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Energy Savings with Variable Frequency Drives (VFD)

Published Jun 3, 2015, 11:18pm

Energy Savings with Variable Speed Drives
If you have an AC motor-driven application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with a Variable Speed Drive (VSD). Variable Speed Drives (Also known as Variable Frequency Drives) allow you to match the speed of the motor-driven equipment to the process requirement. 
Variable Torque Versus Constant Torque
Variable speed drives, and the loads they are applied to, can generally be divided into two groups: constant torque and variable torque. The energy savings potential of variable torque applications is much greater than that of constant torque applications. Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Why Variable Torque Loads Offer Great Energy Savings
In variable torque applications, the torque required varies roughly with the square of the speed, and the horsepower required varies approximately with the cube of the speed, resulting in a large reduction of horsepower for even a small reduction in speed. A motor in a variable torque application will consume only 25% as much energy at 50% speed as it will at 100% speed. This is referred to as the Affinity Laws, which define the relationships between speed, flow, torque, and horsepower.
Energy Consumption
Variable Speed Drives (VSDs) allow you to consume less energy than other speed control techniques when load requirements are less than full speed, as is usually the case in HVAC applications.
Tighter Process Control with Variable Speed Drives
No other AC motor control method compares to variable speed drives when it comes to accurate process control. Full-voltage (across the line) starters can only run the motor at full speed, and soft starts and reduced voltage soft starters can only gradually ramp the motor up to full speed, and back down to shutoff. Variable speed drives, on the other hand, can be programmed to run the motor at a precise speed, to stop at a precise position, or to apply a specific amount of torque.
In fact, modern AC variable speed drives are very close to DC drives in terms of fast torque response and speed accuracy. AC motors, however, are much more reliable and affordable than DC motors, making them far more prevalent.
Most drives used in the field utilize Volts/Hertz type control, which means they provide open-loop operation. These drives are unable to retrieve feedback from the process, but are sufficient for the majority of Variable Speed Drive applications. Many open-loop variable speed drives do offer slip compensation though, which enables the drive to measure its output current and estimate the difference in actual speed and the setpoint (the programmed input value). The drive will then automatically adjust itself towards the setpoint based on this estimation.
Most variable torque drives have PID capability for fan and pump applications, which allows the drive to hold the setpoint based on actual feedback from the process, rather than relying on an estimation. A transducer or transmitter is used to detect process variables such as pressure levels, liquid flow rate, air flow rate, or liquid level. Then the signal is sent to a PLC, which communicates the feedback from the process to the drive. The variable Speed Drive uses this continual feedback to adjust itself to hold the setpoint.
High levels of accuracy for other applications can also be achieved through drives that offer closed-loop operation. Closed-loop operation can be accomplished with either a field-oriented vector drive, or a sensorless vector drive. The field-oriented vector drive obtains process feedback from an encoder, which measures and transmits to the drive the speed and/or rate of the process, such as a conveyor, machine tool, or extruder. The drive then adjusts itself accordingly to sustain the programmed speed, rate, torque, and/or position.
Extended Equipment Life and Reduced Maintenance
Single-speed starting methods start motors abruptly, subjecting the motor to a high starting torque and to current surges that are up to 10 times the full-load current. Variable speed drives, on the other hand, gradually ramp the motor up to operating speed to lessen mechanical and electrical stress, reducing maintenance and repair costs, and extending the life of the motor and the driven equipment.
Soft starts, or reduced-voltage soft starters (RVSS), are also able to step a motor up gradually, but drives can be programmed to ramp up the motor much more gradually and smoothly, and can operate the motor at less than full speed to decrease wear and tear. Variable speed drives can also run a motor in specialized patterns to further minimize mechanical and electrical stress. For example, an S-curve pattern can be applied to a conveyor application for smoother decel/accel control, which reduces the backlash that can occur when a conveyor is accelerating or decelerating.
Problems Caused by Full-Voltage Starters
At the instant of energization, the locked rotor (zero-speed) is about 600% of full-load running current This heavy current then drops off gradually as the load breaks loose, and the motor comes up to speed, but causes unacceptable voltage sag on the power system, adversely affecting other loads. It can also cause shock damage and long-term excessive wear on the motor. Using this starting method may force the utility to impose a limit on the size of motors you can use, since across-the-line starting causes problems upstream into the utility's system, creating problems for other customers. The switching surges of abruptly starting and stopping create stress on the motor insulation.
For further information or to provide feedback on this post, please contact your EnergyCzar account manager or email

Lighting Solutions That Satisfy The Triple Bottom Line

Published Jun 3, 2015, 10:51pm

6 Lighting Retrofits with Dramatic Benefits

A cumulative 85% of lighting energy savings is possible with six achievable retrofits, according to a new study by Carnegie Mellon University researchers Rohini Srivastava, Vivian Loftness, and Erica Cochran.
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A few cost-effective retrofits can save a staggering 85% of lighting electricity demand, according to the Center for Building Performance and Diagnostics at Carnegie Mellon University.
A new study combines post-occupancy evaluations, lighting controls projects, and published research linking health, productivity, resource conservation, and environmental improvements to high performance building systems. The result: six solutions that reflect first cost, energy and carbon savings, maintenance needs, and human health and performance benefits. The study also aims to quantify the dollar value of reduced emissions and improved health.
Could one of these retrofits make a difference on your energy bill?
Consider occupancy or vacancy sensors for closed spaces. Conference spaces are occupied 30-70% of the time, while closed offices can be as low as 35%, the researchers say. Areas like kitchens, copy rooms, and bathrooms range as low as 10%.
Because these spaces account for more than 25% of the typical office building, they can incur significant energy costs despite their sporadic use. The team determined that adding vacancy sensors to one-quarter of a baseline building would cost roughly 65 cents per square foot but save 34 cents, offering a two-year payback.
The baseline facility in the study covers 100,000 square feet. Its lighting consumes 6.8 kWh per square foot at 10 cents per kWh annually.
Daylight sensors that provide on-off or dimming for the first and second rows of lights on the facade ensure savings even without a full automation system.
The researchers recommend combining the sensors ($65 per workstation) with wireless controls and a web-based portal for a total of roughly $190 per workstation. Annual energy savings result in an ROI of 21% and a payback of about five years.
However, many office buildings are capable of daylighting up to 100% of the facility. “Given that, this retrofit measure can save up to 70% of a medium-size office building’s total lighting energy,” the authors wrote. “In deeper section buildings, daylight harvesting can save 10 to 35% of lighting energy.”
U.S. offices frequently exceed 2 watts per square foot with light levels over 500 lux, more than is necessary for most tasks, the team explains. Reduce ceiling lighting by roughly 50% to deliver 200-300 lux and augment with 6-8W LED task lights.
Delamping costs about $32 per employee, while a high-performance LED task light is roughly $164, according to analysis of recorded installations cited in the study.
“Given that less than 50% of office floors are dedicated to individual workstations, and given the shift to predominantly computer-based tasks for which lower ambient lighting levels are preferred, this retrofit measure can save up to 40% of a medium-size office building’s total lighting energy,” the team writes.
Venetian blinds are invaluable for glare control and shading. A well-designed and well-managed set of blinds allows adequate daylight without glare and overheating.
A building with existing blinds will pay about 1 cent per square foot or $2 per employee for the increased time investment in blind management, while the first cost for new blinds would be roughly $2.70 per square foot or $540 per employee, the team determined.
A separate Carnegie Mellon study at the DOE’s Energy Efficient Buildings Hub in Philadelphia reveals an ROI of 5% and a payback of 19 years for new blinds, while better managing existing blinds would offer a quicker payback.
Though cost-intensive, digitally addressable dimming ballasts with automated control enable FMs to bring lightingpower density below 1 watt per square foot and help ensure optimal lighting levels.
The researchers estimate a cost of roughly $630 per employee to install and commission ballasts and an automation system and to train staff on its use. Such a project typically carries an ROI of 15% and has an estimated payback of seven years.
The most expensive but most effective solution includes installing vertically integrated LED fixtures with dimming and IP control in place of existing troffers housing two to four T12 or T8 lamps. Vertically integrated LEDs combine the lamp, ballast, and fixture as one item.
Costs vary depending on the existing lighting being replaced by the LED fixtures; for example, existing wiring might be adequate for the required data and power connections. Replacing only the lamps also helps keep costs down, coming in at about $2.40 per square foot or $480 per employee. The vertically integrated solution runs roughly $4.50 per square foot or $900 per employee.
However, the potential savings are significant. The DesignLights Consortium found a 40% reduction in lighting energy consumption and a 75% increase in work surface light levels by upgrading fixtures.
For further information or to provide feedback on this post, please contact your EnergyCzar account manager or email

Natural gas futures for September, 2014

Published Aug 27, 2014, 3:57pm

Natural gas futures retraced Tuesdays gains and retreated on fears of the tropical storm threats being largely over-blown, a lack of fundamental support and some “positioning” ahead of the EIA storage report. The expectation was for an injection of ~84Bcf which would have outpaced the prior year and 5yr average by 26 and 36 Bcf respectively. Revisions to weather outlooks added to the bearish sentiment as the NWS offered some signs of fall as temperatures across the country are expected to moderate during the next 8-14 days. Short term momentum is higher, but fundamentals point lower until we can get a clearer picture of the long range weather forecast.

Month Price Change Change % High Low Est. Vol.
Sep 14 $3.823 ($0.054) (1.4%) $3.888 $3.792 97,158
Oct 14 $3.860 ($0.048) (1.2%) $3.917 $3.829 58,305
Nov 14 $3.933 ($0.044) (1.1%) $3.983 $3.902 30,643
Dec 14 $4.030 ($0.041) (1.0%) $4.081 $3.998 14,701
Jan 15 $4.108 ($0.037) (0.9%) $4.143 $4.075 17,090
Feb 15 $4.100 ($0.035) (0.9%) $4.134 4.069A 3,560
Mar 15 $4.022 ($0.033) (0.8%) $4.041 $3.990 7,859
Apr 15 $3.782 ($0.031) (0.8%) $3.820 $3.764 5,364
May 15 $3.766 ($0.028) (0.7%) $3.785 $3.752 890
June 15 $3.799 ($0.027) (0.7%) $3.816 $3.787 660
July 15 $3.836 ($0.027) (0.7%) $3.850 $3.822 264
Winter 14/15 $4.039 ($0.038) (0.9%)      
Winter 15/16 $4.123 ($0.016) (0.4%)      

GRP Power Plant Installation

Published Apr 29, 2014, 3:38pm

Generator InstallationOne of the projects EnergyCzar is currently overseeing is the installation of two power plants for a client in Grand Rapids, MI. The project involves three one megawatt Caterpillar generators as well as their respective radiators, switchgear housings, and a bevy of capacitor banks. The first generator was delivered and installed without incident on a typically February day in Michigan which meant snow and sub-zero temperatures. Fast forward to April and generator 1 is up and running smoothly. In the future we'll be publishing a benchmark study on this first installation as the results have been nothing short of incredible. Facility power factor is up from the mid-60s to an average of 95% allowing for greater control and peak shaving netting the customer massive savings. Although the energy needs at the second facility are substantially different we're hopeful the results will be similar in terms of savings and overall performance benefits.

This week brought us the delivery of the remaining two generators and support components for the second facility. Better weather yielded faster installation with both generators and radiators being placed in about two hours. The coming weeks should prove very exciting for the client as their investment will start manifesting tangible returns. We have posted some photo galleries of the process to our facebook and google+ pages as well as some videos below.

Could your facility benefit from onsite power generation? Do you have questions about how increased energy efficiency can help your company's bottom line? Please contact us about how these or any of our services can better serve your energy needs.