The Danger of High Airflow in HVAC 

I have a two stage single compressor that runs 70% in first stage and 100% in second. For these systems you wire Y 1 to Y and Y 2 to the BK terminal which runs the fan at 80% in first stage. This means you have more CFM per ton in first stage than second. My humidity was staying around 52% and then when it went into second stage it would go down to like 45%. It just wasn't consistently comfortable. So I wired it where the fan runs at 50% in first stage by using the Y low terminal. I then turned the fan speed up to 450 CFM per ton. It works great now keeping the humidity below 50% most of the time in both stages.

He's not just blowing air! Listen & Learn! Nice job Zack! 👍

This is unbelievably valuable information. Thank you for sharing it. I (as a nonprofessional layman) have been running off of intuition and thought this might be correct but having it spelled out to me step by step makes this so much easier to conceptualize. Thanks dude seriously, its something I've been struggling with for a while.

I learned this as a teen when I tried to run a car with no thermostat which also served as a flow restriction. It was always overheating. It is all about matching the heat transfer capacity to the mass available for transfer (simplified college level thermodynamics). If the available mass moves to fast, it is difficult for the heat to be transferred efficiently because it needs more saturation time. Moving air slower is also cheaper.

too bad the smart guys on youtube are rarely reflected in the field and it's nearly impossible to find someone that will act like this without significant effort

Tech says i dont know what the CFM should be... then do the calc for CFM. IF YOU DONT KNOW THE CALCULATION........LEARN IT ! !

Great video. I had a new unit installed with 18 speed fan. it was blowing WAY TOO HARD to the extent it was blowing water out of the pan. I brought the pro back out. He slowed the down and now it works very well, and the humidity is lower according to a gauge in my room.

You can tell he knows what he’s talking bout! That’s one sage beard!

Sizing the equipment properly is the first and most important step. If the size is incorrect, everything else will be a compromise when it comes to cooling with moderate to high latent loads.

You can also set most electronic thermostats for a greater 'swing' which will cause the unit to run for a longer time then rest for a longer time. This gives the unit more time to dehumidify the air as well as cool the air.

Especially important on multi stage compressors. Lennox units almost always need to be dialed back.

I am turning down my fan speed to try to get more humidity out of the air. Thanks for the tip!

We live in Central Florida. Lately we have had 95+ degree days. Our humidity in the house has been throughout the day between 35-45% and dry. We recently changed from Merv 8 filters to Merv 11 filters. We just cleaned both coils with a coil cleaner and just changed our filter like we do once a month. We keep our thermostat at 82 and sometimes to 84 during the day and at night we put it down to 77. So far so good but the electric bill will be higher obviously. Great video on this subject. We are looking into Mr Cool or EG4 Mini Splits to put in in the near future in each bedroom and in our living room to help supplement the Central Air Conditioner or keep it completely OFF. That way we can just cook the rooms we want without keeping on the entire system. Jeff -Sunny Central Florida ☀️

If you have a matched system, the ahri rating should have a cfm associated with it. Also, it's critical that the system isn't oversized to begin with so it can run longer for better dehumidification.

Thanks Zac. Keep on keepin on 🤘🏼

Man, That's True Talk and educational 👍

I'm still puzzled that the HVAC gods decided CFM could mean either cubic feet/min or condenser fan motor. What happens when you order 1000 CFMs ?

would you say 50 degree coil can cause mold and bacterial growth? depending on the seer rating coils of 40-45 degrees are perfect 🥴

Almost missed this video. It's almost the end of the month!

CFM's drop when the homeowner installs a far more restrictive (aka allergen) air filter. And when filters clog up over time, CFM's drop too. And then there are homeowners that never change their air filters. Of course people want that AC on the 2nd floor which most installations never get it to do properly. Upstairs hot, downstairs cold scenario. Those coils will dehumidify regardless of speed. At coil temps increase the TXV also senses that and allow in more refrigerant. If coil is still too hot after that then you have too small of a system.

Wow! What an eye-opener! I never thought about the air flow through the evap. You make total sense. Now, does this mainly apply to humid regions? Would the air flow make a big difference in an arid region like the southwest? Thanks!!!

Sad how many companies reward call backs, and eventually sales because the systems they touched become messed up especially when they are pushy Salesman with big muscle and clean white shirts

I liked that. Keep up the good work, Zack.

Tuning the CFM air flow can make a big difference in comfort and electrical consumption of HVAC. Temp & humidity monitors are inexpensive these days. You can not only get the temp and relative humidity reading but the logging also shows the AC cycling time periods versus time of day. Verify humidity at several locations in house as it varies depending on any nearby heating sources like a TV or other equipment that puts out a little local heating. The localized heating will drive the nearby relative humidity lower and temp higher than house average. During AC cycling periods in inactive state, the return grill area will likely dump some humid air back into room from wet evaporator coil in standby mode since evaporator coil is usually a bit higher than return grill. On a single speed system, I always set minimum ON cycle setting in thermostat to at least 5 minutes of running time. Prefer to have a thermostat with adjustable temperature hysteresis control. You can better manage temp vs humidity and ON/OFF cycle time tradeoff by adjusting temp hysteresis setting in thermostat.

Excellent information to know! Thanks

I can't wait for your next videos.

Zach’s my brotha that’s a Bosch 2.0 why r u putting r22 on it 🤦🏽‍♂️

My daughter’s apartment stays at 75% humidity and her fan sounds like a jet engine. The temperature of the air coming from the register is above the dew point of the room air. I think the fan is tapped for too high of air flow. Can we simulate lower air flow by blocking some of the return air duct? What delta T should we be seeing?

So you’re charging that 410 Bosch unit with R22?

Newer systems adjust airflow in real time based on humidity sensors.

That's the upside mini split systems from known brands. It is already set up by the manufacturer. I like to choose my ac mini split slightly too small as I still have a unit with ancient one stage technology. Doesn't cycle the compressor and gets more dehumidification done

It's a matter of perception. Personally I have lived with swamp coolers that saturate the air with moisture while providing high air flow at low temperatures and it feels great. Heat and humidity feel miserable. Cool and humid feels great. I would rather have high air flow with humidity and colder temperatures than to have lower air flow that is less humid with warmer temperatures. To each his own.

Amount of moisture removed vs. temp drop is non-linear? Dropping 1 cfm by 2 degrees removes more moisture than dropping 2 cfm 1 degree? How much more?. Better call an engineer.

My ac runs about 15 min and off 7 min in the hottest part of the day (85 degrees, dewpoint 68). Does that seem right for a properly sized unit? (Thermostat set at 73, never sticky inside.)

Great video

I live in the desert so no humidity to start with

airflow, Airflow, AIRFLOW!

my brand new trane system coil compresor failed at 1 yr had changed but before it would turn of if i set it 76 it would turn on n off every 15 min running then 10 min off , know o set at 77 n never stops its cold n reaches but never stops i have to move the temp to 80 in order for it to turn on n off or else its would go on for hrs. Why could this be happening

What if you increase condensor airflow?

ABC airflow before charge

How can you control the speed of the fan?

The issue is he ran out of shaving razors😂

Enthalpy

❤

This guy looks like he hasn't had a shower in 3 months