Joined on April 16, 2013
Last Post on March 8, 2014
@ June 7, 2013 10:13 AM in High subcoolIf no burn-out, get that SLD out of there fast, as well as that sight glass. If you DID have a BO (better find out before going any farther), the SLD should hug the compressor. You should probably retest the compressor (again, only if a BO) for acid and sludge. I hope somebody didn't scab in a LLD on the low side! ANYTIME you open a system to atmosphere you have to change the LLD; get the biggest one you can. While the system is open you may as well make sure the TXV inlet screen is not plugged. If your manufacturer says it is OK, an Rx11 with nitro purge wouldn't hurt either. Also, make sure your manufacturer is happy with a 10' lineset. The factory charge is for 15' so too short may be trouble unless you add some more tubing.
The first thing that comes to mind with the SG is an overcharge, especially with your tubing so short. Lets hope for no BO, so you're down to getting rid of that SLD and sight glass, removing the LLD and installing an oversized one, checking with your unit's maker regarding the short tubing, and RJs weigh-in method. Fine-tune to manufacturer's chart.
@ June 6, 2013 10:46 PM in High subcoolHmmm. A drier on the low side? Did you have a burn-out? Is the drier next to the compressor where it should be, or in the line set? A burn-out would be the only reason you should have a low side drier, so it is possible the system was not cleaned up adequately, which would again lead us to a possible restriction. I would check your PD (a suction drier will have a service port for that very reason). If not, temperature is the way. If you have to start over, follow RJs lead. Best of luck.
@ June 6, 2013 7:02 PM in High subcoolI would check for non-condensables and restrictions first. Do a static check; with the system off for at least 20 min., your head pressure converted to temperature and your ambient should be the same. If higher than ambient you have something inside that shouldn't be there, causing an abnormally high SC. If OK, check for restrictions. You started that process by mentioning checking temperature or pressure drop across the drier or driers. If three degrees or less the driers are happy, so you might try to recover some refrigerant to see if this helps. Look for kinks in the tubing or an incorrect size. Watch your superheat too!!!!!
@ June 4, 2013 2:04 PM in Air PurifierThis is the issue that is largely ignored in our industry, for reasons I will never understand. I hope this clarifies that last sentence for you. Each and every component you connect to a furnace or air handler creates an air flow restriction. Ducts, fittings, registers, grilles, and accessories such as cooling coils, humidifiers, and your air cleaner or filter. This is fine, as long as you design for it. Think of it this way: if you have a 28' camper, you're not going to tow it with a Ford Ranger, so you wouldn't buy the Ranger after the camper unless you have a fascination for high blood pressure. If you add an air cleaner and the blower wasn't "prepared" for the added restriction, then something is going to suffer (that Ranger can't get the camper up the hill). This means poor heating and cooling performance, a high energy bill, and an air cleaner that doesn't do the job you expected. When you find out what is medically causing your SO's cough, contact me so we can revisit this. Also drop me a line if I didn't clarify the pressure drop issue enough to suit you.
@ June 3, 2013 10:36 PM in Air PurifierDon't spend any money on a product that someone "thinks" will help. Follow Bill's lead and find out what is causing the medical condition and work toward the elimination of the source. IAQ is a carefully planned process of filtration, purification, disinfection, and humidification. It hardly ever is just throwing an air cleaner on your system and hoping for the best. Additionally, if you don't consider the pressure drop created by the air cleaner and how it affects your blower and duct system, you're painting yourself into a horrible corner.
@ June 3, 2013 10:01 PM in cold tempsAssuming you're talking about residential units, low ambients have a greater impact with a fixed metering device. Since there is usually very little load, a machine with a FMD is in danger of not having a high enough superheat to avoid liquid refrigerant coming straight from the evaporator into the compressor. TXVs are more forgiving, as their job is to ensure a constant superheat at the compressor. Now to the other side. If the SH is too low, the compressor has to work very hard to mash liquid (instead of vapor) enough to raise the refrigerant temperature high enough above ambient so we can de-superheat it in the condenser. Since we can't change liquid into a liquid, you can imagine what your high and low side pressures will be, as well as a practically non-existing SC. If the compressor doesn't give up chewing on all of that liquid, it certainly will running when it doesn't have any work to do.
@ May 25, 2013 12:48 PM in Mitz sizing thoughtsI see your point. And, it seems as if the HO is trying to stop a bullet with a bullet.
@ May 24, 2013 6:46 PM in Mitz sizing thoughtsYou should feel comfortable with the size determined by your load calculation, provided it is ACCA Manual J or their sanctioned partner. Oversizing a mini-split with DC inverter technology could mean lack of oil return to the compressor during low load hours.
@ May 17, 2013 9:40 AM in Survey!I believe you will see most manufacturers are going to 15' from 25', so check the unit manual. But that is not lineset length; it is the factory refrigerant charge. You need to add "x" ounces per foot over 15'; again, that info is in the manual. Lineset TEL is in the manual too. It might be 60' for some models and 50' for others. Beyond those limitations you need the software we talked about or call your distributor. Regarding your question about sub cooling numbers: if you have 10 degrees of sub cooling, that means your actual LL temperature is 10 degrees cooler than your LL PSIG converted to temperature. This ensures your 100% column of liquid at the TXV. For example, if your LL is 295 PSIG with R-410A and your LL temperature is 85 degrees, then you have 10 degrees of sub cooling.
@ May 16, 2013 5:02 PM in Dry shipIs there some reason your customer won't choose an AS dry unit? You and your customer are taking a huge risk, as there is no AHRI rating for that combination, you can't guarantee the machine's performance, and there is technically no warranty coverage. If your customer insists and you still want to do the work, at least you have a TXV. weigh in York's recommended charge for your OD unit and lineset (find out if the OD charge includes 15' of lineset) and fine-tune to 10 degrees of sub cooling. Check your superheat too. At least you have done the best you can in a not very healthy situation. All of this is assuming you have cleaned both coils, checked the blower, and done your air flow calculation.
@ 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!