by Rebecca Gatzke
The routine maintenance requirements of all equipment need to be considered in the initial system design. If equipment is difficult to maintain, chances are it will be ignored, reducing its effectiveness and life expectancy.
The maintenance requirements of filters, blowers, and motors are well known, but the level of familiarity with energy wheels isn’t as high. Understanding and implementing maintenance requirements for energy wheels will improve performance, effectiveness, and the life of the wheel.
Most manufacturers’ energy recovery products are designed with routine inspection and maintenance in mind. The components (wheel, filters, motors) should be easily accessible through removable doors.
Routine Energy Wheel Maintenance
Routine inspection: The following maintenance tips apply to various wheel types. As with all rooftop equipment, routinely inspecting the ERV (energy recovery ventilator) is a good practice. Typically, outdoor air filters need to be changed once a quarter. At that time, maintenance personnel can also quickly inspect the wheel.
Besides checking the wheel itself, the service technician should also inspect the following:
Drive belt: Drive belt(s) should be inspected annually. Normal operation eventually causes stretching or wear on the belt(s). Once this occurs, the belt(s) should be replaced.
Turn the energy recovery wheel by hand to verify free operation. Inspect the belt, which drives the energy wheel rotation. Make sure the belt rides smoothly through the pulley and over the wheel rim.
Air seals: Turn the energy recovery wheel by hand to verify free operation. Check that the air seals, located around the outside of the wheel and across the center (both sides of wheel), are secure and in good condition.
Air seals that are too tight will prevent proper rotation of the energy recovery wheel. Recheck the air seals for tightness. Air seal clearance may be checked by placing a sheet of paper, like a feeler gauge, against the wheel face.
To adjust air seals, loosen all eight seal retaining screws. These screws are located on the bearing support that spans the length of the cassette through the wheel center. Tighten the screws so the air seals tug slightly on the sheet of paper as the wheel is turned.
Cleaning schedule: Creating a regular cleaning schedule is critical to maintaining the performance of the energy recovery wheel. The schedule should be based upon particles present in the exhaust air-stream, operating hours, and climate.
The following guidelines may be used in determining the appropriate cleaning schedule for several applications.
- Reasonably clean environments: You’ll find these in schools and office buildings, for example. Reduction in airflow or latent effectiveness may not occur for four to five years.
Energy recovery wheels are self-cleaning in nature with respect to dry material. Because of the counter-flowing airstreams and laminar flow through the wheel, smaller particles enter the media and pass through. When larger particles attempt to enter, they’re blown away from the wheel as it rotates into the counter-flowing air-stream.
- Environments with moderate occupant smoking. Measurable changes in latent energy transfer and some loss of airflow can occur in less than two years.
Tars and fine oils present in cigarette smoke may condense on and cling to the wheel, clogging pores in the desiccant, which are required for effective moisture transfer.
- High smoke environments: You’ll find such environments in lounges, nightclubs, bars and restaurants, and bowling alleys, for example. Latent effectiveness may be severely reduced in less than six months, along with some loss of airflow, due to the build-up of tars and nicotine.
- Industrial applications: These can include welding shops or other companies where machines ventilate high levels of smoke or oil particles. Applications such as these may require cleaning every three to six months.
In all applications, loss of indoor moisture control during the cooling season could indicate the need to clean the energy recovery wheel.
Cleaning Procedure for Polymer Wheels
Cleaning the energy wheel to regain latent effectiveness and full airflow is a relatively simple process. Depending upon the severity of the application, there are two “soaking methods” that can be employed: the 10-minute or overnight soak.
The 10-minute soak— Soak the segments in a solution containing any household detergent, such as Formula 409™, Fantastik™, or a coil cleaning solution and water. Soak each segment for ten minutes and rinse under tap water.
This method is sufficient for environments with moderate to no occupant smoking (clean application). Wheels in clean applications only need to be cleaned every four to five years.
Overnight soak— Soak the segments in a solution containing any household detergent, such as Formula 409™, Fantastik™, or a coil cleaning solution and water for approximately 15 hours. Rinse the segments with tap water.
The overnight soak is most often used for high smoking applications where tars and oils build up on the wheel. Wheels in smoking applications should be cleaned every three to six months. Staining from the tars and nicotine may occur, but it won’t affect the performance.
It may be beneficial in applications where frequent cleaning is required to have a second set of segments on hand. The clean set of segments can replace the dirty set, and the dirty set washed and stored.
Other Wheel Maintenance Considerations
So far we’ve only addressed the polymer energy wheel. One other common energy wheel medium is aluminum. The physical differences between the two media lead to differences in their maintenance requirements.
Will Washing the Energy Wheel Remove the Desiccant?
The continuous ability to transfer moisture between airstreams depends on the bond between the desiccant and energy transfer surface. The polymer wheel uses a unique, proprietary process to permanently bond the silica gel desiccant to its surface. The desiccant is mechanically locked into the polymer without the need for adhesives.
Testing the effectiveness of wheels applied in nightclub and lounge
settings before and after repeated washings has proven that it doesn’t significantly deteriorate the latent effectiveness of the wheels; those wheels showed less than a four percentage point reduction in latent efficiency after three years in operation.
Most aluminum wheel manufacturers recommend cleaning the wheel by vacuuming it, but, because fine oils and tar cling, vacuuming has been proven ineffective. Aluminum wheel manufacturers suggest NOT using any detergents on the wheel, because, as the owners manual states, it may destroy the bond between the desiccant and the aluminum.
Wheel removal— The cassette of the polymer wheel slides out of the housing for wheels less than 56 in. in
diameter. Polymer wheels larger than 26 in. are segmented, with the weight of each segment ranging from 4 to 23 lbs. The segments may be removed without the use of tools.
The majority of aluminum wheels are not segmented, therefore the entire hub assembly must be taken apart to remove the wheel from the cassette. On larger units, the wheel can’t be removed from the unit at all.
Durability— Polymer is obviously non-corrosive, and it's also flexible. If, during maintenance, a screwdriver or other tool impacts the media, it will go right through the media wraps without damaging the heat transfer matrix.
The face of an aluminum wheel is similar to the face of a coil; the fluted design is very delicate. If impacted with a tool of any sort, the flutes bend and block air from passing through the wheel.
Remember that wheel cleaning is crucial to maintaining the energy recovery effectiveness and life of the wheel. Follow these general tips and your customers’ equipment shoud last a long time.
Rebecca Gatzke is a senior applications engioneer with Greenheck, Inc. She is responsible for new product development and product innovation for the energy recovery business unit and provides technical support for engineers, contractors, and Greenheck business partners. Gatzke can be reached via e-mail at firstname.lastname@example.org