2 stage residential systems and humidity

ChrisJ

Hey guys,

Ever since @captainco brought this up it has been bothering me.

I found charts from multiple manufacturers and all seem to point to the same thing. 2 stage systems do NOT have improved moisture removal in low stage, if anything, it's worse!


Here's the high and low charts from a Tempstar aka Carrier 3 ton 2 stage.
I'm not seeing improved moisture removal at low stage, in fact, it looks worse!

What's the deal!?!?

HIGH



LOW

ChrisJ

Here's info on CFM ratings.
What caught my attention was how low it lets the blower run for dehumidification on high stage.

Seems to me, like a single stage with a variable speed air handler is still the best solution for dehumidification. No?

Opinions? Thoughts?

EBEBRATT-Ed

Not famalier with the equipment. 2 compressors or 1, indoor coil two separate circuits piped intertwined or a split coil??

ChrisJ

EBEBRATT-Ed said:

Not famalier with the equipment. 2 compressors or 1, indoor coil two separate circuits piped intertwined or a split coil??

I think it's somewhat of a recent idea.

1 compressor with bypass ports that cut it's output down to 67%. So you run at 67% or 100%. It's a Copeland idea.

Indoor unit is a variable speed setup with 1 coil.

Honestly @EBEBRATT-Ed it's looking more and more like an overpriced gimmick to me which is why I'd like some opinions.


https://youtu.be/uPhthHuZsQk

EBEBRATT-Ed

Best way to dehumidify is:

1. Make sure the equipment is not oversized
2. It probably won't dehumidify as well on low speed. The heat transfer on the refrigerant side is not as good as at full capacity due to the reduction in refrigerant flow through the evap. coil
3. The bypass factor of the air bypassing the coil will improve at low speed because you are pushing less air through the coil which will help.
4. If the equipment is sized correctly and the humidity level is still high the only way to dehumidify more is with a separate dehumidifier or force the cooling to run full tilt and then reheat the room air with an electric duct heater or hot water coil or by using discharge gas (condenser coil in the duct) (because the room temperature will drop as the cooling continues to run).

This I think violates the energy codes because you are heating and cooling the same air.

It usually can only be done for a process lab or in manufacturing where they need a specific temperature and humidity for a process.

ChrisJ

@EBEBRATT-Ed
So you agree, it seems hockey?

What are your thoughts on the air handlers that are setup to drop CFMs when humidity is high, and yet run the compressor full bore?

The one's I'm looking at for example on a 3 ton machine will run as low as 840 CFM with a single stage compressor. 1050 CFM is normal.

The lower airflow should allow the evap to run cooler, which should yield in better dehumidification to an extent, correct?

EBEBRATT-Ed

Yes, you can do that. We all know that 400-450 cfm/ton is normal. I was always told to dehumidify you can go down to 250/300 cfm/ ton. (which the 840 you mentioned is in that range) But you have to watch flood back and icing on the suction line may want to include a suction accumulator.

yes, lower air flow and a colder coil will dehumidify better. Moisture adds load to the coil in that you are removing latent heat from the air.

I don't have a 410 chart but with R-22 for example we used to use hot gas bypass to keep the suction pressure from falling below 57-58 psi which I believe is about 32 deg to keep the coil from frosting. Actually coils do not usually frost until 25 deg and below as long as air is moving across it

GW

Some basics, if the ac is on, you're removing moisture. A two stage system (two stage stat) will run longer cycles, removing more moisture.

Which of those two cycles, which one removes more moisture, I guess that's what you're trying to address

Yes a colder coil/lesser cfm means more latent energy work vs sensible energy work.

Gotta watch your superheat though.

Ac systems aren't dehumidifiers, yet they do dry the air as a byproduct of the ac cycle.

If you want a pimped out system get an UltraAire whole house.dehumidifier. get a good thermostat like Honeywell 9000 series to control the dehumidifier in conjunction with the ac system

I've got the 90h unit, I set it for 55%. I had it at 50% when I first installed it but it was running all the time. 55% feels darn good when it's 75 degrees in the home.

ChrisJ

GW said:

Some basics, if the ac is on, you're removing moisture. A two stage system (two stage stat) will run longer cycles, removing more moisture.



Which of those two cycles, which one removes more moisture, I guess that's what you're trying to address



Yes a colder coil/lesser cfm means more latent energy work vs sensible energy work.



Gotta watch your superheat though.



Ac systems aren't dehumidifiers, yet they do dry the air as a byproduct of the ac cycle.



If you want a pimped out system get an UltraAire whole house.dehumidifier. get a good thermostat like Honeywell 9000 series to control the dehumidifier in conjunction with the ac system



I've got the 90h unit, I set it for 55%. I had it at 50% when I first installed it but it was running all the time. 55% feels darn good when it's 75 degrees in the home.

@GW .
So based on the information from the manufacturer above, would you agree that low stage appears to actually remove less moisture than high stage? The S/T is quite a bit worse (more sensible) in low stage.

Agreed, a dedicated dehu is the way to go ultimately, but I was sold on 2 stage setups until I looked a little closer. I'm confused now.

The efficiency does seem a little better, but dehumidication seems worse.

GW

Yes Chris I believe we are talking about apples and oranges. You cannot dehumidifier ( remove moisture) if you are not running your AC system. A two-stage system will run longer than a single-stage system, not sure if that's really debatable.

So just because second stage has a greater ability to remove moisture doesn't really speak to the fact that a two-stage system will remove more moisture than a single-stage system


Gary

Gordy

I think it's the fact that two stage will run longer than single stage. Not so much which part of a two stage removes more moisture. Like GW said if it's not running nothing happens.

ChrisJ

So what you're saying is, yes the latent to sensible ratio is worse in low stage, but the run time is longer so it makes up for it, and then some?

ChrisJ

@Hatterasguy

Thoughts?

GW

I didn't see the charts, I'm more interested in long run times vs which stage (1st stage or 2nd stage) is more efficient. If I could chat face to face I would better understand you on this topic. the fact that one is more efficient than the other doesn't really deal with long vs short run times..

ChrisJ

GW said:

I didn't see the charts, I'm more interested in long run times vs which stage (1st stage or 2nd stage) is more efficient. If I could chat face to face I would better understand you on this topic. the fact that one is more efficient than the other doesn't really deal with long vs short run times..

The charts are in my first and second posts.

ChrisJ

Here's another interesting note.

Gordy

The extreme version is when a system is oversized for the load. This translates to short on cycles, and poor humidity removal.

I agree with GW's last post.

ChrisJ

Gordy said:

The extreme version is when a system is oversized for the load. This translates to short on cycles, and poor humidity removal.

I agree with GW's last post.

I re-read what he said.

I also missed one thing, the power consumption is down on low stage, but the run time is increased. Not sure what that actually works out to in the end.

njtommy

Comfort works out in the end. A comfortable house is what you want and what your paying for. Two stage will provide that for you along with better humidity control from longer runs times. I know what your charts and grafts say, but I also know what real world experience has shown me.

Gordy

You could always experiment ?

ChrisJ

Gordy said:

You could always experiment ?

Absolutely!
I'll make you a deal, you buy a 3 ton inverter, a 3 ton 2 stage and a 3 ton single stage and I'll experiment with them and give you feedback.

John Mills_5

Most run 75-80% on low. Often the sensible heat ratio is fairly high when on low as EBEBRATT-Ed explained. So I've never bought into the "buy the 2 stage to get lower humidity".

Blower speed probably do you more. Some VS furnaces these days default to 350 CFM/ton unless you override. About every VS has a dehumidify on demand capability with the right indoor control (formerly known as thermostat).

And has been pointed out, nothing dehumidifies when not on and there is a lot of time in most climates where it is humid but not enough sensible load for the A/C to be running.

EBEBRATT-Ed

Hence, why I said the most important thing is to not oversize the equipment.

GW

Not oversize........yet so many systems are.

ChrisJ

Yes,
And according to many mine will be oversized because I won't accept 80F in my house.

Gordy

It will only be oversized for 98% of the cool season

ChrisJ

Gordy said:

It will only be oversized for 98% of the cool season

It'll be no more oversized than any other equivalent system as my house is always cooler.

I tried to help you understand that earlier this year, but I gave up.

GW

Ahh so you want oversized and good dehumication? Hmm that's hard to do!

Gordy

That's why I needed help understanding

ChrisJ

GW said:

Ahh so you want oversized and good dehumication? Hmm that's hard to do!

I WANT IT ALL!


I want oversized, and reasonable dehumificiation.

Honestly, I suspect it'll be fine, I'm just trying to do the best I can.

Gordy

I want it now......where have I heard this?

njtommy

Im sure Chris will be fine. 3 tons and roughly 1600-1800sqft is not uncommon. His biggest problem will be keeping the up stairs cool with out zoneing the ductwork.

ChrisJ

@njtommy I've come to the conclusion that no matter what I do @Gordy is going to disagree with it. It's fine.

Fred

He's going to be cooling from the top down @njtommy . That should help him a lot.

njtommy

@Fred that's is true and hopefully he installs balancing dampers to help adjust flow.

ChrisJ

njtommy said:

@Fred that's is true and hopefully he installs balancing dampers to help adjust flow.

Every takeoff will have manual dampers installed.
In fact, the main return which will mainly serve the first floor is also going to have a damper.

ChrisJ

Just got done cutting down some 10' EMT so I can fit it in the basement and feed it up along side the B vent.

Installed the outdoor disconnect and ran 49' of 10-2

Also, "converted" my Brute II manifold set over to R410 / R22 with YJ's liquid filled gauges and a nice new set of hoses. I could've kept the original hoses, but I wanted the valves.

Spent some time messing around with the new nitrogen flow gauge.

Also got a refrigerant scale and 25 pounds of Dupont R134A.

njtommy

Man @ChrisJ your turning into a. Regular Refer guy now. lol.

ChrisJ

njtommy said:

Man @ChrisJ your turning into a. Regular Refer guy now. lol.

I love this stuff.

My concern right now is I'm pressure testing the manifold and my lowside says 250 PSI but the highside says 225 PSI.

I'm a bit surprised these class 1 gauges are that far off out of the box.

I may need to open the R410A tank and calibrate the gauges using temperature.

EBEBRATT-Ed

I am afraid that you will end up cold and clammy with no dehumidification.

ChrisJ

EBEBRATT-Ed said:

I am afraid that you will end up cold and clammy with no dehumidification.

Because?