EcoRenovator - View Single Post - Ideas for zoning a forced-air system

abogart · 01-24-12, 03:33 PM

I have been doing some research on this subject. It seems that zoning forced air systems is entirely doable and actually not all that uncommon. I found an interesting design manual about it here...

Zoning System Design Manual

Apparently, proper airflow over the heat exchanger or evaporator coil is maintained during periods of low CFM demand by incorporating a static pressure bypass duct, which reroutes excess pressure in the supply plenum back to the return duct. There are automatically modulating bypass dampers that use a pressure sensor, but they are pricey (about $250 each). I would rather go old school and use a weighted-arm-type damper for about $85.

Honeywell SPRD12 static pressure regulating damper, counter balanced, weighted arm to control bypass

This setup would definitely work in my current system. The trick would be to redo the ducting so that all of the upstairs rooms are on one supply trunk, and the downstairs rooms are on the other. That way the house can be easily divided into two zones, upstairs (during the night) and downstairs (during the day). I would only need two rectangular zoning dampers and a static bypass damper to pull it off. Factor in another thermostat and the HVAC zone controller, and it looks like it could be done for around $500. Not bad!

01-24-12, 03:33 PM	#7
abogart Efficiency Afficionado Join Date: Jan 2012 Location: Michigan, US Posts: 68 Thanks: 21 Thanked 6 Times in 4 Posts	I have been doing some research on this subject. It seems that zoning forced air systems is entirely doable and actually not all that uncommon. I found an interesting design manual about it here... Zoning System Design Manual Apparently, proper airflow over the heat exchanger or evaporator coil is maintained during periods of low CFM demand by incorporating a static pressure bypass duct, which reroutes excess pressure in the supply plenum back to the return duct. There are automatically modulating bypass dampers that use a pressure sensor, but they are pricey (about $250 each). I would rather go old school and use a weighted-arm-type damper for about $85. Honeywell SPRD12 static pressure regulating damper, counter balanced, weighted arm to control bypass This setup would definitely work in my current system. The trick would be to redo the ducting so that all of the upstairs rooms are on one supply trunk, and the downstairs rooms are on the other. That way the house can be easily divided into two zones, upstairs (during the night) and downstairs (during the day). I would only need two rectangular zoning dampers and a static bypass damper to pull it off. Factor in another thermostat and the HVAC zone controller, and it looks like it could be done for around $500. Not bad!