To achieve substantial environmental benefits from storm water runoff in Israeli cities, solutions must be found to adapt the infrastructure of existing urban areas. When new neighbourhoods are planned, a hierarchy of flow paths can be designed to link catchment areas at different physical scales to collection areas where the water may be stored (as groundwater by aquifer recharge or alternatively as above ground storage). In existing built-up areas, such pathways may not be easily discernible, and there may be no suitable collection areas at the appropriate scale. This project will seek to promote water-sensitive planning by developing and demonstrating a methodology that addresses two questions: a) How can an integrated and comprehensive network of water pathways, collection areas and storage be identified and mapped onto an existing urban area, incorporating novel storm water harvesting and treatment systems (e.g. biofilters, modular systems) and adjacent aquifer recharge measures? b) What are the most effective patterns of implementing water sensitive urban design (WSUD) elements in existing areas in terms of improvement of pedestrian thermal comfort and reduction of energy demand of buildings? These questions will be explored in the context of dense urban development, characterizing Israeli cities where exposed land is relatively scarce and green open space is limited. GIS will be used to analyze typical urban typologies in conjunction with existing infrastructure and sub-surface hydrology to demonstrate how storm water harvesting may be applied to a selected urban location in a city on the coastal plain. The effect on microclimate of different patterns of vegetation associated with storm water harvesting and treatment elements, as appropriate to the respective urban typologies, will then be studied by means of computer simulation. The outputs of this simulation may then be used to generate detailed data for computer modelling of pedestrian thermal comfort and building energy performance.
Distributed PV is on the verge of becoming a realistic means of generating a significant proportion of Israel’s electricity needs. As the cost of the photovoltaic (PV) panels has come down, the price of electricity generated by BIPV systems is approaching grid parity where installation costs are not exorbitant; the reliability and durability of components has improved vastly; storage systems suitable for homes are being introduced; and familiarity with the technology has led to an overall favorable public attitude. However, the number of installations in dense urban locations is still negligible. Unlike detached single-family homes in low-density neighborhoods, where installation is relatively straight-forward and solar access is generally unobstructed, dense urban areas where most Israelis now live and where most new construction takes place pose special challenges.
Promoting Energy-Saving Behaviour in Residential Buildings in Israel
(with B. Portnov, University of Haifa).
Residential buildings in Israel contribute to some 30% of annual domestic electricity consumption, with seasonal increases of 8 % in winter and about 35% in summer being attributed to space heating and air conditioning, respectively. The conventional energy-saving paradigm suggests that if building envelopes are constructed to a higher standard, following precise technical guidelines laid out in standards, buildings will consume less energy. This assumption, which ignores the role (and responsibility) of building' residents, is likely to be misleading. In particular, over-confidence in building standards and regulations means that other, more effective measures of achieving energy-saving policy objectives might be left unexplored. We hypothesize that substantial energy savings may be achieved by modifying the behavior of home occupants – but that such savings are contingent on appropriate measures to educate and motivate them.
- Retrofit of Residential Buildings in Israel for Energy Conservation
(with Chanoch Friedman and Nir Becker)
Improving the energy performance of buildings is essential if Israel is to moderate the rate of increase in its overall energy consumption and to meet its international obligations to reduce emission of CO2. Because new buildings comprise only a tiny proportion of the building stock, existing houses, including residential buildings, must be renovated, too. The research methodology comprises three levels:
a. Analysis of the economic benefits to the individual of refurbishing an existing building
b. Examination of the social and environmental aspects of building retrofit, and their effects on the willingness of the individual to pay for the renovation
c. A study of the means for promoting energy retrofit of existing residential buildings, and drafting a proposal for government policy in the field
During the first year of the study, typical building prototypes were identified and several renovation strategies were investigated for small, semi-detached houses and for multi-story apartment buildings. Most of the renovation strategies assessed, with the exception of adding thermal insulation on roofs (in all climate zones) and painting roofs white (in Zone D only) are not cost-effective from the point of view of the individual.
Work in the second year comprised two stages. First, an assessment was made of the indirect environment costs of energy conservation in buildings, which includes three aspects: the value of avoided negative environmental emissions associated with power generation in Israel; the value of peak hour cost saving; and the value of delay in construction of new generating capacity. The combined value of these environmental effects, given the actual power generation and consumption patterns in Israel, is 10.78 agorot per kWh of reduced electricity generation. When this additional benefit is introduced to the direct economic saving resulting from roof insulation (the most cost-effective measure), the payback period in each of Israel’s four climate zones is 12 years (zone D); 15 years (zone C); 17 years (zone B) and 21 years (zone A).
The barriers to carrying out building retrofit for energy conservation were then studied by means of a structured survey, encompassing 523 adults of various demographic and socio-economic backgrounds. Analysis of the survey shows that:
· Public awareness of the need to conserve energy is high
· Willingness to pay for energy retrofit of homes is modest, and is limited to relatively small investments. Government subsidies are seen as having a major influence on the decision to invest in building renovation.
· The overall environmental benefits of a 25% subsidy for roof insulation are greater than the cost of the subsidy itself, although the marginal benefit of such intervention is less than the cost.
· The major barrier to building retrofit is the perception – which is supported by our calculations – that the economic benefit to the home owner from resulting energy savings is small and that the payback period long.
· A 5% reduction in electricity fares, or a rebate equal to the environmental benefit resulting from the energy savings, increase substantially the economic reward to the home owner doing the retrofit.
· Certain demographic factors, especially gender and level of education, have a significant effect on the willingness to pay for energy retrofit of homes.
Application of the Canyon Air Temperature (CAT) model in conjunction with the Index of Thermal Stress for assessment of pedestrian thermal comfort in outdoor spaces
(with Daniel Boneh, David Pearlmutter and Pua Bar - Kutiel)
Extensive use of high-albedo materials has been advocated as a means of mitigating the urban heat island, especially in warm-climate cities. The implicit assumptions of this strategy are that by lowering canopy layer air temperature, this strategy will result in a) reduced air conditioning loads in buildings; and b) in improved thermal comfort for pedestrians in outdoor urban spaces.
The second of these assumptions is examined by means of computer modelling: The CAT model is used to predict air temperature, wind speed and surface temperatures in a hypothetical street canyon; the predicted values are then used in the ITS model to assess the combined effect of albedo modification on the thermal stress of a pedestrian in the street, considering changes in net radiation, convection and sweat efficiency. The analysis is carried out for streets of varying aspect ratio and orientation, in different climate regions.
External fluxes of energy on a pedestrian in a N-S canyon with an aspect ratio of H/W=2, for surfaces with different albedos (data for Adelaide, Australia, at noon on Nov. 25, 2000 ).
The research demonstrates that although use of high-albedo materials in urban surfaces may reduce the air temperature to which pedestrians are exposed, this change in temperature has only a small effect on their thermal balance with the environment. Furthermore, reduction in surface temperatures, leading to reduced long-wave emission, is offset by increased reflection of solar radiation. The net effect of increasing the albedo of urban surfaces may thus be a small increase in the thermal stress to which pedestrians are exposed – rather than the expected improvement in thermal comfort.
- Energy performance and irrigation requirements of extensive green roofs in a water-scarce Mediterranean climate
(with Orna Schweitzer)
Green roofs are generally seen as a desirable building element, providing numerous benefits where water availability does not restrict their implementation. However, most Mediterranean locations have long, dry summers, requiring irrigation to sustain vegetation throughout extended dry periods. The cooling effect and water use of several types of plants suitable for extensive green roof systems were assessed using small test cells, which were insulated and equipped with internal thermal mass to provide a thermal response comparable to that of real buildings. The water requirements of the plant species tested ranged from 2.6 to 9.0 L/m2per day. Aptenia cordifolia was the most efficient in its use of water, providing the highest cooling benefit per unit water required for irrigation. However, the cooling efficiency of all roof variants studied was very low, and the reduction in the sensible heat load of the model building attributed to the green roof system was less than 5% of the latent heat content of the water lost to evapotranspiration. In this context, it is hard to justify green roofs in such environments on the basis of their contribution to building energy conservation, although other benefits may nevertheless make green roofs attractive.
- Estimating variations of advected moisture in the Canyon Air Temperature (CAT) model
(with Ingegard Eliasson, Sue Grimmond, Brian Offerle and Terry Williamson)
Site-specific climate knowledge is essential for the development of a building design that responds to the local environment, for accurate design of HVAC systems and for the development of efficient control strategies. The CAT model was developed as a tool to generate such data from measured records at a standard weather station. Evaluation of the model using Gothenburg data demonstrated that accurate modeling of air temperature at any given location also requires a means of establishing the concurrent time-varying moisture. A method was described for incorporating spatial and temporal variations in advected moisture, allowing application of the CAT model with no prior knowledge of moisture availability in the area. The methodology described provides two contributions to the state of the art:
1) It provides independent empirical support for the parameterization of the moisture availability coefficient proposed by Grimmond and Oke (2002).
2) It provides a demonstration of the capabilities of CAT using experimental data obtained independently in Gothenburg, in climate conditions and physical surroundings that are quite different to those in Adelaide on which it was first tested in the original formulation of the model.
Time series showing measured air temperature at a reference weather station (SMHI) and predicted and measured temperature at the street canyon site.
