Classroom Acoustics

Have you ever wondered if acoustics in learning spaces are impacting how a student hears and retains information? Communication between teachers and students is a key component of learning. Many teachers have different communication styles and each student also processes information differently, but if the student cannot hear the information then that is another problem all together. The good news is that it is a correctable problem. This is why high performance facilities are addressing the impact acoustics have on communication between teachers and students in lecture and group activity settings.

In 2002, the American National Standards Institute created ANSI S12.60, the Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. It was last updated in 2009. It provides a standard that sets specific criteria for maximum background noise and reverberation time for unoccupied classrooms.
Currently, ANSI S12.60-2002 is voluntary unless adopted by state or local jurisdiction. It has been adopted by several northeastern and some western school districts as a design standard. There are also European countries that have embraced it in addition to LEED for Schools and CHPS.

In 2010, The US Access Board, a federal agency advancing the ADA began the process of developing regulations for classrooms based on ANSI S12.60 to apply to all new classrooms nationwide in the future.

One of the key ingredients to good acoustics in a classroom that is less than 10,000 cubic feet is keeping the Reverberation Time between (0.4 – 0.6) seconds at 500 Hz. The time is increased to 0.7 seconds and greater for larger classrooms over 20,000 cubic feet) depending on the use. The specified reverberation times allow for optimum acoustic performance of a direct sound to reach the listener before the reflected sound becomes inaudible.

The Sabine Equation is used to calculate the Reverberation Time RT60

A typical classroom of 25x30 with 9 foot ceilings = 6,750 cubic feet

The Sabine Equation takes into account qualities of a typical classroom; such as the square footage areas for floor, walls, ceilings, marker boards, doors, windows, light fixtures and typical furniture; including the sound absorption coefficients of typical finishes used in a classroom. The results vary depending on the absorption qualities of the materials.

ANSI S12.60-2002, recommends that the most benefit of controlling the RT in a classroom under 10,000 cubic feet with 9 foot ceilings; is to place all the sound absorbing material on the ceiling. Part of the direct sound spoken from the teacher is being bounced (reflected) off the floor, ceiling and then the walls. At a volume less than 10 feet the critical location to absorb the sound is at the ceiling. Carpet on the floor provides very minimal absorption and mainly benefits reduction of foot traffic. In order to reduce the Reverberation Time to between (0.4 – 0.6) seconds at 500 Hz the ceiling material needs to have an NRC of 0.70 or higher. The Noise Reduction Coefficient (NRC) is an average measure of how much sound a material absorbs at 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz rounded to the nearest 0.05 when tested in accordance with ASTM C 423.

An (NRC) lower than 0.70 provides too long of an RT at 500 Hz. When the sound is reflected for too long, it is mixing earlier words with later words thus leaving the listener confused. Adults are good at using context clues to figure out what they thought they heard, but children; especially young students and those with learning disabilities or those taking a foreign language are academically affected by the missing words.

The Armstrong website offers a great alternative to calculating the Sabine Equation. It has an Interactive Reverberation Tool that automatically calculates the RT of a space after inputting the square footage and surface materials of a room. It provides numerical and audible before and after data, so you can hear the difference.

To access the tool, visit:
http://www.armstrong.com/commceilingsna/article21088.html

The Ceiling Attenuation Class (CAC) is another part of the puzzle, it blocks sound from escaping through the ceiling and being transmitting to the plenum space and over to the neighboring room, as well as mechanical noise. Air handlers are recommended to be located above spaces that are typically noisy such as cafeterias and corridors. It is preferred not to have units above classrooms, offices or libraries. A CAC of 35 or higher meets the ANSI S12.60.

Overhearing noise from a neighboring classroom seems to be a common problem for teachers. The Sound Transmission Class (STC) is a rating that measures the effectiveness of a wall (such as between classrooms, exterior and corridor walls) to block sound from escaping, just like the CAC for ceilings. The higher the STC the better the wall is at blocking sound transfer. For example, loud speech can be understood fairly well through an STC 30 wall, but should not be audible through an STC 60 wall. According to ANSI S12.60 the drywall classroom partition shall have a minimum STC of 50. This rating is achieved through the series of materials that are assembled. An STC of 50 is made up of two layers of gypsum board on each side of a metal stud with batt insulation. A cmu wall with insulation would also be acceptable. In addition, sealant is necessary to seal any penetration, air-gap, or “flanking” path that can degrade the isolation quality of a wall. Special consideration needs to be given to spaces where the noise transfer concern is other than from speech, such as mechanical equipment or music.

Due to the size of Lecture Hall spaces, these rooms benefit from a longer RT. It is recommended to have a 10’ ceiling or higher and install Gypsum board or a low NRC tile from the teaching wall into the middle of the classroom. Then provide an Acoustical Absorptive NRC = 0.75 or greater along three sides of the perimeter. In addition, acoustical wall panels on three sides of the room shall be added above 9’ to reduce echoes. This helps the direct sound reflect off the ceiling to the listener in the back of the room and then the perimeter tile and wall panels absorb it to NRC of 0.75 on the ceiling then the direct sound would not make it to the back of the room for the listener. The combination and location of the higher NRC at the perimeter creates the necessary balance.

The ceiling is the first line of defense in achieving good acoustics. Investigating how well acoustics are performing in your classrooms can provide valuable information to improving the learning environment for both teachers and students.

For the resources on this topic visit:

The School Noise/Quiet Classrooms www.classroomacoutics.org
ANSI Classroom Acoustic Standard ANSI S12.60 http://asastore.aip.org/
Armstrong www.armstrong.com/schools.

Net Zero Buildings

The other day I was reading an online article about solar and wind energy for residential units. One of the criticisms the article presented was that energy producing technologies at a residential scale won’t solve large-scale energy problems. Large solar or wind plants are needed if one wants to use green energy to solve any kind of large-scale problem. The author then went on to counter-point by asking the question why not the small-scale, local model? What if energy wasn’t produced at a large, centralized location, but instead it was produced at a small, more localized level on a widespread scale? Why can’t the building itself produce its own energy?

Traditionally, buildings constitute 40% of the energy consumption in the U.S. and E.U. There has been a push in the architectural community to reduce this percentage. Net zero or near zero buildings are gaining in popularity and importance for this very reason. Net zero or near zero buildings produce as much energy as they consume. This can be achieved through a combination of energy efficient building systems (geo-thermal and lighting selection), building envelopes (ICF and low-e glazing), building orientation (natural ventilation and shading), and energy producing systems (solar panels and wind turbines).   Net zero buildings don’t have to be fully autonomous. These buildings can still be hooked to the grid. During times of low energy demand, the building can run off its own energy production. If the building is producing more energy than needed, excess energy can be fed back into the grid. During times of high energy demand or low energy production, the building could then draw from the grid as needed.

The idea of having a local, decentralized source of power for buildings may seem far off, but the technology to do this exists right now. Maybe not every building produces its own power. What if different neighborhoods had their own individual power sources? A system like this would be more secure when there are power failures due to intense storms and blackouts. One could also have individual neighborhoods experimenting with new technologies and different systems combinations. What if the neighborhood elementary school became a power contributor?

Here is a diagram of a net zero home. These same concepts can apply to educational facilities. Image courtesy of http://blog.builddirect.com/greenbuilding/net-zero-home-building/. You can also find more information on net zero homes here.

Construction Phase - 2

As your construction project is nearing its completion, there are a myriad of items to follow up on in order to be able to move into the building. Within 60 days of the anticipated completion you should be in communication with the contractor about the suitability of the Work in place, note any defects that need correcting and reviewing the quality control reports. Communicate any unsettled claims with a recommendation for closing those issues. All of these items can be relayed through your design professional. The contractor should be checking the status of the various State and Local Agency's and jurisdictions for any outstanding items. The most important is to secure the Certificate of Occupancy from the city. With out this document completed, you will not be moving into your building! Within 30 days of completion you should be able to establish the date of 'Substantial Completion'. This is the date that you as the owner take over the building. All parties will sign the Substantial Completion form, owner, contractor and architect. This is the contractual end of the project in regards to the time frame, so this document is very important. It also establishes the day and time that the owner's building insurance takes over. Contractually, substantial completion is the day that the owner can 'use the building for it's intended use'. Attached to the substantial completion form is the punch list. The punch list is a list of all of the uncompleted items or items that need to be repaired, replaced etc. For example, the contractor needs to touch up the paint in room #1, or the base board in room #2 is defective and needs to be replaced. These are usually minor items that do not affect the moving in of the owner. Once all of the items on the punch list have been completed, and the architect receives all of the close out documents from the contractor, then the contractor can be paid the final payment. The close out documents include all of the warranties and guaranties of all of the equipment and products in the bldg, air conditioning equipment, roofing, carpet, doors, security systems, data systems etc. Also it includes affidavits that all the contractor's bills have been paid and that there are no outstanding liens on the project. One final item that we always specify is that the air quality of the building be tested prior to occupying the building. You must leave time for the building to breathe. By this I mean allowing the glues and paints to dissipate so that the building is safe to occupy. Contractors are required to use products that have low volatile organic compounds (VOC's). There will be however, a time period when even these products will smell bad. The worst offenders seem to be furniture manufacturers and the glues that they use to build with. Some of the glues off gas formaldehyde which takes approx 2 weeks to dissipate. You need to plan accordingly and leave enough time between moving in the furniture to your new school and then occupying it. Test the air quality of the building after 6 months of occupancy and again at 11 months to establish a base line. This way there can be no disputing that the air quality is safe and no damage has been done to students and staff that are using the building. With all that, now that you are finished with this project, let's get started on the next one! Michael D. King AIA

Greening Existing Facilities

I was listening to a webinar today on simple measures that can be taken to begin the process of greening existing facilities. It is important to establish a baseline to determine where improvements can be made. Below are a few of the items that Allan Skodowski, LEED AP discussed. More information can be found at www.thevirtualgreenexpo.com.

• Visit your building late at night. Conduct a night time audit of all spaces inside and outside of the building, including signage, lighting, plug loads, etc. What is on, what is off, what is just plugged in?
• Compare day vs. night data. What is on at night that doesn’t need to be on?
• Evaluate building start times vs. equipment start times. Often, HVAC systems are scheduled to come on at least an hour before the building is occupied so that it will be comfortable when people arrive.  How long does it really take to get into that ideal range?
• Read all utility meters to understand all utility charges and keep track of trends.
• Evaluate the effectiveness and efficiency of current HVAC systems.
• Utilize the EPA’s EnergyStar website for help. This tool can guide you through what data to collect and track for one or many buildings. (www.energystar.gov)

Once this data is collected, a baseline is established.  What simple improvements can be made without adding cost that will help improve operating costs?

 

• What is on at night unnecessarily? What can be monitored and turned off at night? Can site lighting be dimmed during certain hours? What basic training can be done to encourage staff to improve their habits?
• Try to cut 15 minutes off of the start and end times of HVAC or other timed systems and see if anyone notices the difference.
• Check controls, clean coils, change filters, check dampers on HVAC equipment. Is everything running properly and as efficiently as possible?
• Look at Energy Star’s recommendations for other possible improvements.

 

Many school districts also utilize energy management systems that constantly monitor HVAC and electrical systems. These can be incredibly useful in tracking trends and being able to visualize when something has become out of sync.