Timmons Design Engineers - Innovation & Excellence in MEP & Sustainable Engineering Design

Radiant systems have successfully been used in Europe for more than 15 years as a standard practice of energy efficient cooling and heating. This technology is not well known or understood in the United States, here we will present you with information that explains the basics of the technology and the benefits over conventional forced air cooling and heating systems. TDE likes to incorporate radiant systems into our designs whenever feasible.

What is Radiation?
Radiation is a form of energy transfer. There are three basic methods of transforming heat, which are:
· Conduction: heat transfer between two bodies in physical contact with each other
· Convection: heat transfer between a moving fluid (water, air) and a solid body or another fluid.
· Radiation: heat transfer transmitted through space/air in all directions from a body with more energy to a body with less energy. If one object is warmer than another, the cooler object will absorb heat radiated from the warmer object, cooling one and warming the other. The Sun is a perfect example of radiant heat exchange; the radiant heat travels through cold space until it hits a surface. This is why people and objects feel much warmer when exposed to the sun than when they are shaded. Air is heated very little by radiant energy; it is heated primarily by coming in contact with objects heated by the Sun or other heat source. This same concept is at work in radiant heating and cooling systems.

Forced air conditioning systems’ main function is to cool the air inside of a room or zone, whereas radiant systems are primarily designed to cool the objects (including people) in a room by absorbing or transferring radiant energy. The cooling and heating medium for radiant systems is typically water that may be conditioned by using boilers, heat pumps, chillers, geothermal ground loops, solar thermal panels, etc. There are many advantages to radiant systems over forced air systems, which include:

Space saving
- Low floor-floor height requirements due to decreased ducting, conditioning units and fans between floors. This allows on average an extra 2 vertical feet of usable room space to be available.
- 70% reduction in duct shaft area.
- Ceiling plenum only requires 6-12 inches.
- Allows more freedom to design and create innovative spaces
Human comfort
- The body transmits heat by three methods:
(a) Radiating heat from the skin to cooler surrounding bodies or absorbing heat from warmer bodies
(b) Having cooler or warmer air pass over the skin and transfer heat by convection
(c) Evaporating moisture from breathing and perspiration
Heat exchange by radiation is perceived as the most comfortable method, the heat exchange rate is nearly doubled by radiant panels. Convection and evaporation rates are minimal factors compared to forced air systems, eliminating drafts, noise and greatly reducing perspiration.
- Better climate control
- The surfaces are cooled/heated evenly, the temperature is more evenly distributed
- Greater comfort of employees lead to better productivity, higher profits
Panels can blend in and be indistinguishable from standard ceiling panels
- Can be used for retrofit and historic renovations.
- High quality ceiling finish, high aesthetic appeal and replaces costs for ordinary ceiling panels.
Better air quality, utilizes 100% outside air which meets all ventilation requirements. Greatly reduces chances of sick building syndrome.



		Reduced noise since much less fan power is required. The radiant panel and floor systems themselves are virtually silent; the only noise is from small fans and air vents required for ventilation. Air is only used for ventilation and circulation comfort, no high velocity drafts. Very low maintenance, few moving parts Zoning flexibility, easier to add new zones Energy savings - Exchanges heat with water rather than air (a) Water has more than 4 times the heat absorption capacity of air by mass (b) It takes 3,480ft3 of air do cool the same amount of 1ft3 of water - When cooling, higher temperature settings can be used since the body perceives a higher level of comfort when radiating as opposed to exchanging heat with air. When heating, the same affect applies and the settings can be set higher. Particularly the head (which is most exposed to the panels) determine whether one feels warm or cold. - 30% less energy use than forced air systems - 75% reduced fan size Radiant systems are very helpful in achieving LEED credits. You can apply your radiant ceiling system to the following credits: - EA 1 Optimize Energy Performance - EQ P1 Minimum Air Quality Performance - EQ 2 Ventilation effectiveness - EQ 7 Thermal Comfort - Innovation credit – mechanical ceiling!


		Radiant cooling controls are designed to control both the room temperature and prevent condensation on the chilled ceiling panel or floor surface. A two-way valve is controlled to permit more or less water to flow through the system. This supply water is kept at a constant temperature. To prevent condensation buildup the supply valve is closed as soon as the temperature reaches dew point as measured by a humidity sensor. An additional method of avoiding condensation there is by conditioning the intake air through lowering the relative humidity and dropping the dew point temperature below the temperature of the chilled water pipes. Both temperature and humidity levels must be monitored to achieve this.


		Since radiant systems do not supply or return air to a room the only air provided is for required ventilation. To keep air quality at an acceptable level and remove humidity within the room a ventilation system must be installed to exchange the indoor air with fresh outside air. Since the air does not serve to condition the space so directly there is no need to handle the large volume flow of air typical of forced air systems and only enough air movement to provide ventilation is needed. There is no need to recirculate this air so it can be 100% outside air. Click below for more information on methods of providing radiant conditioning. Radiant Ceilings : Chilled Beams : Radiant Floors