When I had Central Air put in a couple of years ago I said that I wanted an oversized unit for my house. The A/C guy said that giving me a 4 ton when I only needed an 3 ton wouldn’t help it get any cooler. Well on hot days when the outside temp gets in the upper 80’s or 90s espeically with high humidity our A/C cannot even get the temp below 73 especially upstairs. For some reason it seems to get worse at night just when you would think it would work better. So if I were willing to pay any price could they get me a system to keep my house at a cool 65 even if it got to be 100 outside with high humidity? Could they do it for Oprah?
The problems that you describe have more to do with the method being used to distribute the cooled air throughout your house.
The short answer: assuming you have a forced air system you should consider better methods to adjust (equalize) air flow within the rooms of your house. Hot rooms need more air and cooler rooms could be adjusted downward. Equipment could also be installed in the ducts to boost air flow to dead zones.
Of course you can get your house cooled.
Up the road a ways is a big meat warehouse, easily 300,000 cubic feet, that they keep at -50 F even on days when it is 100 F outside. That’s right, they keep it 150 degrees colder than the outdoors. And it is a trucking company, not for Oprah.
I agree that moving and distributing air may well be the important issue here.
What Napier is talking about is NOT a central cooling system, like your air conditioner. That is a refrigeration system that works in a slightly different manner, but on a similar principal. Normally, it’s not practical to cool a home in this way.
The air conditioner in your home works by forcing air across a cooling coil that is made cool by the decempression action of the refrigerant in the system. In your typical forced-air central air system, the maximum differential that can be achieved between your inside air and the outside air is 23 degrees (F). So, if it’s 103(F) outside, the best you can do is 80(F) inside. Now, before anyone jumps up and says, “I’ve been in buildings that are cooler than that when it’s hotter than that outside!”, please provide something other then anecdotal evidence.
As for my figures, I will volunteer that they were accurate sometime around the mid-70’s, so may not apply as accurately anymore - a true HVAC tech should be able to answer more fully.
My freezer works the same way, but it’s a darn sight more than 23 degrees cooler than the outside. Where’d you get the 23 degree number from?
All you need to have more cold is more coils, bigger fans, and better insulation to keep the heat out.
IANAHVACTech.
Now that that is out of the way, this is what my HVAC guy told me when I asked about getting a larger heat pump (which also works as A/C): If the A/C unit is oversized, the air is cooled before it is sufficiently dehumidified for comfort. A too-large unit will leave you feeling cool but clammy. This might only apply in the South where humidity is a Major Problem, but that was his explanation. I think he was probably telling me the truth because he made less money selling me the smaller system.
But again, IANAHVACTech.
Heat pumps and air conditioners are not the same.
Since you request proof, then I will ask the same of you. Please provide me a source that states that the maximum theoretical difference between design outdoor ambient dry bulb temperature and desired indoor dry bulb temperature is 23 degrees F for an air conditioning unit? I sure can’t find anything in the ancient 1972 ASHRAE Handbook of Fundamentals that I have to support your statement.
Correct.
When my father got AC installed in his home, he instructed the technician to install a larger unit. (My father is the king of overkill.) He now wishes he hadn’t done it.
Over-sizing an air conditioner will cause “short-cycling.” Short-cycling causes three problems:
- It is hard on all the mechanical components.
- The compressor doesn’t have enough time to come to a steady-state temperature. It will therefore not be running at maximum efficiency.
- As you mentioned, there won’t be enough time to remove the humidity.
By the side of a hill…build your house deep within said hill.
Deep enough and your house stays around 70 degrees all year round.
No Need for AC.
That 23 degree thing is not possibly correct. It gets above 100 quite frequently here and I assure you we keep the house cooler than 80. If my dad gets his hands on the thermostat we keep it a lot cooler than 80.
Build your home on a large concrete slab, also invest in very well insulated walls and roofing. Situate so that shade trees are near and by a river, lake or pond. Run pipe throughout your subfloor in a tight zig zag then out of your house and through a trench down into a deep portion of the body of water in a coil, attach to a pump. Circulate water through the pipe and install fans to circulate air through your home… it will be very nicely cool.
My grandmother used to live in Manitoba where it regularly gets hotter than 100 degrees, and her house was always below 70.
Obviously, I took no photos of the thermostat or thermometers, but I also think the 23 degree number is crap.
Yeah, I don’t believe that 23 degree number either. You can’t tell me that it’s over 80 degrees in all the Vegas casinos during the summer.