ASHRAE Journal - June 2019 - 68

COLUMN ENGINEER'S NOTEBOOK

68

ASHRAE JOURNAL

ashrae.org

J U N E 2 0 19

Temperature, °F

Radiation

parameters to obtain
FIGURE 2 Ambient air temperature in New York City compared with ASHRAE comfort zones.
those not included in
Psychrometric Chart/Normal Temperature
the original data set.
I-P Units/131 Feet
Barometric Pressure: 29.780 Inches of Mercury
Embedded functions
allow this processing to
Comfort Zone at 0.5 clo and
236 fpm (1.2 m/s) Draft
be performed easily for
Comfort Zone 0.5 clo
all 8,760 instances.
Comfort Zone at 1.0 clo
A particularly valuWeather Data Location:
New_York_Central_PRK_OBS_BELV, NEW_YORK, USA
able study for preWeather Hours
schematic design
15 to 1
involves determination
30 to 16
45 to 31
of the availability of
60 to 46
75 to 61
various forms of free90 to 76
cooling in a particular
105 to 91
120 to 106
climate. For the chart
135 to 121
shown in Figure 3, a
spreadsheet was prepared that evaluated
each hour with respect
to whether each form
of free cooling was
FIGURE 3 Monthly diurnal temperature average and solar radiation data for a California location. (Image produced using Climate
available in that hour,
Consultant, produced by the UCLA Department of Architecture and funded by U.S. DOE.)
based upon rules for
Monthly Diurnal Averages
Location: Climate Zone 10, CA, USA
that form of free coolASHRAE Standard 55-2004 Using PMV
Latitude/Longitude: 33.88° North, 117.27° West, Time Zone from Greenwich -8
Data Source: WYEC2-C-00010 722860 WMO Station Number, Elevation 1,538 ft
ing. The data set from
Hourly Averages
500
110
which this was drawn
Temperature (°F)
was limited to office
450
Dry-Bulb Mean
100
Wet-Bulb Mean
occupancy (7 a.m. to
Dry-Bulb (All Hours) 400
90
7 p.m.). For example,
Comfort Zone
Summer
350
free cooling from air80
Winter
side economizer was
(At 50% Relative Humidity)
300
70
evaluated based upon
250
60
whether the outdoor
air dry-bulb tempera200
50
Radiation (Btu/ft2)
ture was 53°F (11.7°C)
Global Horiz
150
40
Direct Normal
or below, without supDiffuse
ply air reset,and for
100
30
ü Display Dry-Bulb
58°F (11.7°C), while
Temperature
50
20
(All Hours)
part cooling with reset
Temperature Range
* 10 to 110°F
was determined by
10
0
Fit to Data
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
whether or not the outdoor air enthalpy was
less than 28 Btu/lb (66.1 kJ/kg). Full cooling for waterside enough to provide cooling, warm enough to avoid drafts
economizer was based upon whether or not the outdoor and dry enough to overcome internal latent gains in the
air wet-bulb temperature was 39°F (3.9°C) or below.
building according to the criteria established by CIBSE.2
This type of analysis can have significant influence on
Availability of natural ventilation using operable winselection of HVAC systems. High availability of airside
dows tested whether the outdoor ambient air was cool
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ASHRAE Journal - June 2019

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