Energy quality management and low energy architecture Folke Björk

Professor

Siir Kilkis Marco Molinari

Ph.D. Tech. Lic.

Building Technology

KTH, the Royal Institute of Technology

Stockholm, Sweden

Building technology

The subject includes development by design, construction and dimensioning, and also by the building process, to improve building constructions and in particular the building envelope to achieve

•moisture safety

•energy efficiency and

•a healthy indoor climate

Low energy architecture

Building design aiming at

• reducing the heating and cooling demand

•making use of passive building techniques

•exploiting local renewable sources

•and utilizing any energy resource efficiently

Energy quality management

What do we mean by that?

• Energy quality can be expressed as exergy, which measures the useful work potential of a given amount or flow of energy on the supply side.

• Energy quality management is particularly useful to reduce the primary energy use in the built environment.

• This is achieved by reducing the heating and cooling demand, making use of passive building techniques, exploiting local renewable sources, and utilizing efficiently non-renewable energy.

Background in the field of exergy

Annexes within IEA ECBCS

•Annex 37 – Low exergy systems for heating and cooling of buildings

•www.ecbcs.org/annexes/annex37.htm

•Annex 49 – Low exergy systems for high performance buildings and communities

•www.annex49.org

The rational energy management model - REMM

• Presented by Siir Kilkis

•www.diva-portal.org search for Siir Kilkis

A building and a power plant

Exergy on the supply side

Exergy content in the fuel =potential for useful work

Reference temperature

Possible combustion temperature

Energy content in the fuel

𝜀sup 𝑖 = 1 −𝑇𝑔

𝑇𝑓· 𝑃𝑖

Exergy on the demand side

Exergy demand =potential for useful work at the temperature level at the demand side

Reference temperature

Temperature wanted

Energy demand

𝜀dem 𝑖 = 1 −𝑇𝑔

𝑇𝑎· 𝑃𝑖

The exergy efficiency ratio ΨRi

This ratio should be close to 1 for a high efficiency:

The lost work potential from the energy supply will be:

𝜓𝑅𝑖 =𝜀𝑑𝑒𝑚(𝑖)

𝜀𝑠𝑢𝑝(𝑖)

𝜀𝑠𝑢𝑝 ∙ 1 −𝜀𝑑𝑒𝑚𝜀𝑠𝑢𝑝

= 𝜀𝑠𝑢𝑝 ∙ 1 − 𝜓𝑅𝑖

Consider efficiency 𝜂𝑖

The efficiency in the process is ηi, and so for each unit of energy needed an amount P/ ηi

is to be spent.

The lost work potential when also considering efficiency:

𝜀𝑠𝑢𝑝 ∙ 1 −𝜀𝑑𝑒𝑚𝜀𝑠𝑢𝑝

∙1

𝜂𝑖= 𝜀𝑠𝑢𝑝 ∙ 1 − 𝜓𝑅𝑖 ∙

1

𝜂𝑖

Consider CO2

Each unit of energy from the fuel produces an amount ci of CO2, so for meeting the demand of one unit of energy in process i this amount of CO2 is produced:

𝐶𝑂2𝑖 =𝑐𝑖𝜂𝑖· 𝑃𝑖

Replace wasted exergy in process i

Somewhere the work potential that was wasted in the process i would really have been needed.

This wasted exergy will be replaced in the process j:

1 −𝑇𝑔

𝑇𝑓∙𝑃𝑗𝜂𝑗≥ 𝐿𝑜𝑠𝑡 𝑢𝑠𝑒𝑓𝑢𝑙 𝑤𝑜𝑟𝑘 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙

Work in system j replacing the wasted

work

For a fossil fuel:

So we´ll get the simplification:

Wasted work potential in system i

Work in system j

Replacing the wasted work

𝑇𝑔

𝑇𝑓≪ 1

𝑃𝑗𝜂𝑗≥𝑃𝑖𝜂𝑖∙ 1 − 𝜓𝑅𝑖

•And for Pj = Pi = 1 kWh we get:

1

𝜂𝑗≥1

𝜂𝑖∙ 1 − 𝜓𝑅𝑖

Total avoidable CO2-emission

• In the process j each unit of energy from the fuel produces an amount cj of CO2, so for meeting the demand of one unit of energy in process j this

amount of CO2 is produced:

This is avoidable emission of CO2 for 1 kWh in process j.

∆𝐶𝑂2𝑗 =𝑐𝑗𝜂𝑗≥𝑐𝑗𝜂𝑖∙ 1 − 𝜓𝑅𝑖

We combine direct and avoidable CO2-emissions and get the total emissions:

ηT = the efficiency of transmission from power plant to where the energy is to be used

𝐶𝑂2𝑖 = 𝐶𝑂2𝑖 + ∆𝐶𝑂2𝑖 =𝑐𝑖𝜂𝑖+𝑐𝑗𝜂𝑖 ∙ 𝜂𝑇

∙ 1 − 𝜓𝑅𝑖

A case

In a case, we say that the indoor temperature Ta is 295K, which is a typical comfort indoor temperature in the Stockholm area. Tg is 280 K and the Tf for combustion is 2000 K.

Ta= 295 K = 22°C = 71,6°F Tg= 280 K = 7°C = 44,6 °F Tf=2000 K = 1723°C =3133°F

𝜓𝑅𝑖 =𝜀𝑑𝑒𝑚 𝑖𝜀𝑠𝑢𝑝(𝑖)

=1 −𝑇𝑔𝑇𝑎

1 −𝑇𝑔𝑇𝑓

= 1 −280295

1 −2802000

= 0,051

0,86= 0,059

The exergy efficiency ratio ΨRi becomes 0.059

This is not very efficient – improvements are possible!

Compound CO2-emissions

The value of 0,059 for ψRi has impacts in the energy system, with primary energy spending and CO2 emissions Per unit ci, cj, ηi, ηT and Pi, the value of ΣCO2i is found to be:

REMM – from Siir Kilkis thesis

We need to save the renewable resources

Electric coil heating

• Electic coil heating

Tiled stove

Combined heat and power - plant

Birsta bio-fueled CHP plant close to Stockholm

Heat pump

Underfloor heating

Produce and use

fossil energy

as efficient

as possible

Use sustainable sources of energy instead of finite

fossil fuels

Reduce demand for energy by avoiding waste and implementing energy-saving measures

The Trias Energica: TU Delft, The Netherlands Senternovem

1

2

3

The Trias Energetica concept

Plan for renewable energy

Avoid fossil

fuel

Use any energy as efficient as

ever possible

Consider the exergy concept

Reduce demand for energy

1

2

3

A modified trias – considering exergy

Conclusions

• Exergy is a vital aspect for low energy architecture and low CO2 emissions

• The Rational energy management model (REMM) further show how integration of the building in the broader perspective of the community level is crucial to curb building-related CO2 emissions.

• Energy quality management is a way to proceed towards a sustainable development.

Thank you!

Folke Björk

Professor

Siir Kilkis Marco Molinari

Ph.D. Tech. Lic.

Building Technology

KTH, the Royal Institute of Technology

Stockholm, Sweden

Background in the field of exergy

Annexes within IEA ECBCS

•Annex 37 – Low exergy systems for heating and cooling of buildings

•www.ecbcs.org/annexes/annex37.htm

•Annex 49 – Low exergy systems for high performance buildings and communities

•www.annex49.org

The rational energy management model - REMM

• Presented by Siir Kilkis

•www.diva-portal.org search for Siir Kilkis