How Variable Frequency Drives (VFDs) Can Save Energy!

I wanted to discuss Variable Frequency Drive (VFD) technology and how energy savings can be utilized in certain applications. Electric motors, specifically induction motors, account for a significant amount of energy consumptions in industrially developed nations and large developing nations. In fact, statistics shows that electric motors are generally responsible for about 66% of industrial power consumption

in each nation, or about 40% of overall power consumption. VFDs can be utilized to reduce energy consumption for many residential, commercial, and industrial processes. VFDs can provide energy savings by utilizing the affinity laws for variable speed applications. However, constate horsepower loads offer little to no energy savings due to their constant speed application.

Benefits of VFDs:

· Energy saving opportunities through constant torque applications where some constant speed systems include reciprocating compressor, conveyors hoists, positive displacement pumps where 50% speed reduction equates to a 50% power reduction: a linear speed to power relationship.

· Energy saving opportunities through variable torque applications. Common applications for a variable torque type load include fans and blowers (primary air fans, cooling tower fans, ventilation fans, dryer fans, etc.) and centrifugal pumps (chilled water pumps, pressure boosting pumps, cooling tower pumps, wastewater pumps, etc.). Variable torque applications abide by the affinity laws. The affinity law for a variable type of load is given by, Power α Pressure× Flow, where Pressure α Speed^2; and Flow α Speed. Therefore, Power α Speed^3. Therefore, from the affinity laws for a variable type of load, a fifty percent reduction in speed reduces the energy consumption by 87.5%.

· Example: When a centrifugal fan or pump is used with mechanical flow control, converting the application to VFD can save energy if the fan or pump is designed to operate between 40% to 80% of full flow. The same principal can be applied to variable speed HVAC systems if heating and cooling loads don’t require the compressor and fan to run at full load 100% of the time.

Disadvantages of VFDs:

· Little to no energy saving opportunities through constant power applications such grinders and winders. VFDs are not always the silver bullet for energy savings. For example, a properly sized pump always running at constant pressure and flow continuously, then a VFD is not beneficial. In this application, a traditional motor starter, or soft start (for in-rush and mechanical benefits), is more practical.

· Constant-speed motors will usually benefit from a soft start controller instead of a VFD. The benefit from a soft start is that it will eliminate the in-rush current, which significantly reduces the heat build-up thereby extending motor lifetimes—particularly of those motors which are stopped and started frequently.

· VFDs can cause damage to AC motors from increases in shaft currents. VFDs creates damaging voltages on the motor shaft unless they find discharge pathways to ground. There are serval ways to mitigate damage to shaft bearings, thus increasing rate of premature failure, from the increased shaft currents.

There are plenty of opportunities where VFDs can reduce energy consumption and save money. However, not all applications will benefit from installing VFDs and may actually end up costing more money in the long run.

Energy Star Partner

This is not so much a blog, but an announcement that we are really excited. Sustainable Engineering LLC is proud to be a new partner of @EPA’s @ENERGYSTAR Service and Product Provider program! We will be working with ENERGY STAR to help our clients improve the energy efficiency of their facilities and reduce emissions and air pollution.

High Deregulated Utility Rates in Texas

Recently I was looking up utility rates in the Houston area and I found that I had a handful of options (60 to be precise) when it came choosing my power provider. This is because the Houston area participates in a deregulated energy market. In comparison Austin, TX (my hometown) only has one power provider option available, which utilizes the public utility Austin Energy that does not participate in retail deregulation. Power providers in the Houston Area offered residential rates ranging from 13.5₵ - 28.8₵ per kWh, while Austin Energy customers are offered a rate of 10₵ per kWh when consuming the same amount of electricity. Which leads me to ask the question why? If deregulation is supposed to make energy markets more competitive and therefore reduce energy cost, why are deregulated rates in Houston so variable and high compared to a more traditional utility like Austin Energy?

Well first let’s talk about what a traditional utility is and then move onto why a deregulated model became popular. For nearly one hundred years, the fundamental building block of the electric power sector was the vertically-integrated utility, regulated by the public utility commission in the state(s) in which the utility operated. Roughly speaking, the electric power supply chain has three links generation, transmission, and distribution. Most utility regulation occurs through a process known as "cost-based ratemaking" or "rate of return regulation." Under rate of return regulation, the utility sets prices (rates that are paid by retail customers) to recover the costs associated with providing service, plus a level of profit determined by the state public utility commission. Technology improvements and economies of scale caused electric rates to fall until 1970, which made industry and residential customers happy. In 2002 dollars, price fell from about $5.15 per kWh in 1892 to about 9.7 cents per kWh in 1970. The highly regulated structure of the electric utility business created a stable environment for expansion of access to electric power. Beginning in 1970, however, prices for electric power began to rise sharply: 320% in current dollars from 1970 to 1985 (28% in inflation adjusted prices). The price increase was due to growing technical complexity of the grid, over investment in infrastructure, and bureaucratic/political problems. Additionally, hard economic times and rising fuel cost contributed to increased rates.

Let’s get back to Texas and try to figure out why retail market rates are greater in Houston compared to Austin. In Houston your electric bill comes from the Retail Electric Provider that you choose out of dozens that are available in your area. These Retail Electric Providers are middle-men in the transaction, because they purchase electricity from the Electric Reliability Council of Texas (ERCOT) and also have to pay for the transmission and distribution of electricity (transmission lines). ERCOT maintains electrical grid reliability and facilitates competitive wholesale and retail markets. However, ERCOT doesn’t actually produce any power, so they pay power plants (gas, coal, hydro, solar, wind, nuclear, etc.) to produce electricity. If fuel is needed to generate electricity (coal, natural gas, uranium, etc.) then power plants must purchase that from a fuel provider as well. However, Retail Electric Providers don’t have to go to ERCOT to get their energy; they can also buy Intercontinental Exchange (ICE) Futures contracts. At ICE Retail Electric Providers can bid on the cost of future energy and then purchasing electricity at the agreed upon price and date. This route requires payment to futures contract traders.

So why might electricity cost more in Houston than in Austin? Well, I am sure there are many more reasons than I have uncovered in this post, but a highly possible reason is in deregulated markets, especially with retail deregulation, money passes through so many more hands before arriving to consumers when compared to vertically integrated regulated markets. Many of the hands I mentioned above are trying to maximize their profits along the way. A report by the Texas Coalition for Affordable Power stated that Texans in deregulated markets have paid higher average prices than those in regulated ones. Their findings showed that Texas customers could have saved $27 billion from 2002 through 2016 had they paid the same price as customers living in regulated parts of the state. Additional rate hikes have occurred due to the February 2021 winter storm too, but that is for another blog. The fact of the matter is that both regulated and deregulated markets have advantages and disadvantages associated with them, but hopefully we can utilize the beneficial aspects of both systems as we continue to modernize our electric grids to support more clean, distributed, and affordable power generation.