16469 Low Energy Building Design Conflict and Interaction in Environmental

Engineering Design

16469 Low Energy Building Design Conflict and Interaction• design is a complex task, especially in low energy

buildings and where there are multiple design objectives • in this situation there is rarely an “optimum” design

solution– a good choice according to one criteria may be

detrimental when judged against another (conflicting outcomes)

• effectively need to undertake multi-criteria analysis and select a “best” design option

• requires the generation and assessment of multiple design solutions

16469 Low Energy Building Design Conflict and Interaction Challenge:- generate alternative design solutions: to

meet the design objectives while “optimizing” (one or more) performance criteria

- need to appraise the different design options and decide on that which best matches the criteria – perhaps an iterative process

16469 Low Energy Building Design: Conflict and Interaction

Targets:Design criteria can be usefully expressed in terms of targets – e.g. capital cost, energy consumption

16469 Low Energy Building Design: Conflict and Interaction• There are many examples of conflicting outcomes between different design options:

• energy/comfort conflicts-reducing window size: may improve thermal comfort near the window, but will increase heating load in certain circumstances-increasing window size: may lower heating energy consumption but lead to overheating in summer

- energy acoustic conflict-increased thermal mass: may reduce overheating problem but cause acoustic problems

16469 Low Energy Building Design: Conflict and Interaction

• How to choose between options?• need evidence of how design options will

perform – taking account of interactions– simulation

• need to find some mechanism of comparing and ranking options according to design criteria – need a method– subjective comparison (table of options)– PAM– iterative approaches

16469 Low Energy Building Design: Conflict and Interaction

Subjective comparison: - take into account all design objectives- assess suitability of each design choice against

objectives – usually use a matrix- present results via rank-ordering of design

options (possibly after applying weighting factors to the evaluation results)

16469 Low Energy Building Design: Conflict and Interaction• Example compare different design options to maximise solar gain

and reduce heating load (3-good 2-average 1-bad)design option

reduction in heating load

reduction in lighting load

timing of gain

glare risk overheating risk

capital cost

score

south facing glazing

2 3 1 1 1 3 11

south facing glazing plus shade

2 3 1 2 2 2 12

trombe wall

3 1 3 3 3 1 14

16469 Low Energy Building Design: Conflict and Interaction

Subjective comparison: - advantages: results are easy to understand results –

through generating the data to support the assessment may be difficult

- disadvantages: - results depend upon comparative criteria- danger of basing results on opinion rather than

evidence- subjective – which criteria are more important? How

to translate technical result to assessment score?- difficult to compare between very different design

outcomes

16469 Low Energy Building Design: Conflict and Interaction• Example – let’s compare different LEBD options for a

householder trying to reduce their heat and electricity costs

• Get into a group of 3 or 4 and rank the following options based on your existing knowledge ….

16469 Low Energy Building Design: Conflict and Interaction

design option

reduction in heating/ HW costs

reduction in electricity costs

installation cost

running costs

carbon savings

Score

PV

solar thermal collector

micro-CHP

double glazing

cavity wall insulation

loft insulation

16469 Low Energy Building Design: Conflict and Interaction

design option

reduction in heating/ HW costs

reduction in electricity costs

installation cost

running costs

carbon savings

Score

PV 1 2 1 2 2 8

solar thermal collector

3 1 2 2 3 10

micro-CHP

2 3 1 1 2 9

double glazing

2 1 2 3 2 10

cavity wall insulation

3 1 2 3 3 12

loft insulation

3 1 3 3 3 13

• my scores …

16469 Low Energy Building Design: Conflict and Interaction• previous example was very subjective … need to

remove some of the guess work– need to provide technical evidence to back up scores– need to translate technical outcome to score or

(weighting)– how can we do this where there may be a need to

appraise many options• modelling and simulation can play a role

16469 Low Energy Building Design: Conflict and InteractionThe use of simulation for design option appraisal

- virtual design: based on integrated computational tools

- multi-factorial tools available: various demand and supply systems simulation tools

- decision support: iterative appraisal techniques (building energy performance, occupant comfort, renewable supply potential, etc.)

- easily interpreted display: enable designers to quickly identify impacts (PAM)

16469 Low Energy Building Design: Conflict and Interaction• can apply modelling based - multi-criteria analysis at

various levels– strategic – country or city level– individual building

• and at different levels of detail– appraisal of energy supply technologies (demand

supply matching)– appraisal of system performance and different system

design options• in the following examples we have a computationally

based more methodological (sometimes automated) approach

Digital cities

predictedenergy

energy model

database population energy/environment informationoverlaid on maps to supportdecision-makers at all levelssupport for decision-makers

meteredenergy

demand& supply

database ofactual & likelyconsumption

consumption & emissions monitoring;city profiling & property classification;

trend analysis & action planning

governmentlocal authority

institutionsindustryutilities

and others

database analysis

city or region

Supply demand matching

supply v. demand

surplus or deficit

auxiliary duty cycle

goodness of fit

combinatorial search

demandscenario

supply scenarios

Virtual design

filtering of data for perfomance appraisal

The Lighthouse Building in Glasgow

Lighthouse Viewing Gallery Glare Sources (cd/m2)

Version: reference 3 opt 2 + REContact: ESRUDate: Sep-97

Viewing gallery with advancedglazing in all windows.On/off lighting control, EE lighting.TI wall.PV hybrid + ducted wind turbines

Annual Energy PerformanceHeating: 48.99 kWh/m2.aCooling: 0.00 kWh/m2.aLighting: 19.96 kWh/m2.aFans: 0.00 kWh/m2.a

Total: 68.96 kWh/m2.aDWT 25.03 kWh/m2.aPVe 33.79 kWh/m2.aPVh 40.91 kWh/m2.a

Maximum Capacity

48.13

0.0012.00

41.6058.40

38.60

0

20

40

60

80

100

120

140

160

Hea

ting

Cool

ing

Ligh

ting

PVe

PVh

DWT

Thermal Comfort

0

10

20

30

40

50

60

70

80

16.0-18.0 18.0-20.0 20.0-22.0 22.0-24.0 24.0-26.0 26.0-28.0 28.0-30.0Resultant Temperature (oC)

WinterSpringSummer

Daylight Availability

0

5

10

15

20

25

0 1 2 3 4 5 6 7 Distance (m)

major

minor

Emissions

0.001

0.01

0.1

1

10

100

1000

CO2 NOx SOx

Heating Lighting

Energy Demand per Unit Time

020406080

100120140160180200

1 3 5 7 9 11 13 15 17 19 21 23 2 4 6 8 10 12 14 16 18 20 22 24 1 3 5 7 9 11 13 15 17 19 21 23Time (h)

Heating LightingDWT PVePVh

Winter SummerTransition

total demand:68 kWh/m2.yr

total RE supply:98 kWh/m2.yr

PV: 0.7kWe

PV hybrid: 0.8kWe & 1.5kWh

DWT: 0.6kWe

16469 Low Energy Building Design: Conflict and Interaction• model for use of simulation in multi-criteria design

process:

design options appraisal

simulation

literature review