Gulf coast humidity

[gencon]

How do I spec my new ac requirements to get a system that will have high latent heat removal?
Do oversized or undersized evaporators have a higher latent heat capability
gn

[dash]

Go with a variable speed indoor fan,TXV, and great controls,like Carriers Infinity,or next best Tranes Comfort-R,Or whatever brand you choose has,plus a two speed compressor,and you'll be amazed .

Most all our Infinity customers,run the system 2 or 3 degrees warmer,with the lower indoor humidity during cooling.

[udarrell]

That is a good question.
You need a real cold evaporator coil and a lot of run-time.

Therefore, do not oversize equipment!

I will let the other professionals argue over all the different options you could evaluate.

http://www.udarrell.com/air-conditio...tent-heat.html

From an initial cost standpoint I personally would stay with the lower 13-SEER rated units, but you will get a lot of arguments to the contrary. It depends on what the buyer can afford upfront.

As the percent of humidity goes up the latent capacity of the coil goes up! Check the condenser graph on the linked page.
- Darrell

[gencon]

Cant anybody explain in simple language!
How do you get a "cold' evaporator? Undersize relative to compressor? Or do you oversize to increase the fin area to collect more condensation? I current have a 3.5t; some manufactures tech data don't even have 3.5T evaps; some say use a 3T others recommend 4T.

Now I do understand Dash answer; throw cubic $ my way!

[dash]

First use a matched system approved by the manufacturer,if you need 3.5 ton,use the 3.5 coil match.In general the larger coil,say a 4 ton matched to 3.5 outdoor,will not dehumidify as well as the 3.5 ton matched coil.

A TVX(expansion valve)is the prefered metering device ,better humidity control ,in milder weather.


now go back to my first post,lok at at the comfort a top of the line system can provide,then the cost difference,divide by 15 year life,then365 days a year.Then decicde how much real comfort,in your ,is worth per day.Likely less then a beer!!LOL!!

Good luck!

[Carnak]

Air handlers by heat pipe technology dehumidify quite well.

A fresh air intake to the return air and the Air handler fan operating in "Auto" mode will pressurize your home with dry air and reduce humid air from infiltrating in and raising your indoor RH

[gencon]

Dash;
I do appreciate your time. But most of the answers I see are superfical.
Example; I have spent much time downloading detail tech date; two examples of what I found;
One manufacture has a 3.5t condenser units, but only lists 3t or 4t "matching" evaporators. Does the installer guess?
Rheem tech date has 4 3.5t evaps, but no details on what the tech differences are.
I called the local Rheem distr. he said and I quote, "we always order just one number"
Now I expect the Reheem units are probably tall, short, std and high effeciency. I would like to know how do I get the one with the most latent capacity. I asked the man about latent btu's and he acted like I was speaking greek. I don't think the correct answer is get a good contractor, pay top dollar and you will by difinition be happy because you paid the most.
I would just like to get some "sound tech/engr info" I have talked to 4 installers and they don't even agree if you need TVX or a drier installed. The installer recommended by a distributor said he did'nt like TVX's; go figure. And you wonder why the public throws AC guys and lawyers into the same pool. Sorry for the rant, but after hours of diligent work coming up with nothing from the pro's. It's insulting to be told that a Kia is as good as a Lexus if you have a good mechanic!!

gn

[beenthere]

In your example of the 3.5 ton condenser, and both a 3 and 4 ton evap being a match, the 3 ton would have the higher latent capacity with a txv, as a rule, (not engraved in stone).

[drk]

Kia has a ten yr warrenty

[udarrell]

Originally posted by gencon
Cant anybody explain in simple language!
How do you get a "cold' evaporator? Undersize relative to compressor? Or do you oversize to increase the fin area to collect more condensation? I current have a 3.5t; some manufactures tech data don't even have 3.5T evaps; some say use a 3T others recommend 4T.

Now I do understand Dash answer; throw cubic $ my way!

Those are good questions, and the mfg'ers and dealers should have the data available on all the equipment matches for contractors to evaluate.

A more relevant question to the buyer could be - what is the best long-term cost-effective system that will achieve the comfort zone levels demanded.

The answer to that question is dependent on the proper matching of every element of the entire A/C system.

My lowest cost pick is, a slightly undersized system at the absolute peek load levels, that has a larger compressor to evaporator coil area, but with extra coil fin area, and a dehumidistat wired in parallel to get the humidity to the desired level. "Always use a TXV refrigerant control."

The humidistat when it is closed should energize and "open" the closed relay contacts' line to the hi-speed 400-cfm per ton of cooling fan tap and close the N/O contacts to the 325 or 350-cfm per ton blower speed tap. (A double pole double throw fan speed relay; this is "a second fan relay with line power to the N/O side"- comprehend.)

Do an air infiltration test and reduce it to a minimum.

http://www.udarrell.com/latent_heat_condensation.html

[Edited by udarrell on 09-08-2005 at 11:35 PM]

[dash]

Originally posted by gencon
Dash;
I do appreciate your time. But most of the answers I see are superfical.
Example; I have spent much time downloading detail tech date; two examples of what I found;
One manufacture has a 3.5t condenser units, but only lists 3t or 4t "matching" evaporators. Does the installer guess?
Rheem tech date has 4 3.5t evaps, but no details on what the tech differences are.
I called the local Rheem distr. he said and I quote, "we always order just one number"
Now I expect the Reheem units are probably tall, short, std and high effeciency. I would like to know how do I get the one with the most latent capacity. I asked the man about latent btu's and he acted like I was speaking greek. I don't think the correct answer is get a good contractor, pay top dollar and you will by difinition be happy because you paid the most.
I would just like to get some "sound tech/engr info" I have talked to 4 installers and they don't even agree if you need TVX or a drier installed. The installer recommended by a distributor said he did'nt like TVX's; go figure. And you wonder why the public throws AC guys and lawyers into the same pool. Sorry for the rant, but after hours of diligent work coming up with nothing from the pro's. It's insulting to be told that a Kia is as good as a Lexus if you have a good mechanic!!

gn

sorry tried to answer your question,I/We don't handle those brands,and take no responsibility for there information provided.Wish you the best of LUCK.LOL

[cem-bsee]

Carnak: how does one dry the outside ambient air to be able to draw in dry air to reduce the humidity in the house?
The post was from someone on the Gulf Coast = hi humidity ambient, just as here in Huntsville AL where low outdoor ambient humidity equates to something 85% or less ( per the Channel 31 weatherman 2 mo ago).

[beenthere]

genco, post the model # of the equipment you have been quoted, and somebody here might be able to tell you its specs.

[bornriding]

Look at the product literature, the evap coil/outdoor unit combination will be listed with a s/t# ( sensible to total heat ratio ), this number shows how much sensible heat removal the coil has. The rest is latent heat. Find the one with the lowest sensible heat ratio and you will have the one with the best latent heat removal. Check performance data with outdoor unit combination.

Hope this helps,
Richard

[Carnak]

Originally posted by cem-bsee
Carnak: how does one dry the outside ambient air to be able to draw in dry air to reduce the humidity in the house?
The post was from someone on the Gulf Coast = hi humidity ambient, just as here in Huntsville AL where low outdoor ambient humidity equates to something 85% or less ( per the Channel 31 weatherman 2 mo ago).

In my post I mentioned a 'fresh air intake' to the return air duct, and I also mentioned operating the air handler in 'Auto' mode, meaning the air handler blower runs only when the compressor runs.

When this happens, the fresh air is cooled and dehumidifiied by the cooling coil and the home is pressurized the home with dry air.

Dry air then tries to leave the home when the system is running. This reduces the amount of humid air trying to infiltrate into the home from the outside. This keeps humidity from the home in the first place.

The mixed air entering the cooling coil has a slightly elevated dry bulb and wet bulb temperature compared to straight return air. The cooling coil will be able to grab more sensible and a lot more latent heat from this mixed air than it could from pure return air. It is much easier to remove the humidity of the outside air this way, than it is for the cooling coil to try and remove extra humidity from dry return air at 75F and 50% RH, to compensate for the humidity added by the uncontrolled infiltration of humid air.

I am dealing with high humidity as well, ambient dewpoints of 80-81F right now, I do not think it is any higher in the gulf.

You do not have the thermostat fan swith in the "ON" position, as the fan will run steady, constantly re-drying the coil/drain pan when the compressor cylces off. As well running the fan steady will pump humid air into the home when the compressor is not running.

[pstu]

I am a homeowner. From all that I have been told, the installer who said he "didn't like" TXVs has probably identified himself as a hack who couldn't control your house humidity if he wanted. That may be a harsh exaggeration, but you should know that he does not understand your concerns.

If the installer has to choose between 3.0 and 4.0T coils, he should be fully aware that the 3.0T choice will run colder and remove more humidity. But you should not have to manage this decision if you get the right installer. You need to inform him you are interested in humidity control and not just eye popping SEER numbers on paper (which I doubt will pay off for you in the real world). I suggest you ask him how he feels about doing a Manual J and Manual D calcs on your house. If he wants to charge you a sum for it, consider him further. If he indicates he does not do business that way, you are on less firm ground with him. Would the pros agree with this notion?

Some of the things suggested *have* been generalities, but truly there are craftsmanship issues which make a whole lot of difference. My way of knowing this, is finding just how big a goof was made by a prior installer, several times.

There was a question how a fresh air intake, can provide dry air in a humid climate. The answer I see is, that air goes thru the AC before getting into your house and that's how it is conditioned (i.e. dehumidified). The argument is that this fresh air intake tends to eliminate the outside air leaks already present in your house. Any air leaking into your house from other sources, has no opportunity to be conditioned. Measuring this phenomenon would be a great subject for a research paper, but I have not found one on this topic so far.

Hope this helps -- P.Student

[Carnak]

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

[core]

Here's your SIMPLE answer

Go get a load calculation done
Go with the 3.5 ton Condenser (if it matches the load)
Go with the larger Evap. coil (4 ton) WITH TXV
Go with a FanHandler drive (http://<a href="http://www.fanhandle...andler.com</a>
Go with a static pressure control for fanHandler
Go with 300 CFM or lowest permissible CFM

Then
Watch as your skin cracks

If you don't like that then install a whole house de-Humidifyer on the Return duct It will act as a PRE-DRYER for your system.

Core

[teddy bear]

Originally posted by gencon
How do I spec my new ac requirements to get a system that will have high latent heat removal?
Do oversized or undersized evaporators have a higher latent heat capability
gn

Are you looking for humidity control with low/no cooling load? A simple high SEER a/c sized for design conditions with or without an txv valve, with air tight ducts,and low air flow will provide 75^F,<50%RH during peak cooling load,+10 hours per day. During the night hours, moisture or latent load continues, sensible load declines, and indoor %RH rises slowly. Most a/c remove approx. 3,000 btus of latent,(3 lbs)per hour of moisture(75%Sensible heat ratio) with 75^F, 50% RH return air.
3 lbs. X 10 hrs. X 3 ton = 90,000 btus lat.(90 lb)(10 gals.)/day of moisture removal.
This will keep most homes dry with 75^F outdoor dew point. Higher or lower outside dew points require more or less a/c hours operation.
As the outdoor temperature declines, hours of a/c operation decreases. The complicated, expensive, two speed a/c with perfect controls should switch to low speed when the cooling load is reduced 50%. Now we have + 10 hours of low speed or 1.5 ton of a/c, while outdoor dew point(latent load) may be the same. Low speed (1.5) a/c operating 10 hours removes half as much moisture (45,000 btus or 45 lb/day). This is slightly better than cycling a single speed 3 ton for 5 hours. Removing less moisture raises indoor humidity, typically to 60%-65% RH. With a/c, overcooling is required to remove moisture. We need to operate on low speed 20 hours to remove the 90,000 btus of latent (90 lbs). During extended rain at 65^F-75^F, humidity control is impossible. Providing make-up fresh air ventilation makes humidity control more difficult yet.
High indoor humidity in addition to being uncomfortable, also grows mold. Consequently, several manufactures are selling whole house dehumidifiers that are combined with central a/c. When the a/c does not remove enough latent, the dehus automaticly operate until the desired humidity is reached. A 100 lb. per day dehu is capable of maintianing 50%RH without operating the a/c in 2,500 sqft.home. Some dehus have elaborate ventilation strategies to provide fresh air when occupied. These dehu systems are simple and cost less when combined with simple high SEER a/c than multi-speed a/c. The dehus can also be added to the mutli-speed a/c. TB "web dehu peddler"

[2hot2coolme]

I don't get it, there are plenty of 3.5 ton coils at the supply houses I deal with.
I think genco is a general contractor (hense the genco) that wants to DIY.