Stage 1: New Evaluator Nodes

Estimating Embodied Carbon

I thought it would be nice to have a rough estimate of the embodied carbon, so I found a study on high-rise buildings that found the median kgCO2eq per area. My logic allows you to test 3 structural system options: composite, reinforced concrete, or steel.

Note: the values shown below are on a per meter squared basis and I converted to a per sf basis before putting it into my dynamo logic, which is why the values are different.

Research link: A comparative analysis of embodied carbon in high-rise buildings regarding different design parameters - ScienceDirect

Node Logic

This logic built on the square footage custom node logic.

Estimating EUI for Net Zero

I used the solar insolation on the building to estimate the energy generated by PV panels and then took the corresponding floor area to calculate an EUI equivalent metric. This metric estimates what the target EUI for the building should be to achieve net zero energy.

Node Logic

This logic built on the solar insolation custom node logic. I added a reasonable panel efficiency of 20% and then figured I would be conservative on how much of the envelope was actually suitable for a solar facade and said it would only be 50%. Then dividing by 1000 to convert W to kW and dividing by the square footage. The final output is in units of kWh/sf-year.

Results

Points to Ponder

Do the new evaluation metrics that you’ve designed capture the meaningful differences between the building form alternatives?

The new metrics give an overall sense of the carbon that the building will use in materials and the opportunities for savings using solar. However, both metrics were built using oversimplified logic. Ideally, I would want more detail into the embodied carbon based with a more granular definition of materials. The PV offset is also sort of assuming that the building has sufficient storage because I am not looking at the daily insolation vs. supply curve.

What other metrics would be useful to compute to help understand and make the case for which alternatives are truly better than others?

• Cost
• Always an important factor!
• Incorporating the solar facade into the cost would also be ideal.
• Energy usage
• To compare to how much is offset by PV
• Higher insolation might give higher energy collected by PVs, but could also make the building use more energy if there is not proper insulation, too much glazing, etc.

Stage 2

Both of my metrics are sort of related to carbon emissions. One is on the operational side, and one is on the embodied side. I figured I should convert the second metric into terms of kgCO2eq as well. To do this, I looked at the carbon intensity of the grid in the UAE. I am assuming that the grid will be 100% renewable by 2050 (per UAE’s net zero plan), so I’m only considering the operational carbon for 26 years. I’m also assuming a simple linear decline to zero from the current carbon intensity over time. The second metric is in terms of carbon savings that would be avoided by the PVs. So, my overall metric is for carbon savings, so embodied carbon will be subtracted. I also multiplied the embodied carbon by 10 to give it a higher weight to give present day carbon a higher value than future carbon.

The top performing designs based on my metrics are highlighted at the top in blue. The sheet is sorted by performance. Interestingly, twist angle had more of an impact on the metric than height. I think that’s because embodied carbon was a couple of orders of magnitude smaller than the savings from PV, even for just one year. UAE’s grid is fairly carbon intensive at the moment. The more extreme twist angles (0,10,70,80,90) tended to perform the worst. It looks like between 20-40 degrees was the optimal twist for this tower to maximize insolation.

Points to Ponder

What propelled the recommended alternative to the top of the list? Explain your reasoning -- include a brief analysis of why this alternative rose to the top of the list and why you consider it to be the best option.

I think the best option would be the third option (500’ tall, 40 degree twist angle) because it is on the mid-low end of embodied carbon, at the top of carbon saved over a single year, and a lifetime, and it meets the desired square footage, whereas the first and second options are a little too small. It is on the lower end of the square footage range, which helps keep the embodied carbon lower because it requires less materials. It is also on the taller side, which creates more area for sun to hit.

Are there important nuances or tradeoffs that got lost is the single evaluation?

There wasn’t a great way for me to actually compare the two metrics even though I got them to the same units because they were so different in value. Embodied carbon is a one-time thing whereas operational carbon is over time. I couldn’t fully incorporate how the grid will become cleaner over time. It is also hard to value present vs future carbon. In some ways, the carbon emitted now is a lot more important because we are trying to stay below 1.5 degrees Celsius. But, we also need to stay under that in the future, so it is very hard to quantify.