Help! - new system is not cooling adequately

Discussion in 'HVAC Heating & Cooling' started by bldn10, Jul 14, 2016.

  1. DonL

    DonL Jack of all trades Master of one

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    Just to add,

    The low line should be sweating all the way back to the compressor.

    The site glass tells you very little. A Amp Probe tells you more.

    The sight glass was great on automobiles in the day.
     
    Last edited: Jul 16, 2016
  2. bldn10

    bldn10 New Member

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    "They checked the refrigerant..."
    The coil is pretty close to the condenser.
    Haven't sighted a sight glass. The line is cold.
    From all appearances the system is operating correctly but I don't think he has checked the airflow yet. I'm beginning to think that the supply trunks are undersized and the airflow is restricted.

    BTW I bought a General IR thermometer at Lowe's yesterday and started checking temps at the outlets. I was getting crazy low readings. Did my mouth and it was like 60. Let water run hot and it was around 90. Did the wall outside when it was 91 and it was 60ish. Although this unit has pretty good reviews, the one I got is worthless. 20-30 degrees off! LOL What is an accurate one <$100?
     
  3. DonL

    DonL Jack of all trades Master of one

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    A rectal thermometer is the most accurate, But they leave a bad taste in your mouth. :eek:

    Have you tried to close the vents in the cooler rooms ?
     
  4. WorthFlorida

    WorthFlorida The wife is still training me.

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    Look up in your area for a Heating AC supplier. They all should have tools for the trade but call them if you can buy one. Some only restrict sales to trades.
    HD has http://www.homedepot.com/p/Klein-Tools-12-1-Infrared-Thermometer-IR1000/202330832. It's a Klein tool brand and a lot better chance of being more accurate (all are probably made in the same place in China).

    If you think your thermostat temp reading is accurate, measure the wall temp at the Tstat with the infrared. It should read within a degree of the Tstat.

    What is the model number of the compressor? Is it a smart unit 2 stage? You could have a bad compressor or the expansion valve at the evaporator coils is not working. Possible some debris is clogging it up. It'd be rare but guages are still needed because the pressure would not be right.

    There still is one more thing to know. Most new refrigerants must be added in a liquid state. Not gassed off the top of the cylinder. The tank should have been upside down when adding. Most new condenser units do have a charged system with enough extra refrigerant to satisfy a typical install and then the tank is used to top it off, sort of speak.

    If the refrigerant was not added correctly it will give you problems such as you're having.
     
    Last edited: Jul 16, 2016
  5. WorthFlorida

    WorthFlorida The wife is still training me.

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    The well train AC tech how to video's. Here is a two good short video's how to read and added refrigerant.


     
  6. bldn10

    bldn10 New Member

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    I can only assume that this licensed HVAC contractor knows how to check and add refrigerant. I think the problem is more fundamental than that - I don't the the ducting is sized correctly. I suspect they got to the house with the plenums and sized the ducts to fit them. I just checked and the 2 "large" supply trunks are 10" and 12." And there are 2 8s and a 6. I suspect that the 10 and 12 airtites were all they could get on the largest side. Likewise there are 2 returns that are no bigger than 12 and 1 8. Is this enough airflow?
     
  7. DonL

    DonL Jack of all trades Master of one

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    It all adds together. So enough flow should not be a problem. The proper air flow for each room may be. Reducing air flow output on the coldest rooms can help to balance it out. Rooms with closed doors affect flow also.

    Normally about a 15 degree F difference from Vent Outlet to Return Vent is what you get if the system is charged and working properly.

    The way the rules are today, You can buy a set of gauges, But it is illegal to use them without a HVAC licenses.

    You are still allowed to use a thermometer. :)

    Does your T-Stat ever get satisfied ?

    Good Luck.
     
    Last edited: Jul 18, 2016
  8. Dana

    Dana In the trades

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    If you have an unbalanced duct system with improperly sized returns &/or leaky ducts in a not-very-tight house (= almost all houses built in the southeast prior to IRC 2009) the air handler creates room to room pressure differences, and the Great Outdoors becomes part of the return path. When the outdoor humidity is high, this becomes a significant latent cooling load, limiting the ability of even the oversized system to lower the temperature quickly. If any of the ducts or air handler are in the attic, above the insulation, and outside the pressure/air-tightness boundary of the house it only gets worse, since any duct leakage in the attic uses the attic (= unglazed solar collector) as part of the path, at temperatures well above the outdoor ambient.

    A round of air sealing may not be the total cure of a poorly designed poorly implemented system design, but it's start, and cost effective even on reasonably designed reasonably implmented system. Sealing all hard-piped duct seams & joints with duct mastic (or if super-clean, a high quality temperature rated aluminum tape) is a start, along with sealing seams in the air handler with the appropriate tapes. Caulk where duct boots pass through subfloors or ceiling/wall gypsum with polyurethane caulk or expanding can-foam. Sealing all attic floor/upper floor ceiling penetrations by flues/ducts/plumbing/electrical can be a bit tedious, but also well worthwhile. In a full basement or crawlspace type foundation sealing off the foundation walls to the outdoors is equally as important, since the leakage at the top & bottom of the houses are what defines the 24/365 "stack effect" infiltration drive pressure, independent of air-handler driven infiltration issues.
     
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  9. bldn10

    bldn10 New Member

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    The unit is in an attic equipment room w/ 2 gable windows, all R8 flex duct.

    He had the coil in a counterflow orientation and he took it upon himself to turn it around. Seems like it a helped some but still not working great. Had it set on 72 from Mon. afternoon and it was 72 Tues. morning. By 5 it was showing 78 downstairs and 86 in the closet up. Granted the outside temp in that time went from low 80s to 96.

    The Rheem specs show that this blower has a cooling airflow of 1657 cfm @ .70" W.C. E.S.P. There are 2 12" and 1 8" returns. The 12s pull out of stud pockets and 1 of them has very little vacuum - could be blocked by plaster, etc. He estimated the theoretical return flow at 1300 cfm at best. Is this a problem?

    FWIW I'm installing a power vent today.
     
  10. Dana

    Dana In the trades

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    If by "power vent" you mean you are going to install active attic ventilation- DON'T DO IT !!

    Depressurizing the attic with fan pulls conditioned air up from the rest of the house through every air leak in the attic floor, and will INCREASE rather than increase the cooling load on the system. Power venting attics to keep the attic cooler is one of the most ill conceived concepts out there, yet is way too common. More often than not it increases the total power used by the cooling system (over and above the power used by the power vent itself.) Small low cfm solar powered units can sometimes result in slighly lower use, but only if the vent openings are big enough to accommodate the flow without significantly depressurizing the attic.

    The primary purpose & function of attic ventilation is to purge moisture from the attic, not cooling. In most of the southeastern US attic ventilation ends up adding more moisture to the house than it purges- it's really only effective in colder climates, where the attic temps dwell at temperatures below the dew point of the conditioned space air, resulting in high moisture content in the roof deck if not diluted with the much drier cold winter air. In TN that's not much of an issue (except maybe at altitude in the Smokies.)

    A decent scientific paper survey of attic venting issues compiled by building scientists in FL lives here, and is well worth reading before making changes to your attic venting scheme, despite your cooler-than-Florida climate.
     
  11. DonL

    DonL Jack of all trades Master of one

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    That may not help if the system can not keep up.

    What refrigerant does your system use ?
     
  12. bldn10

    bldn10 New Member

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    I am aware of that position, that's why this is a last resort attempt. FWIW both my contractor and another one I consulted and has no dog in the fight disagree.
    If I could get strong opinions on what if anything is wrong with this system, I'd ask the contractor to fix it. He blames it all on insulation, ventilation, Mother Nature.
     
  13. bldn10

    bldn10 New Member

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    It's a brand new system.
     
  14. Dana

    Dana In the trades

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    With R8 ducts and even R19 on the attic floor the additional total cooling load of a 125F attic vs. 90F attic is pretty miniscule. If you haven't air sealed the place adding active ventilation is only going to make it worse unless you have a LOT of free air cross section to the gable vents.

    Take it from people who actually measure this stuff. A best-case would be a small PV operated ventilator, which would still likely in less than a 10% reduction in total energy use as in this instrumented & monitored real-world case, that reduced the power use by a mere 6%.


    A 4 ton system for a 2000' house at code minimum R-values is getting onto ridiculous oversizing. The typical tons/square foot ratio in the southeast for reasonably insulated houses is about a ton per 1000' of conditioned space. Putting the ducts & air handler in a hot attic adds about a ton to the total load with uninsulated or low-R ducts, and with tight R8 ducts it's less than a half-ton, so typ would be 2.5 tons, 3 tons of load would be above at the first standard deviation, and 4 tons of load in a house that size would be a 3 sigma outlier- they exist, but the reasons for the high load are usually obvious (very low R values, a lot of unshaded west facing window, etc.) A 4 ton a system implemented correctly SHOULD be able to keep up pretty easily. Throwing more compressor capacity at it won't fix a poor duct design, if that happens to be the limitation. It also won't fix air-handler driven outdoor air infiltration, if the latent load it's hauling in is adding a ton or more to the load, which it could be if the ducts are unbalanced and the house is really air-leaky.

    If the contractor is blaming it all on "...insulation, ventilation, Mother Nature...", what are your R-values, window types, etc., and the recent weather history? The 1% outside design temp for Memphis is 94F, the 0.4% outside design temp is 96F., so unless it's been well above 100F you should have cooling capacity to spare, if the place is insulated at all.
     
  15. bldn10

    bldn10 New Member

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    I consulted w/ another contractor yesterday and he too was against the power vent so I have not installed it. As to attic cross ventilation, there are 4 gables on the house w/ windows approx. 2' x 2.5'. If that is enough "makeup" air, as a lay person I would think that the power vent would pull primarily through those windows and not any small crevices in the ceiling. I.e. there would not be a huge negative pressure in the attic.

    Alternatively, what about turbine vents? The windows are about 1' off the attic floor and there is no high escape for hot air.

    I don't know where you guys are coming from re sizing. If a contractor here put 1 ton/1000 sf systems in houses I assure you he would not be in business long. Seriously.
     
  16. DonL

    DonL Jack of all trades Master of one

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    Makeup air is not your problem. Your AC system recycles the air. (Gas needs makeup air, Not AC)

    Your system is most likely not refrigerant charged properly.

    That system should make your nipples be on high beam, If it is charged and working properly. Even with the windows open.

    You need someone that knows what they are doing, A HVAC licensed type. If they say they are not licensed say goodbye.

    Good Luck.
     
    Last edited: Jul 21, 2016
  17. bldn10

    bldn10 New Member

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    Makeup was in quotes and was in reference to power vents creating negative pressure in the attic and sucking air out of the conditioned area.
    As I have said several times, I am pretty certain that the system is properly charged. And I AM dealing with licensed contractors.
     
  18. Dana

    Dana In the trades

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    The amount of free air space needed to limit the attic depressurization with active ventilation is substantial. Turbine vents can severely depressurize the attic too. You have no idea just how large the effective hole is in the ceiling, but if history is any guide it's a heluva lot larger than even your wildest imagination would deem reasonable. The leakage paths are not always obvious- it takes a blower door (usually with IR imaging) to fully sleuth out all the thermal bypass air paths. You could fix 1001 small leaks and still be missing a major path that renders those efforts nearly useless. Unless the house has already undergone a round of blower-door directed air sealing the combined path is likely to be approching the size of an open window (!).

    Stop thinking of attic ventilation as a solution to your cooling load issues- fix the real cooling load problems, such as air leakage in the building envelope (which are already aggravated by having the ducts and air handler outside the pressure boundary of the conditioned space).

    If you want to DIY it, start with the most obvious large leaks, such as register boots that haven't been can-foamed to the ceiling gypsum, plumbing stack chances that aren't sealed. If you have a masonry chimney there is likely to be a square foot or two of leak due to code-required clearances to combustibles, that can be air-sealed with sheet metal + fire-rated caulk. Any recessed lighting fixtures need to be boxed-over (with 3" clearance to the box) and can foamed to the gypsum. It goes on, and on , and on, and it's more tedious than actually difficult. All of this comes WELL before weatherstripping the attic hatch/doorway. A primer on air sealing an attic lives here.

    [​IMG]

    When you've fixed all of the stuff you can find, a large (preferably reversible) window fan intentionally pressurizing/depressurizing the attic and a smoke-pencil (or a cobweb- thread, used as an air motion detector) will likely find you a bunch more.

    Partition walls with missing or leaking top plates are a common less-obvious path, with air entering the partition wall cavities from loose or unsealed kick board trim, electrical & plumbing penetrations, etc. Some of these are easy to fix, some not so much, but you have to at least find them to be able to fix them.

    Venting the roof with a soffit-to ridge venting scheme will lower the roof deck temps a few degrees (it won't fix your cooling load problem, but at least it won't hurt). A ridge vent will also depressurize an attic, unless the free air space of the soffit vents are at least 25-50% larger than that of the ridge vent, so don't just slap on a ridge vent without the soffit vents, or you could make the problem worse rather than infinitessimally better.

    Regarding system sizing, I know of an HVAC contractor in central Florida doing geothermal heat pump systems who regularly ends up at load/conditioned space ratio ratios smaller than a ton per 1000', often closing in on a ton per 1500'. This is in reasonably air-sealed houses with sealed-conditioned attics, with as little as R20 open cell foam under the roof deck, usually retrofitted as part of the process. He is able to sell them the roof deck insulation & air sealing for less than the marginal increase in cost of the larger GSHP system it would take to manage the larger loads.. (He uses a theatrical smoke generator to verify that the attic is fully air sealed before the foam installers break down. Plumes of smoke makes spotting the leaks pretty easy.) That's probably not a cost effective solution for you, but there's no way a 4 ton system should be failing to keep up with the load. The fact that a good part of the system is outside the conditioned space would probably keep you from being able to get by with a 2-tonner.

    There's another contractor/blogger in Atlanta GA who likes to measure stuff, including the cooling load of his own house as measured by the duty cycle of his existing sytem. (Strangely, his old air-leaky condo still came in at about a ton per 1000' at 1% outside design temps comparable to yours.)

    Old school HVAC hacks typically specify a ton per 500' on older housing (which is roughly your ratio), a ton per 750' for newer construction and usually end up oversizing it by quite a bit, even with the ducts in the attic.

    A true professional would actually run the Manual-J load numbers, but merely being a licensed HVAC contractor doesn't mean they even know how that's done. (It does mean they should know how to properly charge & test the system, the regulations on handling refrigerants, and should have at least a clue as how to design & install ducts, existence proofs of truly atrocious duct systems notwithstanding.)
     
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  19. bldn10

    bldn10 New Member

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    Wow, all kinds of good info there!
    This is a 90 year old house w/ no wall insulation, some old brown attic insulation that I had supplemented w/ blown in fiberglass, storm windows on most windows, plaster walls and ceilings. I'd say that it is equal or better than most similar houses in Midtown Memphis as far as energy efficiency goes. But it is no where close to your guy's in Central Fla. The house is what it is and it should be made to cool, energy conservation and utility cost aside. I can't help but think that the system is chokes down because of lack of return air: "The Rheem specs show that this blower has a cooling airflow of 1657 cfm @ .70" W.C. E.S.P. There are 2 12" and 1 8" returns. The 12s pull out of stud pockets and 1 of them has very little vacuum - could be blocked by plaster, etc. He estimated the theoretical return flow at 1300 cfm at best." I just want to make sure that I am getting all the system is supposed to put out.
     
  20. Dana

    Dana In the trades

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    Using stud framing bays as a return duct was once popular, but is now a code violation in most areas. If those stud bay are on exterior walls, the odds that you are sucking in MAJOR air infiltration directly into the circulating air is quite high, particularly in a 90 year old house. But even if it's an interior partition wall in a balloon framed house there can be large air leaks to the exterior via floor joist bays. And if the stud bay is blocked by framing or plaster, the resulting infiltration drive goes even higher, even with less air moving due to the constriction.

    It would have been more effective to blow cellulose into the attic than fiberglass, but anything is an improvement. To do it right, they would have spent at least as much time air sealing prior to blowing the fiberglass, but that critical step is often glossed over. Cellulose is opaque to infra-red radiation coming off a hot roof deck, whereas fiberglass is somewhat translucent, which results in the temperature an inch or so into the top side of the fiberglass being a few degrees hotter than the attic air (!), which means you are insulating against a higher temp, with fewer inches of insulation. Hopefully the combined depth of new + old is at least 9-10"(?).

    It's almost certain that you have significant air leakage in those uninsulated walls, and it's almost surely going to be cost effective (on lowered energy use alone) to insulate them with blown cellulose, which is more air-retardent than low-density fiberglass (you'd have to "dense pack" blown fiberglass to 1.8lbs per cubic foot to beat even the lowest standard density of fiberglass on air retardency.) Almost any framed wall can be safely insulated, but how cheap/easy that is depends on the wall stackup & construction. Most 90 year old framed houses have plank sheathing and some sort of rosin paper or tar paper on the exterior side under the siding (or facing 1-2" cavity, if clad in brick or stucco.) What does your wall stackup look like?

    When the other big air leaks like empty wall cavities or plumbing/chimney chases are tightened up it's also worth looking at windows. Does this house have the original windows too? Any storm windows?

    Old wood sash single panes can usually be tightened up considerably with attention to weather stripping and meeting rail etc, and in your climate it's also cost effective to add tight low-E storm windows, which will both cut wintertime heat loss as well as summertime solar gains, as well as cutting air infiltration. Low-E storm windows pay for themselves more quickly than clear-glass, and bring the total performance of an antique wood-sashed window pretty close to that of code min replacement window, yet much cheaper than replacement windows. (The big box store carry Larson storm windows, which can be ordered with low-E glass options.) Pulley pockets and window trim leaks for double hungs in uninsulated plank sheathed houses are often a handful of not-so-obvious square inches of air leak per window. Caulking the trim to the plaster and adding pulley seals can cut that to less than a square inch.
     
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