GEOTHERMAL HEAT PUMP SYSTEMS ARE RED HOT BUT ARE THEY REALLY GREEN?

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1 GEOTHERMAL HEAT PUMP SYSTEMS ARE RED HOT BUT ARE THEY REALLY GREEN? Richard C. Niess 1 Gilbert & Associates / Apogee Interactive, Inc., Gloucester Point, Virginia Phone & Fax (804) ABSTRACT With the greening of America, there is an increasing focus on heating and cooling systems that are not only energy efficient but also minimize the emission of pollutants. To determine the comparative results, an independent study was conducted of several popular residential heat pumps and alternative heating and cooling systems, located in cities representative of six climatic regions in the United States. An approximately 2,000 sq ft single story home was modeled, using a nominal 3-1/2 ton system. The calculated annual energy use of each alternative includes heating, cooling and domestic hot water heating plus appropriate auxiliaries. Five heating and cooling alternatives were studied which included a geothermal heat pump, an air-source heat pump, plus electric cooling combined with natural gas, propane and oil heating. Two heating and cooling efficiency levels were used for each of the five alternative systems. The annual energy consumption values of each energy source were translated into relative on-site and summed with the off-site emissions to arrive at the total emission values for each of the ten systems in each of the six representative cities. These were then plotted graphically for ease of comparison. This presentation discusses the result of this study of the use of energy and the resultant emissions of both the on-site and off-site of these four key pollutants: Carbon Dioxide (CO 2 ) Carbon Monoxide (CO) Sulfur oxides (SOx) Nitrous oxides (NOx). 1 Mr. Niess has been deeply involved with geothermal heat pump systems since the mid-1970 s. He is currently a principal in both Gilbert & Associates, a consulting firm, and Apogee Interactive, Inc., a firm developing and producing multimedia compact discs, both CD-ROM and CD-i versions, for geothermal heat pump systems and other technologies. He is a Fellow and Life member of ASHRAE, is immediate past Chairman and a member of the ASHRAE Technical Committee - Applied Heat Pumps and Heat Recovery and a member of a Technical Committees - Geothermal Energy Utilization and Centrifugal Machinery. He is a repeat contributor to the ASHRAE Systems Handbook and has numerous published technical articles to his credit.

2 1. INTRODUCTION Based on industry publications and other such sources, geothermal heat pump systems are being increasingly recognized as one of the more efficient means (consumes less energy) of heating and cooling residences and other buildings. This relatively high efficiency is due to these major factors. Manufacturers have been introducing high efficiency models, partially as a result of government and other incentives, and the relatively constant temperature of the earth at depths of about 5 feet and lower, compared to the outdoor ambient temperature. Most geothermal systems are of the ground coupled closed loop variety. In this study, a ground coupled closed loop system was compared to the typical alternatives of air-source heat pump systems and electric cooling coupled with gas-, oil- and propane-fired heating. 2. COMPARISON BASIS The comparisons are based on a well-insulated 2,000 sq ft single-story 3- bed room, 2-bath home with living room, dining room, family room, laundry room and kitchen. Indoor design dry bulb temperature is 70 F in winter and 75 F with 50% inside relative humidity in summer. The homes were modeled for six cities representative of six climatic regions in the United States. Typical weather conditions in each of the six cities were used in calculating the cooling and heating loads, with some adjustments in the home construction representative of the weather area. The selected Base Case geothermal heat pump system is an ARI certified nominal 3 ½ ton heat pump with a single speed compressor, using ARI Standard for Ground Source Closed-Loop Heat Pump Equipment. The selected alternate air-source heat pump system also used an ARI certified nominal 3 ½ ton heat pump with a single speed compressor, using ARI Standard 210/ for Unitary Air-Source Heat Pump Equipment. These standards specify standard certified rating conditions of: Cooling: 80 F dry bulb and 67 F wet bulb indoor coil entering air conditions with 77 F entering loop water temperature for geothermal, and 95 F dry bulb air entering loop water temperature for air-source, and Heating: 70 F dry bulb and a maximum of 60 F wet bulb indoor coil entering air conditions with 32 F entering loop water temperature for geothermal, and with 47 F dry bulb and 43 F wet bulb outdoor coil air entering temperature for air-source. For systems using fossil fuel heating, comparisons are with both a moderate and high efficiency gas or oil furnace and electric air-conditioning unit. The average fuel utilization efficiency (AFUE) and the seasonal energy efficiency ratio (SEER) measured defined these efficiencies. Each increase in efficiency brings with it a lower operating cost resulting from the added first cost economic burden. The annual energy use includes a. Heating and Cooling, b. Auxiliaries, and c. Domestic hot water.

3 The auxiliaries are an indoor air fan, supplemental electric resistance heat for the geothermal and airto-air heat pumps, and a blower (fan) kwh for fossil fueled heating. The geothermal heat pump systems include the loop water pump energy, using nine gpm of loop water flow. Domestic hot water is included based on using a desuperheater plus an electric water heater for the geothermal heat pump systems. Electric water heaters are used with the air-to-air electric heat pump and oil systems. Gas water heaters at 70% efficiency are used with these respective systems. The design winter heat loss and summer heat gain calculations were made with software using algorithms based on ACCA Manual J, 7th edition. These equipment alternatives were used in making the comparison of annual energy use and emissions: Geothermal Heat Pump 3.3 COP (heating) 13.9 EER (cooling) ARI Standard 330 Air-to-Air Heat Pump 14 SEER Demand defrost Air-to-Air Heat pump 12 SEER Demand defrost Gas Furnace 90% AFUE 12 SEER Elect Air Conditioner. Gas Furnace 80% AFUE 10 SEER Elect Air Conditioner. Oil Furnace 80% AFUE 10 SEER Elect Air Conditioner. Oil Furnace 80% AFUE 12 SEER Elect Air Conditioner. The comparison was made for each of these selected cities whose weather resembles that in each if these six climatic regions of the United States - Northern Region... Boston, MA Middle Region... Trenton, NJ Southern Region... Atlanta, GA Central Region... Omaha, NE Coastal Region... Houston, TX Pacific Region... San Francisco, CA The summer heat gain and winter heat loss was matched with the HVAC equipment and the annual total kwh of electricity, ccf of natural gas, and gallons of oil was calculated for each of the systems. 3. EMISSIONS CHARACTERISTICS Emissions fall into two major categories -- those that occur at the point- of- use or onsite, and those that occur in producing the energy used by the heating and cooling system (the generation plant) or off-site. Higher efficiency equipment uses less power and thus produces less emissions at the power plant. 3.1 On-site Emissions Characteristics On-site emissions ate a major contributor to urban and suburban air quality problems. Any combustion or burning of fossil fuels generates on-site emissions. There are no local emissions resulting from the use of electric energy. Refrigerant losses through leakage and improper maintenance or disposal are not considered in this study for several reasons. Refrigerant losses on these systems are minimal as hermetically sealed compressors and sealed systems are used, similar to that uses used in a household refrigerator. Secondly, any losses would be the same for each system, as all systems use the same refrigerant cycle for cooling.

4 The on-site emissions of pollutants are characterized by the HVAC equipment efficiency in its use of fossil fuel. The typical on-site emission values were used in calculating the local emissions are Natural Gas = 118.4, #2 oil = 160.2, and Propane = lb. annual pounds of pollutant per million Btu of higher value (MMBtu HHV) of fuel consumed. 3.2 Off-site Emissions Characteristics The HVAC equipment efficiencies in the use of electric energy characterize the emissions resulting from the power generation. Power plant emissions value used for off-site (electric generation) emissions were molded to reflect regional differences. For this study the off-site pounds per kilowatthour values of emissions at the power plant ere derived from the EPRI Projected Base-Case Electricity Generation Data with 1990 Clean Air Act Amendments for these regional average generation mix of coal, gas, oil, nuclear and other type power plants: East Central Region West Central Region South Central Region Southeast Region Northeast Region West Region Even so the emission values used may not be similar to the situation in your area. Your electric utility can supply their specific emissions values. 4. WHAT S THE PROBLEM? There are several problems perceived to occur as the result of unwanted emissions: Global Warming Acid Rain Urban Air Quality Ozone Depletion 4.1 Global Warming Carbon dioxide is believed to be the principal pollutant that is contributing to the potential for global warming. It is a total emissions problem, largely from the combustion of fuels. It does not matter whether the emissions are at an urban site or a remote power plant. Both national and international groups are seeking ways to reduce these emissions. The leakage of natural gas during extractions, processing and distribution also contributes to global warming but has not been quantified, and, therefore are not included in the data in this study. There is also the potential for a further indirect effect caused by increased carbon dioxide emissions from utility power plants and cogeneration plants if the substitute equipment (cooling and heating equipment, heat pumps, etc.) are less efficient than their predecessors. This indirect effect could offset the perceived benefits of switching to an alternative refrigerant with a lower direct-effect global warming potential. The annual pounds of CO 2 figures shown in the Figure 1 include both on-site emissions as well as power plant emissions. Figure 1 illustrates that geothermal heat pumps have by far the lowest overall emissions of carbon dioxide and therefore the least contributor to the potential global warming.

5 4.2 Acid Rain The acidic properties taken on by rain falling through air containing pollutants is also a total emissions problem that is presently addressed by the Clean Air Act. It is largely from the combustion of fuels with SO X emissions perceived as the main offender. Figure 2 illustrates that gas heating with electric cooling have the lowest SO X emissions followed by geothermal systems. Gas Fuels contain little or no SO X so there are no on-site emissions and the total value shown are all off-site (at the power plant). However, SO X emission limits for year 2000 are defined and the relative difference in SO X emissions between the heating and chilling technologies addressed may not be significant as both are within the 1900 Clean Air Act limits. 4.3 Urban Air Quality Urban air quality is an on-site emissions problem. The problem emissions are CO, NO X, and SO X, from the combustion of fossil fuels. Sulfur oxide emissions in the atmosphere are responsible for more than 50% of the visibility reduction on the eastern part of the United States. Note from Figure 2 that only oil heating systems have no on-site emissions to contribute to local area pollution. Figure 3 illustrates that geothermal heat pumps have the lowest carbon monoxide (CO) emissions and they are all off-site so have no impact on urban air quality. All the gas and oil systems do have on-site emissions of CO with oil being the major offender. Figure 4 illustrates that geothermal heat pumps have the lowest nitrous oxides (NO X ) emissions and again all are off-site so have minimal impact on urban air quality. All the gas and oil systems do have relatively small on-site emissions of NO X. 4.4 Ozone Depletion The ozone layer in the upper atmosphere helps to shield us from the harmful wavelengths of ultraviolet radiation. Chlorine is known to contribute to the depletion of ozone. Chlorine is released to the atmosphere in massive amounts of Mother Nature. Although heavier than air, dispersion seems to have caused CFC refrigerants to have also been observed in the stratosphere. They have the potential of breaking down and releasing chlorine atoms that combine with and deplete ozone. Ozone depletion has been addressed by the international banning of CFCs. This is no longer an issue as all today s new cooling systems use environmentally friendly refrigerants. None of the systems compared used CFCs. 4.5 Climate Effects The climatic differences across the United States results in wide variations in the amounts of energy used for heating and cooling. Thus, they have impacts on the resultant on-site and total emissions. Examination of the detailed data in this study indicated the relative emissions of one technology compared to another about the same, regardless of climatic regions.

6 5. CONCLUSIONS Overall Figure 5 illustrates the total annual emissions average for the six cities studied and shows that geothermal heat pumps in general have the lowest emissions of any of the ten systems studied. In summary these seem to be the key comparative points.. Geothermal heat pump systems have the lowest overall relative emissions of CO 2 and CO. They are the green thing to do!. Natural gas and propane heating systems have the lowest overall relative emissions of NO X and SO X. This may not be significant as all technologies are within the 1990 Clean Air Act limits.. Oil heating systems have the highest emissions of all pollutants, sue to the fuel composition and combustion characteristics. REFERENCES Environmental Protection Agency report EPA 430-R (February 1994) Energy Efficiency and Renewable Energy. Electric Power Research Institute report TR (December 1992) Comparing Emissions of End-Use Technologies. Electric Power Research Institute (1997) CLEAN Environmental End-Use Emissions Database and Software (and accompanying EPRI manual TR ). Niess, R.C. (1977) Private communication with Edison Electric Institute on utility emissions in the United States. Niess, R.C. (1977) Private communication with HVAC manufacturer on load calculations.

7 Figure 1: Annual carbon dioxide emissions

8 Figure 2:Annual sulfur oxide emissions

9 Figure 3: Annual carbon monoxide emissions

10 Figure 4: Annual nitrous oxide emissions

11 Figure 5: Total annual relative emissions