Navigating the Twilight Zone: The Hidden Flaw in a Zoned Duct ...

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When it comes to HVAC zone controls, it can be tempting to skimp on the quality of the damper because the cost can add up quickly if you need multiple dampers.  This is a mistake, zone dampers have lots of moving parts and can be a source of many problems.  A quality damper and proper installation are critical to a functional zoning system that will continue to operate for many years or decades.  Scroll below to the "HVAC ZONING DAMPER GUIDE" for installation &sizing information.

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ZoningSupply.com ONLY carries the highest quality dampers.  The most durable & well-made (IN THE USA) HVAC zone control dampers available.  5 Year warranty standard.  The full rubber-seal gasket makes for the lowest air leakage.  All-metal construction (including shaft) & tension washers LOCK the shaft in place so it can't be crushed from any direction.  Industry LEADING BelimoTM actuator used on power damper.  One end is crimped for easy hard duct install & there are ridges (ribs) on each end for "zip-ties" to fit securely when using flex duct.  Click here to buy or see the full damper guide below.

A zoning system can typically use the same duct sizing as a traditional single-thermostat system.  It is important to properly size and install a pressure relief damper as well as properly balance the zones.  To minimize bypass air flow, increase the duct capacity by one size for each zone less than 25% of the total system air flow capacity.  for systems with more than 4 zones, increasing the duct & damper sizes of the smaller zones (or all the zones) will minimize the amount of pressure relief needed when only the smallest zone damper is open. NOTE: Connect dampers directly to the plenum when possible and branch off smaller ducts going to different areas within the zones.  USING this trunk/branch duct design will minimize cost and reduce air noise.

ZONE BALANCE: To maintain optimal equipment performance in a typical zoning application, it is preferable for all zones to be similar in size.  This does not mean that every zone must have EXACTLY the same heat load requirements but the system will work most efficiently if they are approximately the same size in CFM airflow capacity.  This guideline will minimize the amount of pressure relief (bypass) necessary.  NOTE: Avoid creating more than three zones with or zones smaller than 20% of the total equipment CFM capacity when using single speed equipment to ensure best performance.

AIR NOISE: To minimize air noise, install the dampers as close as possible to the supply plenum.  A good rule for acceptable air velocity to minimize noise is 600 - 700 FPM.  Use chart in the bypass sizing graphic below to check the NORMAL CFM chart to select a size damper & duct that will accommodate the zone's CFM.  Using this chart will ensure the air velocity isn't too high.  For zones with multiple dampers, the total (sum) of all damper's CFM will be the zone CFM.

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RETURN AIR:  Undersized return air ducts/registers can result in problems such as increased run time, even equipment failure due to Insufficient airflow (CFM & VELOCITY).  To ensure the Return Air is large enough, verify that its surface area is sufficient to pass FULL SPEED blower CFM. Ensure ALL zones have unrestricted airflow path to a return air grill equivalent to the zone CFM.

SPRING or POWER DAMPERS?:  Power dampers are typically more durable, they have much higher torque and use only a fraction (1/4) or less power than spring dampers.  Spring dampers should only be used when running 3 wires is not possible or it is required by code.  SmartZone can handle either type but if you have an older zone panel, spring dampers may be required.  Power dampers provide a superior reliability and typically are much quieter than spring dampers, even though the cost is slightly higher, it is worth it for the better product quality.

REDUCE BYPASS NECESSITY: Sometimes it is desirable to reduce the size of bypass due to space constraints or other code compliance. One of the simplest ways is by allowing all NON-calling zones to “leak” some air. This can be done with a couple of different methods. First, if ECOJAY power dampers are being used, there is a “minimum open stop” that can be adjusted to leak as much or as little as desired. This works very well but lacks the sophistication of an automated method of “leaking” like the SmartStatic product that uses a pressure sensor to leak the non-calling zones just the right amount. LEARN MORE ABOUT SMARTSTATIC…

Probably the BEST method to reduce the need for bypass is using the fan speed (only on HVAC equipment with multi-speed equipment). DIP SWITCH # 4 on SmartZone can be set to “LOCKOUT” or “2+ ZONES”. This feature will only allow high speed (second stage) heat or cool when two or more zones are calling for the same mode. The newest version of SmartZone version 3.0 also has the ability to take advantage of HVAC systems that have multi-speed fan (often used for dehumidification). This works much the same way as the DIP SWITCH # 4 setting but instead of second stage heat or cool, it only allows low speed fan if one zone is calling and high speed if two or more are calling.

Contact us to discuss your requirements of Bypass Damper(ar,ru,es). Our experienced sales team can help you identify the options that best suit your needs.