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Blinds or No Blinds for Load Calculations

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TLY

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Discussion starter · #1 ·
When doing load calculations, what does Manual J say about blinds for new construction? Arguments can be made both ways whether to include them in load calculations on a new construction. You don't want to oversize a system, but you also don't want to be locked into a 45° blind on every window.

Is there a standard?

Thanks,
TLY
 
#3 ·
7th edition and earlier of Manual J do worst case (no blinds). Gain on fenestration is an average.

8th edition of Manual J use horizontal or vertical blinds on a 45. Gain on fenestration is real time.
 
#4 ·
Ed...

I thought fenestration was only real time when using peak load procedure.

Can you clarify?
 
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#7 ·
Yes...AED.

However, isn't the actual 'load' for the average procedure calculated at 3:00 p.m. sun position?

For example, I run a load with Elite RHVAC and tell the software all the rooms are in one zone and one system. Yes, the software will tell me if I have AED because it's looking at the 12 or 13 hour period of sunlight. However, to actually have a load value other than the 3:00 p.m. snapshot, I have to change the load calculation to multi-zone. That will use the real glass loads to calculate peak BTUH for each zone.

My point is the fenestration gain isn't real time unless you are using peak load procedure.

If I'm wrong, please let me know. I know you teach J8. I think I finally have a grasp on J8, but I want to understand it even better.
 
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#8 ·
I’m on the road and don’t have a full copy of 8 with me, only AE. If I was home I’d look further into it. The 3 PM snap shot could be true, I simply don’t know. I’m pretty sure I recall Hank saying it was an average though.


Open a load on your elite software > System data (little red blower wheel) design tab > bottom right > use CV if mutlizone > click on drop down menu.

That might explain how to set the software, I want to know if I have AED or not, then decide to zone based on the calc.
 
#9 ·
Yeppers. I understand that aspect of RHVAC. Just talking about the fenestration.

I'll grab my J8 tonight. Never stop learning. ;)
 
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#11 · (Edited)
MJ 8 AE:

"All conventional windows and glass doors shall default to internal shade (medium color blind with slats @ 45º) except purpose built daylight windows and skylights which have no internal shade"



I haven't come across that 3 p.m. thing that I recall....I only have MJ8 AE right now. Did I miss something that I need to go back over?


I would think the standard would be using the table and calculations for the window you actually have otherwise you use default.
 
#12 ·
I have the unabridged version. Oh, the joys reading that sucker.

TLY...you run it for the way the HO intends to use the room. You can't assume there will be blinds on the windows. I didn't. ;)

It's just the same as selecting the indoor temperatures for the load calculations. There are defaults, but you ask the HO what they expect to maintain.
 
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#13 ·
It's All About Windows !

TLY said:
Is this for all windows? TLY
Click to expand...
As a practical approach for East, West and South windows, I select blinds only for the bedroom windows.

Modelling blinds on any North windows obviously will not have a noticable impact.

If the windows are well tinted ( S.H.G.C. < 0.55),
the additional effect of blinds is significantly reduced.
 
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Discussion starter · #14 ·
BigJon3475 said:
MJ 8 AE:

"All conventional windows and glass doors shall default to internal shade (medium color blind with slats @ 45º) except purpose built daylight windows and skylights which have no internal shade"
Click to expand...
Could someone define "purpose built daylight windows" for me? If extra windows were placed in a room to gain an added view of a lake, would these windows be considered "purpose built daylight windows?" In a vaulted living room with lots of windows, would these windows be considered "purpose built daylight windows?" In other words, Would Manual J8 recommend calculating a load with 45º blinds on them or nothing on them?

I understand the variable of homeowner preference and existing conditions, but I am looking for what should be a Manual J8 recommendation or standard for a new construction where homeowners' preferences are not a consideration.

TLY
 
#15 ·
Purpose built daylight windows:
See Daylight Windows.





Daylight Windows:
"Windows that are designed to provide natural lighting without compromising the privacy of the occupants (located so there are no sight lines to the street or adjacent properties and not equipped with internal shade)"
 
Discussion starter · #16 ·
BigJon3475 said:
Purpose built daylight windows:
See Daylight Windows.

Daylight Windows:
"Windows that are designed to provide natural lighting without compromising the privacy of the occupants (located so there are no sight lines to the street or adjacent properties and not equipped with internal shade)"
Click to expand...
Thank you. Was that from MJ 8 AE?

TLY
 
#18 ·
Ed Janowiak said:
I’m on the road and don’t have a full copy of 8 with me, only AE. If I was home I’d look further into it. The 3 PM snap shot could be true, I simply don’t know. I’m pretty sure I recall Hank saying it was an average though.


Open a load on your elite software > System data (little red blower wheel) design tab > bottom right > use CV if mutlizone > click on drop down menu.

That might explain how to set the software, I want to know if I have AED or not, then decide to zone based on the calc.
Click to expand...
Found it.

Fenestration load is 13-hour average for average load procedure.

Peak load is obviously based on peak for the orientation of the fenestration.

I also see why you are using the CV option. That keeps the software from using peak values in the calculation. It will use average numbers even though you are 'zoning' the calculation. Let's you see AED answer.
 
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