Zero Carbon: Implications and Issues

Malcolm BellBuildings, Energy and Sustainability Group, School of the Built

Environment, Leeds Metropolitan University, Leeds, UK.

Paper presented to: Towards Zero Carbon Homes

5 July 2007, Milton Keynes, UK.

Towards Zero Carbon

-60%

-40%

-20%

0%

20%

40%

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100%

120%

TER 2006 2010 2013 2016

Year

Per

centa

ge

25%

44%

-49%

Zero Carbon

Towards Zero Carbon

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TER 2006 2010 2013 2016Standard

CO

2 (k

g/a

)

Gas

Electricity

Compliance packages:Zero Carbon

80m2 Semidetached or end terraced 2 storey house

0.0

5.0

10.0

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20.0

25.0

30.0

35.0

Gas Electricity Wood pellets

Fuel

TE

R (kgC

O2/m

2a

Lighting

Fans & pumps

Water heating

Space heating

Base Case - TER Gas Electricity

Roof (U - W/m2K) 0.16 0.16

Wall (U - W/m2K) 0.30 0.2

Ground Floor (U - W/m2K) 0.22 0.2

Doors & Windows (U - W/m2K) 1.80 1.3

Thermal bridging allowance (y) 0.08 0.08

Airtightness (m/h) 7 5

Ventilation Natural Natural

Space and Water 86% 100%

-25.0

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-5.0

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35.0

Gas Electricity Wood pellets

Fuel

TER

Space heating Water heating

Fans & pumps LightingAppliances Renewables

Zero Carbon (TER of -135% to -150%)

Zero Carbon (TER of -135% to -150%)

Gas Electricity Wood pellets

Roof (U - W/m2K) 0.08 0.08 0.08

Wall (U - W/m2K) 0.10 0.1 0.1

Ground Floor (U - W/m2K) 0.09 0.09 0.09

Doors & Windows (U - W/m2K) 0.70 0.7 0.7

Thermal bridging allowance (y) 0.02 0.02 0.02

Airtightness (m/h) 0.5 0.5 5

Ventilation MVHR MVHR Natural

Space and Water 93% GsHP 320% 67%

Low Energy Lighting 100% 100% 100%

Area of solar collector (m2 approx 1360 kWh/a) 10 10 10

Photovoltaic panels (m2 aprox. 2,250 kWh/a) 25 25.0 25.0

Other renewbles - net energy (kWh/a) 1,800 1,100 600

Total renewables 5,410 4,710 4,210

Passive House Standards

Source: Wall (2006), Photo: Hans Eek

Timber frame scheme Göteborg, Sweden (120 m2)

Airtightness 1 m/h

MVHR – 80% with duct heaters

5m2 Solar water + resistance top-up

Passive House Standards

Source: Wall (2006), Photo: Hans Eek

Timber frame scheme Göteborg, Sweden, 120 m2

Source: Wall (2006), Energy and Buildings. 38, pp 627-634

TER (kgCO2/m2)

Design ≈ 10.6Actual ≈ 15.3Under Swedish conditions!

5,868 kWh

6,420 kWh

Total energy = 8,160 kWh/a

Implications and issues

• Lights and appliances represent between 60% and 70% of carbon emissions.

• Over 5,000 kWh/a may need to be generated by zero carbon sources. (more for larger houses)

• What chance at the level of the dwelling?

Solar thermal?

Solar thermal?

Solar thrmal output - 80m2 semi detached

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Panel Area (m2)

Ener

gy

(kW

h/a

)

Micro wind?

Micro wind?

Micro wind?Manufacturer’s general claims:

1.5 kW (max at 12.5 m/s)

Annual energy generated - 2,000 - 3,000 kWhs – depending on position and location.

Carbon displacement – 1.3 tonnes (30% utilisation)

Location:

Average wind speed (DTI database) = 5.1 m/s @ 10m

Energy – 1,473 kWhs

But what about shelter from trees and other buildings?

Micro wind?

0

200

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1600

0 0.2 0.4 0.6 0.8 1 1.2

wind speed reduction factor (mean speed = 5.1 m/s)

Ener

gy

outp

ut (k

Wh/a

)

4 m/s

3 m/s

5.1 m/s

Photovoltaic panels

Cost and scale

Cost and scale• Wind

– small scale – 17 p/kWh– large scale – 4 p/kWh

• PV– Small scale – 55 p/kWh– large scale – 23 p/kWh

• Solar thermal– small scale – 9 p/kWh– large scale – 7 p/kWh

preliminary calculations – Barrett 2007

Biomass?

Biomass in a 2006 dwelling!

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Gas Electricity Wood pellets

Fuel

TE

R (kg

CO

2/m

2a

Appliances

Lighting

Fans & pumps

Water heating

Space heating

Biomass?

-25.0

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Gas Electricity Wood pellets

Fuel

TER

Space heating Water heating

Fans & pumps LightingAppliances Renewables

Biomass in a 2016 dwelling

So what, so far ? • Site based generation is problematic.• Solar thermal - useful demand reduction

• Wind is likely to be cheaper and more effective at large scale

• Biomass may have limited value in CHP but no panacea and an important strategic resource

• Need to link new building to strategic renewable provision.

So what for the industry?

Source: Wall (2006), Photo: Hans Eek

Focus attention on as low an energy/carbon demand as possible

Deal with generation in a strategic way

But! Does new housing do what it says on the

tin?

Notional – v – Real heat loss

Plot No.

Predicted Fabric Heat Loss (W/K)

Predicted Ventilation Heat Loss (W/K)

Predicted Total Heat Loss (W/K)

Measured Heat Loss (W/K)

Measured Heat Loss - Adjusted for Solar Gain (W/K)

13 50.6 13.2 63.8 105.4 111.7

402 54.9 20.3 75.2 136.3 153.4

+75%

+104%

The question is: Why?

Thermal bridges

Thermal bridging & construction Designed performance is almost always degraded

Timber fraction and insulation

Airtightness is improving?

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Permeability Range (m/h @ 50Pa)

Pro

ba

bil

ity

Stamford Brook Data

EST 99 Dwelling Dataset

Passive house Stamford Brook mean EST 99 mean

Sequencing and process

Hidden leakage

A culture of detailed planning?

A culture of detailed planning?

Build – Destroy – Install – Repair

Understanding complex heat loss paths

Party wall heat bypass

Potential CO2 savings

From New Housing built in One Year (~190,000 units)

18,000 tCO2/a

From Existing Stock (built between 1965 and 2006)

694,000 tCO2/a

Assumes Party Wall U Value = 0.5Assumes 10% semi, 20% terrace in stock and new buildCalculations for semis and terraces only – no estimate for apartments

Fabric heat loss is between 40% and 50% greater than currently estimated. Eliminating the bypass would produce large actual CO2 savings

We have been rumbled!

This time customers will notice!

As very low and zero carbon becomes mandatory small things will matter

This time building control will notice!

We cannot hide behind flawed assumptions

The industry must change!

• It has been said before

• But the more it changes the more it

remains the same

• Old problems persist!

• It is time to retool, to retool cultures and

processes as well as technology.

What will change look like?• A fully managed process – inception,

design, construction and support in use.

• Performance will have to be guaranteed.

• A quality control process based on measurement not assumption

• Re-engineering of processes as well as technology will bring economies!

• Constant feedback will bring constant improvement.

So what does zero carbon mean?

The world will not be the same!

Thomas Kuhn

The Structure of Scientific Revolutions

We are entering a new paradigm

So what does zero carbon mean?

As in science, so in construction:

It is time for the industry to Retool!