HVAC contributes nearly 4% of annual carbon emissions.[i] Decarbonizing heating and cooling is essential as efforts to battle climate change continue. But relying on conventional cooling towers likely won’t get you there. From design improvements to more aggressive climate-friendly models, innovative cooling towers can help make meaningful green impacts.
Traditional designs
When it comes to cooling, conventional towers — usually with a counterflow or crossflow design — work well. But conventional designs present several challenges, both in general and to eco-friendliness.
Even if going green isn’t the goal, a traditional cooling tower has several design features that decrease its overall value.
- Side louvers: The most-used style of cooling tower with a top-mounted fan requires louvers — openings through which air passes into the tower to perform the cooling operation. These extend off the side of the tower, and most manufacturers require up to double the louver height (often 12-18 feet) of freeboard clearance to ensure adequate airflow and heat rejection. This takes up an enormous amount of space that not all buildings have available. Conventional crossflow towers placed too close together are prone to recirculating the exiting air during prevailing wind situations, as the top of their louvers are very close to the exit air stream. This can substantially reduce performance.
- Top-mounted fans: In addition to requiring space-hungry side louvers, the top-mounted fans on a traditional cooling tower design can make maintenance dangerous. Technicians must climb to the top of these stories-high structures or use specialized lift equipment to reach the top safely. Also, towers with this design often have a single fan or a pair of fans, which means the tower will be completely out of service if the fan breaks or requires maintenance.
- Open basin: A conventional cooling tower utilizes an open basin. Not only does this allow sediment and other debris to enter the system, but it also allows sunlight to contact the water. This creates an ideal “breeding and feeding” ground for algae and more sinister growth, like Legionella bacteria.[ii] Combatting all forms of contaminants in the system requires lots of maintenance on the basin and nozzles and excessive chemical treatment to avoid the risks of deadly Legionnaires’ disease.
- Field-erected installation: Conventional cooling towers are very heavy and must arrive in pieces to be field-erected. This process takes much longer than a factory preassembled installation and requires special equipment and laborers to be completed correctly and safely.
And, if eco-friendliness is your priority, there are additional concerns for traditional cooling tower designs.
- Drift: An average cooling tower with a load of 1,000 tons can consume 20 million gallons of fresh water each year. Drift, the aerosolized droplets of water and chemicals released into the surrounding air during the cooling process, contributes to water loss and potential environmental impacts. The certified safety rating of drift eliminators ranges but, on most conventional towers, is around 0.005%.[i] At this drift rate and with a typical heat load on a building, this can amount to 216 gallons of lost water a day, or 78,840 gallons each year from a 1,000-ton cooling tower, not to mention the impact of the chemicals on the surrounding ecosystems and buildings.
- Pump head energy use: Physics bears out that the taller the tower, the higher the height the water must travel vertically when pumped (the head) and the harder the pump must work. The harder the pump works, the higher the pump head energy use and costs will be. A conventional counterflow tower is 15 to 35 feet tall, and a conventional crossflow tower is 18 to 35 feet tall.[ii]
Conventional towers can get the cooling job done. But they usually won’t be as efficient and will often bring additional challenges. The shift to eco-friendly towers, thankfully, can be incremental and can make an immediate impact.
Shifting to eco-friendly cooling towers
Many equate “going green” with dollars flying out the window because several environmentally conscious solutions completely replace a legacy product or are a greenfield build. Eco-friendly cooling towers are a more practical solution that can be installed alongside legacy towers to augment cooling and allow for the gradual transition to the greener alternative.
An approach to placing the fans on the bottom eliminates the freeboard area, allowing the towers to be assembled side-by-side in any configuration. The smaller, increased number of fans means greater redundancy and better energy use, as the tower can operate at a partial load during off-peak times. The tower is shorter, which lowers pump head, saves energy, and makes maintenance safer. The inverted design removes the open basin and side louvers, which significantly reduces not only Legionella growth risks but also water consumption. And the tower design also improves on the standard drift rating by an additional 0.001%, or several thousand gallons of water saved a year.
Closed-circuit towers
Many environmentally aggressive areas, like California and Europe, are pushing for the exclusive use of closed-circuit cooling towers. This tower design saves substantial water, energy, and chemicals compared to its open-circuit counterpart. Because the system is closed, new water intake is reduced, and less water is wasted; the same is true for the treatment chemicals in the water. The cooling in a closed-loop tower is usually accomplished via heat-exchanging coils, which is more efficient than the air-cooling method used in open-loop systems, thus using less energy. The closed-circuit model is also preferred for maintaining air quality, as it can further reduce drift. They also help maintain system water quality, as fewer contaminants can enter the system, and there is no place for sunshine to foster algae or bacterial growth.
The core challenge with most CTI-certified, closed-circuit cooling towers is maintenance. Even with stainless steel, the closed-loop design will require routine inspections and maintenance to prevent downtime from catastrophic malfunctions due to metal- and water-related problems, like rust and scaling.
Sustainable materials
Remember to look at a cooling tower’s life cycle when thinking about sustainable options. The conventional cooling tower market heavily relies on steel. But steel production requires an enormous amount energy and releases nearly a billion tons of carbon emissions each week, as it often relies on fossil fuels like coal.[iii] For cases like cooling towers, lower-carbon alternatives are worth considering.
Fiber reinforced polymer (FRP), an engineered material consisting of reinforcement fibers, polymer resin, and additives, provides an extremely strong and durable material for both the structural and internal components of cooling towers. Because it is much lighter than steel, much less of it is needed to produce a single FRP tower, lowering the total by-weight carbon footprint as well as the emissions produced to get the tower to the site. It also arrives at the site in a single piece and often is installed within an hour per 1,000 tons. FRP is also inherently corrosion-resistant, so the structure, walls, and internal elements — like coils and fill media cannot rust — decreasing the overall need for maintenance. Many companies are investing in widening end-of-life options for FRP towers, though most can remain in like-new condition for many decades, which is often twice or three times longer than metal, so less goes to waste.
Case Study: Whisper Valley Community
A housing community focused on sustainability in Austin, Texas, selected geothermal cooling systems powered by ground source heat pump (GSHP) technology to significantly reduce greenhouse gasses produced by traditional HVAC.[iv] Their GSHPs use closed-loop systems, circulating refrigerant through underground pipes to efficiently transfer heat year-round. To enhance the GSHP’s efficiency, FRP cooling towers were added to dissipate heat extracted from the earth and ensure optimal performance. The design allowed the modular towers to blend in with the community surroundings without taking up too much space.
Whisper Valley has achieved net zero status. Their eco-friendly homes boast an average HERS rating of 18, representing a 75%-80% increase in energy efficiency compared to standard homes. The cooling towers contribute to significant reductions in energy consumption, water usage, chemical treatment, and maintenance requirements.
Most projects aren’t aiming for net zero. But this case study shows how a cooling tower built with decarbonization in mind can help further sustainability goals and save water, chemicals and energy.
[ii] https://www.cdc.gov/mmwr/volumes/72/wr/mm7249a1.htm
[iii] https://www.enr.com/articles/2738-new-ideas-ashrae-standard-could-limit-legionnaires-toll
[iv] https://www.long.com/blog/tower-tech-vs.-conventional-cooling-towers
[vi] https://towertechusa.com/case-studies/net-zero-community-cooling-towers
![Figure 1. U.S. Energy-Related Carbon Dioxide Emissions, 1990-2013. [2]](https://www.achrnews.com/ext/resources/ESMAG/ISSUES/2020/07-July/Carbon-and-Water-Consumption_Feb22-2019.jpg?height=200&t=1594601673&width=200 "Figure 1. U.S. Energy-Related Carbon Dioxide Emissions, 1990-2013. [2]")
