Controlling Intake Fan Speed Using Differential Pressure
Slightly random idea. Not sure if it’s a good one, or if I’m an idiot. Let me know if my question doesn’t make sense. Or if it’s a stupid question because there’s an easier/better way.
If I have a tight house, and I need/want to have make-up air for various exhaust fans (bath fans, range hood, vented dryer), is there a reason I can’t have a single makeup air fan, and just ramp it up and down based on the inside vs outside pressure?
I’m sure I could hack something together with an arduino, a pressure sensor [1], and either a PWM output or a controllable potentiometer [2] (if the fan has a voltage control). But maybe there’s already a device available to do this on the market. I just don’t know what it’d be called.
Lloyd
[1] example: https://wiki.dfrobot.com/Differential_Pressure_Sensor_%C2%B1500pa_SKU_SEN0343
[2] example: https://www.adafruit.com/product/4286
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I think the problem you'll run into is that the pressures involved are so low as to be hard to detect.
Let's say you need 400 CFM of makeup air. Let's further stipulate that your house is 3,000 SF, 8 foot ceilings, 24,000 cubic feet of volume. You did a good job of sealing and you get 1.0 ACH50. So one air change is 24,000 cubic feet, doing that in an hour is 400 CFM. So when the make-up fan is running it should generate a pressure differential of 50 Pascal.
Sea level average air pressure is about 101,000 Pascal. A change of 50 Pascal is what you would experience rising about 14 feet. It's indetectable without instruments. When the wind blows and maybe even when someone opens and closes a door your sensor would go off.
That's an interesting thought. I had briefly considered whether the wind might cause a problem, but hadn't yet decided how to handle that.
The specific sensor I linked to at least claims an operating range of "±500pa（±1.5%FS)", so I assumed that would be accurate enough. I might see if I can find one with a smaller operating range as well (eg. [1] or [2]), to get more accuracy. I don't especially want to read absolute pressure, just the difference between inside and outside.
[1] +/- 125 Pa - https://www.mouser.com/ProductDetail/Sensirion/SDP810-125PA?qs=KwaGCOX4wIaNl5Uit0G7rw%3D%3D
[2] +/- 25 Pa - https://www.mouser.com/ProductDetail/Sensirion/SDP610-025PA?qs=wWC4CIiyLaPNNqUFFLuE1g%3D%3D
If you have two sensors, and either one is +/- 25 Pa, the difference between them is +/- 50 Pa -- which is your threshold.
You're much better off sensing whether appliances are running and just assuming a fixed makeup for each one.
My approach to this is not pressure, but rather automation. If you detect fans running, you can ramp a make up air system appropriately. Zooz now sells a 0-10V dimmer that will work in North America...this can be used to control an ECM makeup air fan for variable speeds.
I'm doing this right now with my HRV setup. The kitchen exhaust fan (used a small zWave relay to power on/off) is linked to power use detected by the induction cooktop. When the kitchen fan is active, the HRV ECM fans are set to an unbalanced profile that adds about 60 CFM to the house. The Zooz Zen54 0-10V zWave dimmer is about $40, and you can source an ECM 6" inline fan (AC Infinity Cloudline) good to about 400 CFM for $140 or so. Using the 0-10 V dimmer, you can dial in fan speeds via an off the shelf/consumer automation controller like the Hubitat that I'm using. It's pretty simple to set up.
The same inexpensive controller that manages the pool solar system, house lighting etc. also runs the HRV.
That's an interesting idea. Just measure the voltage and/or current on the power leads heading to the various exhaust fans, and use that to estimate the flow rates. I might have to get someone with a flow hood to measure the actual rates, so I can correlate them, but other than that, it's a good idea. I'll have to think about it more.
You can use "current sensing relays" (a common item available from electrical and mechanical supply houses), you can easily configure things to turn on and off based on other things being on or off. You don't really need any fancy automation system stuff to do this.
Bill
Bill, I've gone to Zigbee and zWave devices for just about everything as once you get them into the mesh of your house or business mesh network, you can do a pretty amazing (and growing) number of tasks with them.
For example, once the supply/return HRV/ERV ECM fans are part of the system you can start in layering in smarter controls. In my case, this means a CO2 monitor allows the HRV system to choose a CFM profile appropriate for occupancy. This sounds "cool" but actually it results in significant power savings as the system will ramp down to 50 CFM (ab0ut 20 watts) vs 100 CFM, about 70 watts. Not only are you reducing consumption on the fan systems, but you're also reducing BTU loss, and power use by the post conditioning heaters in cold weather.
That same HRV system reacts to the kitchen exhaust hood providing make up air in a asymetric flow profile, and it can do the same as other devices (like say a bath fan) is also fired up. When the induction cook top is off, the fan also powers off, so again can not be left on to waste power.
Our home hydro consumption dropped by a surprising 40% with motion sensors and lighting etc. LED light power use can be dropped even further by dimming them based on ambient light from exterior windows etc. A kitchen with 140 watts of LED light may only need 50 watts for much of the day.
Yes, industry has solutions for these as numerous standalone / analog systems. However, these are far more expensive than doing it all on a $200 hub where all the devices can "see" each other and respond with automation rules.
Broan is going this way with their "AI" series system, which is pretty much where the industry is going. You can do all this right now with your "dumb" devices in most cases by just adding $40 relays which fit right into existing boxes.
All of this stuff to me is low hanging fruit in the pursuit of efficiency as unlike some tech, it's actually pretty easy to integrate into existing infrastructure.
This is awesome. Thanks for sharing. I use a Hubitat to control a Fantech FG8-EC supply-only intake fan, but I never thought of implementing dimmer to automatically control how hard the Fantech is blowing. I just keep it set at a constant ~100 cfm. I always wished I could get it to automatically ramp up to 200-300 cfm when my range hood is on. Now you're telling me I might be able to...
If they are just fixed speed, you can use a small zWave relay to power them like the Zooz Zen51. Then you know when the fan is on :-) These convert a "dumb" switch to a smart switch.
Aunsafe, for sure. See this thread where I posted my work with the Leviton ZS057-D0Z 0-10V dimmer: https://community.hubitat.com/t/success-0-10-volt-control-of-ac-infinity-or-any-ec-fan-motor-using-leviton-zs057-d0z-zigbee-dimmer/104450
If you scroll down a bit, you'll see that instead of the Leviton (which does work with a fantech EC fan, see comments in the thread for wiring) 0-10 V dimmer, Zooz has introduced a less expensive "micro-relay" with 0-10V dimming, the Zen54. I've got a few on order to play with them.
This is a quote from that thread regarding a Fantech EC fan:
"
@Kyl did get his Fantech EC fan working using the wiring below, with what he figures is a 10V reference voltage added in (he'll post here with follow up pics)
Fantech red 10v reference AND Fantech yellow 0-10v input -> leviton purple +0-10v
Fantech 0-10v GND (blue) - > leviton -0-10v (grey)
I won't pretend to understand why it works, but Kyl can explain with his follow up post. Just adding this here for reference."