PROPER FIELD VERIFICATION OF PURGE AND SEAL LEAKAGE

WITHIN SEMCO TE, TS TEC, AND PDENERGY RECOVERY AND PASSIVE

DEHUMIDIFICATION WHEELS

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Properly designed energy recovery wheels leak/purge a portion of unconditioned outdoor air from the clean airstreams (outdoor and supply) into the contaminated airstreams (return and exhaust) across the energy wheel seals separating these airstreams. Outdoor air is also lost to the exhaust airstream through the purge section that is used to avoid the transfer of contaminated air that would otherwise be trapped within the wheel media as it rotates from the dirty (return) into the clean (supply) airstream.

Since the energy recovery wheel is the only device within the ventilation system that is “designed” to leak air, it logically becomes the suspected source of any excess air loss when the air balancing and commissioning process concludes that a shortfall in airflow exists. As SEMCO has been producing and testing its TE, TS and TEC wheels for more than 20 years, we are confident that a wheel that has received proper startup and setup will require the purge and seal leakage airflow predicted by the SEMCO submittal. As a result, we offer the following guidelines for helping to identify other potential sources of suspected airflow loss before scheduling a visit to the site by a SEMCO service technician. Following these guidelines has proven to be very effective in pinpointing airflow issues over the years and avoids the expense of a service call when the wheel is determined to be operating properly.

Basics of Purge Airflow and Seal Leakage

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• Confirm that the external static pressures measured to and from all four airstreams of the energy recovery system are as designed. Higher than designed external static pressures will reduce fan capacities and may increase wheel purge and seal airflows.

• Confirm that when taking airflow/pressure readings the frequency inverters feeding the fans and any VAV boxes or other dampers are locked to ensure that readings are collected at steady state conditions.

• Confirm that the external static pressures measured to and from all four airstreams of the energy recovery system are as designed. Higher than designed external static pressures will reduce fan capacities and may increase wheel purge and seal airflows.

• Confirm that airflows are measured within ductwork runs that allow for accurate readings or taken across components with a known face area and not low velocity inlets (i.e. louvers or filter banks, etc.).

• Check all field joints, divider walls separating the supply and return airstreams, walls where perforated panels are used, condensate traps, and electrical conduits to be sure they are well sealed

• Confirm that the SEMCO wheel seals have been properly set before any airflow commissioning and that the correct purge angle is being used based upon the final purge pressures that exist. For a detailed explanation, see the section titled “Adjusting the Seals” in the SEMCO Energy Recovery Wheel Owner’s Manual. Purge index settings are reprinted from the Owner’s Manual in Figure 1 of this document. Please contact SEMCO if there are any questions.

Important items to check when troubleshooting airflow shortages:

VENTILATION

EFFICIENCY

AIR QUALITY

ENERGY RECOVERY WHEELOWNER'S MANUAL

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SEMCO is happy to provide assistance when system airflow questions arise. In order to assist with system analyses, a minimum number of data points are required and should be carefully collected before requesting assistance.

Once the items listed in the previous section are checked and the control system stabilized with all ductwork connected, the following (minimum) data points should be recorded:

• Outdoor, supply, return and exhaust airflows measured in reliable duct locations

• The SEMCO wheel model number

• Purge index setting used (See Figure 1 and Table 1)

• Static pressures measured in locations shown as (P) within Figure 2. More pressure locations are helpful but these minimum locations are essential. Carefully measure and double check the static pressures around the wheel.

• Provide fan curves (if available), motor voltage and amps and measured RPM if available

• If there are two wheels in series (dual wheel unit) provide pressure loss across both wheels

Important data to collect before calling SEMCO for assistance:

After determining the difference between the return and outdoor pressures, use Table 1 to determine the correct purge index.

Use only when nopurge is required.

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1

FIGURE 1. Purge index detail.

Purge Index Setting

PressureDifference

Range(in. w.g.)

Enthalpy Wheel

Sensible Wheel

Passive Dehumid-ification Wheel

0.00 - 0.99 Consult SEMCO1.00 - 1.5 6 3 31.6 - 2.0 5 3 22.1 - 3.0 4 2 13.1 - 6.0 3 2 16.1 - 10.0 2 1 1

> 10.0 1 1 1

TABLE 1. Purge index setting.

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FIGURE 2. Typical ERU layout showing locations where static pressures need to be measured

How will the data collected be used to analyze system airflow discrepancies?

• Do the supply and return airflow quantities predicted by the pressure loss values measured across the energy wheel match that measured by the duct traverse? The pressure loss across the laminar flow wheel media is an excellent indicator of airflow. If there is not agreement, this could point to inaccuracies in the duct traverse.

• Do the measured airflow losses between the outdoor and supply airstreams match the gain measured between the return and exhaust airstreams? If excess air is leaking across the energy wheel these two values have to be the same. If there is a significant difference, then airflow losses through the AHU or ductwork likely exist or the readings reflect inaccuracy in the flow measurements

• Do the actual purge pressure and seal pressures match those used for selecting the wheel and determining purge/seal leakage? If pressures are higher than designed, purge and seal leakage will be greater than shown within the submittal. The purge angle setting may need to be adjusted.

• Are the AHU external static pressures measured in agreement with the design values? Do the fan performance parameters (RPM, amps) agree with the field measured airflows?

Most airflow discrepancies can be resolved without a field visit by SEMCO service when this data is carefully obtained and evaluated. Most airflow issues are quickly resolved by simple steps such as improved sealing of field joints and penetrations, measuring airflow in a reliable location and proper energy wheel purge and seal adjustment.

SEMCO will analyze the data collected at the site and other information provided to assist the design and installation team in determining the following:

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A SEMCO TE-35 wheel was designed to provide 29,000 cfm of supply and return airflow and was installed in a larger custom built ERU operated at high static pressures. The specified purge pressure was 10” across the wheel and the purge volume and seal leakage shown on the SEMCO submittal was 2,851 cfm (approximately 1,550 cfm of purge flow with the remainder seal leakage).

The air balance report reviewed by the commissioning agent listed a supply airflow of 30,040 cfm and an outdoor air flow of 35,286 cfm. The commissioning agent assumed that the difference in measurement (5,246 cfm) was attributed to excess wheel purge and

seal leakage since it exceeded the 2,851 cfm submitted for this purpose. The project would not be accepted by the owner until this airflow discrepancy was resolved so a visit was arranged to the jobsite to collect the data and execute the wheel isolation test as previously described.

The data collected from this field visit is summarized in Table 2. Data was collected in accordance with Figure 2 of this document and two tests were methodically completed; one with the wheel seals and purge section blocked off and a second with the purge and seals set properly.

Example from an actual project:

As previously mentioned, since the energy wheel is the only device “designed” to leak air, all suspected air losses are commonly thought to be associated with the wheels. In practice, this is not the case. Large custom AHUs are often found to contain numerous sources of air leakage, especially when higher pressures are involved. On occasion, it is important to quantify how much airflow is associated with the recovery wheel (purge and seal leakage) and how much is associated with other factors, including measurement error.

A proven procedure exists to isolate the wheel leakage from other factors and, when necessary, a SEMCO service technician can visit the site and work in conjunction with the air balancing contractor to effectively quantify air leakage associated with the recovery wheel (within measurable accuracies).

The procedure consists of measuring the data listed within this document in the “Important Data” section on

page 4. This data is collected two times. First with the recovery wheel purge closed off to a setting of 0 and with all seals pushed up against the face of the wheel (wheel not operating). In some cases, contractors also choose to tape off seals to ensure there is not leakage between the sealing shelf and the bottom of the labyrinth seal (although this has not proven to be necessary).

Next the same data is collected but with the purge section and the seals adjusted properly. The difference in the measured airflow losses comparing the wheel seals and purge blanked off and with the seals and purge properly set provides the best indication of actual purge and seal leakage.

This measurement of isolated wheel seal and purge leakage can then be compared with the quantity included within the SEMCO wheel submittal provided that the actual field measured purge pressure values match that used for the submittal process.

What if excess wheel purge/seal leakage is suspected or there is a specified requirement to quantify purge and seal leakage?

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Field Results from Sample Project:

Readings CollectedPurge Closed and Seals

Pushed Up to Wheel Surface(Wheel locked off)

Purge Open and Seals Adjusted to Proper Gas

(Wheel Operational)Wheel supply entering pressure 5.02 4.89Wheel supply leaving pressure 4.15 4.03Wheel SA flow based on pressure loss 30,026 29,681Supply airflow based on traverse 30,862 30,040Outdoor airflow based on traverse 33,972 35,286

Wheel return entering pressure -4.85 -4.76Wheel return leaving pressure -5.69 -5.59Wheel RA flow based on pressure loss 29,798 29,443Return airflow based on traverse 29,940 28,993Exhaust airflow based on traverse 30,338 31,396

Supply Side Leakage based on traverse 3,110 5,246Return Side Leakage based on traverse 398 2,403Submitted wheel purge and seal leakage flow N/A 2,851

TABLE 2. Example of field measurements and analysis completed to quantify purge/seal leakage

Findings and conclusion

Based on the findings it became clear that the cause of the airflow discrepancy was an outdoor airflow measurement error. Upon investigation it was determined that this airflow reading was taken at the inlet to a filter bank since there was not an outdoor air duct to use for a more reliable traverse. All other data was in very good agreement and was supported by fan curve analyses). All concluded that the wheel purge and seal volumes were in compliance with the submitted values and the commission process was completed and accepted.

1) In both tests, the airflow predicted based on the measured wheel pressure loss agreed very well with the supply, return and exhaust traverse readings. The outdoor air readings did not, making them suspect (see red values in Table 2).

2) The leakage estimated using the return/exhaust airstreams was consistently less than the losses calculated using the outdoor/supply traverses. The return/exhaust leakage estimates agreed well with the submitted (and anticipated) wheel purge/seal values.

3) The outdoor to supply air leakage measured with the wheel purge and the seals blocked off (3,110 cfm) was found to be excessive unless substantial leakage existed within other sections of the ERU. This was carefully checked and only minor leaks were discovered.

4) The wheel seal and purge volume calculated as the difference in leakage measured by traverse across both sides of the wheel averaged 2,017 cfm. The submitted value was 2,851 so it was clear that there was not excessive leakage attributed to the wheel.

Conclusion:

Due to a policy of continuous development and improvement the right is reserved to supply products which may differ from those illustrated and described in this publication. Certified dimensions will be supplied on request on receipt of order. © SEMCO LLC 2015 All Rights Reserved. The SEMCO logo is a registered Trademark of SEMCO LLC.

SEMCO® is a global leader in air

management. We specialize in the design

and manufacture of a wide range of air

climate and air movement solutions.

Our collective experience is unrivalled. Our

constant aim is to provide systems that

precisely deliver the best indoor air quality

and performance, as well as maximize

energy efficiency.

SEMCO® A Fläkt Woods Company Corporate Headquarters

1800 East Pointe Drive

Columbia, Missouri 65201 USA

573 443 1481

sales.semco@flaktwoods.com

WE BRINGAIR TO LIFE

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