Can someone help me with heat load calculation?

[Mike-]

Hi everyone, love your site, I usually just search and find answers.

Looking for help with a heat load calculation for a carriage house I'm going to build in the next few months.

I live in ottawa Ontario

Garage specs are 30' x 40'. 1200 sq'
10' ceiling
Wall area approximately 1120 sq'
3 8'x10' doors r16
Walls 2x6 r24
Ceiling of garage r31
Slab in floor radiant r10
Approximately 30c or 86f temp rise

Here is a photo, I can post top floor/ loft area soon
Thanks so much

 

[Mike-]

Living area specs
978 sq'
Walls r24 area 754sq'
Roof/ceiling r62
Windows 144sq'
Glazing ratio 19.12% (whatever that means)
Temp rise 45c or 113f

Thanks again

 

[Slednut]

This site may help.

http://ecomfort.com/

 

[Mike-]

I took a quick look didn't see a heat load calc!
I actually tried a couple online ones, but the r values would not go high enough!
I'm Getting anywhere from 30000 to 60000btu without entering my proper information!
Does anyone have any other links that have high r values?
Thanks

 

[CJCar]

I took a quick look didn't see a heat load calc!
I actually tried a couple online ones, but the r values would not go high enough!
I'm Getting anywhere from 30000 to 60000btu without entering my proper information!
Does anyone have any other links that have high r values?
Thanks

I was just going to post http://www.loadcalc.net/ until I saw your last comment.

I used the home ($50) version of http://www.hvaccalc.com/main.asp when I designed my house. It was dead on accurate. I do not know if the R Values will meet your needs though.

 

[Mike-]

Yeah I tried load calc but walls only go to R21 and ceiling to R56.
I guess that will be close enough.

Thanks

 

[ksj9393]

Here is another online calculator that may be worth a look: http://heatload.rinnai.us/

When it came to performing my heat load calculation for my garage, I discovered that varying the R-value of my walls and ceiling did not affect the total value in any earth-shaking manner. What DID impact my results were the values chosen for infiltration, which are difficult to quantify for a garage.

If you pick, say 2 ACH for the garage infiltartion - not an unreasonable estimate considering leaky OH doors and average construction technique with modest focus on air barriers - you might find as much as 1/2 your load will be infiltration loss. At least it was in my modeling.

Now, I did not do a blower door test on my garage (I did after framing and insulating my house, though), but I have 2 winters of data to draw from now and I can tell you that the heat load calculators I used online resulted in significant over-estimates. I suspect the reason is that I meticulously air-sealed my garage, even to the point of zip-taping the two overhead doors I was not using, but used a conservative estimate of 1.0 ACH for infiltration.

SO, my point is, worry less about getting everything modeled exactly, and pay attention to the relative contributions of infiltration, ventilation (for living areas), heat loss through wall and ceiling, loss through glazing and slab loss - important for large heated slab as might be found in a garage!

 

[Mike-]

Here is another online calculator that may be worth a look: http://heatload.rinnai.us/

When it came to performing my heat load calculation for my garage, I discovered that varying the R-value of my walls and ceiling did not affect the total value in any earth-shaking manner. What DID impact my results were the values chosen for infiltration, which are difficult to quantify for a garage.

If you pick, say 2 ACH for the garage infiltartion - not an unreasonable estimate considering leaky OH doors and average construction technique with modest focus on air barriers - you might find as much as 1/2 your load will be infiltration loss. At least it was in my modeling.

Now, I did not do a blower door test on my garage (I did after framing and insulating my house, though), but I have 2 winters of data to draw from now and I can tell you that the heat load calculators I used online resulted in significant over-estimates. I suspect the reason is that I meticulously air-sealed my garage, even to the point of zip-taping the two overhead doors I was not using, but used a conservative estimate of 1.0 ACH for infiltration.

SO, my point is, worry less about getting everything modeled exactly, and pay attention to the relative contributions of infiltration, ventilation (for living areas), heat loss through wall and ceiling, loss through glazing and slab loss - important for large heated slab as might be found in a garage!

Thanks for your information and the link, I will give it a try.

 

[magbal8]

I took a quick look didn't see a heat load calc!

1) eComfort's calculator can be found here http://ecomfort.com/content/49-mini-split-sizing-calculator. It's intended for sizing single zone mini splits, but it's the most detailed calculator out there if you're trying to just get an estimate.

2) eComfort has engineers on staff that will give you a free manual J sizing calculation. Just fill out their sizing form (http://ecomfort.com/PDF_files/eComfortSizingWorksheetandInstructions.pdf) and send it back to them and you'll get accurate sizing within a few days.

 

[rburke65]

That e comfort didn't help me any....didn't like my 13' 4" ceiling height but didn't tell me till I was on step 4 of 4, and then rather than just change the ceiling height, I had to start all over again....... If they paid me, I'm not starting all over again. So F---king frustrating. Thanks...... but no thanks. I'll pass.

 

[DonPowers]

The calculation for heat loss is Q=U x A x ∆T
Where:
Q= BTU per Hour
U= 1/R
A= Area in sq ft
∆T= Temperature Difference between inside and outside

So if R=24 and the wall area = 1,120 and ∆T = 86°
Q=(1/24) x (1120) x (86°)
Q= 4,013 BTU per Hr

Do the same for ceiling, floor, doors and windows then add up all the Q’s.

There a lot of other considerations to factor into a heat loss calculation but this will give you a ballpark idea of your heat loss. If you set it up on a spreadsheet you can model options.

 

[rburke65]

Thanks Don P.

 

[Mike-]

The calculation for heat loss is Q=U x A x ∆T
Where:
Q= BTU per Hour
U= 1/R
A= Area in sq ft
∆T= Temperature Difference between inside and outside

So if R=24 and the wall area = 1,120 and ∆T = 86°
Q=(1/24) x (1120) x (86°)
Q= 4,013 BTU per Hr

Do the same for ceiling, floor, doors and windows then add up all the Q’s.

There a lot of other considerations to factor into a heat loss calculation but this will give you a ballpark idea of your heat loss. If you set it up on a spreadsheet you can model options.

Perfect thanks

 

[pseudorealityx]

Keep in mind that using R-19 batts in a stud wall doesn't mean your wall is R-19. Those studs, air pockets, etc bring it down significantly.