Towards Zero Emission Residential Complexes in High Density Neighborhoods

Olga Kolodiy
M.Sc. Thesis, 2018

ABSTRACT:

One of the most significant factors influencing the impact of humans on the environ- ment is population growth. In order to minimize the damage to urban open space, urbanization and urban densification should be encouraged. Proper planning of liv- ing space in crowded areas by intelligent use of existing natural resources will allow protecting open spaces for future generations and reducing the ecological footprint of new neighborhoods.

To minimize damage to open spaces, in the early 2000s an urban renewal plan was developed. Within the framework of the plan, the government of Israel proposed two main tracks for the promotion of municipal urbanization processes (Ministry of Con- struction and Housing, 1999):

1. Urban Renewal (increased building rights)

2. Urban Redesign (clearance and construction)

The aim of both tracks is better land utilization within built-up areas, the creation of a new housing inventory in cities and their improvement by upgrading existing build- ings and infrastructure. In the context of the “Urban Renewal” track, the committee promotes the intensification of built-up areas without demolition activities and max- imal use of existing infrastructures. The “Urban Redesign” route requires fully re- planning of an existing area with significant plot densification and related infrastruc- ture renewal. The case study complex in our work is facing an approved “Urban Redesign” densification program. Plot density will increase by more than 200% compared to the existing condition. The densification plan and general design layout was already approved by District Committee in 2015

The construction industry is responsible for a large amount of the energy con- sumption and greenhouse gas emissions worldwide and therefore taking immedi- ate measures may have environmental and economic benefits with long-term ef- fects. To reduce energy consumption and greenhouse gas emissions generated by the construction industry, buildings must become from energy consumers to energy producers. Zero or nearly zero-emissions/energy building (ZEB) refers to a building that has a very high energy performance, such that the balance of en- ergy needs should be covered by energy from renewable sources produced on- site or nearby (Torcellini et al., 2006).

The building envelope, especially the roof and south facing facades present a huge potential for production of renewable energies in urban areas integrated into buildings such as building-integrated photovoltaics (BIPV) without occupying ad- ditional open areas. In addition, the photovoltaic installations can be integrated in surfaces adjacent to buildings, providing shade that is required during summer. However most of the existing examples that demonstrate zero energy buildings deal with relatively low buildings located in areas with a low urban density, and then with a very high potential for solar collection in PV systems located in their envelope.

Integration of solar systems for energy generation from renewable sources in crowded cities where energy use is very high, is complex and presents new chal- lenges to building and urban design. Mutual shadowing between buildings may be an obstacle to install photovoltaic arrays on the building envelope and open spaces around buildings compromising the feasibility of the ZEB equation.

The aim of this work is to test the feasibility and implications of designing a high- density zero or near zero-energy neighborhood. The study is carried out by exam- ination and comparison of various density design alternatives of an existing urban plot in the coastal climate zone of Israel.

A case study showing the design of a new residential quarter in the city of Tel Aviv is presented comparing its performance as designed, with an alternative design which includes energy saving measures in buildings design on the one side, and the consideration of solar rights at urban level for the exposure of building enve- lope and solar systems, on the other. The relationship between urban density, en- ergy consumption and the limitations on how near we can go on the way to zero emissions are presented and discussed.

At the first stage we checked the existing built-up plot condition and the Renewal condition, addition of one or two floors to each building. The case study plot includes twenty-one identical four-storey residential buildings. It was found, that about 50% of their energy consumption can be generated using PV panels mounted horizon- tally on the buildings roofs. In some cases, additional, west and south facade PV installations are needed in order to archive same consumption-generation ratio. However, none of previously checked alternatives meet new density requirements of the area.

A new design and densification program of the plot was approved that will increase on plot residential units’ number by about 200% in comparison to the existing situ- ation. Increased dwelling units’ number will lead to higher energy use of future plot condition and mutual shading of new high rise residential buildings present to us new challenges. Preserving solar rights within the plot borders and outside for PV systems installation become more complex.

At the second stage we introduce new climate-based design alternatives:

  • –  Approved – plot design as approved by District Committee
  • –  Proposed – redesign of approved building’s volumes to maximize electricity production potential by minimizing mutual shading, and maximizing usable roof area.In case of the approved alternative, big vertical PV array systems can be imple- mented due to the large façade areas of tower type buildings. However, roof sur- faces are small and mostly shaded, therefore PV production potential cannot be maximized. In this alternative roof electricity generation is about 20% of total on plot production.On the other hand, the proposed alternative offers larger, fully exposed roof areas for maximum electricity production. In this case, PV roof array with 20% efficiency, can provide more than 80% of the total plot energy used for HVAC and lighting, and depends less on facades. Facades surfaces area is slightly smaller than in first al- ternative so as electricity production from PV array implemented on them. The pro- posed design enables to produce more energy, although its energy consumption is slightly higher than in case of the approved alternative.As noted before, horizontal roof PV installations have less impact on building ap- pearance. Roof systems are easier to install and provide future maintenance. If PV array on façades is implemented, further aesthetical design issues should be con- sidered:

Façade surfaces covered by PV requires flat, fully exposed facades design. Shad- ing elements or balconies will decrease on facade energy production potential.

PV façade array implementation, limits the cladding material variety. In addition, PV cladding increases expenses of the finishing material and its maintenance. Future developments in PV field may provide more colors, shapes and textures for more various façade designs.

The study shows that according to the comparison between the case study plot energy consumption and electricity production within buildings’ borders, near zero emission goal can be achieved for certain densities and technological conditions.

Although, zero emission or near zero emission goals is difficult to accomplish if ur- ban and building design relies mainly on facade installation. It is important to imple- ment solar oriented design on urban level as much as on smaller building scale in order to reduce energy consumption and maximize energy on-site production. In the future, with increased efficiency of photo-voltaic panels and proper design at urban and building scales, zero energy should be reachable goal for all presented density developments.

Further studies should examine the limitations of zero energy design for higher ur- ban densities with increased mutual shading, and for lower solar radiation in differ- ent countries around the world.