Joined on April 16, 2013
Last Post on November 24, 2013
@ May 16, 2013 8:40 AM in duct sizingDon't burn RJs Trane calculator; it has TELs of most common residential fittings on the back!
@ May 15, 2013 9:02 AM in duct sizingYou are right if your comparison is gas pressure to duct friction rate. FR is from blower outlet to inlet, yet many disregard pressure drops which can occur at any point along that stream. If your blower is rated for 1000 CFM at .50 IWC, then that is your FR. If you add a filter at .08 IWC, then your FR is .42 IWC, and so on. This is one of the reasons you can't read a duct calculator directly, saying for example "an 8 x 12 duct gives me 500 CFM at .10 IWC." No, it doesn't.
@ May 13, 2013 7:37 PM in duct sizingI applaud your efforts in putting this together; you obviously spent a lot of time on this. However, your procedure has to come after you pick the blower, not before. Your plan assumes the blower will deliver a certain desired CFM, yet it will not because there is no account for system pressure drops, nor is there a reference to the blower performance table and corresponding external static pressure. I have no doubt your system works, yet if you take into account these critical issues, you certainly will be at the top of your game.
@ May 13, 2013 2:55 PM in duct sizingDo you have PowerPoint on your computer? The above tests take about 10 minutes. It might be easier to see it rather than reading, and, when I made the slides, I didn't use any big words. I would be happy to send you a copy to any e-mail address you wish. If you don't have PP I can convert them to .pdf format. Also, I'm happy for you that you carry a toolbox all day. I have to drag mine.
@ May 13, 2013 9:19 AM in duct sizingThe first step is to determine your ESP across the blower inlet and outlet. Next, determine the pressure drops across both supply and return duct systems and subtract them from your ESP. The result is what that blower "sees" in the existing ducts, fittings, registers and grilles. Your first early warning is if either the SDs or the RDs are at .20 IWC or above. Your second warning is if the blower "sees" .30 IWC or more. I believe you can imagine what is happening here; if you need 1345 CFM for your new equipment for example, and your blower needs .50 IWC to reach that number, then you're already at .80 IWC. That is crazy-high, and we haven't added a filter or coil! Yikes! Is it no wonder that nationally, duct systems are performing at 57% of their capacity? There is good news, however. Since the SDs are usually hard to modify, the RDs are more easy to get to. The blower doesn't care whether you relieve the pressure on the supply or the return.
Here is a little secret for determining ESP. Since ESP means at the blower inlet and outlet, you can't leave the blower door open on the RA or accidentally drill a hole into your condensate pan on the SA while taking readings. First, check your furnace. My preferred maker gives me a hole in the blower compartment, so I don't have to drill one. perhaps your favorite brand does too. Rather than risking damage to the ID coil, take out the high limit card and tape the opening around your tube. That gets you exactly where you need to be (inlet and outlet) and before or after any pressure drops from components. When drilling holes for the coil and filter, I had my one and only flash of brilliance. I bought magnetic business cards to hide them.
@ May 13, 2013 8:45 AM in duct sizingI believe you are dead right. I am an ACCA disciple and am not that familiar with EF, yet we are looking for the same answer, which is the maker's blower determines the duct size parameters. I use ASP and TEL to determine the design friction rate, while you use ASP and EF.
@ May 12, 2013 9:54 PM in Vertical Seperation limitations.Even though R/R has stated a limit, I would still call them. Those guidelines are for the rule breakers you mentioned to try to keep them out of trouble. R/R may say 25 is 25, or they will help you engineer a way, such as tubing sizes, perhaps a suction line trap, sump heater, hard start kit, or other approved methods. Again, their proprietary software will really help you save time and lower your blood pressure if you run into these situations often.
@ May 12, 2013 9:39 PM in duct sizingOn a new installation, lets assume your load calculation requires 1150 CFM. You then look in the fan table of your chosen unit to see what ESP the selected unit will give you as close to 1150 as possible on medium speed. If that ESP is .60 with a filter, you subtract .06 for your registers and grilles and other components. If the ID coil is .21, and you have no other components, then you have .33 left for your duct system. If the TEL of the ducts is 250' your duct design pressure is .33 x 100/250, or .132. Now you can look at your duct calculator and determine what size duct will give you 1150 CFM at a pressure of .132.
If you would like, I would be happy to discuss existing system methodology as well.
@ May 12, 2013 1:56 PM in What is a Nomograph Chart ?Thanks for the good findings, and to you likewise! I see your point about evaporators up or down. On the typical residential application, as long as the TEL is within specs and the correct amount of compensating refrigerant has been introduced, your maker's SC guarantees a full liquid line. In your mile-high example I'm totally with you; engineering is needed. That's when I pop in the maker's software; getting too lazy to lug around those groovy old manuals like your Carrier set (you know, the folks who practically invented air conditioning). Wouldn't it be great if these situations were only on new jobs, instead of having to rectify the OPMs? (Other people's messes)
@ May 12, 2013 9:58 AM in What is a Nomograph Chart ?Real classics, here! Way too cool; keep them in good condition! What has happened since these wonderful publications is the manufacturer making things more simple for us in the field. A perfect example is practically everyone charges their OD units for the condenser, a 15' lineset, and the smallest AHRI matched ID coil. Then they tell you to add "x" ounces for each foot over 15, up to a certain TEL. Here is where your wonderful nomographs came in, yet they are now on proprietary software programs. You enter the conditions in the field and the program tells you if your LL and SL PDs are OK and what you need to do to make them happy. Upsizing tubing usually is the answer and the software also tells you how much refrigerant to add. If you don't have the software a call to your local distributor gets you your info.
@ May 9, 2013 8:46 AM in What is a Nomograph Chart ?It is the factory chart inside your unit regardless of sub cooling or superheat. If my "x" is ???, then my "y" should be ????. For example, at an IWB of 63, at an ambient of 80, the intersecting lines may indicate 70 PSIG of vapor pressure.
@ May 6, 2013 8:50 AM in subcoolProvided your lineset is sized within factory tolerances, if you have the correct sub cooling, you're a winner. It doesn't go any farther than that, yet again, check your superheat too. Weigh-in, as we have discussed earlier, is for the smallest AHRI coil. It is easy to add refrigerant for longer linesets, yet you don't know how many ounces you may be off if there is an up sized evaporator. Your sub cooling and superheat checks will tell you that. I don't believe you're oddball at all. I take a firm stand against field-invented charging methods such as sight glasses, beer can cold, or charging to a 40 degree evaporator or a certain TD. Our customers and our brother and sister technicians deserve better than that. I mean no disrespects either, but this wall should be an educational tool to keep us all at the top of our game. By the way, regarding LL insulation in an attic: if you have more than 5 uninsulated feet, you're going to create flash gas, and tons of it. So dump away with refrigerant trying to get your sub cooling in line, and you have changed your condensing coil into a liquid receiver. Yikes! I understand your thoughts by putting gauges on first, but allow me to present this: if your airflow is not right, your charge will NEVER be right, and there is no duct calculator involved because that won't tell you anything because you can't read a duct calculator directly. It's all about pressure!
@ May 4, 2013 12:03 PM in subcoolYou are exactly right, provided the following conditions apply: someone has not installed a longer lineset than the factory allows without making approved adjustments; you do not have more than 5 uninsulated feet of LL in an attic, your sub cooling temperature is within the factory's happy range, and your superheat is within the designed range. It is a piece of cake to check just to reassure yourself. If it is 90 degrees outside, then the LL is going to be roughly ambient temperature at the entrance to the evaporator. If the two temperatures (1 at the service valve and 1 at the ID coil) have a substantial difference, you may have a crimped or undersized LL, or any of the above conditions. That is what sub cooling is all about; making sure the TXV gets a mouthful of liquid ONLY. However, I will again stress that the refrigerant charge should be the last thing on your list. Clean ID and OD coils, clean filter, duct pressures within the correct range should ALWAYS be before grabbing the gauges.
@ May 3, 2013 11:48 AM in subcoolI believe there has been some misunderstanding here, and I will certainly blame myself for not communicating well. It was my impression that Paul's question involved a new air conditioner or heat pump installation (not a refrigeration unit) and you can follow that train of thought through these posts. For a "no cooling" call in which you have eliminated other possibilities (refrigerant should always be last on the list) and believe the malfunction is charge related, my part of this session was my firm belief in charging a unit via the manufacturer's recommended method, period, whatever that method may be. Hence the charts inside the unit. In response to your question as to how many of us check for 100% liquid at the TXV, the answer is everyone of us who checks their sub cooling. Yet that is not a stopping point; even with a TXV one should still look at the superheat to ensure health and happiness for the compressor. If the charts are gone on that Friday night call and you're at 10 degrees of sub cooling and 15-18 degrees of super heat, at least you know you're in a safe enough range until you can obtain the maker's data. If you have a fixed metering device, the super heat calculators are OK provided you know the indoor wet bulb temperature.
@ May 3, 2013 11:47 AM in subcoolI believe there has been some misunderstanding here, and I will certainly blame myself for not communicating well. It was my impression that Paul's question involved a new air conditioner or heat pump installation (not a refrigeration unit) and you can follow that train of thought through these posts. For a "no cooling" call in which you have eliminated other possibilities (refrigerant should always be last on the list) and believe the malfunction is charge related, my part of this session was my firm belief in charging a unit via the manufacturer's recommended method, period, whatever that method may be. Hence the charts inside the unit. In response to your question as to how many of us check for 100% liquid at the TXV, the answer is everyone of us who checks their sub cooling. Yet that is not a stopping point; even with a TXV one should still look at the superheat to ensure health and happiness for the compressor. If the charts are gone on that Friday night call and you're at 10 degrees of sub cooling and 15-18 degrees of super heat, at least you know you're in a safe enough range until you can obtain the maker's data. If you have a fixed metering device, the super heat calculators are OK provided you know the indoor wet bulb temperature.
@ May 2, 2013 9:22 AM in subcoolPerfectly said; end of story. Now, if you change your login name to Chubby Checker,........
@ May 1, 2013 11:24 AM in subcoolI agree that many methods may work. However, I still maintain that best method is the one your manufacturer wants.
@ April 28, 2013 7:20 PM in subcoolThe 100% column of liquid your TXV is looking for starts at the exit of the condensing coil. If you don't have it there, it won't magically appear on its way to the TXV. That is what sub cooling is all about; ensuring there is no flash gas in the liquid line and keeping the flash gas that naturally occurs during the metering process within a tolerable percentage. With respect to refrigerants operating at the same temperature, your liquid line would be the same temperature if the pressure is 115 PSIG for R-22 and 254 with R-410A, but I am confused as to how this apples to the use or non-use of sight glasses. Again, if your manufacturer wants you to use one as a charging device, then you are an RTM technician and bless you for it. Nationally, 72% of all installations do not have the correct charge, so we owe our customers and our industry a healthy dose of "get it right."
@ April 28, 2013 12:10 PM in subcoolGood for you! Weighing in with the correct amount of refrigerant for your lineset means you could be mere ounces off instead of not even being in the ballpark. Your outdoor unit comes with a charge for it, "x" feet of tubing, and the smallest AHRI matched coil. If you have used a larger evaporator to up the EER, then you know right away your charge is a little off, yet not enough to cause poor performance until you can return in the right weather. Remember we said earlier to create some indoor load if you have to. Turning on the furnace is all sensible load, so while you check your sub cooling, look at your superheated as well. Both within acceptable range means job well done, and the unit will be happy under any condition.
@ April 28, 2013 12:00 PM in subcoolR-410A operates at pressures 70% higher than we are used to, so a clear glass could easily mean overcharge. The best method is RTM (read the manual) and introduce refrigerant the way your manufacturer wants it done. Then use his charts in the unit to make your system happy. A sight glass won't tell you that you have 10 degrees of sub cooling if that is what your unit needs. What is sub cooling? It is to ensure a 100% column of liquid at the evaporator, yet too much liquid means you know what.
@ April 28, 2013 11:48 AM in subcoolDon't forget that temperature drop also means pressure drop. Since we can't see inside the drier, we can assume the drop equals either moisture or some other nasties. Either way, it's bad news for the system.