ASHRAE Journal - December 2013 - 58

Column Building ScienceS

Supply

AHU

Supply

Return

Figure 3e Buried Ducts. Take the John Tooley option, make the ducts airtight,

make the ceiling airtight and insulate the bejesus out of the ducts by covering
them with lots of "fluffy stuff." You can cut that 10% hit to less than 5%.

than SPF for those nasty holes. And then while you are in
the house with that SPF do the other holes. Like the ones
between the garage and the house. Tight is right.
Note that even when you bury the ducts and foam
them to control condensation it is still not as good as
having all the ductwork and air handler inside the
house. Also note that burying the ductwork and foaming
them is not free. How much does it cost? Depends. But
it seems to be in the same ballpark as moving the ductwork into the conditioned space-except without a lot of
brain damage-read on.
Huh? You mean it is not free to move the ductwork
into the conditioned space? Nope. If you are an industry that has been building hundreds of thousands of
homes with ductwork in the attic for decades and one
day you decide that they should all go inside, you are
going to not have an easy go of it. Brain damage is the
word I use here. There will be clever framing, there
will be soffits and there will be dropped ceilings (Photos
3 and 4), and there will be lots of redesign. Is it worth
it? Yes, to me it is. Should you do it? Yes, I think you
should. But not everyone sees it that way and so the
good news is that we have two other viable options-
bury the ducts or construct conditioned unvented
attics.
How about ducts that are airtight in vented attics but
not buried that have radiant barrier roof decking or
radiant barrier ductwork coverings? Gets you a couple of
58

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D ecem ber 2013

photo 2 (leFt) Condensation Control. Yes, there is a duct under all that spray
polyurethane foam (SPF). You just can't "bury" the ducts or they will sweat. You
have to insulate them with an impermeable layer of spray polyurethane foam
and then you can bury them with "fluffy stuff." Note the impermeable part-only
closed cell, high-density (2 lb/ft3) SPF works. Of course while you are in the
attic with that SPF why not take the opportunity to seal all those holes that are
up there. Nothing works better than SPF for those nasty holes. And then while
you are in the house with that SPF do the other holes. Like the ones between
the garage and the house. photo 3 (top right) Bulkhead Framing. Moving the
ductwork into conditioned space typically requires bulkheads and soffits that are
airtight. photo 4 (bottom right) Soffit for Ductwork and Services. Changes the
appearance. Sometimes folks like it, sometimes not.

percent-probably into the 7ish to 8ish energy hit range.
OK, that helps too. So maybe we have a third option.
Options are always good. But remember the best option
is to keep the stuff inside. Obvious I know, but saying the
obvious is why I get paid the big bucks.

Bibliography
1. Cummings, J.B., J.J. Tooley. 1989. "Infiltration rates and pressure
differences induced by forced air systems in Florida residences."
ASHRAE Transactions.
2. Cummings, J.B., J.J. Tooley, N.A. Moyer. 1990. "Impacts of duct
leakage on infiltration rates, space conditioning energy use, and
peak electrical demand." Proceedings of the ACEEE 1990 Summer Study
on Energy Efficiency in Buildings.
3. Lstiburek, J.W. 1998. "Unvented attic performance." ASHRAE/BETEC
Thermal Performance of Buildings VII.
4. Rudd, A.F., J.W. Lstiburek. 1998. "Vented and sealed attics in hot
climates." ASHRAE Transactions.
5. Rudd, A.F., J.W. Lstiburek, N.A. Moyer. 1997. "Measurement of attic
temperatures and cooling energy use in vented and sealed attics in
Las Vegas, Nevada." EEBA Conference.
6. Tooley, J.J., N.A. Moyer. 1988. "Mechanical air distribution and
interacting relationships." Florida Home Energy Reviews of
Orlando.
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in Somerville,
Mass. Visit www.buildingscience.com.



ASHRAE Journal - December 2013

Table of Contents for the Digital Edition of ASHRAE Journal - December 2013

Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ventilation Control in Terminal Units With Variable Speed Fan Control
Cooling Load Calculations for Radiant Systems
Botanical Research Laboratory
Strategies for Sustainability
Technical vs. Process Commissioning: Preparing a Cx Plan
Standing Columns
Engineer's Notebook
Building Sciences
The Performance Gap
Refrigeration Applications
New Product Preview
Energy Modeling
Emerging Technologies
HVAC Applications
Data Centers
Products
2013 Indices
Classified Advertising
Advertisers Index
ASHRAE Journal - December 2013 - Intro
ASHRAE Journal - December 2013 - Cover1
ASHRAE Journal - December 2013 - Cover2
ASHRAE Journal - December 2013 - 1
ASHRAE Journal - December 2013 - 2
ASHRAE Journal - December 2013 - Contents
ASHRAE Journal - December 2013 - Commentary
ASHRAE Journal - December 2013 - 5
ASHRAE Journal - December 2013 - Industry News
ASHRAE Journal - December 2013 - 7
ASHRAE Journal - December 2013 - Letters
ASHRAE Journal - December 2013 - 9
ASHRAE Journal - December 2013 - Meetings and Shows
ASHRAE Journal - December 2013 - 11
ASHRAE Journal - December 2013 - Ventilation Control in Terminal Units With Variable Speed Fan Control
ASHRAE Journal - December 2013 - 13
ASHRAE Journal - December 2013 - 14
ASHRAE Journal - December 2013 - 15
ASHRAE Journal - December 2013 - 16
ASHRAE Journal - December 2013 - 17
ASHRAE Journal - December 2013 - 18
ASHRAE Journal - December 2013 - 19
ASHRAE Journal - December 2013 - Cooling Load Calculations for Radiant Systems
ASHRAE Journal - December 2013 - 21
ASHRAE Journal - December 2013 - 22
ASHRAE Journal - December 2013 - 23
ASHRAE Journal - December 2013 - 24
ASHRAE Journal - December 2013 - 25
ASHRAE Journal - December 2013 - 26
ASHRAE Journal - December 2013 - 27
ASHRAE Journal - December 2013 - Botanical Research Laboratory
ASHRAE Journal - December 2013 - 29
ASHRAE Journal - December 2013 - 30
ASHRAE Journal - December 2013 - 31
ASHRAE Journal - December 2013 - 32
ASHRAE Journal - December 2013 - 33
ASHRAE Journal - December 2013 - Strategies for Sustainability
ASHRAE Journal - December 2013 - 35
ASHRAE Journal - December 2013 - 36
ASHRAE Journal - December 2013 - 37
ASHRAE Journal - December 2013 - 38
ASHRAE Journal - December 2013 - 39
ASHRAE Journal - December 2013 - Technical vs. Process Commissioning: Preparing a Cx Plan
ASHRAE Journal - December 2013 - 41
ASHRAE Journal - December 2013 - 42
ASHRAE Journal - December 2013 - 43
ASHRAE Journal - December 2013 - 44
ASHRAE Journal - December 2013 - 45
ASHRAE Journal - December 2013 - 46
ASHRAE Journal - December 2013 - 47
ASHRAE Journal - December 2013 - Engineer's Notebook
ASHRAE Journal - December 2013 - 49
ASHRAE Journal - December 2013 - 50
ASHRAE Journal - December 2013 - 51
ASHRAE Journal - December 2013 - Building Sciences
ASHRAE Journal - December 2013 - 53
ASHRAE Journal - December 2013 - 54
ASHRAE Journal - December 2013 - 55
ASHRAE Journal - December 2013 - 56
ASHRAE Journal - December 2013 - 57
ASHRAE Journal - December 2013 - 58
ASHRAE Journal - December 2013 - 59
ASHRAE Journal - December 2013 - The Performance Gap
ASHRAE Journal - December 2013 - 61
ASHRAE Journal - December 2013 - 62
ASHRAE Journal - December 2013 - 63
ASHRAE Journal - December 2013 - Refrigeration Applications
ASHRAE Journal - December 2013 - New Product Preview
ASHRAE Journal - December 2013 - 66
ASHRAE Journal - December 2013 - 67
ASHRAE Journal - December 2013 - 68
ASHRAE Journal - December 2013 - 69
ASHRAE Journal - December 2013 - 70
ASHRAE Journal - December 2013 - 71
ASHRAE Journal - December 2013 - 72
ASHRAE Journal - December 2013 - 73
ASHRAE Journal - December 2013 - 74
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ASHRAE Journal - December 2013 - 76
ASHRAE Journal - December 2013 - 77
ASHRAE Journal - December 2013 - 78
ASHRAE Journal - December 2013 - 79
ASHRAE Journal - December 2013 - 80
ASHRAE Journal - December 2013 - 81
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ASHRAE Journal - December 2013 - 83
ASHRAE Journal - December 2013 - 84
ASHRAE Journal - December 2013 - 85
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ASHRAE Journal - December 2013 - 89
ASHRAE Journal - December 2013 - 90
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ASHRAE Journal - December 2013 - 94
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ASHRAE Journal - December 2013 - 96
ASHRAE Journal - December 2013 - 97
ASHRAE Journal - December 2013 - 98
ASHRAE Journal - December 2013 - 99
ASHRAE Journal - December 2013 - 100
ASHRAE Journal - December 2013 - 101
ASHRAE Journal - December 2013 - 102
ASHRAE Journal - December 2013 - 103
ASHRAE Journal - December 2013 - 104
ASHRAE Journal - December 2013 - 105
ASHRAE Journal - December 2013 - 106
ASHRAE Journal - December 2013 - 107
ASHRAE Journal - December 2013 - 108
ASHRAE Journal - December 2013 - 109
ASHRAE Journal - December 2013 - 110
ASHRAE Journal - December 2013 - 111
ASHRAE Journal - December 2013 - 112
ASHRAE Journal - December 2013 - 113
ASHRAE Journal - December 2013 - 114
ASHRAE Journal - December 2013 - 115
ASHRAE Journal - December 2013 - 116
ASHRAE Journal - December 2013 - 117
ASHRAE Journal - December 2013 - 118
ASHRAE Journal - December 2013 - 119
ASHRAE Journal - December 2013 - 120
ASHRAE Journal - December 2013 - 121
ASHRAE Journal - December 2013 - 122
ASHRAE Journal - December 2013 - 123
ASHRAE Journal - December 2013 - 124
ASHRAE Journal - December 2013 - 125
ASHRAE Journal - December 2013 - 126
ASHRAE Journal - December 2013 - 127
ASHRAE Journal - December 2013 - 128
ASHRAE Journal - December 2013 - 129
ASHRAE Journal - December 2013 - 130
ASHRAE Journal - December 2013 - Energy Modeling
ASHRAE Journal - December 2013 - Emerging Technologies
ASHRAE Journal - December 2013 - 133
ASHRAE Journal - December 2013 - 134
ASHRAE Journal - December 2013 - 135
ASHRAE Journal - December 2013 - 136
ASHRAE Journal - December 2013 - 137
ASHRAE Journal - December 2013 - HVAC Applications
ASHRAE Journal - December 2013 - 139
ASHRAE Journal - December 2013 - 140
ASHRAE Journal - December 2013 - 141
ASHRAE Journal - December 2013 - Data Centers
ASHRAE Journal - December 2013 - 143
ASHRAE Journal - December 2013 - 144
ASHRAE Journal - December 2013 - Products
ASHRAE Journal - December 2013 - 146
ASHRAE Journal - December 2013 - 147
ASHRAE Journal - December 2013 - 2013 Indices
ASHRAE Journal - December 2013 - 149
ASHRAE Journal - December 2013 - 150
ASHRAE Journal - December 2013 - Classified Advertising
ASHRAE Journal - December 2013 - Advertisers Index
ASHRAE Journal - December 2013 - Cover3
ASHRAE Journal - December 2013 - Cover4
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