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Not Cool:

Be kind. I'm not an Airhead nor a chilled wet head. But I have questions.

Where I live now in Florida I bought in 2005. The AC was replaced in 1996 to replace something that was installed in 1982 with some sort of hot water recovery HP unit that had failed. Same usual slam it in system. Louvered door in a closet where the AC is, supply ducted to an unconfined attic space with flex duct. Someone lived here year around (from 1982) until we bought it in 2005. There were no signs of water damage to the ceilings around ceiling grills. If there had been, I would have noticed it. After a few years, I noticed a wet spot on the ceiling above and in front of the unit. I went up into the attic and wrapped it with more insulation and covered the duct work with more batt insulation. Which mostly stopped that. There was never any ceiling wet staining around the ceiling grills until last June (2013) when we moved here. I noticed the ceiling staining, but no worse where I had originally seen it. In other words, it wasn't leaking. At over 100 degrees the old unit would cycle on and off all day with the cooling at 78 or 77. We keep it at 79 mostly. Last Fall (October), I had it serviced. It was fine. I asked them about replacing the attic duct because of the wet spots, it was falling apart, it was 30 years old, and I wanted it upgraded. I asked them to use R-8 duct but they told me that no one around uses it and it had to be special ordered from the supply house. They used R-6 like everyone else. Turned out what I thought was R2 or R4 was actually R-6 anyway. They replaced all the flex board boxes with bigger, better and thicker ones.

While I have the money, and not wanting to face a expensive replacement 5 years down the line on a 15+ YO system, I asked them to replace it. They did a fine job. There was an issue with the new unit inside. The old unit had the intake on the bottom. Its above a water heater. The unit to replace the old one was a 10 SEER (or less from age) and the best they could give me was 14 SEER because of a height limitation through the door. I came up with using steel flat stock across the closet walls but the installer went with two pieces of hanger stock and put a cover plate and moved the intake/filter to the front where I assume it is also designed to go. It is much noisier from an airflow point than the old unit. The ceilings are staining. the unit never shuts off when the temperature is over 98 degrees OAT. It used to cycle at over 100 degrees with 77 degree inside air and not sweat. I get plenty of air from the ceiling registers, the wet isn't dripping out of the vents, it is forming on the metal in the room. It seems like there isn't enough air flow? There is much room for unrestricted air flow when the air enters from the side than would be from the bottom.

There's a lot of things that I could do but it isn't working like the old one. Yesterday, the compressor stopped for unrelated reasons. The installer came and got it going. I told him that the thing didn't work well at all, That my electric bill compared to last year with the old unit was half again as high per KWH, attributable to the AC. He said that it should go down to 75 degrees and cycle. It goes down to 79 and won't cycle. At 12:00 PM.Noon, it was 84 degrees out, and 82 in the house. I turned the thermostat to 79. The OAT went to just over 99 degrees. It has now dropped 94 degrees OAT. it went to 79 degrees after three hours and hasn't stopped running since.

What am I missing? Lack of heavy airflow to be moving air and drying it out? Is the big plastic fan cage in the well known manufacturers unit just not moving enough air? Is it too fat and restrictive in side the return box? I wish they had put in another Rheem unit. I'm suspicious of this. I know that WA/AC units like Plenums. A return plenum is out of the question. Every one of the 240 units in here is the same and they don't have plenums.

And my wife is none too pleased.

Any constructive thoughts? Any "tightening up" of the structure shouldn't figure in. Its just like a common boiler change. They don't understand the mechanics of heat loss, heat gain and the movement of moisture in Florida.

Is it true (like I was told) that in Florida, cold flows through the walls to get to the heat? Same with the moisture?


  • meplumber
    meplumber Member Posts: 678
    edited July 2014
    Having trouble picturing it.

    Chris, it sounds like you have an airflow problem, possibly in combination with something else going on.  To help me get my head around it, I have a homework assignment for you.

    Can you get me the model # of the air handler and the condenser?  Also, any chance of posting a couple of pictures of the air handler and condenser install?  Can you take a temp probe and give us the suction and liquid line temps at the condenser and the air handler? Can you guess at the line length between the evap coil and condenser? That would be a start so we could give you some guidance.

    Good Luck.
  • Techman
    Techman Member Posts: 2,144
    edited July 2014
    not cool,

     Ice,calling us AirHeads, some here(no names) like to call us ReferHeads! LOL!!!! Back uphere in the North East ,AC's were sized based on a 20* TD between indoor/outdoor temps, 80*F in /100*F out, and just like a boiler on a very cold day, if the OA temp goes up to 101* the  AC unit will run continuously, nowadays most units are sized on a 15* TD between in/out temps 100* out /85* in. I do not know what applies to Fla, USA. Get the temp readings as per meplumber, also get temps of the return air at the AHU and then at each supply register. There is something going on . A lot of unit's don't like an "open" return ,meaning some sort of return plenum is, most times required. Next time that AC guy is there get a set of reading of the Freon pressurers ,in/out temp , indoor Wet Bulb if possible. A couple of pict's of the outdoor unit will help. What kind of blower motor is in the AHU? KindaSorta, the slower the air goes the more dehumidification takes place, the air/moisture is in contact w/the cooling coil longer.
  • icesailor
    icesailor Member Posts: 7,265
    Air handler:

    Well, I can't give you all the information you want, but maybe this will help.

    The air handler is a Trane 18-GJ52D1-3 3 ton air handler. They came together. I doubt that the compressor is part of the problem. The installation for the air handler shows that for a vertical installation etc, and heights above electric water heaters etc, that you can use side entrances for the return. There isn't any information. It faces a metal louvered door. They must have bought a kit to convert it to a side inlet. There is a bottom metal plate that covers the bottom, sealing it off. There is a side louvered plate that takes the place of the lower blower cover panel. It has a tray to put a filter in and a clip to hold in the filter. I know that plenums are important. There was no kind of plenum before, and none now. Before the filter was on the bottom. Now it is on the side. The blower assembly is much wider and fatter on the front side against the filter and there isn't a lot of clearance between the left side and the sound insulation.

    It seems like it is a air flow problem and it isn't removing moisture like it could. And bad airflow because there is enough moisture left in the air to condense on the cold surfaces of the grills. It doesn't do it on every grill, just the ones closest to the Air handler. And its not coming out of the vent.

    Its not running 100% at the moment because there is some sort of motorized valve as part of the expansion valve and it stopped working yesterday. Which made a low pressure control drop out and it caused a fault, overheating the compressor outside. It is supposed to be running wide open like the valve is wide open. Or so I was told. Before, the liquid and vapor line were not far apart in temperature, Now, the liquid line is the same but the vapor line is cold. Not freezing but cold. They are coming with a new part on Monday. That hasn't changed the long running times.

    I've seen a lot of installs. This is a nice install and far better than the one they replaced. It sure sounds like a air flow restriction to me. I can't post photos since someone thought my camera was fanny pack and stole it to get the wallet. Which wasn't in there. I haven't replaced it yet.
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014
    Refer heads?

    ReferHeads? Don't they smoke the Kind Bud? As opposed to drinking the kind Bud.

    "Reefer Madness". That campy old terror movie done in the 1930's by the tobacco companies. One hit and a week later, you were dead with a needle in your arm.
  • icesailor
    icesailor Member Posts: 7,265

    Its hard not to intimidate people when you know about their trade. I try to keep to myself. This guy and his company don't make me feel like when I have gone to some dentists down here. Opening my mouth is like opening my wallet. And they all want to grab what's there. For example, in the world which I worked in, if someone asked me about R-8 flex duct and I always used R-6, I would have been on that like stink on horse ship. I'd be giving a price for the entire job in R-6, and an additional increase amount for the R-8. You already know what you need and it isn't going to take you any longer to install it. Like taking Manna from Heaven. Not in Florida. We don't do that. Why be in business if you don't want to get every dime someone is willing to spend.

    Last October, when I had it serviced, I knew nothing about AC. He was checking pressures and he mentioned a 10 degree Delta T. We discussed that up North, we use a 20 degree Delta T as a target. I had no idea that you could tell the temperatures by the pressures on the gauges. Knock me in the head. I asked him yesterday, "So, is it the purple scale or the green scale you're reading?" Purple. Says he. He said the pressures were OK. 7 years ago, it wasn't working properly and someone came recommended by someone. My wife called the company. They sent someone in a beater truck. The driver looked as beat up as his truck. Image is everything. It was low on gas. He told me I had a leak but he couldn't find one. That I needed to replace the lines. They went under the floor, like all the other 240 units do. We left two days later for MA and he was supposed to come and replace the leaking line. He never came back to change them.  It hasn't leaked a drop in 7 years and is still running on the same line set.

    The Rheem had a lot more room inside the blower housing. The blower was all metal and the housing. This one is all extruded plastic. I could see that it might need some breathing room.

    There's a formula for how much louvres cut down on a size. Maybe I need to cut them all off. They are behind the 16" X 16" filter. I took all kinds of temperature measurements with my Multimeter but I discovered that one probe stopped working and the other is way off.
  • Techman
    Techman Member Posts: 2,144
    edited July 2014
    Not Cool

    Being a ReferHead means that you know about the green scale vs the purple scale means the pressurers are different but the temps are the same. At the moment I have 6 different colored drums on board my truck  and 6 more  different colored drums in the shop. Just r22 and r410a, ha!!  I wish it was that simple! There are MANY colored scales but only one temp scale. Get a digital thermometer that has a decimal point in in , like 72.4*F NOT just 72*F . Open the louvered doors before you remove/repair/replace them. Got a picture or two ,of the outdoor unit also. Have the AC guy give you a set of readings the next time he's there along w/ in/out temps and a reading of the discharge air off of the outdoor unit.
  • don_9
    don_9 Member Posts: 395
    edited July 2014
    In agreement

    With techman sounds like you are at design load. Personally I prefer longer run time over the start and stop cycle for comfort reason only.Also keep in mind that a lot of guys assume that if they pulled out a three ton unit 10 seer and put a 3 ton 14 seer in it place they are going to get the same capacity and that not the case when I run the numbers.

    So your first step should be is to run a manual J load calc and find out what your shr is. Then you can check your equipment with the manufacturer data and see if your equipment can handle the load.

    You can also check or have someone do a performance test on your equipment and see if I is giving you the rated capacity.

    I would stick a thermometer on the suction line coming out of the air handler and see what my line temp was.If you have 16 to a 20 degree drop from entering return temps then she doing the job.Then check your temp at the air-handler and then at the duct at the end of the line and compare the two temps that will help you to see if your duct is picking up a lot of heat gain.

    Happy hunting and as for you knowing a lot about what we do, I wish I had more customer that were knowledgeable when it comes to their system it would make my job much easier and help weed out the one getting the job on price alone.
  • RobG
    RobG Member Posts: 1,850

    As you know, there is something way wrong if you cannot maintain 79 degrees in your condo. My wife keeps the A/C at 70 with no problems. Granted, we are in in slightly cooler climate (95 to 100) during a hot spell. Since the system is new, why are you troubleshooting it? I would set it at 72 tonight and show the tech tomorrow that you can barely maintain 79. If you put in a boiler and it would only heat the home to 60 on design day and you designed the the system for 70 I guarantee you would fix it. That's what being a professional is!


  • icesailor
    icesailor Member Posts: 7,265

    The AH is a GAF2A0A36M32SB. The number I gave you before must be a number for the instruction manual.

    The Compressor unit is a 4TTB6036A.

    I had all kinds of really cool and accurate temperature measuring devices that I left behind. I never thought that I would be needing or using them here.
  • icesailor
    icesailor Member Posts: 7,265

    Understand that it isn't really that the system is new, but replaced in kind. Some ducts were slightly increased but the idea was to replace 30 YO flex ducting with newer ducts. The two thingy's between were replaced. Knowing that Florida is the land of the cheap, and technical educations is for Liberal Yankees and retiring snow birds, these problems have probably been there for a time.
  • Techman
    Techman Member Posts: 2,144

    Hay ice, since you haven't sent picture's, YET, I gotta ask. Is supply duct,plenum, coming off of the new AHU the size of the opening of the AHU or is the duct much bigger than the opening of the AHU ?
  • icesailor
    icesailor Member Posts: 7,265
    Knowledgable Customers:

    I've found that to be a problem. We have a 2001 BMW 325XI AWD wagon with 150,000+ miles and it looks almost new. We bought it new in 2001. It recently developed an odd noise in the rear drivetrain that only seldom happened under odd circumstances. You and I know that those are the hardest types of problems to solve if they don't happen repeatedly. "It makes a clunk when you start off but only certain ways and not always". Yeah, right. The large BMW dealer is known for their refusal to give customers a jar of Vaseline and a pair of jeans with a hole in the back. Their solution to a problem situation is to sell you a new car and sell yours to someone who doesn't know there is a problem. We take it to be serviced and repaired to a local service guy that does well and well by us. That didn't work. So I found some person who repaired all kinds of foreign cars. All his mechanics had trained with the top new exotic car dealerships and moved on the better paying shops. The owner started the business from scratch and it was a family affair now. I brought it to him and told him what was up. I immediately felt pull back because I knew more about things that his average wealthy customer (which I am not). But I could be a potential PITA.

    Fast Forward to: I took an Amigo mechanic for a 5 mile ride and of course, not once did it happen. I mentioned that I had a 1966 Ford Bronco that had a limited slip differential and after I drove it 5 or 10 miles and it got hot, when I went around a corner, it would "Hop" around the corner when turning. The dealers guys nicknamed me "Hoppy" behind my back because it wouldn't "hop" for them. Kind of like when I built my first house and the lights would dim occasionally in the evening, repetitively. The power company put recording Current Meters on the service. They named ne "Blinky" because the diming was almost like a blink. They gave me that name after I pointed that the "Blinks" could easily come between the dots on the recording meters. Kind of like why you don't use digital volt meters to look for quick spikes, you use an analog meter. The Amigo knew exactly what I was talking about because the BMW has the Posi unit in a transfer case and the Mercedes has theirs in the transmission tail shaft. They finally figured out that the clutches weren't being lubricated because someone had put the wrong gear oil in the case. Drive it 20 revolutions to the left and 20 revolutions to the right. Open the clutches and it lubricates the disks. Problem solved. After another hand wringing experience, and I had to just completely subjugate myself as an almost know nothing idiot, they took it for a ride themselves and sure enough, it DID do it. The transfer case was empty. Filled for a lifetime with a very small amount of expensive fluid. All is good. The work was excellent. My point is that you have to listen carefully. Especially when you know things that the other person doesn't. Talking things out (like done here) often leads to solutions. Or at least new ideas.

    I'll have to start a new thread.
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014
    Photo's & Sizes:Unintended consequences.

    I don't have a camera that I can take pictures with and post them. My old camera was stolen.

    As far as the outlet size, it is full size as far as it can go into the attic space between the reducer at the ceiling, and between a bottom truss chord. Without measuring it, I could estimate that it might be 4' from the top of the unit to the top of the plenum box in the attic where the take-offs occur. Including the reducer.

    But I think we have figured out the problems. And like you said, maybe they were here all along. How much cooling can a 1200 sq. ft. building with 8' ceilings need?

    3 tons equals 36,000 BTU's? Granted, there isn't a double paned window in the whole entire house. The front faces North, the side faces West. The East is a common occupied wall. The attic is what it is.

    When we bought the place, it looked fine. No peeling paint, the place looked well taken care of by an old retired Jewish widow. Who drove a car until she was 92 and sold it to us so she could move in to an assisted living facility. 3 or 4 years ago, they replaced the roofs. The roof/attic ventilation was provided by full length soffit vents on the overhangs and 4" round/square vents through the plywood a few feet below the ridge. So, all the ventilation of the hot air came from the two or 3 square roof ventilators. Now, they have full length pubic hair ridge vents to help with ventilation and cooler attics. Which I doubt are any cooler. You now have many times the amount of air flow of hot moist air. HOT, MOIST AIR!!!. So, the entire place except for the two bathrooms (small) have "pop-corn" ceilings. Sprayed on to a latex primed Sheetrock. The primer is probably some of that Spec(ulative) grade builder grade white primer that they get in 55 gallon drums. The whole place was sprayed with the stuff with an airless sprayed. Even the edges of the concrete floors. Before I tiled the floors (ceramic tile), I only had to spray it with Krud Kutter and scrape it with 3" sheet rock trowel. Wipe up the rest with warm water and a sponge. The kitchen was the first place I tackled. They had wallpapered the walls and ceiling with Vinyl wallpaper. The ceiling was falling off. It wasn't like that when we bought it. The quality primer was everywhere. The wallpaper came off the ceiling in sheets once I ripped the vinyl off. Spray the primer and It came off with a sponge and a scraper. The ceiling was quite hot during the day. I replaced the entire ceiling with a white 1/4" PVC  beaded board that I glued and nailed to the Sheetrock. End of that ceiling peeling. I painted the two bathroom ceilings that were painted with minor peeling here and there. It wasn't peeling in 2005.

    Modern/new vinyl paint has a vapor barrier in it, they claim. That garbage Contractor primer doesn't and nor does the paint that holds the "Pop-Corn" particles in place. After 30+ years, it looks like it was sprayed yesterday. But, if heat flows to cold, and dampness flows to dryness, how much moisture is migrating through the Sheetrock and adding to the moisture in the room? Probably a lot. And the symptom is the condensation on the coldest ceiling registers, closest to the Air Handler. And brought on by the increased new airflow in the attic airspace with more hot moist air that is supposed to keep the attic space cooler. I'll bet that if I had a way to measure moisture, the moisture content 2" down from the ceiling, it is much higher that 12" down. Ever see a building after a fire and the smoke patterns on walls and ceilings?

    What I need is a whole lot more insulation on the ceiling of the attic.

    I asked the AC guy if his company had anyone that they worked with that did insulation? He said no, they never got involved in that kind of thing. REALLY.

    So, you sell someone new equipment so they can save money with the efficiency, and it still uses the same amount of energy? The customers think you are a pirate. Tell them about tightening up the house AND changing the equipment, and they save big time. And you are a hero. AND, you sold new equipment. They will never tell you that they didn't save anything. They WILL when you get them to do tightening up expenditures that make it look like you really fixed them up. If they chose not to tighten up, and the cost of operation doesn't go down (like mine hasn't), you have something to blame it on. According to my thermometer, the humidity is 47%. According to my Honeywell Humidistat, it is around 54%. NOAA says that the RH ay PBIA is 63% and the Dew Point is 74 degrees. 5 miles away.

    If I am at design limit, what do I do to lower/raise the limit? Cut down on heat loss/gain. I can't change windows and doors. Or insulation in stucco walls, But I can add to attics.

    Of interest to me is, why might a 10 SEER cool better than a 14 SEER 3 ton unit? They are both supposed to put out the same amount of cooling energy.

    I'm teachable.
  • Techman
    Techman Member Posts: 2,144
    edited July 2014
    not cool

    Sizing of the AC. In the 70'S and into the 80's a 1200 sq ft house was a 3ton load and that was 1200 cfm. Then came tighter homes. True 3t is 36k btu's , in the N.E. that was KindaSorta 12k for dehumidification and 24k for temp (sensible) at stabilized conditions. That 10 seer vs the newer 14seer, the higher seer uses a larger evap coil, which raises the suction press a little which raises the lo side temp also.That higher temp reduces the amount of moisture removal.  What is the SensibleHeatRatio in Fla.?

    Ice, one more time cause I'm a little slow. The supply duct coming off of the AHU is about the same size as the AHU? KindaSorta, the discharge air opening of the AHU is about 12 x 16 and that should be the plenum size also, then a few feet away (or so) a transition piece goes up in size to the main trunk size.

    Hi to lo it goes. Moisture goes to dryness and moisture also goes to coldness. The vapor barrier is supposed to be on the warn side of the equation, in the prevalent season. If the moisture gets into the wall it can condense in the wall.
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014
    Unintended Consequences:

    First of all, I really want to thank any and all of you that have taken the time to respond. It is deeply appreciated.

    I found this about the Sensible heat ratio,



    More firmly than ever do believe that anything that someone tries to do better, the laws of unintended consequences will come to play in your sand box. That no good deed goes unpunished.

    So, it seems that if you go from an older, less efficient AC unit to a better and more efficient unit, AND YOU DON"T CAREFULLY UNDERSTABD WHAT CAN HAPPEN, you might want to put in the next size larger. If you have a 3 ton unit, you might need a 4 ton unit to get the same performance.

    Or, you make the building loss smaller. The stories I can tell. The people dying in cellars in New England with portable de-humidifiers that had to open the windows because it was so hot and humid so they had to open the windows to cool off. I'd tell them to put in a Mini-Split. You have no idea how many Mini-Splits I sold for others to solve humidity problems. Installed by people that knew as professionals, far less than I did as someone that isn't in that trade.

    Getting back to my problem, so I now have a technically smaller system than I did before. So, I either change the system, or decrease the cooling load. Which can be done by increasing the insulation and heat gain through the ceiling. Easy to do. If you really want to know that SHR ratio, you could use Miami and Atlanta as a comparison. I'm closer to Miami than Atlanta so it gives you something. It says in the article that the standard comfort level for cooling is 75 degrees. We're perfectly comfortable with 79/78 degrees.  

    Plenum's: The old AH had a 16" X 20" opening. The new one has a 16" X 16" opening.

    Oh ship. When they made the new supply plenum to replace the two piece  old one (part from 1982 the other part from 1996) they reduced it on one side by 5". So, now it is 21" on one side but 10" +/- on the other. Less the inside dimensions. Like the new common practice of running 1/2 CTS PEX (5/8" OD, 3/8" ID) in place of 1/2" nom. Cop Tube (5/8" OD, 1/2" ID). I think they made the box to match the original from 1982 that they had added on to in 1996.

    Moisture goes to dryness and moisture also goes to coldness. The vapor barrier is supposed to be on the warn side of the equation, in the prevalent season. If the moisture gets into the wall it can condense in the wall.

    (( Moisture goes to dryness and moisture also goes to coldness. The vapor barrier is supposed to be on the warn side of the equation, in the prevalent season. If the moisture gets into the wall it can condense in the wall))

    And a adult beverage in a glass with ice condenses water on the glass unless you use one of those Kozee things.

    So, in Florida, the faced/vapor barrier side of batt insulation should face the outside because the outside is warmer than the inside. The inside being cooler (because of AC) can cause mildew growth on the back of the sheetrock or the back side of the fiberglass insulation. In the North, the mold in on the plywood.

    I guess I'll have to find someone that does blown insulation in in July. Not me. I'm so rickety that I have visions of me falling through the ceiling when I tip over.

    (long) Sigh, Mother will not be happy. The other one was working fine. Just the moisture on the sheetrock. From more airflow in the attic for ventilation. And I still have moisture on the sheetrock.
  • Techman
    Techman Member Posts: 2,144
    not cool

    Or a 3 1/2 t cond unit w/ the 3t indoor unit . Can your ducts handle the new 4t AHU which moves 1600 cfm . A proper heat gain estimate might be needed.
  • icesailor
    icesailor Member Posts: 7,265
    Heat Gain:

    I think that the way that the attic is insulted, it might as well not be. Just the ceiling temperature during the day when it is hot out is bad. If the thermostat is set for 79, and the room temperature is reading 79, and a IR thermometer gun says the tile floor/slab in 75, but the sheetrock ceiling is 85 and it is 95 outside, you have a serious heat transfer the wrong way. I think that the new and improved attic ventilation is helping with unintended consequences. I knew a few that thought they were pretty hot moving the air around that would get that Deer In The Headlights look if I asked them about that higher SEER doesn't do humidity as well as the lower SEER one. I'm a guy that never looked at a heating job that I didn't do a complete heat loss calculation and radiation count. Even if it was just a boiler change. Like everywhere. Everyone wants to train and license installers to install the latest high tech equipment. It doesn't mean anyone will use the best training and practices. To make sure that the consumer doesn't get screwed. Then, they can't even do a simple check to be sure that the new equipment is sufficient? I couldn't imagine how they would connect in the closet. Its a small closet. But they took 5" X 21" off one side, room they already had in the ceiling opening. So is the plenum box smaller than the original one?

    Are you one of those like me, who does it yourself because someone you hire to do it for you will screw something up? When I need help, I call me.

    My #1 saying about work.

    There's never enough time to do it right. But always time for someone else to do it over.
  • Techman
    Techman Member Posts: 2,144
    not cool

    A simple test here.Turn the t'stat down to 75-76* at nite and let it run all thru the next day. Do you have a humidity tester? What is the design temp for Miami ? A properly sized AC will run forever at OAT above design temp. The IAT will rise as OAT goes above design air temp's.  
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014
    OAT designs:

    Thanks for the information.

    I try to never ask questions of someone without some clue about the subject.

    So according to the ACCA/ANSI data, where I live (West Palm Beach), and Miami have the same design loads, 90 degrees. I have a moderate swing but Miami has a low swing. Therefore, if it is 90 degrees out, the unit should run continuously. If the indoor temperature is designed to be 75 degrees. Or a 15 degree Delta T? So if the OAT was 95, the indoor moves to 80 degrees. Unless you have extra capacity. So, on a day when it is 95 degrees out, if the system was designed to just provide cooling for 75 degrees inside (IAT) with 90 degree OAT, it will only maintain 80 degrees inside. Its too bad that some don't do their homework and should just stick to changing filters and parts. Leave design and replacement to those that have more than a basic understanding. It isn't like the information isn't available. "Have you ever seen any Web Site like HVAC-Talk.com or heatinghelp.com? There is an incredible amount of information available?" No, I haven't turned on my computer in over three years.

    It shows.

    Don't cop an attitude or get  face on if the customer asks you difficult questions.

    No matter the effect of decreasing the size of the AH outlet, the heat gain will remain the same. If I have the outlet increased, I still have the same gain. My money is always better spent on lessening gains. So, my first money should go to more insulation in the largest cooling loss load in the area, the ceiling. Its like insulation DHW and heating pipes. You don't realize how much it will improve things until you do it. Massachusetts requires all DHW and heating pipes to be insulated. Great work for the insulators. I could hire an insulating contractor to insulate water pipes for less money than I could buy just the insulation.

    So, what do you think of my thesis that improving attic ventilation has the unintended consequences of increasing heat gain or heat loss due to infiltration?  
  • Techman
    Techman Member Posts: 2,144
    not cool

    ice, lets say the 3t -36k is what you need and the problem is the bigger, hi eff evap coil ,then a 3 1/2 t cond will be "oversized", but ,that oversized comp will pull the lo side press down lower. Lower loside press means colder Freon temps causing better dehumidification.

    Or the heat gain calc will show that you need a 3 1/2 t (42k btu)system and your existing system is undersized.
  • icesailor
    icesailor Member Posts: 7,265
    edited July 2014
    Temperature and humidity:

    Maybe we're reading different pages.

    I don't know how accurate those digital indoor/outdoor thermometers with humidity readings are, The temperature on the thermostat and the indoor/outdoor (inside portion) match closely. When the A/H is running for any length of time, the humidity is always below 50%. It is 86* OAT with 66% RH. Inside on the same thermometer, it was 77* IAT and 42% RH. If I take it outside, the RH will go up. When I bring it back in, it goes down. That's worth something.

    It fits in with the numbers at PBIA at this time. 87*F, 63% RH and 73* Dew Point. If you have a inside rise in temperature and a rise in humidity, you have infiltration. If you have a rise in temperature but no rise in humidity/dew point, you have something transferring heat. I guess that would be convection/radiation. You'd be surprised at what you can tell with a IR thermometer gun. The ceramic tile floors are all 75/76*. Some places on walls near the top are 80+*, others are 78. On closet ceiling (one that I know has an insulation problem) is 88 degrees. Remember, I come from a place where 70 MPH wind speed was a "normal" North Easter. That last big draft we had back in March or April, it gusted over 95 MPH. No trees blew down. They have all been wind pruned over the years. I can't change windows and doors. It doesn't blow around here like it does where I came from. All tight single pane windows and slider doors. It might be 3+" fiberglass insulation in the walls. All the places I have worked on in the last 15 years had a minimum of 9" in ceilings. 12+ in the newer. Do something about the chimney can lights. Its over 150 degrees inside them when they are on.

    I'm sure learning a lot.

    I hated the saying old timers often said. "I've forgotten more than he will ever know".  Some of the people I've worked around fall there, Guys here have forgotten more than they will ever learn. And that's not much judging on the extended knowledge base here.
  • Jack
    Jack Member Posts: 1,046
    Have you checked the

    Static pressure on the both sides of the equipment. I'm assuming a .5" external static. Just because they changed the ductwork doesn't mean it is correct. I used to use(pre-digital worl) a Dwyer 100-5 incline manometer for these tests. Today the UEI digital units do really well. I think your problems could be the duct system. Yes?
  • BobC
    BobC Member Posts: 5,380
    edited July 2014
    Leaving the equipment aside for a minute

    It seems insulation may be a large part of your problem (you mentioned having to add bat insulation to get the original system working right) and that some decisions made by the new system installers didn't help matters. I suspect your attic insulation isn't doing the job you need of it. You mentioned bat insulation, you might be a lot better off getting rid of all the fiberglass insulation in the attic and replacing it with a lot of blown cellulose because it does a much better job of conforming to irregularities than the bat type of insulation. Make sure they don't nlock the soffit vents when they do the insulation. If you can stop or at least slow down hot air from coming in contact with  the ceiling the system will perform a lot better.

    Make very sure there are NO LEAKS in the attic ducts, if you want that check done right you probably have to do it yourself. I would try to avoid working with the insulation myself because it's just miserable job, especially in a hot attic,  for those of us who have survived long enough to retire.

    It is important that the new system works the way it should but you should be able to figure that out with some detailed temperature readings. Be careful with IR thermometers, some are very fussy when reading the temperatures of different materials, They work well when looking for the difference between similar surfaces. I trust thermocouples or a good stem thermometer (you can get digital cooking thermometers for almost nothing these days), more for air temps. If I have any doubts about them I test them with a crushed ice bath and then boiling water.

    good luck,

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • icesailor
    icesailor Member Posts: 7,265

    The original insulation is some form of chopped up fiberglass that was blown in. When new, it was probably all fluffy. It might be 6" because the bottom chords of some of the long span wood trusses are probably 2" X 6". There are no Fiberglass batts over what is there. The insulation that I put up was 9" thick X 24" wide is over the exposed ducting in the unconditioned space. It was just to stop heat gain into the flex duct and distribution boxes. The original owner who we bought from had an alarm system installed. It appears to me that in the process of rooting around in the attic to run wires, he/they moved a lot of fluffy insulation around. It isn't all neat and tidy. There's  one of those so called "Florida Rooms" that has pull down stairs. It was renovated at sometime. The alarm system probably went in before the pull down stairs. The area in the attic ceiling where the access in the closet has no insulation. Like where someone had to start crawling. I'd like to think that in my career, I always returned insulation I took up, being returned EXACTLY or better than before I took it up to gain access. I'd be lying.

    The system always worked right. But my wife was only here from November until April or May. I stayed up North to work in comfort and go sailing. The system worked fine last Summer when we moved here permanently. There were a couple of pieces of Flex-Duct that the outside covering had split and come off. The insulation falls off. I could see the clear plastic duct inside. I decided to change the duct work. My first experience with that stuff was the R-2 that was notorious for splitting off like a shrink wrapped boat. I asked for R-8. I got R-6. Which is what I had. A potential customer specifically asks for something that cost more money and you discourage them from using it when it isn't something that will cause you more time to install? Really? And you're in business to make money and someone wants to spend more money? That's  like someone wanting to do a new bathroom over and asks for a $5,000 jetted tub. But you talk them into a $200.00 regular steel tub because they are easier to install. Sometimes, they call "someone else" and they sell and install the $5,000 jetted tub. And all the other work related.

    If you had a steam heat system that had un-insulated pipes, and it was pounding like a jackhammer. And you replaced the boiler and it didn't change, but you heavily re-insulated the pipes, and the pounding went away, did you need a bigger boiler or insulated pipes.

    I'm ranting. Sorry.

    I'll have to find someone to insulate the attic properly. Thanks for the reply.