All right, this video is all about delta T now, Delta T isn't always called delta T. It's often called an air temp split or an air temperature split or just a temperature split, and it's the difference between the air temperature entering the evaporator coil. The temperature of the air itself entering the coil between that and the air leaving at the top of the coil now first mistake, often made in measuring a delta T, is that people will measure it in between a return vent inside the house or building and a Supply vent, an actual supply, diffuser register and the challenge there is is that you're not going to get an accurate reading, because you're gon na have duct losses the potential for duct leakage so to either suck in warm air on the return side and then also for Gains to the ductwork because of them running through a hot attic or a basement or whatever the case may be, or vice versa. If it's cold outside, then it could affect the ducts and negatively in that way.

So you can't test them at the registers inside and get a lot of accuracy unless they're very, very close to the equipment. The correct way to measure is directly above and below the evaporator coil, but enough distance away that there's proper air mixing and that the probe isn't in the line of sight of the evaporator coil so that it's not affected by the radiant heat. We've talked a lot about that in taking proper temperature measurements and when you're measuring air you have to have proper air mixing and you don't want that coil surface to be line-of-sight to that probe. So the way we often say, then the trade is you don't want? The cold surface or a hot surface, looking at a temperature probe because it will affect the measurement of the probe and the greater the mass of the probe.

The more likely it's going to affect that measurement. But regardless for as long as I can remember being in the trade one of the most common measurements, that a technician will take, is the delta T and so they'll take a pocket. Thermometer and they'll stick one in the return and it'll stick one in the supply and the old rule of thumb is you're. Looking for a 20 degree, split a 20 degree Delta, which is Delta, is just another term for difference.

In this case, it's a temperature difference. You're looking for that 20 degree Delta, that is not a good way of looking at temperature split, because there's so many different factors now. It is true that air temperature, splits Delta T's tend to hover around that 20 degrees own, but they can be anywhere from 14 to 23 in typical equipment and that's just typical equipment or you get into abnormal, and it can be all over the place, especially as We add in variable speed, blowers and, as we have different load conditions that affect the equipment. So let's talk about the differences here and why that is first off we're not just removing sensible heat in an air conditioner running in cooling mode.

So we're not just changing the temperature of the air, we're also in almost every market going to be condensing water on that of Aperta coil and that's called removing latent heat and so Layton. He doesn't show up in form of temperature. It doesn't change the temperature of the air another term, for it is hidden and just means latent me really means hidden. That heat is not going to change the temperature of the air, it's going to remove moisture from the air and that will affect your delta T.

So as an example, if you have a higher relative humidity, you have greater moisture content in the air. Then you're gon na have more build up on the evaporator coil. Again, it's the difference between the dew point of that evaporator coil and the temperature of the air going over it. But as you get more water built up on that evaporator coil as it's removing more moisture, more of the work is going towards making water and less of it is going towards changing the air temperature, which means that when your error is more humid under all things Else being the same, your temperature split, your delta T, is going to decrease, and so, when you have very hot humid climates, where maybe the air conditioners been off for a long time, you may see splits that are all the way down.

14 15 degrees. Something like that, and that would be normal under those circumstances normal for the first reason, which is high humidity, more moisture on the coil means a lower split, but also higher, because when the system is operating outside of its normal operating conditions, especially when it's really hot Outside something like that, that can also affect the split so as the system capacity decreases and it will decrease, as the indoor temperature drops and/or as the outdoor temperature goes up. So higher outdoor temperatures and lower indoor temperatures result in lower system capacity. A lot of the rules of thumb that were used to only really work at 400 CFM per ton, which is very typical across the US and at 12,000 BTUs per ton.

Well, a lot of the equipment that we're installing is operating under conditions that are not going to produce 12,000 BTUs per ton, and that can be because the equipment right out of the box doesn't produce that. And then you add in the actual operating conditions. If you're running a system in Phoenix Arizona where it's 115 degrees outside, it is not going to produce the same capacity at 115 degrees that it doesn't 95 and it will produce potentially more capacity when it's warmer inside with a cooler outdoor temperature. So, just it's a sort of a reminder about how compressors work, but a lot of what we do in air conditioning is tied to the mass flow rate of the compressor.

How much refrigerant that thing can move and when you have higher compression ratios higher head, lower suction, that compressor can't move as much refrigerant. Therefore, you're not going to get as much capacity, so there is no chart out there. I'm going to show you a chart. Real quick, a typical delta T chart that takes into account the wet, bulb and dry bulb temperature of the return, air and you'll see those temperatures are all over the place as far as what your delta T will be, but that's just considering that one factor the One factor being changes in the return air humidity, but then we have two other moving parts.

We have the capacity of the equipment at different load conditions like we talked about, and then we also have changing air flow. So when you have a variable speed system, you may have it the system designed to drop down to a lower output when it's in dehumidification mode. We do this a lot in Florida, and so you can't trust it when it's in dehumidification mode. You can't trust Delta.

T when the system is staged down, so if it's a multi-stage equipment and it's not running full speed now you can't trust delta T and so there's just all these factors in general, all things being the same higher delta T tells you that you have lower air Flow, so look at delta. T is essentially a ratio between a couple different things: mass flow rate of the compressor when the compressor moves more refrigerant, your delta T is gon na tend to be higher. So when your system capacity is higher, your delta T will tend to be higher when your system capacity is lower, your delta T will tend to be lower. If everything else stays the same, then you can all next look at air flow.

If you have higher air flow with everything else, working properly, you're gon na have a lower delta T. If you have lower air flow, you're gon na have a higher delta T, then you look at return. Air humidity, if the humidity in the space and therefore going over that of a protocol from the return, is higher. Then more of that energy is going to go to removing moisture you're gon na have a lower delta T.

If the relative minute in this space is lower, then you're gon na have a higher delta T. But you have to know all three of those things to make sense of it, so you can't just take a delta T and say: oh 20 degrees, we're good. You could have a 20 degree delta T and the system may not be working properly at all, because your target may be 23 or 24 or you may have a 20 degree delta T and your target may be 15 and it's actually assigned a very low airflow. So there's a lot of different factors there and delta T is only one of many measurements that you take and taken together can tell you if the system is working but taken by itself, really cannot tell you whether or not the systems working properly.

Now, when you use modern tools like the field piece, JobLink probes with the field piece, job link app or with the measure quick, app now they're going to recalculate on their own, what's your target delta T is and measure quick. Does a neat thing weird actually adjust for normalized system capacity based on the conditions, the equipment's working on, and it can also kind of estimate the airflow. So it's gon na do a better job of finding that target for you, because it's factoring in all three of those factors versus just looking at one and or in the case of the rule of thumb, just saying 20 degrees. That's just not enough.

One side crowded in the return a supply will supply dry-bulb. Now there are sort of like Universal charts out there. That will help. You calculate your target delta T, but in this case, because I have a variable speed unit, I have lower air flow per ton.

This is a 2-ton unit, and so you can still see that I'm on the high side of my target temperature split, but my target is showing as 20.8 because measure quick is normalizing for system capacity, given current conditions, whereas most of the universal ones are figuring. 400. Cfm per ton, they're figuring, you know kind of standard operating conditions and and with this piece of equipment, it's not going to produce the same capacity at in real field conditions as it would under some under standard operating conditions. So they or certainly not going to just per to produce 24,000 BTUs and that's why target delta T calculators can be quite a challenge.

So you can see in this particular case we're in dehumidifier mode. So the air handlers running lower blower speed, which is why we're seeing this current value on our delta T that's higher than even what measure quick is assuming it's, because we are running lower than normal air flows. This is why, as AC technicians, we often get frustrated, for example, with private home inspectors who will go out and they'll shoot a grill with with a laser thermometer with a infrared thermometer and they'll, say well that air is just not cold enough. Well, first off! That's not the place to take the temperature, that's not the tool to take it with, because infrareds are very affected by the acidity of the surface that you're shooting in the distance that you're shooting from and then finally, even saying 20 degrees is kind of a baseline.

That's just good enough unless you happen to know that all conditions are normal, the systems operating normally, then. At that point it can be an indication, but it's a poor indicator at best. Hopefully that helps we'll catch you in the next video.