Intro electronics rectifier

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INTRODUCTION

Geothermal heat pumps, also referred to as ground source heat pumps or geo-exchange, refer to systems that use

the ground, groundwater, or surface water as a heat source or sink. Specific to their configuration, these systems are

referred to as ground-coupled heat pumps, groundwater heat pumps, and surface water heat pumps, respectively.

The first successful commercial project was installed in the Commonwealth Building in Portland, Oregon in 1946. As

of 2004, the United States had 12 gigawatts of installed thermal capacity from geothermal heat pumps, with an

additional 80,000 units installed each year.

Geothermal heat pump system in the Kiowa County Courthouse building in Greensburg, Kansas

Geothermal heat pumps use 25% to 50% less electricity than conventional heating or cooling systems. Relative to

air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature

of the outside air. Considerations including utility rates for electricity, natural gas, or other fuels can impact decisions

to implement this technology. While most sites throughout the United States can utilize geothermal heat pump

technologies, certain site characteristics will influence the type of system most suitable for a site. Available groundarea, thermal conductivity of the surrounding soil, local ground water availability and temperatures, or access to open

water sources can further direct their use in a project.

This overview is intended to provide specific details for Federal agencies considering geothermal heat pump

technologies as part of a new construction project ormajor renovation.Further general information is available on the

U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE)Geothermal Energy

Basicswebsite.

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DESCRIPTION

A geothermal heat pump system is made up of several key components including:

Ground loop

Heat pump

Air delivery system.
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The ground loop is a system of pipes that is buried in the shallow ground near the building. A fluid circulates through

the ground loop to absorb or relinquish heat within the ground. In the winter, the heat pump removes the heat from

the fluid in the pipe, concentrates it, and transfers it to the building. This process is reversed in the summer. The air

delivery system uses conventional ductwork or pipe systems to distribute the heated or cooled air throughout the

building.

How Does it Work?

Like refrigerators, heat pumps operate on the basic principle that fluid absorbs heat when it evaporates into a gas,

and likewise gives off heat when it condenses back into a liquid. A geothermal heat pump system can be used for

both heating and cooling. The types of heat pumps that are adaptable to geothermal energy are water-to-air and

water-to-water. Heat pumps are available with heating capacities of less than 3 kilowatts (kW) to over 1,500 kW.

Types and Costs of Technology

Almost six million feet of 1 in. polyethylene piping was installed with the heat exchangers at Fort Polk

Geothermal heat pump technologies can be utilized to meet both heating and cooling needs in new construction as

well as major renovation projects. Incorporating these technologies into major renovation projects will generally result

in higher installation costs than in new construction projects, but can operate at a greater efficiency than typical

heating and cooling units. Typical geothermal heat pump systems have a coefficient of performance of 3.5 to 4.0,

indicating that for every unit of electricity input to the compression, 3.5 to 4.0 units of heating, or cooling, are

produced. A common gas furnace, for example, has an equivalent coefficient of performance of 0.85. Depending on

the existing heating and cooling systems in place, incorporating geothermal heat pump systems may not be feasible.

Existing buildings with a dedicated boiler and central air handling system are typically most applicable for retrofit

scenarios.

At the present time, ground-coupled and groundwater heat pump systems are the two main types of geothermal heat

pump systems that are being installed in great numbers in the United Statesaround 120,000 units per year.

Groundwater aquifers and soil temperatures in the range of 40F to 90F (5C to 30C) are being used in these

systems. Just about every state in the United States, especially in the Midwest and eastern states are using these

systems; in part, subsidized by public and private utilities. It is estimated that over 1.0 million units (12 kW) are

installed throughout the United States. Annual growth rates are around 15%, the fastest of all the direct-use

applications.


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Ground -Coupled Heat Pump Systems

Also referred to as a closed-loop heat pump, the ground-coupled heat pump system consists of a reversible vapor

compression cycle that is coupled with a heat exchanger in the form of bore holes in the ground. These types of

systems can use both a water-to-air heat pump or a direct-expansion heat pump.

The water-to-air configuration circulates water or a water and antifreeze solution through a liquid-to-refrigerant heat

exchanger and a series of buried thermoplastic piping. In comparison, the direct-expansion heat pump circulates a

refrigerant through a series of buried copper pipes. Both vertical and horizontal heat exchanger configurations are

used in these applications.

Vertical wells generally consist of two small (3/4 in. to 1 in.) diameter high-density polyethylene tubes in a vertical

borehole filled with a solid medium, commonly referred to as grout. Boreholes typically range from 50 to 600 ft,

depending on the local site conditions, including soil thermal conductivity and availability of equipment. Because of

this configuration, vertical wells require relatively small areas of land compared to horizontal trenches.

Horizontal wells generally require the greatest amount of ground area and can be further divided into three

subgroups: single-pipe, multiple-pipe, and spiral-slinky. Single-pipe horizontal ground-coupled heat pumps are

typically installed in a single trench to a depth of 4 to 6 ft. and require the most ground area of the three. While the

required ground area required for multiple pipes, consisting of two to six pipes placed in a single trench, can be

reduced, the total pipe length must be increased to overcome the interference from adjacent pipes. Recommended

trench lengths for the spiral pipe configuration can be 20% to 30% of single pipe trench lengths, but may be

increased to achieve greater thermal performance.

Left:Vertical configuration of a ground-coupled heat pump system

Right:Horizontal configuration of a ground-coupled heat pump system

While the vertical well configuration can yield the most efficient ground-coupled heat pump performance, due to

reduced variability in soil temperature and thermal properties along with reduced piping and associated pump energy,

costs associated with vertical wells are typically more. The expense of equipment required to drill the boreholes along

with the limited availability of skilled contractors also contributes to the higher costs. Because of the reduced

installation costs, horizontal trenches are widely used in residential applications. However, these systems generally


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operate at a reduced efficiency due to the impact of seasonal soil property fluctuations and higher pumping energy

requirements. Vertical systems are typically installed in large buildings with limited land area.

Ground water Heat Pump Systems

Preceding the development of ground-coupled heat pump systems, groundwater heat pump systems were the most

widely used type of geothermal heat pump system. This type of system uses well or surface body water as the heat

exchange fluid that circulates directly through the heat pump system. Once it has circulated through the system, the

water returns to the ground through the well, a recharge well, or surface discharge.

Configuration of a groundwater heat pump system

A typical groundwater heat pump system design consists of a central water-to-water heat exchanger between the

groundwater and a closed water loop that is connected to water-to-air heat pumps located in the building. An

alternate strategy is to circulate the ground water through a heat recovery chiller that is isolated with a heat

exchanger and used to heat and cool the building through a distributed hydronic loop.

Many sites throughout the United States are well-suited for direct preconditioning using groundwater heat pumps.

Ground water temperatures below 60F can be circulated through hydronic coils in series or in parallel with heat

pumps, thereby offsetting energy that would otherwise need to be generated using mechanical refrigeration

equipment. Under the right conditions, groundwater heat pump systems can cost less than ground-coupled heat

pump systems. This, along with the compact space requirements for the water well and availability of water well

contractors, has made this technology popular in large commercial applications and has been used for decades.

Note that potential corrosion issues may require the installation of an intermediate plate-type heat exchanger to

protect the heat pump unit. This issue is site-specific and should be evaluated where this technology is being

considered. This option is practical only where there is an adequate supply of relatively clean water and all local

codes and regulations regarding groundwater discharge are met.

Surface Water Heat Pump Systems


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While the thermal properties of surface water bodies are quite different than other geothermal heat pump

technologies, the applications and strategies are similar. Surface water heat pump systems can be either closed-loop

systems, similar to ground-coupled heat pumps or open-loop systems, similar to groundwater heat pumps.

Configuration of a source water heat pump system

Closed-loop surface water heat pumps consist of water-to-air or water-to-water heat pumps connected to piping loops

placed directly in a lake, river, or other open body of water. A pump circulates water or a water and antifreeze solution

through the heat pump water-to-refrigerant heat exchanger and the submerged piping loop which transfers heat to or

from the body of water.

Open-loop surface water heat pumps can use surface water bodies in a similar way that cooling towers are used, but

without the fan energy and required maintenance. Lake water can be pumped directly to water-to-air or water-to-

water heat pumps.

Because of reduced excavation costs, closed-loop surface water heat pumps can cost less than typical ground-

coupled heat pump systems. While these systems have reduced pumping energy and operating costs along with low

maintenance requirements, there is the possibility of coil damage in public lakes and variable performance in small

and shallow bodies of water resulting from the wide fluctuation of water temperature.

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APPLICATION

Geothermal heat pump systems allow for design flexibility and can be installed in both new and retrofit situations.

Because the hardware requires less space than that needed by conventional heating, ventilating, and air-conditioning

systems, the equipment rooms can be greatly scaled down in size, freeing space for productive use. Geothermal heat

pump systems also provide excellent "zone" space conditioning, allowing different parts of the home to be heated or

cooled to different temperatures.

For water heating, you can add a desuperheaterto a geothermal heat pump system. A desuperheater is an auxiliary

heat exchanger that uses superheated gases from the heat pump's compressor to heat water. This hot water then

circulates through a pipe to the home's storage water heater tank. In the summer, the desuperheater uses the excess
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heat that would otherwise be expelled to the ground. Therefore, when the geothermal heat pump runs frequently

during the summer, it can provide significant water heating capacity. During the fall, winter, and springwhen the

desuperheater isn't producing as much excess heatthe facility will need to rely more on traditional water heating

methods. Some manufacturers also offer triple-function geothermal heat pump systems, which provide heating,

cooling, and hot water. Of note, when a project is using a geothermal heat pump, it is typically more economical toheat water through the heat pump andsolar water heatingmay not be economic.

Economics

It is common for the geothermal heat pump industry to refer to costs for the ground source portion of the system on a

cost-per-ton basis. The table below, focuses on residential-scale systems tracks the actual cost of installed

geothermal heat pump systems in a 2008 review of theIndiana Residential Geothermal Heat Pump Rebate program(PDF

730 KB).

Cost by Geothermal Heat Pump System Type

Tons Total Systems Heat Pump Only

2 $12,285 $8,400

2.5 $13,483 $7,922

3 $13,719 $9,465

3.5 $13,297 $9,959

4 $13,969 $9,765

5 $16,865 $11,188

Total $14,278 $9,990

Information from the Indiana Office of Energy and Defense Development.

In addition, according to a2007 report to Congress on the Ground-Source Heat Pumps at Department of Defense

Facilities(PDF 848 KB), operation and maintenance (O&M) costs of geothermal heat pumps at defense facilities was

estimated at $7.67 per ton per year. The life-cycle for the heat pump portion of the system is similar to other heat

pumps, but the below ground portion is designed to last at least 50 years.Assessing Resource Availability

Geothermal heat pumps can be implemented anywhere in the United States, because they take advantage of the

nearly constant temperature of the shallow ground. They improve humidity control by maintaining about 50% relative

indoor humidity, making them very cost effective in humid areas. Resource assessments for geothermal heat pump

systems depend on the size of the project.

For small, closed loop projects, such as individual homes or businesses where the size of the installation is

approximately less than 6 tons (21 kW), little advanced investigations are normally undertaken. Usually, only the local

experience of designers and installers are sought along with any geological or soil information that might be available.

For larger projects, a thermal conductivity test is normally run. This involves installing a loop in a typical bore hole,

grouting it, and then hooking the supply and return pipe to a machine that inputs heat into the circulating water and
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then measures flow and temperature differences. The test is usually run within 36 to 48 hours, and costs around

$10,000 to perform. The number of tests for a large project will depend upon the variability of the soil and rock

conditions. For open loop systems using well water, the well is pumped to determine flow rate and temperature.

Normally, about three gallons per minute is required for each ton (3.5 kW) of load.

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OPERATION AND MAINTENANCE

Because geothermal heat pump systems have relatively few moving parts, and because those parts are sheltered

inside a building, they are durable and highly reliable. The underground piping often carries warranties of 25 to 50

years, and the heat pumps often last 20 years or more. Since they usually have no outdoor compressors, they are not

susceptible to vandalism. The components in the living space are easily accessible, which increases the convenience

factor and helps ensure that the upkeep is done on a timely basis.

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SPECIAL CONSIDERATIONS

Special considerations for geothermal heat pump systems include relevant codes and standards.

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RELEVANT CODES AND STANDARDS

Design standards for geothermal direct-use systems typically involve two components:

1. Below-ground installation such as drilling wells, casing, and pumps

2. Above-ground installations such as pipelines, pumps, valves, heat exchangers, in-building heat convectors, refrigerationequipment, and low temperature components such as heat pumps.

The below-ground equipment standards are usually specified for high temperatures (above 100C) resources by state

and country regulations and standards that would require special values, such as blow-out preventers and drilling

muds. These are usually regulated and inspected by departments of geology and mineral industries or local level

organizations. Low temperature resources (below 100C) are usually regulated as standard water wells under the

supervision of water resources departments or similar agencies.

Above-ground installation equipment standards are generally not regulated by geothermal requirements, but as

standard off-the-shelf equipment. These standards are specified by agencies such as the American Society ofTesting and Materials and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers in the

United States. Local building codes may also control specifications and installations. The majority of states have not

adopted specific codes or standards for most closed loop systems.
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There has been a recent surge of interest in Ground Source Heat Pump (GSHP or geothermal or GeoExchange)

systems for residential projects. Outrageous claims and misunderstandings about how they work are common. This digest

provides some basic information and definitions, offers advice on how to compare the carbon emissions, and defines

the climate regions and operating conditions for which GSHP systems are best suited.

What Are Heat Pumps?Heat energy naturally flows downhill from high to low temperature. A heat pump is a mechanical device that takes heat at a

lower temperature and pumps it uphill to a higher temperature. For instance, a refrigerator contains a heat pump that

takes heat from its interior and heats a coil at the back of the fridge. As a result the back of the fridge is much warmer than

the interior of the home, and the interior is cooler. The energy cost of doing this is the electricity to run a compressor.

Figure 1: The Fridge

A common heat pump.

An air conditioner is a heat pump that takes heat from a coil in ductwork (which cools the air that passes over it, thereby

cooling the home) and pumps it to an outdoor unit (which is hot, so that the heat is released to the outdoors). These are

familiar and well understood technologies.


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Figure 2: A Standard Ai r Cond i t ionerAn air-to-air heat pump that pumps heat from the interior to the exterior.

What is a Ground Source Heat Pump?

A ground source heat pump either collects heat from the ground and pumps it to a coil inside the ductwork to provide air

heating, or collects heat from the same coil in the ductwork (thereby cooling the air) and rejects it to the ground. An air-

source heat pump, a more mature technology used for decades, collects heat from the exterior air during the heating season

and rejects heat to the exterior exactly the same as a standard air conditioner does. In some systems the heat is not

collected/rejected to a coil in ductwork, but instead uses a loop of tubing in a radiant floor or ceiling application. However, the

fact the outdoor heat source/sink is the air means such systems are still air-sourced heat pumps.

The terms geothermal, geoexchange, or earth energy systems are sometimes used to describe a ground source hea t

pump system. However, geothermal heating is more accurately reserved for systems that tap into hot (ideally hundreds of

degrees) rocks or water in the earth for heating or power production. Areas of the world with geysers and active volcanoes

(notably Iceland and New Zealand) can often make good use of geothermal energy. GeoExchange is a newer and

arguably more accurate term for the older and most accurate Ground-Source Heat Pump. The use of alternate terms

provides little useful information and tends to be the product of marketing groups who have little interest in the underlying

mechanics of GSHP.

Figure 3: A ground source heat pump schematic (operating in heating mode).


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Efficiency

Heat pumps as part of manufactured systems like fridges are rated by the Department of Energy or NRCan for efficiency. A

fridge of certain size (say 18 cu. ft.) is rated based on how much energy it should use in a year (for example, 500 kWh/yr

would be a decent fridge). This makes it very easy for consumers to choose between different products. Unfortunately air

conditioners and heat pumps do not rate efficiency in such a straightforward manner.

Regardless of the application, the best way to measure the efficiency of a heat pump itself is to report the amount of energy

that is pumped relative to the amount that must be added to do the pumping. This ratio is called the Coefficient of

Performance:

COP = quantity of heat delivered / energy required by pump

A typical efficient air conditioner has a COP of about 3.5: this means it can remove heat at a rate of about 3.5 kW while

consuming about 1 kW of electrical energy.

Figure 4:Heat pump coefficient of performance (COP)

The efficiency of all heat pumps increases as the height that must be pumped decreases. For exam ple, to cool a home a

typical conditioner must pump heat from a cold A -coil (the finned, radiator-like device hidden in the ductwork that picks up

heat from the air flowing over it) temperature of about 50 F (10 C) to a hot outdoor condenser temperat ure of about 135 F

(60 C) a height of 85 F (50 C). If the same air conditioner only cooled the coil to 60 F, the COP would be higher and the

heat pump (air conditioner) would be more efficient. If the air outdoor was cool, say 70 F, the outdoor condenser unit sitting

next to the house would be more easily able to reject the heat to the outdoor air and so the outdoor coil might only need to

be at 100 F. In this scenario, the height to pump would be even less, at 50 F, and the COP (efficiency) would be even

higher.


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Figure 5: The COP of a heat pump varies with the required temperature height that must be lifted.

Air conditioning systems are rated based on how much energy they need to provide cooling under specific standard testconditions (a set height to pump). The rating is called the Energy Efficiency Rating (EER): it is the numerical ratio of the

cooling provided (in Btu per hour) divided by the electricity required (in kW). This is a strange measure since it used Imperial

units divided by metric units. It is easy to convert from EER to COP by dividing by 3.412. An air conditioner with an EER=12

would have a COP of about 12/3.412 or 3.5. Because not all hours demanding air-conditioning are equally hot, the Seasonal

Energy Efficiency Rating (SEER) was developed to consider times when cooling is required but the outdoor temperatures

are not as high. The conditions for the standard SEER test are a rather unrealistic 80 F indoors and 82 F outdoors: hence

the temperature lift is small and so advertised SEER rating can often be artificially high (models with SEER=19 or a COP of

5.5!) are now available. In reality, the performance at outdoor temperatures of 95 or 110 F (when one really needs cooling)

are a COP of 3 to 4, and claims of COP over 4 are hard to substantiate under realistic indoor conditions (76 F), and hot

(over 95 F) exterior conditions.

GSHP are unique in that their reported COP efficiency may not include the energy of the fluid or water pump required to

move the fluid through the tubes in the ground. This electrical energy can be significant, particularly if the loop is long, the

pipes are small, or the flow resistance within the heat pump unit is large. The largest factor in pump energy use is design: if

the designer and installer of the loop and the pump are not careful, a major amount of energy can be consumed. Heat also

needs to be removed by a fan or a pump and distributed to the home. To improve heat pump COP, the hot temperature of

the liquid produced is often much lower than for a boiler or furnace (that is, the lift is less). Hence, fan energy can be

increased over that of a furnace. This effect is very small in systems that use low temperature radiant heating systems

(circulation pumps consume relatively little electrical energy).

This leads to a more accurate definition of efficiency for a GSHP system (System Coefficient of Performance):

SCOP = useful heat delivered / (loop pump energy + heat pump energy + distribution fan or pump energy)

In heating mode in a cold climate, the system COP of a heat pump rated at COP=4+ can easily drop to COP=3. In our

experience, a system COP of 3 for a heat pump in heating mode would be considered good in cold climates (cold soil) even

with very efficient heat pump equipment and well-designed and installed pumps. Field heating mode COP values of as high

as 4 are possible in warmer climates (warmer soil) and with the best design and best equipment.

In cooling mode in mixed and cool climates, summer-time system COP values tend to be higher because the ground

temperature in summer (perhaps 60 F) are close to the desired air conditioning coil temperature (40 F), whereas during

winter, the heating coil temperature (at say 100 F) is far from the winter ground temp (say 35). That said, the electrical

energy to run the pumps, fans and compressor of the whole system is useful heat in the winter (the inefficiency in the motors

results in heating, which is the whole purpose) and increases the cooling load in summer (all of the inefficiency results in

heat, which then has to be removed by the heat pump).

Climate and Application Impact on Efficiency


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A GSHP rejects and collects its heat from the ground. Hence, the temperature of the ground greatly influences its efficiency.

Using a GSHP to cool a building when the soil temperature is 60 F will be very efficient (remember the heat pump would

only need to overcome a height of 20 F to create a 40 F coil temperature). Alas, the houses that need the most cooling are

in the deep south, and in the average temperature of the soil is quite warm in this region, closer to 70 F. As the summer

wears on and the GSHP pumps more heat into the ground the temperature of the soil rises well above the temperature

shown on the map below and the efficiency drops. If the heat dumped into the soil during the cooling season is not extracted

by the heat pump for heating during winter, or not removed by a cold winter, there is a danger that the soil temperature will

rise significantly over the years.

This issue is even more significant in cold climates where the soil temperature on average is below 50 F. If a GSHP extracts

heat during the winter it is quite common for the temperature of the soil around the ground loop pipes to drop to below 40 F

and freezing is likely. Hence, the efficiency of the heat pump (which then needs to lift the 32 F ground temperature to 95 F

or higher) drops.

In climate zones with moderate soil temperatures (approximately 50-65 F), the soil can provide more energy for heating in

winter and a better sink for cooling in summer. For mixed-climate zones, where heating and cooling are approximately

balanced, the efficiency of a GSHP system will be higher, perhaps significantly higher, than a COP of 3. In these types of

applications: moderate soil temperatures, nearly balanced annual heating and cooling loads, a GSHP can be an ideal

solution.

Figure 6: Map of average soil temperatures.


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Carbon Emissions

The choice of a GSHP is often made to reduce emissions on the assumption that a COP of 3 would reduce emissions by a

factor of 3. This is not true for most situations because the national electrical grid is both inefficient and carbon intensive

(about 50% of all electrical power is generated using dirty coal plants). On average, the electricity system delivers about

33% of the energy in fossil fuels to the household as electricity. Hence, a unit of grid-generated electrical energy delivered to

a house has three times the carbon intensity and fossil fuel consumption as the same unit of energy delivered via natural

gas to the house.

On average, carbon emissions average 1.36 lbs of CO2per kWh of electricity delivered to a household (this information is

available from the EPA eGRID project). This is based on energy generation, and does not include line and distribution

losses, which tend to add around 10% to the carbon content of electricity. Assuming a system COP of 3, 1.36 lbs of

CO2would be created for the generation of 3 kWh of useful, or 0.45 lbs CO2per kWh of heat delivered.

Burning pipeline-delivered natural gas produces 0.40 lbs of CO 2 per kWh of heat, if burnt at 100% efficiency. If a 92%

efficient boiler operating on natural gas were to be employed to make heat, it would produce about 0.44 lbs of CO 2per kWh

of heat delivered (plus any pump or fan electrical energy).

Although the grid is well interconnected, there are broad regions of the country which have higher and lower CO 2emissions

than average depending on their generation mix. For example, in the Pacific Northwest or Quebec, electricity is generated

from clean hydro, and the emissions are only 0.36 lbs per kWh electricity in Washington State. Hence, a COP=3 GSHP in

Washington would reduce emissions by a factor of over 3 versus a natural gas boiler. Given the mild temperatures, and

usefully warm ground temperatures, a GSHP would often be a good choice for reducing CO2emissions in this situation. In

North Dakota, however, the CO2emissions are 2.39 lb CO2per kWh electricity. Given the cold winter temperatures (ie, large

heating load) and low ground temperature (and hence a much lower COP than Washington state), a GSHP could increase

emissions by 50% above a high efficiency natural gas furnace, and result in a significant increase in total carbon emissions

per household.

Future

As our sources of electrical energy become cleaner (i.e., less carbon intensive) or if electricity is renewably generated wholly

on site, a GSHP system will reduce the operating costs and carbon emissions relative to most other available

heating/cooling technologies. However, to be cost competitive, the building should be very well insulated and airtight with

very good windows, shading, etc. Energy efficiency upgrades are almost always the environmentally and economically

superior approach.

One potential, and likely, vision of the future has super-energy efficient houses coupled to photovoltaic systems that

generate about 50 to 75% of the total annual energy use of the home. Grid connection allows the house to have momentary

surges of power consumption and power production. The 25% to 50% annual energy deficit can easily be made up of no- or

very-low carbon electricity delivered by the grid. In this future it would be desirable to eliminate the carbon emissions of the

already very low emissions generated by burning natural gas.

Heat pump systems, whether air-sourced or ground-sourced are the obvious choice to provide cooling, heating,

and dehumidification in such a future. Hence, continued work on improving the efficiency, reliability and cost effectiveness of

heat pumps must continue if and when such a day comes.

One innovative approach that holds promise in colder regions is the use of solar heating or waste heat to charge the ground

loops during sunny weather so that during the subsequent heating season the COP is significantly higher. The challenge

with this approach is the very significant losses of solar energy injected into ground loops.

Recent advances in refrigerants, modulating compressors, and electronic expansion valves have made air source heat

pumps much more efficient and powerful at very low outdoor temperatures (down to -25 C / -13 F). Such low temperature air

source heat pumps are generally much less expensive to install and require less work on site. Low temperature air source

heat pumps will be the subject of a future Digest.

Summary

Ground Source Heat Pumps are just one of many heat pump systems available. Although claims of very high efficiency are

made, field experience suggests that real systems have somewhat less performance. For climates with moderate ground


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temperatures, and buildings with approximately equal annual heating and cooling loads, GSHP system can be an ideal

solution.

The claim that GSHPs substantially reduce carbon emissions in all cases is difficult to substantiate. Because of the

inefficiency and carbon intensity of the national electrical grid, the carbon emissions of a GSHP system with a COP of 3 is

approximately the same as a natural gas condensing furnace or boiler. In cases where natural gas is not available, or the

electrical supply is cleaner than average, even a COP of 3 will result in carbon emission reductions. In many states, and as

the grid becomes less carbon intensive, a best-in-class GSHP (COP of 4 or 5) using emerging technology will begin to savesignificant quantities of CO2emissions. Of course, until the building is highly insulated, airtight, properly ventilated with good

windows, GSHP should not be specified if cost-effective and resource-effective carbon and energy reductions are sought.

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Intro electronics rectifier