Gulf coast humidity

[wgrr]

Originally posted by gencon
And you wonder why the public throws AC guys and lawyers into the same pool.

gn

I guess I am screwed. I am a commercial HVAC tech and my wife is a lawyer.

[pstu]

>>I guess I am screwed. I am a commercial HVAC tech and my wife is a lawyer.

When you go to a party, don't tell them where you really work, tell them you are from the IRS instead. They will like you better!

Best wishes -- P.Student

[gencon]

Finally getting some action and info!!!

Carnak; completely understand you fresh air concept; Up north I did the same thing to help stop cold infilteration in 70 vintage leaky houses. How big a air inlet for a 3.5t do you recommend, I like the idea.

2hot 2 cool; not even close. I have looked at detail tech data on 2 manufactures now; no 3.5 t coils; they all recommend going with 4t. I thought all the pro keep preaching "matched units" and your going with a generic 3.5t coil? The 4t coils gains in latent is over 1000btu's on most combos vs the 3t coil. Even more interesting is that the seer 14 vs 13 is a hoax. The 13's have more tot btu and more sensible that the 14's. Seems like they are trading total btu and comfort in order to make 14. Also they are derating the 14 by on average about 2000 btu's to reduct power consumtion of the compressor to get the rating. Your right about one thing, I have been a general and an engineer but I don't want to do a DYI. Trust me you don't do bricks, sheetrock or brain surgery yourself! I just want to find someone who understands more than me to put in a "weel engineered system" which I'm more than willing to pay for.
wgrr: My sincere consolences!

On the Rheem site under condenser unit, you can down load some pdf files that are really eye opening.
gn

[Carnak]

Pressurization gets used up north but it runs the risk of driving the humidity into the walls in the winter time.

As a starting point, I would try to estimate the infiltration rate of the home and work backwards from there. It should hopefully work out to a CFM flow of less than 10% of what the air handler moves. Perhaps sensible gain of infiltration divided by 1.08, divided by indoor/outdoor temperature differential.

I would size a short intake for about 10% outside air, in your case I would try an 8 inch round intake with a manual damper. With the system running close off damper until you just feel a slight cool breeze leaving from a cracked door or window. Check all sides of the house.

[Carnak]

Results using heat pipe technolgy air handlers in a commercial application



Everyone laughs at the cheapo thermo-hygrometer, but you let it sit for a while and its pretty good.

[gencon]

It took twice before I got "remove the damper"
I was thinking that 6 or 8 in intake seems hugh; but with a damper you could tune it for max performance.
gn

[Carnak]

The 'remove the damper' comment in the signature is for the benefit of one specific fan of mine in here.

[udarrell]

Less than a design day in the Caribbean, early in the morning.

Partly Cloudy 88°F
Feels Like
101°F
Updated Sep 9 08:00 a.m. Local Time
UV Index: 1 Low
Wind: CALM
Humidity: 75%
Pressure: 29.91 in.
Dew Point: 79°F
Visibility: 6.2 miles

Sweet Home Alabama
Right Now for
Mobile, AL
Save this Location On The Spot Weather

Partly Cloudy 77°F
Feels Like
77°F
Updated Sep 9 08:25 a.m. CT
UV Index: 1 Low
Wind: From N at 7 mph
Humidity: 77%
Pressure: 30.08 in.
Dew Point: 69°F
Visibility: 10.0 miles

Looks like well below design conditions in Mobile but it is still early in the morning right now.

I see dew points of as high as 81 here, however it pretty much hovers around 80 for a good six months of the year, day and night.

We saw dew points in the 80's here in WI a few weeks ago.

The mfg'er equipment engineers could engineer units for those high humidity climates, but the mfg'ers refuse to do it. Mfg'ers ought to optimally engineer for the ultra high humidity climate zones! I would!

I believe the power companies put the squeeze on them to lower the amp draw on equipment to help reduce their peak-load power consumption problems & costs of builder large capacities. Reducing the heat-gain load on the buildings is a far better solution for all of us!

The design engineering might be the reverse of the ultra high SEER equipment with he small compressor & the huge coils. Back in the early 1970's & 1960's, when I would replace those earlier OEM compressors', the OEM Btu/hr called for were higher than the condenser & evaporator's Btu/hr Ratings.

They operated under moderately heavy loads with low suction pressures & temps, the high SEER units due to engineering physics, can't do that.

Now, if you take that combination with fins optimize accordingly, & then size the equipment to achieve long run-time-cycles & optimal total run-time,it will flat suck the humidity out of the air under the toughest load conditions like a good performing dehumidifier.

When properly sized, the two speed compressors' coupled with lower CFM's helping lower coil temps are helping re-mediate the humidity problems. The problem is that the ultra high SEER units have trouble under heavier load conditions keeping pressures down & the E-Coils as cold as I'd like them

Also, do all you can to stop high humidity air infiltration. Balance the Return air from the rooms so you don't have rooms with excessive negative pressures which dramatically increases air infiltration.
http://www.udarrell.com/air-conditio...tent-heat.html

[Carnak]

520 CFM a ton darrel, single stage, PSC motor, humid locale

http://hvac-talk.com/vbb/showpost.ph...8&postcount=94

[Shophound]

Make the house contain its conditioned air better. If overnight everyone with a conventionally constructed house suddenly had an airtight seal between attic and house, the power companies might start griping they aren't moving enough watts through the meters. AND...the level of interior comfort satisfaction would increase remarkably.

[paul42]

There is more than one way to control humidity with several people on this board advocating their own method.

When it comes to humidity control, the house and the hvac system are not separate entities. You have to consider both when trying to find the best method.

If you have typical construction with average to high infiltration, your only choice may be adding a whole house dehumidifier. And for climates that actually have four seasons, it may still be the best answer.

For the hot humid climates, as you get the infiltration under control, other options become available. Which one will work best for you will depend on the sensible load, the remaining infiltration, and how complex you are willing to go with your hvac equipment.

For example, if you have an extremely tight house with low to moderate sensible load, Carnak's approach obviously works. If you have an extremely tight house with very low sensible load, a different approach may be called for. Very few people have either of those conditions. For them, shophound's advice about sealing between the attic and living space is the starting point towards lower energy bills and controlling humidity.

[Carnak]

The house has more of an impact than the system.

It is not my approach, just the same methods recommended by ASHRAE, the Florida Solar Centre, building science etc.

[beenthere]

The first step in controling humidty, is deciding if you want to cure the problem, or the symptom. Or both.

[Carnak]

The first step in controlling humidity is to control how outside air moves inside and to properly condition it before it is introduced to the space.

It is like wearing a condom, as opposed to getting a shot of penecillin

[paul42]

The first step in controlling humidity is to control how outside air moves inside and to properly condition it before it is introduced to the space.

It is like wearing a condom, as opposed to getting a shot of penecillin

That sounds good in theory, but is harder for some of us to do in practice.

Any time an exhuast fan or the dryer runs (unless you have a condensing dryer), you are bringing in outside air to replace the exhaust. You may be able to confine most of that input to a fresh air intake provided for just that.

But, that outside air comes in whether the AC is running or not, and if the AC is not running, it doesn't get conditioned. For my house, the AC is not running about 75% of the time on a hot day, and much less on cooler days.

[beenthere]

The first step in controlling humidity is to control how outside air moves inside and to properly condition it before it is introduced to the space.

It is like wearing a condom, as opposed to getting a shot of penecillin

LOL... An interesting way to phrase it.

[pstu]

>>We saw dew points in the 80's here in WI a few weeks ago.

Could it be possible this is in error? I poked around Weather Underground and for Madison WI saw max dewpoint reported at 75 for the past month. Average dewpoint was 56.
http://www.wunderground.com/history/...lyHistory.html
Then tried Dubuque IA and 76.5 was reported, with an average of 56. Although I took the 1st reporting station available, probably an airport would be more reliable than most amateur stations.

By contrast, Ellington Field in Galveston TX reports over the past month max 77 dewpoint, and an *average* of 73. You can find similar conditions from almost any reporting station. When we say "high dewpoints" in hot-humid climates, it refers to chronic conditions not a rare occurrence for the record books. We cannot open the windows at night and expect to cool off and dry out.

Regards -- Pstu

[Carnak]

>>We saw dew points in the 80's here in WI a few weeks ago.

Could it be possible this is in error? I poked around Weather Underground and for Madison WI saw max dewpoint reported at 75 for the past month. Average dewpoint was 56.
http://www.wunderground.com/history/...lyHistory.html
Then tried Dubuque IA and 76.5 was reported, with an average of 56. Although I took the 1st reporting station available, probably an airport would be more reliable than most amateur stations.

By contrast, Ellington Field in Galveston TX reports over the past month max 77 dewpoint, and an *average* of 73. You can find similar conditions from almost any reporting station. When we say "high dewpoints" in hot-humid climates, it refers to chronic conditions not a rare occurrence for the record books. We cannot open the windows at night and cool off and dry out.

Regards -- Pstu

its probably similar to a person waking up its 90% RH because it is cold out, then when the outside temperature climbs by 20+ degrees they think it is 90 degrress and 90% RH outside, not realizing that RH plummets when temps rise.

[Shophound]

The house has more of an impact than the system.

Well said. To throw more system at a problem that could be mitigated by a better house envelope is becoming more of an expensive proposition with each passing day.

[Carnak]

That sounds good in theory, but is harder for some of us to do in practice.

Any time an exhuast fan or the dryer runs (unless you have a condensing dryer), you are bringing in outside air to replace the exhaust. You may be able to confine most of that input to a fresh air intake provided for just that.

But, that outside air comes in whether the AC is running or not, and if the AC is not running, it doesn't get conditioned. For my house, the AC is not running about 75% of the time on a hot day, and much less on cooler days.

Intermittent exhausts are not a problem, constant exhausts can be disasterous. Look at my graph, some humidity spikes, they go right back down.

The induced infiltration is coming in through path of least resistance not likely all 160 CFM for a clothes dryer comes in through your 6 inch intake even when the AHU is running, so you are sucking some through your walls as well as in from that vented attic of yours.

In some cases it will sweat in your wall cavity. The wall should have a drying process like permeable inside finishes and also the positive pressure cycle will resume and dry it out.


You guys are 30 years behind Canada on what it takes to build a tight house.