Supermarket Introduction

supermarket2Supermarkets have all the water uses of typical retail outlets, such as sanitary fixtures and landscape irrigation, plus much more.  Supermarkets possess certain specialized water uses that provide large water conservation opportunities.  The most notable is the water used to cool the condensers units for the refrigeration systems, such as display coolers and freezers, storage coolers and freezers, butcher shops, delis, bakeries, etc.   In addition, considerable water is used in the cleaning and preparation of the fresh produce, meats, and fish before the products are put onto the shelves.   

Evaporative Condensers

Refrigerated display cases, frozen food cases and storage freezers can use evaporative condensers, a type of cooling tower, as a means to chill the food. On average, half of the water used by a typical supermarkets that has these devices is used in the evaporative condensers, usually amounting to more than 1.5 million gallons per year (5,700 m3) per store, depending on local climate and the size of the supermarket.    The evaporative condensers are most often located on the roof of the supermarket.  Refrigerant pipes connect the evaporative condensers with the various display coolers, refrigerators and freezers inside the supermarket.   In the western United States, evaporative condensers are the most prevalent form of refrigerant cooling for supermarkets, but air cooling is found in most northern stores and much of the east. 

Evaporative condensers operate in a manner similar to all cooling towers, but have a distinct difference.  In cooling air conditioning towers, the cooling water does not come into direct contact with the equipment being cooled.  Cooling tower water passes through a refrigerant-water heat exchanger in the condenser to achieve thermal transfer.   With evaporative condensers, the heated refrigerant is run into coils at the top end of the unit (usually located on the roof) where the tower water is sprayed directly over the coils and a fan blows air through the falling water spray.   As some of the water evaporates, the remaining water becomes cooler through the effect known as latent heat of evaporation.    The cool water then absorbs heat from the tubes of the condenser coil, cooling the refrigerant so that it liquefies.  

As the cooling water evaporates, the minerals in the water remain behind, thus increasing the mineral concentration of the remaining water.  These minerals collect and concentrate to levels that can harm the system; some water has to be periodically drained and fresh water added to dilute the mineral content of the cooling water.   This process of draining old water and replacing with fresh water is commonly called “bleed”.  Bleed rates are adjustable by setting controls on the equipment.

Water efficiency in this equipment is dependent upon bleeding as little water as necessary, while maintaining the entire system in good working order.  If the mineral content of the cooling water becomes too concentrated, the minerals will attach to the surfaces of the condenser coils, forming damaging layers called “scale”.   The build-up of scale will greatly impair the energy efficiency of the equipment, and eventually cause permanent damage if not corrected.  The point of which scale forms depends upon the temperature of the water, the level of minerals (usually measured as Total Dissolved Solids, or TDS), and the pH level of the water.   Fortunately, there are also myriad chemical scale and rust inhibitors that can be added to the water to impair such a build-up.   Most evaporative condensers are maintained and operated by contracted service firms.  These service technicians’ first priority is to assure that the water bleed rate is great enough so that no scale forms.  The service contractor does not pay the water bill and seldom is concerned with water efficiency.  As such, many systems use 50% more water than necessary.

There are varying levels of strategies to improve the water efficiency of this equipment.  First, the bleed rate should be set to the minimal level needed, while still preventing the formation of scale in the system.  This is primarily determined by the quality of input water.  Where water utilities supply relatively soft water (low in TDS), the bleed rates can be adjusted lower, allowing the Cycles Of Concentration to be greater as the water is retained in the system for longer periods.  (COC is a term used in the water treatment industry representing the doubling, tripling, quadrupling, etc. of TDS levels compared to the TDS level of the source water.)   An analysis of the supply water must be made to determine the level of TDS and what type of minerals are present.  (Some minerals, such as magnesium, silica and calcium, are especially problematic for scale build-up)   TDS levels in the water change as the quality of supply water changes (usually seasonally) and the cooling load changes.   The only way to consistently maintain TDS levels and adjust bleed rates accordingly is with a conductivity meter/controller.

Chemical additives can improve water efficiency further by allowing the TDS levels to rise without fear of damaging the system.  Such additives include acid solutions to raise pH levels, rust inhibitors, scale inhibitors, and microbiological agents.  The proper use of these additives is dependent on the skill level of the service contractor maintaining the equipment.

Sidestream filtration offers additional water conserving opportunities.  Evaporative condensers require plentiful outside air flowing through the water spray to achieve evaporation (thus the cooling effect).  This air contains many tiny particles (dust, ash, pollen, mold, etc.) that pollute the cooling water and can eventually accumulate inside the system.  These particles are usually removed by high bleed rates.  Sidestream filtration of the cooling water removes these particles; reducing the need for high bleed rates.   

It should be noted that some cooling tower strategies, such as ozonation technologies, are usually not cost-effective for the smaller sized equipment of evaporative condensers.  Ozone's main use is as a biocide.  Electromagnetic radiation, and electro-static treatment technologies to remove TDS also exist, but have experienced mixed results in preventing scale build-up at water efficient bleed rates.

In addition to system operational improvements, sometimes water savings can be achieved by repairing and preventing leaks in the system.  The water supply to the system is often actuated by a float valve in the water retention pool below the coils.  The supply pipes, overflow tube, and float valve are susceptible to failure.  Often these leaks go undetected for months or years because the water leaks directly to the sewer drain.  A thorough inspection should be performed several times per year.  A dedicated water meter should be installed on the water supply pipe, and read monthly to alert the operator for sudden changes in water consumption.

supermarket1

It is reasonable to improve the water efficiency of most systems by reducing water use by 10% to 60%.  Retrofitting the evaporative condensers of a supermarket with the aforementioned controls and equipment has proven to save 800,000 gallons per year (3,000- m3) for the typical supermarket.  The cost of retrofits (approximately $25,000) is usually offset by reduction in water and wastewater costs.  In addition, most retrofits improve the energy efficiency of the evaporative condensers by more than 5%, saving more than $8,000 in electricity costs per year.  

As with other commercial equipment, water efficiency depends on the cooperation of both the building owner and the service contractor maintaining the equipment.  There are wide skill levels of service contractors; some may not be able to properly manage the more sophisticated equipment of TDS controllers, chemical injectors, and filtration systems.  Most service contractors work under one-year agreements and are selected by the corporate office of supermarket chains.   A water utility must account for these factors when designing a successful program to improve water efficiency of evaporative condensers.

For more information on water efficiency in supermarkets please see the following:

Aquacraft (2004) Water Conservation Opportunities in Urban Supermarkets 

Toilets

Water savings can be achieved by replacing older model toilets using 3.5 gpf (13 Lpf) or greater with new ULFTs (1.6 gpf -6 Lpf), HETs (1.28 gpf - 4.8 Lpf), including dual-flush HETs using 1.6 gpf (6.1 Lpf) for the full flush and no more than 1.1 gpf (4.0 Lpf) for the reduced flush (liquid waste).  The frequency of toilet flushes per toilet is often greater in offices than homes, although the frequency is highly variable from facility to facility.  It is reasonable to assume an average of 2 to 4 flushes per person per 8 hour shift.  Depending on the type of supermarket, transients (visitors and customers) might also incur additional flushing activity.  When conducting benefit/cost analyses, it is important to separate the calculations for women’s toilets versus men’s toilets for two reasons: (1) the ratio of mens room toilets per male worker is usually different than the ratio of womens room toilets per female worker; (2) men will most often use urinals (when available) rather than toilets.  While it is reasonable to use average toilet usage estimates for program planning, performing toilet retrofit projections of water use on individual office facilities requires calculations based on unique site data. 

The dominate type of toilet installed in office buildings is the flushometer valve/bowl combination and the pressure-assist, though gravity-fed, tank-type toilets are found occasionally.  For example, when retrofitting from a 3.5 gpf (13 Lpf) flushometer fixture to an HET flushing at 1.2 gpf (4.5 Lpf), both the bowl and the flush valve of the flushometer valve/bowl combination must be replaced to assure water savings and adequate flushing performance.   The cost to replace a flushometer type toilet usually ranges from $250 to $400, depending on the type of bowl and valve chosen.  Wall-mounted, back-outlet flushometer valve/bowl combinations are the most commonly found in new buildings, while floor mounted fixtures are more common in older buildings.

As with all toilets in the commercial sector, there are a few extra items to consider when choosing products:

  • Building maintenance staff must be trained to only use the proper parts when servicing the flush valves, or all or a significant portion of the expected water savings will likely be negated.  Unfortunately, 3.5 gpf (13 Lpf) parts often fit the new 1.6 gpf (6.0 Lpf) flush valves.
  • There are now hundreds of models of HETs available (Up to 1.28 gpf - 4.8 Lpf) including single-flush and dual-flush. While there are many gravity type toilets suitable for light commercial applications, flushometer valve/bowl combinations or pressure-assist models are preferred in most commercial buildings.
  • Sensor-activated flush mechanisms often result in more frequent toilet flushing than manual flush valves.  There is no evidence the sensor-activated valves save water.
  • If installing dual-flush toilets, it is wise to post instructions for the toilet users, most of whom will be unfamiliar with the dual-flush technology and its operation,
  • Disposable seat covers and paper towels are the most common causes of clogged commercial toilets.  Consider alternate methods of hygiene (sanitizers, continuous roll seat cover dispensers, hot air dryers, etc.), or select new toilets models that exceed 500 grams (1.1 pounds) in the Maximum Performance (MaP) Testing regimen. 
  • Flushing performance is very important for success.  Refer to the MaP testing report before selecting new toilets.
  • Piston-type flush valves (as opposed to diaphragm-type)  more accurately meter the volume of water per flush and tend to have less maintenance issues. 

Urinals

The water-saving benefit of replacing urinals is highly dependant on frequency of use and the type of replacement proposed.  Frequency of use is determined by calculating the quantity of male 8-hour shifts, the average urinal flush per person per 8-hour shift (usually 2 to 4), and the quantity of urinals.  Similar to toilets, visitors to the facility might increase the total number urinal flushes on a given day.

There are many options now for urinal retrofits, from simply replacing the flush valve diaphragm to reduce flush volume, all the way to replacing the entire fixture and valve with a high-efficiency urinal (HEU) combination.  An HEU includes both flushing (maximum flush volume of 0.5 gpf (1.9 Lpf) and non-water using urinals.  There is significant variance in the short- and long-term costs of each type and the long-term benefits. In many cases, marginal water savings can be achieved by simply retrofitting the urinal flush valve to a lower gpf diaphragm on flushometer valve urinals, though some older urinals will not properly function at these reduced flows.  For example, a 1.0 gpf (3.8 Lpf) urinal can usually be reduced in flush volume to about 0.7 gpf (2.6 Lpf) with little, if any, sacrifice in flush performance.  This involves a simple replacement of the flush valve diaphragm with  the lower rated volume.Unfortunately, this type of valve-only retrofit can be easily and mistakenly reverted back to the higher flush volume during routine maintenance.  Much consideration is needed to determine the best retrofit or replacement for any given restroom.   To assure water savings are sustained over time, the best strategy is to replace the entire urinal and flush valve with an HEU (e.g., 0.125 gpf or 0.25 gpf (0.5 Lpf or .95 Lpf) model). 

The U.S. EPA has released a WaterSense specification for flushing urinals and will soon be allowing manufacturers to place the WaterSense label on these fixtures.  Facilities managers, building engineers, and other decision-makers should consult the list of WaterSense urinals before making a product choice.

As with all urinals in the non-residential sector, there are a few extras items to consider:

  • Building maintenance staff must be trained to only use the proper parts when servicing the flush valves or all water savings will be reduced or negated altogether.  Unfortunately, 3.5 gpf (13 Lpf) parts often fit the new 1.0 gpf (3.8 Lpf)flush valves.
  • Sensor-activated flush mechanisms often result in more frequent urinal flushing than manual flush valves due to what is known as “phantom flushes”.  There is no evidence the sensor-activated flush valves save water.
  • Non-water urinals are considered compliant by most, but not all, plumbing code authorities.  The Uniform Plumbing Code and the International Plumbing code allow the urinals, but some local jurisdictions have not yet approved the devices.  It is wise to contact the local jurisdiction before installing non-water urinals. Furthermore, the maintenance costs associated with non-water urinals usually exceed those of flushing urinals.  It is essential that the building engineer or facility manager perform a fully life cycle cost analysis of the non-water urinal and comparing it with a similar analysis of a flushing urinal BEFORE making a purchase decision. 

Lavatory Faucets

Flow rates for wash basin faucets in lavatories can reasonably be reduced to 0.5 gpm (1.9 Lpm) or lower.   (The current national standard and the major model plumbing codes in the U.S. call for a maximum flow rate in non-residential lavatory faucet installations of 0.5-gpm (1. 9 Lpm).)  Projected savings from retrofit (aerator replacement or replacement of the entire faucet assembly) are usually based on usage frequencies similar to toilet and urinal use.  Flow durations are often estimated to be 5 to 30 seconds per use.  Retrofitting aerators on the faucets is the most common and least expensive strategy.   The water savings are small when compared to replacing toilets, but the cost of retrofit is minor, usually less than $1.00 per faucet.

Some lavatories are fitted with mechanical metering valves (automatically shut-off after a preset time span) or negative shut-off valves (user must continue to exert pressure on valve handle to maintain water flow).   These types of valves are required to save water and deter flooding the lavatories.   The metering valves are often adjustable for the duration of the flow.  The flow should not exceed 5 seconds per activation.

There is no scientific evidence that sensor-activated faucets save water.  To the contrary, recent studies have provided valid evidence that sensor faucets use much greater water than manually activated valves.   It is important to note that the growth of the "touchless restroom" has been in large part to the concern for hygiene since fixtures do not need to be touched with the hand.   The studies shows that on the average,  users open the faucet to a flow rate of some 1.0 to 1.5 gallons per minute.  By contrast, sensor faucets open the valve all the way to the maximum flow setting.  If a 2.2 gpm aerator is on the faucet , the flow will be 2.2 gallons per minute, but if a 0.5 gpm aerator is used, the flow will be only 0.5 gpm. 

Irrigation

Supermarkets might also provide opportunities to conserve water used to irrigate surrounding landscape, especially office complexes with extensive common area landscaping.   These landscapes are notoriously over watered because: (1) there are often small landscape islands dispersed through the parking lots that are difficult to water and prone to run-off; (2) the landscape is maintained by a contractor that does not pay the water fees; and, (3) the landscape is usually irregularly shaped without zone separation between turf and lower water use plants.   The greatest difficulty in achieving irrigation savings is coercing the building owner to make the landscape maintenance contractor responsible for water use and waste.

Cooling Towers

Cooling towers can significantly increase the use of water in a supermarket.  Most large supermarkets (more than 10,000 square feet (1,000 square meters ) employ the use of a cooling tower in the HVAC system to cool the building.  Cooling towers use the cooling effect of evaporating water to remove heat from water circulating through the HVAC chillers.  Cooling towers can account for between 15 percent and 50 percent of an office building’s water use, depending on the climate in its location. There are numerous ways for the system to waste water when the system is not properly maintained.   In fact, depending on the climate zone and the cooling system, the water waste can be greater than that used by all the sanitary fixtures combined!  Appropriate retrofits usually require a conductivity controller be installed and properly maintained to achieve a first level water use efficiency.  Conductivity controller retrofits usually cost less than $1,500 per cooling tower, and can save more than $800 per year for a typical office building.

Cooling tower retrofits and maintenance should be part of every water conservation program targeting office buildings.  There are ample technologies available to greatly improve the water efficiencies of most cooling tower systems.  Technology provides the tools for water savings, but does not guarantee water efficiency.  Controller installations and retrofits must be part of an overall customer maintenance and education program to be effective. 

Reclaimed Water

Where the local wastewater treatment agency provides reclaimed water (wastewater treated to drinking water standards, though deemed non-potable), supermarkets provide an opportunity to supplant potable water use with reclaimed water use.   Landscape irrigation is the most obvious opportunity to use this water.  Reclaimed water can also be used to supply water to toilets and urinals.  Depending on the water quality requirements, many cooling towers can also use reclaimed water rather than potable water as their primary source.

In all applications, the reclaimed water must be strictly separated from potable water sources and end-uses.  This requires a clear separation of pipes supplying water to the end use (irrigation system, toilets, urinals, cooling tower, etc.) from those pipes supplying potable water to faucets, drinking fountains, etc.   In large projects, irrigation systems are usually supplied through separate meters; thus, this is the most common application for reclaimed water use. 

The water supply plumbing for toilets and urinals is often interconnected with faucets and drinking water fountains, requiring extensive plumbing system retrofits if reclaimed water is to be substituted for flushing.   Retrofitting a pre-existing plumbing system inside a supermarket is usually too costly to justify the use of reclaimed water to flush sanitary fixtures. 

When constructing a new supermarket, however, the cost to separate the water supply plumbing for sanitary fixtures is marginal.   Some water agencies are now requiring new commercial buildings to be dual-plumbed, so that reclaimed water can be used to flush sanitary fixtures, even if reclaimed water is not immediately available.  Commercial property developers report this has added less than 15% to the total cost of the plumbing system. 

Alternative Water Sources Collection and Use

Alternate sources of water collected on the site of the office building can significantly reduce the use of potable water for non-potable purposes.  These alternate sources include but are not limited to:

  • Rainwater
  • Storm water
  • Gray water
  • Air conditioning condensate
  • Foundation drain water
  • On-site wastewater treatment
  • Pool drain and backwash water
  • Cooling tower blowdown
  • Reverse osmosis reject water

Non-potable uses of water from these alternate sources can include:

  • Cooling tower makeup
  • Landscape irrigation
  • Pollution control
  • Toilet and urinal flushing
  • Swimming pool, fountain and pond makeup
  • Laundry operation
  • Any other use not requiring potable water.

Quality, quantity and time of generation and need all need to be matched and treatment provided, where necessary, to meet the requirements of the end use,  comply with health codes, and satisfy environmental considerations. 

Collecting the storm water or rainwater on the building site (roof, parking lot, hardscape, landscape, etc.) is one of the fastest growing strategies in the water conservation industry and the “green” building efforts.   Supermarkets usually require enormous parking lots, where storm water runoff is massive.  There are three distinct advantages to storm water collection strategies:

  • The collected water can be stored then used to irrigate the landscape during dryer months.  If properly treated and filtered, the water can also be used to flush toilets and urinals where local codes allow.
  • The water collected is prevented from entering the storm water system, which is often overtaxed in urban areas causing flash floods.
  • The pollutants from the building site (fertilizers, herbicides, pesticides, animal waste, automobile fluids, etc) are prevented from being carried by storm water to streams, rivers, and other aquatic ecosystems.

In addition, the condensate drain from the many refrigeration units (see above), and the blow down water from both the cooling towers and evaporative condensers can be collected and used similar to storm water.  Each alternate water source has differing qualities (all are non-potable), and are not necessarily interchangeable in end-uses.  It is important to contact the manufacturer of all appliances and fixtures before supplanting potable water with the alternate water source. 

Waterbrooms

Hardscapes (sidewalks, decks, walkways, etc) are often sprayed with water from a hose and nozzle as part of a cleaning regimen, especially related to food service facilities and patio dining areas.   While dry sweeping the surfaces with a dry broom is preferred, health and sanitation objectives generally require remaining food scraps to be rinsed off the hardscape with water.   The traditional hose and nozzle uses more than 5.0 gpm (19 Lpm), while waterbrooms use less than 2.0 gpm (7.5 Lpm).  Water brooms use an array of high velocity, low water volume nozzles to scour the surfaces.  The majority of users also attest that the waterbroom cleans the surfaces faster and cleaner than the traditional hose nozzle method.