Chapter hvac engineering Fundamentals: Part 1 Introduction

32
T
ABLE
3.2
Climatic
Conditions
in
the
United
States
S
O
URCE
:
Copyright
1993,
American
Society
of
Heating,
Refrigerating
and
Air
Conditioning
Engineers,
Inc.,
www
.ashrae.org.
Abstracted
by
permission
from
ASHRAE
Handbook,
1993
Fundamentals,
Chap.
24,
T
able
1.
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
33
TABLE
3.3 Air Factor Change with Altitude (Approximate Values at 60
ⴗ
F)
includes an air density effect. The formula defining the air factor (AF)
is
AF
⫽
air density
⫻
SH
⫻
60 min / h
(3.1)
where AF
⫽
air factor for determining airflow rate, Btu / h / [(ft
3
/ min)
䡠
⬚
F]
Density
⫽
air density at design elevation and temperature (for air
conditioning, 60
⬚
F is used), lb / ft
3
SH
⫽
specific heat of air at design temperature and pres-
sure, Btu / lb-
⬚
F (SH for dry air is approximately 0.24
Btu / lb-
⬚
F)
For sea level (standard air density) this becomes
3
AF
⫽
0.075 lb / ft
⫻
0.24 Btu / lb
⫻
60 min / h
3
⫽
1.08 Btu / h / [(ft / min)
䡠
⬚
F]
Some designers and handbooks use 1.10 Btu / h / [(ft
3
/ min)
䡠
⬚
F] (ob-
tained by rounding off 1.08).
The air factor (AF) at altitude is obtained by multiplying the sea
level air factor (1.08) by the project altitude density ratio (DR).
3.5
Factors for Load Components
3.5.1
Internal heat gains
Internal heat gains are due to people, lights, appliances, and pro-
cesses. Heat gain from people is a function of the level of activity (see
Table 3.4).
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.

---

34
T
ABLE
3.4
Rates
of
Heat
Gain
fr
om
Occupants
of
Conditioned
Spaces,
Btu
/
h
*
T
abulated
values
are
based
on
78
⬚
F
room
dry-bulb
temperature.
F
o
r
8
0
⬚
F
room
dry-bulb
temperature,
the
total
heat
remains
the
same,
but
the
sensible
heat
value
should
be
decreased
by
approximately
8%
and
the
latent
heat
values
increased
accordingly
.
†
Adjusted
total
heat
gain
is
based
on
normal
percentage
of
women,
men,
and
children
for
the
appli-
cation
listed,
with
the
postulate
that
the
gain
from
an
adult
female
is
85%
of
that
for
an
adult
male,
and
that
the
gain
from
a
child
is
75%
of
that
for
an
adult
male.
‡
Adjusted
total
heat
value
for
eating
in
a
restaurant,
includes
60
Btu
/h
for
food
per
individual
(30
Btu
/h
sensible
and
30
Btu
/h
latent).
§
F
o
r
bowling,
figure
one
person
per
alley
actually
bowling,
and
all
others
as
sitting
(400
Btu
/h
)
o
r
standing
and
w
alking
slowly
(790
Btu
/h).
S
O
URCE
:
Copyright
2001,
American
Society
of
Heating,
Refrigerating
and
Air
Conditioning
Engineers,
Inc.,
www
.ashrae.org.
Reprinted
by
permission
from
ASHRAE
Handbook,
2001
Fundamentals,
Chap.
29,
T
able
1.
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
35
Heat gain from lights is a function of wattage, at a rate of 3.413
Btu / h / W. For fluorescent lighting and industrial-type fixtures, a bal-
last (transformer) factor must be used. A typical multiplier for flu-
orescents is 1.2, resulting in a heat gain of 4.1 Btu / h per nominal
lighting watt. General lighting for offices requires from 1 to 2 W / ft
2
of
floor area. The actual lighting layout and fixture schedule should be
used whenever possible. With ceiling mounted lights (recessed) some
of the heat may go to the ceiling plenum without being a cooling load
in the room. Lighting manufacturers’ literature may treat this condi-
tion.
Task lighting and appliance loads are difficult to predict. The exten-
sive use of computer terminals and electric typewriters has made this
a significant factor. The typical allowance for task lighting and appli-
ances is 1.0 to 1.5 average W / ft
2
, although localized loads may be as
much as 3 W / ft
2
. Some large computer components may impose 10
W / ft
2
in the vicinity of the installation.
Table 3.5 lists possible heat gains from some miscellaneous appli-
ances. Kitchen appliances, cookers, stoves, ovens, etc., can provide
large amounts of heat gain. These loads should be confirmed prior to
final design effort.
Whether motors and variable-frequency-motor speed drives (VFD)
are specified by the mechanical or electrical designer, the heat release
and environmental criteria for the VFDs must be noted and accom-
modated. Transformers mounted indoors must also be acknowledged
and accommodated. The transformer vaults (or room) normally re-
quire power exhaust for heat removal.
Heat gains from manufacturing processes must be estimated from
the energy input to the process.