EuroSun2008-5

CORRESPONDENCE BETWEEN TECHNOLOGICAL. SOLUTIONS AND THE ENERGY LABEL OF RESIDENTIAL. BUILDINGS IN PORTUGAL

Sebastiao Carvalho, Vftor Leal and E. Oliveira Fernandes

FEUP - Faculty of Engineering of the University of Porto
Rua Dr. Roberto Frias, s/n 4200-465 Porto PORTUGAL
* Corresponding Author: Vitor Leal, vleal@fe. up. pt

Abstract

Portugal has new building energy regulation since 2006, coupled with a building energy certification scheme in force since 2007. The regulation for residential buildings has several requirements that must be met, among which are limits to the nominal heating and cooling needs, to the nominal final energy for domestic hot water and to the nominal primary energy consumption. Because most of the requirements are performance goals rather than prescribed measures, there are always several options to meet the regulation requirements. Furthermore the certification/labelling scheme now in place establishes a differentiation between the buildings that comply, ranging from B - to A+ for new buildings.

This study presents an analysis of the correspondence between the constructive and technological solutions adopted and the compliance with the regulation as well as the resulting energy class. This is done using an apartment and a dwelling as case studies, for 7 different locations in mainland Portugal. The analysis of the results places a focus on the relevance of the domestic hot water solar collectors for compliance with the regulation and for the achievement of the best energy classes (A, A+).

Keywords: Buildings, Performance, Certification, EPBD, Solar collectors

1. Introduction

Buildings represent about 37% of the primary energy used in Portugal, slightly more than transportation or industry, and they are therefore a key-sector for achieving a low carbon society. One of the most important mechanisms designed to achieve this goal is the EPDB-related certification and labelling scheme, which in Portugal is called the SCE (decree-law 78/2006, [1]) and is supported on the energy regulations for residential buildings (decree-law 80/2006, [2]) and for energy-intensive buildings (decree-law 79/2006, [3]).

Solar collectors are a direct requirement of the regulation although it can be discarded in some cases (solar exposition not favourable, historic areas). Furthermore, the calculation method used in this labelling system recognizes important credits to solar energy, either that entering through the glazed envelope as direct solar gains or that captured by solar collectors for water heating.

In terms of energy requirements, the fulfilment of the regulation implies the simultaneous compliance with the following requirements:

i) Minimum requirements for the envelope elements (U-value and solar factor)

ii) Heating needs (useful energy, Nic) inferior to a maximum level allowed (Ni).

iii) Cooling needs (useful energy, Nvc) inferior to a maximum level allowed (Nv).

iv) Hot water needs (final energy, Nac) inferior to a maximum level allowed (Na)

v) Total primary energy (Ntc) inferior to a maximum allowed level (Nt).

The calculation of the total primary energy needs Ntc considers that the domestic hot water needs are satisfied at 100%, while the nominal heating and the cooling needs are only satisfied at 10% (due to traditional use patterns). It is computed as (eq.1) :

(kgoe/m2.year)
Ntc	0.1	F +Nac■F puv pua
(eq. l)

where hi and hv represent the conversion factors from final to useful energy, while Fpui, Fpuv and Fpua represent the conversion factors from final to primary energy.

If (and only if) all the previous criteria i) to v) are met simultaneously, then an energy class can be determined. The energy class is established through the quotient between the estimated primary energy use and its maximum allowed by regulation, with class transitions at each 25% improvement. The minimum allowed class for new or significantly retrofitted buildings is B - (table 1).

This study intends to perform an analysis of the correspondence between the constructive and technological solutions adopted and the compliance with the regulation as well as the resulting energy class. This is done using an apartment and a dwelling as case studies, for 7 different locations in mainland Portugal. The analysis of the results puts a focus on the relevance of the DHW solar collectors for compliance with the regulation and for the achievement of the best energy classes (A, A+).