Roofing and energy conservation

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Roofing and energy conservation

Ralph M. Paroli and Hakim Elmahdy

Outline



Introduction



Principles of sustainable roofing



Examples of roofs:

• Garden roofs

• Reflective roofs

• PV

Towards Sustainable Roofing



CIB W083/RILEM 166-MRS Joint Committee

on Roofing Materials and Systems

What is a Sustainable Roof?

“… a roofing system that is

designed, constructed, maintained, rehabilitated and demolished with an emphasis throughout its life cycle on using natural resources efficiently

and preserving the global environment”

Sustainable Low-Slope Roofing Workshop Oak Ridge National Laboratory, 1996

Roofing, Energy and Sustainability



In Canada, buildings account

for 30% of energy use and

27% of greenhouse gas

(GHG) emissions



Buildings displace natural

landscape



In a typical large city, about

• 20% tree canopy/natural coverage

• 30 – 35% rooftops

Urban Heat Island

 City remains warmer (about 2 – 3°C) than its surroundings

 Lack of vegetation and soil moisture (evaporative

cooling or evapotranspiration)

 Sunlight absorbed by roads, parking lots

 Thermal storage effects tends to keep the air

temperature a little higher, relative to suburban areas http://www.weatherquestions.com/

Principles of Sustainable Roofing

Key areas for improvement

1.

Minimize the burden

on the environment

2. Conserve energy

8

Tenet 8

Optimize the real thermal performance, recognizing that thermal insulation can greatly reduce heating or cooling costs

over the lifetime of a building

Commercial Sector

Secondary Energy Use by End Use – Canada 2006

8% Auxiliary motors 7% Space cooling 10% Lighting 16% Auxiliary equipment 9% 49% Space heating 1% Street lighting

Tenet 8



During the lifetime of a building, large quantities

of fuel are used for heating and/or cooling



A significant proportion

is lost through the roof

and it makes sense to

reduce this wherever

possible



A great potential to save

energy in buildings exists

by improving roofs’

Optimize the real thermal performance, recognizing that thermal insulation can greatly reduce heating or cooling costs

over the lifetime of a building

49% Space heating 7% Space cooling

Thermal Insulation



Thermal insulation reduces

heating and cooling costs

• specify proper type and adequate amount

• minimize thermal bridging

• reduce air leakage



Protect thermal insulation

• keep it dry at all times

• use cover boards

Cover insulation at end of workday to keep it dry

Protect insulation from damage during delivery

Structural support Roof membrane Thermal insulation (Extruded Polystyrene) Fabric Ballast / Pavers

Protected Membrane Roof (PMR)

• Insulated Roofing Membrane Assembly (IRMA)TM

• Inverted Roof Membrane Assembly (IRMA)

• Protected Roof System (PRS)

PMR Features

•

Protects membranes against mechanical

damage

•

Maintain roof membrane at constant

temperature

•

Protect membrane from UV

•

Stable base for the membrane (i.e., deck)

•

Reduce the risk of trapping condensation in the

insulation

PMR Cautions

•

Thermal insulation exposed to water from rain

and snow

•

Must use ballast which adds load to structure

•

Cannot be used on all buildings

•

Ballast may be blown away, possible exposing

insulation to UV

•

Difficult to inspect membrane

Tenet 6



Promote garden roof systems on city roofs

(where appropriate)

• reduce energy demand

• mitigate urban heat island

• reduce stormwater runoff

• improve air quality

• replace displaced landscape

• enhance biodiversity

Roof assembly:

Conventional or Protective Membrane Roof Assembly (PMRA)

Root resistant layer Drainage layer

Filter layer

Growing medium Vegetation

Structural support Vapour control layer Thermal insulation Support panel

Reference Roof Garden Roof

VB IN INS SB Layer SM Thermocouple OUT MEM

Heat Flux Transducer

Roof membrane

Principal Components and

Sensor Locations (GRS)

Drainage layer Filter membrane Growing medium Vegetation

0 10 20 30 40 50 60 70 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time T em p er at u re (° C )

Typical sunny summer day

0 10 20 30 40 50 60 70 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time Tem per a tur e ( °C ) IN MEM OUT

Field Data: GRS Temperature Profile

Garden Roof Reference Roof

Field Data: Temperature Profile

Typical winter day with snow coverage

IN MEM OUT IN MEM OUT

Reference Roof Garden Roof

86 Te m pe ratu re (F) 32 -4 86 Te m pe ratu re (F) 32 -4

Field Data Mean Membrane Temperature

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ambient Reference Roof Garden Roof

140 M ean T em perat ure ( °F ) 32 -4 Average of 5 years data

Tenet 9



Thermal and mechanical properties of most

types of insulation deteriorate when they

become wet for long periods of time



Keep insulation dry from the delivery and

storage on site, to the installation and through

the life of the roof



Potential for mould growth on wet insulation

should be avoided for many reasons

Tobiasson, W., and Ricard, J., Moisture gain and its thermal consequence for common roof insulations, Proceedings of 5th Conference on Roofing Technology, NRCA, 1979.

Keep insulation dry to maintain

Tenet 10



Use local labour, materials

and services when practical,

to reduce energy and cost

• transportation

• packaging



Other advantages

• familiar with local environment

• available for long-term roof maintenance

• maintains local economy

Local labour is familiar with local environment and

working practices

Use local labour, materials and services wherever practical (embodied energy)

Tenet 11

 Improved environmental performance by reducing the energy consumed in the production

 Calculating the embodied energy allows for comparing the energy intensity of alternative products and systems

 Take into account advantages/disadvantages of using renewable or non-renewable energy sources

 Must identify period of analysis, e.g., entire life cycle or a specific phase in the process

 Accurate and reliable information for some materials may be difficult to obtain

Measuring Eco-efficiency in Business, National Round Table on the Environment and the Economy, Canada, 1997.

Recognize that embodied energy values are a useful measure for comparing alternative constructions

Tenet 12



The effect of

solar heat gain

on buildings:

– roofs vs. walls



High radiation absorbance

leads to more heat

flow into the building (

if

inadequately insulated):

– higher energy consumption and costs



Effects of roof surfacing, colour and texture,

on energy performance depends on the

geographic location and orientation

Consider the roof surface colour and texture with regard to climate and the effect on energy and roof system performance

Colour and Texture

 Dark roof surfaces contribute to the urban heat island

 Solar heat gain through roofs leads to high cooling costs

 Roof surface colour and texture affect energy

performance

• solar reflectance • infrared emittance  Location and orientation

specific

Installation of reflective roof membrane

Emitted IR radiation

Convection

Conduction

Reflective (Cool) Roofs

To keep a roof cool in the summer, the roof surface should have:

• high solar reflectance (reflectivity or albedo)

• high infrared emittance (emissivity)

Roof surface Incident solar radiation Reflected solar radiation

Solar Reflectance

5% UV (300 – 400 nm) – responsible for sunburn 43% visible (400 – 700 nm)

52% near-infrared (700 – 2500 nm) – felt as heat

Reflective Roofs

 Solar reflectance is not the

only property



Need

high infrared emittance

to

help the roof shed heat by reradiation



Aluminum will not reradiate and as such

stays warmer at night than a white roof



Aluminum therefore will not perform as

well as a white material with

the same

solar reflectance

New

Aged

Aging of Reflective Roofs



Loss of some properties

(e.g., reflectivity)



Change in texture



May affect the overall

performance

Example of Reflectivity Testing

(Stiff Bristle Broom with Detergent)

0.701 0.765 0.802



Conditions at time of reading

• Location: Las Vegas, NV

• Type of Roof: White TPO

• Age of Roof: 48 months

• Temperature: 53°C

Reflective Coatings in Cold Climates?

In cold climates, the heating season dominates:

 Potential economic penalty during heating season



But

winter penalty may be small because:

• During winter, solar angle is small therefore reflectivity and absorption not as critical

• Days are short, so less energy hitting roof

• Snow is on roof

• Roof in the north receives 3 – 5 times more daily sun in summer than in winter

Calculated Average Annual Results for

some U.S. States (LBNL)

State Cooling Energy Saving

kWh/m2 CRA

Heating Energy Penalty

kWh/m2/yr CRA Therm/m2 _{/yr CRA}

Energy Cost Saving $/m2 /yr CRA NV 6.86 2.16 0.0737 0.570 MN 4.17 4.02 0.1370 0.136 IL 4.22 2.93 0.0994 0.217 NH 5.35 3.55 0.1210 0.482

Calculated Average Emission

Reductions for some U.S. States (LBNL)

State CO₂ Reductions kg/m2 CRA NO_x Reductions g/m2 CRA SO₂ Reductions g/m2CRA Hg Reductions mg/m2 _CRA NV 3.64 6.37 4.74 71.80 MN 3.09 7.45 12.40 89.50 IL 2.97 5.48 19.60 89.90 NH 1.82 2.14 6.36 21.60

Summary

– Reflective Roofs

 Extend service life

• reduce thermal stress

• protect from UV damage

 Reflectivity loss

• new vs. aged

 Climatic issues

• heating vs. cooling needs

 Glare and visual concerns

• not suitable on flight paths

• consideration for

neighbors

• additional UV protection

for installers

Photovoltaics and Roofs

 1876 W.G. Adams and R.E. Day

discover a solid material –

Selenium – produced electricity when exposed to light

 1953 Gerald Pearson (Bell Lab)

inadvertently makes a solar cell with silicon

 1980s 50% of households in

Tahiti rely on solar energy

Solar panels cover roof in German apartment complex

 1990s Better, cheaper cells

PV

– Solar and Roofing Become Integrated?



Flat roofs represent billions of square feet of

untapped real estate



Roofs are seen as a financial

liability with

no return on investment



Building integrated photovoltaic (BIPV) systems

have the ability to turn a roof into

energy-producing assets



Produce clean and secure energy for direct use

by building operations and an attractive ROI



Industry

started with

crystalline

technology



Thin film

amorphous

technology

is also

rapidly

expanding

Solar Roofs Net Metering



Maximize energy output by

following the sun throughout

the day with single-axis

trackers



On sunny days

– solar system

generates more power than

needed  electric meter spins

backwards i.e., lend energy to

the utility grid

(or store it in

an array of batteries)



When the sun goes down,

retrieve that energy as needed

Solar Roof

–

Is Type of Roof Important?



Solar cells can last 20

– 30 years



Roof should last as long



Flashing/detailing capability



Fire performance



Reflective cool roofing is beneficial to maximize

solar performance. Heat reduces the output of

power especially with rigid glass panels

Achieving Energy Efficiency in Roofing



Requires proper



MUST

• preserve the environment

• conserve energy

Thank you

 Building Envelope Technology Research (BETR)

 Canadian Roofing Contractors Association (CRCA)

 Carlisle SynTec

 Firestone Building Products

 Sika-Sarnafil

 SunPower Corp.

 Western States Roofing Contractors Association

 Nicole Normandin

 Don Hobbs

 Ana Delgado

 Bas Baskaran