ASHRAE Journal - February 2009 - 58

Figure 2: Roof section. The vent rafters are connected through the roof rigid insulation with a metal bracket and a long roofing screw. Note the 4 in. (100 mm) strip of plywood under the rafter to distribute the load due to the limited compressive strength of the rigid insulation. Photo 3: Ventilation rafter. The 2x4 (standing proud) is connected through the roof rigid insulation with a metal bracket and a long roofing screw. You can purchase 14 in. (356 mm) long epoxy-coated steel screws. Stay away from stainless steel screws because the heads twist off. Stainless steel tends to be soft. Ask me how I know. Figure 3: Extreme structural insulated panel section. A soffit expansion chamber is not used in this detail. However, the ventilated roof cavity is drained and water tight. Note the liquid applied vapor open drainage plane. Most building wraps flutter if they are not supported on both sides. This solves that problem. with the snow getting in anyway. Stuff happens. We can go to a long-dead European by the name of Daniel Bernoulli to help us out. Bernoulli’s equation tells us that if we have a fluid flowing in a pipe, and a sudden enlargement exists in the pipe, there will be a corresponding drop in pressure. If we then shrink the pipe again, we have an increase in pressure. Folks will recognize this as an expansion chamber. We can use the concept of an expansion chamber to control rain entry and snow entry into soffits. If you have a sudden drop in air pressure the air typically gives up the snow or rain droplets it is carrying. By turning the soffit into an expansion chamber, we can collect the snow in the 58 ASHRAE Journal soffit, rather than have it migrate farther up the ventilated roof cavity. Once in the soffit, we can let the snow eventually melt there and then drain the snow melt out. But just in case, because stuff happens, we’ve learned to design the entire ventilated roof cavity to be able to drain snow melt out. Connecting the roof to the wall is not straightforward either. The walls can cause problems with the roof. Solar radiation heats the outside air immediately adjacent the exterior cladding, as well as the air behind the cladding in the ventilation air space. This warm air rises. We do not want this warm air to get into our ventilation space under our roof cladding as it will heat up the roof cladding rather than flush heat away from the roof cladding. We cannot vent the wall into the roof. This necessary constraint leads to ventilated frieze boards and insulated soffits. ashrae.org February 2009

ASHRAE Journal - February 2009

Table of Contents for the Digital Edition of ASHRAE Journal - February 2009

ASHRAE Journal - February 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
     Carbon Dioxide in North American Supermarkets
     Frost on Air-Cooling Evaporators
     Electronic Expansion Valves Versus Thermal Expansion Valves
     Anniversary Feature: Air Handling Unit Design for Energy Conservation
     Redundancy for Data Centers
Building Sciences
Washington Report
InfoCenter
Special Products
Emerging Technologies
People
Products
Classified Advertising
Advertising Index
ASHRAE Journal - February 2009 - ASHRAE Journal - February 2009
ASHRAE Journal - February 2009 - Cover2
ASHRAE Journal - February 2009 - 1
ASHRAE Journal - February 2009 - 2
ASHRAE Journal - February 2009 - Contents
ASHRAE Journal - February 2009 - 4
ASHRAE Journal - February 2009 - Commentary
ASHRAE Journal - February 2009 - Industry News
ASHRAE Journal - February 2009 - 7
ASHRAE Journal - February 2009 - 8
ASHRAE Journal - February 2009 - 9
ASHRAE Journal - February 2009 - 10
ASHRAE Journal - February 2009 - 11
ASHRAE Journal - February 2009 - 12
ASHRAE Journal - February 2009 - 13
ASHRAE Journal - February 2009 - Letters
ASHRAE Journal - February 2009 - 15
ASHRAE Journal - February 2009 - 16
ASHRAE Journal - February 2009 - A1
ASHRAE Journal - February 2009 - A2
ASHRAE Journal - February 2009 - A3
ASHRAE Journal - February 2009 - A4
ASHRAE Journal - February 2009 - A5
ASHRAE Journal - February 2009 - A6
ASHRAE Journal - February 2009 - A7
ASHRAE Journal - February 2009 - A8
ASHRAE Journal - February 2009 - A9
ASHRAE Journal - February 2009 - A10
ASHRAE Journal - February 2009 - A11
ASHRAE Journal - February 2009 - A12
ASHRAE Journal - February 2009 - A13
ASHRAE Journal - February 2009 - A14
ASHRAE Journal - February 2009 - A15
ASHRAE Journal - February 2009 - A16
ASHRAE Journal - February 2009 - A17
ASHRAE Journal - February 2009 - A18
ASHRAE Journal - February 2009 - A19
ASHRAE Journal - February 2009 - A20
ASHRAE Journal - February 2009 - A21
ASHRAE Journal - February 2009 - A22
ASHRAE Journal - February 2009 - A23
ASHRAE Journal - February 2009 - A24
ASHRAE Journal - February 2009 - A25
ASHRAE Journal - February 2009 - A26
ASHRAE Journal - February 2009 - A27
ASHRAE Journal - February 2009 - A28
ASHRAE Journal - February 2009 - A29
ASHRAE Journal - February 2009 - A30
ASHRAE Journal - February 2009 - A31
ASHRAE Journal - February 2009 - A32
ASHRAE Journal - February 2009 - A33
ASHRAE Journal - February 2009 - A34
ASHRAE Journal - February 2009 - A35
ASHRAE Journal - February 2009 - A36
ASHRAE Journal - February 2009 - A37
ASHRAE Journal - February 2009 - A38
ASHRAE Journal - February 2009 - A39
ASHRAE Journal - February 2009 - A40
ASHRAE Journal - February 2009 - Meetings and Shows
ASHRAE Journal - February 2009 -      Carbon Dioxide in North American Supermarkets
ASHRAE Journal - February 2009 - 19
ASHRAE Journal - February 2009 - 20
ASHRAE Journal - February 2009 - 21
ASHRAE Journal - February 2009 - 22
ASHRAE Journal - February 2009 - 23
ASHRAE Journal - February 2009 - 24
ASHRAE Journal - February 2009 - 25
ASHRAE Journal - February 2009 - 26
ASHRAE Journal - February 2009 -      Frost on Air-Cooling Evaporators
ASHRAE Journal - February 2009 - 28
ASHRAE Journal - February 2009 - 29
ASHRAE Journal - February 2009 - 30
ASHRAE Journal - February 2009 - 31
ASHRAE Journal - February 2009 - 32
ASHRAE Journal - February 2009 - 33
ASHRAE Journal - February 2009 -      Electronic Expansion Valves Versus Thermal Expansion Valves
ASHRAE Journal - February 2009 - 35
ASHRAE Journal - February 2009 - 36
ASHRAE Journal - February 2009 - 37
ASHRAE Journal - February 2009 - 38
ASHRAE Journal - February 2009 - 39
ASHRAE Journal - February 2009 -      Anniversary Feature: Air Handling Unit Design for Energy Conservation
ASHRAE Journal - February 2009 - 41
ASHRAE Journal - February 2009 - 42
ASHRAE Journal - February 2009 - 43
ASHRAE Journal - February 2009 - 44
ASHRAE Journal - February 2009 - 45
ASHRAE Journal - February 2009 - 46
ASHRAE Journal - February 2009 - 47
ASHRAE Journal - February 2009 - 48
ASHRAE Journal - February 2009 - 49
ASHRAE Journal - February 2009 - 50
ASHRAE Journal - February 2009 - 51
ASHRAE Journal - February 2009 -      Redundancy for Data Centers
ASHRAE Journal - February 2009 - 53
ASHRAE Journal - February 2009 - 54
ASHRAE Journal - February 2009 - 55
ASHRAE Journal - February 2009 - Building Sciences
ASHRAE Journal - February 2009 - 57
ASHRAE Journal - February 2009 - 58
ASHRAE Journal - February 2009 - 59
ASHRAE Journal - February 2009 - Washington Report
ASHRAE Journal - February 2009 - 61
ASHRAE Journal - February 2009 - InfoCenter
ASHRAE Journal - February 2009 - 63
ASHRAE Journal - February 2009 - 64
ASHRAE Journal - February 2009 - 65
ASHRAE Journal - February 2009 - 66
ASHRAE Journal - February 2009 - 67
ASHRAE Journal - February 2009 - Special Products
ASHRAE Journal - February 2009 - Emerging Technologies
ASHRAE Journal - February 2009 - 70
ASHRAE Journal - February 2009 - 71
ASHRAE Journal - February 2009 - 72
ASHRAE Journal - February 2009 - People
ASHRAE Journal - February 2009 - Products
ASHRAE Journal - February 2009 - 75
ASHRAE Journal - February 2009 - 76
ASHRAE Journal - February 2009 - Classified Advertising
ASHRAE Journal - February 2009 - 78
ASHRAE Journal - February 2009 - 79
ASHRAE Journal - February 2009 - Advertising Index
ASHRAE Journal - February 2009 - Cover3
ASHRAE Journal - February 2009 - Cover4
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