Bryant 50YEW Design Manual page 30

Water-to-Water System Design Guide
Part II: Load Side Design / Distribution Design
The heating capacity of a baseboard system is a factor of the area
of copper tube and fi ns exposed to the air, and the temperature
difference between the air and the fi n tube. The velocity and
volume of water fl owing through the baseboard affects the
temperature of the copper and fi ns. Baseboard units are normally
rated in heat output per length of baseboard at a standard water
temperature and fl ow rate. Manufacturers provide charts, which
will give the capacities at temperatures and fl ow rates below the
standard. Table 2-2 shows approximate heating capacities for fi n
tube radiation using water from 100-200°F [43-93°C].
Table 2-2: Heating Capacity in Btuh/Foot [Watts/
meter] of Baseboard Radiators
Average Water
Temperature
110°F [43°C]
120°F [49°C]
130°F [54°C]
140°F [60°C]
200°F [93°C]
*Table values are in Btuh/ft. [W/m]
The heating capacity in Btuh/foot [Watts/meter] of baseboard
radiators drops as the water temperature is reduced. The heating
capacity of most copper fi n tube baseboard radiators is rated
using 200°F [93°C] water and 65°F [18°C] air temperature. Listed
above is the range of heating capacities of baseboard radiators
at the standard temperatures and the capacities when the
temperatures are reduced to the operating range of a heat pump
system. Some of the factors that affect the capacity of a radiator
are as follows:
• Size of the fi ns - range from 2.75" x 3" [7 x 7.6 cm] to 4" x
4"[10.2 x 10.2 cm]
• Fin spacing - 24 to 48 per foot [79 to 157 per meter]
• Size of copper tube - range from 3/4"[19 mm] to 2" [50 mm]
• Fin material - aluminum or steel
• Confi guration and height of the enclosure
• Height unit is mounted from the fl oor
• Water fl ow through the tubing
Generally, the smaller fi ns with less fi ns per foot [meter] will have
lower heating capacity. Larger copper tube diameter and/or more
aluminum fi ns will have higher capacity. Higher water fl ow will
increase capacity. Adding a second fi n tube to the same enclosure
will increase the capacity by 50 to 60%. Adding two fi n tubes with
enclosures will increase the capacity by 75 to 80%. Baseboards are
available, using two or three fi n tubes tiered above one another
in the same cabinet. The air can be heated enough with the
additional surface area to set up a convection current with water
temperatures as low as 110-130°F [43-54°C].
28
Entering Air Temperature
55°F [13°C]* 65°F [18°C]*
190-380 [184-364] 160-320 [154-308]
240-480 [230-463] 205-410 [197-394]
295-590 [282-568] 265-532 [255-512]
350-700 [338-673] 315-630 [302-607]
700-1400 [673-1345]
Bryant: Whatever It Takes.
The operation of a baseboard radiation system depends on the
ability to set up convection current in the room (i.e. air is warmed
by the fi n tube, rises and is displaced by cool air). It is important
to ensure that the heat output of the system is adequate to meet
the heat loss of the room or building at the temperatures the
geothermal system is capable of producing. Baseboard radiation
is limited to space heating. Cooling is typically provided by a
separate, forced air distribution system.
70°F [21°C]*
150-300 [144-289]
195-390 [187-374]
245-490 [236-472]
295-590 [282-568]
CAST IRON RADIATION
Retrofi t applications for hydronic / geothermal heat pump systems
are often required to work with existing cast iron radiators.
Typically, cast iron radiator systems, as shown in fi gure 2-13, operate
with water temperatures of 125-200°F [52-93°C]. As with
baseboard systems, if an existing home has had weatherization and
insulation upgrades, it is possible that the heat loss of the home
has decreased enough to allow lower water temperatures. Cast
iron radiators can operate well with design water temperature
as low as 110°F [43°C]. Careful consideration must be made,
however, when operating at lower temperatures, as the heat
emission rate is substantially less when operating below 140°F
[60°C]. To determine heat emission for cast iron radiators, calculate
the surface area of the radiator, and refer to table 2-3 for output
capacity. Note: Table 2-3 is for general reference only. The various
cast iron radiator styles and sizes will change the output. Many
resources are available for determining heating capacities. Also
consult the radiator manufacturer's data when possible.
Figure 2-13: Cast Iron Radiator
W
H