A. Augusto1*, G. Carrilho da Gra^a1,2, M. Lerer2
1FCUL, DEGGE, Campo Grande C8, 1749-016 Lisbon, Portugal, 2Natural Works, Lisbon
Corresponding Author, afa@natural-works. com

Abstract

A Net Zero Energy Building (NZEB) is a building that, on annual basis, draws from outside sources an amount of energy that is equal to, or less than, the energy it produces on site from renewable energy sources. Building energy efficiency is a priority in the EU: buildings represent 40% of the total final energy demand. This study aims to size a renewable energy system based on solar thermal (ST) and photovoltaic (PV) systems that meets all energy needs of an optimized single family house for the Mediterranean climate, combining reduced energy needs with efficient building energy systems. The house yearly heating, cooling, and domestic hot water needs are 14.9 kWh/m2, 1.8 kWh/m2 and 33.3 kWh/m2 respectively. After sizing a set of ST and the PV systems, an analysis was performed to identify the best system configuration from a financial and environmental perspective. The cost and performance of the NZEB system shows low sensitivity to the size of the ST, whenever solar hot water is used to its maximum, with the best cases occurring in a wide range of panel areas: 4-8m2. The introduction in the analysis of the renewable Portuguese micro-generation financial incentives scheme shows great potential for financially attractive NZEB homes.

1. Introduction

Energy use in buildings represents about 40% of the European Union final energy demand [1],as a result building energy efficiency has become a top priority [2]. From a building sustainability perspective the goal is to conceive an efficient building that, on annual basis, draws from outside sources an amount of energy that is equal to, or less than, the energy it produces on site from renewable energy sources. In order to avoid on site electrical energy storage the Net Zero Energy Building (NZEB) approach is gaining support: when a building has a surplus in its electricity production, the surplus is injected into the grid, conversely when its production is not enough to satisfy the demand, the building draws from the grid.

With current technology, the off-grid approach seems difficult to implement [3], both from an economical and technical viewpoint, due to the seasonal mismatch between energy demand and renewable energy supply. In the off-grid case, the excess of renewable energy produced in the building is wasted and cannot be used to balance energy needs during periods of building’s higher energy demand.

For the on-grid NZEB concept to succeed, the building should:

• Be energy efficient / have reduced energy needs (natural lighting and ventilation, passive heating and cooling)

• Have efficient building energy systems (including domestic appliances)

• Have renewable energy systems — solar thermal, PV, etc.

• Be served by a flexible energy infrastructure — the on-site energy production system should be adapted to the local renewable energy potential and to the building’s needs; the distribution system (grid) should be able to supply and receive energy to and from the building.

This study aims to identify the most efficient NZEB configuration for an optimized single family house in the Mediterranean climate (Lisbon). Renewable electrical production will be done using PV since it is the most promising technology for urban and suburban areas. For domestic hot water and, in some cases, space heating, solar thermal panels will be used (the system with faster payback for this application).