Scholarly article on topic 'Housing and Transportation: Towards a Multi-scale Net Zero Emission Housing Approach for Residential Buildings in New Zealand'

Housing and Transportation: Towards a Multi-scale Net Zero Emission Housing Approach for Residential Buildings in New Zealand Academic research paper on "Earth and related environmental sciences"

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{"net zet emission house / operation energy emissions" / "embodied energy emissions / user transport energy emissions ;"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Dekhani Nsaliwa, Robert Vale, Nigel Isaacs

Abstract Current approaches of designing and refurbishing residential buildings in urban developments to achieve net zero emission performance focus mainly on operational energy largely in terms of thermal aspects. The embodied energy of buildings and systems and additionally the transport energy of their users are typically overlooked. More recent studies have revealed that these two energy demands can represent more than half of the life cycle energy for over 50 years. This paper initiates an approach which takes into account the energy requirements at the building scale (i.e. embodied and operational of the building and its systems) and the city scale i.e. transport energy (both direct and indirect) of the users of a net zero emission house located in Auckland, New Zealand and evaluates its energy consumption and CO2 emissions. In addition it investigates various scenarios related to transport technology focusing on internal combustion engine vehicles (ICEVs) and battery powered electric vehicles (BPEVs). The main conclusion is that there is a need to develop integrated tools which should enhance the efficiency of net zero emission houses and user transportation modes in a single framework such that each of the embodied, operational and transport energy emissions attributed to the building users can be reduced in order to move towards a low energy society.

Academic research paper on topic "Housing and Transportation: Towards a Multi-scale Net Zero Emission Housing Approach for Residential Buildings in New Zealand"

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Energy Procedia 75 (2015) 2826 - 2832

The 7th International Conference on Applied Energy - ICAE2015

Housing and transportation: Towards a multi-scale net zero emission housing approach for residential buildings in New

Zealand

Dekhani Nsaliwaa*, Robert Valeb, Nigel Isaacsc

a'b'c Victoria University of Wellington,School of Architecture and Design, _139 Vivian street, Wellington 6011,New Zealand_

Abstract

Current approaches of designing and refurbishing residential buildings in urban developments to achieve net zero emission performance focus mainly on operational energy largely in terms of thermal aspects. The embodied energy of buildings and systems and additionally the transport energy of their users are typically overlooked. More recent studies have revealed that these two energy demands can represent more than half of the life cycle energy for over 50 years. This paper initiates an approach which takes into account the energy requirements at the building scale (i.e. embodied and operational of the building and its systems) and the city scale i.e. transport energy (both direct and indirect) of the users of a net zero emission house located in Auckland, New Zealand and evaluates its energy consumption and CO2 emissions. In addition it investigates various scenarios related to transport technology focusing on internal combustion engine vehicles (ICEVs) and battery powered electric vehicles (BPEVs). The main conclusion is that there is a need to develop integrated tools which should enhance the efficiency of net zero emission houses and user transportation modes in a single framework such that each of the embodied, operational and transport energy emissions attributed to the building users can be reduced in order to move towards a low energy society.

© 2015TheAuthors.Publishedby ElsevierLtd.Thisis an open access article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Applied Energy Innovation Institute

Keywords:net zet emission house,operation energy emissions, embodied energy emissions,user transport energy emissions

1. Introduction

Over the past decade, numerous housing projects have been presented as 'net zero energy', 'zero carbon' or 'zero emissions' [1]. Such claims have been made through using a variety of different approaches, notably on-site renewable energy technologies, purchasing green energy credits, etc. However, recent

* Corresponding author. Tel.: +64 0 2230 34855; fax: +64 4463 6204. E-mail address: dekhanijuvenalis@gmail.com.

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Applied Energy Innovation Institute

doi: 10.1016/j .egypro .2015.07.560

studies have shown that, for different cities around the world, the energy demand associated with user transport can be higher than building operational energy and embodied energy combined [1,2,3]. A low or net zero energy/emissions house located in the suburban areas might use more energy overall because the zero operation emissions achieved could be offset by much higher user transport energy emissions.

At the same time, the ever-growing interest relative to the environment in an attempt to eliminate extravagant energy use and reduce emissions in the transport sector has appeared to be a supreme policy target in many countries including New Zealand. New Zealand house-holders have a tendency of highly relying on cars, as evidenced from the Ministry of Transport's Household Travel Survey which indicates that 78% of all trips during 2008 and 2011 were undertaken as either car driver or car passenger [5]. This level of vehicle dependence is considerably higher than other countries, notably the United Kingdom at 68% and the Netherlands at 48% [6, 7]. Nevertheless, although energy use associated with user transport is often overlooked, urban transport is currently almost entirely dependent upon oil and this has allowed the appearance of sprawling urban forms within global cities [8]. The idea of a vehicle transportation sector relying on electricity as its main fuel has since represented a game changing episode from its inception and scientific hype-disappointment cycle to a tangible reality [9]. These underlying factors have directed the eyes of policy makers to alternative fuels and new technologies. There are three types of alternative vehicle fuels currently available: Internal Combustion Engine Vehicles (ICEVs) that use petrol, diesel or natural gas, Hydrogen Fuel Cell Vehicles (HFCVs) and Electric Vehicles (EVs) that use electricity stored in an electro-chemical battery and can be classified further into; Hybrid Electric Vehicles (HEVs), Plug-in Hybrid Electric Vehicles (PHEVs) and Battery Powered Electric Vehicles (BPEVs) [9].

The approach to emission reduction and increase in renewable energy in the residential sector has so far been the deployment of net zero emission houses (Net ZEHs). However, one question that arises in zeroing in on net zero emission housing is: how will we know that we have got there? Besides, the exuberance surrounding Battery Powered Electric Vehicles' (BPEVs) increasing technical and commercial success has led to the societal perception that we have finally reached the tipping point of accepting electrified drivetrain technologies, but as travelers on the electrified transportation road for over 100 years, have we reached our destination yet? This paper will address these questions by exploring the role of integrating in-house energy use and user transport energy use as an approach towards reducing overall emissions. This will encompass both building and city scales by comparing the house technology with respect to the users' transport technologies, focusing on the use of ICEVs versus BPEVs. It should however be noted that the choice of housing location which affects user transport behavior is strongly related to other factors such as the price of property, etc. These aspects fall out of the scope of this paper and are not considered further.

2. Housing

The studied Net ZEH is a 200m2 detached single family house for 2 persons located in, Point Chevalier Auckland, New Zealand[10]. Built in 2012, the home has two storeys of approximately 74m2 upper floor, 73m2 ground floor and 53m2 garage connected to the house. The house is accessed at the street level on the ground floor. It has a roof-mounted 4.16kWp grid connected solar photovoltaic array and a 5000L rain tank supplying toilets, washing machines and outdoor taps. The operation energy reported from monitored data in the first year (2013) was 2,361 kWh while the PV array generated 5,387 kWh. This implies the house generated more energy than consumed and thus satisfied the criterion of net zero emissions in this regard. Considering that the house was built to the current Net ZEH criterion [11], it features a very efficient building envelope. As such, the embodied energy emissions attributed to the building materials were assumed to be approximately equivalent to a high performance house located in Auckland, New Zealand and the figures were derived from [12] who report 502 kgCO2-eq/annum for a typical super-insulated house of 200m2 floor area.

The embodied energy emissions contributed by the multi crystalline 4.16kWp solar panels was calculated as 296 kgCO2-eq/ annum based on [13] for an average insolation of 1,700kWh/m2/annum. Similarly, the embodied energy emissions from the 5000L rain water tank supplementing the mains was calculated as 28 kgCO2-eq/annum based on [14].

3. Transportation

The analysis below examines the direct and indirect CO2 emissions assuming the householders used either electric (BPEVs) or internal combustion engine vehicles (ICEVs). The annual distance travelled is based on usage from "Wells-to-Wheels" in New Zealand taking into account the national electricity grid mixes of renewables and fossil fuel sources and the requirements for fuel extraction to delivery to the fuel tank for the combustion of the fuel respectively. This "Wells-to-Wheels" analysis of transportation fuels and vehicle systems comprises of two parts, the Well-To-Tank (or Power-Plant), and Power-Plant or Tank-To-Wheels steps. Thereafter, the analysis considers a hypothetical comparison of the transport technologies with the house technology taking into account the household size. Vehicles likely to be introduced in 2015 were used in the analysis, as they are much heralded to be more efficient except for the Nissan Leaf and the Tesla Model S which represent ultra-modern powertrain technologies for electric vehicles already available on the market. (Appendix A. 1) outlines the characteristics of vehicles used in the analysis.

The average CO2 emissions from electricity generated in New Zealand is 0.28 kgCO2-eq/kWh [15]. The Wells-To-Wheels CO2 emissions for the three electric vehicles considered in this study were calculated by summing up the Wells-to-Power-Plant emissions, vehicle life cycle emissions and Power-Plant-to-Wheels emissions. Wells-to-Power-Plant CO2 emissions refers to the embodied emissions from primary fuel extraction to delivery to the power plant for use in electricity generation including all intermediate steps and denoted as E Wells-to-Po wer-Plant. This is analogous to Wells-to-Tank emissions for ICEVs. The Wells-to-Power-Plant emissions for each electric vehicle were calculated from the range of powertrain efficiency data given in (Appendix A. 1), the breakdown of the total net electricity generation data for New Zealand given in Table 1 and the Wells-to- Power-Plant emissions for each type of fuel used in electricity generation given in (Appendix A.2).

Table 1: Breakdown of total net electricity generation for New Zealand (GWh/percentage of net electricity generation) [16]

Source of fuel Coal Natural gas Hydro power Geothermal power Wind Net electricity generation

GWh 3432 8580 22737 6006 2145 42900

% of net electricity generation 8% 20% 53% 14% 5% 100%

The Power-Plant-to-Wheels emission refers to the emissions from electricity at the power plant which is delivered to the electric vehicle's battery and used for vehicle operation. These emissions were calculated from the amount of electricity required to run each EV, inclusive of electricity transmission, distribution losses and battery charging inefficiency from (Appendix A. 1), added to the average direct emissions from electricity generation in New Zealand (0.28 kgCO2-eq/kWh) and denoted as OP Power-Plant-to-Wheels. Similarly, this is analogous to the Tank-to-Wheels emissions for ICEVs. The sum of the Wells-To-Power-Plant , Power-Plant-to-Wheels and Vehicle life cycle, Evl (i.e. embodied emissions for production of raw materials, manufacturing and distribution of vehicle components and whole assembly, maintenance and repair of the vehicle throughout its life time until the disposal of the whole vehicle) is calculated using the equation given below. The vehicle embodied emissions were derived from the carbon intensity of similar vehicles in the literature with values ranging from 0.03 kgCO2-eq/km for small cars and 0.054 kgCO2-eq/km for midsized to larger vehicles [17].

Wells-To-Wheelsev {kg/km) = ^ (MJ/km) * [EwtPP + OPPPtw] + Evl (fc%m)

The Wells-to-Wheels emissions for the ICEVs are the sum of Wells-to-Tank, defined as embodied emissions from primary fuel extraction to delivery to the vehicle fuel tank and the Tank-to-Wheels emissions, which are defined as emissions from combustion of the fuel. The Wells-to-Tank embodied emissions were calculated based on the literature figures of carbon intensity of crude oil with an average of ±0.015 kgCO2-eq/MJ (kilograms of CO2-eq per mega joule) [18]. The vehicle embodied emissions were derived from the carbon intensity of similar vehicles in the literature with values including 0.019 kgCO2-eq/km for small cars and 0.038 kgCO2-eq/km for mid-sized to larger vehicles [17]. The Tank-to-Wheels operation emissions were calculated from the average fuel combustion emissions from motor vehicles (0.073 kgCO2-eq/MJ) [18] and the fuel efficiency figures of the ICEVs (Appendix A.1).The Wells-to-Wheels emissions calculated for the three EVs and three ICEVs are given in Table 2 below.

Table 2: Average Wells-To-Wheels emissions for EVs and ICEVs (kgCO2-eq/km) running in New Zealand

EV's Smart EV Nissan Leaf Tesla Model S

0.064 0.124 0.128

ICEVs Smart ForTwo Mini Cooper Porsche Cayenne

0.121 0.157 0.336

The table demonstrates that the size of the vehicle and the fuel mix of the electricity grid are the overwhelming factors in determining the Wells-to-Wheels embodied emissions in the case of EVs. On the other hand, the size of the vehicle and the fuel consumption of the vehicle are the major factors in determining the Wells-to-Wheels emissions in case of ICEVs. Nevertheless, Table 2 also shows that on an aggregate level EVs running on relatively low carbon electricity such as the case in New Zealand appear to perform better than ICEVs. However, high efficiency internal combustion vehicles such the Smart ForTwo ICEV appear to have lower overall emissions than EVs such as the Nissan Leaf and the Tesla Model S. It can therefore be concluded that the relative superiority of EVs as they are perceived over ICEVs is less clear. This is clearly due in part to the much higher embodied emissions of EVs compared to ICEVs, due perhaps to the need to supply and replace batteries. What is very clear is that battery electric vehicles are not a zero carbon option.

4. Hypothetical comparison of user transportation and net zero emission housing

The three EVs and three ICEVs under analysis here differ in size and also in the amount of fuel required for operating them. The average emissions derived from Table 2 can therefore be used to represent those of a hypothetical EV and ICEV fleet required to provide a mobility service to Net ZEH users, although for the current paper they are un-weighted by fleet size or other constraints. The total annual transport operation energy emissions for the household are calculated by multiplying the number of building users by the average travel distance by the average private vehicle per passenger kilometer which is 10, 280km per capita per annum for New Zealand and the carbon intensity of transport mode [5].The assumed household size is 2 persons and the total carbon intensity of each transport technology in (kgCO2-eq/km) is given in Table 2 above. The results are plotted and shown in Figure 1 below.

Figure 1: Hypothetical comparison of emissions from Net ZEH and various transport technologies in New Zealand

5. Discussion and Conclusion

It is the best of times and it is the worst of times. At the best the concept of Net ZEH is a possible long term solution to sustainable housing. At the worst, building operation and embodied energy emissions, which are the sole focus of current policies and market trends regarding Net ZEHs to date, represent only the smaller proportion of the annual emissions of a household. Consequently, the transport energy emissions of their users represent the larger share of the annual emissions. Since transport energy emissions are not considered at present, policies facilitating the improved energy performance of residential buildings with the aim of reducing overall emissions may be directed towards the wrong target. For instance, people living in net zero-energy/emission houses in the suburbs could be liable for more emissions overall than their urban counterparts living in less efficient dwellings, provided that these urban dwellers make use of lower overall emission public transport. It appears that the true benefits of zero emission houses to the whole society remain unclear. This reveals that tools and methods that explore how multi-scale solutions of housing-related emissions and transport-related emissions could provide a way towards better environmental outcomes in planning policy decisions to ensure a low energy society are lacking.

Acknowledgements

The authors would like to acknowledge the support from Victoria University of Wellington for funding this research through the Victoria Research Trust. Also to Shay Brazier and Jo Woods for providing relevant data on the Auckland net zero emission house.

References

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Biography

Born on 31st of October 1987, Dekhani Nsaliwa holds a BSc in Architecture and an MSc in Architectural Engineering (With Distinction) from Heriot Watt University in Scotland, United Kingdom. He then proceeded to New Zealand to pursue his PhD studies in the School of Architecture at Victoria University of Wellington under the supervision of Professor Robert Vale and Nigel Isaacs.

Appendix A.

A.1. Characteristics of ICEVs and EVs: 1[17] 2[19] 3[20]

Vehicles

Characteristics for the ICEVs Smart ForTwo' Mini Cooper"' Porsche Cayenne"'

petrol petrol petrol

Fuel consumption(L/100km) 4.9 5.1 12.9

Efficiency (MJ/km) 1.7 1.8 4.5

Range ( km) 700km+ 700km+ 700km+

Size small mid-size larger

Characteristics for the BPEVs Smart EV"" Nissan Leaf2 Tesla Model S3

Powertrain efficiency (MJ/km) 0.43 0.8 0.85

Battery capacity(kWh) 16.5 24 85

Range(km) 136km 117km 426km

Size small mid-size larger

A.2. Well-to-Power-Plant average embodied CO2 emissions by fuel type used in electricity generation for New Zealand (kgCO2-eq/kWh)[21]

Coal1 Natural gas2 Hydro power3 Geothermal power* Wind"5

Range 0.085-0.135 0.048-0.1 0.002-0.009 - 0.009-0.119

Average^ 0.11 0.074 0.006 0.028 0.014

1For coal this includes mining and transport

2For natural gas this includes gas processing, venting wells, pipeline operation and system leakage in transportation

3 For hydro this include energy use for building dam

4 [22]

5 For wind this includes energy use for building tower and nacelle

6 Used for calculations