A sensitivity analysis of a cost optimality study on the energy retrofit of a single-family reference building in Portugal

  • Sérgio Tadeu
  • António Tadeu
  • Nuno Simões
  • Márcio Gonçalves
  • Racine Prado
Original Article
  • 45 Downloads

Abstract

Improvement of the energy efficiency of residential buildings must ensure compliance with cost optimality criteria, assuming a specific lifespan of the building. At the same time, the energy retrofit of buildings ought to preserve their intrinsic architectural and heritage value. Portuguese residential buildings constructed before 1960 did not follow any energy efficiency rules. They represent 29% of the housing stock in the country and there is a high potential for increasing their energy efficiency. However, it costs more to implement envelope energy efficiency measures through retrofitting works than to provide for them in new buildings. An evaluation based on cost optimality criteria should therefore be performed. This work evaluates the energy performance of a Portuguese reference building typical of the pre-1960 building stock for different thicknesses of thermal insulation retrofit solutions (roof, facade, and ground floor) and systems. The study describes a sensitivity analysis that took a range of climate data, intervention costs, energy prices, discount rates, and energy needs into account. An energy needs factor dealt with the occupants’ habits and the effective reduction of energy consumption compared with the estimated energy needs.

Keywords

Cost optimality Energy retrofit Energy efficiency Residential buildings 

Nomenclature

Abbreviations

AC

air conditioner

DGEG

General Directorate for Energy and Geology

DHW

domestic hot water

ECS

Energy Certification System

EH

electric heater

EPBD

Energy Performance in Buildings Directive

EPCs

energy performance certificates

EPS

expanded polystyrene

EU

European Union

FIN

financial perspective

GB

gas boiler

GW

glass fiber

GWH

gas water heater

HDD

heating degree days [°C day]

HP

heat pump

ICB

expanded cork board

ICB-MD

expanded cork board (medium density)

ICESD

Survey on Energy Consumption in the Domestic Sector

INE

National Statistics Institute

MAC

macroeconomic perspective

MW

mineral wool

NPV

net present value

PE

primary energy

PEF

primary energy conversion factor

PUR

polyurethane foam

VAT

value-added tax

XPS

extruded polystyrene

Symbols

ψ

linear thermal transmittance [W/m°C]

Ci, j

annual costs [€]

Di

discount factor

Eh, k

heating energy needs [kWh/(m2 year)]

Ew, k

domestic hot water energy production [kWh/(m2 year)]

Fs, j

glazing obstruction factor associated with the orientation j

GHGi, j

carbon emission cost [€]

Gs

monthly solar energy on a south vertical surface [kWh/(m2 month)]

Hecs

heat loss to elements in contact with the ground [W/°C]

Henu

heat loss to unheated spaces and to adjacent buildings [W/°C]

Hext

heat loss to the outside [W/°C]

Htr, i

overall transmission coefficient of heat transfer [W/°C]

Hve, i

overall coefficient of heat transfer from ventilation [W/°C]

Ij

initial investment costs [€]

K

number of systems

P

conversion factor between final energy and primary energy

Pd

height of ceilings [m]

Qint, i

internal solar gains [kWh/year]

Qsol, i

glazing solar gains [kWh/year]

Qtr, i

heat transfer coefficient by transmission [kWh/year]

Qve, i

heat transfer coefficient by ventilation [kWh/year]

Rph

nominal rate of renewal of indoor air in the heating season [h−1]

Vτ, j

residual value associated with each measure [€]

aH

function of thermal inertia of the building class [W/°C]

fh, k

percentage of the energy needs for space heating [%]

fw, k

percentage of the energy needs DHW [%]

qint

average internal thermal gain per area [W/m2]

ηH, gn

gain utilization factor

η

efficiency

A

area [m2]

CO2

carbon dioxide

gw

solar factor of the glazing

r

thermal resistance [(m2 °C)/W]

U

thermal transmittance [W/(m2 °C)]

X

orientation factor

G(τ)

global cost [€]

M

duration of the heating season [months]

NM

number of measures

R

real discount rate [%]

e

thickness [m]

λ

thermal conductivity [W/(m °C)]

τ

calculation period [years]

Indices

e

vertical opaque envelope

f

floor

h

space heating

max

maximum requirement

optimum

cost-optimal solution

r

roof

ref.

reference

w

windows

j

corresponds to the each orientation

k

single energy source/system

w

domestic hot water

Notes

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Civil Engineering Construction (PCC) – Escola PolitécnicaUniversity of São PauloSão PauloBrazil
  2. 2.ITeCons - Institute for Research and Technological Development in Construction SciencesCoimbraPortugal
  3. 3.ADAI – LAETA, Department of Civil Engineering, FCTUCUniversity of CoimbraCoimbraPortugal

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