Take a load off

MEP Middle East speaks to Scott Wilson associate director: building services Cathy Crocker.

The “huge proportion” of the electrical load consumed by air-con has resulted in a largescale focus on efficiency measures to try and reduce this consumption. “Over the last eight to ten years, developers have focused on how we can reduce the electrical consumption for cooling. A district cooling solution, in the correct application, with the correct design, can consume up to 55% less energy than the equivalent standalone cooling system,” is Crocker’s main argument.

However, it is also important to try and reduce energy consumption at the source, which means the buildings themselves. This, in turn, means that building services designers play a critical role from very early on. “Basically site selection and the outline design stage are, in my opinion, the key time for the design team to get together to lay a good foundation for a building design.

“This is the time at which you can get the building orientation right, the building form and the building fabric. These three elements have a huge impact on the energy consumption of a building throughout its life. As we move on through the design stage into detailed design and construction, obviously the ability to change the building design diminishes.

Change

“No one will thank a designer, after a detailed design, for suggesting a change in orientation, even if it does bring about a huge reduction in cooling load,” argues Crocker. “Clients, engineers, architects and sustainability consultants really need to get together from day one to agree on a good methodology for the design of a building or the design of a site, so they have a good foundation for an energy-efficient solution.” What elements need to be taken into account in the early design stages? “Building orientation is obviously the key to reducing energy consumption,” points out Crocker. “Here in Dubai it is the early sun in the morning and the late sun in the evening that has the ability to penetrate deepest into the building, and these are the areas we need to concentrate on. The overhead sun, while it has a strong irradiation, does not penetrate as far because it is higher overhead.”

Crocker refers to a project in Dubai where Scott Wilson worked with the architects to come up with a self-shading solution. The building comprised three wings, and to protect the building against the low morning and evening sunshine, a heavyweight, opaque façade was applied to the east and west. “This fairly simple approach had a huge effect on the heat gain, so the building did not suffer from high temperatures in the morning and evening, and we could really drive down the cooling loads,” explains Crocker.

The next critical element for the design to consider is the building fabric. “If we can get the correct building fabric in terms of thermal mass and UV value, we can dramatically reduce the peak cooling load. This, in turn, will drive down the energy consumption and size of equipment,” says Crocker. A simple reduction in a building fabric U value from .45 to .35, applied throughout an entire building, can have a huge and incremental impact on the overall structure.

“Another element which I think is very important for designers to consider is infiltration – the unwanted passage of air in each building due to external pressures. We need to make sure that buildings are well-sealed so that the hot external air does not come into our building and add to the cooling load. This is a design issue, and also a site issue, to make sure that the buildings are detailed and constructed correctly.

“If we address the U values, the thermal mass and the infiltration, I say we can achieve a minimum 30% reduction in peak load. Over recent years, building services designers in the UAE have become more familiar with energy-efficiency measures. Variable speed drives, heat recovery and other measures are being implemented more and more into buildings now as a matter of course, which is great for energy consumption,” says Crocker.

She says that Scott Wilson’s favoured design approach, wherever possible, is deemed ‘mix match’. “In essence it just means turning off the air-con when you do not need it. You have to have a building that is designed correctly to enable natural ventilation – that is, opening windows and a shallow-plan floor plate. In certain periods of the year in Dubai, we do have the capability of turning the air-con off completely.

“The best way to reduce energy use is to turn off the system completely,” Crocker says simply. She acknowledges that this can be problematic in terms of dust and noise, but these issues can be addressed successfully at the design stage. “For residential buildings or leisure facilities, it is very important for us to be able to design buildings so they can be ventilated naturally in winter, as that will save a huge amount of energy. Of course, during the hottest summer period we do need to have air-con, so that will always need to be factored in.

“Another consideration is really to think about increasing the setpoint of the air-con. Just by raising the setpoint from 21°C in summer up to 25°C you almost halve your MW/h of cooling consumption,” argues Crocker. Similarly, the design process also needs to take daylighting into account. “Thermal analysis allows us to experiment with different window designs to ensure we get the correct balance between window size and minimising solar gain. It is a bit of a fine balance because obviously we do not want to introduce too much heat, but we also need to ensure that areas are well lit through natural means wherever possible.”

So what does all this boil down to? Do all the ‘green’ platitudes translate easily into what Crocker terms the ‘construction reality’? “I think it is all very well designing a good building and having good intentions, but we need to make sure this is followed through into construction. Here in the Middle East, some buildings are well built, and some are not. As a design team it is our responsibility to work together so that the intent at the design stage is worked through into installation.

“A key area we need to work harder on I think is commissioning, putting the building to use and making sure it is up and running correctly before it is handed over to the client. If the building is not set up correctly at hand-over, then the client/operator can never be expected to run the building correctly.” This means proper facilities management is equally important. “Again, buildings do not run themselves. We need to ensure the equipment is maintained and working at good efficiency throughout its life.

“An interesting debate in the UK recently is energy certification of buildings. A number of public buildings are getting a rating from ‘A’ to ‘F’, which informs the public at large and the occupier how well the building is performing. I think it will be an interesting analysis in this part of the world to begin considering some form of energy certification,” says Crocker.

How does the design phase interface with district cooling, for example, in terms of energy efficiency? “District cooling has been a popular way of providing cooling to large developments and large areas. The way we approach district cooling systems is, first of all, to take a good long look at the site, at the buildings on the site, and how they will be used. Typically, we would not necessarily advocate a district cooling solution for a purely low-rise development, for example, as it might not be financially viable to do so.

Configuration

“When we work out a district cooling network we look at the best configuration, which is obviously informed by the site phasing, the load profile and then the remote station size. And that, in turn, generates a footprint area for the district cooling plant. The district cooling plant size is generated purely by the load it carries.

“So to return to my earlier point: if we can achieve a 30% reduction in energy use through purely building measures, we can in turn reduce district cooling plant sizes, whereby you can service an increased area through the same plant. Our aim is to really try and demonstrate how interlinked all these elements are. If we can work very hard on the building systems, we can influence the larger utilities infrastructure.

“In conclusion, I believe it is very important for designers to work very hard from day one of design to reduce the electrical load at source. That is the most important step we can take as designers. We need to incorporate passive design measures such as orientation, shading and daylighting, and active design measures such as mixed-mode ventilation and even turning off the air-con and raising the setpoints. That, in turn, will provide benefits to the clients and developers through releasing commercial space, reducing energy consumption and, of course, reducing capital and running costs,” says Crocker.