Facilities Management always requires a close eye on costs. Unfortunately, the HVAC systems that customers depend on for comfortable living and working conditions consume a large part of annual budgets. Along with maintenance costs, the energy and water usage drive the cost of operating an HVAC system. According to the Facilities Engineering Journal, nearly half of the water use in commercial buildings occurs because of cooling and heating.
The operation of cooling towers and recirculating loops in an HVAC system relies on water. For cooling towers, water loss occurs in three different forms.
- Evaporative loss
- Mist and droplets carried by cooling tower airflow
Evaporative loss requires immense amounts of make-up water to maintain the operation of the cooling tower. However, the makeup water source may contain large amounts of iron, organic material, and biological activity. The mineral deposits left by evaporation result in water loss and can lead to increased energy costs. In addition, water loss happens when cooling tower airflow carries mist and droplets away from the system.
One commonly used method for preventing mineral deposits involves discharging water from cooling towers. Although discharging water results in water loss, ignoring the need for discharge allows mineral deposits to build and coat heat transfer surfaces. As systems work harder to maintain normal operation, breakdowns can occur that cause leaks and additional water loss. The possibility of accumulating mineral deposits also results in higher maintenance costs.
HVAC Systems Depend on Water for Heat Transfer and Cooling
Heating, Ventilation, and Air Conditioning (HVAC) systems work through a combination of thermodynamics, fluid mechanics and heat transfer. As the simplified diagram in figure one shows, the forces of compression, condensation, and evaporation work inside a chiller to extract heat energy from a room or facility and then transfer that energy outdoors. While the system extracts heat energy from the indoor air by turning liquid into a gaseous state, it transfers the heat energy outdoors by transforming gas into liquid.
Figure One - Basic Diagram of a Water-cooled Chiller and Cooling Tower
Once water enters the evaporator, heat transfers from the water to the refrigerant. The system distributes the chilled water to spaces that require climate control through the operation of a pump. Thermodynamics comes into play as the heat transfers from hot to cold and the chilled water absorbs ambient heat from the conditioned space. Then, fans in the air handling unit force the cooled air into the conditioned space.
The refrigerant also absorbs heat. As the low-pressure, high-temperature refrigerant travels from the evaporator to the compressor, the temperature and pressure of the refrigerant increase. Water surrounding the refrigerant pipes draws in the heat. From there, the heated water pumps into the cooling tower to release the heat. Condensed refrigerant moves through an expansion valve to reduce temperature and pressure before returning to the evaporator.
HVAC Systems Require Clean Water
While the chiller provides ventilation and thermal comfort, the cooling tower in an HVAC system rejects heat generated by the chiller. During operation, a cooling tower flushes airborne contaminants and dust that accumulate on the heat exchange surfaces. The contaminants include silt, pollen, algae, slime, calcium and magnesium salts, and biocides that increase toxic problems associated with biological growth and corrosion. Total dissolved solids in the water concentrate within the systems and eventually result in scale deposits that clog pipes and hinder pump operation.
Under normal conditions for process cooling, the cooling water absorbs airborne particulates that adhere to surfaces. The gradual accumulation of those particulates foul the cooling water, chilled water, and the surfaces of the heat exchangers. As the diagram in figure one shows, water-borne contaminants can circulate throughout the cooling system. Scale deposits and bacterial activity reduce the efficiency of the compressors found within chillers and reduce the cooling performance of the system. Without any treatment, the circulating water-borne contaminants can cause significant downtime for an HVAC system and an increase in costs.
Magnation Water Technologies Cut HVAC Costs
Many different strategies exist for reducing water consumption in HVAC systems. Those strategies include:
- Using automation to control and shut down towers during off-peak hours
- Prevent overflow conditions by installing upgraded fill valves and overflow alarms
- Redirect airflow within cooling towers with drift eliminators
- Reduce cooling load
- Install sensors and automatic bleed systems to monitor and maintain optimal water levels in cooling towers
- Implement preventive maintenance plans that check pumps, pressure relief valves, expansion tanks, backflow preventers, and automatic air vents for the purpose of maximizing water flow and heat transfer
- Install side-stream filtration
While viable, each of those solutions adds cost to an already costly HVAC system. In contrast to those measures, adding conditioned water to a water-filled HVAC system reduces pumping requirements and mitigates the environmental threat caused by biological growth. Rather than use hard, untreated water for cooling water makeup water, a better approach involves using soft, rainlike water that reduces or eliminates mineral scale deposits and--as a result--cuts the need for bleeding water from a cooling tower. Adding conditioned water to a cooling tower also significantly reduces the amount of total dissolved solids, organic materials, and biological growth in water....and the need for routinely adding biocides.
Although some solutions suggest capturing rain water or reclaimed water for cooling towers, applying additional biocides and other chemicals offsets cost savings. Magnation Water Technologies offers better chemical-free solutions for conditioning water for water-filled HVAC systems through the installation of Magnation’s Rainbolts and Aquabolts. Brian Malone, Chief Engineer, Able Engineering Services at The Gap Headquarters reports that:
“After installing Magnation, we observed 42% savings in energy, less scale formation, higher efficiency in cooling with less demand on compressors for cooling towers resulting in easier chilling cycles, better spray pattern on 15 year old equipment — the manufacturer had never seen that before! And, the cooling tower used to have a foul stink that no longer smells.”
(First Image Above, Magnation's Rainbolt, Second image Above, Magnation's Aquabolt)
For more information about how you may achieve substantial savings in water consumption and energy costs for your HVAC system, contact a water conditioning expert at Magnation at 888.820.0363.