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 Brugmanmbrugman@aeieng.com

This concludes The American Institute of Architects Continuing Education Systems

Course