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Old 01-02-2018, 12:17 PM   #16
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Re: System Sizing


Are your ducts in a conditioned space or attic? The calc shows you have ducts in unconditioned space.
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Old 01-02-2018, 12:21 PM   #17
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Re: System Sizing


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Originally Posted by user_12345a View Post
Are your ducts in a conditioned space or attic? The calc shows you have ducts in unconditioned space.
I see "condition... ". That looks like its conditioned space.

He mentioned that the ducts are in the ceiling of the basement. (Unless I'm losing my mind.)

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Old 01-02-2018, 12:25 PM   #18
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Re: System Sizing


missed the conditioned part and saw r4 ducts.

it said r4 ducts in conditioned, that must be wrong, who insulated resi ducts in conditioned space?
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Old 01-02-2018, 12:28 PM   #19
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Re: System Sizing


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Originally Posted by user_12345a View Post
it said r4 ducts, so that must be wrong then, who insulates residential ducts in conditioned space?
It would be a meaningless value for that application. It may just be a default number, or accidentally selected.

PS. Some ductwork gets internal insulation, more for sound attenuation though.

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Old 01-02-2018, 12:39 PM   #20
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Quote:
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Quote:
Originally Posted by user_12345a View Post
it said r4 ducts, so that must be wrong then, who insulates residential ducts in conditioned space?
It would be a meaningless value for that application. It may just be a default number, or accidentally selected. Alot of people forget to factor in the internal insulation when sizing ductwork..?

PS. Some ductwork gets internal insulation, more for sound attenuation though.

Cheers!
Back in 2008 we done a theater that the first 20ft of the air handler was insulated on the inside and duct board on the outside to try to reduce some of the noise....I hated climing in the duct with a pin gun and glue...The fumes was horrible ..lol... alot of people forget that internally insulating duct work decreases the overall volume of the duct when sizing it..seen it done to many times..

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Old 01-02-2018, 12:44 PM   #21
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Re: System Sizing


^It must change the friction rate too. they should have given you respirator.
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Old 01-02-2018, 12:54 PM   #22
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Re: System Sizing


With 2 level housing and the upper level usually seems to have a hot complaint in the summer months maybe insulating conditioned space ducts isn't such a bad idea.
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Old 01-02-2018, 12:54 PM   #23
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Re: System Sizing


Yes the ducts are in conditioned space made of duct board between the lower and upper levels.. Not sure of the r value of duct board.
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Old 01-02-2018, 01:00 PM   #24
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Re: System Sizing


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Originally Posted by shocker View Post
Yes the ducts are in conditioned space made of duct board between the lower and upper levels.. Not sure of the r value of duct board.
R value won't matter in your case. It should be ignored by the program.

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Old 01-02-2018, 04:55 PM   #25
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Re: System Sizing


How do I determine the tonnage of the system? I see samples that divide the total BTUs by 12,000. Is this correct?
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Old 01-02-2018, 04:58 PM   #26
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Re: System Sizing


yah, but read but i wrote about selecting tonnage in a previous post. the actual capacity is a little lower in real world conditions than the rated tonnage.

some may say nominal tons, but you can get a 2 ton that does 22,000 instead of 24 000.

your design temp looks low too,

i think you'll end up with 2 tons, possibly 2.5 if the house is not well insulated and calc is done accurately.
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Old 01-02-2018, 06:29 PM   #27
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Re: System Sizing


I increased the design temp for both heating(91) and cooling(11). Does the Basement data look correct?
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Old 01-02-2018, 06:33 PM   #28
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Re: System Sizing


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Originally Posted by user_12345a View Post
You can download hvac-calc for $50, it's a limited license. you can get the trial for free and the paid version lets you change the design temperatures.

There are also other calcs online which are probably better - https://www.coolcalc.com/

The A/C units are rated at 80F 60% indoor, 95F outdoor. So the actual delivered capacity is a little lower than rated for the typical user who may want 70 to 75. In the states, manual S is used to see what size you need adjusted for this.

If what you posted is accurate, would probably be looking at a 2-ton.

Looks like a semi-detached house.

The calculation says, air duct R-4 -> are your ducts in unconditioned attic or crawl space.


Have to look at ductwork and furnace too and see if it can handle the cfm the a/c requires.

Here's a good article on where most cooling loads fall: https://www.energyvanguard.com/blog/...thumb-must-die

I'm a bit north of you and the houses I've lived in have cooled fine with 1 ton per 800 sq ft to 1000+. Oversizing seems to be less rampant than in the states.

The smaller unit will do a better job of humidity removal.
Not to be insulting. Cause you didn't know. But nobody in your area sizes to 13°F outdoor winter design. Use 0/ZERO. Next, don't use 89 for summer, 92 min, better to go with 95. I use to live in Harrisburg. Not far from the Governor's mansion.

Your probably going to need a 2.5 ton to meet your sensible and latent cooling loads.

There is something way off in the heating load, its only a thousand BTUs more than the cooling load. Wild guess, your going to need around 42,000 to 48,000 BTUs for heat.
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Old 01-02-2018, 08:04 PM   #29
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Re: System Sizing


ya the calc didn't look right to me either.

not sure why you quoted my post vs the original on this thread. didn't do that calc, op did.

Yes, in my area the design is something like 0F to -5F, and i would probably use as low as -15 since it can drop that low every 2 to 3 years, like it will later this week.

But op is south of that.
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Last edited by user_12345a; 01-02-2018 at 08:07 PM.
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Old 01-03-2018, 01:11 AM   #30
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Re: System Sizing


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Originally Posted by shocker View Post
I increased the design temp for both heating(91) and cooling(11). Does the Basement data look correct?
I'm going to assume that's a typo, you actually reversed those.

Now with everything else people have said, you'll want to add about 20% to the calc for errors. (It doesn't look like that one has it built in.)

You'll also want to change the indoor temps a bit. People change, and so does the temperature they want. I'd put at least 72 for cooling and 75 for heating.

Cheers!

Last edited by supers05; 01-03-2018 at 01:14 AM.
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