Engineering Design - Radiant Cooling

     Radiant cooling system, like radiant heating, obeys the same physical laws of radiant energy
transfer. The difference is that when a space is radiantly cooled, the radiant surface is lowered
to a temperature below that of other surfaces in the room. The radiant ceiling is absorbing radiant
energy from surroundings and occupants that are warmer than the ceiling. The radiant cooling system
is to other air-water system in the arrangements of the system components. Room thermal conditions
are maintained primarily by direct transfer of radiant energy, rather than by convection cooling.
Water circulating through the radiant panels can provide all the heating and most of the sensible
cooling. Air supplied to the space provides ventilation and dehumidification.

      The air handling equipment will be appreciably smaller than if an air cooling system were used alone,
because the radiant cooling system will remove a very high percentage of the sensible heat from a
space. The air flow into a space can, be substantially lower than if the building were entirely air
cooled, thus greatly reducing cold drafts which lead to discomfort. People under a cooled
radiant ceiling radiate energy to the ceiling, losing heat in a more comfortable manner than
blowing cold air across them.

The radiant ceiling will carry away, by conduction and convection, a considerable percentage of
the electric light heat load.

Principal advantages of radiant cooling systems are:

1.) Comfort levels are better than other conditioning systems because radiant loads are treated
      directly and air circulation in a space is at normal ventilation levels.

2.) No mechanical equipment is required on the outside walls improving the wall and floor space.

3.) All pumps, fans, and filters are centrally located, simplifying maintenance and operation.

4.) No space requirement in the mechanical equipment room. This feature is especially important
      in applications where space is at a premium, where cleanliness is essential, or where
      dictated by legal requirements (hospital patient rooms).

5.) Cooling and heating can be simultaneous, without central zone control or seasonal changeover,
      when four-pipe systems are used.

6.) Supply air quantities usually do not exceed those required for ventilation and dehumidification.

7.) Draperies and curtains can be installed at the outside wall without interfering with the
      cooling system.

8.) The modular panel provides flexibility to meet changes in partitioning.

9.) The 100% outdoor air system may be installed with less severe penalties in terms
      of refrigeration load because of reduced air quantities.

10.) A common central air system can serve both the inferior perimeter zones.

11.) Wet surface cooling coils are eliminated from the occupied space, reducing the
      potential for septic contamination.

12.) The panel system can use the automatic sprinkler system piping.

13.) Radiant cooling and minimum supply air quantities provide a draft-free environment.

14.) Noise associated with fan coil or induction units is eliminated.

     Radiant cooling systems are similar to other air-water systems in the arrangement
of the system components. Room thermal conditions are maintained primarily by direct
transfer of radiant energy, rather than by convection cooling. The room cooling loads are
calculated in the convectional manner. Manufacturer’s ratings generally are for total
performance and can be applied directly to the room load. The amount of energy required to
remove heat hydronically is approximately ten percent less than required with an air system.
Also, design temperatures can be as much as five to six degrees higher for cooling than with a
convective system due to the system uniformly controlling the rate of energy transfer among
objects within the space.

     Airborne nosocomial infections is the spreading of infectious bacteria and fungi which develops
in re-circulated air systems nooks and crannies and is redistributed into hospital rooms. Many
infections and even deaths have been traced to fungi and other micro-organisms which find an ideal
breeding place in patient-room units. Hospital design has been influenced by many recent developments
which focus on the necessity for basing selection of hospital mechanical equipment on the physical
well-being of the patient and the economic well-being of the hospital. The cooling source for a
radiant panel cooling system is completely concealed in the ceiling plenum. Since there is no
mechanical equipment associated with a radiant panel cooling system in the patient room, there are no
areas to support the growth of bacteria and fungi and no nooks and crannies in the system components
to collect dust and lint which intensify respiratory problems.

     A radiant panel cooling system supplies most of the cooling requirements through the radiant energy
transfer process. This reduces the air requirements to only the amount of air needed for proper ventilation
and relative humidity control, which is so small it’s economically feasible to completely eliminate re-circulated
air. This will permit the use of 100% outside air to be adequately filtered and conditioned to safeguard
against infiltration of bacteria. This is the main reason why a radiant panel cooling system is the most
technologically advanced approach to providing an environment to control airborne nosocomial infection.

     The use of radiant panel cooling systems to remove sensible heat from a space will reduce
the quantity of air supplied to the room. The air supply system will primarily serve to provide
adequate moisture control, odor control and a constant air supply. The minimum amount of air supplied
for good ventilation should be based on local codes if required or a minimum recommended air supply
quantity of 0.4 CFM per square foot of conditioned area. The design of a radiant panel cooling system
follows the normal design procedure used for an air-water system.


The following items must be taken into consideration when designing a radiant panel cooling system;

1.) Must determine the rooms design dry bulb temperature, relative humidity, and dew point.

2.) Calculate the sensible heat gain and the latent heat gain to the room.

3.) Select the mean water temperature (MWT).

4.) Determine the panel performance from the performance curves.

5.) Determine the panel area available in the room and total panel pick-up.

6.) Determine the minimum air quantity to offset the latent heat gain and in accordance with
     good ventilation practices and local codes.

7.) Determine the design panel area and design air quantity.

8.) Determine the water quantity and pressure drop.