Zoned HVAC systems are like the breath of fresh air in hot seasons. In a two-storied home where a single air conditioner is connected to one downstairs thermostat, the second floor gets much hotter than the first floor. The difference in temperature can even be 2 to 5 degrees. Zoned systems offer an amazing solution to this issue where it enables your AC unit to reduce the temperature in the upper and lower floors separately. However, not all zoned systems work in the same way.
Why it is better not to add zones to a standard HVAC system?
When you add zones to your HVAC system, your HVAC technicians need to install dampers to maintain the air volume in different zones in your location. These dampers stay inside your ducts and respond to calls for air in different zones, opening and closing as required.
Now, the problem arises when the dampers have different zones for opening and closing, this forces your air conditioner to send lots of air through less ductwork.
This situation in the HVAC world is termed as high static pressure. Although every ducted HVAC system is prepared for a certain amount of static pressure, it becomes difficult when there is excessive pressure and you start moving a huge amount of air through less ductwork.
This could lead to
- A system break-down
- Less optimal airflow
- Excessive humidity in summer
- Increase in expense to operate
For all these above-mentioned reasons zoning is never recommended for a single-stage system.
Enter the bypass damper and bypass duct
To control the excess static pressure at the time when zone dampers remain closed, the excess air needs to be redirected. Apart from that, another duct needs to be installed instead of drilling a hole in your ductwork. This duct is known as bypass duct which has a bypass damper in it. the bypass duct builds a connection between your supply plenum and your return ductwork. The damper inside has the power to either restrict or allow air to enter the bypass based on the condition.
So, if you own a standard single-stage air conditioning unit and also thinking of adding zones, you need to make sure that your HVAC contractor installs bypass components.
Facts about bypass dampers and ducts
- Bypass components are unable to fix poor HVAC design
- In case you have a standard system with zones and you do not have a bypass, you should consider having one
- In case you have a standard system, try not to add zones
- When you add zones to a single system, make sure that the installer measures the static pressure for each zone
- You might even need a SOD also known as Shut Off Damper
So, the conclusion is zones are not required when you have a basic air conditioner that turns on when there is a need for cool air and turns off when fulfills your thermostat setting. On the other hand, when you already have zones and a system like that add a bypass.
You must keep in mind that a zoned system with improper bypass is a deadly combination. Similarly having a zoned single-stage system without a bypass is also not recommended as it can cost you big time and result in a whole lot of discomfort.