Method and system for creating and maintaining a frozen surface

A method of manufacturing a tube includes the steps of preparing a composition using ethylene vinyl acetate, extruding the composition to form a tube, and cooling the tube with the tube in a substantially straight configuration so that the tube is substantially set in a substantially straight configuration. Moreover, a system for creating a frozen surface on a medium includes a mechanism for exchanging thermal energy between a medium and a coolant, a mechanism for removing thermal energy from a coolant, and a mechanism for transporting a coolant between the mechanism for exchanging thermal energy between a medium and a coolant and the mechanism for removing thermal energy from a coolant. The mechanism for transporting a coolant includes first and second pipes and mechanism for releasable connecting the first pipe to the second pipe so as to prevent the first pipe from moving axially relative to the second pipe in a first operational state, and to allow the first pipe to be moved axially relative to the second pipe in a second operational state. Additionally, a system for creating and maintaining a frozen surface on a medium includes a mechanism for exchanging thermal energy between a medium and a coolant, the mechanism for exchanging thermal energy between a medium and a coolant having a substantially uniform cross-sectional area for passing a coolant therethrough. The system also includes a mechanism for removing thermal energy from a coolant. The system further includes a mechanism for transporting a coolant between the mechanism for exchanging thermal energy between a medium and a coolant and the mechanism for removing thermal energy from a coolant. The mechanism for transporting a coolant is connected to the mechanism for exchanging thermal energy between a medium and a coolant so that substantially all of a coolant flowing from the mechanism for transporting a coolant to the mechanism for exchanging thermal energy between a medium and a coolant flows directly from the mechanism for transporting a coolant into the mechanism for exchanging thermal energy between a medium and a coolant.

FIELD OF THE INVENTION 
This invention relates to a method of manufacturing a tube. This invention 
also relates to a system for creating and maintaining a frozen surface, 
for example, for recreational exhibitions and athletic competitions at an 
ice skating rink. In particular, this invention relates to a system for 
efficiently conveying a coolant through a medium to be frozen. This 
invention also relates to a system that lends itself to facilitate 
installation and maintenance. 
BACKGROUND OF THE INVENTION 
The earliest ice skating rinks were frozen ponds or lakes. Such ice sport 
venues had the sizeable limitation that their existence was entirely 
dependent upon the temperature of the environment. For a long time, the 
dependency upon naturally-formed ice restricted the enjoyment of ice 
sports in most countries to a limited seasonal period. 
In the late nineteenth century, indoor ice skating rinks were designed to 
provide venues on which ice sports could be enjoyed in most countries 
year-round. These early indoor ice skating rinks used a system of steel or 
iron pipes to carry an artificially-cooled refrigerant, such as calcium 
chloride brine, under a tank of water to create a frozen surface capable 
of being skated upon. The steel or iron pipes were embedded in concrete or 
sand beneath the tank, and had an inner diameter of 1 to 11/2 inches with 
4 inches between the centers. 
While capable of providing a frozen surface which could be skated upon 
indoors year-round, the steel or iron pipe construction had its drawbacks. 
Perhaps, one of the greatest limitations on the steel or iron 
constructions was the surface area that these systems provided for heat 
exchange with the medium to be frozen, also known as the dynamic surface 
area. In the steel or iron constructions, as structurally and 
dimensionally described above, the dynamic surface area was substantially 
less than the area of the skating surface available for heat exchange with 
the environment. The dynamic surface area of the steel or iron 
constructions is estimated to be at most 82% of the skating surface area. 
More recently, ice skating rink systems have been constructed using smaller 
diameter plastic tubing, such as those systems described in U.S. Pat. Nos. 
3,751,935; 3,893,507; and 3,910,059. In operation, a main supply pipe, or 
header, feeds into a plurality of supply subheaders, each of which in turn 
is attached to the proximal ends of a plurality of coolant tubes. The 
plurality of coolant tubes can be fastened at their distal ends to one end 
of a plurality of U-shaped connectors, which in turn are fastened to a 
second plurality of coolant tubes. The second plurality of coolant tubes 
is attached at their proximal ends to a plurality of return subheaders, 
which in turn feed into a main return header. The inner diameter of the 
coolant tubes used in these plastic constructions generally varies from 
1/4 to 1/2 inches. By using a smaller center spacing between smaller 
tubes, thee plastic systems may provide a larger dynamic surface area than 
the steel or iron constructions. 
However, the dynamic surface area is only one factor influencing the 
overall efficiency of a system designed to create and maintain a frozen 
surface. As important to the efficiency of the system as the dynamic 
surface area is the ability of the coolant to flow through the system 
without significant pressure loss or flow interruption. As a consequence, 
even though the plastic systems may have improved the dynamic surface area 
over the iron and steel constructions, the efficiency of these plastic 
systems is often significantly compromised in practice by unsatisfactory 
coolant flow characteristics at various points in the system. 
For example, as shown in FIGS. 1 and 2 herein, one common area for flow 
restriction to occur is at the transfer point between a subheader 30 and a 
coolant tube 32. In the conventional construction shown in FIGS. 1 and 2, 
the subheader 30 has an opening 34, through which is disposed a connection 
fitting 36. The connection fitting 36 is soldered into place with the 
proximate end of the fitting 36 occluding as much as 25 percent of the 
interior cross-sectional area of the subheader 30. This occlusion can 
cause a layer 38 of coolant to build up against the fitting 36, and 
seriously degrade the flow characteristics of the coolant in the area 
adjoining the transfer point. 
Moreover, at the distal end of the tube 32, where the tube 32 attaches to a 
U-shaped connector 40, the conventional methods of construction can cause 
additional flow restriction problems. One flow restriction problem 
commonly occurring in conventional constructions is illustrated in FIGS. 3 
and 4. The U-shaped connector 40 shown is fabricated by bending a copper 
tube having an internal diameter similar to that of the coolant tube 32. 
By using this method of fabrication, the resulting inner diameter at a 
bight 42 of the U-shaped connector 40 may be reduced to approximately half 
the diameter of the original copper tube. The dramatic decrease in the 
inner diameter of the U-shaped connector 40 at the bight 42 has a 
proportionally dramatic effect on the fluid flow throughout the system. 
Additionally, loss of flow pressure can result from the present methods of 
system construction used to join the coolant tubes 32 with the U-shaped 
connectors 40. The coolant tubes 32 are fastened directly to the U-shaped 
connectors 40 by means of glue and a circular clamp or an eyelet, as shown 
in FIGS. 3 and 4. As a consequence, the tubes 32 have a tendency to leak, 
or even pop off of the U-shaped connector 40, spilling coolant directly 
into the medium to be frozen and underlying foundational material and 
decreasing the pressure and flow rate at which the coolant is being 
transported throughout the system. 
Furthermore, these plastic systems are often constructed using a type of 
plastic coolant tube having unfavorable performance characteristics. 
Commonly, polyethylene or polypropylene tubing is used for the coolant 
tubes in plastic ice skating rink systems. During manufacture, the 
polyethylene or polypropylene tubing is usually extruded, and then passed 
through a standard length (10-14 foot) cooling tank before being 
machine-coiled on to spools for delivery. As a consequence of this method 
of fabrication, the polyethylene or polypropylene tubing thermally sets 
with a curved, rather than a straight, structure in the memory of the 
plastic. Therefore, when the tubing is uncoiled to be used in the plastic 
construction illustrated in the patents mentioned above, the tubing does 
not naturally lay straight and flat, but takes on a serpentine structure 
in at least one plane. 
As a further consequence, when these polyethylene or polypropylene ice rink 
systems are installed, the coolant tubing will commonly force its way 
under pressure to the skating surface, and protrude from the surface of 
the ice, providing a substantial obstacle and hazard for persons, for 
example skaters, using the frozen surface. It is therefore necessary to 
resubmerge the tubing under the surface of the ice through a method known 
as "burning in". The tubing is "burned" into the surface of the ice by 
melting the surrounding ice, and then holding the tube in place under 
pressure until the ice reforms around the problematic section of tubing. 
Because of the pressure of the coolant running through the tubing, as well 
as the thermally-set disposition of the tubing to return to the serpentine 
structure, it may be necessary to repeat the "burning in" process a number 
of times each season to maintain a skating surface free from obstructions 
and to prevent damage to the tubing. 
However, polyethylene and polypropylene tubing is sensitive to repeated 
bending. Repeated bending of the polyethylene or polypropylene tubing has 
been known to cause permanent damage to the tubing, and can result in the 
cracking or rupture of the tubing with a concomitant loss of coolant 
pressure in the system. 
SUMMARY OF THE INVENTION 
According to an aspect of the present invention, a method of manufacturing 
a tube includes the steps of preparing a composition using ethylene vinyl 
acetate, extruding the composition to form a tube, and cooling the tube 
with the tube in a substantially straight configuration so that the tube 
is substantially set in a substantially straight configuration. 
According to another aspect of the present invention, a system for creating 
a frozen surface on a medium includes a mechanism for exchanging thermal 
energy between a medium and a coolant, a mechanism for removing thermal 
energy from a coolant, and a mechanism for transporting a coolant between 
the mechanism for exchanging thermal energy between a medium and a coolant 
and the mechanism for removing thermal energy from a coolant. The 
mechanism for transporting a coolant includes first and second pipes and a 
mechanism for releasable connecting the first pipe to the second pipe so 
as to prevent the first pipe from moving axially relative to the second 
pipe in a first operational state, and to allow the first pipe to be moved 
axially relative to the second pipe in a second operational state. 
According to a further aspect of the present invention, a system for 
creating and maintaining a frozen surface on a medium includes a mechanism 
for exchanging thermal energy between a medium and a coolant, the 
mechanism for exchanging thermal energy between a medium and a coolant 
having a substantially uniform cross-sectional area for passing a coolant 
therethrough. The system also includes a mechanism for removing thermal 
energy from a coolant. The system further includes a mechanism for 
transporting a coolant between the mechanism for exchanging thermal energy 
between a medium and a coolant and the mechanism for removing thermal 
energy from a coolant. The mechanism for transporting a coolant is 
connected to the mechanism for exchanging thermal energy between a medium 
and a coolant so that substantially all of a coolant flowing from the 
mechanism for transporting a coolant to the mechanism for exchanging 
thermal energy between a medium and a coolant flows directly from the 
mechanism for transporting a coolant into the mechanism for exchanging 
thermal energy between a medium and a coolant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In general terms, the system of the present invention creates and maintains 
a frozen surface, such as ice, by removing thermal energy from a liquid 
medium, such as water, and exhausting the thermal energy at a location 
remote to the medium to be frozen. Specifically with reference to FIG. 5, 
pressurized, chilled coolant passes through a plurality of tubes spaced 
within a tank or container 46 holding the medium to be frozen. As the 
coolant passes through the plurality of tubes, thermal energy is 
transferred from the medium to the coolant through the walls of the tubes. 
The coolant then passes from the tubes to a pump 54, and from the pump 54 
to a refrigeration unit 70. The refrigeration unit 70 extracts the thermal 
energy from the coolant and returns the chilled coolant to the collection 
tank 68, whereupon the cycle is repeated. 
According to an embodiment of the present invention, a system 44 for 
creating and maintaining a frozen surface is shown in FIG. 5. The system 
44 in FIG. 5 is shown fitted in a tank or rink 46. The rink system 44 
includes a main supply header 48, a main return header 50, and a plurality 
of panels 52. Unlike the constructions discussed above, the panels 52 used 
in the embodiments of the present invention discussed herein are placed 
within the medium to be frozen, rather than being embedded in or placed 
underneath inches of sand or concrete beneath the rink 46, although such a 
configuration is possible using the present invention. As a consequence of 
the direct thermal energy exchange relationship between the coolant in the 
panels 52 and the medium to be frozen, the efficiency of the system 44 is 
improved as a whole as it is unnecessary to first cool the floor of the 
tank 46 prior to cooling the medium to be frozen. 
To preserve the advantages of this direct thermal energy exchange 
relationship by preventing thermal energy from entering the tank from 
surface below the tank 46, an insulation layer or blanket 53, as shown in 
FIG. 6, is placed beneath the panels 52. The insulation layer 53 is 
fabricated in a sandwich construction in which two layers of bubble 
packaging material 53a are laid face to face such that the bubbles of one 
layer fit within the dimples of the other layer. The two layers 53a are 
then covered on the externally facing surfaces 53b, 53c with a layer 53d 
of foil on the surface 53b, and a layer 53e of foil, or polyethylene, on 
the surface 53c. During installation, the layer 53d is placed against the 
surface below the tank 46, while the layer 53e faces and is covered by the 
medium to be frozen. 
A pump 54 is connected at an outlet 56 to the main supply header 48 via the 
refrigeration system 70 and the collection tank 68, and forces a coolant, 
for example, a mixture of either ethylene glycol or propylene gylcol and 
water, into the main supply header 48 under pressure. Under most 
conditions, the coolant is, for example, a mixture of either ethylene 
glycol or propylene glycol and water in a ratio of 45:55. If the system 44 
is intended for use in a environment where the temperature of the 
surrounding environment is less than -20 degrees F., the coolant is, for 
example, a mixture of either ethylene glycol or propylene glycol and water 
in a ratio of 55:45. The coolant passes from the main supply header 48 and 
into the individual panels 52. 
Each panel 52, generally indicated in FIG. 5 and shown in greater detail in 
FIGS. 7 and 8, is four feet wide and 100 feet long, and includes a supply 
subheader 58, a return subheader 60, first and second plurality of tubes 
62, 64, and a plurality of U-shaped connectors 66. The pressurized coolant 
flows from the main header 48 into the supply subheader 58, which feeds 
into the first plurality of tubes 62. As the coolant flows through the 
medium, thermal energy is transferred from the medium to the coolant 
through the walls of the tubes 62. The coolant then passes through the 
plurality of U-shaped connectors 66 and into the second plurality of tubes 
64. As the coolant flows through the medium for a second time, additional 
thermal energy is transferred from the medium to the coolant. 
The coolant feeds from the plurality of tubes 64 to the return subheaders 
60, which are connected to the return header 50. The coolant is 
transported along the return header 50 to the pump 54, from which the 
coolant returns to the refrigeration system 70. The refrigeration system 
70 extracts the thermal energy from the coolant, and exhausts the thermal 
energy to the environment. The chilled coolant is then returned to the 
collection tank 68, for example a 15 gallon tank, to be re-introduced into 
the main header 48. 
Alternatively, the system 44 may be configured to accommodate placement of 
the refrigeration system 70 and pump 54 at the center of the rink 46. As 
shown in FIG. 9, with like numbers used for like elements, a central 
supply header 72 is connected through the refrigeration system 70 and a 
collection tank 68 to the pump 54, branching off at a first T-joint 74 to 
form two main supply headers 48, one for each half of the rink 46. The 
supply headers 48 each feed into a plurality of subheaders 58, which in 
turn feed into a plurality of panels 52 in a direct thermal energy 
transfer relationship with the medium to be frozen. The coolant returns to 
the refrigeration system 70 via a system of return subheaders 60 and 
return headers 50. The return headers 50 are connected at a second T-joint 
76 to form a main return header 78, which feeds directly into the pump 54. 
Because the system 44 can be assembled to accommodate rinks of different 
widths and lengths by adding additional panels 52, the requirements for 
the pump size and the pressure and flow rate of coolant (expressed as 
gallons per unit of time) will necessarily differ according to the exact 
dimensions of the assembled system 44. The coolant has an inlet 
temperature (as measured at the inlet of the supply header 48) of 18-20 
degrees F., and an outlet temperature (as measured at the inlet of the 
pump 54) of 20-24 degrees F. It has been found experimentally that to 
provide a uniform thermal energy transfer, or thermal energy extraction, 
from the medium to be frozen, the velocity of the coolant in the system 44 
should be at least 1 foot/second. 
In an embodiment of the present invention, wherein the rink system 44 may 
be assembled and disassembled, for example at the end of a seasonal period 
or after an athletic competition or exhibition, the supply header 48 and 
the return header 50 are made from lengths of pipe 80, for example, 
enhanced PVC pipe (type 1, grade 1, 2000 psi hydrostatic stress material, 
in accordance with ASTM D1784) with an inner diameter of between 2 to 6 
inches, for example 4 inches, joined together at spaced intervals by 
connectors 82, 84, also fabricated from enhanced PVC schedule 80 pipe. The 
lengths of pipe 80 are joined together at four foot intervals to coincide 
with the four foot width of the panels 52. 
The connector 82, as shown in FIGS. 10, 11 and 12, is used in the main 
supply header 48 and the first section of the main return header 50 
upstream to the U-shaped joint 86 in the system 44 shown in FIG. 5, and 
U-shaped joints 88 and 90 in the system 44 shown in FIG. 9. The connector 
82 is also designed to connect the main supply header 48 and the main 
return header 50 to the supply subheaders 58 and the return subheaders 60. 
The connector 82 may include a pipe section 92, a flexible hose 94, a fixed 
coupling 96 and either a male or female coupling 98. An opening 100 is 
machined in the pipe section 92 at half the distance from the ends. The 
opening 100 is then tapped to accept the threads of the fixed coupling 96. 
The pipe section 92 and the fixed coupling 96 are screwed together until 
the pipe section 92 and the fixed coupling 96 mate securely. 
A first, proximate end of the flexible hose 94, which has an inner diameter 
of one inch and is manufactured as shown in FIG. 13 with a helical steel 
spring 102 embedded within the wall of the hose 94, is then placed over a 
portion of the distal end of the fixed coupling 96 and secured using a 
circular clamp, for example, a stainless steel clamp. The second, distal 
end of the flexible hose 94 is then placed over a portion of the proximate 
end of the attachable coupling 98 and secured using a circular clamp, also 
a stainless steel clamp. The attachable coupling 98 allows the connector 
82 to be connected to a mating male or female coupling 99 attached at the 
ends of the subheaders 58, 60. 
Alternatively, the attachable coupling 98 is attached directly to the fixed 
coupling 96 of the supply header 48, while a mating male or female 
coupling 99 is attached via a flexible hose 94 to the supply subheader 58 
and return subheader 60 corresponding to the given panel 52, as shown in 
FIG. 8. The mating couplings 99 are alternated between the supply and 
return subheaders 58, 60 for a given panel 52, i.e., each of the supply 
subheaders 58 may have a male coupling 99, while the return subheaders 60 
may have a female coupling 99. In this fashion, when the system 44 is to 
be disassembled to be transported or stored, the coolant in the panel 52 
can be isolated in the panel 52 by attaching the male coupling 99 of the 
supply subheader 58 to the female coupling 99 of the return subheader 60. 
Moreover, the panels 52 may be isolated in operation as well as in storage 
by disposing a valve 104, for example, a brass or stainless steel ball 
valve, between the fixed coupling 96 and the attachable coupling 98 on the 
spline-connector 82, as shown in FIGS. 7 and 12. By connecting the valves 
104 to the supply and return header connectors 82, the coolant in a panel 
52 may be isolated by closing the valves 104. 
By way of example only, isolation of the panel 52 could be advantageous 
should one of the coolant tubes 62, 64 of a panel 52 rupture. Isolation 
could prevent loss of the coolant into the medium to be frozen and the 
underlying foundational material, prevent loss of pressure throughout the 
system 44, and otherwise allow the repair of the panel 52 with the 
ruptured tube 62 or 64 to be performed while maintaining the frozen 
surface on the portions of the medium unaffected by the loss of coolant 
flow through the isolated panel 52. 
Additionally, again by way of example only, isolation of the panels 52 
could be advantageous during the freezing of the medium. Specifically, the 
panels 52 could be isolated so that the medium is frozen in stages, panel 
by panel, until all of the medium in the rink 46 is frozen. Such a staged 
process could be especially advantageous when attempting to freeze a 
medium when the temperature of the surrounding environment is 
substantially greater than the temperature at which the medium will 
freeze. 
FIG. 14 shows the locking mechanisms used in any of the embodiments of the 
connectors 82 shown in FIGS. 10, 11 and 12. Particularly, each end of the 
connector 82 is machined to include a shoulder 110, an interior o-ring 
groove 112 and an interior spline groove 114. Similarly, each end of the 
pipe 80 is machined to have an exterior spline groove 116, which 
corresponds axially with the interior spline groove 114 of the connector 
82 when the end 118 of the pipe 80 abuts the shoulder 110 of the connector 
82. 
In operation, an O-ring 108 is first placed in the interior O-ring groove 
112. The pipe 80 is then placed into the connector 82 until the end 118 
abuts the shoulder 110. The o-ring 108 and the exterior surface of the 
pipe 80 thus forms a first sealing and locking mechanism 120 preventing 
relative movement of the pipe 80 and the connector 82 in the axial 
direction. A second locking mechanism 122 is formed when the spline 106 is 
placed through a hole 124, the hole 124 being connected through the wall 
of the connector 82 to the interior spline groove 114. The spline 106 
fills the channel formed by the corresponding interior and exterior spline 
grooves 114, 116, also preventing the relative movement of the pipe 80 and 
the connector 82 in the axial direction. 
A further embodiment of the spline-connector, designated 84 in FIGS. 5, 7, 
8, and 9, is used to couple the pipes 80 used in the second section of the 
main return header 50. Because the connectors 84 are not intended to be 
connected to the return subheaders 60, the connectors 84 are not 
manufactured with the opening 100 into which the fixed coupling 96 can be 
screwed. The connectors 84, like the connectors 82, however, do feature 
both the first and second locking mechanisms 120, 122. 
As shown in FIGS. 7 and 8, the panel 52 is defined by of the supply 
subheader 58, the return subheader 60, the first and second plurality of 
tubes 62, 64 and the plurality of U-shaped sections 66. As further 
illustrated in FIGS. 15 and 16, the supply and return subheaders 62, 64, 
fabricated from copper pipe, are machined with plurality of openings 126. 
A barbed saddle fitting 128, for example a copper fitting, is soldered 
over each opening 126, using a silver based solder. Use of the saddle 
fitting 128 is advantageous in that there is limited obstruction of the 
fluid flowing from the subheader 58, 60 into the tubes 62, 64 and the 
subheaders 58, 60 have a substantially uniform cross-sectional area. One 
end of one of the tubes 62, 64 is fitted over the barbed end 130 of saddle 
fitting 128 and fastened with a circular clamp. The use of barbed ends 
allows a secure attachment between the tubes 62, 64 and the subheader 58, 
60 to be formed. 
The tubes 62, 64 are made with a 1/2 inch inner diameter from a composition 
prepared using ethylene vinyl acetate (EVA), for example , from a 
composition prepared using 18% by weight of EVA combined with 82% by 
weight of polyethylene. The percentage of EVA may vary from between 15-25% 
by weight, while the polyethylene may vary from between 75-85% by weight. 
During manufacture, the composition is extruded to form the tubes and is 
passed through a cooling tank at a rate of 1 foot per second. Unlike the 
conventional methods for manufacturing the polyethylene or polypropylene 
tubing described above, the EVA/polyethylene tubes are passed through a 
cooling tank or tanks for a distance of between 25 and 36 feet with the 
tubes in a substantially straight configuration. The tubes may be cooled 
by spraying the tubes with water in the cooling tank or tanks, or by 
passing the tubes through a water bath maintained in the cooling tank or 
tanks. It is thought that the time spent by the tubes in the cooling tank 
or tanks allows the EVA/polyethylene tubes to thermally-set in a 
substantially straight configuration. The extruded, cooled product, having 
a final inner diameter of 1/2 inch, is then hand-coiled with the effective 
diameter of the coil being no less than 2.5 feet, and placed into a 
gaylord container for shipping. The tubes are fabricated in length s of 
between 515 to 520 feet. 
The tubes 62, 64 are joined in pairs, the proximate end of the tube 62 
attached to the supply subheader 58 and the proximate end of the tube 64 
to the return subheader 60. Similarly, the distal ends of the pair of 
tubes 62, 64 are connected to one of the ends of the plurality of U-shaped 
connectors 66. 
As illustrated in FIGS. 17 and 18, each U-shaped connector 66 has a 
U-shaped section 132 and a pair of barbed fittings 134. The U-shaped 
section 132 and the barbed fittings 134 are made of copper. The distal 
ends 136 of the barbed fittings 134 are placed inside of ends 138 of the 
U-shaped section 132 and soldered in place using a silver based solder. As 
shown in FIGS. 19 and 20, one of the distal ends of tubes 62, 64 is then 
placed over each of the barbed, proximate ends 140 of the barbed fitting 
134, and fastened into place using a circular clamp 139. 
The U-shaped section 132 is of a constant inner diameter, for example, of 
nearly equal diameter to the tubes 62, 64 and thus provides a 
substantially continuous and substantially uniform cross-sectional area 
through which the coolant medium can pass. Furthermore, the barbed ends 
140 of the fitting 134 provide for a secure attachment site to attach the 
ends of the tubes 62, 64 to the U-shaped connector 66. 
A uniform spacing between the centers of the tubes 62, 64 is achieved in 
part by welding a bar 142, for example, a brass bar of hexagonal or 
rectangular cross-section, to the U-shaped bend in each of the U-shaped 
connectors 66 that make up the panel 52. As shown in FIGS. 7 and 8, the 
bar 142 can be straight or curved to keep the proper spacing between tubes 
62, 64 even in the rounded corners of the ice rink 46. In addition, 
spacers 144, for example, made of polyethylene, are placed at intervals 
along the tubes 62, 64 to maintain the spacing between the tubes 62, 64 
and the spacing between the tubes 62, 64 and the surface over which the 
system 44 is installed. The spacing between the centers of the tubes 62, 
64 is between 1 and 11/2 inches, while the spacing between the spacers 144 
is approximately 14 inches. 
The spacers 144 may either be removable or non-removable. If the spacers 
144 are non-removable, i.e. enclose the entire circumference of the tubes 
62, 64, then it is preferable to place the tubes 62, 64 through the 
spacers 144 before attaching the tubes 62, 64 to the barbed saddle 
fittings 128 of the supply and return subheaders 58, 60. If the spacers 
are removable, i.e. may be snapped around the tubes 62, 64, the spacers 
may be attached to the tubes 62, 64 after the tubes 62, 64 are connected 
to the respective supply and return subheaders 58, 60. 
Still other aspects, objects, and advantages of the present invention can 
be obtained from a study of the specification, the drawings, and the 
appended claims.