6 ms·

I don’t think this is intended to be used in isolation. Cooling dry air is much less energy intensive than cooling dry air + a bunch of water. So, this device

I don’t think this is intended to be used in isolation. Cooling dry air is much less energy intensive than cooling dry air + a bunch of water. So, this device efficiently removes the moisture from the air, allowing the ac system to do less work.

criddell 4y ago
AC systems are pretty good at dehumidifying as well. I'm going to be replacing my home AC system soon (it's 13 years old) and was asking our AC maintenance guy about getting an oversized system. In central Texas days approaching 110 seem to be the norm these days. In this weather, my "correctly" sized system can only drop the temperature around 25 degrees different than the outside. He advised against going oversized because apparently a big system cools faster than it removes moisture and you can end up with a block of ice at the exchanger or get condensation and then mold inside. I was thinking a smarter thermostat should be able to monitor humidity in the air and run the AC at a low level, ramping up as moisture goes down, but that doesn't seem to be a feature in any of them (product idea?). Maybe a separate dehumidifier like the one in the article combined with an oversized system could work?
- istjohn 4y ago
  If you dehumidify first, you it'll be much easier for your existing system to cool the air.
  - criddell 4y ago
    My AC guy said that a right sized system in Texas will never be able to pull the temperature down more than about 25 degrees Fahrenheit. This is the limit I’m trying to get around and I know it’s possible because systems in hotter places can do (like in Arizona) and commercial systems in shopping malls and stadiums can do it too.
    - UncleEntity 4y ago
      Just guessing here but “right sized” might be relative to historic temperatures and don’t take into account the extremes? In Arizona 117 is common enough that you’d expect the AC to handle it with no problem but Texas it probably isn’t that common (guessing). Think the hottest it got since I’ve lived there was 122. People also commonly don’t cool their houses too low because it gets expensive, my sister used to have a McMansion and their AC bill was a lot (something like $400/month) and they were only cooling to around 78 or so.
      - criddell 4y ago
        Your guess is exactly right. There are a couple of standards that are used to calculate the correct size of unit and it shoots for something that will work most of the time. Now that weather is getting more extreme I question if those manuals are still correct.
    - rowanG077 4y ago
      Wouldn't the fix be to just get an "incorrectly" sized AC?
      - criddell 4y ago
        That’s exactly what I’m trying to figure out. The guy basically told me that they won’t install an incorrectly sized AC and I’m trying to figure out why. The best that I can determine is that they are worried about humidity issues but I don’t see why a smart thermostat and variable speed system couldn’t work around that. Commercial spaces have giant units that cool much more than I want. What are they doing differently?
- lostapathy 4y ago
  > Maybe a separate dehumidifier like the one in the article combined with an oversized system could work? Wouldn't a "right sized" system plus dehumidifier be better? If you oversize the AC to the point it short cycles, it won't be providing as much dehum as you have now, so you'd just be shifting that load to the dehum, not helping overall.
  - criddell 4y ago
    If it’s a variable speed system, why would it short cycle? Seems like it should be able to avoid that state.
    - lostapathy 4y ago
      In a lot of the US, getting a variable speed system can actually cost a hell of a premium, even though the wholesale cost of the equipment doesn't vary by much.
      - criddell 4y ago
        Fortunately, that’s not the case where I live. They seem to push the variable speed units.
- andrewmg 4y ago
  I’m no expert, but my understanding is that most residential systems don’t run at variable speeds. In effect, the AC is either on or off. And that’s what makes an oversized system a poor choice: there no way to slow it down. One exception is Carrier’s Infinity system, which is variable speed. It’s relatively more expensive, still not all that expensive, and may be overkill if you don’t have multiple zones, which it can also handle. Also, you’re stuck with Carrier’s matching thermostats. But it may be a good choice if you’re looking for flexibility.
  - ClumsyPilot 4y ago
    In EU all AC systems must be variable by law
  - 41b696ef1113 4y ago
    >...most residential systems don’t run at variable speeds. Any reason why? I would naively think that putting in a variable speed motor with a dial would be peanuts on the total cost?
    - pandaman 4y ago
      It's not quite peanuts: when I had been replacing my AC system I was quoted the single speed system at $X, dual speed at $1.5X and variable speed at $2X. You need two variable speed motors: in the compressor (which is the most expensive part) and in the air handler (it's low power compared to compressor) and you also probably want a variable furnace, which is can be way more expensive than a fixed power furnace as you cannot just throttle your gas line to get less heat: that will cause condensate in the heat exchange and quick end of the furnace.
      - mcbishop 4y ago
        > and you also probably want a variable furnace Or just get a variable-speed heat pump to handle cooling and heating.
        4y ago
- pandaman 4y ago
  My variable speed AC came with humidity control in the thermostat. Perhaps you are looking at the single speed products, which cannot have a "low level"?
- giardini 4y ago
  I'm in a similar climate and have an oversized unit on the roof of a condominium building . Perfect for us would have been a 1.5 ton unit but the installer put in a 2.5 ton and told us it would be fine. Reality is... The temperature rises and the AC kicks on. The plenum chamber in the AC unit, which is near the roof and is hot is flushed out to the condo interior. So we get a blast of hot dry air, followed by a blast of cold dry air for a brief period. The large unit quickly cools the condo and then switches off. So on a hot day the unit is cycling all day. This still happens on the hottest days of summer [in contrast, perfect would be a unit that, in the hottest weather, turns on and runs all day, barely keeping up]. To boot, this raises the electrical bill and stresses the AC unit. So don't get a unit that is too big. Go to the trouble to have the unit sized properly. The dehumidifier sounds great but it will decrease reliability and be one more thing to fail. It might be worth trying. Definitely don't use it with an oversized system - use it with an undersized system!
  - criddell 4y ago
    I take it yours isn’t a variable speed system?
    - giardini 4y ago
      Yes, our system has neither a variable speed fan motor nor a variable speed compressor motor.

criddell 4y ago

AC systems are pretty good at dehumidifying as well. I'm going to be replacing my home AC system soon (it's 13 years old) and was asking our AC maintenance guy about getting an oversized system. In central Texas days approaching 110 seem to be the norm these days. In this weather, my "correctly" sized system can only drop the temperature around 25 degrees different than the outside. He advised against going oversized because apparently a big system cools faster than it removes moisture and you can end up with a block of ice at the exchanger or get condensation and then mold inside. I was thinking a smarter thermostat should be able to monitor humidity in the air and run the AC at a low level, ramping up as moisture goes down, but that doesn't seem to be a feature in any of them (product idea?). Maybe a separate dehumidifier like the one in the article combined with an oversized system could work?

istjohn 4y ago
If you dehumidify first, you it'll be much easier for your existing system to cool the air.
- criddell 4y ago
  My AC guy said that a right sized system in Texas will never be able to pull the temperature down more than about 25 degrees Fahrenheit. This is the limit I’m trying to get around and I know it’s possible because systems in hotter places can do (like in Arizona) and commercial systems in shopping malls and stadiums can do it too.
  - UncleEntity 4y ago
    Just guessing here but “right sized” might be relative to historic temperatures and don’t take into account the extremes? In Arizona 117 is common enough that you’d expect the AC to handle it with no problem but Texas it probably isn’t that common (guessing). Think the hottest it got since I’ve lived there was 122. People also commonly don’t cool their houses too low because it gets expensive, my sister used to have a McMansion and their AC bill was a lot (something like $400/month) and they were only cooling to around 78 or so.
    - criddell 4y ago
      Your guess is exactly right. There are a couple of standards that are used to calculate the correct size of unit and it shoots for something that will work most of the time. Now that weather is getting more extreme I question if those manuals are still correct.
  - rowanG077 4y ago
    Wouldn't the fix be to just get an "incorrectly" sized AC?
    - criddell 4y ago
      That’s exactly what I’m trying to figure out. The guy basically told me that they won’t install an incorrectly sized AC and I’m trying to figure out why. The best that I can determine is that they are worried about humidity issues but I don’t see why a smart thermostat and variable speed system couldn’t work around that. Commercial spaces have giant units that cool much more than I want. What are they doing differently?
lostapathy 4y ago
> Maybe a separate dehumidifier like the one in the article combined with an oversized system could work? Wouldn't a "right sized" system plus dehumidifier be better? If you oversize the AC to the point it short cycles, it won't be providing as much dehum as you have now, so you'd just be shifting that load to the dehum, not helping overall.
- criddell 4y ago
  If it’s a variable speed system, why would it short cycle? Seems like it should be able to avoid that state.
  - lostapathy 4y ago
    In a lot of the US, getting a variable speed system can actually cost a hell of a premium, even though the wholesale cost of the equipment doesn't vary by much.
    - criddell 4y ago
      Fortunately, that’s not the case where I live. They seem to push the variable speed units.
andrewmg 4y ago
I’m no expert, but my understanding is that most residential systems don’t run at variable speeds. In effect, the AC is either on or off. And that’s what makes an oversized system a poor choice: there no way to slow it down. One exception is Carrier’s Infinity system, which is variable speed. It’s relatively more expensive, still not all that expensive, and may be overkill if you don’t have multiple zones, which it can also handle. Also, you’re stuck with Carrier’s matching thermostats. But it may be a good choice if you’re looking for flexibility.
- ClumsyPilot 4y ago
  In EU all AC systems must be variable by law
- 41b696ef1113 4y ago
  >...most residential systems don’t run at variable speeds. Any reason why? I would naively think that putting in a variable speed motor with a dial would be peanuts on the total cost?
  - pandaman 4y ago
    It's not quite peanuts: when I had been replacing my AC system I was quoted the single speed system at $X, dual speed at $1.5X and variable speed at $2X. You need two variable speed motors: in the compressor (which is the most expensive part) and in the air handler (it's low power compared to compressor) and you also probably want a variable furnace, which is can be way more expensive than a fixed power furnace as you cannot just throttle your gas line to get less heat: that will cause condensate in the heat exchange and quick end of the furnace.
    - mcbishop 4y ago
      > and you also probably want a variable furnace Or just get a variable-speed heat pump to handle cooling and heating.
      - 4y ago
pandaman 4y ago
My variable speed AC came with humidity control in the thermostat. Perhaps you are looking at the single speed products, which cannot have a "low level"?
giardini 4y ago
I'm in a similar climate and have an oversized unit on the roof of a condominium building . Perfect for us would have been a 1.5 ton unit but the installer put in a 2.5 ton and told us it would be fine. Reality is... The temperature rises and the AC kicks on. The plenum chamber in the AC unit, which is near the roof and is hot is flushed out to the condo interior. So we get a blast of hot dry air, followed by a blast of cold dry air for a brief period. The large unit quickly cools the condo and then switches off. So on a hot day the unit is cycling all day. This still happens on the hottest days of summer [in contrast, perfect would be a unit that, in the hottest weather, turns on and runs all day, barely keeping up]. To boot, this raises the electrical bill and stresses the AC unit. So don't get a unit that is too big. Go to the trouble to have the unit sized properly. The dehumidifier sounds great but it will decrease reliability and be one more thing to fail. It might be worth trying. Definitely don't use it with an oversized system - use it with an undersized system!
- criddell 4y ago
  I take it yours isn’t a variable speed system?
  - giardini 4y ago
    Yes, our system has neither a variable speed fan motor nor a variable speed compressor motor.