How do Variable Frequency Drives Work to Reduce Energy Consumption?

Variable frequency drives (VFDs) also called variable speed drives or inverters work to electrically change the speed of a motor. There is a technical explanation of how this is done using terms like vectors, flux, feedback,motor slip, etc. There is also a practical way to understanding how they work and how they help save energy. Since we want to know how to save money, this is the route we'll take.

Motors are everywhere in commercial and industrial facilities. Fans, pumps, conveyors, air conditioners, air compressors are all driven by motors, and the list goes on. Most of these devices are sized for maximum conditions such as maximum flow rate for a pump or fan, maximum output for an air compressor and so on. In the old days these devices normally ran at full capacity (meaning full load and maximum energy consumption). The output was then throttled in some way with valves, dampers or bypasses. This was a very inefficient way to operate and this is why the VFD is such a wonderful device. It helps precisely match the motor speed with the needed output.

Typical motors in the US run at a frequency of 60 hertz or 60 cycles. This is the normal alternating current frequency for US power plants. Motors are designed to run full speed at 60 hertz. Slower speeds are directly proportional to the AC frequency fed to the motor. So at 30 Hz the motor is running at half speed and so on. As the name implies, it is the job of the variable frequency drive (VFD) to alter this frequency and change motor speed as needed.

VFD's can work in two ways, manual or automatic. In manual mode the operator has to manually adjust the motor speed by manually selecting the frequency setting. This works fine for speeds that infrequently or never change. Settings such as conveyor speed, a summer and winter fan speed, etc. are good examples of when a manual speed change works fine.

In automatic mode, electronic controls constantly monitor conditions and adjust the VFD accordingly. For example it may monitor pump pressure and automatically adjust speed to meet the pressure set point. This setting requires some additional controls and control feedback but, when set up properly, the speed control is remarkable.

VFD's save money (and potentially lots of it) by running the motor only at what speed is required. No more running with the gas pedal at full throttle and adjusting the speed with the brakes! We now have a cruise control that tells the motor to only do the work required and no more.

Preheat Dishwasher Water?

There are a lot of questions about preheating dishwasher water. Here are the answers:

1. Should I preheat dishwasher water? No. It takes the same amount of energy to heat water inside the dishwasher or in the hotwater heater. Reduce hot water temperature as much as possible (target 120 degrees) in your hot water heater. This lets you still have a very warm bath or shower (hot tubs are less than 110 degrees). Heat the water in the dishwasher only. The goal is to heat water at the point of use as much as possible, not in a storage tank. The dishwasher is good at this. It monitors the water temperature and heats it at the point of use and only to the temperature required to get the dishes clean.

2. How can I reduce my dishwasher cost?

Use air dry only. Heat drying actually uses the dishwasher's heating element to heat the air in the washer. This drys the dishes but is very expensive. New dishwashers are very energy efficient. In fact it is cheaper to wash a full load of dishes in the dishwasher with air dry than to hand wash.

Wash with full loads only. It takes the same amount of water for a full load or a partial load.

Wash when you are gone or at night. The higher humidity from the hot water isn't as objectionable and doesn't add humidity to the house during the middle of a hot summer day. This also reduces air conditioning load.

Don't Gamble with Energy Conservation

Energy conservation doesn't have to be a gamble. It's not poker. Saving energy and reducing cost can be a sure bet with the following tips:

1. Have a plan to win! Identify your highest energy consuming equipment (air conditioning, heating, hot water heating for the home, air conditioning, compressed air, chillers, boilers for commercial and industrial). and focus on reducing these by 10%.

2. Don't roll the dice. Get help from a qualified energy consultant. In many cases there are local, state or federal grants to help pay for these energy audits.

3. Keep an eye on the cards (monitor and chart utility bills on a monthly basis to identify trends). This will help identify winning strategies.

Reducing Heat Loss and Infiltration with Air Curtains

For busy retail and commercial establishments, the simple fact of people coming and going can get expensive by the loss of conditioned or heated indoor air. Every time the door opens you are bringing in undesirable outside air, bugs, dust, pollen, etc. One solution for this problem is an air curtains at each doorway. These air curtains are mounted above the primary entrance/egress doors. Each time the door opens this air curtain turns on and blows a blast of air on the inside of the door locally pressuring this area. This slight pressurization and turbulence helps prevent the loss of expensive treated indoor air or the infiltration of outdoor conditions. It also helps to maintain indoor air quality.

Air curtains are inexpensive, easy to install and offer quick payback.

Reducing Fuel Cost with Videoconferencing

By far the best way to reduce fuel cost and other associated automobile costs are to, well, eliminate them. In today's world this isn't as far fetched as it may seem with videoconferencing.

Many people are familiar with and use consumer level videoconferencing like Skype and Microsoft Live Messenger. These products work adequately for home use. They have the ability to conference call multiple parties. They are also free. They are especially useful for one to one video conferencing with low to mid range quality.

The next level of quality is the high end professional level conferencing. One product is DimDim. This is an open source videoconferencing product. You can pay a small fee to use DimDim's servers or download the source code, install it in your office and use it totally free. DimDim is a high quality videoconferencing solution that can be used for pure conferencing, computer training, etc.

Another pay as you go solution is Cisco's Webex. This service is especially useful for computer training.

With some use of technology, fuel cost can be dramatically reduced.

Reducing Heating and Air Conditioning Cost by Reducing Chimney Drafts with Chimney Plugs

Fireplaces are an often overlooked source for reducing heating and cooling cost. Fireplaces are vented to the outside by the chimney. This is an opening of several square feed for flue gases and smoke to escape. This is necessary for the fireplace to operate safely and effectively. Unfortunately this is also potentially one of the largest openings in your house to loose your expensive heated and air conditioned air.

The chimney was originally installed with a door to reduce this air flow when not in use. This chimney damper is a heavy steel door that you should close when the fireplace isn't in use to prevent drafts through the chimney. At best the damper will act as a small window opening to the outside. In many cases it will act as a door wide open to the outside. Over time these dampers can break, warp or otherwise not close properly. This can be detected by smoke or other odors coming in throught the chimney, and cold drafts in the winter. When you fell cold drafts through the chimney in the winter you are also loosing expensive heat up the chimney.

There are a couple of options to fix this. If the fireplace is no longer being used, consider having a professional cap the chimney. This will permanently close the window to the outside. Many houses built with fireplaces have never been used or are no longer being used.

Another cheaper and less permanent option is an inflatable chimney plug. These chimney plugs (also known as Chimney Balloon (tm) or Chimney Pillows (tm)) act like a large, heavy duty inflatable fireplace damper. When not in use, these plugs are installed in the top of the chimney and plug off the chimney opening like a cork. When the fireplace is going to be used, the plug is deflated, removed and set aside for later.

Chimney plugs or balloons are durable, effective and inexpensive. These plugs can easily pay for themselves in one heating season.

Reducing Air Conditioning Cost with Wind Chill

We all know the effect called wind chill. How a stiff wind makes wind chill numbers plummet below the actual temperature. The wind chill effect is more accurately called the evaporative cooling effect. Note that wind chill doesn't actually reduce the temperature of the air, it just makes the body feel like it is colder. This works because the wind blowing across the body evaporates moisture from the skin. This evaporative cooling effect will slightly lower the temperature of the skin from the evaporation and make the body feel cooler.

So how do we reduce air conditioning cost? Simple, we bring the wind chill inside by using fans. Fans blowing across the body make you feel more comfortable at a higher temperature. So buy energy efficient ceiling fans or portable fans, place them in highly occupied areas and turn the air conditioning set point up. This will keep the air conditioning from running as much, make you feel more comfortable and save money all at the same time!