Abstract:
A hybrid dehumidification system uses both mechanical cooling and ventilation to control humidity under control of a system which selects the best mode of operation under a given set of conditions. A purge mode using 100% outside air and exhaust is also supported to decontaminate a space. Either a single large plate heat exchanger or multiple small plate heat exchangers may be employed in the system.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to dehumidification in high moisture load environments. 
       BACKGROUND OF THE INVENTION 
       [0002]    Dehumidification can be accomplished by mechanically lowering the dew-point of air, using a refrigeration based system, to a predetermined temperature and humidity level that removes a desired amount of moisture or by using outdoor air that is at the predetermined temperature and humidity level or lower. 
         [0003]    In many geographic locations, dehumidification using only outdoor air is not practical because the outdoor dew point exceeds the indoor dew point too frequently. Under these conditions indoor humidity is not controlled, causing discomfort and the growth of mold and mildew. Consequently, most systems use refrigeration based dehumidification to maintain indoor humidity for some portion of the year. 
       OBJECTS OF THE INVENTION 
       [0004]    It is therefore an object of the present invention to provide a dehumidification system which can be used in high moisture load environments. 
         [0005]    It is also an object of the present invention to provide a hybrid dehumidification system which utilizes both mechanical and ventilation modes and which promotes modulated dehumidification of air in an enclosed space. 
         [0006]    Other objects which become apparent from the following description of the present invention. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention uses both refrigeration and ventilation to control humidity; with a control system that determines which mode is best under a given set of conditions. 
         [0008]    In the mechanical dehumidification mode, the required outside air and exhaust air for ventilation is furnished by a minimum outside air and minimum exhaust air damper that introduces the outside air necessary to ventilate the enclosed space and exhaust air sufficient to maintain negative pressure within the enclosed space as may be required by design or code and to avoid “pushing” humid air into adjacent spaces or into cold wall cavities where it can condense and cause damage. In the outdoor air dehumidification mode the ventilation is easily met except possibly at very low outdoor temperatures, in which case the outdoor air required to meet the ventilation requirement may cause the indoor humidity to fall below set point. An air bypass is also provided with regulating orifice in the event that additional airflow is needed to meet the total system airflow requirement. The invention has a purge feature that allows the system to operate with 100% outside air/100% exhaust to purge the enclosed space of contaminants such as excessive chloramines in an indoor swimming pool environment. 
         [0009]    For indoor pools, a certain amount of outside air needed to meet minimum ventilation standards. This outside air is used to ventilate chemical odors and to supply fresh air for the occupants. During unoccupied periods outside air for ventilation is not necessary. Also, during unoccupied periods in summer, relative humidity can be allowed to rise to higher levels without danger of hidden damage due to condensation inside wall and ceiling cavities. Therefore, in the interest of saving energy, either of two strategies can be used for unoccupied periods.
       1. Place the system in outside air ventilation mode regardless of the season. Using this strategy, the indoor humidity may be higher than design with the space unoccupied but this is of little concern when the outdoor temperatures are higher. Energy savings occurs as a result of shutting down mechanical dehumidification.   2. Shut down the minimum outside air damper when operating in the mechanical dehumidification mode. Using this strategy the indoor humidity is maintained year round. Energy savings occurs as a result of reduced outside air to be treated.       
 
         [0012]    The invention may use single large plate heat exchangers and the invention can use multiple small plate heat exchangers as taught in U.S. Pat. No. 5,816,315, Plate type crossflow air-to-air heat exchanger having dual pass cooling and U.S. Pat. No. 6,182,747, Plate-type crossflow air-to-air heat-exchanger comprising side-by-side-multiple small-plates. A manifold T2/T3 must be added for the invention to work with multiple-small-plate technology. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention can best be understood in connection with the accompanying drawings. It is noted that the invention is not limited to the precise embodiments shown in drawings, in which: 
           [0014]      FIG. 1   a  illustrates a single large plate heat exchanger with airflow paths in the mechanical dehumidification/occupied mode with the minimum outside air and minimum exhaust air dampers open, the outside air and exhaust air dampers closed and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0015]      FIG. 1   b  illustrates a single large plate heat exchanger with airflow paths in the mechanical dehumidification mode during unoccupied periods with the minimum outside air damper closed and minimum exhaust air damper open, and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0016]      FIG. 2  illustrates a single large plate heat exchanger with airflow paths in the outside air dehumidification mode with the minimum outside air and minimum exhaust air dampers closed and the outside air damper and exhaust air fan modulating to meet the dehumidification requirements and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0017]      FIG. 3  illustrates a single large plate heat exchanger with airflow paths in the purge mode with the minimum outside air and minimum exhaust air dampers closed and the outside air damper wide open and the exhaust fan full volume to purge the enclosed space of contaminants while maintaining sufficient quantity of exhaust to keep negative pressure in the enclosed space. 
           [0018]      FIG. 4  illustrates 3 views of the invention in the multiple-small-plate configuration. Here, the T2/T3 manifold can be seen. 
           [0019]      FIG. 5   a  illustrates the configuration of  FIG. 1   a  using multiple-small-plate heat exchangers with airflow paths in the mechanical dehumidification/occupied mode with the minimum outside air and minimum exhaust air dampers open, the outside air and exhaust air dampers closed and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0020]      FIG. 5   b  illustrates the configuration of  FIG. 1   b  using multiple-small-plate heat exchangers with the minimum outside air damper closed and minimum exhaust air damper open, and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0021]      FIG. 6  illustrates the configuration of  FIG. 2  using multiple-small-plate heat exchangers with airflow paths in the outside air dehumidification mode with the minimum outside air and minimum exhaust air dampers closed and the outside air damper and exhaust air fan modulating to meet the dehumidification requirements and the exhaust fan removing sufficient quantity of exhaust to maintain negative pressure in the enclosed space. 
           [0022]      FIG. 7  illustrates the configuration of  FIG. 2  using multiple-small-plate heat exchangers with airflow paths in the purge mode with the minimum outside air and minimum exhaust air dampers closed and the outside air damper wide open and the exhaust fan full volume to purge the enclosed space of contaminants while maintaining sufficient quantity of exhaust to keep negative pressure in the enclosed space. 
           [0023]      FIG. 8  is a flow chart of the hybrid dehumidification systems control sequences. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The invention uses at least one modulating outside air damper  26  and at least one modulating exhaust air damper  34  and a variable volume exhaust fan  38  to achieve fully modulated dehumidification in the outside air operating mode and to switch the airflow between outside air dehumidification and mechanical dehumidification modes. An air bypass  48  is also provided with regulating orifice  49  in the event that additional airflow is needed to meet the total system airflow requirement. Modulating exhaust air damper  34  may be of the passive or non-powered type where only pressure differential in the correct direction will open the damper. Both supply fan  16  and exhaust fan  38  are in a “draw-through” position relative to the plate heat exchanger  8 , thereby minimizing the stress on the plates caused by pressure differential. Plate heat exchangers are positioned in a counterflow arrangement and condensate, in both operating modes, flows downward in the same direction as airflow, thereby ensuring complete drainage and minimizing pressure drop from suspended water. 
         [0025]      FIG. 1   a  illustrates the invention with a single large plate heat exchanger  8 , operating in the mechanical dehumidification/occupied mode. Return airstream  2  enters the process where it gives up a portion of its volume to minimum exhaust airstream  46  through minimum exhaust air damper  44  where it continues on to exhaust fan  38  where it discharge outdoors through airstream  40 . Meanwhile, airstream  23  continues on to mix with minimum outside airstream  22  through minimum outside air damper  4 . Airstream  6  enters the first pass of heat exchanger  8 , where it is cooled and dehumidified emerging as airstream  42  which travels through dehumidifying coil  30  for final cooling and dehumidification prior to entering the second pass of heat exchanger  8  where it is heated and emerges as airstream  10 . Airstream  10  receives further heating or cooling in heating and/or cooling coil  12 , emerging as airstream  14  prior to entering supply fan  16  where it is supplied back to the enclosed space  50  through supply airstream  18 . 
         [0026]      FIG. 1   b  illustrates the invention with a single large plate heat exchanger  8 , operating in the mechanical dehumidification mode during unoccupied periods. Operation is the same as  1   a  above except that minimum outside air damper closes. 
         [0027]      FIG. 2  illustrates the invention with a single large plate heat exchanger  8 , operating in the outside air dehumidification mode where minimum outside air damper  4  and minimum exhaust air damper  44  are closed and dehumidifying coil  30  is inactive. Return airstream  2  enters heat exchanger  8  directly as airstream  6  where it gives up heat to a mixture airstream  28 , of incoming outside airstream  24  and airstream  42 . Air stream  6  exits heat exchanger  8  as air stream  32  which then divides into either a) airstream  36  through damper  34  as exhaust airstream  39 , where it is exhausted through exhaust fan  38  as exhaust air  40 , or, else, b) air stream  6  exits heat exchanger  8  as air stream  32  divides to become air stream  42  in a direction from airstream  28  to airstream  28 , where it reenters heat exchanger and then emerging the heat exchanger  8  at airstream  10  where it continues on for cooling or heating as needed at heating and/or cooling coil  12 , emerging as airstream  14  where it enters supply fan  16  and is discharged to the enclosed space  50  through supply airstream  18 . 
         [0028]      FIG. 3  illustrates the invention with a single large plate heat exchanger  8 , operating in the purge mode where minimum outside air damper  4  and minimum exhaust air damper  44  are closed and dehumidifying coil  30  is inactive. Return airstream  2  enters heat exchanger  8  directly as airstream  6  where it gives up heat to 100% outside airstream  24 , emerging the heat exchanger  8  at airstream  10  where it continues on for cooling or heating as needed at heating and/or cooling coil  12 , emerging as airstream  14  where it enters supply fan  16  and is discharged to the enclosed space  50  through supply airstream  18 . Exhaust fan  38  operates at full volume to remove airborne contaminants. 
         [0029]      FIG. 4  illustrates the invention in a configuration with multiple small plate heat exchangers, where T1/T4 manifold  1  distributes air entering  6  and exiting  10  the heat exchangers  8  which are is arranged in parallel arrangement with regard to airflow and manifold  29  at T2/T3 is introduced to collect and distribute air to and from multiple small plate heat exchangers  8  and dehumidifying coil  30 . At least one modulating outside air damper  26 , At least one modulating exhaust damper  34  and manifold  29  at T2/T3 are clearly visible. 
         [0030]      FIG. 5   a  illustrates the invention with multiple small plate heat exchangers  8 , operating in the mechanical dehumidification/occupied mode. Return airstream  2  enters the process where it gives up a portion of its volume to minimum exhaust airstream  46  through minimum exhaust air damper  44  where it continues on to exhaust fan  38  where it discharge outdoors through airstream  40 . Meanwhile, airstream  23  continues on to mix with minimum outside airstream  22  through minimum outside air damper  4 . Airstream  6  enters the first pass of heat exchangers  8 , where it is cooled and dehumidified emerging as airstream  42  which travels through dehumidifying coil  30  for final cooling and dehumidification prior to entering the second pass of heat exchangers  8  where it is heated and emerges as airstream  10 . Airstream  10  receives further heating or cooling in heating and-or cooling coil  12 , emerging as airstream  14  prior to entering supply fan  16  where it is supplied back to the enclosed space  50  through supply airstream  18 . 
         [0031]      FIG. 5   b  illustrates the invention with multiple small plate heat exchangers  8 , operating in the mechanical dehumidification mode during unoccupied periods. Operation is the same as la above except that minimum outside air damper closes. 
         [0032]      FIG. 6  illustrates the invention with multiple small plate heat exchangers  8 , operating in the outside air dehumidification mode where minimum outside air damper  4  and minimum exhaust air damper  44  are closed and dehumidifying coil  30  is inactive. Return airstream  2  enters heat exchangers  8  directly as airstream  6  where it gives up heat to a mixture airstream  28 , of incoming outside airstream  24  and airstream  42 , emerging the heat exchangers  8  at airstream  10  where it continues on for cooling or heating as needed at heating and/or cooling coil  12 , emerging as airstream  14  where it enters supply fan  16  and is discharged to the enclosed space  50  through supply airstream  18 . 
         [0033]      FIG. 7  illustrates the invention with multiple small plate heat exchangers  8 , operating in the purge mode where minimum outside air damper  4  and minimum exhaust air damper  44  are closed and dehumidifying coil  30  is inactive. Return airstream  2  enters heat exchangers  8  directly as airstream  6  where it gives up heat to 100% outside airstream  24 , emerging the heat exchangers  8  at airstream  10  where it continues on for cooling or heating as needed at heating and/or cooling coil  12 , emerging as airstream  14  where it enters supply fan  16  and is discharged to the enclosed space  50  through supply airstream  18 . Exhaust fan  38  operates at full volume to remove airborne contaminants. 
         [0034]    As also shown in  FIGS. 2 ,  3 ,  6  and  7 , damper  26  and/or exhaust fan  38  modulate to insure that airflow  42  travels from airstream  38  to airstream  28 , and never in reverse, to avoid short circuiting of outside air  20  away from heat exchanger  8 . 
         [0035]      FIG. 8  is a flow chart of the hybrid dehumidification systems control sequences, where “SA” indicates “supply airstream”, “OA” indicates “outside airstream”, “RA” indicates “return airstream”, “EA” indicates “exhaust air”, “Dp” indicates “dew point” and “Rh” indicates “relative humidity”. The first step in the control sequence is whether the supply airstream SA fan is “on” or not. If “on”, then there are different modes of operation. 
         [0036]    For example, as shown in  FIG. 8 , in the dehumidification mode, if the dewpoint Dp of the outside airsteam OA is less than the set point of the dewpoint Dp of the supply airstream SA, then the system operates in a winter mode or an optional unoccupied summer mode, where minimum outside airstream OA dampers and minimum exhaust air EA dampers are closed and modulation of outside airstream OA and exhaust airstream EA occurs for humidity control. However, in the summer mode where the dewpoint Dp of the outside airsteam OA is greater than the set point of the dewpoint Dp of the supply airstream SA, then the outside airstream OA and exhaust air stream dampers are closed and the minimum outside airstream OA and minimum exhaust airstream EA dampers are opened. Then the return airstream RA is measured as to relative humidity set point. If less than or greater than the return airstream RA predetermined set point, then cycle stages of mechanical dehumidification or chilled water valve are implemented to maintain the set point. If not, then all stages of dehumidification are “off.” 
         [0037]      FIG. 8  also shows the heat/cool mode, where the dry bulb Db of the return airstream RA is calculated as to whether it is greater than a predetermined set point. If the answer is “yes”, in the cooling mode, cooling is activated by cycling stages of mechanical cooling or by opening of the chilled water valve. If the answer is “no”, in the heating mode, heating is activated by cycling stages of electric heat or by opening the heating valve. 
         [0038]      FIG. 8  further shows the exhaust fan mode, where it is first determined if the outside airstream OA damper is partially opened. If not, then the minimum exhaust air EA damper is determined to whether it is fully opened, and, if not, then the exhaust fan is turned off. If however the minimum exhaust air EA damper is fully open, or if the outside airstream OA damper is partially open, then the speed of the exhaust fan is ramped up to maintain a preset negative pressure in the enclosed space. 
         [0039]    Moreover, in the purge mode shown in  FIG. 8 , it is first determined whether the purge relay is energized. If not, then it must be determined whether the supply air SA fan is on or not, and if so, whether the purge relay is then energized. If the purge relay is energized, then the minimum outside airstream OA damper and the minimum exhaust air stream EA damper are both shut down, and the open airstream OA damper and the exhaust airstream damper are opened to maximum. 
         [0040]    In the foregoing description, certain terms and visual depictions are illustrative only: However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only and are not meant to limit the scope of the present invention. 
         [0041]    It is further noted that other modifications may be made to the present invention, without departing from the scope of the invention, as noted in the appended claims.