Water Conservation Through HVAC Technology
Sustainability by the Drop
Headlines out of Cape Town, South Africa, this year made clear that sustainability isn’t only about saving electricity or the fuels often associated with power generation. It is difficult to imagine a city running out of water, but it’s no longer impossible. Water conservation is getting more important in the U.S., and HVAC systems on a large scale represent a chance to make an impact (or not).
It’s good news, then, that the wider realm of HVAC energy efficiency provides the chance to conserve water both near and far.
More directly, when availability tightens at all, environmental impulses in the commercial sector often get a nudge from a most traditional area of concern: profit margin.
Judith Peters, LEED AP of Daikin Applied, confirmed that water and wastewater price escalation has contributed significantly to efficiency efforts in the commercial HVAC sector. However, the situation varies from region to region.
Peters pointed to a Department of Energy (DOE) study from 2017, which stated that on average, annual escalation rates for water range from 0.6 percent in the West-Mountain region, to 8.6 percent in the Northeast, and wastewater escalation rates range from 1.3 to 5.1 percent. In comparison, energy escalation calculators from the DOE predict average annual escalation rates from 0.35 to 1.78 percent in U.S.
Tom Carter is a senior program manager, Heat Rejection Technology, Industrial Refrigeration, for Johnson Controls’ Building Technologies & Solutions team. Carter also hears from customers whose water and water treatment costs are rising faster than electricity costs, and some customers who have their own corporate sustainability goals that include water footprint.
“We’re also seeing a shift in some markets and applications toward air-cooled chillers, especially where applications can use higher chilled water temperatures, such as data centers,” he said. “Absorption heat pumps using waste heat are another area of growth.”
Attitudes and levels of interest can be as important as the equipment itself. Ian Dempster is a senior director of product innovation at Optimum Energy and a certified energy manager. Optimum sells many of its optimization projects on a return on investment (ROI)-basis, so the attention to what customers will get for their efforts is constant.
“Most customers want to understand exactly what those savings and efficiencies will gain them,” Dempster said. “That taught us to focus and refine our facility energy modeling tools and to train our engineers to be very accurate in producing baselines, along with projected baselines that show, in almost real time, how well the products are performing. Customers really like being able to look at a screen on their computer, or an app on their smartphone, and see how much their facility is saving in energy, dollars, CO2, and water.”
|THIS PERIOD||THIS YEAR||LAST 12 MONTHS|
|MONEY SAVED ($)||$64,693||$243,082||$430,411|
|ELECTRICITY SAVED (kWh)||287,356||1,088,497||1,850,824|
|CO2 SAVED (lbs)||431,034||1,632,745||2,776,235|
|WATER SAVED (gal)||280,536||938,885||1,220,858|
|CHILLED WATER SAVED (TON-HRS)||620,834||1,078,383||1,568,577|
WHERE ARE THE OPPORTUNITIES?
Peters looks to the cooling tower and frames her answer in terms of cycles of concentration (COC). COC is the ratio of blowdown conductivity to makeup water conductivity. The higher the COC for a water-cooled chiller plant, the less water is used.
“Many systems today operate at two to four COC; however, it may be possible to increase to six or even eight COC for locations with high-quality water (low levels of minerals) or through chemical-free technology,” she said. “If an owner increases their COCs from three to six, it reduces cooling tower makeup water by 20 percent and cooling tower blowdown by 50 percent.”
Dempster sees well-selected equipment upgrades and using optimization software as the two largest opportunities. He described an older building where a secondary/primary pumping gets converted to variable primary.
“Effectively getting rid of the second set of pumps and performing some piping rework, the savings can be phenomenal,” he said.
Team that with replacing decades-old chillers or boilers, and customers can gain anywhere from 15 to 35 percent efficiency improvements for that system, which will translate to less water use, Dempster added.
Carter noted that electricity production consumes water, so reducing energy use at a building also reduces water use upstream (no pun intended).
“When it comes to using chillers, the more efficient a water-cooled chiller, the lower the heat of compression, and therefore, less overall heat needs to be rejected in the cooling tower,” he said. “This leads to a reduction in cooling tower evaporation.”
Carter added that integrating a combination of air- and water-cooled chillers can also make a difference.
OFF THE SHELF AND ON THE CASE
In the realm of product development, three companies take different tacks.
“We are making use of the mountains of data we have collected over the past 12 years that show how HVAC systems and equipment respond to differing conditions,” Dempster said. “Using this information, we created three modules that use machine learning to gain intelligence over time and make actionable decisions that gain even further results. To date, we have seen these modules deliver 5 to 7 percent additional savings above the typical optimization savings of 30 percent.”
At Daikin, Peters cited the company’s variable volume ratio (VVR) technology to enable chillers to help a building respond better to climate and changing loads.
The Applied Navigator® is a screw compressor water-cooled chiller that uses VVR and variable-speed technology to meet or exceed ASHRAE 90.1-2016 levels and IPLV as low as 0.36, according to Peters. It’s designed to sense the precise amount of lift needed while adjusting the compression ratio to deliver optimal efficiency throughout the day, she said.
Meanwhile, Johnson Controls’ BlueStream Thermosyphon Cooler played a key role in the National Renewable Energy Laboratory (NREL) reducing its data center water consumption by almost 50 percent, Carter said.
“Many systems with year-round heat rejection needs can significantly reduce their annual cooling tower water usage by employing a hybrid cooling system, such as the BlueStream,” he continued. “BlueStream intelligently combines and controls a specialized dry cooling device, the Thermosyphon cooler, upstream and in series with an open cooling tower.”
MICRO TO MACRO
When asked for an equipment or operations idea that is overlooked, Peters was concise.
“Consider an air-cooled chiller,” she said. “While air-cooled chillers are less efficient than water-cooled chillers, the owner saves water as well as maintenance and chemical costs.”
Meanwhile, Carter cites water-to-water chiller/heat pumps as one of the most overlooked opportunities to conserve water in large, central cooling and heating plants.
“By rejecting chiller heat into the plant’s heating system, instead of cooling towers, you can save large amounts of water annually while generating hot water and chilled water at a combined COP of over 6.5,” he said.
Absorption heat pumps are also driven by steam, hot water, or other forms of waste heat, and therefore reduce water consumption, Carter added.
Dempster promotes holistic control here, but with a lesson about unintended consequences when it comes to deploying seemingly beneficial measures like adjusting chiller supply temps.
“This is a very good strategy with proven results,” he said, “but if the temperature is raised too high, all savings may be lost.”
“Because as AHU [air-handling unit] fans ramp up to provide more air to the building, they are not cooling the air enough,” Dempster said. “Controlling the system holistically prevents this type of scenario.”
DRIFTING IN THE RIGHT DIRECTION
To wrap up, the trio of professionals each took a moment to compare customer awareness and concern now to how it used to be.
Carter sees customer awareness on the rise because of the last decade’s significant droughts in the Southeast, Texas, the Southwest, and California. Specifically, more owners understand that cooling towers on chiller systems often represent the building’s most significant water-consuming device.
Peters has seen the U.S. Green Building Council’s LEED certification for new and existing buildings increase owner sensitivity to the issue significantly.
“Interestingly,” she added, “LEED v4 currently has a pilot credit that serves as an alternative compliance path for the cooling tower water use credit. A project can earn points for not including a cooling tower or use of a district cooling system. The intent behind the credit is to increase water efficiency, eliminating the need for a cooling tower.”
Talking to building owners directly for over 16 years about optimizing chillers has let Dempster see an evolution in attitudes regarding the bigger efficiency equation.
“One of the large concerns we consistently ran into many years ago was the worry that installing VFDs on electric motors would decrease the motors’ life span and create problems,” he said.
Now, of course, it is readily accepted that VFDs, in tandem with optimization strategies, can make a real difference. However, misconceptions remain.
“Contrary to standard belief, using less equipment is not a guarantee of reduced water consumption and better energy savings,” Dempster said. “Operating two or more units of modern variable equipment (such as cooling towers or chillers) at reduced speed and load oftentimes allows the machines to operate at lower temperatures.
“This can save more energy than having one of those pieces operating at close to full speed and load,” he added.
Just when more building owners are getting used to thinking about water efficiency, it turns out that the best approaches might require thinking twice.
Publication date: 10/29/2018