Choosing contractor/unit size

[DGIO-Not]

Only if no standing water per my favorite energy consultant. But he highly recommends this. Makes the crawl almost a basement. Seems that some exterminators resist this though.

Ideal leakage is zero, right?

Depends on application, rule of thumb is 4. We can get tighter but we have these pesky architects and Building Science people who want adjustable dampers ( :-) rightly so, my only complaint is when they over engineer and want trunk and supply.) We can gasket them, set stops so not to adversely affect system, and when they let us set them up we are at an impressive 3.2. But they have a battle within themsleves. We have had one system, that we worked directly with HO that was 2.2, but alas...those moveable parts.

[DGIO-Not]

ReREAD Post # 33.
I don't see much that one could state as atypical.

A friendly Southern Lady is TYPICAL IN GA.
Party a few hours once a month does N O T equal day care. ! !! !!! !!!! !!!!!

I am only friends with people who are good listeners and readers.

Never claimed to be Best Friends, just a better than average listener? Besides, I did eat my crow...just didn't think it required eating a Murder of crow.

[needhelp7]

Hubby & I are researching & discussing the benefits/drawbacks to the system Cont. E put together - 3.5 Am St. with 95% AFUE 2 stage variable speed &
4T hi-eff evap coil versus the oft-recommended & makes-sense-to-me 4T system with 2-stage cooling. Want to have some info before talking to contractor in the morning. Teens are chomping at the bit to get into their new rooms, so we can't wait until all envelope enhancements are finished, then run blower door, then decide on unit. So, any thoughts on the above 2 possibilities?

[needhelp7]

Most 2 stage A/C (including the Am/Std it appears you are leaning toward), run at about 70% of capacity in low stage... that would be about 33,600 BTU or 2.8 ton. I am just guessing here, but if the system is sized for a design ODT of 95*, and the HO wants, lets say, 78* inside, the low stage will hold fairly well around 90* or less outdoors... or a degree or so lower when the human/cooking loads build up... ...
When I say the VS blower will handle the latent load (humidity), I am saying IF the contractor sets up an on demand dehumidification (ODD) cycle in the system. AM/Std approaches this a little different, be sure your contractor understands how to have a sensor (and not the comfort cycle) handle humidity.

So, with the 4T 2-stage cooling, it will actually only be a 2.8T for at least part of the time, and "ramp up" as needed for days over 90 - thus using less electricity & delivering better humidity control than a straight 3.5T with a 4T evaporator coil?

Do 2stage cooling units wear out faster than 1 stage?

[ga-hvac-tech]

So, with the 4T 2-stage cooling, it will actually only be a 2.8T for at least part of the time, and "ramp up" as needed for days over 90 - thus using less electricity & delivering better humidity control than a straight 3.5T with a 4T evaporator coil?

Do 2 stage cooling units wear out faster than 1 stage?

I was hoping you would not 'jump' on the smaller unit without considering more things...

Surprisingly, the less start/stop cycles, the longer the life of a unit... regardless of run time. Yeah, that sounds 'wrong', but it is true.

The way a 2 stage is usually set up is with a 2 stage T-stat. Lets say you have the A/C set for 78*... when the indoor temp reaches 79*, stage one comes on... when it reaches 81*, stage 2 comes on. Now there are lots of variables here... One is that you can adjust the parameters of a quality T-stat. Another is that on a moderate Spring day of, lets say, 85* outside... as soon as the stat calls for cooling at 79*, it will cool down to just when the stat switches from 78 to 77*, then shut off. ONLY when low stage has been 'trying' for a while, and cannot keep up (system has been running and temp is still rising), does it switch to high.

So yes, in essence you have 2 sizes of systems in one box.

Having said this: Remember the other things I mentioned:

*ODD (on demand dehumidification)
*Run the fan continuously between cyucles (it will use about as much elec as a 100w bulb).
*Use the HoneyWell YTH9421 thermostat, as it can handle 2 stage heat, 2 stage cool, and the de-humidity cycles.
*And of course get the AprilAir 2200 filter.

Now, does this answer your questions?

[needhelp7]

I was hoping you would not 'jump' on the smaller unit without considering more things...


Now, does this answer your questions?

I think I'm making this more difficult than it needs to be. Interested to talk to contractor in morning & find out why he went with that configuration instead of the 4T 2speed compressor. Have notes from the previous post re: thermostat. We might be able to use a whole-house filtration installed years ago & he is willing to service it, IF we can find the filters - you'll laugh, I'm sure, it is a Pureatech system. The odor control was great, we got a decent install, and didn't know any better (didn't have internet at the time!). Otherwise, he does like the AprilAire & AirBear (? - haven't researched that one yet)- suggested the Accuclean because I mentioned odor control. Now that I understand that 2 stage compressor a bit better, am giving up for the night. Thanks again for reading & answering so much!

[ga-hvac-tech]

I think I'm making this more difficult than it needs to be. Interested to talk to contractor in morning & find out why he went with that configuration instead of the 4T 2speed compressor. Have notes from the previous post re: thermostat. We might be able to use a whole-house filtration installed years ago & he is willing to service it, IF we can find the filters - you'll laugh, I'm sure, it is a Pureatech system. The odor control was great, we got a decent install, and didn't know any better (didn't have internet at the time!). Otherwise, he does like the AprilAire & AirBear (? - haven't researched that one yet)- suggested the Accuclean because I mentioned odor control. Now that I understand that 2 stage compressor a bit better, am giving up for the night. Thanks again for reading & answering so much!

I remember the puretech... good idea but not a good unit.

IMO AprilAir is better than AirBear. I suggested AprilAir because of the allergies and Asthma. I try to get all customers to go with the AirBear as a standard... just a better idea. The folks wiht health issues get an AprilAir.

Best to you.

[dan sw fl]

The sizing idea is the system can run to 72 - which sounds like is never your goal anyway! I bet they didn't run a manual J for 79 indoor temp target.

Look, when you know people are coming over, get the moisture and heat out of the house early - run it to 74 or so -

Think of it as a pendulum, when you know you'll be challenging the load, get it swinging the right way early.

Indoor Design Temp is likely 75 or 76'F. It might take ~ 12 to 16 hours to lower and maintain 72'F EARLY. Unit Derating for <<< 80 'F standard AHRI indoor temperature creates a Real problem in trying to "pre-cool".

[quickcat46]

and it is 38882 btuh (3.8T)

12,000 btu equals one ton

[needhelp7]

Indoor Design Temp is likely 75 or 76'F. It might take ~ 12 to 16 hours to lower and maintain 72'F EARLY. Unit Derating for <<< 80 'F standard AHRI indoor temperature creates a Real problem in trying to "pre-cool".

Indoor design temp was 74 - pricing the 4T 2 -stage unit now, with tstat that will handle the dehumidification function. If we can run it at the 1st stage - 2.8T, right? during most of spring & fall, I'm thinking we'll use less energy (maybe a bigger issue in a few years as costs continue to rise) and control that humidity better. Just hoping we can afford it on the front-end.

On the pre-cooling, I generally lower the tstat to maybe 74, just for about an hour before company arrives - if we can keep it around 80ish even with a houseful of children/people running in & out, we're good.

Back to sizing, he used the "tight" option, but doesn't have any actual numbers from a blower door.

The search for a good contractor yielded a great one, I think - he'll even loan us a heater for the several days we'll be out of heat. And he's listening well, answering some questions more than once because I still don't understand all this inside & out.

[jerryd_2008]

...

The way a 2 stage is usually set up is with a 2 stage T-stat. Lets say you have the A/C set for 78*... when the indoor temp reaches 79*, stage one comes on... when it reaches 81*, stage 2 comes on. Now there are lots of variables here... One is that you can adjust the parameters of a quality T-stat. Another is that on a moderate Spring day of, lets say, 85* outside... as soon as the stat calls for cooling at 79*, it will cool down to just when the stat switches from 78 to 77*, then shut off. ONLY when low stage has been 'trying' for a while, and cannot keep up (system has been running and temp is still rising), does it switch to high.

So yes, in essence you have 2 sizes of systems in one box.

Having said this: Remember the other things I mentioned:

...
*Use the HoneyWell YTH9421 thermostat, as it can handle 2 stage heat, 2 stage cool, and the de-humidity cycles.
...

Not the way my Honeywell VisionPro IAQ tstat with remote equipment interface module works. It will never show a temp less than or greater than the set temp unless you fool around with a new setting. It maintains EXACTLY the set temp which probably implies a tolerance of less then 1/2 degree (or it may be lying to me). It definitely does NOT have the +1 and -1 tolerances of the old tstat.

Am I missing something here?

[seatonheating]

Weeding through 11 contractors and still nit-picking??

IMO, she wasted a lot of good people's time and energy when they had no chance of getting the work.

I sure would hate to go clothes shopping with this lady.

[needhelp7]

Weeding through 11 contractors and still nit-picking??

IMO, she wasted a lot of good people's time and energy when they had no chance of getting the work.

I sure would hate to go clothes shopping with this lady.

Actually, they wasted mine. Coming to my home (6 did), pretending to know what they're doing, sizing the unit completely wrong - if we had done business with them it would have cost us lots of $$ in the long run, and we would have been both sweating & freezing in the summer. It would have been much easier for me to just to get bids from the 3 contractors who had personal/professional recommendations & go with the low guy. It is unfortunate, but true, that "buyer beware" is still applicable.
Meanwhile, I'm spending inordinate amounts of time researching what I can so we can make an informed decision - and the information on this website has been tremendously valuable, but also brought up questions I didn't know to ask before.
Details will delight or destroy.