Manufacturers have capacity tables with the latent and sensible capacities listed at various air flows. The equipment capacity should come close to matching your load requirements for your area.

Assumption is that the unit is set up & operating properly and the load calculations are correct.

Duke power may provide assistance if they are your power provider. Some inspections departments may provide assistance since code specifies that the cooling capacity on a heat pump not be more than 25% over sized.

Check your indoor temperature difference across your coil, I would expect 17 - 20*f with your high humidity.

 

Funny how this all works out. Your old single speed a/c was probably on a smallish duct system with a smallish a/c coil. The small coil and duct system choke air and removed a moisture.

You put a 2 speed a/c in that has a large coil that operates on low speed whenever it can with a duct system that is too big on low speed. The results that it does a lousy job of dehumidifying. Nobody new why the old one did so good. And why the new one does not remove moisture.

I can see why it may not remove moisture to your satisfaction, but do not know exactly how to fix. It is matter of getting the air flow adjusted to remove enough moisture to get the temperature and %RH you will be satisfied with. Probably 75^F,- <50%RH would make you happy.

One more issue, I will bet that you were not getting adequate fresh air change with the old system evenings because your home did not have moisture problems. Today we are realizing that a healthy home has a fresh air change in 3-4 hours to purge indoor pollutants and renew oxygen. But because the old a/c dried out the home during the hot days and the lack of fresh air during the evenings and rainy days, you did not notice that your old system was not removing much moisture when the little or no sensible cooling loads.

You can get your new system working as good as the old a/c finding a good tech that knows how to setup your new a/c. Insist on s factory trained tech to adjust the a/c blower on the high and low speed to remove less sensible heat and more latent heat. You want a/c to provide <70% sensible heat and +30% latent heat/moisture. That will get a dry home on a hot day.

Evenings and rainy days will little better but provide 75^F, 50%RH. If you want that, you will need a whole house dehumidifier or reheat. Suggest a whole house dehumidifier with optional fresh air ventilation and merv 13 air filtering. Units like the Santa Fe Ultra, Broan, or Trane include a merv 13 air filter which will remove mold spores/p0llen from the fresh air and house air. Experts say you will be more comfortable and may live- longer.

Your thoughts.

Regards Teddy Bear

 

You have experienced exactly what was being warned about in the video.
The new SEER2 standards focus on sensible performance. Manufacturers need their products to rate highly in order to sell, sell, sell. So new equipment has good sensible performance but lousy latent removal. And customers clamor for rebates, which are principally on the high sensible performance equipment. So they end up with high humidity.
I don't care for 2 stage equipment because most of it doesn't have enough capacity reduction to make a comfort difference in humidity.
Carrier Greenspeed and ICP 5 stage equipment (there may be some others) have a reheat dehumidification feature which negates the need for a dehumidifier by using a small portion of the electric heater package.

HVAC equipment is essentially for heating, cooling, and ventilating. Notice no mention of dehumidification in the acronym. Latent heat removal needs to be considered separately (or in addition to) the cooling aspect.

As contractors, we are faced with the challenge of educating customers WHY better (and properly sized) equipment is the best choice for them. But it often boils down to the price. Multi-stage equipment does cost more and takes longer to install and set up so the customer bases their decision on the cost. That is, until they live with the cheaper installation for a while and find out the shortcoming which are a consequence of their decision.
I'm not saying you made your decision based on the price, but that's how the vast majority of people choose.

 

I'd love to look at the Manual J report for your house. Could you post that, please?
What equipment and what size did you get?
Did the installers provide a commissioning report? May we see that too?

I've seen some Manual J reports that were fudged. Higher design temps, extra loads, etc.

 

There is much confusion about how much flexibility our a/c units have. All ducted a/c units require an adjustment to the blowers to match them to the onsite duct system and in some cases the furnace blower. True that many get installed without this setup. And many work fine mainly because the duct system are not over-sized or the air filter restricts the air flow. The choke on the air flow makes the a/c remove more moisture. We occasionally have posters on the this site where the air flow is so low the coil freezes or the ducts sweat excessively. Many manuals include a chart that slows the a/cs performance at the various temperatures and air flow rates. The highest efficiency units which are higher sensible and less latent cooling are adjustable to get the desired 70% sensible/30% latent ratio needed to keep a home dry during significant sensible cooling loads. The 70/30 ratio gets you 3 lbs. of dehumidification per ton of cooling per hour.

Here is the other area of confusion. In a green grass climate typical outdoor dew points med-day are 60-75^f 24 Hours a day while sensible cooling peaks mid-after noon with low/no sensible cooling load during early morning hours. The a/c will remove significant moisture from noon to 6:00 pm while the moisture load is probably higher evenings and rainy days. One speed a/c will remove significant moisture evenings and rainy days. while two or VS speed a/cs are only slightly better. An occupied home with adequate fresh air infiltration/ventilation will have a high indoor dew point than the outside dew point because of the moisture that occupants add to the ventilation air that is passing through the home. Another big problem with multi-speed a/cs is uneven conditioned air distribution through out the home during the different seasons of the year.

Here is the solution for "green grass climates", add a whole house dehumidifier with fresh air ventilation and a simple single speed a/c. Setup the a/c to maintain <50%RH during significant sensible cooling loads. Set your t-stat for 75^F, and your dehu-stat <50%RH. Be comfortable and live a longer, healthier life. Get a dehumidifier with merv 13 air filter that will filter the fresh air and house air with the merv 13 air filter.

Anyone want to tell us how the any type of a/c will provide the temperature and %RH in a simpler, more cost effective way.

Regards Teddy Bear

 

Another big problem with multi-speed a/cs is uneven conditioned air distribution through out the home during the different seasons of the year.

Here is the solution for "green grass climates", add a whole house dehumidifier with fresh air ventilation and a simple single speed a/c. Setup the a/c to maintain <50%RH during significant sensible cooling loads. Set your t-stat for 75^F, and your dehu-stat <50%RH. Be comfortable and live a longer, healthier life. Get a dehumidifier with merv 13 air filter that will filter the fresh air and house air with the merv 13 air filter.

Anyone want to tell us how the any type of a/c will provide the temperature and %RH in a simpler, more cost effective way.

Regards Teddy Bear

I'd like to have more information about that. Are you saying that this is the case especially in 2 story houses?
We have 5-stage units in several 2 story houses and have not had complaints of poor distribution.
My 5-stage unit keeps the air perfectly distributed in my house. Admittedly it's a single story house, but the duct to the office goes from the trunk in the crawlspace up to the unconditioned attic and travels 25' to a "Y" fitting to feed the den and the office. It is considerably longer than all the other branch runs in the house.
I seem to recall an expert on the subject (Alex Meaney or Ed Janowiak, I don't remember which) stating the it is impossible to have residential ducts be too big.

 

I live in Charlotte, NC
and I had 2 new Heat pump HVAC units installed this summer (sized correctly using manual J),
and I immediately noticed the humidity in the house went up,
and it's not comfortable at any temp.

It regularly reads 60-75%RH.

I've had the installer come out several times,
and I believe the fan is on it's lowest setting,
but I'm trying to confirm that with him.

I recently watched an HVAC 2.0 video (Unintended Consequences....)
that talks about how these higher efficiency units use larger coils,
and how they are worse at removing humidity from the air,
and wouldn't you know it,
he uses the unit that I just bought as an example of how bad some of these units
are at removing humidity (Carrier/Bryant 38MURA w/ 40MUAA).

He backs up his theory with charts that show the manufacturer's "cooling performance" and "S/T" values (Latent cooling capacity ratios).

I bought these units because I was led to believe that these new,
2 stage units were much better at
making the entire house more comfortable than my 15+ year old single stage heat pump units.

I was also told that they are better at removing humidity. "I don't think so Tim"

Bryant offers a 100% satisfaction guarantee for 1 year,
and a full refund.
I think I'm going to take them up on that offer.

I never really wanted to know what dip switches were, or what S/T values are, but here I am.
I trying to get my house back to a comfortable level
after I paid a heck of a lot of money on a new system that was supposed to be so much "better."

I feel like I can't really trust the salesman anymore and
I feel like I need to actually verify "cooling performance" charts prior to purchase.

Is this info avail to consumers (I cannot find it)? YES, see Attachment

What should we be looking for when shopping for a new HVAC unit when humidity is an issue?

Any recommendations?

Thank you!

2-stage set at 360 CFM/Ton
Commissioning Report to verify that DT across the evaporator coil > 21'F

CHARLOTTE, NC __ House < 25 years Old
TWO 2.0 TON Heat Pump Systems should BE ADEQUATE for UPTO ~ 3,600 sq feet floor area.

38MURA _ 2 TON PERFORMANCE

695 CFM
77.0'F Indoor Temp 64.4'F Wet Bulb
___ 86.0'F Outdoor Temp ________95.0'F
S/H 0.73 ____ ____________ 0.75_
TC 23,608 BTU/HR


Problem is NOT the Equipment, Installer IS the vast majority of the time.

 

Update:

Thanks for all the replies and the attachments! Let me try and answer some of your questions.
1. I tried to attach the Man J below that they sent me (I haven't seen a commissioning report...). We originally had two, 2.5Ton units. We downsized, and now have 2.5Upstairs, 2.0Downstairs. 2792 sqft, 1254 downstairs, 1160 up. The upstairs unit runs most of the day on hot days. Attic has blown insulation and all the HVAC supply lines are insulated. House is on a crawlspace with a vapor barrier, built in 1979.
2. The temp split between the return and vents usually varies from 9° to 15°. Today it's cooler outside 74°, so i've got a 14-15° split
3. The installer is factory certified. He came over the other day to try and help solve the humidity problem, and he was talking with a factory rep the whole time. They tried several things including turning on a dehumidify mode that slows the fan down and is supposed to help with humidity. It doesn't seem to be working. Our upstairs RH right now is 70%+. Currently outside is 75° and 89%RH. A neighbors house, which is very similar to mine is at 48%RH right now.
4. My old system didn't need a dehumidifier and the house was more comfortable. My neighbors don't have dehumidifiers. My moms houses doesn't have one and she too is usually in 50% RH zone. The expense of whole house dehumidifiers are pretty high, especially when you consider that you'll probably need to replace it at least once during the life of your AC. I'd like to avoid purchasing this if possible. I'd really like to find and AC that just takes care of it, if possible.

Let me know what you think.

 

Thanks for all the replies and the attachments! Let me try and answer some of your questions.
1. I tried to attach the Man J below that they sent me (I haven't seen a commissioning report...). We originally had two, 2.5Ton units. We downsized, and now have 2.5Upstairs, 2.0Downstairs. 2792 sqft, 1254 downstairs, 1160 up. The upstairs unit runs most of the day on hot days. Attic has blown insulation and all the HVAC supply lines are insulated. House is on a crawlspace with a vapor barrier, built in 1979.
2. The temp split between the return and vents usually varies from 9° to 15°. Today it's cooler outside 74°, so i've got a 14-15° split
3. The installer is factory certified. He came over the other day to try and help solve the humidity problem, and he was talking with a factory rep the whole time. They tried several things including turning on a dehumidify mode that slows the fan down and is supposed to help with humidity. It doesn't seem to be working. Our upstairs RH right now is 70%+. Currently outside is 75° and 89%RH. A neighbors house, which is very similar to mine is at 48%RH right now.
4. My old system didn't need a dehumidifier and the house was more comfortable. My neighbors don't have dehumidifiers. My moms houses doesn't have one and she too is usually in 50% RH zone. The expense of whole house dehumidifiers are pretty high, especially when you consider that you'll probably need to replace it at least once during the life of your AC. I'd like to avoid purchasing this if possible. I'd really like to find and AC that just takes care of it, if possible.

Let me know what you think.

I need to see the commissioning report.
As stated previously by more than one of us, old equipment was great for dehum. New equipment must be carefully selected and meticulously set up.
What thermostat are you using? If it's a Nest, THAT'S a problem. They all are.

 

Is all you have on the load calc that screenshot? Or can you click on the manual8 links?

Id be happy to stop by and look things over for ya if you like.

 

Those are just screenshots. I can see if they can send me the report. Others were asking about a conditioning report as well. The owner is coming back out again today because the dehumidification mode isn't working as planned on the downstairs unit. The upstairs unit is working, however the humidity is still 72% right now at 70° (it's set for 72° and using the overcool by 2°). Outside air 76° 91%RH. The dehumidification mode slows down the blower. If I'm reading it correctly it slows it from 894CFM to 806CFM.

Yeah, if my guy can't figure it out, I wouldn't mind getting a second opinion from you.

 

The facts are that if your occupied home has a fresh air change in 3-4 hours evenings and rainy days without significant sensible cooling loads, your homes moisture level will be be similar to outside moisture levels.



What am I missing?

Here is what I think most of your missing, A fresh air change in 3-4 hours.

Regards Teddy Bear

 

Perhaps you could raise the temperature setting for the 1st floor system and lower the setting upstairs so at least one system could run a longer cycle.

 

if you have a ecobee tstat, the dip switches would all have to be set for nominal performance. could be adjusted for air flow and dehumidifiy modes air flow as well, looking at the manual for the indoor unit. that system may also have a dedicated tstat for that system, "communicating" tstat, but they are $$$.

not familiar with this system, others may be able to tell if the settings are good looking at the dip switch settings.

my 2 stage trane is 50/100% (I believe yours is demand driven variable speed), normally runs 50/100% capacity. w the trane tstat, runs 35% airflow on first stage (50%) capacity. can drop the humidity pretty well if bump tstat down a degree. 50% rh in house is normal at 76 degrees.

 

update

The full manual J report is not available as the person who did my calculation left the company. I was able to get a little more data, not sure if it helps. I'll also post a pic of the dip switches.

 

The full manual J report is not available as the person who did my calculation left the company. I was able to get a little more data, not sure if it helps. I'll also post a pic of the dip switches.
View attachment 879569
View attachment 879557 View attachment 879559

How long with a/c running when you got the measurement? The home is a little high on %RH. The a/c is suppling dehumidified air. The a/c is reducing the dew point 6-7^F which will remove 3 lbs. of moisture per hour per ton of cooling. Running will get the a well designed home down to <50%RH. But evenings and rainy days will not run enough to remove significant moisture. But it is a good start on getting control of the moisture levels in a home. If you want <50%RH, get a whole house dehumidifier 1-6 lbs. of dehumidification of per hour.

Regards Teddy Bear

 

The db and wb split do look good, pretty typical I see on systems.

 

Teddy,

Just to clarify, my HVAC guy recommended sealing the crawl and installing a dehumidifier in the the crawl, and that should take care of the humidity in the house. You're saying to seal the crawl, but add the dehumidifier somewhere in the house (upstairs or downstairs?) and add a fresh air supply, correct?

(I do not know how long the system was running when he took those measurements)

 

Well Ya. You could put the dehumidifier in the crawl. Bring in fresh air and larger return from the main floor connected to dehumidifier return. Connect the dehumidifier supply to the a/c supply and a small duct to the crawlspace. Put balancing dampers in all four ducts. A dehumidistat on the main floor. Adjust the damper for a fresh air change in 3-4 hours. Adjust the crawl damper for +-50%RH.

Try to explain all this to your a/c contractor. Tell him that you want a merv 13 air filter in the dehumidifier. Units like the Santa Fe Ultra, Broan, or Trane have merv 13 air filters.

Tell us what he thinks.

Regards Teddy Bear

 

connection point in the upper left of pic, dh/ r/ c, to left of red and blue wires. is dehumidification mode connection. this boosts latent cooling, but like teddy says, only helps if ac is running.


my rh got up to 62% today. bumped down temp setting 1-2 degree to force cooling. now low 50% range. but had to set temp lower to do this.

 

I'd be happy in the 50's. Even in the dehumidification mode, I didn't get below 60% RH today. I bought a portable dehumidifier as a temp fix as the house is uncomfortable with this new "efficient" system.

 

dehum made cannot be running, the space for the connection has no wire. unless jumper removed and in permanent mode, but temperature numbers do not seem to indicate dehum mode.


maybe there is duct leakage bringing in humid air from outside. sometimes and old canvas connector splits, or air leakage behind/under air handler where difficult to access to even see .


trane tech rep yrs ago mentioned he went to an install that had one of highest latent units on market (not just trane line-up). turned out unit in attic had gross air leakage in ductwork, causing poor performance, even though unit was working well.

 

I believe dehumidification mode is the brown wire that's hooked up to the DH on the right side of the panel. S4-2 "OFF" removes the jumper from R to DH. Do you believe it is hooked up incorrectly?

 

I suppose that's possible. I had 2 companies suggest downsizing the 1st floor (which I did), and keep the upstairs the same (which I also did). Then I had 2 other quotes that just said "keep everything the same" and I know they didn't do any calculations whatsoever. The company I went with told me they did the calculations. The units have long runtimes in the summer and with the variable speed they can slow down and increase the runtimes, so I don't think I'm too far off on sizing. I had 4 quotes in total, and I certainly didn't go with the cheapest option. I feel like some people are trying to place the blame on the homeowner and I don't think it's fair (unless they ignored advice and opted the cheapest option.) I've had multiple installations in the past and I've never had a problem with humidity. Had I been presented with the option of saving on my power bill, or having a comfortable home, I would have absolutely choose the latter. In fact, that's what I thought I was choosing. I still haven't heard from anyone if there are (new) units that are better at latent cooling than others. If anyone has those charts, or recommendations, please share them.

 

Have you tried putting highly restrictive air filters in your unit yet?

 

No. I was actually thinking about increasing the size of a 16x20 to a 20x20, because it's got a little bit of a whistle, there's also a 12x12 return on that 2.5t unit. But this is something I am willing to try. Are these just the expensive filters at your local hardware store?

 

When adding portable dehumidifiers, avoid locating them close to the a/c returns. The warm dry air should be applied to the coolest, dampest areas. Warm dry air from a dehumidifier supplied to the a/c return air decreases the drying capacity of the a/c. Your target %RH <50%RH with 75^F-76^F space temperature.

Keep us posted.

Regards Teddy Bear

 

Ok. Yeah, I tried experimenting in different locations, including directly under the return, and I found that it didn't work so good there. We've been using it all summer. My wife hates the noise, so I typically run it for a few hours prior to bedtime and shut it off when we go to bed. If I let it run all day, we could probable empty it's 5 gallons, 3 times a day, no joke.

FYI. I talked with my HVAC guy about a dehumidifier and the fresh air, and he wasn't keen on the fresh air, as my main struggle has been with humidity. Our Ecobee showed up "poor" for VOC's and CO2 this morning, so I opened the windows. I'm almost thinking about buying a legit air monitoring sensor for $200 just to see, because I don't really trust Ecobee with any of it's measurements including temp and humidity. I'm always tweaking those values because they're always off, even with silicone sealing off the hole behind the wall.