Identifying the Best ofthe Walling Alternatives Presented By: Manfred Braune, Technical Executive GBCSAOn Behalf of: WSP Green by Design and ClayBrick.org

OPTIMAL WALLING SOLUTIONS FOR ENERGY EFFICIENT HOMES IN SA

The 130 m² House Model

Derived from CSIR Garsfontein Control House

? 130m² FootprintHallway, lounge, dining room, kitchen,

3 bedrooms, 2 bathrooms

The 130 m² House Model

Example

Insulated brickJohannesburg(CR = 100 h)

Insulated brickDurban

(CR = 60 h)

Walls with Regional CR Specifications

Passive Case Thermal ComfortSingle Skin Walling ~ Upington

Hourly Predicted Mean Vote (PMV) ~ Values over a Year

Zero PMV line represents line of greatest thermal comfort.Deviation from it reflects increasing discomfort.

Wall 3.3: 140 mm Concrete Block, Bag and Paint both sidesPassive Case reveals nature of the materials alone.

Passive Case Thermal Comfort

Comparison

Passive Case Thermal Comfort

Daily PMV Amplitude ~ Upington

Passive Case Thermal Comfort

Active Case

Heating Energy ~ Upington

Active Case

Cooling Fan Energy ~ Upington

Active Case

Heating and Cooling Fan Energy ~ Upington

Annual Heating & Cooling Fan Energy

6 Climatic Regions in South Africa (1/2)

Annual Heating & Cooling Fan Energy

6 Climatic Regions in South Africa (2/2)

CR Product Value of a WallJ = Joule (a measure of heat energy)

C = Thermal Capacity – the ability to absorb, store and release heat energy, or the heat energy needed to raise the temperature of the material by 1°C. (kJ per °C)

R = Thermal Resistance – from thermal conductivity, or the ability to conduct heat energy, or the heat energy lost per second for a difference in temperature on either side of the material. (J per °C.s),

C x R = 370.4 x 0.88 x 1000/3600= 91.54 hours,

the time constant property of the wall system

For every m2

Wall TypeDouble Brick

(DB)DB with 50mm

air cavity

DB with R=0.5Cavity

insulation

DB with R=1Cavity

insulation

DB with R=1External

insulation

Cact (kJ/m2.K) 139 149 157 162 270

CR (hours) 40 60 90 130 130

CR Product defined

Active Case EnergyHeating & Cooling Fan Energy use per Annum vs. External

Wall CR Product for 130 m² House as Modelled, Upington

Basis for Costing

Total cost comprises:

External walling construction External walling maintenance over a 50 year period and Heater and cooling fan energy use over a 50 year period

Discount rate for future cash flows 10 % / yr

Initial energy cost (start of year 1) 83 c / kWh

Year 1 energy escalation 25.9 % / yr

Year 2 energy escalation 25.9 % / yr

Remaining years energy escalation 7 % / yr

Maintenance expense escalation 7 % / yr

Present Value

Total Costs for 50 Years (1/2)

Present Value

Total Costs for 50 Years (2/2)

High Thermal Capacity Walls:

– moderate swings in daily thermal comfort

– reduce cooling fan energy (all S.A. climates)

Correlation agrees with CR theory:

- Heating and cooling fan energy minimised by high

CR walling e.g. insulated brick

Single Skin Walls (Low C • Low R)

- Poor choices for envelope walling systems in terms of energy use and thermal comfort.

Conclusions for all South African Climates 1/5

(Valid for 130m² house as modelled only)

Conclusions for all South African Climates 2/5

– .. Musina

– .. Durban

– .. Pretoria

– .. Upington

– 2nd Cape Town

– 1st Johannesburg

(Valid for 130m² house as modelled only)

Choice of external walling more critical in terms of absolute energy use and energy cost, as one moves through the climates in the following order:

Conclusions for all South African Climates 4/5

(Valid for 130m² house as modelled only)

Lightweight walls are not paying back high construction

cost with sufficient energy savings in this scenario.

• Cost

• Regulatory or Standards Compliance – SANS 10400, SANS 204, Green Star

• Thermal Comfort

• Sound Transmission

• Local Availability

• Aesthetics

• Preference

Conclusions for all South African Climates 5/5

(Valid for 130m² house as modelled only)

Different Selection WarrantedDepending on Actual Goals :

Questions for Further Study?

(Valid for 130m² house as modelled only)

• How does an air conditioning in a house with increased cooling energy use affect energy ranking of walls?

• How can active thermal capacity be used to gain further insight?

• What is the sensitivity of the costing to changes in the various parameters such as future electricity tariff escalation?

Low Cost House ~ 40m²

Low Cost House ~ 40m²

Percentage of Time Occupants Experience Thermal Discomfort ~ Johannesburg

LSFB not SANS 517 compliant

Low Cost House 40m²Low Cost House ~ 40m²

Monthly Cost of Heating Energy ~ Johannesburg

LSFB not SANS 517 compliant

66 c/kWh tariff assumed

Low Cost House ~ 40m²

Energy Required to Achieve Comfort on Winter Solstice ~ Johannesburg

LSFB not SANS 517 compliant

Low Cost House ~ 40m²

Monthly Cost of Heat Energy in the Different Climatic Zones66

c/k

Wh

tarif

f as

sum

ed

Low Cost House ~ 40m²

Monthly Heating Energy in Low Cost House ~ Average of 6 Climate Zones

LSFB not SANS 517 compliant

Low Cost House ~ 40m²

c

Increase in Annual Energy Consumption ~ Light Steel Frame & Clay Brick

LSFB not SANS 517 compliant

Low Cost House ~ 40m²

In Johannesburg, using two leaf brick as opposed to concrete block saves enough energy yearly to light the household for 55 days. 24 hours a day.

Heating Energy per Annum

LSFB not SANS 517 compliant

Low Cost House ~ 40m²

Carbon Footprint (Construction and Operational Heating Energy) ~ Johannesburg

LSFB not SANS 517 compliant

Low Cost House ~ 40m²

Construction and Annual Energy Costs ~ Johannesburg

LSFB not SANS 517 compliant

66 c

/kW

h ta

riff

assu

me

d

(Valid for 40m² house as modelled only)

Conclusions ~ 40m² Low Cost House

Single skin concrete block falls short of conventional clay brick in thermal comfort, electricity cost for heating.

Clay brick walls overall best performers.

Insulated ceilings should be mandatory ~ significant thermal benefit for reasonable outlay.