2013 01 27 Radiant Viega Final

© Viega1Friday, January 23, 2015

Energy and Comfort Performance of Radiant Slab Systems Advantages and differences from air systems

Fred Bauman, P.E.Center for the Built EnvironmentUniversity of CaliforniaBerkeley, California

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Presentation outline

1. Introduction to radiant systems2. Radiant slab vs. air systems3. Thermal comfort4. Energy efficiency5. Design considerations6. Case studies7. Upcoming Viega/CBE training sessions on radiant systems

2Friday, January 23, 2015

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Embedded Surface System (ESS)

Thermally Activated Building System (TABS)

Radiant Panels (RP)


Slab sections for 3 main types of radiant systems

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TABS vs. Radiant panels


TABS

• Overhead slab or floor slab• Cooling and heating• Thermal mass, slower response• Possible pre-cooling to reduce peak

cooling loads• Larger surface area• Moderate costs ($2-7/ft2)

Radiant panels

• Suspended or surface-mounted ceiling panels

• Cooling and heating• Faster response, easier to control• No pre-cooling• Typically less surface area• Relatively high cost for large

surface areas ($15-20/ft2)

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Air vs. radiant cooling systems


Air systems• Address ventilation, sensible and latent

loads• Designed to meet a single peak cooling

load value• Designed to maintain constant zone air

setpoint temperature• Remove heat using convection only

Radiant systems• Provide sensible load control with

separate air system for ventilation and latent load control (e.g., dedicated outdoor air system, DOAS)

• Cooling load is more complex• Designed to maintain operative

temperature within comfort range• Remove heat using convection and

radiation

© ViegaPhoto: Peter Rumsey

Specific heat DensitykJ/kg°C Btu/lb·°F kg/m3 lb/ft3

Water 4.2 1 1,000 62.4Air 1.0 0.24 1.25 0.08

Water can store 3,400 times more thermal energy per unit volume than air!

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Comparison of water pipes and air ducts


Image: Viega

Dimension of the radiant pipes (hidden in the slabs)

Dimension of the air ducts

Dimension of the air ducts (square section)

Image: The NovaFrex Group Image: The NovaFrex Group

Radiant system Air system

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Comparison of floor sections



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Comparison of building heights



Illustration: 6-floor building with radiant vs. air system(floor-to-floor height of 9 ft)


Thermal comfort

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Thermal comfort

• Assess comfort using operative temperature – to capture the combined effects of the air and mean radiant temperature


• Air systems control zone air temperature and primarily remove heat by convection

• Radiant slab systems control the temperature of the building mass and the zone air temperature. They remove heat by both radiation and convective heat transfer

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Air vs. radiant systems


System type Air RadiantMean air temp. 73.4°F 76.5°FMean radiant temp. 79°F 76°FOperative temp. 76.2°F 76.2°FComfort (PPD) 5% 5%

Typical conditions for the two systems:

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CBE comfort tool for ASHRAE-55


cbe.berkeley.edu/comforttool

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CBE occupant survey results Satisfaction with thermal comfort


CBE benchmark (buildings with conventional

HVAC since 2004)

Buildings with radiant systems (since 2004)


Energy efficiency

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Radiant slab vs. air systems: Improved energy efficiency

1. Water vs. air as heat transfer fluid• Heat capacity and density of water vs. air

2. Use thermal storage in slab to reduce peak cooling loads and shift operating times to nighttime and off-peak times

• Nighttime pre-cooling strategies• Smaller chilled water plant capacities and piping sizes as cooling load is

spread out over a 24 hour period, reducing first cost

3. Relatively warmer chilled water temperatures improve chiller efficiency• Cooling towers• Heat pumps• Ground heat exchange

4. Disadvantage: Smaller-sized air system reduces potential for outside air economizer savings (in suitable climates)


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Cooling load comparison: Air vs. TABS


TABS with nighttime pre-cooling reduced peak cooling load by more than 50% compared to air system in west perimeter zone of an office building

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Real examples using these systems


Air system

Radiant with chiller

Radiant with ground source heat pump

Radiant with cooling tower

Architect: Solomon E.T.C.Image: Tim Griffith

Architect: EHDD ArchitectureImage: David Wakely

Architect: StantecImage: Wakely & Stantec

Architect: SmithGroup JJRImage: hdcco.com

David Brower Center, Berkeley

IDeAs Z2 Building, San Jose

SMUD ECOC, Sacramento

Sutardja Dai Hall, UC Berkeley

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Maximum theoretical coefficient of performance (COP) comparison


Needs COP

Air system Te= 2°C (36°F) Tc =34°C (93°F) 8.6

Radiant with chiller Te= 14°C (57°F) Tc =34°C (93°F) 14.4

Radiant with ground source heat pump

Te= 14°C (57°F) Tc =19°C (66°F) 57.4

Radiant with cooling tower ‘Free cooling’ – no refrigerant cycle needed, only power for water pumps and cooling tower fans.

For a refrigerant cycle:Te = evaporator temp, Tc = condenser temp

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Design considerations for radiant slab systems (1/2)

1. Provides only sensible cooling• Must be integrated (combined) with ventilation system that typically also

provides latent cooling, e.g., dedicated outdoor air system (DOAS)• In humid climates, dehumidification is required

2. Cooling capacity is limited by dew point temperature (condensation), comfort, building materials, and surface area

• Floor surface temperature must be moderated to maintain comfort: 19ºC to 29ºC (66ºF to 84ºF), from ASHRAE Std. 55-2013

3. High performance envelope design is required – limit heat gains that radiant system must address

4. In spaces with high solar load (atria, airports, etc.), radiant cooled floor slab has increased capacity to directly remove solar gain (up to 44 Btu/h-ft2 [140 W/m2])


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Design considerations for radiant slab systems (2/2)

5. Avoid rapid changeover from heating to cooling with radiant slab system. Decision to heat or cool should be made once per day

6. Integrated control strategy• Use hydronic slab for “steady state” base cooling (slow response)• Use air system for transient “trim” control (quick response)

7. Reduced airflows (by 50-80%) allows smaller AHUs and reduced ductwork

8. Allows reduced floor-to-floor heights and façade/structural savings

9. Consideration must be taken of acoustic quality of exposed concrete surfaces


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Modeling tool selection


Tools Modeling methodCapability to capture the dynamic

radiant behavior

IES (VE) Heat balance method YesTRNSYS Heat balance method Yes

EnergyPlus Heat balance method YesESP-r Heat balance method YesDOE-2 Weighting factor method No

eQUEST Weighting factor method NoTRACE RTS method or TF method No

Source: Feng, Bauman, Schiavon (2014)


Case studies

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Online map of radiant systems


Map: bit.ly/RadiantBuildingsCBE

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Current status of radiant system database


Categories Sub-category Buildings

Radiant system typeEmbedded Surface System 51Thermally Activated Building Systems 39Radiant Panels 8

Building type

Office 31School (K-12) 5University 14Laboratory 8Museum/Exhibition 9Retail 5Theater/Assembly 1Hotel/Dormitory/Residential 7Transportation 3Multi-purpose 12Other 3

Total number of buildings 98

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Online map of radiant systems



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ARTIC Project, Anaheim, CA



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ARTIC, Anaheim, CA

General• 17700 ft2, Anaheim Regional

Transportation Intermodal Center• LEED Platinum

Features • Steel tubular structure with ETFE

and glass• Cooled thin slabs over structural

slabs; Viega PEX barrier tubingDesigners

• HOK and Parsons Brinckerhoff (Architects)

• Buro Happold(MEP/Radiant system designer)

• Viega (Radiant manufacturer)


Image: HOK

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Infosys SDB-1, Hyderabad

29Friday, January 23, 2015 Source: Sastry and Rumsey (2014)

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Infosys: Energy use


Radiant system used 34% less energy than VAV system

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Infosys: Energy use


Thermal comfort satisfaction

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Radiant slab case studies

David Brower Center, Berkeley, CA

• 45,000 ft2, LEED Platinum• Radiant slab ceiling with

UFAD• Advanced shading, operable

windows• PV panels• Solomon E.T.C. – WRT,

Integral Group


Source: Tim Griffith

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David Brower Center: Energy performance analysis


Performance MetricsCurrent

(Ending 6/30/2010) ENERGY STAR

LabelNationalAverage

ENERGY STAR Rating 99 75 50

Energy Use Intensity

Site ( kBtu/ft2) 47 109 147

Source ( kBtu/ft2) 68 157 212

Source: Center for the Built Environment

45% savings over Title 24-2005

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Radiant slab case studies

Sacramento Municipal Utility District (SMUD) East Campus Operations Center

• 200,000 ft2, LEED Platinum• Radiant slab, ceiling fans• Chilled beams• Geothermal exchange,

thermal energy storage• PV panels • Stantec


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Radiant slab system control in early December


Radiant cooling valve turning on at 10:00– 12:00 each day

Zone air temp.

Slab surface temp.

Wat

er v

alve

pos

ition

(%)

Tem

pera

ture

(ºF)

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Radiant slab system control during warm weather


Outside air temperature: July 28-Aug. 3, 2014

Jul 28 Jul 29 Jul 30 Jul 31 Aug 1 Aug 2 Aug 3

110

100

90

80

70

60

Tem

pera

ture

(ºF)

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Radiant slab system control during warm weather


Radiant cooling valve precooling slab at 23:00 – 5:00 each weekday

Zone air temp.

Slab surface temp.

80

78

76

74

72

70

68

66

Tem

pera

ture

(ºF)

0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00

120

100

80

60

40

20

0

Wat

er v

alve

pos

ition

(%)

Compressor cooling not used during day


Next steps

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Status of zero-net-energy (ZNE) buildings

New Buildings Institute (NBI) conducted two reviews of ZNE commercial buildings

2012 • 21 buildings

• 50% of buildings with HVAC systems used radiant systems, the most of any HVAC system

2014• 160 buildings • Continuing trend away from

forced-air HVAC systems and increased adoption of radiant systems


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Upcoming Viega/CBE radiant training sessions

Two all-day training sessions planned in 2015• May 12, Washington, D.C.• November 3, San Francisco

Preliminary agenda• Heat transfer fundamentals• Energy use• Thermal comfort• Hydronic system design and sizing examples• Load calculation and design tools• Control strategies• Case studies and lessons learned

Viega will provide registration information


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New CBE research grant on radiant slab systems

Title: Optimizing Radiant Systems for Energy Efficiency and ComfortSolicitation: EPIC Grant Program, $3M, 3-year project, 2015-2018Scope of work

• Fundamentals: Laboratory studies • Design and Controls: Development of simplified web-based design

and operation tool• Field Studies: Conduct three detailed field studies • Surveys: Collect energy, cost, and occupant survey data from 50

buildings with radiant systems• Codes and Standards: Propose changes to California Title-24 and

relevant ASHRAE Standards, Handbooks, and Guidelines on radiant systems


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Summary

• Radiant systems can be more energy efficient than air systems• Pre-cooling of radiant slab systems can be used to significantly reduce

peak cooling loads compared to air systems• Radiant cooled floor slabs have increased capacity to directly remove

incident solar gain• Radiant slab systems are slower to respond to control changes• Radiant systems (both slabs and panels) are quick to respond to zone

thermal loads• More research is needed to determine if radiant systems are more

comfortable than air systems• More radiant projects are being installed, particularly in low-energy and

ZNE projects• Upcoming Viega/CBE training sessions and CBE research will address

need for more information on radiant slab systems


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Acknowledgments

Center for the Built Environment, UC Berkeley• Paul Raftery, PhD, Professional Researcher• Stefano Schiavon, PhD, Assistant Professor• Caroline Karmann, Graduate Student Researcher

Taylor Engineering, Alameda, CA• Jingjuan (Dove) Feng, PhD, Mechanical Designer, CBE PhD

Graduate


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Questions?

Fred [email protected]


ARTIC Project, Anaheim (Image: HOK)

Documents

2013 01 27 Radiant Viega Final