Radiant heating systems rely on the delivery of heat via a system located in the floor, or in some cases, ceiling or wall mounted panels. The delivery can be either via a hydronic system coupled to a boiler (or other source of hot water) or using electric radiant panels. In the case of radiant cooling systems, delivery is typically via a hydronic system that is supplied with chilled water from a chiller or other cooling source. One of the most important factors of a radiant cooling system design is the control of the chilled water temperature that is supplied to the system. If the chilled water temperature supplied results in the radiant delivery system surface temperature falling below the dewpoint in the space, condensation will occur on the surface. The result of this would be moisture on the floor or ceiling, depending upon the location of the delivery system. As such, the chilled water supplied to the radiant system will be maintained at a higher temperature than a conventional chilled water system. This higher chilled water temperature will need to be accounted for in the energy modeling as it will impact both the pumping energy use as well as the chiller energy use. "Radiant" heating or cooling systems that utilize concrete slabs may be very slow to react to load changes. Simulation programs should be chosen that account for this or these systems should only be modeled in spaces that will have very slow load changes. Since these systems rely upon the radiant delivery of heating and cooling, no fans are associated with the radiant component of the system. However, it is common that a fan is associated with the ventilation system. Modeling of the fan associated with the ventilation will depend upon how the ventilation system is configured. One approach is to utilize a Dedicated Outside Air System (DOAS). The modeling procedures for this type of system are described elsewhere in this chapter. Another approach used with radiant systems is to use a displacement ventilation system, in which case modeling of this component will follow procedures dictated elsewhere in this chapter. In some cases, radiant systems utilize natural ventilation as the source of outside air. These procedures are also addressed in this chapter. The baseline building does not have radiant heating or cooling.