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Old 02-19-2012, 10:29 PM
 
Location: plano
5,952 posts, read 7,490,732 times
Reputation: 5006

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Quote:
Originally Posted by jasonamd View Post
It depends on the system but the overall design of the coils, valves, compressor is what is changed to improve SEER. Air flow over the indoor coil should be the same no matter what the SEER is...400cfm per ton. The lowest SEER that can be installed today is 13. To get above about 15 SEER you start getting into 2 stage systems with variable speed blowers.
On older systems it was probably normal to get a 20-30 degree temp drop but on anything available today it is usually between 15 and 20. To remove humidity you just need the coils to be below the dew point of the air to condense water.

Oversized systems that don't run more than 10-15 min will probably never reach the dew point resulting in poor humidity removal. Systems with too much air flow also won't remove as much humidity because the air doesn't stay in contact with the coils long enough. Some of the higher end systems actually control humidity by slowing the blower speed below 400cfm.
Thanks, I had a system with two stages to keep the temp drop expected with moderate and very hot weather. Perhaps my system was oversized though, as I had 5 tons for around 2300 sf.

I also heard the design condition of A/C was not specifically for higher humidity areas but more like the typical conditions in the US such as the midwest. Is it true that the units installed in Houston are the same design as one installed in say Arizona? If so how does the system address the large humidity differences?
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Old 02-19-2012, 10:45 PM
 
165 posts, read 326,447 times
Reputation: 109
I have a 3 ton Goodman. The condenser sits right outside the kitchen in my townhome. I feel it is too noisy, and my patio is right there as well so its all in close proximity. Its definitely too small for my place, 2 story 1820 sq ft. The chart shows I should have a 3.5 ton. In addition when I was talking to an HVAC guy, he said its not uncommon to add an extra .5 ton for a 2 story.

Air Conditioner Ratings, Air Conditioner Reviews From A Pro's Perspective
AC4 Life - How to Size Your System
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Old 02-20-2012, 06:28 AM
 
9,780 posts, read 7,644,489 times
Reputation: 6160
Central City Air installed HVAC for my son in the Heights. His electric bill was always a lot lower than any of his neighbors.
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Old 02-20-2012, 07:25 AM
 
Location: League City
681 posts, read 1,535,732 times
Reputation: 425
Quote:
Originally Posted by Johnhw2 View Post
Thanks, I had a system with two stages to keep the temp drop expected with moderate and very hot weather. Perhaps my system was oversized though, as I had 5 tons for around 2300 sf.

I also heard the design condition of A/C was not specifically for higher humidity areas but more like the typical conditions in the US such as the midwest. Is it true that the units installed in Houston are the same design as one installed in say Arizona? If so how does the system address the large humidity differences?
Yes, the same A/C system could be used in both locations. The difference comes from the calculations done to determine the system size needed. An area with lower humidity will need less cooling capacity than an area with high humidity at the same temperature. A properly installed system will have had a Manual J calculation performed by the installer to determine the correct size. It takes into account the size of the house, the insulation, which way and how much of the house faces a certain direction, the number of windows, etc as well as the design conditions for the part of the US it is being installed in. I believe the design temperature for Houston is 98, I don't recall the humidity though. If selected and installed properly, at design conditions the system should be able to maintain a temperature of 78 inside. At design condition the system may run continuously to keep that temperature and would be perfectly normal. Of course you can request it maintain a lower temperature but then you end up being oversized most of the year when it isn't that hot and have poor efficiency and poor humidity removal. A 2-state system would help with that, but probably still not be efficient as it could be. If a installer bases a system on sqft or some chart, find a different installer.

If you keep an indoor temp of 80, you should be able to maintain humidity in the 55-60% range...which is in what is considered "comfortable". If you keep an indoor temp of 70, you should be able to get humidity in the 50-55% range.

If you want more control over humidity you need a system capable of doing such. Some systems will let you set a target humidity and by lowering the blower speed the temperature of the coils will be colder allowing the system to maintain lower humidity.

A way to speed up humidity removal is to install a larger indoor coil. You could have say a 4 ton coil installed with a 3 ton condensor. This will give the coil a lot more surface area for water to condense on.
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Old 02-21-2012, 06:54 PM
 
58 posts, read 291,252 times
Reputation: 43
Thank you, everyone who answered. I learned much more than I expected to. I'm much more prepared now to make this decision.
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Old 02-21-2012, 06:59 PM
 
Location: plano
5,952 posts, read 7,490,732 times
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Quote:
Originally Posted by jasonamd View Post
Yes, the same A/C system could be used in both locations. The difference comes from the calculations done to determine the system size needed. An area with lower humidity will need less cooling capacity than an area with high humidity at the same temperature. A properly installed system will have had a Manual J calculation performed by the installer to determine the correct size. It takes into account the size of the house, the insulation, which way and how much of the house faces a certain direction, the number of windows, etc as well as the design conditions for the part of the US it is being installed in. I believe the design temperature for Houston is 98, I don't recall the humidity though. If selected and installed properly, at design conditions the system should be able to maintain a temperature of 78 inside. At design condition the system may run continuously to keep that temperature and would be perfectly normal. Of course you can request it maintain a lower temperature but then you end up being oversized most of the year when it isn't that hot and have poor efficiency and poor humidity removal. A 2-state system would help with that, but probably still not be efficient as it could be. If a installer bases a system on sqft or some chart, find a different installer.

If you keep an indoor temp of 80, you should be able to maintain humidity in the 55-60% range...which is in what is considered "comfortable". If you keep an indoor temp of 70, you should be able to get humidity in the 50-55% range.

If you want more control over humidity you need a system capable of doing such. Some systems will let you set a target humidity and by lowering the blower speed the temperature of the coils will be colder allowing the system to maintain lower humidity.

A way to speed up humidity removal is to install a larger indoor coil. You could have say a 4 ton coil installed with a 3 ton condensor. This will give the coil a lot more surface area for water to condense on.
Thanks for your comprehensive and make sense response. I dont know what you do but has to be engineering or systems design for HVAC I hope.
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Old 02-22-2012, 07:34 AM
 
112 posts, read 112,567 times
Reputation: 104
I highly recommend Long Air (281) 550-0113. Very prompt and affordable.
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Old 02-22-2012, 06:00 PM
 
Location: League City
681 posts, read 1,535,732 times
Reputation: 425
Quote:
Originally Posted by Johnhw2 View Post
Thanks for your comprehensive and make sense response. I dont know what you do but has to be engineering or systems design for HVAC I hope.
Nope...don't do anything with HVAC. Just interested in it and did a lot of research before having a home built. Plus it involves things I've studied in the past (weather, physics).
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Old 02-23-2012, 06:47 PM
 
42 posts, read 133,043 times
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Couple of things first, Goodman is a good company. They are based here in Houston. One of the family memebers is the guy you are hearing about having just adopted his 42 year old girlfriend in the news.

He is heir to the company, but that doesn't mean much, other than they have been around a long time. I would not, in any way, consider the playboy/heir aspect in any decision.

There are lots of great a/c providers. I was surprised Carrier wasn't mentioned.

Regardless, the big thing to consider is how your home is designed.

The old rule of thumb, was 1 ton for 700 sq ft, roughly. So for what you have described, an older home w/ 2200 sq ft, 5 tons makes no sense, unless there is something else we don't know. Newer homes/system designs utilize new technology and are very differnt compared to our old rules of thumb, but that isn't relevant here.

The SEER rating is in relation to how "efficient" the system it is, but can be deceiving. More SEER isn't always better, it depends on your home. We live in a humid environment. The systems we have here stick to the founding principles of Louis Carrier. He was trying to find a way to remove moisture from an environment. He found he could do it by running ambient air acroos a cooling coil. Yes moisture was removed, but a side effect was the air that was left was cool.......

Systems here are different than systems in the desert.

A system will consist of an outdoor unit and a coil (generally in the attic). they have to be sized at the same level. The cheapest way is to match up what is ther, if available. Otherwise, you will have to replace both. And then, there is the ducts and how good they are....

On and on it goes.....
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Old 02-23-2012, 07:01 PM
 
Location: plano
5,952 posts, read 7,490,732 times
Reputation: 5006
Quote:
Originally Posted by buyahomenowkleintx View Post
Couple of things first, Goodman is a good company. They are based here in Houston. One of the family memebers is the guy you are hearing about having just adopted his 42 year old girlfriend in the news.

He is heir to the company, but that doesn't mean much, other than they have been around a long time. I would not, in any way, consider the playboy/heir aspect in any decision.

There are lots of great a/c providers. I was surprised Carrier wasn't mentioned.

Regardless, the big thing to consider is how your home is designed.

The old rule of thumb, was 1 ton for 700 sq ft, roughly. So for what you have described, an older home w/ 2200 sq ft, 5 tons makes no sense, unless there is something else we don't know. Newer homes/system designs utilize new technology and are very differnt compared to our old rules of thumb, but that isn't relevant here.

The SEER rating is in relation to how "efficient" the system it is, but can be deceiving. More SEER isn't always better, it depends on your home. We live in a humid environment. The systems we have here stick to the founding principles of Louis Carrier. He was trying to find a way to remove moisture from an environment. He found he could do it by running ambient air acroos a cooling coil. Yes moisture was removed, but a side effect was the air that was left was cool.......

Systems here are different than systems in the desert.

A system will consist of an outdoor unit and a coil (generally in the attic). they have to be sized at the same level. The cheapest way is to match up what is ther, if available. Otherwise, you will have to replace both. And then, there is the ducts and how good they are....

On and on it goes.....
Tell me more about why higher SEER isnt necessarily better for Houston's humid climate and about how you design a different system for a desert and humid climate like Houston. This sounds like the same thing Central City Air told me when they desiged a system for my home in Houston
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