4 FM quick reads on HVAC
1. Water Treatment Programs Can Solve Three Problems
Today's tip comes from James Piper, contributing editor for Building Operating Management.
When HVAC water circulation systems go unattended, problems can develop rapidly. If those problems are not swiftly detected and corrected, they can cause downtime, reduce operating efficiency and shorten equipment life. Proper water treatment is warranted. Without proper water treatment, both open and closed systems are at risk for three types of problems: corrosion, scale and biological fouling.
Corrosion is the process of metal dissolution. Uncorrected, it can lead to the loss of system integrity.
Scale occurs when suspended solids precipitate out and become attached to interior surfaces of pipes and heat transfer equipment. Scale can significantly reduce the efficiency and capacity of the entire system.
Biological fouling occurs when bacteria, fungi and algae grow in the circulating water. Uncorrected, it can foul heat transfer surfaces, plug lines and contribute to corrosion.
Water treatment requires careful planning, a commitment of resources, proper training of maintenance personnel and a focus on safety. But a properly implemented program can reduce or eliminate the effects of corrosion, scale and biological fouling.
2. Retrocommissioning Can Solve Three Common Controls Problems
Today's topic is retrocommissioning.
Controls that weren't properly designed or programmed, or that have been overridden or otherwise gotten out of whack, can increase energy costs while making building occupants uncomfortable and shortening the life of equipment.
Most of the issues that retrocommissioning identifies have to do with controls, say experts. Perhaps the most common problem is scheduling. Often equipment is running more than it needs to. A pump, for example, may be running longer than it should to satisfy building demand - possibly even all day and night — without anyone knowing it. Not a glamorous problem, perhaps, but it's expensive. The pump will wear out sooner than it should; meanwhile, energy dollars will be wasted.
A second big category of problems has to do with economizer dampers. They may be stuck in one position or there may be errors connected with the control sequences or the sizing of dampers.
Setpoints - supply air temperature and pressure as well as condenser and chiller water temperature - are a third common opportunity for improvement. Retrocommissioning can tune those setpoints to match demand more closely. Retrocommissioning — or recommissioning, if the building was commissioned in the past — is especially important in multitenant buildings and other facilities that undergo a significant amount of change.
3. Condensate Line Maintenance for Good IAQ
Striving for good IAQ in your facility means keeping an eye on a million little things, such as condensate drain lines. Condensate drain lines should be adequately trapped to overcome fan pressures and should be piped to drains on both rooftop and interior HVAC equipment.
If the static pressure of the fan on the air handling unit is greater than the depth of the trap and the condensate drain is on the negatively pressurized side of the air handling unit, air is pulled back through the drain trap. As the air enters the interior of the unit, it's like a little geyser of water from the drain line. Water from the drain line and the condensate pan could hit the interior insulation in the unit, and once that happens it becomes a likely site for microbial growth.
Condensate drain lines should not only be adequately trapped, but should be piped away from HVAC equipment to roof or floor drains. Condensate water that is not piped to drains can accumulate in low spots on the roof or in mechanical rooms. This water again becomes a breeding ground for microbes and could infiltrate the HVAC system through a rooftop outdoor air intake or a mechanical room that is acting as a mixing plenum for return and outdoor air.
4. Monitoring Is an Essential Part of Water Treatment Program
Effective water treatment is a complex process involving steps designed to address system-specific problems such as scale, corrosion and fouling. Each category of problem requires its own specialized treatment. That may be the use of biocides to control microbiological fouling, the addition of chemicals to limit the build up of scale, and the use of different chemicals to reduce corrosion.
But it's not enough to implement those measures. Rather, it is essential to monitor the water within the system to ensure that problems are not developing. For example, many biocides are corrosive. If too high a level of biocide is used, it may cause corrosion; if the level is too low, however, the biocide may not be effective at controlling microbiological growth. What's more, make up water conditions can change from season to season, or if a new source of make up water is used.
To ensure that the water treatment program is effective, weekly monitoring is generally advisable. For example, dip slides can be used to keep track of bacteria levels. Although testing involves labor and possibly some equipment costs, that cost is a small price to pay in comparison to the problems it can prevent.
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