Overhead hydronic radiant ceiling panels may be concealed or visible. Choosing
whether to design for a visible or invisible system is perhaps the most challenging
hurdle to the selection of a radiant ceiling system. System visibility and appearance
are subjective. System selection and performance design are normally objective.Yet,
whether a system is visible or invisible significantly impacts design and can impact
comfort and energy performance.
4.9.1 Concealed Radiant Hydronic Ceiling Systems
Concealed radiant ceiling panels are normally field-constructed. Concealed design
of radiant hydronic ceiling panels defines the ceiling as the panel and radiant delivery
surface. As with all radiant panels, the objective is maximization of radiant
frontal output and minimization of side and back heat loss. Regardless of building
construction, panel surface output is maximized when the panel contact with cold
building surfaces is buffered by an enclosed air space and separated by insulation. A
defined and closed air space eliminates thermal bridging and conductive heat loss.
(See Fig. 4.9.) Insulation reduces heat transfer outside of the space to which the
panel is designed to radiate heat, and should be designed based upon cost-effective
site analysis.
Concealed panel composition and construction alternatives impact panel performance,
control, and energy consumption. For embedded ceiling panel systems,
determination of conduit material and design configuration is an important factor
determining mass minimum thickness and material composition alternatives. Mass
thickness and material composition define thermal mass and heat transfer design
alternatives.Weight and architectural constraints may establish boundary conditions
for concealed radiant system design. For example, a concrete floor may be impractical
except as a slab or basement floor.
In the case of panels that are designed using flexible hydronic conduit routed
through ceiling joists, the same panel design principles apply. Energy efficiency
and performance will depend upon comprehensive definition of the radiant concealed
panel in relation to the performance design.The emergence of this application
is driven by the economics of competition with ducted warm-air heating
systems. An important factor for performance success is panel design simplicity
and plan detail that ensures consistent field construction and installation. As with
any concealed system, detailed comprehensive documentation of installation, con-
nections, operating control settings, and the like is essential to system service and
management.
Encapsulated or concealed radiant ceiling systems, whether PEX tubing or
narrow-diameter capillary tubing or mats, are inherently higher-mass systems. (See
Fig. 4.10.) The key performance design factor of mass systems is determination of
temperature change–time increments under dynamic external and internal design
conditions. Thermal stability, mass temperature lags, and mass charges and discharges
are characteristics that are essential design inputs. Solar impact, occupancy
patterns, and energy source for fluid heating are but a few of the interacting factors
that must be integrated into overall system design and control.
Surface characteristics of the panel face are not a design constraint on concealed
or other radiant systems.The emissivity of the normally encountered building materials
used for building ceilings is on the order of 90 percent whether painted or textured.
The surface temperatures are also within the range tolerated by standard
surfacing materials, paints, and finishes. The placement over the ceiling of wood or
other materials that provide thermal resistance will impact performance and will
require careful analysis. The details of ASHRAE Research Project 876, Impact of
Surface Characteristics on Radiant Heat Transfer, are covered in more detail in Chap.
5 at the end of Sec. 5 of this Handbook.
Concealed radiant ceiling heating is commonly specified and designed for conditions
where it is practical to turn the heating on to a set point that is maintained over
the entire winter period until turned off for the summer. Interim adjustment is not
recommended because short-term adjustment may not be economic or practicable
due to the thermal inertia of a concealed ceiling system. Selection of the optimum
operating protocol is essential to the energy efficiency and comfort performance of
all heating systems, including concealed radiant ceiling systems.
Economic heating system operation involves a strategy designed to complement
and maintain building mass at temperature levels compatible with occupant comfort
or other building use specifications, thereby minimizing the initial start-up heat
energy investment. For concealed radiant ceiling systems, it is important to account
for the thermal properties of the ceiling material in designing ramp-up and rampdown
strategies to avoid cracks, expansion, and contraction stress, or other problems.
In some cases, the material limitations prevent rapid warm-up. In new
installations, the mass materials must always be dry and fully cured naturally before
any heat is applied. Even though there may be adequate conduit heat capacity, the
thermal transfer properties of the panel design or material may prohibit exploitation
for rapid warm-up or cool-down. On the plus side, high-mass systems provide an
even longer period of building thermal stability than low-mass radiant systems,
which is an important benefit of any radiant system during power, energy source, or
equipment outages.
Overhead hydronic radiant ceiling panels may be concealed or visible. Choosing
whether to design for a visible or invisible system is perhaps the most challenging
hurdle to the selection of a radiant ceiling system. System visibility and appearance
are subjective. System selection and performance design are normally objective.Yet,
whether a system is visible or invisible significantly impacts design and can impact
comfort and energy performance.
4.9.1 Concealed Radiant Hydronic Ceiling Systems
Concealed radiant ceiling panels are normally field-constructed. Concealed design
of radiant hydronic ceiling panels defines the ceiling as the panel and radiant delivery
surface. As with all radiant panels, the objective is maximization of radiant
frontal output and minimization of side and back heat loss. Regardless of building
construction, panel surface output is maximized when the panel contact with cold
building surfaces is buffered by an enclosed air space and separated by insulation. A
defined and closed air space eliminates thermal bridging and conductive heat loss.
(See Fig. 4.9.) Insulation reduces heat transfer outside of the space to which the
panel...
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