Heat Island Effect

Hi Everyone!

I am currently involved in the very early design stages of a fairly large mixed-use development that will comprise of a number of neighbourhoods. It is a rare case where environmental assessment comes before design. My goal is to use both tools in their full capabilities and perhaps suggest (I would say create if I could code a line) new ones.

I was wondering about if there is already a capability of Heat Island Effect assessment in ladybug. Solar adjusted radiation modelling seems to approach something similar. I have seen variables such as material absorption. I realize that usually a CFD simulation is performed to assess Heat Island Effects but such a simulation could be enhanced with data provided from Ladybug or perhaps it could be done completely in the tool.

A simple checklist of the top of my mind, just as a brainstorming exercise, would be:

- percentages of softscape and hardscape materials in the area

- thermal properties of all materials (SRI, absorption, U-values, etc.)

- Leef Area Index of softscape (to account for shading from greenery)

- Water bodies and/or irrigation (to account for evapotranspiration)

- Open sky views, to account for reflections of light between surfaces that trap heat

- Roof and glazing reflectance of buildings (I'm guessing that is already somewhere there).

- Wind assessment to account for blockage, turbulence, etc. (this is essentially the CFD?)

- ...

I am quite new to the tools, and the scene, so I hope this topic makes a bit of sense (i.e. it can be in the least feasible or not already completely provided).

Kind regards,

Theodore.

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Replies to This Discussion

Permalink Reply by Theodoros Galanos on January 31, 2015 at 12:09am

I realize there is no edit.

The purpose of such a capability would not just be to measure the Heat Island Effect in an urban area, since that can be already maybe approximated by historical data of temperature differences in urban and suburban areas. The idea is to parametrically desing strategies to mitigate the effect on a district level or to quantify improvements of those strategies (the holy grail of acceptance these days).

Permalink Reply by Chris Mackey on February 1, 2015 at 3:54am

Hi Theodoros,

You bring up an important topic, which is actually how I first became involved in climate science and thermodynamics. There have been a lot of topics that together have fallen under the umbrella of Urban Heat Island (UHI) and I am going to try to separate them out in order to give you a sense of the current capabilities in LB+HB.

1) UHI as defined as a recorded elevated air temperature in an urban area:

If you have access to epw files for both an urban area and a rural area, you can use Ladybug to visualize and deeply explore the differences between the two weather files. Ladybug is primarily a tool for weather file visualization and analysis and it can be very helpful for understanding the consequences of UHI on strategies for buildings or on comfort. This said, if you do not have both rural and urban recorded weather data or you want to generate your own weather files based on criteria about urban areas (as it sounds like you want to do), this definition might not be so helpful.

2) UHI defined by air elevated air temperature but viewed as a computer model-able phenomenon resulting primarily from urban canyon geometry, building materials, and (to a lesser degree) anthropogenic heat:

This definition seems to fit more with they type of thing that you are looking for but it is unfortunately very difficult and computationally intensive such that we do not currently have anything within Ladybug to do this right now. I can say that the state-of-the art for this type of modeling is an application called Town Energy Budget (TEB) and this is what all of the advanced UHI researches that I know use (http://www.cnrm.meteo.fr/surfex/spip.php?article7). Unfortunately for those trying to use it in professional practice, it can take a while to get comfortable with it and it currently runs exclusively on Linux (this does mean that it is open source, though, and that you can really get deep into the assumptions of the model). A couple years ago, a peer of mine translated almost all of TEB into Matlab language making it possible to run it on Windows if you have Matlab. He wrapped everything together into a tool called the Urban Weather Generator (UWG), which can take an epw file of a rural area and warp it to an urban area based on inputs that you give of building height, materials, vegetation, anthropogenic heat, etc. I would recommend looking into this for your project, although, bear in mind that is it not open source like the original TEB tool and that you may need to get a (very expensive) copy of MATLAB (http://urbanmicroclimate.scripts.mit.edu/uwg.php).

3) UHI as defined by a thermal satellite image of an urban area depicting an elevated average radiant environment that reaches a maximum a the city center and changes by land use:

This is the definition of UHI that I am most familiar with and was the basis of much of my past research. I feel that it is also a definition of UHI that is a bit more in line with where a lot of contemporary UHI research is headed, which is away from the notion of UHI as a macro-scale meteorological phenomena that is averaged as an air temperature over a huge area towards one that accepts that different land uses have different microclimates and (importantly) different radiant environments. While the air temperature difference between urban and rural areas usually does not change more than 1-4 C, the radiant environment can be very different (on the order of 10-15 C differences). The best way to understand UHI in this context is with Thermal satellite images, for which there is ha huge database of publicly available data on NASA's glovis website (http://glovis.usgs.gov/) or their ECHO website (http://reverb.echo.nasa.gov/reverb/#utf8=%E2%9C%93&spatial_map=...). I tend to use thermal data from LANDSAT 5-8 and ASTER satellites in my research. Unfortunately, there is a lot f bad data with a lot of cloud cover mixed in with the really good stuff and it can take some time to find good images. Also, there aren't too many programs that read the GeoTiff file format that you download the data as. I know that ArcGIS will read it, a program called ENVI will read it (I think that the open source QGIS can also red it). I have plans to write a set of components to bring this type of data into Rhino and GH (I may get to it a few months down the line).

4) UHI as a computer model-able notion of "Urban Microclimate" with consideration of local differences and the local radiant environment:

This is where a lot of my research has lead and, thankfully, is an area that Honeybee can help you out a lot with. EnergyPlus simulations can output information on outside building surface temperatures and these can be very helpful in helping get a sense of the radiant environment around individual buildings. Right now, I am focusing just on using this data to fully model the indoor environments of buildings as you see in this video:

https://www.youtube.com/watch?v=fNylb42FPIc&list=UUc6HWbF4UtdKd...

I have plans to move this methodology to the outdoors once I complete this initial application to the indoors. For now, you can use the "Surface result reader" and the "color surfaces based on EP result" components to get a sense of variation in the outside temperature of your buildings.

I hope that this helped,

-Chris

Permalink Reply by Theodoros Galanos on February 1, 2015 at 6:57am

Hey Chris,

Thank you so much for your educated answer. I will go over the links and suggestions you offered.

I have to admit that indeed the 4th option is closer to what I was thinking. My idea was on the one hand to model the impact, on the microclimate of an area, of the creation of an urban environment. And on the other hand, to use this model to understand it, identify measures to reduce it, and quantify those impacts.

I understand of course that a model is not necessary for all this. Most people know that more softscape, more vegetation, water bodies, reflective surfaces (to some extent), and more can help reducing UHI. What I want is to really understand the effect it has on the small, livable, scale (i.e. outside and around buildings, in pedestrian walkways, roads, squares, etc) of a community.

I would love to know more about your "moving out" phase of your research, as it is one of my main goals in upcoming projects. Let me know if I can help (or participate) in any way.

Thanks again for your answer! Good luck!

Kind regards,

Theodore.

Permalink Reply by JASON PRICE on May 9, 2015 at 4:24am