Abstract:
An expansion relief header and its method of operation are disclosed for use in an HVAC heat transfer coil. The expansion relief header includes a main body adapted to be secured to bends in fluid coils of the HVAC fluid tube system. The main body includes holes in alignment with holes formed in the bends to enable fluid to pass from the bends into the expansion relief header. The expansion relief headers include one or more relief devices, such as valves, that automatically open, preferably in response to pressure exceeding a predetermined threshold value or temperature falling below a predetermined value, to release fluid from the expansion relief header and then reseat themselves.

Description:
RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 14/071,022, filed on Nov. 4, 2013, and claims priority from U.S. Provisional Application No. 61/727,799, filed Nov. 19, 2012. The disclosures of both applications are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to devices for use on heating, ventilating and air conditioning (HVAC) systems that prevent fluid tubes in the HVAC system from splitting when the fluid expands. In particular invention is directed to devices that allow for fluid expansion, and possibly fluid removal with the use of temperature and/or pressure relief devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fluid tubes are commonly used in HVAC systems, primarily in air handlers and similar cooling or heating systems. These systems are commonly used with cool or hot water, but could also be used to condense steam into a liquid in a heating system. Typically, these HVAC systems have a heat transfer medium, in the form of fluid. As used herein the term “fluid” covers both liquid and steam. The fluid circulates throughout tubes to acquire or lose heat. The common industry term for these HVAC heat transfer components is coils. The tubes in the coils are subject to damage when the fluid in the tubes are exposed to wide temperature differences, and as a result, is subject to changes in state. In the case of water, for instance, it will change from a liquid to a solid (ice) at low temperatures. At temperatures at or below 32 degrees F., the water in the tubes is subject to freezing and the expansion of the water may result in splitting of the tubes. 
         [0004]    Historically, ice masses form inside the tubes and expand outward creating excessive pressure in the tubes and at the return bends. The effect of freezing may cause the tubes to expand and split. Upon thawing, the water is released through the damaged return bends thus flooding the air handler, an area around the air handler on the level the air handler resides, and any levels below. This may create a series of expensive repairs, not only to the tube and the frozen equipment but now to all building components that are around and below the area of the flooding. In addition, costly shut down time of offices, manufacturing spaces, labs and all other building areas can result. This shut down time of operations of any facility requires emergency measures with possible excessive costs depending on the sensitivity of the operations involved. 
         [0005]    Past tube or return bend damage prevention has taken the form of bladders, freeze plugs and various other devices. The use of these devices presents many problems to the maintainers of these systems. First and foremost, these devices, once they are activated, require labor to repair or replace. Furthermore, freeze plugs which are designed to blow out in the event of excessive pressure caused by freezing, which results in flooding after the blow out of the plugs upon thawing of the ice. 
       SUMMARY OF THE INVENTION 
       [0006]    A device designed for the condition where the water (or other fluid medium) in tubes of an HVAC system changes from a liquid state (water) to a solid state (ice). The device includes piping expansion relief headers arranged to connect to bends in the tubes and to allow the water to enter the expansion relief header and to permit pressure to build within the expansion relief header as the water in the tubes expands during freezing in order to prevent damaging (e.g., splitting) of the tubes. The piping expansion relief headers include one or more relief devices, such as valves, to enable water to be automatically released from the expansion relief header when the pressure within the expansion relief header exceeds a predetermined value or the temperature of the fluid is below a predetermined value so as to prevent damage to the tubes and return bends. The expansion relief headers with the relief devices, are configured to work repeatedly over many periods of freezing and thawing and also over many periods of changes in pressure with minimum human intervention and minimum need for maintenance. The use of the expansion relief headers with relief devices (valves) enables an HVAC system to be “freeze safe” or “change of state safe”. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For the purpose of illustrating the invention, the drawings show a form of the invention which is presently preferred. However, it should be understood that this invention is not limited to the precise arrangements and instrumentalities shown in the drawings. 
           [0009]      FIG. 1  is a general perspective representation of coil assembly including the relief system according to the present invention. 
           [0010]      FIG. 2  is a top view of an expansion relief header in the coil assembly of  FIG. 1 . 
           [0011]      FIG. 3  is a side view of an expansion relief header in the coil assembly of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0012]      FIGS. 1-3  illustrate various views of an example embodiment of an expansion relief header utilized on an HVAC heat transfer coil. The use of the expansion relief header provides an HVAC system that is “freeze safe”. The expansion relief header enables fluid to flow out of the tubes and into an additional volume or area to accommodate fluid expansion caused by a change in fluid state (e.g., water turning to ice). The expansion relief header may also provide additional pressure relief from expansion and/or phase change of the fluid used in the tubes. The expansion relief header not only relieves pressure to protect the return bends of the fluid tubes but also allows for the resealing after expansion. 
         [0013]      FIG. 1  illustrates a perspective view of an example expansion relief header utilized on an HVAC heat transfer coil. As illustrated, various elements of the HVAC heat transfer coil are “cut away” to make it clear to the observer the basic ideas of this “change of state safe” system. The HVAC heat transfer coil includes a system casing  11  that has fins  12  formed therein for heat transfer. The casing  11  also has holes  14  running there through that secure fluid tubes  10 . Fluid tube return bends  13  are utilized to connect fluid tubes  10 . Piping  17  is utilized to supply/return fluid to main headers  16  that feed the fluid tubes  10  (e.g. supply on right side and return on left side). The main headers  16  include vent connections  15  for air removal and/or draining. 
         [0014]    The expansion relief headers  18  are configured to align with and connect to the bends  13 . The expansion relief headers  18  may include holes, connectors or the like (not separately numbered) in alignment with the bends  13 . The bends  13  may have holes (not separately numbered) formed therein. The alignment of the holes in the expansion relief headers  18  and the holes in the bends  13  allows for fluid expansion from the tubes  10  into the expansion relief headers  18  if and when necessary. The expansion relief headers  18  may also include vent connections  15  for air removal and/or draining (not separately numbered). The expansion relief headers  18  may include holes or connectors (not separately numbered) for receiving relief devices  19 . The relief devices  19  may be on opposite side of the holes in alignment with the bends  13 . The relief devices  19  may open to allow fluid to escape from the expansion relief headers  18  if additional fluid expansion is necessary. The relief devices  19  may include temperature and/or pressure relief devices designed to open at set values (e.g., temperature, pressure) so that a portion of the liquid will be dispersed and the tubes  10  are “change of state safe”. The number of relief devices  19  utilized may vary depending on various parameters, including the size, shape and type of unit and the anticipated environmental (e.g., weather) conditions. The relief devices  19  may automatically reseal after opening for fluid expansion (once the pressure and/or temperature returns to a certain value). In an alternative embodiment, the relief devices  19  may not automatically reseal after being opened for fluid expansion. These types of relief devices may need to be replaced and/or reset after opening or risk leakage of fluid therefrom even when fluid expansion is not required. 
         [0015]      FIG. 2  illustrates a top view of an example expansion relief header utilized on an HVAC tube system. The tubes  10  run through the system and the bends  13  connect adjacent tubes  10 . The piping  17  is utilized to supply/return fluid to main headers  16  that feed a single column of fluid tubes  10  on each side of the device. The expansion relief headers  18  are connected to the bends  13  and may have one or more relief devices  19  connected thereto. 
         [0016]      FIG. 3  illustrates a side view of an example expansion relief header utilized on an HVAC tube system. The main headers  16  are mounted on each side of the system. The main header  16  on the right has the piping  17  connected to the top in order to supply the liquid while the main header  16  on the left has the piping  17  connected to the bottom in order to return the liquid. The main headers  16  include vent connections  15  for air removal and/or draining. Note, the vent connections  15  are only illustrated on the top for ease of illustration but would also be included on the bottom. The expansion relief headers  18  are connected to each of the bends  13  and may include a plurality of relief devices  19 . 
         [0017]    The present invention provides a significant advance over prior systems since it incorporates a valve which is preferably selected with material properties similar to metals used in the majority of HVAC coils. As this valve requires a double seat (one for the spring and one for the thermal element), the inventor determined, after experimentation, that brass or alloy may be a more preferable material to plastic as it is far more durable and can handle the pressure generated by the heavy spring design required in this particular invention. Typically the valve is installed on the expansion relief header approximately six inches from the bottom of the header, which is above the drain and therefore less prone to clogging in the event that particulate deposits at the bottom of the header during the life of the coil. In some embodiments, used multiple valves have been incorporated per expansion relief header depending on the overall height of the coil. However, one valve per expansion relief header is sufficient for the majority of the installations. 
         [0018]    In one preferred embodiment, the present invention combines two relief features: an automatically re-seating temperature and pressure relief valve, and expansion relief headers. This design does not necessarily prevent a coil from freezing, which was thought to be the only possible solution in the past. With the present invention, the fluid in a coil is permitted to freeze without causing any bursting. The pressure in the expansion relief header portion of the invention, which links the coil tubes together at the return bends, increases as the ice masses form in the tubes that are in the face of the coil/air stream. As the pressure increases, the relief device(s)  19 , which is preferably a combination pressure-temperature valve, that is connected to the expansion relief header releases a small amount of water and then re-seats itself when the pressure drops below and/or temperature rises above a predetermined value. This controlled relief protects the coils from bursting upon freezing, thus reducing related coil damage and subsequent flooding. 
         [0019]    In one embodiment, the pressure-temperature valve is selected with a pressure relief setting (opening) of approximately 150 psi, which is between the normal operating pressures of a typical HVAC system (i.e., approximately 30 to 130 psi) and the typical tubing burst pressures (approximately 1,500 to 3,000 psi). This has proven to be effective in actual customer beta test sites and factory wind tunnel experiments and testing. 
         [0020]    In the preferred embodiment, the valve is selected with a temperature setting of approximately 35° F. where the valve will open to release excess cold water as an added layer of protection. The industry standard temperature for chilled water being supplied to a coil typically does not go below 40° F. Therefore, when temperatures drop below this standard, the valve further protects the coil by sensing the internal (and, if desired, can sense external) temperatures, thus allowing a small volume of water to bleed off when the internal temperature drops below 35° F. The amount of water released can be preset or the valve can reseat upon the temperature rising above 35° F. 
         [0021]    It is to be understood that even though numerous characteristics and advantages of the present invention have been presented above, together with details of the structure and function of the invention, the disclosure is illustrative only and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.