Chapter hvac engineering Fundamentals: Part 1 Introduction

36
T
ABLE
3.5
Estimated
Rate
of
Heat
Release
fr
om
Cooking
and
Miscellaneous
Appliances
S
O
URCE
:
Copyright
1985,
American
Society
of
Heating,
Refrigerating
and
Air
Conditioning
Engineers,
Inc.,
www
.ashrae.org.
Abstracted
by
permission
from
ASHRAE
Handbook,
1985
Fundamentals,
Chap.
26,
T
ables
20
and
21.
(Subsequent
editions
provide
more
extensive
data.)
Design Procedures: Part 1
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.

---

Design Procedures: Part 1
37
Figure 3.4
Thermal storage effect. (
SOURCE
: Copyright 2001, American Society of Heat-
ing, Refrigerating and Air Conditioning Engineers, Inc., www.ashrae.org. Abstracted by
permission from ASHRAE Handbook,
2001 Fundamentals,
Chap. 29, Fig. 2.)
3.5.3
Transmission through the
building envelope
Chapter 18 discusses heat transfer and the determination of
U
factors—overall heat transmission coefficients—for the elements of
the envelope. The criteria pages must include a description of each
wall, roof, partition, and floor section which forms a boundary between
conditioned and nonconditioned space. From the description a
U
factor
is determined; note that the direction of heat flow (up, horizontal, or
down) makes a difference. The units of the
U
factor are Btu per hour
per square foot of area per degree Fahrenheit of temperature differ-
ence from inside to outside air.
For calculating the cooling load due to heat gain by conduction
through opaque walls and the roof, the
sol-air
temperature con-
cept may be used. For a complete discussion of this concept, see the
ASHRAE Handbook
2001 Fundamentals.
3
Figure 3.5 (p. 43) illustrates the energy transfers which give rise to
the sol-air concept in a wall. Both direct and diffuse solar radiation
have a heating effect on the exterior surface of the wall. The surface
temperature will usually be greater than the outside air temperature,
which then has a cooling effect. When the exterior surface tempera-
ture is greater than the internal temperature of the wall, heat transfer
into the wall will take place. Some of this heat will be stored, increas-
ing the internal temperature of the wall. Some heat will be transferred
by conduction to the cooler interior surface and then to the room, as
Design Procedures: Part 1
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.

---