# to many tons?



## beenthere (Mar 5, 2009)

A house doesn't really need to be 70° when its 100° outside.
A 5 ton may be able to do a 30° difference between indoor and outdoor temps.
But, if it can't get the humidity below 60% when its 90 outside.
Its just an energy hog.

A unit sized to the actual load would be a better.
80° indoor temp with 45%RH at 100° outdoor temp is better for people and the home then 70° with 60%RH.

As long as the RH is kept low. People will be fine.


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## flashheatingand (May 3, 2008)

Hey B.T. I would have liked to respond earlier, but we had company and there was plenty of real work as well. I realize the hvac world is bigger and more knowlegeable than me. I realize there are standards, which need to be followed. So, it is better not to do things "my way", but to follow the directions. That being said, and this is just talk from one hvac guy to another: Most of my customers keep the stat set between 70-75. That is where they like it. I don't know of any house that has a psychrometer that controls the hvac system. If you say that bringing down the rh to 45% is more critical than the temp, I believe you. But, how come none of the manufactorers of t-stats factor the humidity level in the control? The stat kicks on & off based on temp. You mentioned that if the system cannot bring down the humidity level below 60%, it would be a waste of energy. But, it takes more energy to change the latent load than sensible load, so, the appliance will have longer run times. Which isn't bad on the equipment, but, it will turn the meter more. You ever go to an art gallery and see something priced at $17,000. "I don't know much about art, but I do know about $17,000." comes to mind. The same principle applies to rh. The two forms of measurement that most homeowners know is degrees and dollars. I am not proposing to oversize the equipment. In this guys case, I believe it would work, especially since his money is spent already. I fill out a caculation form and whatever the size is, I use. However, I feel, it is better to size the equipment based on extreme conditions as opposed to normal conditions. Are there drawbacks? yes, but the equipment needs to keep the home cozy, especially during the extreme days.


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## flashheatingand (May 3, 2008)

Wow, that was a lot of words, damn homey how about a little sentence structure?


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## beenthere (Mar 5, 2009)

It doesn’t actually take more energy to remove moisture, per say.
Just most oversized systems don’t run long enough to do it.
Once humidity is lowered. You get as much as 50% of the units latent ability back as sensible ability.
So it actually becomes more efficient, to have a lower humidity level in the house.
My own area by the book is sized to 93 Do, and 74 ID.
But, most of us, size to 95OD, and 72 or 70 ID.
People that have systems sized to 93 and 74, don’t mind the days of 98 and 100°, as long as their hoes RH is low.
If its not, yes, they will complain.
One problem. Most people don’t check out the existing duct work to see if it can handle the air flow the home needs.
Some oversized equipment will dehumidify pretty good. When it’s a 3 ton unit, only moving 900CFMs.
There are. And have been for some time now. Several thermostats with built in humidistat.
That will run the A/C to dehumidify the home. And, also slow the blower on VS blower systems.
Honeywell, Carrier, WR’s are the first companies that have thermostats that have built in cool to dehumidify, that come to mind.
Units without VS blowers can also be slowed with those thermostats sometimes.
Another solution for units without a VS blower. Is to simply slow the blower. IF, you check its CFM and find its meeting or exceeding 400 CFM per ton.


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## flashheatingand (May 3, 2008)

Ok, I will check it out at my own home. Which w/r stat do you reccomend. Would 78 degrees & 45% rh be a good setting? 

We have a low rh level around here, about 50-55%. I have my doubts, but look forward to this test. I hope it does make a huge difference, both in comfort and utility bill. 

Have a good week


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## beenthere (Mar 5, 2009)

Don't use WR too often.

I prefer the Honeywell IAQ(YTH9412)

Do you have a VS blower?


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## flashheatingand (May 3, 2008)

You killing me with the IAQ, and the blower is a 1/3 horse multi-speed.


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## beenthere (Mar 5, 2009)

Then you'll need to add a relay to switch the blower to a slower speed.

The IAQ is a good stat.
Cost a few dollars. But well worth it.


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## flashheatingand (May 3, 2008)

I do take your comments seriously and all. And, I am ready to give it a shot, but, I can't pull the trigger on the IAQ. If it makes a big difference, I will make the investment later. But, for now, I found a de-humidistat that works in conjunction with a t-stat. It's been pretty busy today and this week, so I will install it perhaps this week-end.

Hope work is good for the rest of the week.


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## flashheatingand (May 3, 2008)

Hey, you see post #17, in the thread titled "need some ballpark estimates", there is a response from a guy who lives in Alabama. He states what I was saying, in the south, it gets awful. He just mentions oversizing cause it gets nasty.


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## beenthere (Mar 5, 2009)

You see he uses the phrase "charts", good indication, he doesn't know how to do a loadcalc.

Probably also has a home that has high infiltration.
So istead of addressing that issue. He'll just pay more for his cooling bill.

He also doesn't say if his duct work is in the attic or not. A leaky duct system in the attic will cause some people to think they need a larger unit. When its really the duct system.

Wouldn't surprise me if his leak rate was .6 ACH in the summer.


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## Verbal (Jul 9, 2008)

AC below 90 is indulgant?? how many blood thinners you taking?


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## NickTech (Feb 13, 2005)

holy shiiiit jk,a 2000 sq ft home pretty much =a 3.5 ton house
+ or- a 1/4 ton. get the ol' 3 estimate from local contractors, they know there clients and hopefully their man j


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## maninthesea (Nov 11, 2008)

I was wondering if relitive humidity is a problem becuase the unit does not run for long enough times to condense enough moisture out of the air, would it decrease relitive humidity if you adjusted the temp range between on and off(say it was 2 degrees and you made it 4 degrees or 6 degrees) would that make a difference or would the humidity climb back up during the longer off times? Just curious?


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## beenthere (Mar 5, 2009)

Yep, just gain the moisture back from the longer off time.

Plus your that much more uncomfortable as the temp gets hotter in the house before the unit runs again.


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## Electric_Light (Nov 25, 2007)

When are VFD variable capacity systems going to become readily available for common residential split systems? They're already in use for BIG commercial systems, as well as the wall-mount split, like the Mitsubishi Mr.Slim.


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## beenthere (Mar 5, 2009)

They have been out for 1 or 2 years now.
Nordyne has them. Even in heat pump versions this year.
23 SEER as I recall.


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