Can you run HVAC fan continuously for better air circulation?
DegBuild
| Posted in Energy Efficiency and Durability on
Hello everyone, we’ve recently done a bunch of HVAC work to address air quality and humidity concerns. We installed a Santa Fe ventilating dehu which is controlled by a Haven IAQ controller which measures the air in the duct. Currently it’s configured so that the HVAC fan doesn’t come on when the dehu is running or when the ventilating damper is open, only the dehu fan is running in those cases.
This setup works okay for us when either the AC or heat is coming on very frequently. But during times of the year where the temps are more mild the dehu fan doesn’t seem like it’s powerful enough to circulate the fresh air through the house enough. The house still feels comfortable but our air quality monitors in the bedrooms pick up high concentrations of CO2 and VOCs.
We have two ideas for how to address this. We could wire up the HVAC fan to the dehu so that whenever the dehu fan comes on, the HVAC fan also starts up. Our original HVAC installer has told us that the 2 fans will compete with each other a bit so it might mean slightly lower CFM from the ventilating dehu.
The other option is to install a smart thermostat like the ecobee and set a schedule to run the HVAC fan 5 minutes (or some other interval) every hour. This option is probably more expensive but it would allow us to adjust this depending on the season.
Some days we’ve set the HVAC fan to run continuously and it does seem to help with air quality numbers in the house. Just wondering if there’s any downsides to running the HVAC fan too much.
Any opinions on these options or other recommendations would be appreciated.
Thanks in advance!
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Replies
good question. interested in the answer as well
Do you know how many watts your HVAC fan pulls?
I have seen some over 500 watts. Running 24/7/365, that's 12 kwh per day, over 4000 kwh per year.
I would go with "wire up the HVAC fan to the dehu so that whenever the dehu fan comes on, the HVAC fan also starts up" .....depending on the run times for the dehu
With these kinds of numbers, youve also effectively got a small electric resistance space heater running all the time adding to your cooling load
Our original HVAC installer has told us that the 2 fans will compete with each other a bit so it might mean slightly lower CFM from the ventilating dehu.
This isn't the issue. The dehumidifier needs low airflow. With higher airflow the coil in the dehumidifier can't cool the air enough and it doesn't dehumidify as much. That's why the manufacturer insists on a lockout.
What you want is:
* Heating or cooling locks out dehumidifier
* Dehumidifier locks out vent fan
* Vent fan runs either on a timer or in response to IAQ sensor when neither HVAC nor dehumidifier are running.
Thanks for the response! I just want to clarify a few things to make sure we're on the same page. The ventilating dehu has its own return in the house and then it connects to the supply plenum for the HVAC. It has a damper to control whether it's bringing in fresh air or not but the fresh air damper and the dehu are together using the same fan on the Santa Fe ventilating dehu.
So my question is with that setup is it helpful to have the HVAC fan (furnace fan) running when the dehu is also running or would it be more helpful to have the HVAC fan (furnace fan) run on a timer (5 min every hour or seomthing) so that we can have better circulation in the house for times of the year when not much heating or cooling is needed?
In that situation the fans are fighting each other and when the HVAC fan is running the dehumidifier will see reduced or even reversed flow. Dehumidifiers work best with a certain amount of air flow, with more or less their capacity is reduced.
I would do the HVAC fan on a timer with a lockout to keep it from running when the dehumidifier is running. If the dehumidifier has a remote humidistat this is straightforward, the exact wiring depends on the choice of timer. I can help with the wiring diagram.
Thanks for your help! Just curious if there's any downsides to running the HVAC fan for longer periods of time like 30 minutes every hour, other than the energy usage and the possibility of humidity increasing from blowing condensation off the AC coils.
Thanks again!
Most of the benefit of running the fan is going to come at the beginning. Once you've circulated the air there's no advantage in circulating it further.