Ventilation

Radiant systems provide sensible cooling or heating only. Therefore, the ventilation requirement and latent load must still be met by an air delivery system. The traditional method of supplying air to ventilated spaces is known as mixed flow ventilation. This is a system in which cool air is blown in through the ceiling or wall and dilutes the room air in an attempt to provide an even temperature and contaminant level through the space. The flow is driven by the inertia of the supply air. The volume of the air supplied for mixed flow ventilation is calculated proportionally to the supply air and room air temperature.

An alternative solution is displacement ventilation, which coupled with radiant technology, represents a promising integrated approach that combines the energy efficiency of both sub-systems with the opportunity for strong ventilation performance. Displacement ventilation is an air distribution technology that introduces cool air into a zone at low velocity, usually also at a low level. Buoyancy forces ensure that this supply air pools near the floor level, allowing it to be carried up into the thermal plumes that are formed by heat sources. Research indicates that displacement ventilation is effective at delivering fresh air to occupants and removing many of the contaminants associated with heat sources, while creating a comfortable environment that is less subject to drafts. In addition to higher indoor air quality, displacement ventilation offers the benefit of flexibility. As load distribution changes within the space, a displacement system will be able to compensate. For example, if the space was designed to have a fairly even load distribution and now has the loads concentrated to one side, the system is able to compensate as the buoyant forces drive the supply system and will draw the supply air towards the loads.

Displacement systems present many potential opportunities for energy savings. The lower pressure drop associated with displacement ventilation outlets and the corresponding selection of smaller fan components may allow for a reduction in fan energy. The supply air temperature is typically higher for displacement systems than for overhead mixing systems, and can lead to free cooling from increased economizer hours. Combined with a higher return temperature than overhead systems, the warmer supply temperature of displacement ventilation systems can cause an increase in chiller efficiency. Due to high ventilation effectiveness, the amount of outdoor air that must be conditioned can also be decreased when compared with a mixing system. This is especially significant in humid climates, where dehumidification of outdoor air is a significant cost. It is also worth noting that green building rating systems, such as LEED and Green Globes have credits that are applicable to displacement ventilation systems.

As sustainable construction increasingly focuses on curtailing rising energy costs and improving life-cycle cost, natural ventilation systems are increasingly employed to leverage freely available resources such as wind and outdoor air to satisfy cooling loads and provide occupant comfort. In its most basic form, natural ventilation provides openings in the building façade to allow fresh outdoor air in one area of the building and out another. As the fresh outdoor air passes through, heat is removed and ventilation is provided. Designers should note, however, that this technology is only appropriate where climatic conditions allow. In the right situations, the use of mechanical heating and cooling in combination with natural ventilation, as a hybrid or mixed mode system, can extend the acceptable climate conditions where natural ventilation can be effectively applied to utilize free cooling for a large portion of the year.

Computational Fluid Dynamics (CFD) Modeling—Validating Design Before Construction

CFD modeling is a valuable analysis tool that allows designers to evaluate the performance of a system before construction begins. It is particularly helpful in solving variables associated with chilled sails such as the temperature profile and air velocity along with other various thermal comfort indices. In addition to saving time and money, design options can be evaluated quickly in terms of air quality, thermal comfort, and other parameters. CFD can also help earn LEED credits (Credit 7.1). Typically, results are presented in easily comprehensible formats, using either 2D contour plots, 3D iso-volumes or flow streamlines. A contour plot, for example, can show the variation of a variable such as velocity or temperature on a 2D plane in the space. Variable values are assigned different colors within a given range, facilitating visualization of results. An iso-volume highlights a volume inside the space where a specific variable is above or below a certain value—a visual that is valuable in understanding draft discomfort in the indoor environment. Image courtesy of Price Industries

 

Involving the Manufacturer Early On

Architects are increasingly finding that a supplier's involvement with integrated design can offer real value. In today's construction market, designers are continually pushing the boundaries of building performance, integration, and differentiation. When evaluating design options against these goals, the supplier can provide guidance as to how a design will rate in terms of performance (aesthetic, lighting, thermal, acoustic, etc.), cost, and development time. Additionally, it is likely that a supplier has industry partners that can simplify coordination efforts or, at minimum, suggest types of integration or coordination that have worked well in the past.

Ultimately, the successful realization of the project will rest on the management, contracting, and supply teams. The role of the supplier in the design phase is to offer guidance on performance, finishes, coordination, and manufacturability. This often includes the facilitation of testing, aesthetic and performance mockups, and prototype development. In more complex cases, this information is invaluable to designers trying to identify options that will meet the design intent, while not jeopardizing schedule or comfort. Close collaboration with the manufacturer can facilitate interesting, innovative options that the team may have discounted as overly complex or impractical. Conversely, the manufacturer can quickly analyze designs that may pose serious challenges and provide feasible alternatives.

Radiant Heating and Cooling: A Smart, Stylish Solution

Coupled with the right ventilation solution, radiant heating and cooling can lead to a very efficient mechanical system. The technology has been used in Europe for many years, and designers in North America are increasingly recognizing radiant systems as a way to save on energy costs, increase occupant comfort, and enhance the architectural appeal of interior spaces.

 

ENDNOTES
1	Corina Stetiu, “Energy and Peak Power Savings Potential of Radiant Cooling Systems in U.S. Commercial Buildings,” Energy and Buildings, v. 30, no. 2 (1999).

 

Price Industries is the leading manufacturer of air distribution products in the North American market, and works to bring about the vision of the design community by collaborating on high-quality, high-performing, and customizable air distribution solutions. www.price-hvac.com