Chapter 5.4.3 - Design Characteristics

The insulation and routing of heat transfer plumbing lines or circuit tails is important
for the overall performance and energy efficiency of the system. ASHRAE
SPC-152P, Method of Test for Determining the Steady-State and Seasonal Efficiencies
of Residential Thermal Distribution Systems, details a methodology for determining
the heat loss from the point of heat origin to the point of heat delivery for residential
and heating and cooling systems. Transmission loss reduces the actual point-ofuse
heat or cool output of the radiant panel, baseboard, or forced-air register or
diffuser. Normally found to be in the range of 15 to 40 percent or more in residential
forced-air convection systems, duct sealing and new construction design duct loss
targets are 15 percent or less. Energy transmission loss is not likely to exceed 5 percent
for a radiant system. (See Fig. 4.2.)

Design strategies for minimization of transmission and panel heat loss are well
known.When the specification for reducing heat loss is detailed, implementation is

successful and installed performance matches design. Fluid leaks are usually unrelated
to heat loss, except in the case of freeze-ups. Though sometimes damaging,
fluid leaks are quickly detected. Forced-air system leaks may go undetected until
the system is actually tested as a result of high bills, or discovered during service
inspection that includes duct pressurization or system balancing. In either case,
repair is more difficult when either the air duct or the radiant conduit is not readily
accessible.

In addition to transmission loss, other potential heat loss from the radiant panel
is also detailed in ASHRAE SPC-152P. Such loss may occur at the perimeter and
backside of the radiant hydronic panel system. (See Fig. 4.3.) Insulation, planar location,
and nature of surrounding space usage are among the conditions defining the
magnitude of heat transfer potential from surfaces other than the designed primary
radiant output surface.

Radiant hydronic floor heating panel performance is affected by the addition of
any material that changes the rate of designed panel heat transfer. For example,
carpeting, furniture, walls, or cabinets may be added, which would impact the
designed rate of heat transfer from the panel to the occupied space. (See Table 4.2.)
Other factors to be considered relate more to the potential likelihood of penetration,
which is also a concern for radiant ceilings when lighting, ventilation, smoke
detection, security, or other equipment is installed. For any concealed system the
installation documentation is essential to reduce the risk of system damage from
penetration.

The insulation and routing of heat transfer plumbing lines or circuit tails is important
for the overall performance and energy efficiency of the system. ASHRAE
SPC-152P, Method of Test for Determining the Steady-State and Seasonal Efficiencies
of Residential Thermal Distribution Systems, details a methodology for determining
the heat loss from the point of heat origin to the point of heat delivery for residential
and heating and cooling systems. Transmission loss reduces the actual point-ofuse
heat or cool output of the radiant panel, baseboard, or forced-air register or
diffuser. Normally found to be in the range of 15 to 40 percent or more in residential
forced-air convection systems, duct sealing and new construction design duct loss
targets are 15 percent or less. Energy transmission loss is not likely to exceed 5 percent
for a radiant system. (See Fig. 4.2.)

Design strategies for minimization of transmission and panel heat loss are well
known.When the specification for reducing heat loss is detailed, implementation is

successful and installed performance matches design. Fluid leaks are usually unrelated
to...