ASHRAE Journal - November 2021 - 26

COLUMN ENGINEER'S NOTEBOOK
Keep People Comfortable
Meet the heating load in extreme
weather. Some safety factor is needed.
You probably don't need to maintain
72°F (22°C) when it's below design
conditions outside, but it should be
livable and first cost vs. a few hours
outside of design conditions should
be discussed with the owner. The
actual design condition will depend on your client's
needs. The 99.6% design condition in Madison, Wis.,
is -6.8°F (-22°C), but two winters ago the city recorded
-26°F (-32°C), which resulted in HVAC and sprinkler
freezes and shutdown of many air-cooled heat pump
and VRF systems.
Keep your entrance staff happy. If 14,000 cfm
(6607 L/s) of -10°F (-23°C) air comes through your vestibule
into your elevators and up to the penthouse due
to negative pressure, the people entering the building
will be happy in their winter clothing, but the greeting
staff in street clothes will not be happy at all. We had this
situation on a project that had 12 elevator doors creating
stack effect from the lobby.
The solution was to add a tempered glass wall on the
mezzanine level, so we had only six elevators connected
to the lobby; add a third set of doors at the elevator lobby
to increase the odds that all three sets are not open
simultaneously; and add infrared heat on a dial controller
to heat the backs and shoulders of the entrance staff.
A revolving door would also have solved the problem,
but that was not acceptable to the client, who was very
happy with our solution.
Getting heat to the floor to minimize tracking of snow
indoors is important. Ceiling-mounted cabinet heaters
with no supply ducts do not work adequately due to
stratification. Inverted hydronic cabinet heaters that
discharge hot air to the floor work well. If something
more architecturally pleasing is desired, refer to Figure 2.
Human thermal comfort is best predicted by operative
temperature (To), which is described in ANSI/ASHRAE
Standard 55, Thermal Environmental Conditions for Human
Occupancy, Appendix A, and can be approximated as (dry
bulb temperature + mean radiant temperature)/2 in
still air (<40 fpm [0.2 m/s]). Mean radiant temperature
is effectively the average of the surface temperatures in
a space. This means that in cold weather, in rooms with
perimeter windows people will feel the radiant effect
26
ASHRAE JOURNAL ashrae.o rg N O V E M B E R 2021
FIGURE 2 All-glass vestibule.
Horizontal Cabinet Unit Heater.
Can Be Completely Concealed Above the
Ceiling, But Needs a Grille in the Ceiling.
The Face Hinges Down for Filter Access. If
The Unit is Above the Ceiling, There Must
Be Enough Height Above the Ceiling to
Permit the Full Face to Hinge Down
Linear Grille With Zero or 15 Degrees Toward the
Exterior Deflection and Throw Sufficient to Go
Down the Wall and Across the Floor
Vertical Blue Lines Represent Glass
Hinged for Cleaning. Doesn't Have to Be
Gasketed. Only Include This Item if the Vestibule
Ceiling is at Least 10 ft Above Finished Floor
(chill) of the window even if the thermostat is satisfied.
People will increase the thermostat setpoint to offset the
effect of the cold window, which is the opposite of what
to do for energy conservation.
The best solution is to improve the window U-value to
increase the indoor surface temperature and thus the
tendency to raise the thermostat. This also saves energy.
If you must use overhead air for heating in spaces with
large amounts of glass, a good solution is linear diffusers
located about 8 ft (2.4 m) from the glass with two slots
pointed toward the glass (for winter comfort) and one
toward the interior (for summer comfort). Fin tube or
radiant panel heat always works but is often precluded
by cost or aesthetic considerations. ASHRAE RP-4262 has
an excellent explanation of what will and will not provide
adequate comfort. Fan-powered VAV boxes can also
increase warm air throw down exterior windows.
Mounting thermostats on exterior walls is discouraged,
even with thermal bases because they are likely to
sense temperatures lower than the room temperature in
cold weather.
Issues with Snow
Rooftop air intakes should be above the snowline.
Figure 3 shows an exhaust hood (you can tell because it
melted the snow near it) that probably should have been
on a taller curb. If it had been an intake hood, it would
have been buried in snow and/or would have sucked in
snow. Intakes near a vertical wall can be especially challenging
due to snow drifts.
Louvers and even hoods such as in Figure 3 cannot stop
all snow penetration. Especially in very cold weather,
snow tends to be very low density and can easily move
upward in light wind currents. This is probably why no
industry rating exists for louver or hood snow penetration-nothing
would pass. Louvers are best located away
from the prevailing winter wind and with their bottoms
well above the roof line and away from corners to avoid
COURTESY IMEG CORP.
http://ashrae.org

ASHRAE Journal - November 2021

Table of Contents for the Digital Edition of ASHRAE Journal - November 2021

Contents
ASHRAE Journal - November 2021 - Intro
ASHRAE Journal - November 2021 - Cover1
ASHRAE Journal - November 2021 - Cover2
ASHRAE Journal - November 2021 - 1
ASHRAE Journal - November 2021 - Contents
ASHRAE Journal - November 2021 - 3
ASHRAE Journal - November 2021 - 4
ASHRAE Journal - November 2021 - 5
ASHRAE Journal - November 2021 - 6
ASHRAE Journal - November 2021 - 7
ASHRAE Journal - November 2021 - 8
ASHRAE Journal - November 2021 - 9
ASHRAE Journal - November 2021 - 10
ASHRAE Journal - November 2021 - 11
ASHRAE Journal - November 2021 - 12
ASHRAE Journal - November 2021 - 13
ASHRAE Journal - November 2021 - 14
ASHRAE Journal - November 2021 - 15
ASHRAE Journal - November 2021 - 16
ASHRAE Journal - November 2021 - 17
ASHRAE Journal - November 2021 - 18
ASHRAE Journal - November 2021 - 19
ASHRAE Journal - November 2021 - 20
ASHRAE Journal - November 2021 - 21
ASHRAE Journal - November 2021 - 22
ASHRAE Journal - November 2021 - 23
ASHRAE Journal - November 2021 - 24
ASHRAE Journal - November 2021 - 25
ASHRAE Journal - November 2021 - 26
ASHRAE Journal - November 2021 - 27
ASHRAE Journal - November 2021 - 28
ASHRAE Journal - November 2021 - 29
ASHRAE Journal - November 2021 - 30
ASHRAE Journal - November 2021 - 31
ASHRAE Journal - November 2021 - 32
ASHRAE Journal - November 2021 - 33
ASHRAE Journal - November 2021 - 34
ASHRAE Journal - November 2021 - 35
ASHRAE Journal - November 2021 - 36
ASHRAE Journal - November 2021 - 37
ASHRAE Journal - November 2021 - 38
ASHRAE Journal - November 2021 - 39
ASHRAE Journal - November 2021 - 40
ASHRAE Journal - November 2021 - 41
ASHRAE Journal - November 2021 - 42
ASHRAE Journal - November 2021 - 43
ASHRAE Journal - November 2021 - 44
ASHRAE Journal - November 2021 - 45
ASHRAE Journal - November 2021 - 46
ASHRAE Journal - November 2021 - 47
ASHRAE Journal - November 2021 - 48
ASHRAE Journal - November 2021 - 49
ASHRAE Journal - November 2021 - 50
ASHRAE Journal - November 2021 - 51
ASHRAE Journal - November 2021 - 52
ASHRAE Journal - November 2021 - 53
ASHRAE Journal - November 2021 - 54
ASHRAE Journal - November 2021 - 55
ASHRAE Journal - November 2021 - 56
ASHRAE Journal - November 2021 - 57
ASHRAE Journal - November 2021 - 58
ASHRAE Journal - November 2021 - 59
ASHRAE Journal - November 2021 - 60
ASHRAE Journal - November 2021 - 61
ASHRAE Journal - November 2021 - 62
ASHRAE Journal - November 2021 - 63
ASHRAE Journal - November 2021 - 64
ASHRAE Journal - November 2021 - 65
ASHRAE Journal - November 2021 - 66
ASHRAE Journal - November 2021 - 67
ASHRAE Journal - November 2021 - 68
ASHRAE Journal - November 2021 - 69
ASHRAE Journal - November 2021 - 70
ASHRAE Journal - November 2021 - 71
ASHRAE Journal - November 2021 - 72
ASHRAE Journal - November 2021 - Cover3
ASHRAE Journal - November 2021 - Cover4
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