Snow Melt Applications - Bryant 50YEW Design Manual

Water-to-Water System Design Guide
Part II: Load Side Design /
Distribution Design
SNOW MELTING APPLICATIONS
Although snow melting is now considered somewhat controversial
due to the energy use, geothermal systems are quite capable of
heating sidewalks and driveways for melting snow. As with any
hydronic heating system, the load calculation is the fi rst and most
important step in designing a reliable and cost-effective snow melt
system. Consult the ASHRAE HVAC Applications Handbook
for slab piping design and temperature requirements. This will
determine the Btu/hr [kW] requirement of the water-to-water
equipment. Follow procedures above for sizing the equipment and
buffer tank.
The hot water in the piping system will heat the slab, melting the
snow. Snow melt controls are available that actually "sense" when
conditions are right for snowfall. Snow/ice melt detection is used
to automatically start and stop a snow melt system. When there
is snow on the sensor, the sensor melts the snow/ice, detects the
moisture and allows the control to start the melting process. This
prevents accumulation of snow on the slab and provides a faster
response. Automatic snow/ice detection is safer, more convenient
and consumes less energy than manual (ON/OFF) type systems.
In systems where snow and ice removal is critical, such as hospital
ramps, the pick up time for a snow melting slab can be reduced
by maintaining the slab at an idling temperature. The idling
temperature may be just below the freezing point. When snow
melting is required, the slab temperature is increased. When
the slab and outdoor temperatures are warm enough, the snow
melting system should automatically turn off.
Another important aspect of choosing a good controller is slab
protection. Snow melt systems deal with extreme temperature
differences. Limiting the rate of heat transfer into the slab
provides slab protection. This is done by slowly ramping up the
temperature difference across the slab and limiting the maximum
temperature difference. This function prevents cracking of the slab
due to thermal expansion caused by high heat output.
Piping design and component selection for a snow melt system
are identical to systems used for hydronic heating (see drawings
2-3 and 2-4). The difference is simply the load on the system. In
other words, the size of the water-to-water unit and the related
components is calculated based upon the amount of heat needed
for a sidewalk [for snow melting] instead of the amount of heat
needed to condition a structure.
COOLING SYSTEMS
Cooling an existing building with a radiant heating system can
be a challenge. If radiant heating emitters (radiators, baseboard
convectors, radiant fl oor piping) are cooled lower than the dew
point, condensation will form on the fl oor or drip off the emitters.
A limited amount of cooling can be accomplished by circulating
chilled water through the piping in the fl oor or through radiant
ceiling panels. This can be effective in buildings with high solar
loads or lighting loads, where much of the heat gain is radiant heat.
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Cooling and dehumidifying fresh air used for ventilation as it is
brought into the building (using a dedicated outside air system) can
sometimes provide the additional cooling needed. Care must be
taken to avoid cooling the radiant surface below the dew point.
A water-to-water heat pump system can provide chilled water to
ducted or non-ducted fan coil units. A reversible water-to-water
heat pump can provide chilled water to cool the building, as well
as hot water for the heating system. Buildings with fan coil units
can generally be retrofi tted for cooling quite easily. The diffi culty, as
mentioned above, is using existing fan coils for heating, especially if
they were originally sized for higher water temperatures.
For optimal cooling and dehumidifi cation, Bryant recommends a
separate water-to-air heat pump for cooling. Controls are much
simpler when a water-to-water unit is used for space heating
and/or domestic water heating, and a water-to-air unit is used for
cooling. Since the water-to-water and water-to-air units can share
one ground loop, the installation cost of using a water-to-air unit
for cooling is simply the incremental cost of the unit. Generally, no
additional ground loop is required, and the cost of the water-to-
air unit is usually less than the cost of chilled water/fan coil units,
especially if the cost of additional piping/valving/controls and labor
is considered. The cost of a water-to-air unit is approximately
the same as a ductless mini split, and is much more effi cient. The
advantages of geothermal heat pumps for cooling (no outdoor
unit, no refrigerant line sets, longevity, etc.) should be considered
when cooling is required.
Bryant: Whatever It Takes.