This is absolutely the best explanation of Delta T that I have ever seen or heard. I've understood the whole high humidity less Delta T thing for about a year, but your explanation stating (paraphrasing) "The higher the indoor humidity, the more energy is put toward removing it "making water" and less energy toward lowing air temperature" is priceless. Back a year or so ago when I started my self education journey about HVAC, I had trouble wrapping my head around the whole humidity thing for a bit, but if I would have watched this video back then, I would not have had trouble getting it at all. From a newcomer, newbie, apprentice, student perspective this video is awesome. Thank you and keep up the great work. People like you that freely give back to the community (and the trade) are rare and very much appreciated.
The delta T depends on the entering air enthalpy, not just the entering air temperature. In some instance humidity, which is latent heat, can be most of the load, and will have an effect on the actual temperature split. The more humidity in the return air, the lower the temperature split will be. This is the reason we always measure the indoor entering wet bulb temperature.. Most equipment is not capable of producing more than 80% of its rated capacity, if the load is all sensible, as the manufacturers figure an 80% sensible heat ratio. And assume at least 20% latent heat.
I love you Bryan, but you seriously need to talk s-l-o-w-e-r :) It's too much, too quick for a newbie to take in all at once! A great teacher once told me... "Tell them what you'll teach them, teach them, then tell them what you taught them." Gives it time to sink in. It works!
@@shawnd567 Hi Shawn. It's called "Communication 101" and people to to college for 4 years to earn a degree on how to effectively communicate and pass on their knowledge in a way that people can absorb and understand. Pauses between sentences are there, or should be, in order to give the audience time to think about what was just said. Bryan runs all his words together and sentences together and it just becomes one long ramble, which is definitely not the way to communicate effectively. He is a genius when it comes to HVAC, but he is clueless about how to communicate his knowledge to others. And I love the guy, just wish he would take a course in presentation and improve his skills in that regard.
I just want my HVAC system fixed. A building inspector said that the delta T was too low. A repairman said I need the thermo expansion valve replaced for $1300. Many other contractors turned down the job or simply did not have enough knowledge to repair the problem. What do I do???
Fact is taking a reading from your return and your incoming will give you a rule of thumb if your system is working properly. 15-20 delta is fine to keep your home comfortable and not cost you extra kilowatts. Good luck if you call your local HVAC guy to figure this videos science out. It's not that difficult.
If you run a small duct from the supply back to the return lowering the temp of the air going back into the return will that lower the air temp even more coming out the supply?
Hey great video, can you make a video on why an ahu sweats excessively, for example tons of water in the e pan. I have found it could be from dehumdification settings set too low, a break on the iceining insulation causes more humidity, dirty evap coil, speed tap too high on blower motor, but sometimes although I check all of those I still get stumped. Can we get a video on all the possible things that can cause excess condensation on the ahu and supply plenum. Thanks, love your content, made me a better tech all around
Other day I swapped an outdoor unit. Had 16 degrees split on a 3ton American standard heat pump. 70 degrees inside. 81 outside but holy hell it was soooooo muggy that morning. At 1030am when I was done, prolly 75% humidity, if not more.
Great info but a little to quick on explaining some of the reasoning behind delta T. As with any calculations mass flow rate or even net refrigeration effect it takes some time for people to absorb the info.
Do you ever encounter duct condensation issues when a system is running in dehumidification mode or if airflow is set to something lower than 400 cfm/ton? The scenario being lower airflow causing lower supply air temperatures which in turn creates colder ductwork that may cause the duct’s surface temperature to fall below the dew point?
Often with chillers we play with the condenser water temperature to gain capacity beyond design. HVAC is no different. If it’s hot outside beyond design you lose capacity but if it’s cool outside you gain capacity. That’s why coil misters on the condenser can truly help for a undersized unit.
Brian, Do the Fieldpiece Job Link Pros adjust for altitude and provide Btus of enthalpy for pound of dry air? Meeting the parameters you outlined and adjusting for altitude, I take db and wb of return air and db and wb of supply air and I verify superheat at outdoor unit per manufactures specs. , I monitor system for 6.7 Btus of enthalpy for pound of dry air.
Really informative, thank you! Still, it seems like a simple delta t measurement can at least alert you if something is seriously wrong and you need to dig carefully in to the system? If it's hot / humid inside, "about" 15 is in the ballpark, and if the system has been on, "about" 20 is also in the ballpark. Or am I being naive thinking that way?
That seems about right and how I understand the system performance as well. 15-20 is target range, anything over or under, the system needs to be addressed.
Love the video format, with the words nice and big right there, highlighting the details of your lesson. Brilliant technique. I am retaining the info easier.
Great video. Thanks. One question. With all of those variables (humidity in particular) how can coils be rated with a fixed percentage of sensible, and latent capacity? I could see how they could be rated for a maximum of latent heat that it could absorb, but I can't understand how it can operate at a fixed percentage, when the conditions change. Would a coils sensible/latent rating affect the target Delta T?
If you look at the performance chart for a particular unit, it shows how the sensible and total capacities change with varying conditions, you will have higher capacities with lower indoor wetbulb and outside air temps and those numbers also change with cfm across evap, there's areas on the chart where sensible = total capacity. To find out what your delta t should be at a given moment, there's a formula you would use,or if you use measurequick it figures it out for you. I havnt actually used the formula in years but I think it's your sensible btus ÷ (1.08xcfm)=delta t
Is there a package for a complete go thru or a way of selling new. What’s pricing for doing the complete go thru. Is any testing done on a new one ? There needs to be a sheet filled out for comparison. Seems like majority r lookin for a quick buck sell.
I have found a bunch on delta T in cooling mode, but not much about heating mode for cold weather heat pumps. Any recommendations on an approximate delta T in heating mode?
Thanks for this video. I had a house built and the home inspector did what you said with the infrared and found the Delta T was off. I didn't pay attention to this since I wasn't knowledgeable about homeownership as I am now.
I was told in a manufacturer's class that subcooling and superheat are not applicable in VRF systems. Would you make a video explaining your troubleshooting of VRF systems?
In a normal system, anything over 20 is an air flow problem. I like to see 15-20° Delta T on a cool home, with 75-85° outdoor. Anything under 15° is a concern and potentially a dirty condenser.
That is not true at all. Take a look at the performance charts for the units you're working on. You can have a delta t of 30 with proper airflow, or 12 with proper airflow. It's when you compare what you have to the chart that will tell you if there's issues or not with airflow
That was EXCELLENT. I am a homeowner who has taken the bull by the horns and started to work on and understand my own system better. We live in the challenging hot humid environment of New Orleans in a large (8,300 sq ft) old Victorian home built in 1895. It has been retrofitted with central HVAC and runs 6 units total (two twin systems and two independent). It has been a challenge finding qualified and trustworthy technicians. With some refrigeration background from our previous family business, a little common sense, a lot of reading, and now YOUR VIDEOS, I have been able to fine-tune and get my systems operating better than ever. Thank you so much!!!
I think I understand this. If I don't have the fieldpiece tool and app that you are hawking I can't really check delta T ! I will be looking at your videos with more skepticism.
I don't think you have to have Fieldpiece to get Delta T but with Fieldpiece and Measure Quick App it Factors in just more than Delta T and gives you some Insight into what actually is going on inside the System to fine tune into things to look for with all your measurements of refrigerant and air flow to better understand the Dynamics of the equipment
This is absolutely the best explanation of Delta T that I have ever seen or heard. I've understood the whole high humidity less Delta T thing for about a year, but your explanation stating (paraphrasing) "The higher the indoor humidity, the more energy is put toward removing it "making water" and less energy toward lowing air temperature" is priceless. Back a year or so ago when I started my self education journey about HVAC, I had trouble wrapping my head around the whole humidity thing for a bit, but if I would have watched this video back then, I would not have had trouble getting it at all. From a newcomer, newbie, apprentice, student perspective this video is awesome. Thank you and keep up the great work. People like you that freely give back to the community (and the trade) are rare and very much appreciated.
Thanks Craig!
instablaster...
The delta T depends on the entering air enthalpy, not just the entering air temperature. In some instance humidity, which is latent heat, can be most of the load, and will have an effect on the actual temperature split. The more humidity in the return air, the lower the temperature split will be. This is the reason we always measure the indoor entering wet bulb temperature.. Most equipment is not capable of producing more than 80% of its rated capacity, if the load is all sensible, as the manufacturers figure an 80% sensible heat ratio. And assume at least 20% latent heat.
I was just looking at this today.... hmm, fone must have been 👂
and the rule of thumb nowadays:
get yourself fieldpice probes.
Really good concise explanation to try to help in dispelling the myths of Delta T
I love you Bryan, but you seriously need to talk s-l-o-w-e-r :) It's too much, too quick for a newbie to take in all at once! A great teacher once told me... "Tell them what you'll teach them, teach them, then tell them what you taught them." Gives it time to sink in. It works!
Slow down the video on RUclips. I think it's perfect speed.
@@shawnd567 Hi Shawn. It's called "Communication 101" and people to to college for 4 years to earn a degree on how to effectively communicate and pass on their knowledge in a way that people can absorb and understand. Pauses between sentences are there, or should be, in order to give the audience time to think about what was just said. Bryan runs all his words together and sentences together and it just becomes one long ramble, which is definitely not the way to communicate effectively. He is a genius when it comes to HVAC, but he is clueless about how to communicate his knowledge to others. And I love the guy, just wish he would take a course in presentation and improve his skills in that regard.
Top of the line info. Just that you speak very fast...
I just want my HVAC system fixed. A building inspector said that the delta T was too low. A repairman said I need the thermo expansion valve replaced for $1300. Many other contractors turned down the job or simply did not have enough knowledge to repair the problem. What do I do???
Fact is taking a reading from your return and your incoming will give you a rule of thumb if your system is working properly. 15-20 delta is fine to keep your home comfortable and not cost you extra kilowatts. Good luck if you call your local HVAC guy to figure this videos science out. It's not that difficult.
I'm no HVAC technician but this makes sense to me. Thank you for explaining in a way a layperson can understand.
If you run a small duct from the supply back to the return lowering the temp of the air going back into the return will that lower the air temp even more coming out the supply?
Yes in my experience an infrared thermometer is waaaay inaccurate when aiming at a vent...
Hey great video, can you make a video on why an ahu sweats excessively, for example tons of water in the e pan. I have found it could be from dehumdification settings set too low, a break on the iceining insulation causes more humidity, dirty evap coil, speed tap too high on blower motor, but sometimes although I check all of those I still get stumped. Can we get a video on all the possible things that can cause excess condensation on the ahu and supply plenum. Thanks, love your content, made me a better tech all around
Yes, this please! I am having similar issues on two properties. Factory reps can't even figure it out.
Check for dirty evap and dirty blower fan blades. Essentially you have low air flow from my observations.
FANTASTIC video, Thank You.
Other day I swapped an outdoor unit. Had 16 degrees split on a 3ton American standard heat pump. 70 degrees inside. 81 outside but holy hell it was soooooo muggy that morning. At 1030am when I was done, prolly 75% humidity, if not more.
Great info but a little to quick on explaining some of the reasoning behind delta T. As with any calculations mass flow rate or even net refrigeration effect it takes some time for people to absorb the info.
Do you ever encounter duct condensation issues when a system is running in dehumidification mode or if airflow is set to something lower than 400 cfm/ton? The scenario being lower airflow causing lower supply air temperatures which in turn creates colder ductwork that may cause the duct’s surface temperature to fall below the dew point?
Please slow down for a rookie it's so much information to try and absorb
Often with chillers we play with the condenser water temperature to gain capacity beyond design. HVAC is no different. If it’s hot outside beyond design you lose capacity but if it’s cool outside you gain capacity. That’s why coil misters on the condenser can truly help for a undersized unit.
Brian, Do the Fieldpiece Job Link Pros adjust for altitude and provide Btus of enthalpy for pound of dry air? Meeting the parameters you outlined and adjusting for altitude, I take db and wb of return air and db and wb of supply air and I verify superheat at outdoor unit per manufactures specs. , I monitor system for 6.7 Btus of enthalpy for pound of dry air.
They do when you use them with MeasureQuick
Home inspectors during a real estate inspection use delta T 20 degrees like it’s law.
Like everything is always more to it thanks
It's called Psychrometrics
Really informative, thank you!
Still, it seems like a simple delta t measurement can at least alert you if something is seriously wrong and you need to dig carefully in to the system? If it's hot / humid inside, "about" 15 is in the ballpark, and if the system has been on, "about" 20 is also in the ballpark. Or am I being naive thinking that way?
That seems about right and how I understand the system performance as well. 15-20 is target range, anything over or under, the system needs to be addressed.
Great information on delta and can see this is true on many of my service call videos.
Love the video format, with the words nice and big right there, highlighting the details of your lesson. Brilliant technique. I am retaining the info easier.
Great video. Thanks. One question. With all of those variables (humidity in particular) how can coils be rated with a fixed percentage of sensible, and latent capacity? I could see how they could be rated for a maximum of latent heat that it could absorb, but I can't understand how it can operate at a fixed percentage, when the conditions change. Would a coils sensible/latent rating affect the target Delta T?
If you look at the performance chart for a particular unit, it shows how the sensible and total capacities change with varying conditions, you will have higher capacities with lower indoor wetbulb and outside air temps and those numbers also change with cfm across evap, there's areas on the chart where sensible = total capacity. To find out what your delta t should be at a given moment, there's a formula you would use,or if you use measurequick it figures it out for you. I havnt actually used the formula in years but I think it's your sensible btus ÷ (1.08xcfm)=delta t
I used the technician test mode in variable speed unit. Thank you for the video
What about for mini splits? Can I calc the temp split by simple return and supply readings then, since no duct loss or anything?
No
Solid lesson again Bryan. Thank you.
I’m confused on what’s higher and what’s lower. I’m looking at like 70 to 50 20 delta T being higher and say 70 to 60 10 delta T being lower
Is there a package for a complete go thru or a way of selling new. What’s pricing for doing the complete go thru. Is any testing done on a new one ? There needs to be a sheet filled out for comparison. Seems like majority r lookin for a quick buck sell.
Fantastic explanation. No fluff. Great visuals. This is like the best of the old RUclips and new RUclips.
Great info and presentation as usual. But talk just a bit slower so the listener has a chance to absorb your statements. Thx.
U can slow down the video or rewind buddy
Look for the settings in RUclips to change the speed to 0.75 - can make a huge difference.
I have found a bunch on delta T in cooling mode, but not much about heating mode for cold weather heat pumps. Any recommendations on an approximate delta T in heating mode?
Thanks for this video. I had a house built and the home inspector did what you said with the infrared and found the Delta T was off. I didn't pay attention to this since I wasn't knowledgeable about homeownership as I am now.
I was told in a manufacturer's class that subcooling and superheat are not applicable in VRF systems. Would you make a video explaining your troubleshooting of VRF systems?
My house has two floors. Upstair I got about 20 delta T; but downstair I got about 10 for delta T; so I wonder what is going on with downstair.
Nice and informative.
Can you make something about temperature approach (condenser temperature approach and evaporator temperature approach)
Thanks
I know a few home inspectors around town that could use this video.
In a normal system, anything over 20 is an air flow problem. I like to see 15-20° Delta T on a cool home, with 75-85° outdoor. Anything under 15° is a concern and potentially a dirty condenser.
That is not true at all. Take a look at the performance charts for the units you're working on. You can have a delta t of 30 with proper airflow, or 12 with proper airflow. It's when you compare what you have to the chart that will tell you if there's issues or not with airflow
really informative about the different variables behind varying delta T on Evap. Thank you
That was EXCELLENT. I am a homeowner who has taken the bull by the horns and started to work on and understand my own system better. We live in the challenging hot humid environment of New Orleans in a large (8,300 sq ft) old Victorian home built in 1895. It has been retrofitted with central HVAC and runs 6 units total (two twin systems and two independent). It has been a challenge finding qualified and trustworthy technicians. With some refrigeration background from our previous family business, a little common sense, a lot of reading, and now YOUR VIDEOS, I have been able to fine-tune and get my systems operating better than ever. Thank you so much!!!
What y’all do?
What temperature scale are we using ? F or C ?
Explain the use of LRA SIR THANKS
Dude, that was sweet!! Thanks for being there for all of us.
Great job and video like always
Thanks for the video, helps me understand the science behind the work
Glad to help
Awesome video!
Very nice explanation but only talk a bit slower so we can follow up what you say pls.
Awesome
I wanna be like you when I grow up! Great video!
I’m not grown up
@@HVACS Haha. Love the vids man!
👍
Can you just lower a little freon pressure to make your vent colder , don't let to much out or it will start to freeze over.
No,don't do that
What about getting readings from a package unit
I think I understand this. If I don't have the fieldpiece tool and app that you are hawking I can't really check delta T ! I will be looking at your videos with more skepticism.
Or just find someone you trust and watch their videos. All the best to you.
I don't think you have to have Fieldpiece to get Delta T but with Fieldpiece and Measure Quick App it Factors in just more than Delta T and gives you some Insight into what actually is going on inside the System to fine tune into things to look for with all your measurements of refrigerant and air flow to better understand the Dynamics of the equipment
Thanks for the information. It helps!