Patent Publication Number: US-2022228325-A1

Title: Subsurface Warming System For An Athletic Field

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 63/138,663, filed on Jan. 18, 2021, entitled “Root Zone Warming System For Natural Turf Athletic Field,” which is expressly incorporated by reference herein, in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a method and system for warming the subsurface of an athletic field. If the athletic field is natural grass, then this invention relates to warming the root zone of the natural turf, to buffer the root zone temperature and thereby reduce the onset, the degree, or the duration of dormancy during the winter season. If the athletic field is an artificial turf, then this invention reduces the onset, the degree, or the duration of freezing that may otherwise occur during the winter. 
     BACKGROUND OF THE INVENTION 
     Over the years there have been a number of technical developments that have enhanced the performance of natural turf, particularly natural turf used as part of an athletic field, or athletic playing surface. 
     For example, Daniel et al. U.S. Pat. No. 3,908,385, issued Sep. 30, 1975 and entitled “Planted Surface Conditioning System,” discloses a natural turf athletic field equipped with a drainage system that includes vacuum to promote enhanced drainage of water from the natural turf. This vacuum-enhanced drainage feature enables the natural turf to be playable sooner after a downpour, or even during a downpour, by pulling moisture from the natural turf much faster than would otherwise occur via mere gravity drainage. Given the prevalence at that time of short-pile artificial turf, often referred to as “Astroturf,” this feature better enabled natural turf to compete with such then-new artificial turf systems. 
     In general, this type of system included a water impermeable membrane over a compacted subsurface, covered by a fill layer of sand with a drainage network buried therein and a natural turf playing surface above the fill layer. The roots of the natural turf extend downwardly into the fill layer, to create a subsurface root zone. Some of the pipes in the drainage network include openings to accommodate gravity drainage and also vacuum-enhanced drainage. As a pioneer in the technology related to natural turf athletic fields, Dr. Daniel recognized the advantages that could be achieved by using a uniform subsurface particulate for a natural grass athletic field, how the uniformity of the particulate material enhanced the consistency of drainage and sub-irrigation, and also how it complemented the capability for vacuum-enhanced drainage. 
     Thereafter, Dr. Daniel developed an improvement to his original system, as taught in U.S. Pat. No. 5,350,251, issued Sep. 27, 1994 and entitled “Planted Surface Moisture Control System.” The system disclosed in the &#39;251 patent reduced the installation and construction costs associated with incorporating vacuum-enhanced drainage into a natural turf athletic field, primarily by eliminating the need for underground concrete vacuum pump pits. This reduction in costs made the vacuum-enhanced drainage feature more widely available for natural turf athletic fields, and thereby also increased the availability of natural turf athletic fields. 
     The present applicant has successfully practiced the technology taught in the Daniel &#39;385 and &#39;251 patents, primarily under the trademarks “PRESCRIPTION ATHLETIC TURF,” or “PAT.” Moreover, as disclosed in U.S. Pat. Nos. 5,752,784, entitled “Low Profile Drainage Network For Athletic Field Drainage System” and U.S. Pat. No. 5,944,444, entitled “Control System For Draining, Irrigating and Heating An Athletic Field,” applicant has improved upon this technology. More specifically, the 784 patent discloses the use of low profile couplings in the subsurface piping network, at each intersection of a low profile conduit row and a lower level pipe row, with all of the low profile conduits and the lower level pipes residing above a water impermeable barrier. These low profile couplings reduced the overall vertical profile of the athletic field, and thereby reduced the overall amount of fill layer material needed, and the corresponding costs. The low profile couplings also simplified the subsurface work, because in such a system all of the trenches for the piping network are parallel, for the lower level pipe rows, and there are no perpendicular trenches needed. 
     Further, the 784 patent discloses the use of multiple subsurface water level sensors that measure the actual physical level of the water above the membrane. This improved the overall reliability of the system with respect to water level sensing, and thereby facilitated further automation of the system controls, particularly with respect to the vacuum-enhanced drainage feature. 
     Thereafter, the &#39;444 patent disclosed the use of a remote computer to control such a system, and also added a subsurface feature that involved the flowing of heated water, from a heat exchanger, between adjacently located subsurface sections of the field. The subject matter of each of the 784 and &#39;444 patents is expressly incorporated by reference herein, in its entirety. 
     Subsequently, as shown in German Utility Model DE 29903998 U1, systems were developed to push air into an athletic field from below, using the same subsurface piping network that is used for drainage. As disclosed in this publication, the system includes a fan that generates the air that is blown to the subsurface. While enroute to the subsurface piping network, the blown air moves through a heat exchanger that is operatively connected to a burner, or furnace, such that the air becomes warmed before it reaches the subsurface of the field. U.S. Pat. No. 7,413,380 discloses this same general concept, in the context of a system and method for conditioning the natural turf of golf course greens. Moving warmed air into the subsurface root zone of a natural turf has the potential for reducing the time period when the roots are dormant, during the winter months. 
     In more recent years applicant has also continued its efforts to improve upon the concepts and features initially devised by Dr. Daniel, by designing and installing natural turf athletic fields with gravity drainage, vacuum-enhanced drainage, irrigation (including subsurface irrigation) and positive pressurization to aerate the athletic field. In one instance applicant also used a subsurface heat exchanger that was based on geothermal principles to warm the air supplied to the subsurface of the athletic field for aeration, to warm the root zone of the natural grass. 
     One less than optimal aspect of this particular structure is that the pressurizing air always must flow through the heat exchanger, even when there is no need to warm the air flow. For some relatively temperate climates, where the warming feature is largely unused, the heat exchanger represents added structure that is mostly unneeded, yet nonetheless still needs to be maintained. 
     Other field installers have also incorporated the use of positive pressurization into their athletic field systems, to push air into the subsurface root zone of a natural turf field through a subsurface piping network, and then upwardly to atmosphere. For some of these other known systems this aeration feature includes generating the air flow with a large fan, and then directing the air through a furnace before routing it to the piping network. 
     Such systems present some significant practical disadvantages. For instance, such systems require a significant amount of floor space and ceiling height, due to the space requirements of a sufficiently sized fan and a correspondingly sized furnace. Moreover, these components must be located relatively close to the athletic field, or in the vicinity of the stadium or the structure where the athletic field is located. 
     The most efficient way to operate such a system is to place the large fan and the accompanying furnace in a restricted room located adjacent to the athletic field, preferably in the stadium. But if such a location is not available, due to space limitations, then the furnace needs to be located remotely from the piping network that is located under the athletic field, and the routing of the air from the remotely located furnace will cause further heat and energy losses for the system. These issues can be especially problematic if the athletic field is located within a stadium that is landlocked, as is often the case in urban environments, where it has now become popular to build natural turf stadia for soccer. 
     Further, such systems consume an inordinate amount of energy, due the type of fan and the type of furnace used. For example, one known system is described as using four fans wherein each fan is capable of supplying air at up to 140,000 cubic feet per minute at up to 32 inches WC status pressure. A fan of this type consumes a significant amount of electrical energy during continuous operation. For this same system, the furnace, which typically operates on natural gas fed by a 4 inch supply line, itself is believed to require a floor footprint of about 1000 square feet, and to require a relatively high ceiling, maybe even as high as about 16 feet. 
     It is an object of the present invention to warm the root zone of a natural turf athletic field in a manner that is more practical, more flexible, and also significantly lower in cost and in energy consumption than the current conventional systems. 
     It is another object of the present invention to incorporate a relatively low cost root zone warming feature into a known and dependable system used with a natural turf athletic field, wherein the system accommodates gravity drainage, irrigation, vacuum-enhanced drainage, and aeration, wherein the added root zone warming feature does not require such a large amount of additional space and does not consume such a disproportionate additional amount of energy. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the above-stated objects by incorporating an economical and space saving air supply and warming structure into a system for providing gravity drainage, vacuum-enhanced drainage, irrigation, and optionally sub-irrigation for a natural turf athletic field. This air supply and warming structure includes a constant air supply source, preferably a positive displacement blower, in fluid communication with the natural turf via a subsurface piping network and a conduit operatively connected thereto, with a variably controllable valve residing along the conduit between the constant air supply source and the natural turf. The variably controllable valve includes, or is fitted with, an actuator with modulatory capability, such that it can be variably opened a desired amount, from 0 to 100%, to control flow through the conduit. 
     By variably controlling actuation of this valve located adjacent the outlet of the constant air supply source, a user is able to selectively impede the air flow, i.e., to apply friction, or flow resistance, to the output end of the constant air supply source. When the output air flow is impeded in this manner, the constant air supply source must then work harder to continue to supply the same volume of air, which results in an increase in the operating temperature within the constant air supply source. This temperature increase transfers to the air that flows from the output end of the constant air supply source, through the valve, and eventually to the natural turf, to achieve warming of the root zone of the natural turf. 
     By using a constant air supply source that is able to supply a generally constant volume of air, which for one installation is known to be in the range of 1000 to 3000 cubic feet per minute, while consuming minimal electrical energy, in cooperation with a variably controllable valve that is selectively actuatable, the disclosed system is more practical, and is significantly lower in cost and more energy efficient than conventional systems that are currently used to warm athletic fields. Among other reasons, the disclosed system does not require a furnace to warm the air that is supplied to the root zone of the natural turf. The elimination of the need for a furnace represents a substantial savings in terms of energy consumption and corresponding costs, as well as physical space requirements within the venue. 
     Further, with the disclosed system the constant air supply source and the controllable valve can be readily incorporated into an existing system for supplying gravity drainage, vacuum-enhanced drainage, irrigation, and sub-irrigation to a natural turf athletic field, without requiring any additional disproportionate amount of space. More specifically, as presently disclosed, the constant air supply source occupies a relatively small footprint, in terms of floor space and height. 
     Comparatively, with existing conventional systems that use a furnace to convectively heat air that is supplied through a duct at a flow rate needed to sufficiently warm a natural turf, the furnace/fan assembly itself will generally require a minimum footprint of 1000 square feet, and a height of 10 feet or more. For an athletic field that is part of a stadium located in an urban environment, and perhaps landlocked, in some situations this space will simply not be available. Even if the space is available, the use of such a furnace in the stadium still requires a disproportionate amount of space that could otherwise be used for other stadium operations. Alternatively, locating a furnace remotely would add to the costs associated with delivering warmed air to the root zone of the natural turf. Further, even without considering the additional losses associated with remotely locating a furnace, the use of a furnace to heat the air supplied to a natural turf already consumes a disproportionately high amount of energy resources. Thus, remotely locating the furnace makes a bad situation even worse. 
     Still further, with the disclosed system a user is consistently and readily able to control the temperature of the air supplied to the natural turf, because there is a known correlation between the air flow impedance at the output of the constant air supply source, as measured by the amount that the variably controllable valve is open, and the corresponding temperature of the air supplied to the turf. For example, with the preferred positive displacement blower, when the variably controllable valve is closed further, so as to produce an increase of one pound per square inch in fluid pressure at the valve, there is a corresponding temperature increase of 13 degrees Fahrenheit in the air supplied by the blower. This correlation remains relatively constant. And conversely, progressive opening of the variably controllable valve results in reduced friction, and a lower temperature of the air flowing from the constant air supply source. 
     Therefore, by knowing the pressure at the variably controllable valve, i.e., the percentage that the valve is open, the user knows the temperature of the air that is flowing therethrough. As a result, a user can reliably and repeatably deliver warmed air to the natural turf at known temperatures and flow rates. Also, to assure reliability, the system preferably also includes temperature sensors in the piping network to measure the temperature of the air flowing therethrough. The temperature sensors enable the user to verify and/or recalibrate the blower and/or the variably controllable valve, as needed, to achieve the desired air flow conditions, and to identify the blower and valve settings that correspond to those desired conditions, to achieve the desired root zone temperature. 
     According to a presently preferred embodiment of the invention, a natural turf athletic field includes a particulate subsurface that supports the roots of the natural turf and in which a piping network resides. A constant air supply source is in fluid communication with the piping network, and residing therebetween is a variably controllable valve, preferably electrically actuatable, fitted with a modulating actuator. A subsurface vault also resides therebetween, located adjacent to or below the constant air supply source, and the vault serves as the connection point for the primary components of the system. More specifically, the vault serves as the discharge point for the piping network, and it also connects to the constant air supply source via a conduit along which the variably controllable valve resides. 
     The vault serves as the routing point for all water and air that flows to or from the natural turf and the other components of the system. For example, a discharge line with a downturn connects to the vault. The discharge line is the largest pipe of the overall system. Water above the discharge line flows by gravity outwardly from the vault via the discharge line. The largest pipe of the piping network that drains the athletic field, referred to as the “main” pipe, connects to the vault at a level above the discharge line. This main pipe includes an electrically actuated main valve located adjacent the vault, to selectively open or close fluid communication between the piping network and the vault. If the main valve is open, rain falling in the athletic field will naturally flow by gravity through the main pipe, past the main valve and into the vault, and then out of the vault via the discharge line. 
     A vacuum pump operatively connects to the vault near the top thereof. With the main valve open the vacuum pump is operable to selectively apply vacuum to the vault, and hence to the piping network and to the turf, to achieve vacuum-enhanced drainage. As stated above, the positive displacement blower also operatively connects to the vault, via the conduit, with the variably controllable valve located along the conduit, near an output end of the blower. The constant air supply source is isolated from the vacuum when the vacuum pump is operating, by completely closing the variably controllable valve. Conversely, the vacuum pump outlet is closed off, i.e. isolated, when the constant air supply source is pushing air into the vault. Thus, at any given time only one of these two components operates. They never operate simultaneously. 
     The vault is preferably of conventional size and located adjacent the athletic field. The vacuum pump may reside on top of the vault, and typically requires only about 10 square feet of floor space. According to the present invention, the overall size and the spacing of the components that supply warmed air to the root zone of the natural turf is relatively small, particularly when compared to conventional systems that require a large fan and a furnace. 
     A controller operatively connects to the blower, the controllable valve, the vacuum pump, the main valve, and also to a plurality of temperature sensors located within the subsurface particulate of the athletic field, and preferably also to another plurality of temperature sensors located in the piping network. Further, the controller can also be operatively connected to a water source and to at least one of a standard above-ground watering system and a subsurface-irrigation system. This enables the user to selectively control and coordinate one or more of: above-ground watering, watering via sub-irrigation, gravity drainage, vacuum-enhanced drainage, aeration of the natural turf, or aeration of the natural turf with warming of the air supplied to the root zone thereof. If desired, a chilling device could be used to introduce cooling as to the vault, and then to the root zone. 
     Another advantage of the current root zone warming system is that the warm air conduits are of reasonably small and easily manageable size. For example, the diameter of the conduit is the same as the outlet end of the constant air supply source, and is preferably about only 10 inches. This conduit connects to a vault that has an internal volume of about 400 cubic feet, and the pressurization air flows therefrom into the piping network via a main pipe of about 15-18 inches in diameter. This diameter is less than 2× the diameter of the outlet and the conduit, which is 20 inches. Thereafter, the air flows to pipes that are of successively smaller diameter, and in the preferred embodiment, eventually to the horizontally elongated pipe. 
     The present invention more consistently and readily varies, and thereby controls, the temperature of warming air that is supplied to the root zone of a natural turf athletic field, with a high degree of reliability. Moreover, it does so in a relatively simple manner, that is flexible in operation, and lower in cost and space requirements. 
     Further, the present invention supplies warm air pressurization to a natural turf athletic field, with the warm air having a temperature generally in the range of about 0-105 degrees Fahrenheit above ambient air temperature. The present invention supplies this warm air pressurization for an extended duration of time, while consuming minimal energy, and also while occupying only minimal floor space and height. In one application of this invention, with a standard sized soccer field, the invention supplies the warm air at a volume flow rate in the range of 1000-3000 cubic feet per minute. However, for a larger field, higher volumes could be delivered, up to perhaps 6000 cubic feet per minute. 
     Those skilled in the art will recognize that this technology is suitable for athletic fields that comprise entirely natural turf, and also those athletic fields wherein some or all of the field surface includes a stabilized natural turf, which is sometimes referred to as a “hybrid” natural turf, wherein an artificial turf component are incorporated into the root zone, and sometimes also into the turf canopy. 
     Up to this point, this specification has described the invention in the context of a natural turf and that is how the invention originally developed. However, all of the same general principles could be used to minimize or even eliminate the adverse effects of subsurface freezing for an infilled artificial turf. As is known, such a turf includes upstanding artificial grass-like fibers that are in part supported by a subsurface infill of particulate material. Such artificial turfs can be susceptible to accelerated wear effects due to sub-freezing, or freezing, or near-freezing ground temperatures. Also, the shock absorption capability of the artificial turf can be considerably less under such conditions. 
     Given the relatively low cost in terms of equipment, and space requirements, it makes sense to consider using the present invention for treating the subsurface of an artificial turf. The general structure of such a system would be the same, although the subsurface vertical dimensions could be reduced, and the piping network could be reconfigured and/or simplified. So even though the following section specifically refers to a natural turf, those skilled in the art will recognize that this invention is applicable to athletic fields in general, including to a current conventional infilled artificial turf athletic field. Accordingly, the claims of this application are more general than those of earlier related applications. 
     Also, those skilled in the art will more readily appreciate and understand the features of the present invention when considered in the context of the accompanying drawings, which are briefly described in the next section and then described in more detail in the section thereafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic top plan view of a root zone warming system for a natural turf athletic field, according to a currently preferred embodiment of the invention. Directional arrows generally show the direction of water drainage from the athletic field. 
         FIG. 1A  shows the same schematic top plan view of the same athletic field, but in  FIG. 1A  the directional arrows generally show air flow into the athletic field, to pressurize the subsurface. 
         FIG. 2  is a vertical cross-sectional view along lines  2 - 2  of  FIG. 1 . 
         FIG. 2A  shows the same view as  FIG. 2 , but in a different location so the view does not include the structure of the piping network that resides below the barrier, compared to  FIG. 2 . 
         FIG. 3  is a transverse cross-sectional view along lines  3 - 3  of  FIG. 2 . 
         FIG. 4  is a schematic horizontal cross-sectional side view of a vault that is included in a root zone warming system of the present invention, according to a preferred embodiment, with the vault shown operatively connected to a number of additional components of the system. 
         FIG. 5  is a schematic top view of the vault shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a system  10  for warming the root zone of a natural turf  11  according to a currently preferred embodiment of the invention. In this specification the phrases natural turf and athletic field are used interchangeably for convenience and because they occupy the uppermost portion, i.e., the surface, of the structure served by the system  10 . The system  10  includes a subsurface piping network  12 , which is shown schematically in plan view in  FIG. 1 . Those skilled in the art will appreciate that the particular numbers of rows of the pipes shown herein, and the dimensions stated for the pipes in those rows, can be varied to accommodate different considerations. This particular piping network  12 , as shown and described, represents a currently preferred embodiment for one particular known venue. However, depending on other considerations, such as environment, costs, and availability, the piping network and its components are amenable to alternative variations.  FIGS. 1, 1A, 2, and 3  show the details of the piping network  12 , while  FIGS. 4 and 5  show the details of the system. Although applicant has used polyethylene, the piping network  12  may comprise components made of any suitably strong and durable material. 
     More specifically, the piping network  12  includes eleven rows  13  of longitudinally extending pipes. Each of these longitudinally extending pipe rows comprises a low profile pipe having a horizontally elongated shape, in transverse cross section, so as to occupy a relatively minimal volume of the subsurface, as disclosed in the 784 patent. Nonetheless, compared to the 784 patent, these longitudinally extending pipes  13  include transversely oriented openings in the downwardly directed surfaces thereof, preferably on the ridges, or outermost surfaces of the corrugations thereof. These openings enable fluid communication between the system  10  and the natural turf, i.e., water drainage and air flow, as described in more detail with respect to the other Figures. 
     As shown in  FIG. 1 , the eleven rows of longitudinally extending pipe  13  intersect with five rows of transversely extending pipes  14 , each of which preferably has a six inch diameter. At each of the intersections of the longitudinal rows  13  and the transverse rows  14 , a low profile coupling  15  is used, also as disclosed in the above-identified 784 patent. A barrier  16  resides below the longitudinal rows  13  and the transverse rows  14 . Preferably, the barrier  16  is water impermeable, so as to enable water conservation practices. Depending on the customer&#39;s preference, and other considerations such as cost and available materials, the barrier does not necessarily need to be water impermeable. In the embodiment shown, the barrier  16  is water impermeable and isolates the natural turf  11  from the substructure located therebelow. Generally, the barrier  16  resides about 14-16 inches underground. Part of the piping network  12  is located above the barrier  16 , as explained above, and part of the piping network  12  is located below the barrier  16 . 
     Below the barrier  16 , the piping network  12  includes two more longitudinal rows  17 , preferably each of ten inch diameter. These two longitudinal sub-barrier rows  17  connect to the five transverse rows  14  via, preferably, inverted T-connectors  18 , with one inverted T-connector located at each of the ten intersecting locations shown in  FIG. 1 . Each T-connector  18  interconnects one above-barrier transverse row  14  with a sub-barrier longitudinal row  17 , and in a manner that assures a circumferential seal between the outer surface of the inverted T-connector  18  and the barrier  16 , so as to maintain the seal and to prevent any water or air leakage from the subsurface of the natural turf  11  to locations below the barrier  16 . 
     The two sub-barrier longitudinal rows  17  in turn connect to two sub-barrier transverse rows  19 , at four intersecting points as shown in  FIG. 1 . The sub-barrier transverse rows  19  preferably have a 12 inch diameter. These two sub-barrier transverse rows  19  in turn connect to the main sub-barrier pipe  20  that extends longitudinally along one side of the athletic field  11 , and is preferably 16 inches in diameter. The main  20  extends to a vault  21  that is preferably located adjacent to the athletic field  11 . The main  20  has a main valve  22  located adjacent the vault  21 , to close off the fluid connection between the piping network  12  and the vault  21 , if desired, for example, during time periods when conserving root zone water is beneficial. Watering may occur either by an above-ground sprinkler system (not shown), or by sub-irrigation (also not shown), or by natural rainfall. By closing the main valve  22  water can be held in the piping system  12 , which eventually saturates the natural turf  11 . 
       FIG. 1  also shows that the vault  21  operatively connects to a discharge line  25 , a vacuum source, i.e., a vacuum pump,  26 , and a constant air supply source  27 , which is a device that supplies constant air flow independent of the downstream air flow resistance, at least within certain operating parameters, as explained in more detail below. The constant air supply source  27  connects to the vault  21  via a conduit  28 , with a variably controllable valve  29  residing along the conduit  28 . The conduit  28  is preferably PVC, but could also be made of any other suitably strong and durable material. A controller  38 , not shown in  FIG. 1 , controls operation of these components of the system  10 . 
       FIG. 2  shows a longitudinal cross-sectional view of the same system  10  and the same natural turf  11  that are shown in  FIG. 1 , but as viewed from the sideline of the athletic field. With this view,  FIG. 2  better shows the vertical relationships of the components of the system  10  relative to the natural turf  11 , the piping network  12 , and the barrier  16 . Although only the transverse rows  19  are shown in this view, and not the main  20 , the main  20  resides lower beneath the ground surface than the two sub-barrier transverse rows  19  to which the main  20  is connected, and the two transverse rows  19  are of reduced cross-sectional dimensional, compared to the main  20 . However, both the main  20  and the transverse rows  19  have uppermost portions that reside in about the same horizontal plane. Moreover, these two sub-barrier transverse pipe rows  19  extend lower below the surface than the two transverse sub-barrier longitudinal rows  17  to which they connect, which are also of smaller cross-sectional dimension than the pipes residing below. And again, as shown at least partially in  FIG. 2 , uppermost portions of the rows  17  reside in the same horizontal plane as the uppermost portions of the rows  19 , and therefore also partially in the same horizontal plane as the main  20 . 
     In addition to showing the barrier  16  and the above-barrier transverse rows  14  which intersect with the longitudinally extending above-barrier rows  13  of low profile pipe,  FIG. 2  also shows more details of the natural turf  11 . More specifically, the natural turf  11  includes natural grass plants that extend above the surface of the ground, and roots that extend downwardly into a particulate subsurface material, also called a fill layer. In the embodiment shown, the fill layer includes an upper layer of sand  33 . Nonetheless, the particulate subsurface material may comprise other particulate material that is conducive to the growing of natural grass plants. The fill layer  33  is preferably homogenous, at least with respect to each horizontal level, so that the flow of any air or water flowing therethrough is consistent and uniform across the entire surface area of the natural turf  11 . The downwardly extending roots of the natural turf  11  extend into the upper layer and define a vertical band of the subsurface referred to in this specification as the root zone. The particulate subsurface is porous enough to enable pressurized air to flow upwardly therethrough when air is pushed into the piping network  12  from the constant air supply source  27 . Again, the fill layer is of consistent particulate, thereby to promote consistency in drainage, whether gravity drainage or vacuum enhanced drainage, and also consistency in aeration. 
     In the preferred embodiment shown, the subsurface fill layer includes a lower layer of uniformly sized gravel  35 , with this lower layer  35  having a depth of about 6 inches above the barrier  16 . The upper layer  33  of sand is about 10 more inches, and so there is about 16 total inches of subsurface located above the barrier  16 . As noted previously, the low profile pipe  13  includes corrugations, and the openings of the piping network  12  reside along the corrugations in the bottom surfaces thereof, and are directed downwardly. This places the water/air flow openings directly opposite an upper surface of the barrier  16 . The lower layer  35  of gravel surrounds these longitudinal pipes  13  in between the rows and also for a few inches thereabove. 
     With this type of particulate subsurface, the athletic field  11  is water and air permeable. More specifically, water drains relatively quickly in a downward direction due to gravity, and the downward flow can be enhanced via the application of vacuum.  FIG. 1  includes directional arrows to show this flow into and through the piping network  12 , to the vault  21  either by gravity alone or vacuum-enhanced. Additionally, by supplying positive pressurization into the piping network  12  via the openings in the pipes  13 , the system  10  pushes air upwardly through the athletic surface  11  and into the atmosphere.  FIG. 1A  includes directional arrows that generally show the pressurization flow, from the vault  21  into the piping system  12  out of the pipes  13  and into the subsurface, then upwardly from the athletic field. The general principle of aerating an athletic field via pressurized air flow is already known in the industry. However, applicant has provided this explanation of these structural features because the system  10  is not known. And this explanation of this particular piping network  12  of this system  10  will enable a reader to better understand its operation. Additionally, although not specifically shown, applicant further contemplates an alternative embodiment of the invention whereby each of the eleven rows of longitudinally extending pipe is truncated into row segments that are disconnected between each of the corresponding rows of transversely extending pipes. This alternative structure would thereby have two opposing “dead ends” connected to each transition joint  15 . This alternative embodiment would create heat dissipation at each of these terminating segments, or dead ends. 
       FIGS. 2 and 2A  show that the barrier  16 , which in this case is preferably water impermeable, serves as a boundary between upper and lower parts of the piping network  12 . The inverted T-connectors  18  extend therethrough and then downwardly therefrom, preferably a vertical distance of about 8 inches. In one embodiment, the inverted T-connectors  18  include a surrounding flange that is welded circumferentially to the barrier  18 . 
     Within the piping network  12  there is a first plurality, or set, of temperature sensors  40  located within the main  20  or the rows  19  connected thereto, and preferably also a second set of temperature sensors  41  located at a second, higher vertical level, preferably within the transverse rows  14 . Further, the system  10  includes a third plurality of temperature sensors  42  in the upper layer  33 , to measure the temperature in the subsurface where the roots reside. Each of the third plurality of sensors  42  is preferably located about 3 inches below the surface, and the sensors  42  are spaced generally equidistantly around the field  11 . All of the sensors  40 ,  41 , and  42  operatively connect to the controller  38 , by hardwire or by wireless connection, as desired. By locating these three sets of sensors  40 ,  41 , and  42  at different vertical levels, a user is able to measure the warming effect on the subsurface root zone as the warm air progresses from the vault  21 , in terms of how long it takes to get the upper layer  33  to a desired temperature, and the extent of any heat loss as the warm air flows from the vault  21  to the natural turf  11 .  FIGS. 2A and 3  show the relative vertical positions of the second and the third pluralities of sensors  41  and  42 , respectively. 
       FIG. 4  shows a schematic view of the vault  21  located adjacent the athletic field  11 , including the discharge line  25  that extends into the vault  21  and has a turndown  36  to help isolate the discharge line  25  from the above-water atmosphere in the vault  21 . This turndown  36  assures that some water will always remain in the bottom of the vault  21 , up to the horizontal level of the bottom of the discharge line  25 . Above the discharge line  25 , the main line  20  terminates at the vault  21 , and the main line  20  can be isolated from the vault  21  by a main valve  22 , which is actuatable between on and off positions. The controller  38  operatively connects to the main valve  22 , and also to the variably controllable valve  29  located along conduit  28 . Again, the operative connections to the controller  38  may be a hard wire or wireless, i.e., remote, depending on the particular conditions of the athletic field  11  and the owner preference. 
       FIG. 4  also shows the vacuum pump  26  operatively connected to a top end of the vault  21  and operable to supply vacuum to the inside thereof. When the main valve  22  is open and the vacuum pump  26  is operating, the vacuum pump  26  applies vacuum to the vault  21  which causes vacuum to be applied to the piping network  12  via the main  20 , and eventually to the rest of the piping network  12  and then to the natural turf  11  located thereabove. As described above, the application of vacuum to the piping network  12  provides vacuum-enhanced drainage capability for the natural turf  11 . When there is no need for vacuum-enhanced drainage, the vacuum source  26  is isolated from the inside of the vault  21 . As shown in  FIG. 4 , the vacuum source  26  also operatively connects to the controller  38 . 
     Further, as shown in  FIG. 4 , the constant air supply source  27  operatively connects to the vault  21  via the conduit  28 , and the variably controllable valve  29  is located on the conduit  28  near an outlet end of the source  27 . Each of the source  27  and the variably controllable valve  29  also operatively connects to the controller  38 . In  FIG. 4  the directional arrows show air flow that occurs during aeration of the athletic field  11 , with the air flowing from the source  27  through the conduit  28 , including past the variably controllable valve  29  and into the vault  21 , into the main  20  (with main valve  22  open), into the rest of the piping network  12 , and then outwardly from the bottoms of the uppermost pipes  13  and into the lower layer  35  of gravel  35 , then the upper layer  33  of sand, and thereafter upwardly from the athletic field  11  and into the atmosphere. In this pressurization mode, air supplied from the air source  27  flows into the vault  21  and eventually upwardly from the athletic field  11 , via the openings in the bottom surface of the longitudinal extending pipes  13 . 
       FIG. 5  shows a top view of the vault  21 , and the relative positions of the various components from that view. 
     Although any one of several different structural components could potentially be suitable for use as the variably controllable valve  29  disclosed herein and shown in the Figures, applicant has used a Center Line Series 200 resilient seated butterfly valve, sold by Crane Chem Pharma &amp; Energy, in combination with a Series 44000 on/off rotary electric modulating actuator also sold by Crane, as shown at www.craneenergy.com. The material linked at this website is expressly incorporated by reference herein, in its entirety. This type of variably controllable valve  29 , i.e., a valve fitted with a modulating actuator, is controllable so as to specifically vary between 0 and 100% the amount that the conduit  28  is open for air flow therethrough. Stated alternatively, the valve  29  can be set at a particular percentage of the transverse cross sectional area of the conduit  28 . The amount of openness of the valve  29  determines the flow resistance, or flow impedance, in the conduit  28  near an output end of the constant air supply source  27 . For example, opening of the valve  29  to 100% open optimally reduces the air flow resistance, while closing the valve  29  to 0% open closes off all air flow entirely. And between those two extreme boundaries, the percentage of openness corresponds to a particular air flow resistance. 
     When the constant air supply source  27  is operating, the degree of openness of the valve  29  correlates to a flow resistance as measured by pressure, specifically in pounds per square inch. Further, although any one of a number of different components could potentially serve as the constant air supply source  27  that is disclosed herein and shown in the Figures, applicant has used a positive displacement blower sold by United Blower Inc., particularly Model/Style UBI.  250  (LHS). The specifications for the above-identified valve  29  and this blower  27  are expressly incorporated by reference herein, in their entireties. This blower  27  preferably includes an output end with a size that matches the dimensions of the conduit  28 , preferably a circular transvers cross sectional shape, with a diameter of 10 inches. The blower  27  has temperature sensor and pressure sensors/transmitters (not shown) at the output end thereof, which are used to supply temperature and pressure measurements to the controller  38 . The blower  27  is preferably located adjacent the vault  21 , and at a location where there is a continuous and uninterrupted supply of ambient air to feed the blower  27 . 
     This blower  27  is a type of rotary blower. Within the relevant operating ranges related to inlet air flow, blower speed (in r.p.m.), horsepower, and outlet air flow (in cubic feet per minute), for every increase of one pound per square inch in the flow resistance in the conduit  28 , the blower  27  experiences an increase in temperature of about 13 degrees Fahrenheit above the ambient air temperature in the environment of the room that houses the system  10 . This temperature increase occurs because the nature of the blower  27  is to, within certain parameters, work harder to continue to supply a constant air flow at the desired volume. This need to work harder to continue to supply a constant air flow generates heat within the blower  27 , and this heat transfers to the air that is being supplied to the conduit  28  at the constant flow rate. This heated, or warmed, air then successively flows to the vault  21 , the piping network  12 , out from the bottom openings in the uppermost rows  13  and into the lower layer of gravel  35 , and then upwardly through the fill layer  33  and through the natural turf  11  and into the atmosphere. 
     The blower  27  operates so as to supply a constant air flow into the conduit  28 , to warm the air supplied to the root zone. The operating settings of the blower  27  do not need to be continuously maintained or varied by the user during the time that the warm air is being supplied to the root zone of the natural turf  11 . Rather, the controller  38  monitors the operating parameters to assure continuous operation, and the desired settings or parameters can be programmed into the system  10 . Thus, independent of the blower  27 , by operating the controller  38  the system  10  controls the valve  29 , as needed, to change the flow resistance and the corresponding air temperature in the conduit  28 . The changes in flow resistance in the conduit  28  can occur independently of the normal operation of the blower  27 . Nonetheless, over time, by sensing the temperature and pressure of the air as it flows from the output end of the blower  27 , and correlating the sensed air temperature and the sensed air pressure with the known positions of the valve  29  and the operating frequency of the blower (in Hz), the system  10  can reliably and repeatably control the temperature and the volume of the air that flows into the vault  21  and thereafter into the piping network  12 . Further, by sensing the temperature of the air at one or more specific locations within the piping network  12  or the subsurface, via the sensors  40 ,  41 , and  42 , the system  10  can determine the amount of heat loss, if any, in the air as it moves from the vault  21  to the fill layer  33 . And still further, by sensing the temperature of the fill layer  33  during the time when the warmed air is supplied by the blower  27 , via sensors  42 , the system  10  can determine the amount of warmth that is ultimately delivered to the natural turf  11 . Thus, this system  10  provides a high degree of capability for measuring the volume and the temperature of warmed air that is supplied to the root zone, and these measurements can then be used to identify and correlate optimum control conditions for the system  10 , for a particular environment. 
     For example, once the upper layer  33  has reached a desired temperature, the fill layer, and particularly the lower layer  35 , may hold the warmth and therefore require less continuous warm air and/or a lower air temperature in order to continue to maintain the same desired temperature in the root zone. This means that the user may be able to reduce the operating frequency and therefore the power (in horsepower) supplied to the blower  27  in order to maintain the same temperature for the root zone. In one initial test of a system  10  in place, applicant tested and learned the following helpful parameters. 
     
       
         
           
               
            
               
                   
               
               
                 PARAMETER CHART 
               
            
           
           
               
               
               
               
               
               
            
               
                 Outlet 
                 Valve % 
                 Freq. 
                   
                 Motor 
                 Outlet 
               
               
                 Air Temp 
                 closed 
                 (Hz) 
                 Flow Rate 
                 Amps/hp 
                 Pres 
               
               
                   
               
               
                 163 
                 68 
                 60 
                 3000(cfm) 
                 130/114 
                 7.0 
               
               
                 F. 
                   
                   
                   
                   
                 p.s.i. 
               
               
                 148 
                 66 
                 50 
                 2600 
                 125/110 
                 6.6 
               
               
                 145 
                 76 
                 40 
                 1700 
                 124/110 
                 6.8 
               
               
                 163 
                 81 
                 30 
                 1500 
                 132/116 
                 7.8 
               
               
                   
               
            
           
         
       
     
     In this chart, the second column represents the limit on the amount of closing of the valve  29 , at that particular operating frequency, such that any further closing would likely cause a risk of overloading the motor of the blower  27 . If the operating parameters shown in the first row succeed in achieving the desired temperature at the root zone temperature sensors  42 , then the user may choose to reduce the flow rate by reducing the operating frequency of the blower  27 , and correspondingly opening the valve  29  to a higher percentage of openness. Conversely, if thereafter the user determines that the temperature needs to increase, the user could increase the operating frequency, and the corresponding flow rate, while also opening the valve  29  an appropriate amount. Stated alternatively, and as shown in the chart, the degree to which the valve is closed may be the reference used, so long as there is consistency. 
     With this system  10 , a user is able to reliably and repeatably supply warmed air to the root zone of a natural turf  11 . One primary advantage of this system  10  is that it reduces the time period during which the roots of the natural turf remain dormant during the winter months. More particularly, at the end of the fall this system  10  enables the roots to remain viable for additional time, while at the beginning of spring this system  10  enables the roots to begin reviving sooner. It is not the purpose of this system  10  to melt snow, or to maintain a natural turf field in an unfrozen condition over the entire winter. In that respect the system  10  should be understood as supplying conditioning or buffering for the roots. Nonetheless, if desired, the system  10  could be combined with a heating system, for instance via, hydronics or electric cable if the field owner chooses to be more aggressive in maintaining a viable natural turf surface over the entire winter. 
     From a dimensional perspective, this system  10  saves a tremendous amount of space, compared to conventional systems. For example, according to the specifications with which application is familiar the preferred blower  27  has a floorprint, or footprint, of 64 inches (5’ 4″) by 79 inches (6′7″), which is less than 36 square feet. It also has a height of just under 84 inches (7′), which means the cubic volume of the blower is less than about 252 cubic feet. In some situations, some additional dimensional flexibility may be needed to accommodate service access. Regardless, in comparison, the volume occupied by the furnace or furnaces of other systems is known to be at least about 10,000 cubic feet, or possibly even more. As noted above, in some environments, especially where the field site is landlocked, there is not that much available space. 
     Further, the blower  27  is preferably located directly over or spaced only several feet from the vault  21 , to provide a sufficient amount of space, or volume, for the valve  29 . The vault  21  preferably has a height of 13′, and internal horizontal dimensions of 6′ by 6′. Often, the vault  21  is designed to be below ground. These components are preferably housed in a space where a ready and constant unimpeded supply of intake air will be available for the blower  27 . 
     From a consumption of energy perspective, this system  10  presents a significant savings because it eliminates the need for a furnace to supply warmed air to the root zone of a natural turf  11 . For the system  10  currently in place, the blower  27  and the valve  29  occupy minimal space, yet supply warmed air in a temperature range of 0-105 degrees Fahrenheit above ambient temperature, at a volume of up to about 3000 cubic feet per minute, and require only minimal electrical energy. In this context, ambient temperature could be in the range of about 25-90 degrees Fahrenheit. This flow rate will increase with a larger athletic field, possibly going as high as 6000 cubic feet per minute. Regardless, even with a larger field, conventional systems require significantly more space and consume significantly more electrical energy, and also more natural gas. 
     This specification discloses one presently preferred embodiment of the invention. Nevertheless, those skilled in the art will recognize that this specification is exemplary, and that the invention is not limited by the specific structural details of the presently disclosed preferred embodiment, as shown and described. Various permutations may be possible. Accordingly, applicant intends for each of the following appended claims to define the scope of the invention.