Acoustical Effects of Liners in Terminal Units

We take lots of questions from designers and acoustical consultants regarding how terminal unit liners affect room sound levels. As you are probably aware, our published sound levels are based on ½” thick dual density fiberglass or EcoShield unless otherwise stated. Our TEAMS selection software adjusts the acoustical performance based on the lining material, but still many people question these results. So let’s look at the various liners.

Standard Liners – Most people consider these to be ½” dual density fiberglass or EcoShield. These materials perform almost identically with respect to both thermal insulation and acoustical performance. We therefore do not distinguish between the two when estimating sound levels.

Heavier Liners – When additional protection against condensation is desired, most people opt to go with 1” dual density fiberglass or EcoShield. For applications involving attenuators and/or fan-powered units, the additional thickness may provide reduce radiated and discharge sound levels.

Foil Liners – For critical environment applications, most people choose either SteriLoc or foil-faced EcoShield. These liners are intended to prevent insulation fibers from reaching the air stream. For this reason, these liners are installed using galvanized Z-brackets and foil tape to seal all cut edges. The foil covering reduces the sound absorption while slightly increasing the transmission loss of the casing. This could result in slightly higher discharge sound levels and slightly lower radiated sound levels.

Dual Wall – For specifications calling for dual wall construction, we offer UltraLoc. UltraLoc is solid 22g. galvanized steel over 1” dual density fiberglass. This liner is considered a heavy-duty alternative to the foil-faced liners. It is intended to prevent insulation fibers from reaching the air stream, but it is less susceptible to damage in the field. The solid inner wall prevents any sound absorption and greatly increases the transmission loss of the casing. This generally results in higher discharge sound levels and lower radiated sound levels.

Engineered Polymer Foam Insulation – For specifications calling for non-fiberglass liners, we offer FibreFree. This is a polymer foam insulation. It provides a reasonable amount of sound absorption while its density provides a slight increase in transmission loss to the casing. For most customers, the sound difference between this liner and exposed fiberglass or EcoShield would be negligible. It should be noted that EcoShield is a lower cost option when meeting non-fiberglass spec requirements.

There are many reasons why people question sound performance with regard to liners. For instance, switching the liner from ½” EcoShield to 1” EcoShield doesn’t change the sound levels of a DESV without an integral attenuator. This is surprising, but it doesn’t have any effect because the damper is at the discharge end of the casing. This means that the air stream never really comes in contact with the liner, so there’s no effect on discharge sound levels. And the extra thickness doesn’t increase the transmission loss of the casing enough to reduce the radiated sound level by any measurable amount.

If we look at that same DESV with an integral attenuator, going from ½” EcoShield to 1” EcoShield still doesn’t change the radiated sound level, but the additional casing length allows the choice of liner to reduce discharge sound levels. Sometimes people question why a particular liner doesn’t seem to provide the expected drop in sound level. That often occurs only looking at sound levels in terms of noise criteria (NC) levels. Very often sound reductions may be occurring in so-called non-critical octave band frequencies that do not change the overall room sound level. This can be deceptive because although the NC may remain the same, the overall resulting room sound quality may be improved by removing annoying high frequency tones or sound in the speech interference bands (500, 1000, 2000 Hz).

You might wonder about the effects of heavier critical environment liners like foil-faced EcoShield, SteriLoc, and UltraLoc. These liners are thicker and have a hard facing, so they tend to block or reflect sound. They don’t absorb sound energy, so they often increase discharge sound levels and render optional attenuators ineffective. They do however add enough transmission loss to the casing to lower radiated sound levels. The same is true to lesser extent for our FibreFree material. It provides sound absorption to a lesser extent than a soft liner, but the density provides some reduction in radiated sound levels.

Dual duct terminals are available with integral mixer/attenuators. The main purpose of this feature is to mix hot and cold airstreams together. Any resulting sound attenuation really only serves to reduce the amount of noise generated by the mixing process, so bear this in mind. These are really air mixers and not attenuators.

Fan-powered terminals, both series and parallel-flow, are affected differently by liner selections. Soft liners like fiberglass and EcoShield allow sound to radiate in all directions with a little additional sound coming from the induction port. Increasing the thickness of a soft liner will tend to provide a slight decrease (1-2 NC points) in radiated sound.

Estimating the effects of a high transmission loss liner like UltraLoc in a fan-powered terminal is very difficult for several reasons. First of all, this type of liner tends to block sound radiating from the top and side panels. That can reduce the chance of having low frequency noise coming out the bottom of the unit, but it tends to create a very directional and concentrated noise from the induction port. If this directional noise travels across the ceiling and is absorbed by the ceiling plenum, room sound levels could be very low. If this sound reflects off nearby ductwork or is contained by a constricted plenum space, the room sound levels could be higher.

Lab testing in accordance with ASHRAE Standard 130 is of little use when predicting the effect of these liners, because these products are tested in reverberant chambers. This type of sound room removes all directionality from the sound source, so it isn’t very useful when dealing with a directional sound source. Therefore the best way to determine the performance of a fan-powered terminal with a high transmission loss casing is through mock-up room testing. Titus offers this service to our customers whenever it is required.

Hopefully this information will help improve your understanding of terminal unit liner options and how they may impact the acoustical performance when making product selections.

For information on this topic, please contact Randy Zimmerman at rzimmerman@titus-hvac.com or Titus Communications at communications@titus-hvac.com.

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ECM Retrofit - Things to Consider

As most people in our industry are well aware – a newer fan motor technology can provide huge energy savings and extended service life. There are many existing buildings full of older permanent split capacitor (PSC) motors that typically last for 10-12 years in a series fan-powered unit. These motors are 20-60% efficient and service life may suffer if operating at lower speeds. As soon as these motors start showing an increasing pattern of failures, building owners who are aware of electronically-commuted motors (ECMs) may express an interest in upgrading to this newer technology. ECMs have a minimum efficiency of 80% and a service life of 25-30 years. It is possible to attempt this type of retrofit, but there are a few things to be aware of.

Were the unit models in question ever available with ECM?

If a particular unit model has been available with an ECM option, all the parts and pieces should be readily available. Of course the most important part is the motor itself and it must be programmed for a given blower cabinet. Although it may be possible to assemble parts and pieces that will fit into an existing unit, motor programming could be an issue if the unit was never developed for an ECM option. Depending on the number of units involved, it may be cost prohibitive to develop custom ECM programming for each cabinet size. One possible solution would be to factory program the ECMs for constant torque rather than pressure independent control. This could limit or eliminate the need for any development work.

Will the existing electrical service handle the ECM?

The ECM replacement will likely be rated for a different horsepower and full load current. Although the resulting operating current draw should be less than the PSC motor it replaced, motor nameplate ratings may require upsizing the supply circuit in order to provide the necessary electrical safety. Obviously, this could greatly complicate the retrofit process and add a lot of cost.

Did you know that the UL/ETL listing will be voided?

Any field modifications to a UL/ETL-listed product that results in a change of electrical characteristics such as current draw or motor horsepower will void the listing. This is true even if factory parts are field installed by factory personnel. Once a UL/ETL-labeled product leaves the factory, any changes that do not match the data found on the unit label will void the listing. The only way to reinstate the label would involve having a UL/ETL inspector visit the jobsite and field label the units. This could be very costly but may be unnecessary if local inspectors will not be involved in the retrofit process.

Have you considered the total amount of parts that will be required?

ECM retrofit doesn’t just mean replacing the motor. It generally means replacing the motor, the speed control, and blower assembly. It will likely also require additional components like power cables, communication cables, and a power filter. It could even require changing internal options like line and/or motor fuses.

Have you considered the cost of field labor required?

All of these modifications will have a field labor cost. It could easily take an hour to access each unit and swap out the various parts. It may take longer depending on the accessibility of a given unit. In an occupied building this work may need to be carried out at night or on weekends. Additional hours of electrician time would be required for any modifications to the supply circuit.

In summary

Although the temptation to upgrade from PSC motors to ECM is strong, remember that the process is not as simple as just changing motors. It involves many more parts and could require electrical work too. That doesn’t necessarily rule out the possibility on an ECM retrofit. Many building owners have contacted their local Titus representative to investigate the possibilities. ECM technology is quickly taking over this industry and it’s important to understand exactly what a retrofit may entail so that you can provide the right answers to your customers.

For information on this topic, please contact Randy Zimmerman at rzimmerman@titus-hvac.com or Titus Communications at communications@titus-hvac.com.

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