decreased humidity control with higher seer

[heetseeker]

I was wondering why the higher seer units are supposed to be less able to dehumidify. My old unit, carrier 4 ton 1982 kept the house comfortable at 78 degrees 50% RH and my new 12 seer a/s 4 ton feels warmer at 78 degress 54% RH. I am hoping turning on comfort R will help. Why do the higher seer unit dehumidify less?

[ruud-man]

Higher SEER - lower compression ratio- lower head, higher suction- higher suction and larger evap- less latent heat capacity.

Certainly there are other factors but this is the one that greatly reduces hunidity control.

Thats my story and I'm stickin' to it.

[docholiday]

I dont know, I think some of that is silly nonsense. While some is legitimate.

In this case we have a wet bulb of 65.01 last year and 66.19 this year. Depending on your location the summer was significantly different than last year and yet we only have a 1 degree WB difference and that is uncomfortable. My suggestion would be set it to 77 and be done with it. If you get the wet bulb to 65.01, then you would have to ask yourself, how much is in your head?

No two systems are alike, the airflow is different from your previous system, the capcity is different (4 ton is not always 48,000 btuhs). The latent and sensible capacity differences between models. There are too many variables. Was the house rearanged to where now you spend your time in a different part of the room? Were there any duct changes to address room issues? Is the hygrometer calibrated the same as it was previously?

[heetseeker]

The a/c was installed the end of august and nothing has changed other than the equipment. I don't understand the talk about wet bulbs. Is the coil not as cold making it more difficult to dehumidify?

[docholiday]

wet bulb temperatures are basicly the combination of heat and humidity. The coil is probably not as cold as your previous set up but it is larger in all likelyhood. The larger coil should make up for the difference in temperature. Engaging comfort R may resolve your issue.

[teddy bear]

The indoor %RH is a function of the hours of cooling per day, the amount of moisture removed per hour, and the outdoor dew point. Comparing the %RH Aug/Sept which has fewer hours of cooling plus this year the midwest has had high outdoor dew points. Slowing the air flow more will increase the latent removal of any coil regardless the size. For times with little or no cooling, use a good dehumdifier to control %RH. TB

[big al2]

It is like the difference between an old 6-cylinder chevy truck and a race car. The race car runs better, but requires more things to be tuned properly.

We will see more people complaining about 12 SEER system. They should be complaining about the cheap install job they saved soo much money on.
Most of those complaints could be solved that Aeroseal stuff. Seal the ducts and leave more of the outside air outside.

Also you can't overcharge TXV systems and get the same results we got from cap tube systems.

[beenthere]

Your new 12 seer unit may have a slight higher indoor coil temp, and if it does it won't remove as much moisture.

Also, the new VS blower may be moving more air, and that means its also cooling the house a little quicker, which means its removing less moisture.

Activating comfort r should help.

[udarrell]

The lower the sensible ratio the better; i.e., a .75 sensible is better for latent control than a .82 sensible ratio.
An extremely important factor is NOT to oversize the system, a little undersized is better because you need more run-time to remove moisture. (Always use a TXV refrigerant control!)

Have a blower door test done to indicate the amount of air infiltration and seal your home as tight as possible. That will stop most of the moisture infiltration.

Slow the blower to around 350-cfm per ton (12,000-BTUH) of cooling.

The cooling coil's capacity to remove moisture increases with an increase in humidity; that helps!

http://www.udarrell.com/air-conditioning-latent-heat.html

The ultra high SEER units operate with a higher evaporator pressure and temperature, and therefore have to use a lot of other more expensive aids to reduce the humidity.
- Darrell - udarrell

[jrbenny]

Here's an idea...install equipment with a SHR that matches the load.

[amickracing]

My vote is it's not set up right. Most come from the factory set kinda high (air flow), to be safe. Plus most newer units come with a comfort system that should suck way more moisture out than the older models.

[docholiday]

I like JRBenny's answer best. Thats why they print spec sheets. That way, the right system for the job can be selected.

[heetseeker]

jrbenny
What is SHR? Is it sensible heat rating? Shouldn't I consider both sensible and latent heat loads?

[mdman]

Spec sheets are full of too much bull ****.

udarrell and jrbenny speak the unspoken truth. SHR increase and ADP increase with the higher Evap Sat Temps of a same capacity higher SEER /EER system.

Also righteous, is the idea of a Blower Door test and some ZPD to benchmark tightness, and identify opportunities to reduce depress, supply / return imbalances, and total infiltration into the space (read: all house suck, usually because most supplies leak out)

Redneck Techs will be of no help in any of the above. Sorry.

[mdman]

for heetseeker, Member...


delta Hs / delta Ht
(Sensable BTU's removed over Total BTU's removed)

delta Hs = (1.08)(CFM)(deta T DB)
delta Ht = (4.5)(CFM)(delta H *you need a psych chart*)
delta Hl = (4750)(CFM)(delta W *same*)

[jrbenny]

Originally posted by heetseeker
jrbenny
What is SHR? Is it sensible heat rating? Shouldn't I consider both sensible and latent heat loads? SHR = Sensible Heat Ratio = Sensible BTUH / Total BTUH. It does consider sensible and latent.

We get wrapped around the fact that higher efficiency systems have a warmer coil. Who cares? Not me. It's not an issue IF the system is selected based upon the sensible/latent split or sensible heat ratio. The SHR must match the load of the structure.

So many people in this industry continue to use rules of dumb to size. This is where the warmer coil on higher efficiency equipment hurts them.

Here's the example I use in training. 8 SEER 3-ton nominal system. 42 to 45 degree coil. Ductwork is undersized. So, airflow is lower than expected (900 to 1000 CFM). Thus coil is even colder. Home was cooled well, and it even took care of humidity. Now, flash forward 15 to 20 years. H/O gets replacement 14 SEER 3-ton system with a V/S blower because salesman just asked questions about comfort instead of running a load calc. Now, we are delivering 1200 CFM and the coil is warmer. The SHR is higher. Thus, thermostat will satisfy before latent work is complete. H/O complains that they are keeping the thermostat on 73 instead of 77 as they did with old system. Dealer or technician doesn't understand, and immediately gripes about those damn warm high SEER coils.

Load calculations matched with product data and proper duct design eliminate these problems. A majority of the load calculation software has the product data built into the program. It will show you the products that match your load. That way you don't have to decipher the product data to match your design temperatures.

Hope that helps.

[udarrell]

That is an excellent explanation for techs to take to heart, jrbenny.

To best serve their clients, --they ought to first explain why an energy heat-gain/heatloss audit be performed to pointpoint areas that need addressing should be accomplished in order to reduce energy usage.

Energy costs are going to continue to rise and being able to down-size and right-size equipment would make a big difference in their heating and cooling costs. That would optimize their payback time-peroid, if that is important to them and to all of us. Optimizing energy conservation ought to be the top proactive agenda of every powerful entity in America as well as worldwide. The mass media ought to do (PSAs) Public Service Announments to help connect the auditors to those in need of them.

Due to accelerating energy costs, a lot of folks will not be able to afford to adequately heat their homes this winter.
That is a threat to the health and even the lives of some human beings.

- Darrell



[Edited by udarrell on 09-24-2005 at 12:07 PM]

[heetseeker]

Beenthere and jrbenny
Great Posts. I think there is an excellent chance that you hit the nail in the head. I had a standard blower and now a Vs blower, My system is restrictive so likely I am getting more airflow and less removal of latent heat. Thanks to everyone for their answers.
jrbenny, I didn't know that load calc programs could match equipment to load calc. I used HVAC calc and there didn't seem to be a product matching feature. For the H/O matching the load data to the equipment is intimidating and I couldn't get a real load calc from any contractor. Are you talking about commercial programs?
I saw in another post that Trane is coming out with a thermostat thru honeywell that will control fan speed to control humidity. Anyone hear anything about this?

[Edited by heetseeker on 09-26-2005 at 01:11 AM]

[mdman]

The major problem with any load calc is that there is no way in hell it can do anything but guess, or ask you to guess at infiltration rates. This is a serious variable that can only come from Blower Door and ZPD testing. If you find another way, please tell me.

CFM50 and Nat ACH are needed to complete the model. The added benefit is that DB testing can lead to weatherization work that may reduce the load by a ton. If this results in you buying a 2.5T instead of a 3.5T then the BD and Wx work will return on first costs and the return on utility will be enjoyed for 10 years.

Blower Door Test, then seal the house, test out again
Duct Blaster, then seal the ducts, test out again.
Load Calc
Now choose and install your 13 SEER plus Air Source Heat Pump (with fossil fuel kit if in very heating dominate climates) and **maintain** it well.
Also, ask the installer how he is charging it. If you don't hear the word "sub cooling" and "demand conditions" then tell him to leave now. If the installer does not measure TESP, RESP, and SESP then don't write the check until they do. If it's a VS model using GE ECM and they don't change the defaults then default on the payment.

All that seams like a lot up front in a business that usually just "same sizes" and low balls, but I can show you a $250 / month electric bill on a 1300 sq ft home at 10 cent/ KWH (about 2000 KWH per month) that goes on for ever. I'm sure I could beat that load in half, that's almost $1500 per year at current rates.

Do you think energy will go down in the future?

[udarrell]

Originally posted by mdman
The major problem with any load calc is that there is no way in hell it can do anything but guess, or ask you to guess at infiltration rates. This is a serious variable that can only come from Blower Door and "ZPD testing." If you find another way, please tell me.

All that seams like a lot up front in a business that usually just "same sizes" and low balls, but I can show you a $250 / month electric bill on a 1300 sq ft home at 10 cent/ KWH (about 2000 KWH per month) that goes on for ever. I'm sure I could beat that load in half, that's almost $1500 per year at current rates.

Do you think energy will go down in the future?


Energy is likely to shoot up, including electricity especially if natural gas generated rather than coal.

For those that don't know what ZPD testing is:

Use this Link:

http://www.energyconservatory.com/

http://www.energyconservatory.com/download/fall02.pdf

MN and WI are up on a few things.

http://www.ornl.gov/sci/roofs+walls/

- Darrell

[Edited by udarrell on 09-25-2005 at 05:57 PM]

[dash]

Originally posted by jrbenny

Originally posted by heetseeker
jrbenny
What is SHR? Is it sensible heat rating? Shouldn't I consider both sensible and latent heat loads? SHR = Sensible Heat Ratio = Sensible BTUH / Total BTUH. It does consider sensible and latent.

We get wrapped around the fact that higher efficiency systems have a warmer coil. Who cares? Not me. It's not an issue IF the system is selected based upon the sensible/latent split or sensible heat ratio. The SHR must match the load of the structure.

So many people in this industry continue to use rules of dumb to size. This is where the warmer coil on higher efficiency equipment hurts them.

Here's the example I use in training. 8 SEER 3-ton nominal system. 42 to 45 degree coil. Ductwork is undersized. So, airflow is lower than expected (900 to 1000 CFM). Thus coil is even colder. Home was cooled well, and it even took care of humidity. Now, flash forward 15 to 20 years. H/O gets replacement 14 SEER 3-ton system with a V/S blower because salesman just asked questions about comfort instead of running a load calc. Now, we are delivering 1200 CFM and the coil is warmer. The SHR is higher. Thus, thermostat will satisfy before latent work is complete. H/O complains that they are keeping the thermostat on 73 instead of 77 as they did with old system. Dealer or technician doesn't understand, and immediately gripes about those damn warm high SEER coils.

Load calculations matched with product data and proper duct design eliminate these problems. A majority of the load calculation software has the product data built into the program. It will show you the products that match your load. That way you don't have to decipher the product data to match your design temperatures.

Hope that helps.




Exactly!Now if that salesman sells them a two speed/stage it can keep you out of trouble,but the correct size would be even better.

[docholiday]

Originally posted by jrbenny
Here's the example I use in training. 8 SEER 3-ton nominal system. 42 to 45 degree coil. Ductwork is undersized. So, airflow is lower than expected (900 to 1000 CFM). Thus coil is even colder. Home was cooled well, and it even took care of humidity. Now, flash forward 15 to 20 years. H/O gets replacement 14 SEER 3-ton system with a V/S blower because salesman just asked questions about comfort instead of running a load calc. Now, we are delivering 1200 CFM and the coil is warmer. The SHR is higher. Thus, thermostat will satisfy before latent work is complete. H/O complains that they are keeping the thermostat on 73 instead of 77 as they did with old system. Dealer or technician doesn't understand, and immediately gripes about those damn warm high SEER coils.

Load calculations matched with product data and proper duct design eliminate these problems. A majority of the load calculation software has the product data built into the program. It will show you the products that match your load. That way you don't have to decipher the product data to match your design temperatures.

Hope that helps.



You nailed it and I think you even eluded to the point. In this case 3 tons was not being delivered by the original system because the airflow was too low the capacity was reduced. The system was oversized and the ductwork poorly done but with the energy prices back then, it was a non issue. If this were a heat pump, it would likely have had problems.

The problem with the new unit is that it merely replaced exsisiting equipment and now, as a result of ECM technology, the airflow is correct for the tonnage and yet the installer didnt properly set the dip switches correctly for a latent reduction. Had he set the airflow to a 10 or 15 or even 20% reduction in airflow for cooling, he would have mimicked the older system by reducing the total capacity and addressed the latent load while at the same time operating at a better efficiency.

[jrbenny]

Thanks for finishing my thought, Doc. Exactly where I go in training.

Heetseeker: The load calc programs to which I refer are not the HO version of HVAC Calc. I'm not sure if the PRO version has equipment. I've used Wrightsoft, Elite, and Rezcalc. They have equipment tables in them.

[Edited by jrbenny on 09-26-2005 at 07:17 AM]

[heetseeker]

?

[Edited by heetseeker on 09-26-2005 at 11:55 AM]

[heetseeker]

When the dipswitches are changed, at any time, should the temp drop for a/c or the heat rise be measured? Is it unlikely that at the lowest airflow set by the dipswitches on A/S equip will freeze the coil or overheat the HX?
Doc in your post you refer to improved efficiency at lower airflow. Is this because the blower is using less electricity or because the thermostat can be set higher or both? Wouldn't seer be maximized at at higher airflow at altho possibly with decreased comfort?

[docholiday]

heetseeker, the sooner we all try to forget SEER once the unit is installed the better. SEER is a measure of efficiency with little regard to the actual output breakdown. Yes the return air is broken down to sensible and latent but leaving air is not. Efficiency and comfort cannot be interchanged. This is not to say a high efficiency system can not be comfortable.

If you had accurately measured the airflow of the old system, taken into account any index to capacity differences and applied them to the new system, you would likely find you could do the same level of work at a lower cost, maybe not proportionately but at a lower cost none the less.

SEER is in regard to efficiency, a matter of how many watts to produce X Btu's. SHR is not a factor in SEER. Comfort is a factor of installation and fine tuning of everything from fan configuration to duct design and yes, even equipment selection. Additional comfort is added work and added work costs more energy. High SEER systems dont just plug and play on every exsisting duct system no matter how many hillbillies try to think it will.

[teddy bear]

Originally posted by ruud-man
Higher SEER - lower compression ratio- lower head, higher suction- higher suction and larger evap- less latent heat capacity.

Certainly there are other factors but this is the one that greatly reduces hunidity control.

Thats my story and I'm stickin' to it.
I agree with most of this, but! You forgot "increase air flow" of the high SEER systems, which is the major difference in latent removal. Decreasing the air flow increases the latent to near the same as a small coil. High SEER two speed use large coils on low speed high latent mode. Large coils have more mass and takes a few minutes longer to get cold. Also large coils retain more condensate and take longer to dry. The high SEER specs claim the same S/R ratios as the smaller coils. Remember no cooling load, no dehumidification. You know the rest of the story. TB "a recovering dehu peddler"