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Commissioned by the School of Architecture and Planning at The University of Auckland.
Funded through the NICAI Faculty Research Development Fund.
January 2010; Author: Jessica Grove-Smith, Jürgen Schnieders
Corrected version November 2011
The Passive House concept is a highly energy efficient building standard. Passive Houses consume very little energy and yet provide a very high living comfort for the residents throughout the entire year. This is achieved with a vastly improved building envelope with reduced transmission losses and optimised use of solar gains, as well as with minimised ventilation heat losses by means of comfort ventilation with highly efficient heat recovery. A high level of thermal comfort and excellent air quality can thus be guaranteed.
As a direct consequence of the very low required heating load of around 10 W/m², a Passive House can be kept warm solely by heating the supply air needed to cover the fresh air demand; complex and expensive heating systems therefore become dispensable. From experience, such buildings have a heating demand of about 15 kWh/(m²a) in cool temperate climates . Many residential and non-residential (e.g. schools, sports halls, offices etc.) buildings have already been successfully built to the Passive House standard in and around Germany. In these cases, the concept for reducing the energy demand is focused primarily on thermal protection in winter for reducing heat losses. The Passive House concept is now becoming increasingly popular on an international level where it must always be adapted to the respective local climatic conditions. In warm and humid climates, for example, an additional focus lies on keeping the indoor temperatures and air humidity in a high comfort range during summer. The basic approach, however, is always the same: The climate-independent objective is to plan buildings that can be heated and cooled via the supply air mass flow required for a good indoor air quality or, as the case may be, a building that does not need any active air conditioning at all.
This report documents the results of a study carried out to determine basic planning criteria for Passive Houses in typical climates of New Zealand. Three different climate zones were selected (chapter 2), in which the thermal and hygric behaviour of a selected example building with varying parameters was studied by means of dynamic simulations. The example building is an end-of-terrace house with a living area of 120 m²; all calculations are based on the simulation model from [Schnieders 2009]. As a first step, reference Passive Houses were defined for all three locations that can be heated via the supply air. The general characteristics of these reference houses and the specifications of individual components are described and explained in detail in chapter 4. In a second step, these reference buildings were then also projected with the Passive House Planning Package, PHPP, which is described in chapter 5. The results verify that the simplified algorithms used in the PHPP are valid for planning buildings in New Zealand, which lies on the southern hemisphere. Based on the defined reference buildings, various parameter studies were then carried out (chapter 6) that illustrate the influence of the insulation level of individual constructional elements (wall, roof, basement ceiling), the building’s thermal mass and the size of the north-facing window area i.e. the solar gains. These parameter variations were calculated both with the dynamic simulation tool, as well as the PHPP, in order to test the reliability of this simplified stationary computing method. Finally, in order to ascertain the considerable energy saving potential of Passive Houses in climates of New Zealand, comparisons were made with conventional new builds in the respective region (chapter 7).
The results presented and explained in this report serve as basic planning criteria for Passive Houses in New Zealand. Based on an example residential building (an end-of terrace house with a living space of 120 m²), the quality requirements and energy relevance of various building components were systematically reviewed. The results point the architect/designer who wants to build a Passive House in New Zealand in the right direction by providing a guide for initial approaches and reliable calculation methods.
The first part of the study consisted of defining reference Passive Houses for three climate zones in New Zealand, represented by the cities of Auckland, Wellington and Christchurch. This was achieved based on the results of dynamic simulations carried out with DYNBIL, a software package developed by the PHI. Various characteristics of the exemplary building and its components were subsequently analysed with respect to their effect on overall energy efficiency and living comfort. The conclusion is that the Passive House standard can easily be reached, mainly due to the comparatively mild temperatures and high solar radiation in all three climate zones. The quality requirements for the building envelope in order to reduce transmission losses, for example, are less demanding than in the Central European climate, so that slightly lower levels of insulation and double-glazing will usually suffice. The relevance of the building’s orientation, its compactness, the ventilation concept (heat recovery, airtightness, summer ventilation) and the shading situation of the building were also analysed. Optimal use of solar gains is of great importance. In winter they can compensate thermal losses and heat the building passively, whereas in summer, too much sun will lead to overheating. With careful planning, the available solar radiation can easily be used to the building’s advantage. The absolute humidity of the outside air in the climate of New Zealand is higher than e.g. in Germany, so that moisture-related problems are more likely to occur. The results presented in this report show, however, that in a well-planned and well-built Passive House there will be no condensation and no mould. The basic prerequisite for successful implementation of the Passive House concept is quality assurance during the construction phase.
The results presented in the second and third chapter verify that the current version of the well-established Passive House Planning Package, PHPP, can be reliably used also for projects planned on the southern hemisphere. The tool allows the planner to quickly and easily identify the influencing factors on the energy balance, thereby making it possible to see which components should best be optimised to reach the Passive House standard. The discrepancy of the defined reference Passive Houses’ heating demands calculated dynamically with DYNBIL and with the stationary PHPP method is less than 4 kWh/(m²a) for all three locations. The PHPP calculations are always on the safe side. Differences in the results occur mainly due to the stationary calculation of the complex dynamic influence of the solar gains. Parameter studies of the north-oriented window areas, the insulation thickness of individual building components and of the thermal mass confirm that the respective influence of these parameters are accurately calculated by the PHPP. More insulation and wider windows decrease the heating demand; very large window areas, however, can lead to uncomfortably high indoor temperatures if there is no adequate shading. The building’s thermal mass influences its thermal inertia and stabilises the indoor temperatures, which is particularly advantageous for summer comfort on sunny days. However, the results clearly show that optimising the building envelope (insulation, minimised thermal bridges, appropriate window quality etc.) and creating a good design (compactness, shading, orientation etc.) play a far more important role for the overall energy performance than thermal mass.
The comparison with dynamically simulated exemplary conventional new builds in accordance with New Zealand’s building regulations shows that the heating demand of a Passive House is at least 80 % lower. Additionally to saving energy, Passive Houses also feature a much improved living comfort with pleasant temperatures and an excellent air quality throughout the year.
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