Already a core part of CBE’s research team, Carlos Duarte completed his PhD dissertation earlier this year and has joined CBE as a post-doctoral researcher. We caught up with him via Zoom while the campus is still closed due to the ongoing concerns of Covid-19.

What drew you to doing a PhD in building science at Berkeley?

I was an undergraduate in mechanical engineering at the University of Idaho, and my senior year I took a class on building science and learned about things like the relationship between buildings and greenhouse gas emissions. There was a call for graduate student researchers for the Integrated Design Lab (IDL) there. Usually the GSRs there were from architecture, I was the first ME student to work there. My advisor liked my research and suggested that I do a PhD program. I learned I could use many methods, and also do projects in the field. This was interesting to me as I like to work with my hands too. I was happy to land at one of the top universities in this area, and to work with Berkeley’s world-class researchers.

Narrowing down a dissertation topic can be challenging. How did you decide on yours?

While I was at IDL I started looking into cooling loads, how different components affect it, and thermal mass was an interesting part. At Berkeley I was working with Paul [Raftery] and Stefano [Schiavon] on the large radiant systems research project, looking at the impact of high thermal mass. I saw a lot of potential to do advanced controls studies, to reduce energy and GHGs.

It helps to have funding behind your research too.

I had a lot of interest in this topic beyond the funding, the interesting part for me was how to use thermal mass and controls to get rid of the chiller, and rely only on evaporative cooling. We learned that with even high thermal mass, people are sizing these systems the same as they do for air systems. I co-authored a study to create a new design methodology and to reduce the cooling plant size. We developed new control ideas and tested them in field studies in Berkeley and Sacramento, and eventually we learned these systems can operate at any time.

This means you can shift the cooling to any time of day? That is a huge benefit considering the emerging importance of load shifting. 

Yes, we tested by cooling only at evening and night, it turned out to be better than the baseline control approach. It shows these systems are also resilient. At the Sacramento site there was an equipment failure, and we saw from the data visualizations that no cooled water was going to the slab. We told the operators about the problem, and they saw it was from a failed variable frequency drive. For over a week it was not working. This was in middle of summer with temperatures over 90 degrees, but the temperature inside did not shoot up, it just increased slowly, and even without cooling people were not complaining.

You created a new design tool and used feedback from CBE’s industry partners. How did you tailor this tool for expected users? 

This design tool, which we call the RadTool, was an important product from this research. First, we simply incorporated ISO standards to determine the cooling capacity, this was limited because it only takes into account the steady state conditions. We included this first as people are familiar with that, and we standardized it which provides a big productivity benefit.

I understand that creating the tool required millions of energy simulations, which then had to be integrated into it.

With EnergyPlus there is no easy way to create, run, and post-process multiple simulations in parallel. I wrote a script that does all these things. It was actually more than two million simulations, so I rented a virtual machine from Amazon with 70 CPUs.

The industry consortium is a unique aspect of CBE’s organization. How have you worked with the CBE partners?

They were excited about the standard tool, it’s simple enough you can use it with a phone, they liked the interface and output. However, for the transient tool they were pleased to see how you can shift time of day, how the operative temperature reacts, this shows the benefits these systems offer. We have a web tracking tool that tells me how people are using the tool, and the use of transient tool is increasing. It is being used all over the world, by hundreds of people.

It must be satisfying to have this work being widely used. What is the next big project you will be working on?

I will working with Paul and researchers at LBNL on the Brick project. We will be working to standardize the descriptions of data points and equipment. We hope this will help building operators to get actionable information. There is so much data available from buildings, but not many people are taking advantage of it.

This seems like a huge challenge. Is there a disconnect between the complexity of buildings, and the capabilities of facility managers?

Managers don’t have the time to do data analysis, they just want to know if things are working. I had an opportunity to work with the manager of the David Brower Center in Berkeley. I would shadow him, for example when a broken VFD needed replacement. Another time a conference was going on and the room felt like being inside a refrigerator, so he called me to see if I had any suggestions, and we did troubleshooting using the BMS while the conference was going on. It didn’t work, so the controls vendor came in and found that wires were switched, the heat pump was cooling beyond the setpoint. I guess that is why we have commissioning, but things still get missed.

What are your next goals for your work at CBE?

I would like to become a principal investigator and manage my own projects, so next I want to get more experience working on proposal writing. I had my first experience was writing an ASHRAE proposal, and although we scored highest, we did not win it because the award is based on dollars per point. But it was still good experience writing the proposal.

How are you and your family managing working during the pandemic? I know you like cooking, so are you doing more of that these days?

At first, trying to write my dissertation at home with a two-year-old was overwhelming, my son wants attention and the downstairs neighbors would complain about him running around. So my wife took him to her parents’ house in Idaho, this helped for couple of months. We don’t really go out to eat much, we take turns cooking. I have been told my cooking is good, and I once considered pursuing being a chef if the engineering didn’t work out!

Share This