This article appeared in Dialogue, December 2001, No. 54.
Mahadev Raman is a mechanical engineer and a principal in the New York office of Arup. He joined Arup in 1978 and later took a leading role in a number of prominent projects, such as the European Court of Human Rights in Strasbourg and the Kansai International Airport in Osaka. He has worked exclusively on multidisciplinary design teams directing the design of HVAC system on a wide range of projects throughout the world ensuring their integration and coordination with other disciplines. He has focused on the design of energy efficient buildings and has pioneered the use of sophisticated analytical techniques to improve the performance of low energy designs. His current projects include the Austrian Cultural Institute in New York, MIT student dormitory, and the Church of Year 2000 in Rome, Italy. In the following interview he talks about his career, projects, and various ideas about sustainable design.
MF I would like to begin by asking about your background. How did you become a mechanical engineer?
MR My parents were teachers in Zambia and that’s where I received my early education until the age of sixteen. During this time I was more interested in biological sciences than in physics. In the last year of junior high school I had a new biology teacher who somehow put me off the subject. It’s interesting how teachers can have these profound impacts.
So when I went to senior high school in England in 1974, I decided to study physics, chemistry and math. When I later chose to study engineering, I didn’t want to choose a specific branch and kept my education general for as long as possible. When I graduated from Durham University in 1978 with a degree in engineering it was a broad based degree – three parts mechanical, two parts structural and one part electrical. By then I knew I was leaning towards the mechanical discipline, but I wanted to keep my options open.
There was no pattern to the jobs I applied for after college - computer programming, gas turbine design, even bioengineering. I had no clear idea of what I wanted to do. During this time I came across an advertisement from Ove Arup & Partners in London looking for mechanical and electrical engineers to join their building engineering division. I applied for the job and had a lengthy interview with Keith Dawson. At the end of the interview he said, “It seems you don’t know that much about mechanical engineering for buildings.” I had to admit that I didn’t. He said, “I am going on vacation for two weeks. Go and find out about the subject and call me after I return.”
Keith directed me to the Building Bookshop in London where I found a book produced by the Building Research Establishment on building services engineering. As I went through the book I found that this was a field that actually spanned across a wide range of engineering subjects. I realized that if I pursued this profession, I could avoid specializing in some obscure and esoteric aspect of engineering. So when I spoke to Keith again, perhaps he detected some passion in my voice, he gave me a job. There was no premeditation, and here I am twenty-three years later still with the same firm!
MF What are the unique qualities of Arup that attracted you in the first place and have kept you there for your entire career?
MR I can’t compare Arup to any other firm as I have not worked anywhere else. One thing that struck me about Arup was the ‘intelligent’ atmosphere. You met a lot of bright and talented people and they were always ready to share their knowledge and experience.
I remember the very first assignment I had was to size a simple exhaust system in a shopping center. It took me an entire week to understand the issues and to produce anything useful. Every two minutes I would go to the senior project engineer and ask him a stupid question. At no time did he turn me away or criticize my lack of knowledge. The job I did in that one week, I could probably do it in fifteen minutes today.
What was wonderful about those early days was that I was given the time to learn the ropes in a very substantial way. Furthermore, many of the projects I worked on were architecturally interesting. As I was learning about building engineering, I was also having my eyes opened to the world of architecture.
MF What were some of the earlier projects that you worked on?
MR One of the earliest was Lloyds of London. From 1978, when I join the firm, to 1980 we developed all the main engineering concepts for the building. The Arup team was led by Tom Barker, a true visionary. Way back then he was already exploring ventilated façades and the use of thermal mass. I was pretty good at math and at developing numerical methods for thermal modeling. So there was Tom with the vision, and two or three senior engineers in charge of the mechanical engineering, while I tried to figure out how the unusual systems would perform and what the energy consumption of the building would be. That was my job.
MF The Lloyds building, the Pompidou Center, and some other buildings of that era all have exposed mechanical systems. Even though the technology is better now, there aren’t many new buildings like that. Is it simply a change in visual style or has the way we perceive technology changed?
MR Buildings with exposed systems represent a very specific form of expression which brings with it certain technical difficulties. In the early 80’s I worked on the PA Technology building in Princeton by Richard Rogers. Many years later I had a chance to talk to the Facilities Manager about how the building and its systems had weathered. While he didn’t seem to have any serious problems, he did admit that they had to adhere to a very strict maintenance regime to avoid deterioration. When you express the building systems, there are huge surface areas exposed to the weather, with lots of joints and penetrations where things could go wrong. During the design of the Lloyds building, an enormous amount of effort was put into the detailing of exposed systems to ensure their longevity. Nevertheless, water did subsequently get into certain places and there were a few corrosion problems. So I see three probable reasons why people don’t design such buildings anymore. Clearly, there is the element of architectural fashion. The second reason is the maintenance issue. Finally such buildings, when they are done well, tend to be expensive.
MF Can you talk about the use of the computer as a tool? How has it developed in your field?
MR Folklore has it that one of the earliest serious uses of a computer at Arup was in dealing with the complex geometry of the Sydney Opera House. When I joined Arup in 1978, we had a fairly sophisticated mainframe computer with early versions of thermal analysis programs. All the input at that time was done with punched cards and you were in deep trouble if the cards got mixed up!
In the workplace, slide rules were in use up to the mid 70’s when they started losing ground to early scientific calculators. In my second year at Arup, I remember spending half a month’s salary on a top-of-the-line TI programmable calculator – it had an amazing impact on my productivity. Today, two weeks of a young engineer’s salary would buy a fairly respectable PC and everyone has come to expect a powerful computer on each desk.
Certainly the advent of the computer now allows us to very quickly perform calculations that would have been all but impossible using manual techniques. For example, when doing an annual energy consumption calculation for a building, you have to perform a heat transfer calculation for every surface of the building for every hour of an entire year. There is no way you can do a calculation like that by hand within any reasonable time frame. It is interesting to note that in 1980 it took nearly a month to prepare the data and run our mainframe based energy program for the Lloyds building. Today we could do a more sophisticated analysis in a matter of days.
MF How significant are the improvements in computational techniques and how important is Computational Fluid Dynamics (CFD) that we now hear a lot about?
MR The interesting thing is that the fundamental equations that describe energy and fluid flows have been known for at least a century. The simplified calculation methods used to estimate, for example, heating and cooling loads in buildings have become more sophisticated with the advent of computers and there has been some improvement from the start of my career to now - but not a quantum improvement. Similarly, there has been some improvement in energy analysis techniques.
The big advances have taking place in computational fluid dynamics. Again, the equations have been around for a very long time. What has improved is our ability to do more and more calculations in less and less time. In a computational fluid dynamics model, as the mesh becomes finer, the results becomes more accurate. But the finer the mesh, the more computer power you require and the longer the model takes to converge on a result.
We started to do CFD work in a big way on the Kansai Airport project around 1989. At that time, there was an interesting coming together of two analytical techniques. One was the development by Michael Holmes of a powerful dynamic thermal modeling program, called ROOM, which we still use today. This program models all the heat transfers and radiant heat exchanges in a space providing a 24-hour profile of all surface temperatures. The ROOM program became the generator of boundary conditions for our CFD analysis work that was also being developed at that time. It is important to note that CFD analysis, without a rigorous examination of boundary conditions, will produce meaningless results. Without CFD, we could not have designed the macro jet system at Kansai with any degree of confidence.
MF Your recent project, the courthouse in Phoenix, Arizona, involved the use of sophisticated CFD analysis. How did the project come about? It seems strange, from an environmental perspective, to propose a glass box in a desert climate!
MR When we were introduced to this project, there was already a well developed set of schematic design drawings. It was presented as, “we want to build this fully glazed atrium in Phoenix. What can you suggest to make it work environmentally?” It was clear that any mechanical cooling system would be horrendously expensive and it was equally obvious that there was a great deal of potential for using evaporative cooling in that climate. Although the principle was simple, the challenge was, firstly, the scale of the installation and secondly, predicting its performance.
It took a lot of sophisticated CFD work and weather data analysis to determine exactly what conditions would be achievable. The results showed that evaporative cooling could achieve good comfort conditions for all but 17% of the time. Even when normal comfort conditions were not achievable, the atrium would still be a lot cooler than conditions outside. We went to a lot of trouble to present information to the Federal Judges and the General Services Administration (GSA) so that they wouldn’t have any false expectations. They agreed with the proposal on the basis that the atrium is a transient space. So the glass box could be achieved without incurring huge energy costs.
The system works by injecting high-pressure water from special nozzles at the top of the space. The water droplets are so fine that they evaporate almost instantaneously thereby creating a cascade of cooled air that descends to the atrium floor under gravity. In order for the nozzles to have a long life, the water needs to be extra clean. We therefore have a reverse osmosis plant that purifies the water.
The sad part of the story is that we were not given the commission to do either the detailed design of the system or the site supervision during construction. If we had remained involved, we would probably have spotted the fact that the water purification equipment that was installed had only a quarter of the capacity originally specified! So surely enough, during the last summer when there was a really hot period, the system regularly ran out of water two hours into the day. Repairs are now underway but this deficiency has had the effect of discrediting the entire concept. This is very frustrating and we have had to go to considerable trouble and expense to set the record straight.
MF Many glass buildings, especially in Europe, use a double skin façade. Is that a good way to design an energy efficient building?
MR Many architects will not like to hear my answer to this. Anybody who says that a fully glazed ventilated façade is the most energy efficient way to clad a building is just plain wrong!
It all depends on what you are trying to achieve. If the architectural objective is transparency with floor-to-ceiling glass, then the ventilated double façade is a good way to achieve reasonable energy efficiency. The system will arrest solar gain in the summer and create an insulating barrier during the winter. The double façade thereby allows a fully glazed building to have a relatively respectable thermal performance. However, the double façade does not perform any better than an opaque insulating wall with, say, 35% punched windows. In other words, you cannot justify the double façade on energy terms alone.
Don’t get me wrong, I love many of these glass buildings, and think that they look really great. However, you cannot say that they are better thermally and you definitely cannot say that the energy saved will pay back the additional capital cost within any reasonable time frame.
I will give you an example. We carried out a detailed investigation of the single glazed curtain wall of the United Nations Secretariat Building. We opened up many panels and, quite surprisingly, found the construction to be in immaculate condition - like the day it was built. The wall therefore did not need replacement due to physical deterioration. A little calculation showed that if you replaced the wall with another one with a much better thermal performance, the payback period would exceed 25 years. So the right thing to do was to just leave the existing wall.
Now that’s a very counter-intuitive conclusion - if you don’t need to change the façade for reasons of physical deterioration, you can’t justify changing to insulating glass based on energy savings alone. (Never mind going to a ventilated double façade.) This is just a reflection of how cheap energy is. If you make energy ten times more expensive, then the picture changes radically.
MF Many of these double façade buildings in Europe allow the use of natural ventilation. How much variation in temperature can a person take? Do you need a mechanical system as a back up?
MR This is actually a very complex issue that involves a number of different factors. The first thing to realize is the importance of climatic differences. Let’s just compare New York City with London. You look at the climate in New York and it is humid over a long period of the summer. In London, the temperature can get to quite high levels (not as high as in New York) but humidity is rarely a problem.
So, if you look at houses in the two cities, it is very rare that you will find any house in London with air conditioning. On the other hand, air conditioning is very common in the US and people feel they need it one way or another, even if it is just a window unit. Remember, natural ventilation cannot provide cooling. If the temperature outside the building is X, the temperature inside is X plus. Ventilation will not get the temperature to X minus. (However, when you have air movement over your body it increases evaporation and gives a cooling sensation. That’s how ceiling fans work.)
Another aspect is people’s expectations. In places like Germany and England, people have come to expect summer temperatures in their work place to be 26 to 28 Celsius. That’s not considered uncommon, and people deal with it. They don’t necessarily feel totally comfortable but such temperatures are expected, even in an air-conditioned buildings. In the US, on the other hand, people expect a temperature of 21 or 22 Celsius at all times. Because there is so much air conditioning about, with much of it poorly controlled, places are actually over-cooled. Overall in the US, people have become accustomed to high levels of cooling.
So, when you put these two factors together, a well designed, naturally ventilated building in England or Germany, with solar shading and thermal mass, can potentially do without mechanical cooling and stay within the elevated comfort temperatures that are locally accepted. If you put a group of Americans in that building, they will immediately complain. If you then transfer that building design to the US, you will find that there is nothing in the system that will deal with humidity.
One ‘holy grail’ in sustainable design is to find a passive way to dehumidify the air. It is the one process that, for now, has defied passive control and requires some kind of active system, and that usually means a refrigeration plant. There are times in New York when you can work with natural ventilation, but no matter how well you design the building, you can never eliminate the cooling system.
MF Given the difficulty in dealing with humidity, what are some ways for designers in humid climates to do a sustainable building?
MR ‘Sustainable’ is a difficult word because it means different things to different people. It also has broad ramifications well beyond mere energy conservation. With regard to the thermal performance of buildings, I like to think of sustainable design as an integrated process of ‘prevention’ and ‘cure’.
‘Prevention’ is exercised in the basic design of the building. You make the building perform as well as it possibly can without mechanical intervention. The ‘cure’ part is to provide minimal mechanical systems to deal with the peak periods when the building cannot cope on its own. So the problem with high humidity climates is that there will always be times when you need mechanical intervention. But, by judicious design, you can make those interventions as small as possible.
I don’t accept the notion that the use of a mechanical system automatically makes a building unsustainable. It is also very important to understand that sustainable design does not mean ‘one size fits all’. Different solutions are appropriate to different situations. The key is to examine the specifics of your site, climate and building program and to design something that is the best it can be inherently. Then put in minimal systems to deal with extreme conditions.
MF Thermally active slabs have been used a lot in European countries. Is it a good idea to use that system in a tropical environment?
MR Thermal mass will help you in any environment but it works best in a desert environment where you have huge differences between day and night temperatures, and no humidity problem. When we were doing a concept design for the Denver courthouse, we tried to persuade the client to eliminate the cooling system altogether by using passive thermal storage and harnessing the arid climatic condition at the site. We never quite got to that point, but it is nevertheless feasible, in those conditions, to use thermal storage - cool it at night and use it during the day.
For example, our San Francisco office designed a slab cooling system for the Gap headquarters building that reduces the size of the chiller by roughly ten percent. The energy saved is around 15 to 20 percent per year. So you get reductions in both capital and operating costs.
This approach probably works least well in a tropical climate with high levels of humidity and less variation in day and night temperature. You don’t want to flush the building with humid air, which can lead to all sorts of problems. However, you can run the cooling system at night, dehumidify the air and cool the building structure. The system will operate more efficiently at night, so there are some benefits but by no means as many as in the arid climate.
MF A sustainable building often seems to cost more than a normal building. While studies can be done to show that a sustainable building will have lower operating costs, often times the owners are reluctant to spend extra money in the beginning of the project. I wonder if there are some other ways to persuade owners to pay for a better building. Is it possible to argue that a sustainable building can increase productivity?
MR That’s another ‘holy grail’! The energy cost in a typical building is about one dollar per square foot. The average cost to employ someone, including overheads and benefits, is typically about 100,000 dollars per year. Since a person occupies about 200 square feet, the annual cost of an employee is about 500 dollar per square foot.
If you can achieve a one percent increase in productivity as a result of better design, that’s 5 dollars per square foot per year. You can see that the minute you can make a tangible relationship between productivity and the quality of the environment, you can generate a load of cash to put back into the building. This connection is very difficult to establish but there are some recorded cases.
Randolph Croxton designed a new daylit factory for Varifone adjacent to a conventional factory. The two buildings have the same kind of area and house similar activities. The old building is a dumb opaque shed with industrial lighting while the new building has a lot of daylight. The productivity in the day-lit space is much higher and people fall ill less. Apparently there is a long waiting list of people to move from the old factory to the new one. This implies that there is a productivity gain.
West Bend Mutual in Milwaukee built a new building with an under-floor air system and individual controls. They claim to have a measurable increase in productivity as a result of a system that helps individuals achieve a more comfortable environment.
There are some other studies that are shakier. One study I saw, for a commercial office building, concluded that people around the perimeter of the building were more productive than those in the center. They concluded that proximity to daylight was the deciding factor. However, it is usually the more motivated senior people, in most organizations, who are placed at the perimeter, so they had better be more productive than the lesser mortals in the center!! So is it really daylight or just the social architecture of the office arrangement? This is the problem with this entire subject area. It is very hard to do a controlled experiment and to get verifiable and repeatable results. People intuitively understand that being in a better environment makes you feel better and more productive. But it is very hard to put numbers to it. If you can make the connection, you can unlock a whole new area of funding for environmentally sound projects.
Having said all that, I do want to emphasize that I do not believe that there is a direct correlation between sustainability and higher cost. It is possible to achieve significant improvements even within normal cost constraints. I do however feel that the design professionals will need something like 15% more fees in order to deliver the better building. Some extra time will also be needed in the early stages to think things through and to provide integrated solutions.
MF Aside from cost, the benefits of an under floor system are well known. Why haven’t we seen more of them? Are they less flexible than a ceiling system?
MR To the contrary. I will use the Gap building again as an example. A cost-benefit analysis, based on a well-documented churn rate, was done during design. The study showed that the client would save enough money in their fit out costs to pay for the raised floor in about two to three years. In reality, the churn rate was much higher than anticipated and the payback period was actually only about six months. So they are definitely convinced that the under floor system is a more flexible approach. Also, it deals with variations in loads a bit easier. If you take an area that is an ordinary office and suddenly want to convert it to a conference room with higher occupancy, you can achieve that more easily with an under floor system. When you are dealing with an owner/occupier and program requirements are well defined, it is much easier to achieve the under floor system. If you are talking to a developer and he wants to meet the needs of a wide spectrum of tenants, he will go with the conventional overhead system, even in Europe. Often times, the developers want a raised floor but only for cables and not HVAC.
MF One element of sustainable design is to provide individual controls for occupants. Does it make it harder to design where there are more variable elements?
MR It is more an issue of cost rather than technology. Let’s take a very conventional and commercial variable volume system. It works by sending air out at a constant temperature. Within each space, there is a terminal device that adjusts the air flow rate to get the desired condition. The degree of control then simply depends on the size of your zones. If you go with a 500 square foot zone, you will have one large unit that creates an average condition for that area. If you decide to use the same infrastructure and give people their own control, you will design to have 100 square foot zones. Not surprisingly, a 100 square foot zone costs more than 1/5 of the cost of a 500 square foot zone.
MF Can you talk about the use of geothermal energy in buildings?
MR Geothermal is a much-misused term. If you think about getting energy from the ground, the classical geothermal system is what you have in Greenland. They actually harness hot springs that come out of the ground and use the hot water for heating.
Geothermal has, however, come to include a whole range of other technologies. One of them involves using the ground itself as a heat source by burying long lengths of tubing vertically or horizontally. The surfaces of the tubing exchange heat with the ground. In the winter you use them to draw heat out of the ground via a heat pump and in the summer you take the heat out of the building, through the heat pump back into the ground.
Another system uses ground water as in The European Court of Human Rights, by Richard Rogers, in Strasbourg. Water is drawn from an underground aquifer with a constant temperature of 13 degrees Celsius throughout the year. In the winter, it forms a very good heat source for heat pumps and in the summer, an efficient means of heat rejection. This system is quite prevalent in that region of France.
MF How much energy can a building generate and is it economical? For instance, photovoltaic cells generate some energy but seem to have long payback periods.
MR First, let me talk about how much energy one can generate. We did a number of studies to investigate this, with Kiss and Cathcart, which were published by the National Renewable Energy Laboratory. We came to the conclusion that, in most parts of the US, one square foot of horizontal, unshaded, photovoltaic panel can generate enough energy for one square foot of air conditioned space (including all requirements such as lighting and ventilation.) If you take a twenty-story building and cover the roof with photovoltaic panels, you can only generate 1/20 of the building’s energy requirements. So one of the main problems with PV’s is that you need a large area to generate the energy. The system will work well in a large, low-rise building like a convention center for example.
In New York, you get about 2300 hours of bright sunshine in a typical year. In most places in Europe, you get only around 1500 hours. The one-to-one area relationship therefore doesn’t work so well in Europe.
The biggest impediment to widespread PV use is probably the unit cost, which won’t come down until the production volume goes up. In a typical photovoltaic installation, where you might only care about the engineering and not the aesthetics, you can probably achieve systems that will pay for themselves in 15 to 20 years. If you want to achieve a more architecturally interesting installation, the payback period goes up to 25 to 50 years. Therefore, PV’s are not really viable in that regard. This is also a function of energy costs, which are very cheap in the U.S. but more expensive in Europe. Even though there is less sunshine in Europe, the high energy costs there make PV’s a little more viable. Nevertheless, you are still looking at long payback periods. Clients with short horizons will not necessary accept this technology.
If the photovoltaic industry is encouraged with more incentives, then they can build volume. However, volume is increasing in any case and I look forward to a time when the cost is going to come down to more reasonable levels.
MF With the advent of sustainable design, we are seeing many references to traditional models. Are these models useful for modern buildings?
MR I would worry about blindly using these models. Most of these models yield their secrets to analysis. It’s not as if there is some magical thing at work and nobody knows why. You can certainly get a lot of insights by looking at these models. But it is important to understand how they function before you apply them to a modern building. For example, the heat generated by computers in buildings is much higher than it used to be. 20 years ago, you would allow for 5 watts per square meter of heat generated by equipment. By the 80’s that had gone up to 10, and now you are looking at 15 or 20W/m2. These numbers may go down in the future because the equipment will get more efficient. Nevertheless, they can make the difference between success and failure in passive systems. Additional factors like this are clearly not accounted for in the evolution of traditional models.
MF You spoke about some holy grails in mechanical engineering. What are some other holy grails? What are some of the researches being done in your firm and in your field? What are some of the future trends in mechanical engineering?
MR There is research going on in many places. Although we have an R&D group, it is more focused on applications rather than fundamental research. I am probably not the best person to comment on the state of academic inquiry. There is a lot of work going on at Carnegie Mellon to find the relationship between productivity and the environment.
On the issue of passive dehumidification, there is a lot of work being done on desiccants. The problem with desiccants is you have to transport them. You have a place where they absorb moisture and another place where they give up moisture. To achieve that with a passive system is very difficult.
Photovoltaics will become a very important feature of buildings and much research is being done to improve conversion efficiency. You can already see that in Germany with thousands of square meters of photovoltaic panels being installed in various buildings. It is only a matter of time before it catches on in other places, including the US. The energy problems in California have put more focus on the issue of renewable energy.
I do want to emphasize one point in this regard. The current sustainable design movement is quite different from the energy conservation movement of the 70’s. At that time, it was very clearly all about energy and in the process, people and their needs were forgotten. All sorts of things were done – horrible dark buildings, small windows, reduced fresh air ventilation, and reduced comfort levels. The measures saved energy but were somewhat anti-human; the people that occupy buildings became rather incidental to the process.
This is quite contrary to today’s approach where we place the occupants at the center of our considerations; and not just the current occupants but future generations as well. We are no longer talking about making just minimum energy buildings but are seeking to create comfortable, healthy, safe buildings with good environments and minimal ecological impacts.
Some of the good ideas that came out of the 70’s, (you know it wasn’t all bad,) have been enshrined in codes and have become normal practice. Nobody thinks about them as specific energy saving measures any more because they have become the norm.
I am therefore hopeful that in another decade or two, many of the approaches that we are developing now, with regard to good and sustainable building practice, will be similarly enshrined in daily life and we can all forget about the term “sustainability” because it will be the normal way we do things.
The interview was held on October 12, 2001 in New York City.