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NATURAL VENTILATION AND HYDRONIC COOLING IN HUMID CLIMATESGULF COAST GREEN 2013
Matthew Brugman, MSCE, LEED AP BD+C
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.
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.
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
OUTLINEHUMID CLIMATES
THERMAL COMFORT
NATURAL VENTILATIONBENEFITSAPPLICABILITY & APPROACHES
HYDRONIC SYSTEMSCONDENSATIONCHILLED BEAMSRADIANT SYSTEMS
HUMAN THERMAL COMFORTPHYSICAL FACTORS IN THERMAL COMFORT
METABOLIC RATECLOTHING LEVELSAIR TEMPERATURERADIANT SURFACE TEMPERATURESAIR SPEEDRELATIVE HUMIDITY
HUMAN THERMAL COMFORT
HUMAN THERMAL COMFORTTHERMAL COMFORT MODELS
STATICStatic 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)
ADAPTIVEAdaptive 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.
HUMAN THERMAL COMFORTASHRAE 55
The typical comfort standard adopted throughout the US, ASHRAE 55-2010 provides for both STATIC and ADAPTIVE 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 OPERATIVE TEMPERATURE.
HUMAN THERMAL COMFORTASRHAE 55 – STATIC COMFORT MODEL (PMV)
Air Speed = 30 fpmMetabolic Rate = 1.2 met (standing)Clothing = .5 clo (summer indoor clothing)
Air Speed = 30 fpmMetabolic Rate = 1.7 met (slow walk)Clothing = .36 clo (shorts & t-shirt)
HUMAN THERMAL COMFORTASRHAE 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.OPERATIVE TEMPERATURE 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.
HUMAN THERMAL COMFORTASRHAE 55 – ADAPTIVE COMFORT MODEL
Air Speed = 60 fpm Air Speed = 180 fpm
90% acceptability
80% acceptability
HUMAN THERMAL COMFORTLOCAL 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.
HUMAN THERMAL COMFORTLOCAL DISCOMFORT
VERTICAL TEMPERATURE 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 SURFACE TEMPERATURE – 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.
HUMAN THERMAL COMFORTWHAT DOES IT ALL MEAN?
If building occupants are allowed to adapt their clothing to ambient conditions, comfort boils down to controlling three aspects:
RADIANT SURFACE TEMPERATURESAIR TEMPERATUREAIR SPEED
VERNACULAR SOLUTIONSWHAT DID WE EVER DO WITHOUT A/C??
DEEP SHADES TO CONTROL SURFACE TEMPERATURE
VERNACULAR SOLUTIONSWHAT DID WE EVER DO WITHOUT A/C??
CROSS FLOW AND STACK VENTILATION TO INCREASE AIR SPEED
NATURAL VENTILATIONBENEFITS
OCCUPANT CONTROL – Providing individual control over natural ventilation reduces occupant comfort complaintENERGY SAVINGS – When outside air conditions allow for natural ventilation, cooling and heating energy use can be reduced or eliminatedROBUSTNESS – Buildings with natural ventilation can continue to function even during mechanical failuresHEALTH – Natural ventilation provides direct access to outside air and has been shown to reduce the spread of infection in healthcare settings
NATURAL VENTILATIONAPPROACHES – NATURAL VENTILATION
STACK VENTILATION – 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
UNIVERSITY OF WASHINGTON – HUSKY UNION BUILDING
PLAIN, WI – GREEN TTEC
UC RIVERSIDE – SCHOOL OF MEDICINE
KAUST
NATURAL VENTILATIONDRAWBACKS – NATURAL VENTILATION
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
NATURAL VENTILATIONAPPROACHES – MIXED MODE VENTILATION
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 timeCHANGE-OVER – Same space, different timeZONED – Different spaces
UNIVERSITY OF WASHINGTON – MOLECULAR ENGINEERING
NATURAL VENTILATIONCONTROLS - MIXED MODE VENTILATION
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
NATURAL VENTILATIONDRAWBACKS – MIXED MODE VENTILATION
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
NATURAL VENTILATIONAPPLICABILITY IN THE GULF COAST
HOUSTON NEW ORLEANS MIAMI FRANKFUR
T80% 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
NATURAL VENTILATIONCONTROLLING 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
PHASE CHANGE MATERIAL CEILING INSTALLATION
AIR SPEED IS CRITICAL!
HYDRONIC COOLINGWATER VS AIR
HEAT TRANSFERWater is a much more effective heat transfer medium than air
VOLUMEThe 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)
PUMPINGWater pumps are mechanically more efficient than fans, reduced noise
HYDRONIC COOLINGTYPICAL SYSTEM TYPES
RADIANTWater is used to heat/cool surfaces for radiant heat transfer (includes chilled sails)
FAN UNITSSmall fan/coil combinations that blow warm/cold air into a space (includes wall induction units)
CHILLED BEAMSA special diffuser/coil combination that induces space air to flow over a coil filled with chilled water. Can be active or passive.
HYDRONIC COOLINGCHILLED BEAMS - PASSIVE
~ 6 watts of cooling capacity per linear foot
HYDRONIC COOLINGCHILLED BEAMS - ACTIVE
~ 12+ watts of cooling capacity per linear foot
FROM EXPERIMENTAL TO MUNDANE
HYDRONIC COOLINGCHILLED BEAM MOISTURE CONTROL
MOISTURE SENSORSMoisture sensors on the chilled beam coil can reset the water temperature in the beam
DEW POINT CONTROLBy 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
HYDRONIC COOLINGDEDICATED OUTSIDE AIR SYSTEMS (DOAS)
DOASDOAS 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 traditional VAV system.
HYDRONIC COOLINGTYPICAL 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
PLAIN, WI – GREEN TTEC
STANFORD – CESI ADMIN
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
Tempe
rature
(°F)
Date: Fri 01/Jan to Fri 31/Dec
Surface temperature: (proposed.aps) External dew-point temp.: USA_CA_San.Jose.Intl.AP.724945_TMY3.epw (USA_CA_San.Jose.Intl.AP.724945_TMY3.epw)
DEWPOINT VS SLAB TEMP – 66F SLAB
DEWPOINT VS SLAB TEMP – 62F SLAB
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
80
70
60
50
40
30
20
10
Tempe
rature (°
F)
Date: Fri 01/Jan to Fri 31/Dec
External dew-point temp.: USA_CA_San.Jose.Intl.AP.724945_TMY3.epw (USA_CA_San.Jose.Intl.AP.724945_TMY3.epw) Surface temperature: (proposed at 62 wo sails.aps)
HYDRONIC COOLINGRESPONSE TIME
Radiant systems (especially slabs) respond slowly to changes in thermal load, so good application of radiant technology will include strategies to reduce thermal gains:
OrientationShadingSufficient InsulationProper Glazing Selection
Pick the low-hanging fruit first!
HYDRONIC COOLINGRESPONSE TIME
01 02 03 04 05 06 07 08 09 10 11
88
86
84
82
80
78
76
74
72
70
Tem
pera
ture
(°F)
Date: Thu 01/Jul to Sat 10/Jul
Air temperature: Flex Space (sesi radiant floor.aps)
HYDRONIC COOLINGCAPACITY
MAKING THE CASE FOR NAT VENT & HYDRONICWHAT 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
QUESTIONS?
Matthew [email protected]
This concludes The American Institute of Architects Continuing Education Systems
Course