Carrier Infinity choosing a system, please advise
Installing central A/C in my 60s house.
I am not worry about the heat loss; my house has a radiant heating system.
The furnace heating capabilities would be just to speed up the heating process in the morning and as a back up.
The main task is a cooling system, where efficiency is not the key; the key is to have as much as comfortable air temperature, humidity control and the noise. The noise is the main factor.
A few techs came up with the 3.5T size for my 1600sqft split level in Chicago area. I was a bit suspicious about the size.
I have purchased software HVAC - Calc Residential, run the calculations, the result for 95F summer outside and 75F inside:
Total heat gain 30,200 BTUH, sensible 26,600, latent 3,600.
After reading on this site I put a system pieces together, planning to go with Infinity:
24ANA136 - A/C
The first thought was that the cooling capacity might be to big (24ANA1 is not available in 2.5T size), but if it is a hotter than 95F day and a few people visiting house and some kitchen, heat generation activities, the total heat gain goes up to 32,800 where the sensible heat gain portion is 28,300 BTUH. I was not be able to find any data on the sensible cooling capacity for 24ANA136, but I would assume that this size would not be too big.
The first stage of 24ANA136 has a cooling capacity of 25,800, what would perfectly benefit for the lower outside temperatures during the night and providing lower acoustical noise. This unit would also provide more precision temperature and humidity control.
I was originally going with the 2.5T Performance 24APA530, better matching size and lower noise system.
But the two stage 24ANA136, even over capacity a bit, would provide more flexible operation since it has a lower power 1st stage.
Now about the acoustical noise, since the noise is the key factor. It seems to me strange that the two stage Infinity 24ANA136 has a higher noise level than 24APA530. According to Carrier site it is 70dB and 68dB respectively. The product data sheet is showing a standard rating 73dB (high stage) and 68dB respectively. But the weighted sound level tables show that the typical octave band spectrum noise levels are actually lower by one or two dBs for the Infinity two stage A/C.
My question is, which unit is actually quieter?
My A/C most of the time would work only at a first stage.
Is this is considered good approach to design the system?
I need to place an order in a few days.
I would greatly appreciate for any advises, criticism or ideas.
Nice choice,use the search function on this site and see what other Infinity owners think of their Infinity!!
Dash, thanks for your reply.
I just want to add, it will be a new installation, currently I have a window unit. The furnace unit will be in crawl space. All ductwork will be new, any sizes might be chosen. I would appreciate for any suggestion on a duct work.
1. Is it a good A/C sizing approach to have an oversized system system running on the first stage most of the time?
2. Is the 3T system really oversized, since I do not know the real sensible capacity numbers?
3. Are the system pieces are matching?
I will rephrase.
My load calc. shows 30,200 total heat gain.
Is it a good sizing approach to choose a 36,000 BTUH A/C equipment (25,800 on the first stage) if my load calc. show lower?
I am worry that the system would be jumping continuously from one stage to the other, since neither one has a capacity matching with the heat gain needs.
Can some one advice please.
First,both the sensible and latent btus for the equipment most be more then the load calc..
Second,many rating you will find for the equipment are at 80° indoors and 95° outdoors,so they need to be adjusted to match what was used in your load calc..
To answer your question,there will be many hours that the low stage capacity will be more then you need,like at night,milder then load calc design temperature.
A good control system ,like an Infinity,will let it start in low stage,then switch to high if needed,then cycle off.So I wouldn't worry about it switching back and forth.
I also would consider the Infinity 58UVB060 model instead of the MVB060.... you gain just a bit of efficiency which isnt a big deal in your case but the UVB rates at 95% Afue-- and qualifies for a Federal Tax Credit. ( as does your A/C)
Dash, thanks for clearing things up.
Novakht, I have thought about this model, but I need a horizontal unit for my crawl space. 58UVB comes only as a vertical.
It was a day when I was needed to place an order. Unfortunately I need to reconsider my system, it was over my budged.
I have a last shot.
I want to use a little bit lower cost system:
24APA536 - A/C
My worst weather case calculations showing 30,000 BTUH.
The new choice system would be only one stage:
1. Should I still consider a 36,000 BTUH unit or go to smaller 30,000, what is actually calculations show?
2. Is furnace going to work in the two stages (speed) for cooling and provide a good humidity control if the A/C is only one stage?
3. Is it even a right thing to build a system in this way, when a furnace is an Infinity series and the A/C is Performance single stage, non communicative? Is it going to work properly or is better to have a fully Performance series system?
1. You/they need to look at the load calcs.,sensible and latent btus,then be sure the equipment selected covers both.Very important that the equipment rating be adjusted for the number of degrees below standard indoor temp. of 80° F.ACCA's Manual S addresses this.
2.It should/will be setup for 350 cfms per ton,which is better dehum. then 400,then when it needs to dehum., it will run at 80 of 350 cfms per ton.
3.It'll be just fine,not as good as the two stage,but likely far superior to anything you have l experienced.
Dash, thanks, now I am getting closer to my final decision.
The last thing bothers me is the system size (cooling wise) selection.
I have done a heat gain calculation with HVAC – Calc, using worst case Chicago weather scenario at 95F summer outside and 75F inside, 113 grains of moisture, 50% rel. humidity inside.
The load calc. show 30,200 BTUH total heat gain (sensible 26,600, latent 3,600) for my 60s split level 1600sqft house.
I did not find in the 24APA536 data sheet any sensible either latent cooling capacity numbers, only a total, which is 36k BTUH.
The other extreme scenario would be when a few people visiting house along with some kitchen heat generation activities, the total heat gain goes up to 32,800 where the sensible heat gain portion is 28,300 BTUH.
I know that over sizing the A/C system is really not the good thing.
Should I still consider a 36,000 BTUH unit or go to smaller 30,000 BTUH
Sorry for so amateur questions in this forum. The HVAC – Calc makes only Manual J, I do not know how to perform your suggested "below standard indoor temp. of 80° F.ACCA's Manual S addresses this". Would not be enough only Manual J with worst weather case numbers?
That's a good question. I have also wondered if you are near a capacity, slightly over, whether you should round up and get the bigger system or round down and get the smaller system. I read somewhere that you should always round up, but somewhere else, maybe these foums, it was posted that you should consider whether you plan to make explansions or improvements to your home that would affect the capacity you will need in the near future. Wish I had a better answer for you. BTW, how easy was the HVAC Calc program to use? Thanks.
step 1-establish your expectations
step 2-hire a qualified contractor and convey your expectations to him
step 3- make the solution fit the problem, not the other way around.
step 4-let the contractor do what he's getting paid for.
all due repect, why can't the contractor handle the details? wrong contractor or wrong customer?
I know this is rather late but why do you need the furnace with the radiant? heating system?
Have you thought about dropping the furnace in lieu of a var spd air handler and 3 ton two stg Infinity heat pump? How are your electric rates?
Just an idea.
Not sure where you found 36,000 btus total for that equipment match.
Like I stated before"1. You/they need to look at the load calcs.,sensible and latent btus,then be sure the equipment selected covers both.Very important that the equipment rating be adjusted for the number of degrees below standard indoor temp. of 80° F.ACCA's Manual S addresses this."
You are at 95° outdoors ,so no problem,no adjustment needed.
For 75° indoors the deduct is sensible btus is 835 btus ,per degree less then 80° ,per each 1,000 cfms.
So,5X835X1.05= 4383 btus to deduct
I show your equipment at 35555 total and 26150 sensible,then a 3% deduct as the match in the book is for a different coil then yours,which likely won't fit any way.
So,26150 x .97=25365 - 4383= 20982 sensible btus.
Looks like 3 ton is too small,assuming your load calc is correct.