FAQs - Energy Recovery Ventilators
- Can we incorporate supplemental heating and/or cooling devices into the ERV?
- Does the energy recovery wheel act like a filter?
- How does the total energy wheel compare to flat plate exchangers in energy transfer efficiencies?
- How is the energy recovery wheel cleaned? What can be used to clean it?
- How much cross leakage is expected through the energy recovery wheel?
- Is it difficult to change an ERV wired for 460/60/3 to 208/60/3?
- Is the ERV performance data certified?
- What is desiccant dehumidification?
- What is the energy recovery wheel made of?
- What is the expected life of the energy recovery wheel?
- Where can energy recovery be used?
- Can the plate develop frost?
- How do I clean the plate?
- What applications could I use a plate-type heat recovery device?
- What certifications does the PV carry?
- What is the plate made of?
Q: Can we incorporate supplemental heating and/or cooling devices into the ERV?A: Yes, using our Model ERT. This model allows downstream heating and cooling of the preconditioned air from the energy recovery wheel. The available cooling options are direct expansion (DX) coils or chilled water coils. The heating options are electric heat or hot water coils.
Q: Does the energy recovery wheel act like a filter?A: No. These products are designed to induce laminar or smooth airflow, which allows small particles to pass through the wheel. Pre-filters are available to prevent dust and other outdoor pollutants from entering the building. Larger particles, which may impinge on the wheel surface, are blown off as the wheel rotates into the other, counter-flowing air stream.
Q: How does the total energy wheel compare to flat plate exchangers in energy transfer efficiencies?A: Metal flat plate exchangers transfer sensible heat (temperature) only and do not transfer moisture (latent), which reduces the total effectiveness of the energy transfer. A 75% efficient plate typically only has a total effectiveness of 30%. Even plates, such as the Mitsubishi Lossany core, transfer limited latent energy. Latent effectiveness for Lossany typically is in the 40% to 50% range. Greenheck energy recovery products transfer moisture, as well as sensible heat. Our wheel is about 70%-80% efficient in both latent and sensible. (Lower velocity will tend to have higher efficiency.) This dramatically increases the total effectiveness of the energy exchange and significantly shortens the pay back period of the unit. The April 1997 Update had an insert article titled "Plates vs. Wheels", which addresses this question in much greater detail. The Greenheck web-site contains several technical articles including "Plates vs. Wheels".
Q: How is the energy recovery wheel cleaned? What can be used to clean it?A: Cleaning can start after the wheel media is removed from the cassette housing. The energy wheel media can be cleaned in any of the following ways:vacuumingsoaking the wheel media in cleaner or detergent/water solutionspraying the wheel media with cleaner and brushing through pressure washing (on a low setting). Details on cleaning are on page 17 of the ERV 1998 IOM. Cleaning fluid temperatures should be kept below 140°F, otherwise damage to the media could occur.
Q: How much cross leakage is expected through the energy recovery wheel?A: Cross leakage through the energy recovery wheels ranges from 2% to 5% between the supply and exhaust air streams. This amount of cross leakage is minimal and in comfort ventilation applications is perfectly acceptable. These leakage rates are also acceptable for Class 3 Air (toilet room exhaust). According to ASHRAE Standard 62-89R committee, up to 10% cross leakage of Class 3 Air is acceptable for the purposes of energy recovery.
Q: Is it difficult to change an ERV wired for 460/60/3 to 208/60/3?A: When you have an ERV wired for the wrong voltage, it can be corrected. However, voltage change outs on ERVs are time consuming and expensive. Several components must be changed out including: Fan motors, if the motors are not multi-voltage. Fan drives, if the motor frame size changes. Motor starters, contactors and overloads will need to be changed out in most cases. Disconnect size may change. Wiring will need to be rerun to handle higher amp draws at the lower voltage. Please double check voltage requirements before releasing orders.
Q: Is the ERV performance data certified?A: Currently, only the air performance on Greenheck ERVs is certified through AMCA. The American Refrigeration Institute (ARI) and the American Society of Heating, Refrigeration Engineers (ASHRAE) are currently defining energy transfer ratings and test methods, respectively. Both will be completed within the next year. Greenheck has taken a proactive role on the ratings committee helping to define proposed test methods and rating systems for energy transfer in energy recovery technology.
Q: What is desiccant dehumidification?A: Desiccant dehumidification includes a heating device (regenerator) in the exhaust air stream to raise air temperature to 140 degrees F or greater. The hot air causes most of the moisture to be released from the wheel. The result is a capability to dry outdoor air to very low humidity levels (as low as 10 grains of moisture/lb of air). Desiccant dehumidification equipment is expensive and consumes a lot of energy with the regeneration process. It is really designed for processes requiring very dry air. Comfort ventilation applications are really a misapplication of this product.
Q: What is the energy recovery wheel made of?A: Greenheck energy recovery products use a "total energy recovery" or "enthalpy" wheel. The energy transfer media in the wheel is constructed of lightweight polymer with permanently imbedded silica gel desiccant. The polymer media transfers the sensible heat, while the silica gel desiccant transfers the moisture or latent energy.
Q: What is the expected life of the energy recovery wheel?A: The energy recovery wheels used in Greenheck products have been operating in commercial and institutional buildings for over 10 years. In that time, performance of these wheels has been excellent and only occasional freight and installation damage has been cause for replacements. In addition to a long, reliable history of performance, Greenheck warrants the energy recovery wheel for five years.
Q: Where can energy recovery be used?A: Energy recovery can be applied in any commercial or institutional comfort ventilation application. Some examples of applications: Educational facilities: Schools, Dormitories, and Offices.Commercial facilities: Office buildings, hotels/motels, beauty/nail salons, retail stores, and restaurants.Institutional facilities: Nursing homes or assisted living buildings.Public buildings: Fire and police stations, jails and prisons, military facilities. The pay back period of an ERV is quickest in an application meeting the following criteria:Air conditioned buildings requiring outdoor ventilation air. Climate has a 0.4% design wet bulb greater than or equal to 75°F or a design dew point greater than 66°F. The Southeastern, Midwestern and Eastern United States have excellent climates for energy recovery. Energy recovery pay back is lengthened in the Western part of the US due to climatic conditions. However, there are still many applications and climates where energy recovery provides significant benefits.Buildings with long hours of operation, like nursing homes, fire stations or retail stores.
Q: Can the plate develop frost?A:
Yes, the PV could frost if the outdoor air is cold enough and there is enough moisture in the exhaust air from the building. Controls are offered that will mitigate the frosting of the plate unit.
Timed exhaust is an economical way of dealing with frost. When the plate is frosting (determined by plate exhaust air temperature), the supply blower will turn off while the exhaust blower continues to blow warm air through the plate which melts any frost.
Face and bypass is another option for applications where there must be a constant supply of outdoor air. If the plate begins frosting, the face damper closes (while the bypass damper opens) and diverts the outside air around the plate. Once the plate has defrosted, the dampers switch and the outside air is brought through the plate.
Q: How do I clean the plate?A: Vacuuming is an effective way to clean dry particles off of the plate's surface. Simply washing the plate with water (water hose-not a pressure washer) is also an effective way of cleaning the dirt and dry particles off. The PV includes a drain pan for easy draining of any water that comes off of the plate during cleaning or under normal operating conditions.
Q: What applications could I use a plate-type heat recovery device?A:
Low leakage applications are a good place to use a heat recovery instead of the energy wheel. The plate ventilator units have 0% cross-leakage through the core, which compares to 1-4% through the energy wheels. The plate recovery device does not need a motor or belt to transfer energy.
In regions where latent loads are not a concern, the plate-type recovery device can be an economical and very effective way of transferring dry energy.
Q: What certifications does the PV carry?A: The PV unit is ETL listed for electrical safety. It carries the AMCA seal for Air Performance, and the AHRI certification for energy performance on the plate. These certifications are important to have on the unit to reassure engineers or owners that the performance published by a manufacturer is what they will actually get.
Q: What is the plate made of?A: The PV unit uses an aluminum cross-flow heat exchanger (plate) to transfer sensible energy between the supply and exhaust airstreams.