2 stage residential systems and humidity

Gordy

Don't worry the wifey will be the true test Chris

ChrisJ

Gordy said:

Don't worry the wifey will be the true test Chris

You don't know me or the wife.
I'm far more picky.

EBEBRATT-Ed

Cause oversized and dehumidification are are opposed to each other

Gordy

what happens on below design day........

njtommy

It runs at 20,000 btus of cooling on first stage so he should be ok. Below design days.

Gordy

I thought two stage was still up in the air? Chris?

ChrisJ

njtommy said:

It runs at 20,000 btus of cooling on first stage so he should be ok. Below design days.

Gordy said:

I thought two stage was still up in the air? Chris?

2 stage is still up in the air, just not sure yet. I'll figure it out when the time comes.

36,000 unit runs at around 27,000 in low stage.

ChrisJ

Right now I'm trying to get my YellowJacket Brute II's to stop leaking, and I'm not impressed at all.

Factory installed NPT connectors for the hoses were not even close to tight and were leaking. I cranked them in to what I felt was correct and am now testing.

Confidence is high, repeat, confidence is high.

ChrisJ

EBEBRATT-Ed said:

Cause oversized and dehumidification are are opposed to each other

Hatterasguy said:

Ed, it's not oversized if he wants a 20F drop on the design day.

And, that is exactly what he wants.

Ed,



It's "oversized" to those who find an indoor temp of 80F acceptable.
I do not, 75F is about as warm as I want to see. We generally want to run 70-72F depending on the outside temp. Previously have used 2.5 tons worth of window units and they fell short of what I feel is appropriate. Just before I pulled them out I did some testing on them to make sure they were performing properly, and they were.


When doing the manual J we messed around with the settings some, such as 75F @ 95F, and 70F @ 90F and it was still close to 3 tons. If I recall, 75 @ 90F got me down to about 2.5 ton. This also did not take duct loss into the attic into consideration and even though I'm using R8 for everything I'm sure there's going to be a noticeable loss when the attic is 120F. Duct work will be primarily 14" hard pipe with short runs (2-3 feet) of R8 flex and 10" hard pipe drops to the first floor, likely insulated with R4 or R6 just for condensation concerns but most of it will be in the attic, which stinks, but it is what it is.

Fact is, no one makes a 2.5 ton 2 stage unit anyway so it's actually a moot point so I'm still back to 3 ton if I go 2 stage.

BobC

Say what you will about window shakers but they can do a great job. My first floor is 625 sq ft, the house is 100 years old and had little insulation in the walls. A single 13,400 BTU Panasonic window unit could keep that whole first floor at 70 when it was 95 out and had no difficulty doing it. It was cool and bone dry.

Las summer I had the walls insulated and installed a 12,000 BTU Mitsubishi mini split. It works ok but the old Panasonic did a much better job, it cooled faster and it dehumidified better despite the uninsulated walls at that time.

I've found it does a better job of heating than it does of cooling, I can keep the first floor at 68 down to about 30F outside.

Bob

GW

Chris, you did a manual J but you did not account for the ducks in the Attic? Can you redo the manual J? That is all a part of the whole process

ChrisJ

GW said:

Chris, you did a manual J but you did not account for the ducks in the Attic? Can you redo the manual J? That is all a part of the whole process

I wasn't planning on any ducks.
Do I have to have ducks in the attic?


A friend from the forum did it with me, I don't think his program allowed compensation for that, but I can surely ask. He helped out a lot and I don't want to outstay my welcome.

@BobC
I had a 12,000 btu/h window shaker doing 800sqft on the first floor.

It did ok except for during very hot days.

Second floor had 19,000 which did ok most of the time as well, except we weren't cooling a big center area.

JUGHNE

PTAC's, which are expensive wall shakers, seem to be the single largest heat loss if not running. Go to any hotel when they are off and it is like a metal ice cube stuck on the wall. Turn them on and there seems to be no heat loss.
I realize these are in the heating mode......but the point is that any wall penetration is both a conductive and air infiltration heat gain/loss factor. Any window AC has to devote part of its cooling to overcome the losses incurred by the fact of it's installation thru the wall/window.

Also, there is the psychological effect of the noise that lets you know it is cooling your body off. Most of the ones I have been around seems that when they cycle off, you start to feel hot again.
So adding up the total cooling Btus of window AC's may not be a good indicator of what you need for central AC. FWIW

BTY, ducks in your attic only add to the R-value of insulation by virtue of their feathers.

BobC

Down is great insulation, not sure about the duck poop.

Bob

GW

My apologies, I was voicing the text and didn't proof my efforts.

Yes the manual J process must account for where the ducts are, what level of duct sealing is present and how much insulation in on the ducts

ChrisJ

GW said:

My apologies, I was voicing the text and didn't proof my efforts.



Yes the manual J process must account for where the ducts are, what level of duct sealing is present and how much insulation in on the ducts

I asked, his program doesn't offer that, nor did the manual J sheet I got from someone here, may have been @JUGHNE.

The ducts will be sealed most likely primarily with clear RTV, I doubt there will be much leakage if I can help it.

Truth is, if anything, adding the attic losses is going to make the system even bigger and I'm not going to a 3.5 ton.


Perhaps we can trade the window shaker losses for the attic duct losses @JUGHNE ?

njtommy

Just go duckless and be done already. Lol.

EBEBRATT-Ed

I agree with @JUGHNE about the window units. They have their place, I am not putting them down but central air (properly done ) has better air distribution. I have yet to see a job where central air couldn't do the job with less tonnage.

Me, I find I am perfectly happy @74-76 if the humidity is being controlled.

The lower the evap. temp the more your efficiency drops due to the increased compression ratio which will happen with 70 deg room air.

Also your still going to be able to make 70 deg with the 2 1/2ton just not on a design day. On a design day the unit will be running constantly (2 1/2ton) and will be dehumidifying better because it is running. Unless you stare at the thermometer you will never know that the sensible temp is creeping up a few degrees.

How many design days are there anyhow?? And when the sun goes down the unit can catch up, same thing in the morning just because it's 90 out the heat hasent been absorbed into the house yet.

Guess if your staying with 3 tons I would go 2 stage

njtommy

Here's some of the info from my area of Nj this past summer. It was pretty consistent. Chris's is probably pretty similar.

njtommy

Here's my data logs from this past summer.
1800 sqft rancher
3 ton single stage unit.

ChrisJ

So after tightening the hose connectors into the aluminum manifold and dunking in water again and then pressure testing two, or 3 more times, I can't remember, I'm confident in my Brute II set from 2008.

It seems there's always a slight drop in the beginning, but they held pressure for 90 minutes with no drop after the initial slight drop. I assume the hoses stretch, or something. This is done using dry nitrogen of course.

I'm not used to dealing with this, the highest I've ever gone pressure testing a Monitor Top was 20 or 30 PSI and that's pushing the limits.





So, onto the next step.

ChrisJ

So,

The project I started back in August of 2016 is finally starting up. Just ordered the rest of the parts and insulation for the ductwork.

It's amazing how expensive duct work becomes as things add up, without labor.

Gordy

Believe me the insulation for the attic ductwork will not be a waste. Have you decided on two stage?

ChrisJ

Gordy said:

Believe me the insulation for the attic ductwork will not be a waste. Have you decided on two stage?

Not yet, no.
Luckily, it doesn't really effect anything so I can put that off until the end.

What I will say, is I'm still not impressed by the tiny effect the 2 stage systems have (36,000 only dropping to 28,000), and the worse SHR.

Chances are, I'll end up with a cheap single stage outdoor unit, and a decent variable speed air handler. I really like the idea of running the blower really slow.

Gordy

I think you will want near constant circulation to eliminate hot blasts of warm soaked ductwork between calls.

ChrisJ

Gordy said:

I think you will want near constant circulation to eliminate hot blasts of warm soaked ductwork between calls.

Negative.
Constant blower dries off the evaporator, into your living space.

Bad idea.

Gordy

You'll see.

ChrisJ

I've dealt with it at work for 10 years there's nothing to see

Tinman

I think what you're looking for is a Liebert unit that's used for server rooms.

Tinman

When my wife and I bought this house, it had a 2.5 ton system in it. We buttoned up the envelope and and now cool it with 10,000 BTU/h. If it were up to me, we'd keep it cool enough to hang meat from the ceiling. But there's no need for that if you size the equipment properly and control the humidity.