HVAC Delta T Explained! What Temperature Should it be?
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- Опубликовано: 7 дек 2019
- In this HVAC Training Video, I Explain what Temp the Target Delta T Should Be for Single and Two Speed Air Conditioning Systems as well as Minisplits and Gas Furnaces! I Show how to Measure the Delta T. I also Explain How to Use Delta T measurements for Troubleshooting HVAC Units! Make sure to use Test Holes within a few feet before the unit in the Return and a few feet after the Unit in the Supply Duct. Supervision is needed by a licensed HVACR Tech while performing tasks as Experience and Apprenticeship garners Wisdom and Safety.
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Nothing better than Sunday morning coffee and Hvac videos. Thanks for sharing.
Thanks a lot Dean! I appreciate it!
Mixed with a NFL game
Thank you AC Service Tech LLC. Your videos are a huge help in learning the trade. You are my go to resource along with a few books and technical manuals. I wish you all well for the services you provide us. Respect from an HVAC/R apprentice in Virginia.
It seems you have a video for something I’m worried about not fully understanding. It’s uncanny and amazing. Thank you sir. I’m going to send you a check when I make some real money in the business , for all the help you’ve given me. 🙏🏾
I have your book and I went to ivy tech for a Tech degree. I will say you put it in words that I understand. Thank you.
Thank you very much! That's awesome!
As a HVAC instructor your book is really great. Keep up the good work.
Thank you Bronchee! I appreciate it!
I bought your book and as a HVAC instructor you explain everything really well my student really like your book
That's awesome, thanks for letting me know! Is the book something that you may choose in the future to use for your students in the classroom? Thanks!
Honeywell has an online essay, “Why Delta T is the Magic Number.” My 2010 edition of AHRI’s Fundamentals has a simple graph on page 662 adjusting return dry air for RH, and on page 668 makes the straightforward observation that a low Delta T indicates heat removing capacity has been reduced.
Thanks man for sharing your knowledge! You are the best!
Glad to help Marcus!
Always clear and concise.
This guy explains the best!!!! Thank you Sir!
Thank you for the support!!
Great instruction Craig! Helps me a lot.
Thanks a lot Nick!
Another thing to take note of is that an evaporator delta T is also related to the Sensible Heat Ratio in your area. Having a high SHR (0.85 or above) means most of your heat in the home is just sensible heat, and you would have a larger delta T and less condensate. A lower SHR (0.75 or even lower) is an indication of your home having lots of humidity. The coil will remove more heat from water vapor in the air, so more condensate, but less delta T. These values can be found in the literature provided with your equipment, and are used when doing a Manual D or Manual S.
Absolutely priceless information you offer in this video. You are the best
Bart glad you enjoyed the video!!!
@@acservicetechchannel selective answering lol
Great tutorial Craig.
Great stuff, very explained !
Much appreciated!
Excellent video partner thank you for sharing!!!!!.
Thanks Jimbola77! always happy to see your comments!
Watching this during my test
Nice job and video
Had one last week, leaky ducting, sucking air from wall cavity and attic space. Cut inspection hole under unit, spray foamed and sealed best I could and temp came right back up. Had to recover some juice from it also being over charged, without thinking it through first 2 other techs condemned the 7yr old unit.
The delta T you will get in the air conditioning mode depends on the entering air enthalpy (sensible heat + latent heat, or in layman’s terms, return air temperature + return air humidity, plotted on a psychrometric chart). This is the reason you have to take a wet bulb temperature at the return air to determine what the DeltaT should be. Delta T can run from 16-26 degrees on a normally running system, depending on return air enthalpy. The old way of calculating heat pump delta T, without running strip heating in the old days was called the output rule. The rule stated that at 70 degrees outdoor temperature, a heat pump would produce 30 degrees Delta T. For each ten degree drop from 70 degree outdoor temperature you loose 3 degrees on the Delta T, so at an outdoor temperature of 50 the delta T would be 24. This rule applied to the old R22 systems. I do not know if it is applicable to the newer systems, it was a good rule of thumb, that I used may times, when I did not have the manufacturers specifications.
😂😢😢😢😂
Best on youtube....
Craig. Great video. It’s well outlined. For a moron like myself, any way to add graphics with each point presented. Thank you for all you do.
Ha ha, it helps us all! Thanks!
👍🏾👍🏾 another great video
Thanks piz11!
Ive been doing this kind of work over 20 years including 2 years of trade school and I have never heard the term delta t until today. I was taught to call it the differential or differential temperature. 🤷♂️
Just did a Delta T check on a old R22 unit with my new ST4 , only a 6 degree drop, lol.
I have your book it’s great ! Bu when is a furnace book coming ?
Yep I've had that happen to me where the temp split is 10degrees and everything was installed fine. It was just ridiculously hot. Outside was 118 and inside was 99. The system was able to level off by the time night came around and cooled off to 95 outside where inside settled around 75.
my heat pump alone just gives a 10-12 deg difference. Inlet gets 65F and out the vents is like 75-77F ..... while its 45F outside.
Hey love your stuff bro…can you tell me what is meant by start up process when installing a new unit
Thanks for this video. I have a 4-head Mitsubishi mini-split system. Delta-T varies at each head: 13, 14, 15, and 20 degrees. Less than a year old. Last year, a week after initial installation there was a leak in one of the lines found (I spotted oil from the leak running down the exterior of the house). The tech fixed it but said there was plenty of refrigerant and so didn't add any after the incident. Should I be concerned?
Buddy you are the best! I did 2year program for hvac and have learned more watching your videos.
I am full time licensed sheet metal. I do furnace swaps occasionally some gas lines and a little service for furnaces . But have wanted to get more into the refrigeration side.
What would you recommend for simple basic gauges and first tools to buy . For new installations and some servicing on the side.
Thank you !
That is awesome! Glad it was helpful
Could you please do a video of combustion analyzer of roof top package unit ? Thanks you
Lilin, thanks for letting me know what you would like to see!
How about a new video like this one on static pressure. Also, what percentage of calls do you find SP within spec. One of the most overlooked measurement drastically killing SEER ratings.
Yes I am planning to do one in the future, thanks a lot AD and it's awesome that you are looking at the details! They all add up for sure!
80-90% of the time I find high static pressure...
Mass air density will be influenced by air temperature. Denser air can absorb (or reject) more heat per unit volume. So correction factors will attempt to measure heat change for a given mass such as BTU gain per pound of air. One might also want to measure the change in humidity to determine how much water was condensed (or vaporized) and include that heat too. Ah sensible heat and latent heat. Drying the air will reduce its volume 2 to 4% or total mass by 1 to 2%. or about 44 BTUs per cubic meter to reduce humidity 50%.
20 degree split is always what I aim for.
Part number for the 3/8" rubber plugs to cover the holes in ductwork?
Hi Craig, I was wondering how to measure return temperature on a handler that has no return duct. It's an upflow in a closet (louvered door). Would I measure at the bottom opening of the handler (where filter is located) or should I stick my temp probe through the louvered panel? The supply duct is easily accessible and I can measure that one fairly easily. But unlike in this video, there is no return ducting, the return is the door itself (in a centralized location). Just curious, any tips to help this new tech would be appreciated.
I just have a question, do you use a wet wetbulb sock while doing a delta T measurement?
Would you please turn the captions on for this video. It makes it easier to follow for those that want captions. Thank you!
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?
I get 20° but was curious if I was to do this if it would lower the temp by doing this.
Can you do this same calculation on a furnace or is it only meant for air conditioning?
For some reason this season, I’ve come across numerous package units pulling 30 degree dT’s. With proper charge, fixed speed fan, is there anything else besides airflow to rule out?
I have a heat pump. In heat mode the out door unit shuts down on high pressure safety according to a HVAV technician. He checked air flow across indoor coil and said it was ok. His conclusion was that systems with R410A should not be ran in heat mode when outside air temp is 65 deg or above. Is this true?
Hello Craig, I tried to find a email to you but could not. Off topic question if you don't mind. Would you have a long form of a manual J you would copy and sell? and What manual J program would you recommend buying for heat gain and heat loss calculations? Is there a good app out there that makes this easier. Thanks in advance. Great book by the way.
So for cooling, is it bad to reduce fan speed to increase the delta temp to be within range?
Can you confirm the formula shown at 51s. It shows supply minus return.
Where can I find the Delta T values for mini split units?
Thanks for great video.. I have a question? how do you set only the electric heating strip? do you set the tstat in emergency heat.
Yes emergency E terminal at the tstat, thanks!
Hey Craig how can I get your book. Right now I'm in UAE
so the true delta T is to be measured at the return and supply duct at the unit itself now at the return grill or any supply grill??
Excellent explanation but what's opinion on my delta T my return temperature is 73 and the supply is 48 so that's a 25 degree delta T but I have my thermostat on 72*, and the outdoor temperature is 84* today
If its a standard single speed unit and not a minisplit, the high delta T likely means low airflow.
Hi your videos are informative! Hi I have a single ductless 12,000 BTU heat pump my set temp is 24° but my room temp is 18 could you explain what may be happening it is -10 outside thanks
12000btu is the problem.
What’s the difference between the E book and the other book that looks like it ?
Question: Is the temp rise in a gas furnace the same for both stage 1 and stage 2? Hope I am asking this right?
In a gas furnace yes they are usually close temp rises since both the gas output and airflow speed both reduce but will depend on airflow speed and most use a variable speed. The most important thing to watch for is that the temp rise does not continue to rise as the furnace runs indicating low airflow, thanks!
at 0:50 , the equation is wrong, i believe the supply should always be colder than return, because the air go through the vapor coil ? shouldn't be return air - supply air = 19 , is it the calculation left/right position wrong ?
Can you measure temperature difference comparing ambient temperature vs outdoor condenser temperature?
David Arroyo measure inlet ( thermometer on side of condenser), then measure outlet ( thermometer measuring the air coming out of the top of the condenser) should be about a 10 degree difference. I.e. 90 degree inlet, 100 degree outlet
The Delta-T is a relationship to the TXV or Fixed Piston of Air Flow
Yes for indoor airflow, thanks
would the delta t be off with a mismatched unit ?
What do you use to cover the holes that you drilled into the Return and Supply Ducts in order to check the Delta T?
Hard cast, pookie, or both
Juicy fruit, he likes yellow 😆
Quick question what happens if your sub & superheat are good, pressures are good, but you're only getting a 13 delta T? I ran across this twice both were rheem units.. heat strips weren't on either
It could be the airflow is set too high or there is too much humidity in the building or both, thanks!
Craig, great info! Really dumb question if you have a moment. Is it possible in AC mode to have a “normal” 20 degree delta T and be significantly low on charge (maybe just above where a coil would ice over)? What I’m struggling with is despite the fact that the refrigerant is there to do it’s job, in theory, because of a lack of refrigerant, the coil should be very cold and still cooling the air going through it. Is this situation possible? Thank you!
The only way you could have 20 degree across the coil and be low on refrigerant is if you are low on airflow too. This would result in a lower overall system capacity, thanks!
@@acservicetechchannel Thank you so much Craig!!
Now I know what is Delta T , my company everyone keep call TD ^_^
They mean Temperature Drop. My company use to say the same thing.
ZE KENZY - actually TD refers to temperature differential which is the the same as delta t. Just another way of saying it. As the Greek triangle (Delta) means “change in”. Thus the equation DeltaT= T2 - T1
I read that too fast. TD is different than Delta T. TD is the temperature difference between the return air db temp and the saturated refrigerant temp in the evap coil. Example: 70 degree return air minus 40 degree refrigerant sat temp= 30 DB. The higher the TD, the more humidity will be removed from the building. The word difference being used means the temp of two different mediums where as Delta T is the change in temp of one medium. DB is common for refrigeration when talking about humidity levels needed to store different types of products. Thanks and great question!
AC Service Tech LLC - amount engineers, TD is the same as Delta T.
Temperature Differential
My old co. Called it "the split" 😃
Hey Craig, my ac thermostat got reset by accident. I gave an question..... my ac thermostat is saying it’s 79 in here, which I KNOW it’s not. I went and brought in an external thermostat and it’s showing 77 which it definitely feels like, that’s way more accurate. So the issue is that my ac keeps showing a higher temp than actual temp, so ac keeps turning on. I feel like it has something to do with the cooling stage 1 on or off? I could be wrong but what should the setting be on, as far as inside/outside cooling stage 1?? Or does that have nothing to do with what’s going on? UGH! 😩😫 pleeeease help
Adjust for 2 degree offset or replace tstat?
Ie you want it 75, keep at 77
Where can I purchase your books?
at our website at www.acservicetech.com and also www.amazon.com/shop/acservicetech and the full outline and sample pages are at www.acservicetech.com/ac-book thanks!
hi, for fixed orifice system. high heat load would caused high superheat. high super heat would caused high pressure on the high side. wouldn't this high pressure on the high side PUSH MORE refrigerant into the evap to compensate? so the amount of refrigerant going through the orifice varies/changes based on pressure differential between high side and low side. please help me to clarify this concept because you're saying the orifice ALWAYS ALLOWS the SAME amount of refrigerant through and this is where i get confused. your book is just amazing. Thank you.
It seems you answered your own question?
For it not to always allow same amount would seem to me to be the case of severe undercharge, restriction before orifice, faulty compressor.
Think of it like water through a pipe that had a cap midway with a drilled hole in it perhaps?
Only a certain amount of water could go through the hole regardless of pressure granted it meets the minimum
are there similar rules for condenser unit Delta T
We usually don't because the fluctuation in the outdoor db temp is much higher than the indoor. The indoor db temp may be 68 to 78 degrees whereas the outdoor db temp may be 70 to 105 and this will affect how much heat is able to be rejected outside, thanks
@@acservicetechchannel thanks alot for these important information
@@acservicetechchannel can you please make a video about dirty condenser and insufficient condenser fan air flow (like someone make the wrong replacement for condenser fan)
Ahmed, thank you for letting me know what you would like to see!
I think the Supply temperature and Return temperature is reversed for AC mode.
Yeah it doesn't matter about the negative sign. You are just taking a differential and once you get it, it would be referred to as a positive number. I just didn't switch the two probes when moving from heating to cooling, thanks!
Who's one is right
Means any conditions for these 2 cases
Plz help
∆T = SAT - RAT
or
∆T= RAT-SAT
or Both right
Delta T can technically mean both but when you are talking heating Delta T can also be referred to as "Temp Rise". I will say that you hear the term Delta T used more in air conditioning mode where RAT-SAT thanks!
At 51 second on the video, I think the formally is incorrect
Do you calibrate everytime you use your dual sensors?
No just calibrate maybe once a month but continually watch if the t1 minus t2 seems high when they are in the same location to see if one is getting off. If one seems off then calibrate to verify. Always have another in the truck because the sensor could go bad at any time due to the small thin wire resistance changing if there is a twist or nick in the wire, thanks!
@@acservicetechchannel thanks for replying. In school they have us test em every time
Ice water every time? I guess if you don't know who was using the tool before you then you should check. Did you do this every day or was this a once or twice a week in the shop time? Thanks
causes of LOW delta T?
Can you measure Delta T at the vents? It's 65 degrees outside, and inside my house is 75 degrees. The AC is set to 74 has been running for over an hour and the temp is still 75 degrees. Coming out of the vents is about 66 degrees, which is a Delta T of 9, but I don't know if I can check it at the vents.
No
I thought electric resistant heat Delta t was like 35 f
Two digital thermometers from harbor freight will save you money than buying that delta t meter