ASHRAE Journal - February 2014 - 50
COLUMN HVAC APPLICATIONS
a 20°F (11°C) DT heating is assumed, the throw will
be reduced by 20% because hot air wants to rise. This
means that there will be a 40% change in downward
projection moving from heating to cooling. However,
the problem is that the hot air needs to penetrate the
occupied zone. Using this design example, the cooling air will likely create drafts by hitting the floor
and moving toward the interior. How can this be
prevented?
One solution is to reduce the airflow in cooling, but
in doing so, it is unlikely that the cooling demand
loads will be met. Instead, it is recommended that an
array of air outlets be established that extends into
the interior zone supplying the required cooling airflow. The interior diffusers should be selected so that
they have short throws to prevent excessive jet collisions at maximum design cooling airflow rates, which
could produce unacceptable drafts. Interior diffusers
are then shut off when heating, using a single duct
VAV box, which will increase the air delivered to the
perimeter.
It is strongly recommended to keep the heating DT
as low as possible to avoid excessive stratification and
occupant discomfort. ASHRAE Standard 62.1-2013
states that when discharging warm air from the ceiling at more than 15°F (8.3°C) above room temperature, the ventilation rate must be increased by about
20% (divide the value by 0.8). Standard 62.1 also
demands the 150 fpm (0.76 m/s) throw value reach
within 4.5 ft (1.4 m) from the floor, or again, increase
ventilation.
By understanding the physics of air distribution
and following these rules of thumb, a design engineer can successfully design a diffuser layout and
provide air quantities and temperatures that are not
only able to meet thermal loads, but also deliver the
comfort requirements and ventilation needs of the
space.
www.info.hotims.com/49801-25
50
ashraE JourNal
ashrae.org
FEBRUARY 2014
ASHRAE Journal - February 2014
Table of Contents for the Digital Edition of ASHRAE Journal - February 2014
ASHRAE Journal - February 2014
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Understanding Salaries in the A/E Industry
Improving Operating Room Contamination Control
Standing Columns
Engineer's Notebook
Saving Energy with Cooling Towers
Building Sciences
ACREX India 2014 Show Guide
HVAC Applications
Technical vs. Process Commissioning: Design Phase Commissioning
Data Centers
IAQ Applications
Energy Modeling
InfoCenter
Refrigeration Applications
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - February 2014 - ASHRAE Journal - February 2014
ASHRAE Journal - February 2014 - Cover2
ASHRAE Journal - February 2014 - 1
ASHRAE Journal - February 2014 - 2
ASHRAE Journal - February 2014 - Contents
ASHRAE Journal - February 2014 - Commentary
ASHRAE Journal - February 2014 - 5
ASHRAE Journal - February 2014 - Industry News
ASHRAE Journal - February 2014 - 7
ASHRAE Journal - February 2014 - 8
ASHRAE Journal - February 2014 - Letters
ASHRAE Journal - February 2014 - Meetings and Shows
ASHRAE Journal - February 2014 - 11
ASHRAE Journal - February 2014 - Understanding Salaries in the A/E Industry
ASHRAE Journal - February 2014 - 13
ASHRAE Journal - February 2014 - 14
ASHRAE Journal - February 2014 - 15
ASHRAE Journal - February 2014 - 16
ASHRAE Journal - February 2014 - 17
ASHRAE Journal - February 2014 - Improving Operating Room Contamination Control
ASHRAE Journal - February 2014 - 19
ASHRAE Journal - February 2014 - 20
ASHRAE Journal - February 2014 - 21
ASHRAE Journal - February 2014 - 22
ASHRAE Journal - February 2014 - 23
ASHRAE Journal - February 2014 - 24
ASHRAE Journal - February 2014 - 25
ASHRAE Journal - February 2014 - 26
ASHRAE Journal - February 2014 - 27
ASHRAE Journal - February 2014 - Engineer's Notebook
ASHRAE Journal - February 2014 - 29
ASHRAE Journal - February 2014 - 30
ASHRAE Journal - February 2014 - 31
ASHRAE Journal - February 2014 - 32
ASHRAE Journal - February 2014 - 33
ASHRAE Journal - February 2014 - Saving Energy with Cooling Towers
ASHRAE Journal - February 2014 - 35
ASHRAE Journal - February 2014 - 36
ASHRAE Journal - February 2014 - 37
ASHRAE Journal - February 2014 - 38
ASHRAE Journal - February 2014 - 39
ASHRAE Journal - February 2014 - 40
ASHRAE Journal - February 2014 - 41
ASHRAE Journal - February 2014 - Building Sciences
ASHRAE Journal - February 2014 - 43
ASHRAE Journal - February 2014 - 44
ASHRAE Journal - February 2014 - 45
ASHRAE Journal - February 2014 - 46
ASHRAE Journal - February 2014 - 47
ASHRAE Journal - February 2014 - 48
ASHRAE Journal - February 2014 - ACREX India 2014 Show Guide
ASHRAE Journal - February 2014 - SCover2
ASHRAE Journal - February 2014 - S1
ASHRAE Journal - February 2014 - S2
ASHRAE Journal - February 2014 - S3
ASHRAE Journal - February 2014 - S4
ASHRAE Journal - February 2014 - S5
ASHRAE Journal - February 2014 - S6
ASHRAE Journal - February 2014 - S7
ASHRAE Journal - February 2014 - S8
ASHRAE Journal - February 2014 - S9
ASHRAE Journal - February 2014 - S10
ASHRAE Journal - February 2014 - S11
ASHRAE Journal - February 2014 - S12
ASHRAE Journal - February 2014 - S13
ASHRAE Journal - February 2014 - S14
ASHRAE Journal - February 2014 - S15
ASHRAE Journal - February 2014 - S16
ASHRAE Journal - February 2014 - S17
ASHRAE Journal - February 2014 - S18
ASHRAE Journal - February 2014 - S19
ASHRAE Journal - February 2014 - S20
ASHRAE Journal - February 2014 - S21
ASHRAE Journal - February 2014 - SCover4
ASHRAE Journal - February 2014 - HVAC Applications
ASHRAE Journal - February 2014 - 50
ASHRAE Journal - February 2014 - 51
ASHRAE Journal - February 2014 - Technical vs. Process Commissioning: Design Phase Commissioning
ASHRAE Journal - February 2014 - 53
ASHRAE Journal - February 2014 - 54
ASHRAE Journal - February 2014 - 55
ASHRAE Journal - February 2014 - 56
ASHRAE Journal - February 2014 - 57
ASHRAE Journal - February 2014 - Data Centers
ASHRAE Journal - February 2014 - 59
ASHRAE Journal - February 2014 - 60
ASHRAE Journal - February 2014 - 61
ASHRAE Journal - February 2014 - IAQ Applications
ASHRAE Journal - February 2014 - 63
ASHRAE Journal - February 2014 - 64
ASHRAE Journal - February 2014 - 65
ASHRAE Journal - February 2014 - 66
ASHRAE Journal - February 2014 - 67
ASHRAE Journal - February 2014 - Energy Modeling
ASHRAE Journal - February 2014 - 69
ASHRAE Journal - February 2014 - InfoCenter
ASHRAE Journal - February 2014 - 71
ASHRAE Journal - February 2014 - 72
ASHRAE Journal - February 2014 - 73
ASHRAE Journal - February 2014 - Refrigeration Applications
ASHRAE Journal - February 2014 - 75
ASHRAE Journal - February 2014 - Products
ASHRAE Journal - February 2014 - 77
ASHRAE Journal - February 2014 - 78
ASHRAE Journal - February 2014 - Classified Advertising
ASHRAE Journal - February 2014 - Advertisers Index
ASHRAE Journal - February 2014 - Cover3
ASHRAE Journal - February 2014 - Cover4
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