impact of drawing water at 5 to

5 10 gallons per minute from the water supply. The performance efficiency is impressive having a coefficient of performance (COP) rating over 4.0 and cooling efficiencies with an energy efficiency rating (EER) over 16.5 (see How Heat Pumps Are Rated on page 11). Open loop systems are not heavily promoted in the Southern Maryland area. The well pump may add up to a one-horsepower load, which means increased energy use, and the mineral deposits created by the well water must be cleaned from the geothermal unit. In addition, Southern Maryland Electric Cooperative (SMECO) does not offer rebates for this type of system. The Closed Loop System T he closed loop system utilizes a "loop" that is buried in the ground either vertically or horizontally to heat or cool your home. A solution of water and a nontoxic anti-freeze fills the loop and is continuously circulated by a very small, low wattage pump. The anti-freeze solution used in Southern Maryland is generally 80 percent water and 20 percent propylene glycol or methanol. Under extreme winter heating conditions, heat from the earth is absorbed at an increased rate. As a result, the ground gets colder and loop temperatures may drop to 30 degrees F. The anti-freeze in the solution prevents any ice buildup in the loop, which would inhibit proper water circulation. The loop is made of polybutylene or polyethylene pipe which has a 50-year warranted service life if 5

6 it is installed by a certified dealer. All pipes, couplings, joints, tees, and fittings are joined by actually melting connections together by a thermal process called fusion fitting. This technique creates a connection stronger than the pipe itself. Another reason for using polybutylene or polyethylene is pliability: it must expand and contract with fluctuating loop water temperatures. This is important because once the pipe is buried, leaks or breaks can be very difficult, if not impossible, to repair. The linear length of pipe to be buried is dictated by the selected loop configuration, the soil classification (clay, sand, or loam) and the unit s capacity measured in Btu s per hour. Horizontal Loop System 6 Horizontal loop systems may be used when there is sufficient open space such as a field, large yard, or parking lot. Many options are available for the horizontal layout of a loop system. The soil classification and actual available open space dictate the design. The linear length of pipe generally runs from 250 to 550 feet per ton of heat pump capacity

7 depending on soil conditions and loop layout design. Some designs can be as short as 80 feet using the slinky design or when the loop is immersed in a pond or lake. Vertical Loop System Vertical loop systems are used when there is limited open space. One vertical loop is required for each ton of heat pump capacity. Each loop is inserted into a bore hole 150 to 200 feet deep and six inches in diameter. The bore holes are placed 10 to 15 feet apart. These installations require the loop pipe to be filled, capped, and pressure tested before being inserted into the bore hole. A vertical loop system disturbs minimal ground area making it popular for sites with beautiful yards and trees or limited space. The efficiencies of closed loop geothermal systems, either vertical or horizontal, are impressive. During the winter, COP ratings can be over 3.0 even if loop water temperatures are at 32 degrees F. During the summer, even if loop water temperatures are over 75 degrees F, the EER can be over 15. 7

8 S A n Added Bonus ince geothermal systems use a stable energy source to transfer heat, they can also heat water for domestic use very efficiently. The system makes use of excess heat energy from the compressor by using what is called a desuperheater or hot water assist. The desuperheater transfers the excess heat to a preheat tank for household use. In the preheat tank, the water temperature increases by about 30 degrees F; the water temperature increases another 30 to 40 degrees F in the standard water heater. This method can reduce conventional water heating costs by up to 50 percent. 8 T Purchase and Installation Costs he purchase price of an air-to-air heat pump or fossil fuel furnace with a central air conditioner depends on the brand, model, and capacity of the unit: this is also true for geothermal systems. Costs for duct design and duct installation are determined by the floor plan of the home or business. These costs would be incurred for any type of central heating/air conditioning system and must be estimated on an individual basis. In addition to the cost of the unit, the cost of installing the loop for a geothermal system will vary depending on the capacity required, the type selected (open or closed loop), and the loop design (horizontal or vertical layout). Soil classification and moisture content are factors which may affect the loop design

9 and installation cost. New techniques, materials, and technologies are becoming available each year, and as a result, installation costs are declining. Below is a general range of costs for installing piping for open and closed loop systems in Southern Maryland. Open Loop: An open loop system with an expanded water reservoir to an existing well, a larger storage tank, a cased recharge well, and piping may cost $3,000 to $4,000. Vertical Closed Loop: A six-inch bore hole 150 to 200 feet deep with pipe and manifold connections may cost $800 to $1,100 per ton. For each ton of unit capacity, a separate bore hole is required. For example, a twoton system will cost twice the given estimate. Horizontal Closed Loop: A trench or ditch five feet deep, which may accommodate a single or multilayer loop configuration, may cost $550 to $750 per ton. N E nergy Savings o matter which loop configuration or brand of system you select, a geothermal system is the most energy efficient heating, cooling, and water heating system available. Actual costs of operation will depend on the size of your home or business, selected room temperatures, and hot water consumption. No matter what the requirements, a geothermal system will still be the least costly system to operate. 9

10 L isted are average expected costs for heating and cooling a 2,800 square foot home. A four-ton geothermal system is compared to alternative central heating and cooling systems. E stimated Costs of Operation The estimates listed below are based on heating to 70 degrees F and cooling to 75 degrees F using ten-year average winter and summer weather conditions. All estimates include the cost of energy consumed to operate blower motors, burners, pumps, compressors, and induction fans. Estimated costs of operation are based on the performance of high efficiency units in new construction installations with correctly designed duct systems. Closed Loop Geothermal System HEATING $377 COOLING $158 High Efficiency Natural Gas Furnace with Air Conditioner $639 $268 High Efficiency Oil Furnace with Air Conditioner $676 $268 High Efficiency Propane Gas Furnace with Air Conditioner $1,047 $ High Efficiency Air to Air Heat Pump $607 $231

11 H ow Geothermal Systems Are Rated To decide which heating and cooling system will provide the lowest operating cost, compare a system's tested performance ratings. Most geothermal systems are tested by the Air Conditioning and Refrigeration Institute (ARI) for their cooling EER and heating COP. a. The EER signifies the geothermal system s cooling efficiency. The higher the EER, the more efficient the system is. The formula for calculating the EER is below. Cooling Capacity Output (Btu/Hr) = EER Electrical Power Input (Watts) 48,000 Btu/Hr = 14.3 EER 3,357 Watts b. The COP rating signifies the geothermal system s heating efficiency. ARI-certified ratings use entering water temperatures of 50 degrees F for open loop systems and 32 degrees F for closed loop systems; systems are rated by how efficiently they heat to an indoor temperature of 70 degrees F. The formula for calculating the COP is below. Heating Capacity Output (Btu/Hr) = COP Electrical Power Input (Watts) 43,000 Btu/Hr 9,773 Watts = 4.4 COP 11

12 A nnual Performance/Safety Maintenance Costs: Geothermal Systems $0.00 Fossil Fuel Furnace $ NOTE: Does not include homeowner's cost for cleaning or replacing air filters. E nergy Efficiency Ratings Geothermal COP 4.2 EER 14.3 Oil Furnace AFUE* 85.0% Natural Gas AFUE 92.8% Propane Gas AFUE 92.8% Air Conditioner SEER** 12.1 Heat Pump HSPF*** 9.1 SEER 13.4 * AFUE - Annual Fuel Utilization Efficiency ** SEER - Seasonal Energy Efficiency Rating *** HSPF - Heating Seasonal Performance Factor T he following fuel costs were used to estimate the costs of operation on page on 10. These fuel costs were derived from the U.S. Department of Energy s Information Administration 1994 national average for residential fuel costs. For a site-specific fuel cost comparison using up-to-date regional figures, contact SMECO's marketing and customer services division. F uel Costs 12 Electricity Fuel Oil Natural Gas Propane Gas $.081/kWh $.96/gallon $.73/therm $1.14/gallon

13 O verall Benefits of a Geothermal System * lowest heating and cooling costs available * no outdoor unit, fuel storage, or flues * long equipment life and little maintenance * uses a truly renewable energy source * quiet and clean operation * heating register temperatures degrees F * good humidity control * water heated by surplus energy I f you decide a geothermal system is the system you want for your home or business, be sure to take these steps: 1. Have the heating and cooling Btu/Hr loads calculated. 2. Make sure you have proper duct design to maximize efficiency and comfort. 3. Make sure you have proper loop design to match building loads and soil conditions. 4. Select a qualified contractor certified by a geothermal system manufacturer. 13

14 14 F or more information Whether you are building a new home, expanding a business, or just replacing an old heating system, give SMECO a call. We have qualified individuals who can help answer your questions or concerns. These individuals can give you detailed information on sizing a heating and cooling system, loop design, duct layout, energy savings, and rebate details so you can make the best decision for an energy efficient home. Under the umbrella of SMECO's VISION 21 programs, you are eligible for a rebate when you invest in a geothermal system. The PowerSaver Home program awards rebates to new home buyers who choose energy efficient design technologies which include geothermal systems. The PowerSelect program awards rebates to customers who replace heating and cooling equipment with high efficiency electric models. Because a geothermal system is the most efficient way to heat and cool a home, the rebates are higher as compared to other systems. When customers reduce their energy consumption through the VISION 21 programs, they experience lower monthly energy bills and higher levels of comfort in their homes. At the same time, these systems help to defer the need for new power plants. For more information on any of these programs or information about geothermal systems, call your nearest SMECO office and ask to be transferred to the marketing and customer services division.

15 S MECO Office Information HEADQUARTERS OFFICE P.O. Box 1937 Hughesville, MD (301) (301) (301) (301) CALVERT DISTRICT OFFICE P. O. Box 37 Prince Frederick, MD (410) (301) CHARLES/PRINCE GEORGE'S DISTRICT OFFICE P.O. Box 248 White Plains, MD (301) (301) (301) ST. MARY'S DISTRICT OFFICE Rt. 1 Box 12-B Leonardtown, MD (301)

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