Fraunhofer CSE’s Building Technology Showcase is a far-reaching, energy-efficient retrofit of a 100-year-old historic structure in Boston’s Innovation District. In this new series, we look ‘under the hood’ to explore some of the systems and technologies driving this project.
If you are truly serious about designing an energy-efficient building, how you heat and cool that building is a crucial factor in achieving that goal. A recent report by the International Energy Agency (IEA) estimated that heating, cooling, and hot water accounted for about half of worldwide building energy consumption. Introducing low-carbon or energy-efficient heating and cooling solutions in new buildings and building retrofits could potentially eliminate up to 2 billion metric tons of global CO2 emissions by 2050, saving the equivalent of over 5.2 billion barrels of oil.
With this in mind, the cooling and ventilation system in Fraunhofer CSE’s new Building Technology Showcase cuts energy consumption in three key ways:
1. Using Demand Controlled Ventilation to gauge building occupancy and reduce the amount of air drawn into the building for ventilation purposes accordingly.
2. Reducing the Amount of Cooling Needed by pre-conditioning air before it enters the building, drawing on “free” cooling sources like natural ventilation, and using more efficient lighting that gives off less heat.
3. Using More Efficient Cooling Systems that require less energy to create a comfortable environment.
To achieve this, the Showcase takes advantage of a number of different technologies, ranging from the established to the cutting-edge.
Ventilation systems draw outdoor air (OA) into the building, cool or heat it, and circulate it to where it is needed. The greater the amount of OA drawn in, the harder the systems have to work to condition that air, and the more energy is consumed. In the Building Technology Showcase, the amount of air drawn in is regulated by demand-controlled ventilation (DCV). This system uses building management tools provided by Siemens to measure CO2 levels within the building; based on this information, it estimates how many occupants are currently in the building and adjusts OA intake accordingly.
That adjustment is made possible by variable frequency drives donated by Yaskawa and Taco; these allow system components such as pumps and fans to run slower or faster depending on current loads, rather than restricting them to a single fixed speed. This creates substantial energy savings throughout the building.
Cool Roof Membranes
Cool roofs use solar-reflective surfaces to reduce the amount of heat a building gains from exposure to sunlight. This further cuts the need for air conditioning, and has other advantages as well: reducing the roof’s temperature can increase its durability and reduce surrounding air temperatures, which improves air quality and slows the formation of smog. Best of all, cool roofs are cost-competitive compared to their conventional counterparts.
The Building Technology Showcase uses cool roof membranes donated by the Cooley Group.
Energy Recovery Ventilation
Before air enters the building proper, it passes through an energy recovery ventilation system (ERV). The ERV pre-conditions air by running it through a heat exchanger, a piece of equipment that exchanges heat and moisture between the outdoor air drawn into the building and the outgoing air being exhausted from it. This cools the incoming air and can also dehumidify it, lowering the perceived temperature in the building. The end effect not only saves energy, but can also allow heating and cooling equipment to be downsized, reducing building costs.
Mixed-Mode Ventilation System
Parts of the Building Technology Showcase support mixed-mode ventilation, which combines natural sources of ventilation like open office windows with mechanical ventilation systems for maximum effectiveness. This offers the best of both worlds: natural ventilation can provide a certain level of “free cooling” by using outdoor air, not chillers and air conditioners, to cool the space, while the mechanical ventilation ensures that there is sufficient airflow to maximize this free cooling effect and supplements it as needed.
A lot of the cooling we use in the Building Technology Showcase is hydronic, meaning it’s distributed using water rather than air. There are many advantages to this approach in terms of energy consumption, as water has a much higher volumetric specific heat: in practical terms, you can move in the same amount of heat in a 1″ water pipe as you would in an 18″ air duct:
A hydronic system not only moves the same amount of heat or “cool” as an air-based system at a lower energy cost, but takes up significantly less space in the building. Some hydronic systems also operate at a higher temperature than their air-based counterparts, which improves chiller efficiency and further reduces energy usage. Finally, there are potential benefits in terms of occupant comfort, as hydronic equipment can be quieter than air-based ventilation.
Chilled Beams and Sails
Active chilled beams and sails donated by Price Industries form a major part of the building’s hydronic cooling system. They are suspended above CSE’s offices and laboratories, delivering conditioned outdoor air to our work spaces. Though both devices use water to provide cooling, they work in notably different ways. With active chilled beams, outdoor air is delivered to the beam through a duct system, passes over a water-cooled coil, and is chilled.
Chilled sails, also known as radiant chilled panels, are cooled with water to allow them to absorb heat from the surrounding environment. Additional cooling takes place as the sails transfer heat to floor-level objects via natural convection. Both systems deliver the same levels of occupant comfort as a conventional air conditioning unit at a substantially lower energy cost.
The Showcase also features an air-based displacement ventilation system provided by Price. A traditional air conditioner blows cold air at high speeds that mixes with warmer air throughout the space to lower the overall room temperature. The displacement ventilation system supplies cooled air at much lower speeds from vents at ground level. As that air comes into contact with heat sources, such as people or equipment, it warms and rises, drawing in cooler air.
The rising air not only cools the room’s occupants, but also carries away air contaminants, increasing air quality. Slower air speeds and pressure drops also mean lower energy consumption from ventilation.
While these are some of the most prominent energy efficiency measures in the Building Technology Showcase, there are many other donated partner technologies that contribute to heating and cooling in the building. These include pumps and equipment provided by Taco, an evaporative cooling tower furnished by the Baltimore Air Coil Company, an energy-efficient Multistack MagLev Drive chiller, and a Dolphin WaterCare water treatment unit from the Clearwater Systems Corporation.