Monday, March 19, 2018
The acoustical environment created by an HVAC system may or may not be a critical issue for tenant or building owner, but understanding the sound data published by manufacturers is necessary in order to make an appropriate diffuser selection. Since diffusers are the system components in closest proximity to the occupants, they must be selected properly in order to produce suitable room sound levels.
The first thing to understand is the meaning of the NC numbers that manufacturers publish. NC stands for noise criteria. This is a single number that assigns an overall room sound level based on relative loudness and the speech interference level of a given sound spectrum. NC charts plot sound frequency (Hz) versus sound pressure level (dB). Sound pressure is the sound level measured in a space after some amount of sound power
has been absorbed by the environment.
Here are some recommended sound levels for common applications as found in the ASHRAE Handbook of HVAC Applications:
- NC20 - Concert and Recital Halls
- NC25 – Places of Worship, Music Rooms
- NC30 - Conference Rooms/Hospital Patient Rooms/Hotel Rooms/Meeting Rooms/Courtrooms with Unamplified Speech/Classrooms
- NC35 - Operating Rooms/Courtrooms with Amplified Speech
- NC40 - Open Plan Offices/Lobby Areas
- NC45 - Gymnasiums
NC15 is generally accepted to be total silence or the threshold of hearing for healthy adults. You might wonder why some manufacturers publish sound levels less than NC15. The purpose of doing this is to allow multiple products that may be individually inaudible to be added together to predict a combined sound level.
NC30 is typically the lowest sound level that can be achieved in most buildings without going to special lengths to sound proof the structure. NC30 is fairly easy to achieve in a suburban or rural setting, but much more difficult in an urban or industrial environment. Spaces requiring sound levels less than NC30 include broadcast and recording studios as well as opera and concert halls.
Although it’s been said that a noisy diffuser is good diffuser because you can hear it working, that’s not true. There are many issues that can cause diffuser noise to be audible including inlet conditions, neck-mounted dampers, and undersized or misapplied devices. Diffusers tend to make their highest sound levels in octave bands 4 (500 Hz), 5 (1000 Hz), and 6 (2000 Hz). These are known as the “speech interference bands” because they are the same frequencies we use when speaking. A noisy diffuser would therefore create a poor speaking environment and should be avoided.
The best way to avoid noisy diffusers is to select them for sound levels at least 10 NC points lower than the desired room sound level. This allows the diffusers to disappear into the background without contributing to the room sound level. As a general rule, diffusers should not be selected for sound levels greater than NC25 for any occupied spaces other than industrial applications.
For information on this topic/product, please contact Randy Zimmerman at firstname.lastname@example.org or Titus Communications at communications
Wednesday, February 14, 2018
Thursday, January 11, 2018
One of the more frequently asked questions we receive in application engineering is in regards to surface mounting Titus diffusers. When a ceiling grid is not present, surface mounting is specified and the installation questions arise. Linear diffusers are available with concealed mounting, square and rectangular diffusers with square or round inlets are not.
The most important thing to know about surface mounting is that it normally requires additional framing to which the units will be secured. We often receive calls for mounting instructions after the sheetrock has been installed which is too late to provide framing without removing the installed surface.
|Titus mounting frames make installation of grilles, diffusers and other ceiling components in plaster and sheet rock ceilings as simple as inserting them in a standard T-bar type ceiling.|
Framing requirements will vary from one job to the next, but there are some general guidelines and terminology we use.
Obviously installing screws in the face of a diffuser will work as it does for grilles but the duct return flanges behind diffuser edges are generally not available to provide a secure mounting base for screws. Also, many surface mount frames do not have a flat surface nor is there a screw hole fastening option available. Furthermore, screw fastening certainly does not enhance the aesthetics of the installed diffuser.
All sheetrock is mounted to ceiling joists. Joists are usually parallel to each other and spaced at two to three feet apart depending on local building codes, and in most cases, the framing for the diffuser can be mounted to the top of, and perpendicular to the joists. Screws are then used to mount the back pan to the framing. Framing members should be centered on the diffuser location to allow sufficient clearance for the diffuser inlet and associated duct. Additional care must be taken so as to avoid any protrusions or features that will occupy the space necessary for the framing on the rear side of the diffuser. Framing should also be at a depth that will allow the diffuser to firmly seat against the sheet rock. Most diffuser back pan heights are less than the depth of the joist. The sheet rock or ceiling surface is installed into an opening provided for the diffuser.
The diffuser core should be removed prior to installation to allow for screws to be installed in the top of the back pan transition; this is the flat portion on the rear of the back pan. Screws are then used to secure the back pan to the framing. It is helpful to use washers to prevent the screw heads from being driven through the back pan if the framing is not flush to the rear of the pan. In most cases the screws can be placed in a manner to not be visible from the occupied space after the diffuser core or face is re-installed.
As an alternative to the framing process, and one that we suggest if the ceiling surface has been installed without prior framing for the diffuser mounting, is to use our rapid mount frame. The TRM frame can be installed in the space between the joists following the installation of the ceiling.
The TRM replicates a standard ceiling grid module and a lay-in (type 3) frame diffuser. The diffuser can then be laid in the TRM frame. The TRM frame does add a border to the finished appearance of the diffuser, but also can be utilized as an access port to the space above the ceiling by simply pushing the diffuser up and out of the opening.
While the TRM does represent additional diffuser cost, the reduced labor requirement and flexibility of the installation sequence offers a distinct advantage.
The TRM is available in steel and aluminum and is ordered as a separate line item. Remember, when using the TRM frame, the (type 3) diffuser frame must be used instead of the (type 1) diffuser frame.
For information on this topic/product, please contact Mark Costello at email@example.com or Titus Communications at communications
Monday, December 4, 2017
Laboratories are not known for their energy efficiency. These spaces can consume up to 10 times more energy than office buildings, leading facility managers and engineers to prioritize finding ways to reduce energy consumption and operating costs – without sacrificing efficiency. One way to do that is by using chilled beam systems, which have grown increasingly popular in the U.S. in the last decade. Chilled beams have proven to be viable alternatives to traditional Variable Air Volume (VAV) systems, demonstrating energy savings upwards of 20% in laboratories compared to VAV Reheat.
To better understand how and why chilled beams are effective in laboratories, let’s examine the usage of these systems, strategies for effective design and operation in laboratory environments.
How Chilled Beams WorkThere are two types of chilled beams, passive and active.
Passive chilled beams cool spaces using natural convective forces and include a heat exchange coil in an enclosure that is suspended from the underside of the building structure. Chilled water flows through the coil and cools the surrounding warm air; the denser cool air falls back into the space. Passive beams require separate air diffusers to carry dehumidified ventilation air into the space, usually at the floor level. For this reason, they are rarely, if ever, used in laboratories.
Active chilled beams rely on pretreated primary air delivered from central air-handling units (AHU’s) to pressurize a series of small induction nozzles within the chilled beam unit. These nozzles create jets of air causing room air to be induced across a coil where flowing water heats or cools this (secondary) air.
Both passive and active beams are designed to provide sensible cooling only with the latent cooling (i.e. space dehumidification) being accomplished by the central AHU’s. Depending on the lab use and loads, the primary air is delivered to the active chilled beams as constant or variable volume, with the cooling/heating output being controlled by either two position or modulating control valves to vary the water flow through the integral coils. Chilled beams can be integrated into suspended ceiling systems or hung from the structural slab for exposed use.
Because chilled beams provide most of a space’s sensible cooling, the central air handling system can be much smaller than usual since its primary purpose is to provide the ventilation air and latent cooling to the space. This effectively decouples the sensible cooling from the ventilation requirements. And since chilled beams have no moving parts, maintenance is limited to infrequent cleaning of the coils.
Laboratory HVAC Energy Use
The ventilation requirements for laboratories are different from the needs of a typical office building. Minimum ventilation rates are dictated by safety requirements rather than cooling or heating loads, while maximum rates are determined by either the make-up air requirements for the fume hoods or the sensible cooling requirements of the space (if the equipment cooling load is high). There are special requirements for laboratories where chemicals or gases as present as well. They cannot use recirculating AHU’s, so the ventilation air must be 100% outdoor air at all times.
Overall, these parameters can result in an air system sized for ventilation air changes rates from 6-to-12 or more, depending on the lab use and equipment loads.
A traditional "all-air" system will typically deliver cool air to the building at around 55°F when there is demand for OA dehumidification, or to satisfy the sensible cooling requirements of the highest load lab in the building. This often results in a mismatch of ventilation air and cooling requirements, forcing the zone VAV boxes to reheat the cooled air to prevent over-cooling the space when sensible loads are low. Even more reheating occurs when ventilation air is increased to provide make-up air for the fume hoods, resulting in lower efficiency.
And decreased efficiency hurts the bottom line: Energy studies have shown that cooling and reheating air can account for as much as 20% of the total HVAC energy costs in laboratories.
Eliminating Reheat and Saving EnergyActive chilled beams can help boost energy efficiency in a number of ways.
One is by eliminating most of the reheat energy resulting from decoupling ventilation and cooling demands. With active chilled beams the ventilation air can be delivered at a warmer temperature through a 100% outside air AHU, commonly known as a dedicated outdoor air system (DOAS). With the DOAS primary air set to around 65-70°F space overcooling is far less likely to occur, even in labs calling for high volumes of make-up air for the fume hoods. The water coils within the chilled beams provide cooling or heating capacity on a zone-by-zone basis. During OA dehumidification hours, the DOAS unit removes moisture by cooling the air to 55°F or below and is reheated with energy recovered from the exhaust air using enthalpy wheels, heat pipes or run around coils.
Another is through using water to transport heat, resulting in an air system size reduction of 60 percent compared to VAV Reheat. This feature reduces overall fan energy consumption and is ideal for laboratories with high sensible loads and low fume hood densities.
The increased efficiencies associated with chilled beams also help laboratories maximize their space. The reduced reheat and boosted transport efficiencies of water mean the main plant items (chillers, boilers and AHU’s) can be smaller than with a traditional system’s. The duct distribution system is also more compact, which reduces service congestion in the ceiling interstitial. Finally, a smaller system can translate into lower first costs for an HVAC system compared to VAV Reheat.
There is a challenge with using chilled beams in labs, however: the need for dual chilled water temperatures. Specifically, a low temperature circuit (LTCHW, 40-45°F) for the DOAS and medium temperature circuit (MTCHW, 56-58°F) for the active chilled beams. The most common strategy is to design a closed secondary loop separated by a plate and frame heat exchanger, ensuring that the LTCHW cannot accidentlly find its way into the active chilled beams. That could potentially cause condensation on the coils.
Building Humidity Control
The best chilled beam system designs equip the building with a small number of room dew point sensors. This allows the building management system to monitor the humidity across the building and reset the DOAS air dew point or reschedule the MTCHW loop temperature if the space dew point rises above a preset temperature. Facilities engineers can use the room dew point sensors to precisely control the amount of OA latent cooling at the DOAS unit to further reduce energy costs, an operational strategy that is more difficult to accomplish with a VAV Reheat system. Despite being used in early system designs; pipe mounted condensation sensors are rarely used today since room dew point monitoring provides enough advance warning of potential condensation.
Chilled Beams Misconceptions
Despite growing in popularity over the last 10+ years, there are still a number of persisting myths and misconceptions about chilled beams. For instance, despite there being several successful installations in the likes of Florida, Hawaii and even the Caribbean, there is still hesitancy among designers and owners to use the system in humid climates because of condensation concerns. The reality is the system can be used in any building where the space humidity can be controlled; however, energy savings will not be realized in applications where the internal latent gains are high, such as wet labs. In other cases, engineers may be reluctant to consider active chilled beams because they are simply unfamiliar with the design of these systems.
Cost is also a concern. Mechanical contractors unfamiliar with chilled beams will be wary of underpricing a system they have never previously installed, but several case studies have shown chilled beams have been installed cost competitively with traditional systems.
It didn’t happen overnight, but a larger number of engineers and facility managers have realized – and are realizing -- the advantages chilled beam systems can offer to laboratory applications, specifically in terms of energy and space savings. Debunking misconceptions and educating laboratory owners on the construction of and design using chilled beams is the first hurdle to overcoming barriers to adoption. Then it’s about showing what the technology can do. Those who have installed these systems have realized greater energy efficiency, substantial cost savings and improved performance.
For information on this topic, please contact Nick Searle at firstname.lastname@example.org or Titus Communications at communications
Tuesday, October 10, 2017
Monday, September 11, 2017
Titus has participated in the variable air volume (VAV) diffuser market for a number of years now. We currently offer two great options; our T3SQ-4 Thermal version and T3SQ-2 Digital version. They both have features that make them great for their particular application. The benefit of the thermal T3SQ-4 is that it requires no power, making it ideal for applications where energy is the focus. The benefit of the digital T3SQ-2 is you get the great accuracy you normally get with digital controls as well as the added benefit of individual comfort control.
Helios - the ambient-light powered digital vav diffuser
Introducing HELIOS, the new line of energy-harvesting VAV diffusers that creates a new standard of individual comfort and control for indoor environments. Powered by the same ambient energy-harvesting technology as our popular EOS diffusers, HELIOS is easy to install, requiring no special wiring or ductwork. That saves money!
Wherever individual indoor comfort is needed, HELIOS is a perfect solution. It’s easy to install. Each individual unit uses a unique digital logic system so it can operate on a narrow temperature band, giving more unique zones and much greater user control. Gone the days of inter-office thermostat feuds.
HELIOS solves many problems for engineers and contractors. The individual comfort functionality addresses LEED EQ Credit 6.2, while the fact that units require no outside electrical power means complying with LEED EA Credit 1, too.
The HELIOS brings new meaning to the term "stand-alone". For the installer, and the individual placing the order, the best feature for this diffuser is no complicated wiring or cabling to count or keep track of. No longer do you have to concern yourself with whether or not you have enough, or the correct, cables. The distance from the power supply is not an issue anymore because the power source is the light in the room. No longer will you have to drag cables across ceiling plenums and down walls or do any time-consuming trouble shooting because you suspect a cable is bad. Like our T3SQ, the HELIOS still has various neck sizes to accommodate different size ducts. It also has a neck heater for supplemental heat. Look for this innovative product to be available in the Fall of 2017.