Where should I be measuring static pressure to adjust inline booster fan speed
aston01
| Posted in Mechanicals on
Due to space constraints on duct size, I ended up needing to pair a higher static pressure inline booster fan with my whole house dehumidifier to compensate for the additional restriction. The assembly works just fine, but I’ve always been a little fuzzy on what the static pressures should be ideally at different points in the system.
My original intention was, with the inline fan on, for the dehumidifier to operate as largely unrestricted, but I didn’t want to pull air through the system so fast that it negatively impacted moisture removal.
Given the supply ducting after the booster fan has to run at a slightly higher pressure should I be measuring the TESP for the dehumidifier at the orange/magenta locations as opposed to the green/magenta?
Santa Fe 120H – Dehumidifier
350 CFM @ 0.0″ WG
285 CFM @ 0.2″ WG
210 CFM @ 0.4″ WG
AC Infinity 8in Inline Fan
807 CFM
746Pa (~3.0 inH20)
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I would measure at orange and red, with the booster fan running as Sante Fe has provided flow numbers with the static pressures. You should see those values change as you tune the inline fan speed.
You could also measure at green and orange, if you can source a pressure vs airflow chart from AC Infinity on the fan. Terrabloom provides these with their inline fans (attached for their 10" inline at 950 CFM), but I've yet to see this information from AC Infinity.
Thanks for the info.
I actually have some of the airflow charts for a few of the AC Infinity sizes (attached below) if they are of any benefit to you. You're right though about them being almost non-existent online.
Be careful with the booster fan, too much airflow and you can kill the SHR on the humidifier. I would keep the pressure drop across the 120H somewhere near the middle of their spec.
I don't know how the SantaFe runs, but if between runs, the internal fan is shut off, your booster fan should also shut down.
The midpoint makes good sense just to keep things safe 👍.
My setup is a little more advanced on the control side, since I have the booster fan I have a normally closed damper on the fresh air duct and added a normally open damper on the dehumidifier return. All of this is attached to a 4-circuit relay linked run through Home Assistant and automated based on interior sensor logic.
It gives me the ability to open the fresh air duct, close the return duct and just ventilate the house with the inline fan pulling through the dehumidifier when it is off or other configurations in other scenarios and synchronizing the fans is definitely part of that.
But if I moved I'd convert it back to something more basic 😉.
BTW - You've answered a few of my questions over the years and your answers are always solid... so thanks for the help again.
I’m with you on the automation…with the right bits in place you can manage pretty much any scenario.
Using the chart for the 8” fan, check pressures at green and orange. Looks like around 400 Pa is your target.
Are you using 0-10V control via automation with the booster, or just setting speed manually with their controller? If 0-10V you could ramp the booster only (with humidifier off) to get to your target vent rate…that may be more efficient with the EC fan.
I've had success with 0-10V speed control the AC Infinity EC fans with a few new products : https://community.hubitat.com/t/success-0-10-volt-control-of-ac-infinity-or-any-ec-fan-motor-using-leviton-zs057-d0z-zigbee-dimmer-or-zooz-zen54-zwave-0-10v-dimmer/104450