| Architects Say "Yes!" to Radiant Heating &
Cooling |
A person feels too hot or cold if
their body’s heat loss is less or greater than the heat generated by
their body while performing activities. We are comfortable when heat
loss is equal the heat generated by the body (thermal equilibrium).
The body loses heat in several ways. Radiation to
surrounding surfaces (e.g. walls, glazing) accounts for about 45% of the
total heat loss from a person performing typical indoor activities. 35%
is lost through convection to the air, and 20% through evaporation
(e.g. breathing, sweating).
Typical heating and air conditioning systems only
control air temperature, which works well for most situations. Very tall
spaces, such as atria, can be challenging to control due to
stratification (hot air supplied to these spaces rises to the top,
rather than staying in the occupied zone), particularly in the winter.
Spaces with large amounts of glazing present an additional challenge.
The glass surface temperature varies with the outdoor conditions, and
radiation between the occupants and the glass can be difficult to offset
by controlling air temperature alone.
Radiant heating and cooling systems have been
successfully applied to many different types of buildings and can
effectively condition tall spaces and areas with glazing. By controlling
the surrounding surface temperatures, radiant floors, ceilings, or even
walls can handle the largest component of a person’s heat loss and
comfort.
Save Energy While Increasing Comfort
In typical heating and air
conditioning systems, the air temperature is set to compensate for
radiant losses. For example, in a space with full-height glass on a
sunny day, the occupants may be uncomfortable from such a large hot
surface unless the air temperature is reduced to keep them cool. If the
surface is hot enough, reducing the air temperature may not be able to
keep them comfortable, no matter how cool it is. More energy is needed
to maintain the lower air temperatures, and the difference between the
air temperature and glass surface temperature may be uncomfortable to
the occupants.
Radiant floors provide some control of the radiant
heat loss from building occupants and can offset the radiant heat
transfer from glass. The improved control of the radiant portion of the
heat transfer equation, allows the air temperature to be set warmer
while still maintaining comfort and efficiency. The result is energy
savings and increased comfort.
During winter operation, the same reasoning applies
to achieve improved energy and comfort. Additionally, radiant floor
heating addresses the stratification that occurs with many air systems,
allowing further improvements in energy and comfort.
An
Architectural and Engineering Landmark: Seamlessly Integrating Radiant
Floors for the Eugene Courthouse
The new Wayne L. Morse Courthouse
in Eugene, Oregon, is set to become an architectural landmark,
collecting awards even before construction has begun. The project is one
of thirteen projects to receive a 2004 "Progressive Architecture"
design award from Architecture magazine. The sweeping curved metal and
glass fa€ades will make a significant contribution to the architectural
significance of the the town of Eugene.
Visitors to the courthouse will notice the
spectacular views, but they may not realize that what they cannot see is
very progressive. Below the floor will be a radiant heating and cooling
system, designed to save energy, increase comfort, and seamlessly
integrate with the architecture of the building.
The radiant system for the courthouse consists of
PEX tubes encased in a concrete floor slab. The tubing distributes
heating water or chilled water from the central boiler and chiller
plants through the floor slab. The radiant floors condition the atrium,
public corridors, and jury assembly area, all of which contain high
ceilings and extensive areas of glazing.
This type of floor system in a heating application
has been used for decades in the U.S. and has been proven to be a
reliable, cost-effective means of heating. By using the same system for
cooling, the design is taking a departure from standard engineering
practice and venturing into new territory. In order to calculate the
floor cooling capacity, Glumac collaborated with the radiant floor
manufacturer to perform a finite-element analysis of the floor at
various conditions.
The historical concern with radiant floor cooling
has been condensation on the floor. Space humidity sensors and floor
slab temperature sensors are employed to prevent condensation and ensure
comfortable operation. The system design and control sequences
developed by Glumac, incorporate the current state-of-the-art thinking
on radiant floor cooling and lessons learned from previous radiant
cooling projects
Architectural
Integration: Floor Construction
When designing a radiant floor
system, care must be taken to ensure that the heat transfer is directed
up, to the conditioned space, rather than down, wasted to the space
below. This is achieved by insulating underneath the radiant floor and
by not insulating on top of the floor. In the Wayne L. Morse Courthouse,
the insulation under the floor was already part of the architectural
design to maintain the floor level with adjacent spaces. An underfloor
air distribution system is used throughout the building, except in the
public spaces in which the architect desired a tile floor. The tile
floor is raised on a rigid foam and concrete topping slab construction
in order to maintain a consistent finished floor level throughout the
building. The tile floor covering provides very little thermal
resistance to the heat transfer between the tubing and space, and the
foam underneath prevents energy waste below. The arrangement is ideal
for the radiant floor, at no added cost to the project.
Air
Distribution
A supplemental air system provides
ventilation air and a portion of the cooling capacity for these public
spaces. The air system is as integrated into the architectural design.
The air is delivered through the wall stud cavities to hidden grilles at
the bottom of the walls. The air is supplied at a low level and low
velocity, a classic displacement ventilation system. The air
distribution capabilities and noise level produced by the system were
tested during the design phase.
The air system with a radiant floor is smaller than
that without the radiant floor. The reduced shaft sizes and duct
distribution benefit the architecture of the building.
