According to the Department of Energy fans consume nearly 80 billion kilowatts of energy per year. Optimizing how fans work functionally in mechanical applications can reduce energy use and save energy dollars for end users. Assuming the design engineer selected the proper fan and proper installation in well designed system what can a facility manager do to save energy dollars and increase performance by looking at the fan systems in their building(s)? To make a good evaluation you need to look at several different factors in fan operation.
- Fan Control
- Fan Performance
- Fan Maintenance
HVAC Fan Control
The first area to be covered for saving energy dollars are schedules of the equipment. Schedules are appropriate for buildings that occupied during certain times of the day and do not apply to buildings occupied or in use 24/7. Where some buildings have DDC control systems with integration with all mechanical systems adding a schedule can save a lot of energy dollars for the building(s). For buildings that do not have DDC control or only partial DDC integration with mechanical systems adding timer switches or motion sensors to electrical lighting and fan circuits can save money.
Energy Saving Examples
For example, a church with no DDC systems can realize savings in energy dollars by installing timer or motion sensor switches in restrooms. With the proper circuit in place the timer or motion sensors can also be paralleled with the lighting so the restroom exhaust fan cycles on at the same time the lights cycle on so after the occupants depart the restroom the timer or motion sensor times out and the lights and the exhaust fan turn off. Compare that to a typical light switch where the occupants uses the restroom and does not turn off the lights after leaving the restroom and exhaust fan and lights continue to operate indefinitely waiting for someone to turn these energy consumers off. Depending on the cost of electricity at the location and the number of lights and fans used one can roughly calculate the savings realized by making a simple change to the lighting and fan circuitand integrating the two together. Of course you have to factor in the cost of making the change for a professional to wire the circuit and by the new timer or motion sensor switches however, under the right circumstances and conditions, savings can be realized after the first year making a simple change pay for itself for years to come.
DDC Energy Savings
If the building is equipped with DDC and these systems are integrated then the schedule for all integrated systems should be scrutinized so the mechanical and electrical systemsthat are integrated with the DDC systems can be placed on a schedule appropriate to the occupants use of the spaces being served by these systems. Looking beyond the schedule, minor changes in electrical circuits can make a big difference such as the example above especially in lighting circuits and exhaust fans that only need to run when a particular space is occupied. Motion sensors and timer switches can save energy dollars if implemented properly.
Modern Technology is a Win Win
In mechanical systems that are integrated with a good control system such as DDC more savings can be realized by optimizing the schedule to shut down unnecessary equipment when the building is not occupied. Strategies with schedules can include an automatic over-ride method so that occupants can be comfortable if unplanned occupancy of the space is needed. For example, a worker is working overtime to complete a task. The worker arrived on Sunday morning to finish a project that needs to be ready by Monday morning. Typical schedules call for the HVAC and lighting systems (aside from minimum emergency lighting) to be off or on a setback schedule only. The worker is uncomfortable and adjusts the DDC thermostat. Manual adjustment of the DDC thermostat triggers the HVAC and lighting system in the zone to activate to the normal schedule for two hours (or whatever the facility manager dictates). This allows the customer to be comfortable even in odd hours when work is typical not scheduled. Additionally, a good DDC system has the ability to monitor this extra energy use and bill the client of that space for extra energy use. It is a win win for the facility manager. Performing a system evaluation for the building should include scrutinizing schedules, how they operate, how they are controlled, and what is the return on investment for making simple changes that will save in energy dollars through control of the fans.
HVAC Fan Performance and Installation
Put simply fan performance is the power needed to produce a specific amount of airflow and pressure for a specific purpose. The Department of Energy outlines fan performance curve for efficiency as the BEP or Best Efficiency Point for the fan. Is the fan oversized and is it the correct horsepower for the application it is serving. By finding the fans BEP one can reduce wear and tear on the fan and increase performance. When the fan is operating outside of the BEP the bearing load and noise of the fan increases which decreases fan performance. The result is increased energy use and cost to operate the fan, reduce life of the fan, and increased maintenance (ie greasing the bearings, changing belts ect, ect, ect…..). For more information about fan efficiency you should consult a certified Test and Balance Company to find out if your fans are at their BEP. Another aspect of fan performance which may help is adding variable speed abilities to a fan system. Variable frequency drivescan save energy dollars in the long run for many fan applications that are currently running at constant speeds.
HVAC Duct Work
A Test and Balance Company can do an evaluation of fan performance and perform tests on the duct work system. In addition to performing Duct Air Leak Testing(DALT testing) of the duct work to ensure there are no leaks little tweaks can be made such as sheave changes and adjusting speeds of motors to optimize performance and gain more efficiency not only in energy savings but also in maintenance and repair costs. Additionally, a good Test and Balance Company can find design flaws where the system was changed in some way after initial construction or perhaps it was a design flaw that was missed in initial design of the system. Other hidden or unknown problems can also be found and repaired depending on the amount of testing the facility manager wants to do for the budget. In older buildings a good evaluation of the system and a plan of action to solve issues and increase performance can pay for itself very quickly in energy savings and long term maintenance and repair costs.
HVAC Fan Maintenance
Basic fan maintenance includes filter maintenance, inspecting fans and duct systems including fan controls, a good lubrication schedule for the fan bearings, replacing the belts, checking alignment, and cleaning the fan and blowers driven by the fan motor. Performing basic fan maintenance increases reliability by reducing unexpected downtime and increases performance leading to lower energy costs. Basic fan maintenance includes:
- Checking the system for unusual noise, high temperatures on sheaves or bearings, and unusual vibrations.
- Fans or blower wheels should be cleaned to work at optimum levels. This includes filters, heat exchangers, and coils. A more thorough look at the duct work for leaks, secure turning vanes, diffusers, and any baffles in the system should also be included in a periodic fan maintenance schedule.
- Belts should be tight and aligned properly from sheave to sheave. Adjustments on adjustable sheaves should be avoided without a Test and Balance company making or checking the adjustment for proper CFM of the fan.
- Motors should be checked for proper amp draw with a clamp on amp meter and this data should be compared to the motor data plate on the motor. For larger motors the motor can be megged with a special meter that reads megohms. Anything less than 2 megohms indicates a possible insulation failure and a future dead short in the windings.
- For VAV systems or pressure dependent variable capacity systems where a pressure transmitter controls the speed of the fan a magnehelic should be placed in the duct to check the calibration of the pressure transmitter on a periodic basis.
Saving energy dollars is directly related to a good fan maintenance schedule. Additionally slight changes to the controls, schedules, and electrical circuits can give the building additional savings in energy dollars.