from building to district retrofit:contrasting the optimal...

From building to district retrofit: contrasting the optimal strategies through a multi-objective approachAlessandro Prada, University of Trento, Trento, ItalyFrancesca Cappelletti, University IUAV of Venice, Venice, ItalyAndrea Gasparella, Free University of Bozen-Bolzano, Bolzano, Italy

Outline

1. Introduction

2. Methodsa. Building Archetypes and Stocks

b. Energy Efficiency Measures

c. Optimization Algorithm

3. Results

4. Conclusions

50. Međunarodni kongres i izložba o KGH, Beograd, 4–6.12.201950th International HVAC&R Congress and Exhibition, Belgrade, 4–6 Dec. 2019

1. Introduction

Cost optimization

• EPBD reference approach to

– define minimum energy performance requirements

– major renovation of existing buildings

– replacement or retrofit of building elements

• Reference target: individual buildings or dwellings

• Minimize the Net Present Value (NPV) for any given Energy Performance (EPh) and choose the solution with the minimum overall NPV

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20.6 k€

222.0 kWh/m2

61.1 k€


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1. Introduction

Possible limitations:

• The owner may want to minimize the Investment Cost (IC) instead of NPV

• Public authority needs to achieve a specific EP reduction target

• PA sometimes invests directly with limitedresources (subsidies or public buildings)

Research question:

• Assume a given savings target for the stock (ex. 50 %)

• Objective: optimizing each individual building (NPV) or miminize the IC at a stock level?

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61.1 k€

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1. Introduction

Aims• Quantifying the advantages of optimizing the retrofit of the existing stock instead

of each single building.Contents• Three reference building archetypes • Different mixes to represent existing building stocks• Four groups of Energy Efficiency Measures (EEMs):

(i) opaque envelope, (ii) windows, (iii) heat generation system, and (iv) mechanical ventilation

• IC saving optimizing (i) the stock vs (ii) each single building• EEMs in the optimal solutions• Additional EPh savings when reinvesting IC savings


2. Methods: building archetypes and stocksOpaque envelope

• Non-insulated

• Reference resistance

R = 0.97 m2 kW-1

HVAC System

Generator: Standard

Emission: Radiators

Control system: On-Off

Distribution: Moderate insulation

Ventilation: Natural

Milan Transparent Envelope

• Single glass pane

Ugl=5.7 W m-2 K-1

• Timber frame

Ufr=3.2 W m-2 K-1

• South oriented

3 Saving targets

• 50 %• (60 %)• (70 %)EPh Primary energyfor heating0

% 10

0%

0.6

66 Stock mixes

0.3 1.0

Compactness Ratio S/V Archetypes

0.6 (0.63)

1.0 (0.97)

0.3 (0.30)1

2

3


2. Methods: energy efficiency measures

External insulationUp to 20 cm (step 1cm)• Wall• Roof• Floor

Windows replacement

Improved Frame• DH – Double, High SHGC• DL – Double, Low SHGC• TH – Triple, High SHGC• TL – Triple, Low SHGC

Heating system

Efficiency on LHV• Modulating Boiler, η=96%• Condensing Boiler, η=101%

Ventilation system

Introduction of mechanicalventilation with heat recovery


2. Methods: algorithmsAlgorithm: multi-objective optimization through NSGA-II with customizations:• Initial Sampling• Data-set recordings • Convergence criterionEnergy Simulation:• TRNSYS hourly simulation• Energy Performance index for heating (EPh)Economic evaluation:• Cost-optimal approach according to EU 244/2012 and EN 15459• NPV summing the discounted cash flows related to each intervention• Including: initial investment, annual energy cost, maintenance cost, replacement cost, and residual value• Lifespan of 30 years


3. Results: IC savings (all mixes) - target 50 %

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3. Results: IC savings (all mixes) - target 50 %

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3. Results: type 2-3 mixes - target 50 %

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6115,3

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IC vs ΔEP

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IC [EUR] vs ΔEP%

W R F WIN HSYS VMC W R F WIN HSYS VMC

Chart Title20 cm

10 cm

TL

TH

DL

DH

COND

MOD

STD

MEC

NAT

20 cm

10 cm

TL

TH

DL

DH

COND

STD

MEC

NAT

MOD

3 2 % of type 2 in red

0 % 2100 % 3

100 % 20 % 3

32

EEM mixes


3. Results: type 2-3 mixes – same IC (50 %)

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IC vs ΔEP%

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IC [EUR] vs ΔEP%

W R F WIN HSYS VMC W R F WIN HSYS VMC

20 cm

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TL

TH

DL

DH

COND

MOD

STD

MEC

NAT

20 cm

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3. Results: extra EP savings (2 and 3) - target 50 %

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Sav

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(%)


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Conclusions

• Significant savings in terms of IC or EP can be obtained whenoptimizing the stock instead of each single building

• Preliminary study:– Results change for higher savings targets – less compensation possible

between different buildings

– Do not account for minimum requisites

– Higher targets: can be achieved through a multi-step approach (long term) which minimizes the initial IC and reinvests the savings in a period in further EEMs in a following period


Thank you

Alessandro Prada, University of Trento, Trento, ItalyFrancesca Cappelletti, University IUAV of Venice, Venice, ItalyAndrea Gasparella, Free University of Bozen-Bolzano, Bolzano, Italy

from building to district retrofit:contrasting the optimal...

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