Whole House Air Conditioning Ratings

Here in the desert we don't have much humidity. Our A/C needs tonnage to stay afloat. We've got a 45 degree difference at times in the summer between the inside desired temperature and the outside temp. At least 1 ton per 400 square feet. On a new energy efficient home, you might be able to stretch it a tiny bit. But any less than that you'd be living like an iguana in an aquarium. No thanks.
 
No, not true. It dehumidifies based on the amount of cooling it does, not whether it does it from continuous duty or on/off cycling. That cooling by itself causes the condensation from the air. I'd like to see a rebuttal to that if you have a source? I worked in HVAC a lifetime ago, still have a cousin that does.

Running constantly to reach some temperature is more efficient energy wise, but does not reduce humidity more, and after a certain point in the duty cycle will wear it out faster.

This is also true for the window units, less efficient and wear out faster than a (semi-modern) central unit, though you can again save energy by only cooling to a lower temp, the rooms you need to. Plus several window units are higher maintenance than one central unit, though the upside to them is if you aren't well versed in DIY HVAC, you may avoid labor costs by replacing your window units instead of calling in an HVAC company to replace central unit parts. These days just having an HVAC company make a house call, before parts+ costs, can cost about as much as a modest sized window unit.
After further thought. You are right and I was wrong. The higher Btu unit should reduce the humidity equally. And the net energy drain should be the same.

I would say though that the smaller unit running more 'seems' to get humidity lower. I will have to think about it. And I still think that smaller may be better for some people like me. Obviously the Florida climate will need a larger unit insulation is not super good.

My point though is: You were right and I was wrong
 
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Unless ur house is extremely tight with a very good vapor barrier 37% rh is almost impossible. 45% would be fantastic in Pa. Humidity is like temperature flows from high to low, hot to cold. Im not a fan of running the blower in the on position as other wrote pulls rh off evap coil when compressor is off thats where a ceiling fan comes in. RH is funny how it relates to temperature 70° @50% raise the temp a few degrees rh % drops. The higher the efficiency a ac or heat pump is above 16 seer the sharper the service person has to be. More electronics, variable speed fans and compressor. Possibly a lap top with the correct up to date program and cabling.
 
Having lived in SE Asia for several years it became a sense of relativity when it came to temperature and comfort. With outside temps in the 90’s and above and humidity around that 90% mark I knew the air conditioning would not keep up. What I found was that the reduction of humidity inside the house along with a lower temperature helped along with additional fans blowing air whether they were ceiling fans or floor fans. The floor or stand fans worked better actually. So if I could get the inside temperature down to 80°F and get the humidity down along with the fans going it became comfortable.

There were a nimbler of factors involved here including south facing windows and concrete and metal construction which contributed to a sort of heat sink effect in the house.
 
After further thought. You are right and I was wrong. The higher Btu unit should reduce the humidity equally. And the net energy drain should be the same.

I would say though that the smaller unit running more 'seems' to get humidity lower. I will have to think about it. And I still think that smaller may be better for some people like me. Obviously the Florida climate will need a larger unit insulation is not super good.

My point though is: You were right and I was wrong
If were talking strickly ac the proper size unit that runs 100% at the design temperature will pull out more rh than a larger unit. A larger unit the run time is shorter just makes the house clammy because the rh is above 55 - 60%. Get the rh 50% or less the house will feel great. Sensible heat ratio 75% of energy is used to just cool the air 25% is pulling the latent heat out (rh). 20° difference in supply / return temp is average , slowing the blower down to 24°( air temp difference) if the refrigerant temp stays above 32° so the coil doesn't freeze to increase the amount rh it will pull out.
 
After further thought. You are right and I was wrong. The higher Btu unit should reduce the humidity equally. And the net energy drain should be the same.

I would say though that the smaller unit running more 'seems' to get humidity lower. I will have to think about it. And I still think that smaller may be better for some people like me. Obviously the Florida climate will need a larger unit insulation is not super good.

My point though is: You were right and I was wrong
Short cycling is an issue. But at the end of the day, the bits to reduce x mass of air y degrees and condense the water is the same. I will say that when it’s caught up, our 8k btu (IIRC) in our pantry can keep most of our dosnatairs comfortable on most days. But that’s once the thing is under control which takes some time, and another 1.5 tons of AC running downstairs.

That said, the continuous mixing of air vs stagnation does affect humidity. There’s also something to be said about the time it takes to get the thermal energy in/out of the mass that is furniture, countertops, etc if the changes are drastic.

I think some of the variable elements associated with comfort play in here more than just keeping a machine running vs cycling.
 
Most houses with say 2,000 sq ft. in central PA have 2.5 to 3 Tons of AC installed. If I had whole house and needed a unit I would go no larger than 2 Ton. on a hot day (90F in PA) those compressors cycle mega times. It makes more sense to have a smaller unit that DEHUMIDIFIES way more than a larger unit.

I have a ranch type house and use window units.I have a 6,000 Btu unit in my addition that is 20x20 with a cathedral and 3 exposed walls. Now that room has a doorway and a "window opening" to the rest of the house. If it remains warm at night I sometimes run the unit 24/7 and the temp in the addition will be maybe 76.5+. If I closed the door it would be cooler. I do have AC window units in both my bedrooms and they are 5K Btu.

If I run all three the house is comfortable but right now (only running it16 hours/day its 77F....BUT... the humidity is 37%. It is honestly quite comfortable. I realize contractors over install by 30%bc they obviously don't want calol-backs.

My point of posting.

1. I enjoy arguments
2. It may get a person or two to rethink capacity if they are installing a new outdoor unit. The more it runs the more it dehumidifies. Even for a window unit. It is recommended 1/2T for 250 sq ft. And remember I have 400 sq ft and a cathedral ceiling and have a 1/2 T unit.
I have a Carrier Infinity system with a 2 stage compressor and a variable speed blower. Runs on low most of the time with long run times on hot days. 77 degrees is quite comfortable. I won't own a home without central air
 
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