OT – Home HVAC Filter Pressure Differential.

Any recommendations for a DIY home automation suppler that has a inexpensive WiFi device that I can use to monitor my HVAC filter.

Thanks,
Bob O.

Hey Bob,

These have Modbus http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Transmitters/SeriesMS2

I am also sure they have a contact closure model then you could just use a simple input but I would check with Dwyer, they have great products

Or... you could just change the filter every 3 months

Edit: This one may also be a good fit https://www.elitechustore.com/produ...al-pressure-gauge?_pos=1&_sid=5e7d24949&_ss=r

Thanks Mark!


I could change it every three months but what fun would that be? I have fairly simple home life right now so I might as well try to complicate it a bit.

I think what you need is a differential pressure transducer.
So you can see the pressure differential across the filter.

https://www.wolfautomation.com/pressure-transmitter-ultra-low-differential/

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/pressure_sensors/differential_pressure_transmitters/dpta-20-05?gclid=Cj0KCQjws_r0BRCwARIsAMxfDRgBfiC6AANrfKyu1w7nRmutrw8EwrpFgvALBs5o1IhX6YRz3wnm1FkaAhqmEALw_wcB

https://www.grainger.com/product/24Z021?gclid=Cj0KCQjws_r0BRCwARIsAMxfDRijENjQbiXeBSZLySR8pyYXUvnYpr1phikGWOd7Q3YriuWc3RX4F_saAu3GEALw_wcB&cm_mmc=PPC:+Google+PLA&ef_id=Cj0KCQjws_r0BRCwARIsAMxfDRijENjQbiXeBSZLySR8pyYXUvnYpr1phikGWOd7Q3YriuWc3RX4F_saAu3GEALw_wcB:G:s&s_kwcid=AL!2966!3!281733071183!!!g!444137882591!

from my jar of silly ideas:


how about a water manometer? You are only interested in this as an alarm, right? Put colored water in a clear tube and do it optically, or slightly salty water and two wires. Hmm, evaporation might be a problem, you'll probably have to replace the water several times per filter replacement. Oil might work (lower density => greater displacement).



How about a position indicator? As the filter collects dust, it will start to deform toward the fan (it also gets more effective as a filter) and you could put a wire on it that initially has insulation against a contact, but as the filter deforms the wire would be pulled up to make contact with bare wire where the insulation stops, and you could use that for an input. Basically turn your filter into the diaphragm of a pressure transducer.


Fan speed would be another indicator: as the fan clogs, the pressure drop goes up and the flow goes down (deltaP x d(V)/dt vs. constant power from motor, to first order), so the fan speed increases; google [fan performance curve]. (and I may be way off on the fan curve explanation, but the fan does run faster when inlet flow is restricted - put your hand over your desktop fan to see).


Sensitivity will be the tough nut to crack, I expect, however change should be gradual but hopefully noticeable and constant with a newish filter and then accelerate near the end.


For calibration put a piece of plastic over a new filter with a hole say 10% of the gross area of the filter.

https://temcocontrols.com/shop/pressure-sensor/

Not WiFi but has Modbus tcp. Other device's have WiFi. I personally don't use any wireless stuff in my home. Not sure if I am just old school or that I am a electrician. I am about to pull the trigger on purchasing T-stats, air quality, and bunch of stuff from them soon. It will all talk Modbus Rtu to a micrologix 1400 so I can see what's actually going on with the system. As it's already a bit complicated one 3 zone unit with fresh air in take one single zone unit so 4 T-Stats to keep track of. So i figured I'll make it less complicated by my own system (probally more complicated but this is what I do. lol) I haven't found any of the shelf HVAC controls for home automation that aren't wireless. I have been looking for almost a year. I don't like the idea of a system that depends on something that can go out of wack becuase a signal gets blocked or dropped off unexpectedly or a firmware download happens "all by it self" and I wake up mid night sweating in Nevada's 100 + degree nights.
End rant lol.
Good luck in finding what you need.

Cheap? Yup.
Complicated? Probably.

https://www.digikey.com/product-detail/en/nxp-usa-inc/MPX53DP/MPX53DP-ND/951812

7.25 PSI differential sensor, works at the ESP32's voltage range. $12.74



https://www.amazon.com/Icstation-AD620-Microvolt-Amplifier-Adjustable/dp/B072N57L7H

100uV to 300mV 1.5x to 1000x amplifier, also works at the ESP32's range. $5.99 + $2.99 shipping



https://www.amazon.com/HiLetgo-ESP-WROOM-32-Development-Microcontroller-Integrated/dp/B0718T232Z

ESP32 complete with WiFi and Bluetooth. $10.99

U tube water manometer made from a length of transparent plastic tubing





and a wi-fi web cam

danw said:

U tube water manometer made from a length of transparent plastic tubing ... and a wi-fi web cam

Click to expand...

I just remembered: put oil on top of the water on either side to reduce evaporation (and to attract ****roaches).

danw said:

and a wi-fi web cam

Click to expand...

Dan I like the U-tube but put in a Cognex cam... this way you could get the alarm and not be just visual

I may look for a manometer “laying” around the plant and the WI-Fi would be me getting off my lazy South side to periodically look at the damn thing.


Thanks All.

Want some fun, Tape a small PLC with an analogue card to the back of your tv, mount an HMI on the top & there you go, HVAC monitoring should keep you busy for a day or too, with the spare I/O, build yourself a system that pulls a can from the fridge and delivers it to your armchair.

parky said:

, build yourself a system that pulls a can from the fridge and delivers it to your armchair.

Click to expand...

And make the dog training obsolete? Spent too much time and money on that to stop using it.

One other thing about the oil in the manometer (IIRC): if you put different amounts of oil on either side then it makes it more sensitive (more movement on the oil side per inH2O of head).


Inclining one of the tubes is another way to increase sensitivity.