Navigant Research Blog

Rethinking Water Use in Buildings

— September 8, 2014

Bad news about the water supply keeps rolling in.  In July, a study on the groundwater in the Colorado Basin found that 53 million acre-feet of water (65 billion cubic meters) had been depleted between December 2004 and November 2013.  The historic drought in the western United States is so severe that it is causing mountains to rise.  And ominous signs of water scarcity are not limited to the United States.  Farmers in Vietnam are converting rice paddies to shrimp farms as the dry season gets dryer and the rising South China Sea turns coastal freshwater ponds salty.  Water scarcity threatens much of the world economy, from the food industry to the mining industry to the petrochemical industry.

Though climate change accounts for a part of the unfolding water crisis, water management practices are driving the problem.  Water has long been treated as a free and inexhaustible raw material.  As a result, it’s used inefficiently.  While great progress has been made in increasing awareness of energy efficiency, water continues to be taken for granted.  Without major changes, two-thirds of the world’s population could be living in water-stressed conditions by 2025.

Water Scarcity and the Built Environment

Buildings account for about 12% of water use in the United States.  Already, water conservation efforts and greater efficiencies in using water have led to a reduction in water withdrawals.  But, for further gains, fundamentally rethinking the built environment is necessary.  For the most part, everything that needs water in a building is provided with potable freshwater.  Similarly, all wastewater is treated the same.  But not everything needs potable water.  And rather than being disposed of, some wastewater can be recycled.  Water from a sink can be reused to flush a toilet.  Water from a bathtub can be used for landscape irrigation.  When water is cheap and abundant, it makes sense to have a single system for all water needs and a single system to dispose of all “used” water.  But meeting all water needs with potable water may soon no longer be an option.

Similar recycling efforts can be achieved with stormwater runoff.  Many municipalities treat stormwater runoff and domestic sewage the same, using a combined sewer system to transport them in a single pipe to a sewage treatment plant (though heavy rainfall or snowmelt can create undesirable outcomes for combined sewers).  Rather than building infrastructure to capture and transport stormwater through gutters and sewers, capturing it to recharge groundwater or for direct nonpotable consumption can directly improve the water situation.  Indeed, the Pacific Institute estimates that urbanized Southern California and the San Francisco Bay region have the potential to increase water supplies by 420,000 to 630,000 acre-feet per year simply by better managing stormwater runoff.

One Word: Graphene

Of course, when we talk about water scarcity, we refer to only freshwater, which accounts for only 2.5% of total global water.  Desalinating abundant seawater is a seemingly attractive workaround, a way to solve water scarcity without the difficult task of changing water use habits.  Unfortunately, desalination, for now, is expensive and energy-intensive.  The most common form of desalination, reverse osmosis, forces seawater through a polymer membrane.  The membrane allows water molecules to pass, but blocks salt molecules.

Graphene, an allotrope (i.e., a different structural form) of carbon, which shows promise in battery technology, quantum computing, health monitoring, and solar cells, could reduce the cost and energy associated with desalinating water.  The gaps in polymer membranes are determined by the physical and chemical properties of the polymer used.  Gaps in graphene must be punched, so they can be sized to reduce the amount of pressure needed to pass water through but still prevent salt from passing through.  Lockheed Martin and the Massachusetts Institute of Technology are both working on overcoming the engineering problems associated with graphene membranes.  Commercial viability may still be several years away, but graphene may make desalination accessible enough to meet the world’s needs for clean water.


Refrigeration’s Chilling Effect on Energy Efficiency

— August 6, 2014

China’s meteoric rise has had profound impacts on its economy, people, and environment.  Navigant Research has examined the consequences this growth has on energy used by buildings and cities.   As the country of 1.3 billion becomes more prosperous, the next transformation occurring is in cold storage.  In a recent article, The New York Times Magazine delved into the adoption of refrigeration in China.  On the consumer level, China’s domestic refrigerator ownership has grown from just 7 % in 1995 to 95% in 2007.  As a result, the cold chain (the temperature-controlled storage and distribution infrastructure) is growing as well.

The United States, which leads the world in cold storage, currently has about 3 times the cold storage per capita as China does.  In China, less than one-quarter of meat and 5% of fruits and vegetables travel through a cold chain, compared to about 70% of U.S. food.  As China’s living standards rise, refrigeration and energy use are set to explode.  Currently, cooling accounts for only about 15% of global electricity consumption.

The threat associated with increased living standards is not isolated to China.  An estimated 40% of fruits and vegetables in India are lost to spoilage as a result of poor infrastructure.  Although the Indian economy has not performed as robustly as China’s, there is hope that growth will pick up shortly.  However, with that hope comes the risk of unsustainable energy consumption on a staggering scale, as India and China combined account for more than one-third of the world’s population.  As such, vast advances in the energy efficiency of refrigeration are needed.

Birth of the Cool

Refrigeration, like air conditioning, relies on the vapor compression cycle.  The vapor of a refrigerant is compressed to the point where it is superheated and then travels through a condenser where heat is rejected from the refrigerant vapor and it is condensed into a liquid.  Next, the liquid goes through a throttle valve where it evaporates into a low-temperature, low-pressure mixture of liquid and vapor.  Lastly, this mixture travels through an evaporator that absorbs heat from the space being refrigerated and evaporates the mixture so that it can be compressed and the cycle can start again.

Incremental improvements have been made in the efficiency of refrigeration, but there is a physical limit to how efficient the vapor compression refrigeration cycle can be.  It may be time to rethink the fundamentals of refrigeration.  The U.S. Department of Energy, for instance, has been investigating the use of non-vapor compression technology.  But the answer may not be cooling at all.  Cooling is a means to an end; it is an effective method of inhibiting microbial growth.  But it is not the only method to do so.  Fenugreen FreshPaper uses naturally occurring antimicrobials to keep fruits and vegetables fresher longer – with near-zero energy use.


Energy Efficient Solutions for Retail Stores Begin to Emerge

— July 23, 2014

The retail landscape is in flux, to say the least.  Earlier this year, Staples announced the closure of 225 stores.  Troubled Best Buy isn’t closing any stores this year, but it was one of several retailers to close stores in 2013.  Things aren’t all so bleak for big box retail, though.  Costco is in the midst of a 5-year plan to open 150 new stores.  Meanwhile, Walmart announced a strategy of shifting toward 10,000 SF to 40,000 SF grocery and convenience-type stores, away from 200,000 SF superstores.  Large retailers are rethinking their physical footprint.  Part of the shifting landscape comes down to the fact that brick-and-mortar stores, particularly warehouse-type stores, are costly to operate.  Moreover, the energy efficient operation of these assets is hindered by factors such as unpredictable occupancy, high ceilings, and vast open space.  Yet, smart building technologies are being developed for the specific challenges that face retail buildings.

There are numerous approaches to improving the energy efficiency of buildings (see Navigant Research’s reports Energy Efficiency Retrofits for Commercial and Public Buildings and Building Energy Management Systems).  But many of these aren’t appropriate for large, big box retail buildings.  A recent brief from Johnson Controls’ Institute for Building Efficiency provides a thorough analysis that quantifies the cost and payback of various building efficiency improvements for commercial office buildings.  It details 16 measures that represent 90% of possible energy savings.  Unfortunately, most of those do not address big box retail; they focus on using energy for building occupants, not for empty spaces.  That translates to providing cooling, lighting, and even power for computers only when occupants are in the space.  Although these measures work in office buildings, healthcare facilities, schools, and many other commercial buildings, they don’t provide the same opportunity to many retail spaces.

What Does Smart Retail Look Like?

Many retailers have aggressively pursued demand-controlled ventilation, lighting and controls upgrades, and advanced efficiency compressors for HVAC and refrigeration to reduce operating costs.  But the cutting edge of smart building technology for retailers focuses more on the consumer experience than on energy efficiency.  GE Lighting and BryteLight, for instance, are using next-generation LED fixtures to provide location-based services for retailers.  Similarly, the Open Group, a consortium that enables the achievement of business objectives through IT standards, has outlined a use case of using sensors to provide real-time information to retail customers.

However, MIT’s SENSEable City Lab has recently unveiled a concept to use smart sensing technology to reduce energy consumption.  Local Warming creates a controllable heating zone around an individual occupant, leaving the rest of the space at a neutral temperature.  The solution relies upon a Wi-Fi-based motion tracking system that controls a system of mirrors and rotating motors to direct an infrared energy beam onto an occupant.  In the future, LED technology can further reduce the complexity of the system by allowing a more distributed source of infrared heat.

Local Warming Concept

(Source: SENSEable City Lab)

While the system is not specifically designed for retail, the most compelling application for Local Warming is clearly big box retail.  These retail spaces are typically large and sparsely occupied.  Additionally, infrared heating has long been employed in large retail spaces.  Infrared heaters, which transfer heat through radiation rather than convection, warm occupants without having to warm the air.  In warehouse-like stores, with lots of air relative to the number of people in it, infrared provides an efficient method of heating.  Local Warming may signal a shift in the use of advanced sensor and location-based services in retail to the development of more advanced efficiency solutions.


Li-Fi Turns Light into a Data Stream

— July 13, 2014

Since Harald Haas demonstrated the ability of light-emitting diode (LED) lights to transmit data during a TED Talk in 2011, the promise of Li-Fi (short for light fidelity) has received a lot of attention.  As researchers develop faster and faster communication speeds, the application of the technology to the building space appears both realistic and attractive.  Commercially, General Electric (GE) has demonstrated the viability of the technology through its launch of LED-based communication for retail environments.  Li-Fi could be cheaper and consume less energy than existing wireless communication technologies that rely on radio frequencies (RF).  Smart buildings, which require a dense and flexible control network, present an interesting application for a Li-Fi deployment, particularly with the increased adoption of LED lighting.


Li-Fi seems to be a compelling alternative to the RF technologies that are currently in use today.  First, the RF available to building automation is crowded.  Moreover, as the Internet of Things becomes more pervasive, more and more communication nodes will further saturate the environment.  RF travels through walls.  So, a node in an adjacent room will be competing for detection.  But Li-Fi is impervious to this problem.  Since the range of any individual Li-Fi node extends only to the nearest wall, the communication in one room will never interfere with other communication in a different room.  In other words, the inherent limitations on Li-Fi range are an ideal solution for saturated networks.  Moreover, more than just crowding, interference from microwaves and other devices can be a problem, particularly in medical environments.  Li-Fi is immune to RF interference.

Security is another area of concern for wireless communication.  It’s relatively easy to hack a Wi-Fi network.  Li-Fi, on the other hand, has a shorter range and requires line-of-sight.  As a result, it is inherently more secure.  You have to be within the range of the transmitter and receiver, shifting the threat of IT security to more manageable physical security.

The Bad News

The technology faces some serious technical challenges before widespread adoption, though.  In addition to enhancing security, the line-of-sight requirement also presents challenges.  Though Li-Fi is immune to RF interference, it is susceptible to interference from a more ubiquitous source: the sun.  Receivers placed close to windows could be rendered ineffective.  Additionally, lighting in buildings is typically designed to be unidirectional, from the light source to the space to be illuminated.  But communication networks must be bidirectional to both send and receive data.   In order to create a Li-Fi network, lights would need to be installed to point at each other, which is at odds with their intended functionality.

Despite these drawbacks, Li-Fi could overcome several of the barriers facing wireless.  Though most of the current buzz focuses on visible light communication, using infrared light could solve many of the hurdles.  Windows can be designed to block infrared light but allow visible light to pass, eliminating problems of solar interference.  Infrared also has greater potential throughput of up to 5 to 10 gigabits per second.  Overall, the challenges facing Li-Fi are no greater that the challenges facing RF.  The technology appears to be several years away from successful deployment in building automation.  But it’s coming.


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