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Cogeneration Technologies, is based in Houston, Texas and provides the following power and energy project development services:
We are specialists in Renewable Energy Technologies, Demand Side Management and in developing clean power/energy projects that will generate a Renewable Energy Credit, Carbon Dioxide Credits and/or Emission Reduction Credits. Through our strategic partners, we offer "turnkey" power/energy project development products and services that may include; Absorption Chillers, Adsorption Chillers, Automated Demand Response, Biodiesel Refineries, Biofuel Refineries, Biomass Gasification, BioMethane, Canola Biodiesel, Coconut Biodiesel, Cogeneration, Concentrating Solar Power, Demand Response Programs, Demand Side Management, Energy Conservation Measures, Energy Master Planning, Engine Driven Chillers, Solar CHP, Solar Cogeneration, Rapeseed Biodiesel, Solar Electric Heat Pumps, Solar Electric Power Systems, Solar Heating and Cooling, Solar Trigeneration, Soy Biodiesel, and Trigeneration. For more information: call us at: 832-758-0027 Groundsource Heat
Pumps
The geothermal
heat pump, also known as the ground source heat pump, water-source heat
pump, and earth-coupled heat pump, is a highly
efficient renewable energy technology that is gaining wide acceptance
for both residential and commercial buildings. Geothermal heat pumps are
used for space heating and cooling, as well as water heating. Its great
advantage is that it works by concentrating naturally existing heat,
rather than by producing heat through combustion of fossil fuels. The
technology relies on the fact that the Earth (beneath the surface)
remains at a relatively constant temperature throughout the year, warmer
than the air above it during the winter and cooler in the summer, very
much like a cave. The geothermal heat pump takes advantage of this by
transferring heat stored in the Earth or in ground water into a building
during the winter, and transferring it out of the building and back into
the ground during the summer. The ground, in other words, acts as a heat
source in winter and a heat sink in summer. The
system includes three principal components:
Earth
Connection
Using
the Earth as a heat source/sink, a series of pipes, commonly called a
"loop," is buried in the ground near the building to be
conditioned. The loop can be buried either vertically or horizontally.
It circulates a fluid (water, or a mixture of water and antifreeze) that
absorbs heat from, or relinquishes heat to, the surrounding soil,
depending on whether the ambient air is colder or warmer than the soil. Heat
Pump
For
heating, a geothermal heat pump removes the heat from the fluid in the
Earth connection, concentrates it, and then transfers it to the
building. For cooling, the process is reversed. Heat
Distribution
Conventional
ductwork is generally used to distribute heated or cooled air from the
geothermal heat pump throughout the building. Residential
Hot Water
In
addition to space conditioning, geothermal heat pumps can be used to
provide domestic hot water when the system is operating. Many
residential systems are now equipped with desuperheaters that transfer
excess heat from the geothermal heat pump's compressor to the house's
hot water tank. A desuperheater provides no hot water during the spring
and fall when the geothermal heat pump system is not operating; however,
because the geothermal heat pump is so much more efficient than other
means of water heating, manufacturers are beginning to offer "full
demand" systems that use a separate heat exchanger to meet all of a
household's hot water needs. These units cost-effectively provide hot
water as quickly as any competing system. Types
of Geothermal Heat Pump Systems
There
are four basic types of ground loop systems. Three of
these—horizontal, vertical, and pond/lake—are closed-loop systems.
The fourth type of system is the open-loop option. Which one of these is
best depends on the climate, soil conditions, available land, and local
installation costs at the site. All of these approaches can be used for
residential and commercial building applications. Closed-Loop
Systems
Horizontal
This
type of installation is generally most cost-effective for residential
installations, particularly for new construction where sufficient land
is available. It requires trenches at least four feet deep. The most
common layouts either use two pipes, one buried at six feet, and the
other at four feet, or two pipes placed side-by-side at five feet in the
ground in a two-foot wide trench. The Slinky™ method of looping pipe
allows more pipe in a shorter trench, which cuts down on installation
costs and makes horizontal installation possible in areas it would not
be with conventional horizontal applications.
Vertical
Large
commercial buildings and schools often use vertical systems because the
land area required for horizontal loops would be prohibitive. Vertical
loops are also used where the soil is too shallow for trenching, and
they minimize the disturbance to existing landscaping. For a vertical
system, holes (approximately four inches in diameter) are drilled about
20 feet apart and 100–400 feet deep. Into these holes go two pipes
that are connected at the bottom with a U-bend to form a loop. The
vertical loops are connected with horizontal pipe (i.e., manifold),
placed in trenches, and connected to the heat pump in the building.
Pond/Lake
If
the site has an adequate water body, this may be the lowest cost option.
A supply line pipe is run underground from the building to the water and
coiled into circles at least eight feet under the surface to prevent
freezing. The coils should only be placed in a water source that meets
minimum volume, depth, and quality criteria.
Open-Loop
System
This
type of system uses well or surface body water as the heat exchange
fluid that circulates directly through the GHP system. Once it has
circulated through the system, the water returns to the ground through
the well, a recharge well, or surface discharge. This option is
obviously practical only where there is an adequate supply of relatively
clean water, and all local codes and regulations regarding groundwater
discharge are met.
Benefits
of Geothermal Heat Pump Systems
The
biggest benefit of GHPs is that they use 25%–50% less electricity than
conventional heating or cooling systems. This translates into a GHP
using one unit of electricity to move three units of heat from the
earth. According to the EPA, geothermal heat pumps can reduce energy
consumption—and corresponding emissions—up to 44% compared to
air-source heat pumps and up to 72% compared to electric resistance
heating with standard air-conditioning equipment. GHPs also improve
humidity control by maintaining about 50% relative indoor humidity,
making GHPs very effective in humid areas. 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 HVAC systems, the equipment rooms
can be greatly scaled down in size, freeing space for productive use.
GHP systems also provide excellent "zone" space conditioning,
allowing different parts of your home to be heated or cooled to
different temperatures. Because
GHP 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 25–50 years, and
the heat pumps often last 20 years or more. Since they usually have no
outdoor compressors, GHPs are not susceptible to vandalism. On the other
hand, 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. Because
they have no outside condensing units like air conditioners, there's no
concern about noise outside the home. A two-speed GHP system is so quiet
inside a house that users do not know it is operating: there are no
tell-tale blasts of cold or hot air. Selecting
and Installing a Geothermal Heat Pump System
Heating
and Cooling Efficiency of Geothermal Heat Pumps
The
heating efficiency of ground-source and water-source heat pumps is
indicated by their coefficient of performance ( Manufacturers
of high-efficiency geothermal heat pumps voluntarily use the EPA ENERGY Many
geothermal heat pump systems carry the U.S. Department of Energy (DOE)
and EPA ENERGY Economics
of Geothermal Heat Pumps
Geothermal
heat pumps save money in operating and maintenance costs. While the
initial purchase price of a residential GHP system is often higher than
that of a comparable gas-fired furnace and central air-conditioning
system, it is more efficient, thereby saving money every month. For
further savings, GHPs equipped with a device called a "desuperheater"
can heat the household water. In the summer cooling period, the heat
that is taken from the house is used to heat the water for free. In the
winter, water heating costs are reduced by about half. On
average, a geothermal heat pump system costs about $2,500 per ton of
capacity, or roughly $7,500 for a 3-ton unit (a typical residential
size). ). A system using horizontal ground loops will generally cost
less than a system with vertical loops. In comparison, other systems
would cost about $4,000 with air conditioning. Although
initially more expensive to install than conventional systems, properly
sized and installed GHPs deliver more energy per unit consumed than
conventional systems. And
since geothermal heat pumps are generally more efficient, they are less
expensive to operate and maintain — typical annual energy savings
range from 30% to 60%. Depending on factors such as climate, soil
conditions, the system features you choose, and available financing and
incentives, you may even recoup your initial investment in two to ten
years through lower utility bills. But
when included in a mortgage, your GHP will have a positive cash flow
from the beginning. For example, say that the extra $3,500 will add $30
per month to each mortgage payment. The energy cost savings will easily
exceed that added mortgage amount over the course of each year. On
a retrofit, the GHP's high efficiency typically means much lower utility
bills, allowing the investment to be recouped in two to ten years. It
may also be possible to include the purchase of a GHP system in an
"energy-efficient mortgage" that would cover this and other
energy-saving improvements to the home. Banks and mortgage companies can
provide more information on these loans. There
may be a number of special financing options and incentives available to
help offset the cost of adding a geothermal heat pump (GHP) to your
home. These provisions are available from federal, state, and local
governments; power providers; and banks or mortgage companies that offer
energy-efficient mortgage loans for energy-saving home improvements. Be
sure the system you're interested in qualifies for available incentives
before you make your final purchase. To
find out more about financing and incentives that are available to you,
visit the Database of State Incentives for Renewable Energy (DSIRE) Web
site. The site is frequently updated with the latest incentives. You
should also check with your electric utility and ask if they offer any
rebates, financing, or special electric rate programs. Evaluating
Your Site for a Geothermal Heat Pump
Because
shallow ground temperatures are relatively constant throughout the Geology
Factors
such as the composition and properties of your soil and rock (which can
affect heat transfer rates) require consideration when designing a
ground loop. For example, soil with good heat transfer properties
requires less piping to gather a certain amount of heat than soil with
poor heat transfer properties. The amount of soil available contributes
to system design as well — system suppliers in areas with extensive
hard rock or soil too shallow to trench may install vertical ground
loops instead of horizontal loops. Hydrology
Ground
or surface water availability also plays a part in deciding what type of
ground loop to use. Depending on factors such as depth, volume, and
water quality, bodies of surface water can be used as a source of water
for an open-loop system, or as a repository for coils of piping in a
closed-loop system. Ground water can also be used as a source for
open-loop systems, provided the water quality is suitable and all ground
water discharge regulations are met. Before
you purchase an open-loop system, you will want to be sure your system
supplier/installer has fully investigated your site's hydrology, so you
can avoid potential problems such as aquifer depletion and groundwater
contamination. Antifreeze fluids circulated through closed-loop systems
generally pose little to no environmental hazard. Land
Availability
The
amount and layout of your land, your landscaping, and the location of
underground utilities or sprinkler systems also contribute to your
system design. Horizontal ground loops (generally the most economical)
are typically used for newly constructed buildings with sufficient land.
Vertical installations or more compact horizontal "Slinky™"
installations are often used for existing buildings because they
minimize the disturbance to the landscape. Installing
Geothermal Heat Pumps
Because
of the technical knowledge and equipment needed to properly install the
piping, a GHP system installation is not a do-it-yourself project. To
find a qualified installer, call your local utility company, the
International Ground Source Heat Pump Association or the Geothermal Heat
Pump Consortium for their listing of qualified installers in your area.
Installers should be certified and experienced. Ask for references,
especially for owners of systems that are several years old, and check
them. The
ground heat exchanger in a GHP system is made up of a closed or open
loop pipe system. Most common is the closed loop, in which high density
polyethylene pipe is buried horizontally at 4-6 feet deep or vertically
at 100 to 400 feet deep. These pipes are filled with an environmentally
friendly antifreeze/water solution that acts as a heat exchanger. In the
winter, the fluid in the pipes extracts heat from the earth and carries
it into the building. In the summer, the system reverses and takes heat
from the building and deposits it to the cooler ground. The
air delivery ductwork distributes the heated or cooled air through the
house's duct work, just like conventional systems. The box that contains
the indoor coil and fan is sometimes called the air handler because it
moves house air through the heat pump for heating or cooling. The air
handler contains a large blower and a filter just like conventional air
conditioners. Most
geothermal heat pumps are automatically covered under your homeowner's
insurance policy. Contact your insurance provider to find out what its
policy is. Even if your provider will cover your system, it is best to
inform them in writing that you own a new system. ELECTRIC-POWERED
HEAT PUMPS Resistance Heat
Air-to-Air Heat Pumps
EARTH-COUPLED HEAT PUMPS An earth-coupled heat pump takes advantage of the more constant earth temperatures to operate. Transferring of heat from the ground is accomplished by placing a closed loop of pipe under the ground. The pipe is then filled with water, brine or antifreeze. During the heating season, the thermal energy of the ground warms the liquid in the pipe, and this warm liquid is pumped to the house where it is used by the heating system. In the cooling season, heat from the house is transferred to the liquid in the pipe, and pumped through the pipe back to the ground where it loses heat. The most common way of using the energy extracted from the earth is to couple the coils with a water-to-air heat pump. Heat pumps increase the benefits of using the earth as a source of energy, can be used in many different situations, and can provide both heating and cooling. When heat pumps are coupled with earth loop systems, they are used to extract heat from the water (or brine or antifreeze) that is circulated through the systems. These heat pumps are called water-source heat pumps because they draw heat from the water or other liquid circulating through the coils or pipes. If the heat pumps use a forced air system to heat the home, they are called water-to-air heat pumps. Water-to-air heat pumps are the most common type of residential water-source heat pumps. In Louisiana, the temperature of the earth at a depth of twelve feet averages 67 degrees in the south, and about 65 degrees in the northern part of the state. This ground temperature is much more stable than air temperature where extreme highs or lows increase the cost of operating the equipment. While the efficiency of an earthcoupled heat pump depends on the temperature of the earth, a COP range of 3 to 4 is normal. The higher the COP, the higher the efficiency. One of the disadvantages of earth-coupled heat pumps is the relatively high initial cost. The retail cost of a residential water-source heat pump can be as high as $3000. Wells or earth coils also add to the cost, often as much as the cost of the heat pump itself. If a heat pump replaces a heating system that uses forced air in an existing house, duct systems may need to be changed, adding more to the cost of the system. Most heat pumps available now are well made and reliable, but because they are more complex and have more moving parts than furnaces, conscientious maintenance is important to keep them operating at their peak. The combination of high initial cost and varying operating costs, requires a full and careful analysis of long-term economics before purchasing a heat pump system.
HIGH EFFICIENCY AIR CONDITIONING When selecting new air conditioning equipment, remember that an air conditioner has two functions. In addition to cooling the indoor air, it also removes excess humidity. In Louisiana's climate, the removal of humidity is at least as important as cooling the air. If a unit is not sized properly, it will not perform both of these functions satisfactorily. A unit that is oversized for the building it services cools the air quickly, but does not run long enough to remove excess humidity. This means that to provide comfort, the thermostat must be turned lower, thus using more energy. Moreover, the unit cycles on and off frequently. This uses more electricity than running continuously for longer periods. Manufacturers are now making air conditioning equipment that is far more efficient than standard equipment of a few years ago. Efficiency for central units is rated according to the Seasonal Energy Efficiency Rating. This indicates how well the system performs over an entire cooling season. The higher the rating, the more efficient the equipment. Determining the most advantageous rating to purchase depends on the balance between the cost of the new equipment and the money saved over the life of the system. A few years ago a rating of 8 was considered efficient. Today, central units with a rating of 15 are available. Generally, money spent on the initial cost of efficient equipment pays for itself quickly. To determine if the cost will be worth it to you, use this formula to compare the cost of operating equipment with different SEER ratings. The newest development in efficient air conditioning equipment is the use of variable speed fans. By circulating the air at 900 cfm for a longer period of time, greater dehumidification, and thus greater comfort, can be achieved.
COST ANALYSIS TO COMPARE DIFFERENT KINDS OF EQUIPMENT The best way to evaluate the cost effectiveness of a heating and cooling system is to calculate a life cycle cost analysis. This method of analysis uses three main cost factors: the initial cost of buying and installing the equipment, the cost of energy over the lifetime of the equipment, and the cost of maintaining the equipment. A thorough life cycle cost analysis should also consider three economic factors that can have a dramatic effect on life cycle costs: the interest rate, the fuel cost escalation rate, and the general inflation rate. For example, more expensive equipment may have to be paid for with borrowed money, and higher interest rates mean that the equipment will cost more because money is more expensive. On the other hand, the higher the escalation rate for fuel costs, the more money an efficient system will save. Unfortunately, interest rates, inflation and fuel costs over 20 or 30 years are impossible to predict, and the formulas for considering these variables are complex. The cost analysis method that follows is a relatively simple way to find out how the costs of different heating and cooling systems compare using three basic cost elements: equipment costs, energy costs, and maintenance costs. It does not consider the economic variables, and the numbers used in the examples are very generalized. Despite the limitations, the cost information presented provides a basic yet useful way to compare costs of different heating and cooling systems. DETERMINE THE COST PER UNIT OF ENERGY A long-term energy price rise may be inevitable, but the rise may not be as dramatic as in the past. It also is difficult to say how the price of one energy source will compare with another. Consequently, current energy prices and trends may be used to give some indication of the relative costs of different energy sources in the future. Energy prices also vary by location. Utility companies (or your utility bill) can provide the current prices for your energy sources. Natural
Gas* Electricity* *Utility rates reflect actual costs of base rates plus fuel adjustment charges paid by customers of Louisiana utilities in January, 1987. DETERMINE THE COST PER MILLION BTU's To compare the cost effectiveness of various heating and cooling systems, it is necessary to convert the costs of different energy sources to a common base. The cost per million British thermal units (MBtu's) is commonly used. To find the cost per MBtu's multiply the unit costs by the multipliers used in this example. Natural
Gas Electricity DETERMINE THE ENERGY EFFICIENCY OF THE HEATING AND COOLING SYSTEMS To find out how different options translate into savings, and how the savings between systems compare with each other, the efficiencies of all systems being considered must be known. Find out the efficiency ratings of each piece of equipment that you are considering. If a heat pump is one of the options, be sure to get both the COP and SEER ratings. If electric central air conditioning may be used in conjunction with a gas-burning furnace, the efficiencies of both units must be considered. DETERMINE THE COST PER MBTU OF HEAT DELIVERED Now that the cost of energy and the efficiencies of the heating and cooling systems are known, the cost per MBtu's can be calculated. Divide the cost per MBtu's of energy that goes into the heating system by the efficiency rating for the system to get the cost per MBtu's of heat delivered. FOR EXAMPLE:
DETERMINE THE ANNUAL ENERGY CONSUMPTION IN BTU's An analysis of conservation and weatherization opportunities is the necessary first step in deciding on the size and characteristics of the heating and cooling equipment that will be needed. This step in the cost analysis assumes that existing homes have been suitably weatherized and that new homes have been planned with conservation in mind. For new construction, a thermal load analysis should be an integral part of planning for the heating and cooling system. For an existing weatherized home, a careful energy audit and thermal load analysis will provide information on the amount of heating that will be required. Utility records for existing homes normally do not differentiate between heating and cooling energy demand and other energy uses, such as lighting and appliances. For the average Louisiana home, about 60 percent of the total energy consumption is for cooling and heating. The energy consumption for heating and cooling in well insulated, tight houses can be reduced by as much as one-half. Because energy consumption patterns can vary so much, annual heating and cooling demand should be based on a thermal load analysis, rather than simply summing up a year's utility bills and eliminating 40 percent for uses other than heating and cooling. DETERMINE THE ANNUAL HEATING AND COOLING COST To find the annual heating and cooling cost, simply multiply the cost per MBtu by the annual heating and cooling energy requirement. In the following examples, it is assumed that 30 MBt l's would be required to heat the house for a year and 70 MBtu's would be needed for cooling. The heat pumps would be used for both heating and cooling, requiring 100 MBtu's per year. For Example:
DETERMINE THE LIFETIME ENERGY COSTS Most heating and cooling units should have useful lives of 20 to 30 years. Consequently, their costs and potential savings should be figured over that period. This lifetime energy cost, which in this case does not consider fuel cost escalation, is calculated by multiplying the annual cost of energy by the chosen lifetime. For example:
DETERMINE THE COST OF THE EQUIPMENT When the heating and cooling costs have been computed, consider the heating and cooling equipment costs. The easiest way to determine new equipment costs is to get estimates from dealers. Some of the variables associated with heating and cooling equipment costs are hard to estimate without knowing the details of the installation. One of these variables is ductwork. For new construction, any forced air system will require a new duct system, and the costs will be about equal for furnaces or heat pumps. For heat pumps installed in existing homes, duct modify ication costs can range from nothing to nearly $1,000. Prices vary widely in different parts of the country, but here are some rough estimates of retail equipment costs (not including installation) to indicate the relationship between systems of comparable size (approximately 30,000 Btuh to 40,000 Btuh).
DETERMINE THE COST OF MAINTENANCE Emergency maintenance costs are nearly impossible to predict, but dealers may be willing to give estimates of general, annual maintenance costs. However, even these estimates are likely to vary. Heat pumps and air conditioners have one maintenance item that sets them apart from other systems. While actual performance varies considerably with specific circumstances, the compressors on heating and cooling heat pumps may have to replaced after 12 to 15 years. (The U.S. Department of Energy Technology and Consumer Products Branch indicates that the average compressor life is 5 to 7 years.) Compressor reliability is increasing all the time, and there is less stress on water-to-air heat pump compressors than for air-to-air heat pump compressors, but as of today, one compressor replacement would be expected for a 20-year life-span. Here are some maintenance cost estimates for the sake of comparison.
*Cost of compressor replacement represents 1987 estimate DETERMINE THE LIFETIME, "LIFE-CYCLE" COST A basic lifetime cost of a heating and cooling system can be determined by adding up the lifetime energy costs, the initial cost of equipment, and the cost of maintenance. Remember, this does not consider changes in fuel costs, inflation, and interest rates over the next 20 years. For Example:
COST COMMENTS In the final example, an earth-coupled heat pump would cost $5,340 less to own for 20 years than a gas furnace and electric central air conditioning. This example assumes you are considering replacement of original equipment on a house built prior to 1980 with an earth-coupled heat pump. A quick review of the cost analysis step reveals that electric resistance heat would be the least expensive to buy initially and is virtually maintenance free, but the electricity costs for 20 years are $14,060, about the same as would be spent for electricity for both heating and cooling if an earth-coupled heat pump had been installed. The real lesson of this analysis should be that every situation is unique and must be carefully analyzed. Any one of the factors considered in this analysis, and the economic variables that are not, (interest rates, fuel escalation rate, and general inflation rate), may change the outcome. For example, look at the results if natural gas prices were increased to $8.00 per mcf and electric rates were $.10 per kWh. Or consider the advantage to be gained with an earth-coupled heat pump if the annual cooling load is twice the annual heating load. Even when a cost analysis is done as completely as possible, there will be room for considerable speculation about what the effects of general economic trends will be. But remember, any cost analysis will be more meaningful when it is based on the most specific information available at the time. How
Does an Absorption Chiller Work?
Absorption
chillers use heat instead of mechanical energy to provide cooling. A
thermal compressor consists of an absorber, a generator, a pump, and a
throttling device, and replaces the mechanical vapor compressor. In
the chiller, refrigerant vapor from the evaporator is absorbed by a
solution mixture in the absorber. This solution is then pumped to the
generator. There the refrigerant re-vaporizes using a waste steam heat
source. The refrigerant-depleted solution then returns to the absorber
via a throttling device. The two most common refrigerant/ absorbent
mixtures used in absorption chillers are water/lithium bromide and
ammonia/water. Compared
with mechanical chillers, absorption chillers have a low coefficient of
performance (COP = chiller load/heat input). However, absorption
chillers can substantially reduce operating costs because they are
powered by low-grade waste heat. Vapor compression chillers, by
contrast, must be motor- or engine-driven. Low-pressure,
steam-driven absorption chillers are available in capacities ranging
from 100 to 1,500 tons. Absorption chillers come in two commercially
available designs: single-effect and double-effect. Single-effect
machines provide a thermal COP of 0.7 and require about 18 pounds of
15-pound-per-square-inch-gauge (psig) steam per ton-hour of cooling.
Double-effect machines are about 40% more efficient, but require a
higher grade of thermal input, using about 10 pounds of 100- to 150-psig
steam per ton-hour. A
single-effect absorption machine means all condensing heat cools and
condenses in the condenser. From there it is released to the cooling
water. A double-effect machine adopts a higher heat efficiency of
condensation and divides the generator into a high-temperature and a
low-temperature generator.
In
short, absorption cooling may fit when a source of free or low-cost heat
is available, or if objections exist to using conventional
refrigeration. Essentially, the low-cost heat source displaces
higher-cost electricity in a conventional chiller. In
Practice
Annual
Savings = 300 tons x (12,000 Btu/ton / 4.0) x 4,000 hrs/yr x $0.05/kWh x
kWh/3,413 Btu = $52,740
Determine
the cost-effectiveness of displacing a portion of your cooling load with
a waste steam absorption chiller by taking the following steps:
Absorption Chiller Refrigeration CycleThe basic cooling cycle is the same for the absorption and electric chillers. Both systems use a low-temperature liquid refrigerant that absorbs heat from the water to be cooled and converts to a vapor phase (in the evaporator section). The refrigerant vapors are then compressed to a higher pressure (by a compressor or a generator), converted back into a liquid by rejecting heat to the external surroundings (in the condenser section), and then expanded to a low- pressure mixture of liquid and vapor (in the expander section) that goes back to the evaporator section and the cycle is repeated. The basic difference between the electric chillers and absorption chillers is that an electric chiller uses an electric motor for operating a compressor used for raising the pressure of refrigerant vapors and an absorption chiller uses heat for compressing refrigerant vapors to a high-pressure. The rejected heat from the power-generation equipment (e.g. turbines, microturbines, and engines) may be used with an absorption chiller to provide the cooling in a CHP system. The basic absorption cycle employs two fluids, the absorbate or refrigerant, and the absorbent. The most commonly fluids are water as the refrigerant and lithium bromide as the absorbent. These fluids are separated and recombined in the absorption cycle. In the absorption cycle the low-pressure refrigerant vapor is absorbed into the absorbent releasing a large amount of heat. The liquid refrigerant/absorbent solution is pumped to a high-operating pressure generator using significantly less electricity than that for compressing the refrigerant for an electric chiller. Heat is added at the high-pressure generator from a gas burner, steam, hot water or hot gases. The added heat causes the refrigerant to desorb from the absorbent and vaporize. The vapors flow to a condenser, where heat is rejected and condense to a high-pressure liquid. The liquid is then throttled though an expansion valve to the lower pressure in the evaporator where it evaporates by absorbing heat and provides useful cooling. The remaining liquid absorbent, in the generator passes through a valve, where its pressure is reduced, and then is recombined with the low-pressure refrigerant vapors returning from the evaporator so the cycle can be repeated. Absorption chillers are used to generate cold water (44°F) that is circulated to air handlers in the distribution system for air conditioning. "Indirect-fired" absorption chillers use steam, hot water or hot gases steam from a boiler, turbine or engine generator, or fuel cell as their primary power input. Theses chillers can be well suited for integration into a CHP system for buildings by utilizing the rejected heat from the electric generation process, thereby providing high operating efficiencies through use of otherwise wasted energy. "Direct-fired" systems contain natural gas burners; rejected heat from these chillers can be used to regenerate desiccant dehumidifiers or provide hot water. Commercially absorption chillers can be single-effect or multiple-effect. The above schematic refers to a single-effect absorption chiller. Multiple-effect absorption chillers are more efficient and discussed below. Multiple-Effect Absorption Chillers In a single-effect absorption chiller, the heat released during the chemical process of absorbing refrigerant vapor into the liquid stream, rich in absorbent, is rejected to the environment. In a multiple-effect absorption chiller, some of this energy is used as the driving force to generate more refrigerant vapor. The more vapor generated per unit of heat or fuel input, the greater the cooling capacity and the higher the overall operating efficiency. A double-effect chiller uses two generators paired with a single condenser, absorber, and evaporator. It requires a higher temperature heat input to operate and therefore they are limited in the type of electrical generation equipment they can be paired with when used in a CHP System. Triple-effect chillers can achieve even higher efficiencies than the double-effect chillers. These chillers require still higher elevated operating temperatures that can limit choices in materials and refrigerant/absorbent pairs. Triple-effect chillers are under development by manufacturers working in cooperation with the U.S. Department of Energy. How Does an Engine Driven Chiller Work? Packaged natural gas engine-driven water chillers and direct expansion (DX) units are now available. Commercially proven custom and packaged engine-driven refrigeration units offer excellent reliability and economic advantages for ice rinks, refrigerated warehouses and other applications. The industry is also focusing on developing small, engine-driven heating and cooling systems suitable for small commercial applications. Operation: Engine-driven cooling systems employ a conventional vapor compression cycle. Their main components are the compressor, condenser, expansion valve and evaporator. * Requires no more room than conventional electric chillers * Lowest operating cost of any available chiller * Depending on electric rates and natural gas rates, an engine driven chiller may operate at up to 1/2 of the cost of direct-fired absorption chillers * Like absorption chillers, engine driven chillers reduce on-peak electric demand charges. * Depending on your electric and/or natural gas supplier, there may be rebates available for purchasing a new absorption chiller or engine driven chiller from your utility supplier. * Environmentally friendly. For more information on absorption chillers, call us at: 832-758-0027 * Some of the above information from the Department of Energy website and Louisiana Department of Natural Resources.
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