Flowmeters improve HVAC system performance

Energy efficiency efforts have risen in recent years as environmental and economic concerns have grown, particularly with the recent economic recession.

By Marisa Fedele, Siemens Industry Inc. November 15, 2011

There has been no shortage of studies, discussions, and debates surrounding the concept of energy efficiency over the past 40 years. In the early 1970s, when two international petroleum crises led to dramatic rises in the cost of energy, the major industrial countries were forced to consider a sobering possibility: that the world’s supply of energy resources might be finite. Throughout the same decade, scientific studies began to suggest a relationship between greenhouse gas emissions and global climate change, strengthening the belief that human activity was harming the environment.

However, while efforts to reduce energy usage may not be new, energy efficiency has risen to even greater prominence in recent years as energy costs and environmental concerns continue to increase exponentially. No one is more aware of this trend than the HVAC industry, which must contend with an ever-expanding list of regulations, guidelines, and initiatives emphasizing the importance of energy-efficient heating, cooling, and ventilation systems in buildings.

As facility managers are now being held more accountable for the overall energy consumption of the buildings they oversee, having access to highly accurate and reliable flowmetering technology has become vital. Flowmeters make it possible for facility managers to measure the performance of various HVAC systems and ultimately make the best possible decisions to optimize efficiency and manage energy consumption.

Several different flow measurement technologies can adequately meet the needs of the HVAC industry. After reviewing a few of the most important regulations that necessitate the use of flowmeters as part of HVAC systems, this article will examine four types of flowmetering technologies that are particularly well suited for HVAC flow measurement.

Growing appreciation for energy efficiency

Reducing energy consumption offers a variety of benefits to individuals, businesses, and industries alike. From an economic standpoint, energy efficiency leads to reduced energy costs, which in turn enhances a country’s ability to remain commercially and industrially competitive. In addition, efficient energy use improves the security of a country’s energy supply by decreasing the need for energy imports. It also reduces energy shortages, which can be a boon to economic development. Of course, energy efficiency has major environmental advantages as well—namely a significant decrease in greenhouse gas emissions.

There is a growing global appreciation for the far-reaching benefits of energy efficiency, a trend reflected by the substantial number of laws and initiatives cropping up each year in countries throughout the world. Although there is still much potential for further progress, these efforts have already made a significant impact. In fact, according to a recent report from the World Energy Council, since 2004 energy consumption has grown much less rapidly than the economic activity in all world regions except the Middle East. Additionally, the reduction in energy intensity between 1990 and 2008 in most world regions resulted in a large savings of both energy and carbon emissions, estimated at 3.6 Gigatons of Oil Equivalent of primary energy and 8 GTOE of carbon emissions.

HVAC systems within buildings have the potential to consume a tremendous amount of energy and generate a great deal of air pollution. For example, the American Council for an Energy-Efficient Economy estimates that buildings account for more than a third of energy use and carbon emissions in the United States. This is why so many recent regulations and initiatives, several of which are summarized below, have centered on energy-efficient buildings and have had a direct impact on the HVAC industry.

Kyoto Protocol

Aimed at reducing the effects of global warming, the Kyoto Protocol was adopted in 1997 in Kyoto, Japan, and entered into force in 2005. Under the Protocol, 37 industrialized countries and the European community made a binding commitment to decrease emissions of four greenhouse gases and two groups of gases (including hydrofluorocarbons, commonly used by the HVAC industry as refrigerants) by 5.2% against 1990 levels between 2008 and 2012.

Energy Policy Act of 2005

Passed by the U.S. Congress and signed into law by former President George W. Bush, the Energy Policy Act of 2005 focuses on reducing energy consumption in a number of ways, including establishing tax incentives and loan guarantees for energy-efficiency measures on new buildings and HVAC systems. The act also requires that all federal buildings install advanced metering systems capable of measuring energy consumption on a daily basis by October 2012.

Leadership in Energy and Environmental Design (LEED)

Developed by the U.S. Green Building Council in 2000, LEED is an internationally recognized green building certification system providing third-party verification that a building or community meets strict environmental standards in such categories as energy efficiency, greenhouse gas emissions, and indoor air quality.

American College and University Presidents’ Climate Commitment

The Presidents’ Climate Commitment was officially launched in 2007 as an effort by a network of U.S. colleges and universities to address global climate disruption. Each participating institution has made a commitment to reduce emissions from specific campus operations and ultimately become “climate neutral” (eliminate all emissions) by a target date.

Clinton Climate Initiative

In 2006, former President Bill Clinton and his charitable foundation established the Clinton Climate Initiative with the goal of cutting global greenhouse gas emissions. One of the major programs stemming from this initiative is the Energy Efficiency Building Retrofit Program, which operates in large cities worldwide to retrofit existing buildings with energy-saving products, technologies, and systems.

Additional guidelines for energy-efficient HVAC systems are set forth by technical organizations such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), which boasts an international membership of more than 50,000. ASHRAE regularly publishes updated building standards that are widely accepted by building engineers and HVAC professionals, including standards related to energy efficiency in HVAC system design and operation.

How flowmeters can help

It is clear that energy efficiency is not a passing trend, but rather a sweeping influencer of worldwide social, political, and economic thought. Accordingly, legislation related to the more efficient use of energy by buildings is likely to increase in both abundance and stringency in the coming years. This makes it crucial for facility managers to carefully monitor the performance of the various HVAC systems responsible for maintaining the environmental comfort of a building—whether it is a small residential apartment complex or an immense international airport.

Today, a variety of flowmeters with advanced capabilities are available for use by the HVAC industry to measure flow in hot or chilled water systems and provide the baseline and load profile information necessary to evaluate—and ultimately improve—the efficiency of a system. Certain flowmeters demonstrating a very high rate of accuracy can also be commissioned as revenue-grade thermal energy meters, used to monitor a customer’s energy usage for billing purposes and provide an accurate picture of their energy consumption behaviors.

Differential pressure

The most traditional method for measuring the flow of liquids, gases, and steam, differential pressure flowmeters enjoy a long-standing reputation for reliability. This tried-and-tested technology has been utilized by the HVAC industry for many years to measure flow in a variety of applications, depending on which primary elements (pitot tubes, Venturi tubes, orifice plates, etc.) are paired with the meter. Appropriate applications include natural gas boilers, air ducts, combustion intakes, boiler stacks, and chilled water.


Suitable for measuring the flow of almost all electrically conductive liquids, pastes, and slurries, and an appropriate replacement for traditional mechanical flowmeters when greater functionality is required, electromagnetic flow technology is the right choice for the vast majority of hot and chilled and water applications, including new installations and small line sizes below 12 in (30.5 cm).

Electromagnetic flowmeters offer several important benefits to the HVAC industry, including ease of operation and maintenance due to a lack of moving parts, a high level of durability, and the flexibility for either compact or remote installation using the same sensor and transmitter.


Vortex flow technology can provide accurate volumetric and mass flow measurements of steam, gas, and liquid flow independent of conductivity, viscosity, temperature, density, or pressure, and is not negatively impacted by high moisture content. This makes vortex flowmeters ideal for measuring energy consumption in HVAC applications that experience fluctuating temperatures and/or pressures, including burners, boilers, and compressed air systems.

Like electromagnetic flowmeters, vortex meters have no moving parts to wear or foul, ensuring maximum functionality with minimal required maintenance. Another significant benefit is that these meters comprise one of very few technologies currently capable of measuring steam flow, including both saturated and superheated steam.

Clamp-on ultrasonic

While other flow technologies often have difficulty coping with low load periods and low flow, clamp-on ultrasonic flowmeters are capable of accurate flow measurement at any velocity. Clamp-on meters are particularly useful for retrofit projects in which the pipeline cannot be isolated, as well as for hot and chilled water submetering. Overall, clamp-on technology is optimal for measuring flow in a wide range of building management, power plant, university, and district energy heating and cooling applications, including condenser water, potable water, glycol, thermal storage, river and lake water, lake source cooling, chemical feed, and ammonia feed.

Clamp-on ultrasonic flowmeters also offer the benefit of being quick, easy, and cost-effective to install and maintain as part of an existing HVAC application. This is due to their externally mounted sensors, which require no cutting of pipes, interruption of flow, or periodic cleaning. Such features make clamp-on flowmeters among the most versatile on the market, as they can be installed anywhere along a hot or chilled water line. By using a dual-channel model, it is even possible to measure two pipes simultaneously in order to manage the distribution of energy throughout a system.

For facility managers needing an accurate way to charge an individual customer or tenant for measured energy usage, clamp-on ultrasonic flowmeters can serve as revenue-grade thermal energy meters for billing. In this type of application, a high-accuracy meter is paired with precision-matched clamp-on or insert temperature sensors. The meter is then able to calculate BTUs by measuring the flow rate of hot or chilled water as well as the supply and return temperatures.

Case study: NYC building complex

A commercial real estate corporation that owns, develops, and operates premier properties throughout North America was designing a prestigious four-tower building complex in New York City. Rather than installing four individual HVAC systems to regulate temperatures inside each tower, the company elected to install a single central district cooling plant consisting of 10 chillers to satisfy the cooled water needs of all four buildings. The cooling plant was supported by a 3.3-million-gal chilled water thermal storage system consisting of 13 tanks with a capacity of 250,000 gal of water each.

Once the plant was completed, the real estate corporation sought a flowmetering solution that could accomplish two vital tasks: allowing for the individual metering of tenant utility usage and ensuring that the cooling plant was operating at optimal efficiency. The company required flowmeters that could be installed, repaired, and, if necessary, replaced without ever having to cut open the pipes, which would simply be too expensive and labor intensive.

The chosen meters also needed to be low-maintenance and demonstrate a high level of accuracy and reliability. After careful consideration and testing of several options, the right choice became clear: clamp-on ultrasonic flow technology.

To accommodate the requirement for individual tenant billing, multiple clamp-on ultrasonic flowmeters were installed in strategic locations around the complex. Since the cooling plant distributed chilled water to each tower individually, a single-channel meter measured the amount of water leaving the plant while additional meters monitored what was received at each tower. Another device tracked the amount of energy stored in the thermal storage tanks during the charging cycle and monitored the amount drawn down during peak hours.

With this setup, facility managers were able to keep track of the exact amount of water flowing from the chillers to the tenants and the difference in temperature between the supply and return water, which is all they needed to accurately calculate how much energy was being consumed by each tenant. The system also served as a way to monitor flow between the pumps and the chillers, which is a prerequisite for determining energy efficiency level and detecting performance issues.

A smart decision

As energy consumers are compelled by legislation, social pressure, and the desire for a better quality of life to seek innovative new methods of reducing their “carbon footprint,” the demand for energy-efficient buildings will only continue to grow.

To remain in compliance with regulations and building codes while satisfying the needs of environmentally conscious customers, the HVAC industry must take steps now to ensure that the systems they build and maintain are operating at maximum efficiency. Installing flowmeters specially designed to work with HVAC systems is an ideal way to accomplish this important goal—and one of the smartest decisions a facility manager will ever make.

Fedele is a marketing communications specialist for Siemens Industry Inc.