This document provides an overview of natural ventilation and hydronic cooling systems in humid climates like the Gulf Coast. It discusses human thermal comfort, natural ventilation approaches and benefits, mixed-mode ventilation, hydronic cooling system types like chilled beams, and design considerations for controlling humidity and moisture. The key advantages of these systems are energy savings when conditions allow for natural ventilation and more effective heat transfer through water-based systems. Controls integration and addressing humidity are important challenges.
2. AIA/CES
“Affiliated Engineers, Inc.” is a Registered Provider with The
American Institute of Architects Continuing Education Systems
(AIA/CES). Credit(s) earned on completion of this program will
be reported to AIA/CES for AIA members. Certificates of
Completion for both AIA members and non-AIA members are
available upon request.
This program is registered with AIA/CES for continuing
professional education. As such, it does not include content that
may be deemed or construed to be an approval or endorsement
by the AIA of any material of construction or any method or
manner of handling, using, distributing, or dealing in any
material or product.
Questions related to specific materials, methods, and services
will be addressed at the conclusion of this presentation.
3. COURSE DESCRIPTION
This session is intended to review the benefits and design
realities of using natural ventilation and hydronic (water-based)
cooling systems in humid climates, with a special emphasis upon
the Gulf Coast. Issues related to occupant comfort, system
control, design implications, and potential failure mechanisms
will be discussed.
4. LEARNING OBJECTIVES
At the end of this presentation, participants will be able to:
1. Identify the applicability of hydronic cooling and/or natural
ventilation systems in humid climates
2. Understand the basic thermal comfort and mechanical
design challenges of these systems
3. Have a basic understanding of the control implications for
these systems in humid climates
4. Have a basic understanding of the of architectural design
implications of hydronic cooling and natural ventilation
8. HUMANTHERMAL COMFORT
THERMAL COMFORT MODELS
STATIC
Static comfort models are based entirely upon
physiological criteria and assume that human
perceptions of comfort do not adapt to changes in
environment. Local discomfort issues typically
ignored. (Also called the PMV Method)
ADAPTIVE
Adaptive comfort models assume that human
notions of thermal comfort change based upon the
prevailing outdoor conditions. Comfort criteria are
built from field observation, surveys, and statistical
analysis of occupant responses as well as
physiological calculations.
9. HUMANTHERMAL COMFORT
ASHRAE 55
The typical comfort standard adopted throughout
the US, ASHRAE 55-2010 provides for both STATIC
andADAPTIVE comfort criteria in system design.
STATIC comfort criteria ranges in ASRHAE 55 are
expressed as a range of allowable air temperatures
and relative humidity values for given conditions.
ADAPTIVE comfort ranges are expressed in terms of
prevailing mean outdoor air temperature and the
OPERATIVETEMPERATURE.
10.
11. HUMANTHERMAL COMFORT
ASRHAE 55 – STATIC COMFORT MODEL (PMV)
Air Speed = 30 fpm
Metabolic Rate = 1.2 met (standing)
Clothing = .5 clo (summer indoor clothing)
Air Speed = 30 fpm
Metabolic Rate = 1.7 met (slow walk)
Clothing = .36 clo (shorts & t-shirt)
12. HUMANTHERMAL COMFORT
ASRHAE 55 – ADAPTIVE COMFORT MODEL
The ASHRAE 55 ADAPTIVE comfort ranges are
generally used when determining the comfort of a
natural ventilation scenario as it assumes that
occupants are free to adapt their clothing and other
conditions.
OPERATIVETEMPERATURE is the combined
temperature that humans actually experience when
the mean radiant temperature and dry bulb air
temperature are accounted for together. At its
simplest, it’s the average of radiant and dry bulb
temperatures in space.
13. HUMANTHERMAL COMFORT
ASRHAE 55 – ADAPTIVE COMFORT MODEL
Air Speed = 60 fpm Air Speed = 180 fpm
90% acceptability 80% acceptability
14. HUMANTHERMAL COMFORT
LOCAL DISCOMFORT
There are specific instances when discomfort local to
a small area must be addressed:
RADIANT ASYMMETRY – Large differences between
radiant surface temperatures create asymmetrical
heat loss/gain, a condition which distracts occupants
and can lead to discomfort.
DRAFTS – High air speeds at low temperatures can
create localized excessive cooling.
15. HUMANTHERMAL COMFORT
LOCAL DISCOMFORT
VERTICALTEMPERATURE DIFFERENCE – A change
of more than 5 to 7 degrees from head to toe is often
uncomfortable. Especially important for stratified
systems such as displacement ventilation and under
floor systems.
FLOOR SURFACETEMPERATURE – Low floor
temperatures can create too much conduction of
heat out of the feet, creating excessive cooling the
extremities. Floor temperatures below 62F should be
avoided, with 65F or higher being preferable.
16. HUMANTHERMAL COMFORT
WHAT DOES IT ALL MEAN?
If building occupants are allowed to adapt their
clothing to ambient conditions, comfort boils down
to controlling three aspects:
RADIANT SURFACETEMPERATURES
AIRTEMPERATURE
AIR SPEED
19. NATURALVENTILATION
BENEFITS
OCCUPANT CONTROL – Providing individual control
over natural ventilation reduces occupant comfort
complaint
ENERGY SAVINGS –When outside air conditions
allow for natural ventilation, cooling and heating
energy use can be reduced or eliminated
ROBUSTNESS – Buildings with natural ventilation
can continue to function even during mechanical
failures
HEALTH – Natural ventilation provides direct access
to outside air and has been shown to reduce the
spread of infection in healthcare settings
20. NATURALVENTILATION
APPROACHES – NATURALVENTILATION
STACKVENTILATION – Moving air primarily via
natural convection currents and thermal
buoyancy
WIND DRIVEN – Positioning openings to take
advantage of pressure differentials and wind to
move air through a space
CROSS FLOW vs SINGLE SIDED
34. NATURALVENTILATION
DRAWBACKS – NATURALVENTILATION
MOISTURE – Full natural ventilation systems
offer no means to control moisture and humidity
NOISE & POLLUTION – Negative exterior
conditions are difficult to address with natural
ventilation systems
FINE CONTROL – Natural ventilation provides
only coarse control over pressure and
temperature relationships
35. NATURALVENTILATION
APPROACHES – MIXED MODEVENTILATION
MIXED MODE – A combination of traditional
mechanical solutions and natural ventilation.
Mechanical systems supplement natural
ventilation processes when thermal comfort
cannot be maintained.
CONCURRENT – Same space, same time
CHANGE-OVER – Same space, different time
ZONED – Different spaces
40. NATURALVENTILATION
CONTROLS - MIXED MODEVENTILATION
FULLY MANUAL – Occupant control over
opening and mechanical system interactions.
FULLY AUTOMATIC – Building automation
system runs actuators to control natural
ventilation openings along with mechanical
system controls. (Best option for hot and humid
climates)
MIXED CONTROLS –Typically achieved by
contact sensors to detect when occupants use
openings, HVAC systems adjusts automatically
41. NATURALVENTILATION
DRAWBACKS – MIXED MODEVENTILATION
CONTROLS – Integration of control systems can
be difficult, and training staff in proper system
control is critical
FIRE & SMOKE – Concerns over smoke migration
ENERGY CODES – Many energy codes and
authorities deter the use of operable windows
and mechanical HVAC in the same space
42. NATURALVENTILATION
APPLICABILITY INTHE GULF COAST
HOUSTON
NEW
ORLEANS
MIAMI FRANKFURT
80%
ADAPTIVE
COMFORT
40% OF
HOURS
9AM-6PM
46% OF
HOURS
9AM-6PM
61% OF
HOURS
9AM-6PM
17% OF
HOURS
9AM-6PM
90%
ADAPTIVE
COMFORT
29% OF
HOURS
9AM-6PM
33% OF
HOURS
9AM-6PM
44% OF
HOURS
9AM-6PM
12% OF
HOURS
9AM-6PM
If we can manage humidity, the Gulf Coast has a very
large potential for natural ventilation systems to be
effective
43. NATURALVENTILATION
CONTROLLING HUMIDITY
MIXED MODE SYSTEMS – Allow the use of
mechanical system when needed
SCHEDULING – Night flush and pre-cooling can
allow a space to ride through hot periods
AIR SPEED – Increased air speeds counteract the
discomfort of increased humidity levels
CONCURRENT DEHUMIDIFICATION –
Dehumidification through Dedicated Outside Air
Systems (DOAS), in situ dehumidifiers, etc
51. HYDRONIC COOLING
WATERVS AIR
HEATTRANSFER
Water is a much more effective heat transfer
medium than air
VOLUME
The volume of water needed to carry a certain
amount of heat is much smaller than the same
volume of air (1” pipe can carry as much energy as
18” rectangular duct)
PUMPING
Water pumps are mechanically more efficient than
fans, reduced noise
52. HYDRONIC COOLING
TYPICAL SYSTEMTYPES
RADIANT
Water is used to heat/cool surfaces for radiant heat
transfer (includes chilled sails)
FAN UNITS
Small fan/coil combinations that blow warm/cold air
into a space (includes wall induction units)
CHILLED BEAMS
A special diffuser/coil combination that induces
space air to flow over a coil filled with chilled water.
Can be active or passive.
57. HYDRONIC COOLING
CHILLED BEAM MOISTURE CONTROL
MOISTURE SENSORS
Moisture sensors on the chilled beam coil can reset
the water temperature in the beam
DEW POINT CONTROL
By properly dehumidifying the air supplied to a
chilled beam or space, the dew point can be
suppressed to avoid condensation
*Active chilled beams create a microclimate around
the coil surface and can operate with water several
degrees below the dew point without forming
condensation
58.
59. HYDRONIC COOLING
DEDICATED OUTSIDE AIR SYSTEMS (DOAS)
DOAS
DOAS systems are intended to condition only
outside ventilation air supplied to a space, and are
typically design to filter and dehumidify air with or
without energy recovery. DOAS systems are often
constant volume, but at very low supply volumes.
Because DOAS systems are not the primary cooling
system, ductwork tends to be much smaller than in a
traditionalVAV system.
60.
61.
62.
63.
64. HYDRONIC COOLING
TYPICAL RADIANT SYSTEMS
RADIANT SLAB –Tubing is embedded in a floor
or ceiling slab to heat and cool the surface
PANELS – Metal panels are heated or cooled to
create the radiant surface, typically ceiling
mounted
CHILLED SAILS – A radiant cooling panel with
multiple openings meant to provide more
convective cooling
73. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
75
70
65
60
55
50
45
40
35
30
25
20
15
10
Temperature(°F)
Date:Fri01/JantoFri31/Dec
Surfacetemperature: (proposed.aps) External dew-pointtemp.:USA_CA_San.Jose.Intl.AP.724945_TMY3.epw(USA_CA_San.Jose.Intl.AP.724945_TMY3.epw)
DEWPOINTVS SLABTEMP – 66F SLAB
74. DEWPOINTVS SLABTEMP – 62F SLAB
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
80
70
60
50
40
30
20
10
Temperature(°F)
Date:Fri01/JantoFri31/Dec
External dew-pointtemp.:USA_CA_San.Jose.Intl.AP.724945_TMY3.epw(USA_CA_San.Jose.Intl.AP.724945_TMY3.epw) Surfacetemperature: (proposedat62wosails.aps)
75.
76. HYDRONIC COOLING
RESPONSETIME
Radiant systems (especially slabs) respond slowly
to changes in thermal load, so good application
of radiant technology will include strategies to
reduce thermal gains:
Orientation
Shading
Sufficient Insulation
Proper Glazing Selection
Pick the low-hanging fruit first!
77. HYDRONIC COOLING
RESPONSETIME
01 02 03 04 05 06 07 08 09 10 11
88
86
84
82
80
78
76
74
72
70
Temperature(°F)
Date: Thu 01/Jul to Sat 10/Jul
Air temperature: Flex Space (sesi radiant floor.aps)
79. MAKINGTHE CASE FOR NATVENT & HYDRONIC
WHAT DOES IT COST?
FIRST COST – First costs can be higher than
traditional HVAC systems, especially mixed mode
natural ventilation
BUILDING REUSE – Because nat vent and
hydronic systems take up less space, older
facilities can be successfully reused
LIFE CYCLE COSTS –Typical NV and radiant
systems have very beneficial life cycle costs, but
not short term (less than 10 year) paybacks
