FortaCool® Variable Speed Compressor Racks are proven to be 20-50% more efficient than conventional systems, resulting in
enormous energy savings for our customers. The Key to our energy savings is the use of Variable Frequency Drives (VFD’s)
Our Variable Speed Drives control the speed of the motor as needed, bringing the motor to operating speed by soft starting it over a period of 30 to 45 seconds, resulting in more energy efficient compressors.
Variable Speed Drives lower power bills because the compressors only run at the speed necessary to match the refrigeration loads and greatly reduced demand charges because the compressors are “soft started”
Over 500% of normal running power is needed to start Conventional motors, resulting in a power “spike” with high “demand charges” which can have a considerable effect on the electric bill.
Conventional motors come to operating speed from a dead stop to 1800 or even 3600rpm within one second, putting significant physical stress on the motor, causing more failures and maintenance costs.
See more information at our webpage dedicated to Variable Speed Energy Savings
www.fortacool.com/vfd.html
Wednesday, September 21, 2011
Tuesday, September 20, 2011
60 ASHRAE Journal ashrae.org April 2010
Variable Frequency Drives, Part 1: The Technology
Does Energy Savings Trump Costs?
By John Dieckmann, Member ASHRAE; Kurtis McKenney; and James Brodrick, Ph.D., Member
ASHRAE
A variable frequency drive (VFD) is a power electronic device that drives the common “squirrel cage” induction motor over a range of speeds by converting standard frequency and voltage ac power from the electric utility to variable frequency, variable voltage power to energize the motor. Over the years, improvements have been made to VFDs’ effiency and reliabilty. They are now viable alternatives to other motor technologies.
Induction motors operate at a speed that is proportional to the frequency of the input power (minus a small amount of slip that varies with the torque load on the motor). In HVAC&R, the common motor loads are refrigerant compressors, fans, blowers and pumps. By varying the speed of a motor and its driven load, the capacity can be varied to meet the real-time cooling, heating or ventilation load. As a result, significant energy savings can be realized, along with better comfort control. Other advantages include quieter operation and longer equipment life as a result of reduced average speed and soft starting of motors, which reduces the in-rush current and impact loading on equipment at startup.
VFDs are alternately called variable speed drives, inverters, adjustable speed drives, or adjustable frequency drives. The focus of this article is on VFDs for induction motors. However, it is important to note that brushless dc motors, sometimes called permanent magnet rotor motors or electronically commutated motors, are another important class of electronically driven variable speed motors, used in applications such as blower motors and refrigerant compressors.
Figure 1 is a simplified block diagram of a typical VFD. It has four basic subsystems: an ac/dc converter, a dc bus (also called the dc link), an inverter, and a control system. Alternating current from the electric utility is converted to dc in the ac/dc converter, generally a full wave rectifier bridge. The dc link maintains a steady dc voltage level using a capacitor upstream of the inverter. The inverter converts the dc back to ac at the frequency and voltage level needed to drive the motor at the desired speed.
In most instances of VFD-driven motors, the ac output is three-phase to drive a three-phase motor. The control system manages the inverter so that it produces the desired voltage and frequency, and generally includes fault monitoring features.
Figure 2 shows the elements of the inverter in detail. The diode bridge shown is for three-phase ac input. The inverter section consists of six pairs of power transistors and freewheeling diodes.
While there are various ways to synthesize a three-phase ac output from a dc source, the most commonly used method is pulse width modulation (PWM).
As shown in Figure 3, the transistors are switched on and off rapidly (pulsed), at a carrier frequency that is much higher than the desired output frequency.
The on-time of each pulse is varied to generate an approximation of a sinusoidal wave form. During the off-time of the pulse, the inductance of the motor winding draws current flow through the freewheeling diode such that the current flow is continuous and close to being sinusoidal.
Applications for VFDs are sometimes classified as “variable torque” or “constant torque.” Variable torque does not mean randomly variable torque and constant torque does not mean that the torque is fixed under all conditions.
Variable torque refers to applications where the maximum torque load on the motor decreases as the speed decreases from the maximum speed to lower speeds. Centrifugal pumps, axial fans and centrifugal blowers are examples of variable torque applications in HVAC.
Constant torque refers to applications where the maximum required torque does not fall off appreciably as the speed decreases from the maximum. Positive displacement compressors and pumps are examples of constant torque applications in HVAC.
As a general rule, a given VFD will have a higher motor power rating for a variable torque application than for a constant torque application. There are numerous technical considerations and potential pitfalls in applying VFDs, including damage from reflected voltage waves, higher peak voltages within the motor windings, motor noise, increased motor heating, unwanted harmonics on the ac input line, and induced currents in the motor bearings.
ASHRAE TC 1.11, Motors and Motor Control, maintains a chapter called “Motors, Motor Controls, and Variable-Speed Drives” in the HVAC Systems and Equipment volume of the ASHRAE Handbook (Chapter 44 in the 2008 edition). Technical considerations of VFDs are discussed in this chapter.
In many instances in HVAC equipment, the variable frequency drive is applied in a packaged system (e.g., a variable air volume air handling unit, a variable air-volume packaged rooftop unitary air conditioning system, or a large chiller with a variable speed compressor), and the manufacturer of the system has engineered the drive-motor-load-control system so that these pitfalls are avoided.
Energy Saving Potential
According to the DOE Buildings Energy Data Book1 space cooling, ventilation, and refrigeration in residential and commercial buildings consumed 8.2 quadrillion Btus (quads) of primary electric energy in 2006, the bulk of which is consumed by refrigerant compressors, fans, blowers, and pumps, and therefore can be reduced by implementing VFD technology.
Additionally, space heating in buildings consumed 1.7 quads of primary electric energy in 2006, a percentage of which (with the notable exception of electric resistance heating) can be reduced by applying VFDs as well.
In the next four articles, covering the major potential applications of VFDs in HVAC&R, we will break down the potential for energy savings in each of these areas. Here, we provide a brief overview of three of the major ways that efficient, variable speed operation of motors can save substantial amounts of energy in HVAC&R applications.
• The speed cubed fan and pump power law dictates that for propeller fans, centrifugal blowers and centrifugal pumps in systems with fixed-flow resistance, the air or water flow rate will vary with the rotational speed (RPM) while the power will vary with the cube of the speed, as shown in Figure 4. For example at 50% of maximum speed and flow, the power input drops to only 1/8 of the power at maximum speed. HVAC systems operate at part load most of the time, so modulating the flow, rather operating cyclically at full flow, can save significant amounts of energy.
• Continuous operation of cooling equipment at reduced capacity, instead of on-off operation at full capacity, results in less temperature lift, and hence increased compressor COP, as shown in Figure 5.
• Continuous operation of cooling equipment at reduced capacity, instead of on-off operation at full capacity, eliminates on-off cycling losses.
Market Factors
Acceptance of variable frequency drives was slow initially (going back 20 or 30 years) because of three basic factors:
high cost, questionable reliability, and limited experience in
properly applying VFDs.
Over time, all of these factors have been mitigated substantially.
Costs of full-featured, general-purpose drives
and of drives tailored for specific applications have fallen
significantly.
The reliability of VFDs has improved significantly at the
component, system, and application levels, and OEMs have
become more expert in applying drives cost-effectively, while
staying within reliability parameters.
As with any energy-saving technology, the added cost must
be offset by energy cost savings in an acceptable period of time
to be attractive in the market. With simple payback periods
often less than a few years, VFDs are now in widespread use
for variable speed blower drives, for compressor drives in
large chillers, and for chiller auxiliaries.
The next column will discuss the application of VFDs to blowers
in commercial building air-conditioning and ventilation systems.
Variable Frequency Drives, Part 1: The Technology
Does Energy Savings Trump Costs?
By John Dieckmann, Member ASHRAE; Kurtis McKenney; and James Brodrick, Ph.D., Member
ASHRAE
A variable frequency drive (VFD) is a power electronic device that drives the common “squirrel cage” induction motor over a range of speeds by converting standard frequency and voltage ac power from the electric utility to variable frequency, variable voltage power to energize the motor. Over the years, improvements have been made to VFDs’ effiency and reliabilty. They are now viable alternatives to other motor technologies.
Induction motors operate at a speed that is proportional to the frequency of the input power (minus a small amount of slip that varies with the torque load on the motor). In HVAC&R, the common motor loads are refrigerant compressors, fans, blowers and pumps. By varying the speed of a motor and its driven load, the capacity can be varied to meet the real-time cooling, heating or ventilation load. As a result, significant energy savings can be realized, along with better comfort control. Other advantages include quieter operation and longer equipment life as a result of reduced average speed and soft starting of motors, which reduces the in-rush current and impact loading on equipment at startup.
VFDs are alternately called variable speed drives, inverters, adjustable speed drives, or adjustable frequency drives. The focus of this article is on VFDs for induction motors. However, it is important to note that brushless dc motors, sometimes called permanent magnet rotor motors or electronically commutated motors, are another important class of electronically driven variable speed motors, used in applications such as blower motors and refrigerant compressors.
Figure 1 is a simplified block diagram of a typical VFD. It has four basic subsystems: an ac/dc converter, a dc bus (also called the dc link), an inverter, and a control system. Alternating current from the electric utility is converted to dc in the ac/dc converter, generally a full wave rectifier bridge. The dc link maintains a steady dc voltage level using a capacitor upstream of the inverter. The inverter converts the dc back to ac at the frequency and voltage level needed to drive the motor at the desired speed.
In most instances of VFD-driven motors, the ac output is three-phase to drive a three-phase motor. The control system manages the inverter so that it produces the desired voltage and frequency, and generally includes fault monitoring features.
Figure 2 shows the elements of the inverter in detail. The diode bridge shown is for three-phase ac input. The inverter section consists of six pairs of power transistors and freewheeling diodes.
While there are various ways to synthesize a three-phase ac output from a dc source, the most commonly used method is pulse width modulation (PWM).
As shown in Figure 3, the transistors are switched on and off rapidly (pulsed), at a carrier frequency that is much higher than the desired output frequency.
The on-time of each pulse is varied to generate an approximation of a sinusoidal wave form. During the off-time of the pulse, the inductance of the motor winding draws current flow through the freewheeling diode such that the current flow is continuous and close to being sinusoidal.
Applications for VFDs are sometimes classified as “variable torque” or “constant torque.” Variable torque does not mean randomly variable torque and constant torque does not mean that the torque is fixed under all conditions.
Variable torque refers to applications where the maximum torque load on the motor decreases as the speed decreases from the maximum speed to lower speeds. Centrifugal pumps, axial fans and centrifugal blowers are examples of variable torque applications in HVAC.
Constant torque refers to applications where the maximum required torque does not fall off appreciably as the speed decreases from the maximum. Positive displacement compressors and pumps are examples of constant torque applications in HVAC.
As a general rule, a given VFD will have a higher motor power rating for a variable torque application than for a constant torque application. There are numerous technical considerations and potential pitfalls in applying VFDs, including damage from reflected voltage waves, higher peak voltages within the motor windings, motor noise, increased motor heating, unwanted harmonics on the ac input line, and induced currents in the motor bearings.
ASHRAE TC 1.11, Motors and Motor Control, maintains a chapter called “Motors, Motor Controls, and Variable-Speed Drives” in the HVAC Systems and Equipment volume of the ASHRAE Handbook (Chapter 44 in the 2008 edition). Technical considerations of VFDs are discussed in this chapter.
In many instances in HVAC equipment, the variable frequency drive is applied in a packaged system (e.g., a variable air volume air handling unit, a variable air-volume packaged rooftop unitary air conditioning system, or a large chiller with a variable speed compressor), and the manufacturer of the system has engineered the drive-motor-load-control system so that these pitfalls are avoided.
Energy Saving Potential
According to the DOE Buildings Energy Data Book1 space cooling, ventilation, and refrigeration in residential and commercial buildings consumed 8.2 quadrillion Btus (quads) of primary electric energy in 2006, the bulk of which is consumed by refrigerant compressors, fans, blowers, and pumps, and therefore can be reduced by implementing VFD technology.
Additionally, space heating in buildings consumed 1.7 quads of primary electric energy in 2006, a percentage of which (with the notable exception of electric resistance heating) can be reduced by applying VFDs as well.
In the next four articles, covering the major potential applications of VFDs in HVAC&R, we will break down the potential for energy savings in each of these areas. Here, we provide a brief overview of three of the major ways that efficient, variable speed operation of motors can save substantial amounts of energy in HVAC&R applications.
• The speed cubed fan and pump power law dictates that for propeller fans, centrifugal blowers and centrifugal pumps in systems with fixed-flow resistance, the air or water flow rate will vary with the rotational speed (RPM) while the power will vary with the cube of the speed, as shown in Figure 4. For example at 50% of maximum speed and flow, the power input drops to only 1/8 of the power at maximum speed. HVAC systems operate at part load most of the time, so modulating the flow, rather operating cyclically at full flow, can save significant amounts of energy.
• Continuous operation of cooling equipment at reduced capacity, instead of on-off operation at full capacity, results in less temperature lift, and hence increased compressor COP, as shown in Figure 5.
• Continuous operation of cooling equipment at reduced capacity, instead of on-off operation at full capacity, eliminates on-off cycling losses.
Market Factors
Acceptance of variable frequency drives was slow initially (going back 20 or 30 years) because of three basic factors:
high cost, questionable reliability, and limited experience in
properly applying VFDs.
Over time, all of these factors have been mitigated substantially.
Costs of full-featured, general-purpose drives
and of drives tailored for specific applications have fallen
significantly.
The reliability of VFDs has improved significantly at the
component, system, and application levels, and OEMs have
become more expert in applying drives cost-effectively, while
staying within reliability parameters.
As with any energy-saving technology, the added cost must
be offset by energy cost savings in an acceptable period of time
to be attractive in the market. With simple payback periods
often less than a few years, VFDs are now in widespread use
for variable speed blower drives, for compressor drives in
large chillers, and for chiller auxiliaries.
The next column will discuss the application of VFDs to blowers
in commercial building air-conditioning and ventilation systems.
Wednesday, September 7, 2011
FortaCool News
FortaCool® Compressor Racks are custom built, UL Certified, Variable Speed Refrigeration Systems, designed to meet the specific needs of any facility. FortaCool® systems are the most energy efficient refrigeration compressor systems available and guarntee to give customers amazing savings on energy costs, as well as savings on overall cost of ownership.
FortaCool® Variable Speed Refrigeration Systems use computer programmed drives that control the speed of the compressor to match refrigeration loads. FortaCool® systems focus on high levels of energy efficiency, lowering the cost of ownership, and allowing for superior performance while saving customers money.
FortaCool® Variable Speed Refrigeration Systems use computer programmed drives that control the speed of the compressor to match refrigeration loads. FortaCool® systems focus on high levels of energy efficiency, lowering the cost of ownership, and allowing for superior performance while saving customers money.
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