Abstract:
Frost in a freezer and/or traffic between the freezer and an anteroom is controlled. The frost is controlled by estimating a condition of the anteroom that promotes the frost in the freezer and by opening a door in the doorway in response to the estimated condition in order to supply cold air from the freezer to the anteroom. The traffic between the freezer and the anteroom is controlled by detecting the traffic approaching the doorway and by opening the door in the doorway in response to the detected traffic.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to the control of traffic and/or an environmental condition in a structure having both a cold storage room and an anteroom of the cold storage room. For convenience, the cold storage room will be referred to herein as a freezer. However, it should be understood that the present invention relates to any cold storage rooms including freezers. 
   BACKGROUND OF THE INVENTION 
   The demand for frozen or refrigerated goods has resulted in a concomitant demand for refrigerated storage facilities. A variety of refrigerated storage facilities have been used to store refrigerated goods. 
   For example, freezers have been equipped with doors that provide access to such freezers from loading docks or other adjacent spaces. Such doors can be opened and closed manually or automatically to allow vehicle and pedestrian traffic access to the freezers. Such doors are intended to permit refrigerated goods to be moved into and out of the freezers with increased energy efficiency. 
   However, traffic through such doors is frequently heavy, particularly at peak periods of the day. Accordingly, during these peak periods, the doors are necessarily open for large amounts of time, and many doors are kept open continuously during such peak traffic periods. Such open doors can present problems both with regard to the operation and maintenance of refrigeration equipment and with regard to the productivity and safety of the facility. 
   As has been recognized, an open door to a refrigerated space permits the heavier refrigerated air to flow out of the refrigerated space through the lower portion of the door opening and a more or less equal mass of warm humid air to flow inward through the upper portion of the door opening. The warm air entering the refrigerated space is typically referred to as infiltration air, and the cold air escaping the refrigerated space is typically referred to as exfiltration air. 
   When a warm, more humid air mass encounters a cold, less humid air mass, precipitation commonly occurs. This precipitation is in the form of water droplets on the warm side of the door and air born ice crystals in the freezer. 
   Air born ice crystals in the freezer is usually visible as haze, while visible fog frequently appears on the warm side of the door as cold air escapes from the lower portion of the door opening and mixes with the warmer humid outside air. Fog can obstruct the vision of personnel, including vehicle operators, working in the area. In addition, water droplets on the warm side of the door frequently causes wet slippery floors in the vicinity of the door with consequent hazards not only to personnel but also to equipment and material. 
   Air born ice crystals in the freezer result in frost or snow accumulation on ceilings, walls, freezer room appurtenances, and on the goods stored in the room. Frost can grow to many inches in thickness and can result in icy floors that present extremely slippery and hazardous conditions for personnel and for vehicles such as forklift trucks. Further, air born ice crystals may be drawn into the refrigeration equipment and produce premature clogging of the coils of the equipment, thereby reducing the refrigeration effect and adding to the burden of defrosting the coils. The result is a substantial reduction in refrigeration efficiency and may require installation of additional evaporator coils or oversized refrigeration equipment. 
   Many attempts have been made to reduce air exchange through open doors of refrigerated spaces. One common approach employs an air curtain across the doorway opening. The forced flow of relatively high velocity air of the air curtain across the opening serves to restrict the normal air exchange that results due to the temperature differential across the doorway. This forced flow of relatively high velocity air also serves to mix any cold air escaping from the freezer through the air curtain with the air in the high velocity air stream. Thus, the escaping cold air is diluted which reduces the precipitation rate. 
   It is also known to heat the air used in such air curtains thereby further reducing precipitation both inside and outside the refrigerated space. 
   Air curtains, however, are expensive to install and use, and do not of themselves result in energy efficient and low frost operation. 
   Air conditioned vestibules and anterooms have also been used. The conditions in these vestibules and anterooms can be controlled somewhere between outside air conditions and the conditions inside the freezer in order to reduce the water and frost problems described above. However, vestibules and anterooms have not been also controlled so as to efficiently use energy and minimize frost in the freezer. 
   Air curtains have been combined with vestibules and anterooms. Such arrangements, while effective in reducing precipitation in both the freezer and the vestibule or anteroom, are expensive to install. 
   Strip doors have also been used to restrict the flow of air through an open door of a freezer. Such strip doors typically employ transparent vinyl strips. These strips part when personnel and vehicles pass through them, and they then quickly fall back into place when personnel and vehicles clear them. These strips, therefore, act as an air flow barrier. 
   However, strip doors do not sufficiently reduce frost in the freezer and the consumption of energy. The use of strip doors is also objectionable because the strips tend to become less transparent with use and age, and may, therefore, obstruct vision. Further, frost or fog condensation on the strip surfaces not only obstructs vision, but the wet, cold surfaces are generally considered objectionable by personnel passing through the door. The relatively heavy plastic strips can also drag lightweight items such as empty cartons from material handling equipment. 
   The present invention overcomes one or more of these or other problems. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a method is provided to control the dew point temperature in an anteroom separated from a cold storage room by a doorway. The method comprises the following: determining a value for the dew point temperature in the anteroom; and, supplying cold air from the cold storage room to the anteroom in response to the value of the dew point temperature in the anteroom. 
   According to another aspect of the present invention, a method is provided to reduce frost formation in a cold storage room separated from an anteroom by a doorway. The method comprises the following: estimating a condition of the anteroom that promotes no frost in the cold storage room while substantially minimizing heat addition to the cold storage room; and, supplying cold air from the cold storage room to the anteroom in response to the estimated condition. 
   According to still another aspect of the present invention, a method is provided to reduce frost formation in a cold storage room separated from an anteroom by a doorway and to control traffic between the cold storage room and the anteroom. The method comprises the following: detecting traffic approaching the doorway; opening a door in the doorway in response to the detected traffic; estimating a condition of the anteroom that promotes no frost in the cold storage room while substantially minimizing heat addition to the cold storage room; and, opening the door in the doorway in response to the estimated condition in order to supply cold air from the cold storage room to the anteroom. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages will become more apparent from a detailed consideration of the invention when taken in conjunction with the drawings in which: 
       FIG. 1  shows a freezer and an anteroom with a door separating the two rooms and also shows a control system that controls the door and the conditions within the two rooms; and, 
       FIGS. 2A and 2B  comprise a flow chart of a program executed by the control system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   As shown in  FIG. 1 , a door  10  separates a freezer  12  from an anteroom  14 . As viewed in  FIG. 1 , the freezer  12  is behind the door  10 , the anteroom  14  is in front of the door  10 , and the door  10  has door panels  16  and  18  that open into the anteroom  14 . 
   The freezer  12  is sufficiently large to permit a desired amount of refrigerated goods to be stored inside, and may be large enough to accommodate a motorized vehicle to assist in moving the refrigerated goods into and out of the freezer  12 . The anteroom  14  is sufficiently large to permit movement of refrigerated goods therethrough, and may be large enough to accommodate movement of a motorized vehicle carrying refrigerated goods. 
   The door  10  is preferably, although not necessarily, a fast acting rigid door with a viewing window to provide a field of view of the freezer  12  from a vantage point within the anteroom  14  and a field of view of the anteroom  14  from a vantage point within the freezer  12 . The normal position of the door  10  is the closed position. 
   Although the door  10  can be of any desired configuration, the door  10  as shown in  FIG. 1  has the panels  16  and  18  that are operated by corresponding actuators  20  and  22  coupled by a bus  24  to a system controller  26 . The actuators  20  and  22  are arranged to open the door  10  so that the panels  16  and  18  swing into the anteroom  14 . 
   A proximity sensor  28  is positioned to sense traffic in the anteroom  14  approaching the door  10  and is coupled by the bus  24  to the system controller  26  such as a microprocessor or other computer. A proximity sensor  30  is positioned to sense traffic in the freezer  12  approaching the door  10  and is coupled by the bus  24  to the system controller  26 . Accordingly, in response to the proximity sensors  28  and  30 , the system controller  26  opens the door  10  whenever traffic in either the freezer  12  or the anteroom  14  approaches the door  10 . 
   Alternatively, motion sensors can be used in place of the proximity sensors  28  and  30  such that, whenever traffic in either the freezer  12  or the anteroom  14  is sufficiently close to enter the field of view of the corresponding motion sensor, the system controller  26  operates the actuators  20  and  22  to open the door  10 . In order to enhance this alternative door control, distance sensors can be used in combination with the motion sensors so that the door  10  is opened when the traffic is at an optimum distance from the door  10 . 
   Whenever two vehicles approach the door  10  at the same time, the system controller  26  may be arranged to give priority to the vehicle on a particular side of the door  10 . For example, the vehicle in the freezer  12  may be given priority over the vehicle in the anteroom  14 . Accordingly, collisions between vehicles are avoided. 
   A traffic light  32  is positioned to be seen by traffic in the anteroom  14  as the traffic approaches the door  10  and is coupled by the bus  24  to the system controller  26 . A traffic light  34  is positioned to be seen by traffic in the freezer  12  as the traffic approaches the door  10  and is coupled by the bus  24  to the system controller  26 . The traffic lights  32  and  34  may have any desired configuration that can be used to stop traffic and to permit traffic to proceed. For example, each of the traffic lights  32  and  34  may have a red light to stop traffic and a green light to indicate that traffic can proceed. 
   Accordingly, when traffic in the freezer  12  and in the anteroom  14  approach the door at roughly the same time, the traffic on the side of the door  10  having the higher priority is given the green light to proceed, and the traffic on the side of the door  10  having the lower priority is given the red light to stop. 
   A manual door switch  36  is positioned in the anteroom  14  near the door  10  and is coupled by the bus  24  to the system controller  26 . Similarly, a manual door switch  38  is positioned in the freezer  12  near the door  10  and is coupled by the bus  24  to the system controller  26 . Either of the manual door switches  36  and  38  can be operated at times when traffic volume is high in order to open the door  10  manually and to keep the door  10  in the open configuration. Alternatively, the system controller  26  can automatically control the stay open time of the door  10  during periods of time when traffic volume is high by employing a learning algorithm that learns time dependent traffic volumes based on outputs from the motion and/or proximity sensors. 
   A door closed sensor  40  senses when the door  10  is closed and is coupled by the bus  24  to the system controller  26 . A door open sensor  42  senses when the door  10  is open and is coupled by the bus  24  to the system controller  26 . The door closed sensor  40  and the door open sensor  42  provide feedback to the system controller  26  on the open and closed states of the door  10 . 
   A traffic speed sensor  44  is positioned to sense the speed of traffic in the anteroom  14  and is coupled by the bus  24  to the system controller  26 . Similarly, a traffic speed sensor  46  is positioned to sense the speed of traffic in the freezer  12  and is coupled by the bus  24  to the system controller  26 . The traffic speed sensors  44  and  46  may be used by the system controller  26  in conjunction with the proximity sensors  24  and  30  to determine the optimum time to open the door  10  to permit traffic therethrough so as to maximum energy conservation. 
   A frost sensor  48  is provided in the anteroom  14  at floor level near the door  10 , and a frost sensor  50  is provided in the freezer  12  near the top of the door  10 . The frost sensors  48  and  50  are coupled by the bus  24  to the system controller  26 . 
   A fan and coil unit  52  is located in the anteroom  14  and has a fan inlet  54  and a fan outlet  56 . The fan and coil unit  52  conventionally includes an evaporator coil and a fan to blow air across the evaporator coil and into the anteroom  14 . A fan and coil controller  58  includes a coil reheat relay and a coil evaporator pressure regulator relay for controlling the fan and coil unit  52 . The fan and coil controller  58  is coupled by the bus  24  to the system controller  26 . 
   A fan and coil unit  62  is located in the freezer  12  and has a fan inlet  64  and a fan outlet  66 . The fan and coil unit  62  conventionally includes an evaporator coil and a fan to blow air across the evaporator coil and into the freezer  12 . A fan and coil controller  70  includes a fan speed control  72  and a coil evaporator pressure regulator relay  74  for controlling the fan and coil unit  62 . Also, a coil frost sensor  76  is positioned to sense frost build up on the evaporator coil of the fan and coil unit  62 . The fan speed control  72 , the coil evaporator pressure regulator relay  74 , and the coil frost sensor  76  are coupled by the bus  24  to the system controller  26 . 
   If desired, an air transfer fan  80  is provided to transfer air from the freezer  12  to the anteroom  14 , and an air transfer fan  82  is provided to transfer air from the anteroom  14  to the freezer  12 . A transfer fan controller  84 , which may an on/off controller, is coupled by the bus  24  to the system controller  26  so that the system controller  26  can control the operation of the air transfer fan  80 . Similarly, a transfer fan controller  86 , which may an on/off controller, is coupled by the bus  24  to the system controller  26  so that the system controller  26  can control the operation of the air transfer fan  82 . 
   Various other sensors are also coupled by the bus  24  to the system controller  26 . Accordingly, a sensor package  90  is located in the anteroom  14  and may include a dry bulb temperature sensor, a relative humidity sensor, and/or a dew point temperature sensor. Similarly, a sensor package  92  is located in the freezer  12  and may include a dry bulb temperature sensor, a relative humidity sensor, and/or a dew point temperature sensor. 
   Thus, each of the sensor packages  90  and  92  may comprise any number of sensors. As an example, each of the sensor packages  90  and  92  may include two of the above described sensors because the condition sensed by the third sensor can be determined based on the other two sensed conditions and the psychometric chart. For example, dry bulb temperature and relative humidity can be used in combination with the psychometric chart to determine dew point temperature. 
   Because outdoor air infiltrates into the anteroom  14 , the conditions in the anteroom  14  are not continuously at steady state. The dry bulb temperature (DBTa) and the dew point temperature (DPTa) in the anteroom  14 , therefore, fluctuate. The system controller  26  reacts to these fluctuations so as to maintain the anteroom  14  at a desired dew point temperature (DPTa) and, thereby, minimize the creation of snow and ice build up in the freezer  12  and ice build up and condensation in the anteroom  14 . 
   The system controller  26  determines the optimum operating conditions for the anteroom  14 , and controls the anteroom  14  at these optimum operating conditions so that air infiltrating from the anteroom  14  into the freezer  12  will not cause fog, ice, and/or snow in the freezer  12 . For example, the system controller  26  may be arranged to determine the optimum operating dew point temperature of the anteroom  14  and to control the anteroom  14  at this optimum operating dew point temperature so that air infiltrating from the anteroom  14  into the freezer  12  will not cause fog, ice, and/or snow in the freezer  12 . 
   Additionally, the system controller  26 , in response to the frost sensors  48  and  50 , controls conditions in the anteroom  14  so that ice will not accumulate in the anteroom  14  at the bottom of the opening of the door  10  or in the freezer  12  at the top of the opening of the door  10 . 
   Accordingly, the system controller  26  flags the fan and coil unit  52  in the anteroom  14  so as to cause the speed of the fan in the fan and coil unit  52  to increase to maintain better air circulation and mixing, and also flags the fan and coil unit  52  to convert to heating mode. When the ice from the opening of the door  10  is removed and the dry bulb temperature of the anteroom  14  is operating at set point, the system controller  26  flags the fan and coil unit  52  to operate at normal conditions. 
   Also, the system controller  26  is responsive to the coil frost sensor  76  that is positioned to sense frost build up on the evaporator coil of the fan and coil unit  62  in order to reduce this frost build up by increasing the speed of the fan of the fan and coil unit  62  and/or by increasing the surface temperature of the evaporator coil in the fan and coil unit  62  by increasing suction pressure. 
   The system controller  26  continuously monitors conditions in the anteroom  14 . For example, when the actual dew point temperature in the anteroom  14  is above set point, the system controller  26  operates the actuators  20  and  22  to open the door  10  so as to dehumidify the anteroom  14 . The door  10  can be maintained in this open condition until the actual dew point temperature in the anteroom  14  returns to set point. Additionally or alternatively, the door  10  can be maintained in this open condition for a time period determined by a heuristic algorithm, by a predetermined schedule, by a learning algorithm, or by a combination of these strategies. The cold air infiltrating into the anteroom  14  through the open door  10  mixes with the air in the anteroom  14  so that the mixture will be at the desired dew point temperature. 
   Additionally or alternatively, the air transfer fans  80  and  82  can be operated to control the mixing of cold air from the freezer  12  with the air in the anteroom  14 . For example, in the case where the open door  10  cannot itself provide sufficient air infiltration to lower the dew point temperature of the anteroom  14  to set point, the system controller  26  can control the air transfer fans  80  and  82  to transfer additional cold air from the freezer  12  to the anteroom  14 . 
   Moreover, the freezer  12  can be maintained at a set point dry bulb temperature (DBTf) and at a set point relative humidity (RHf). These set point conditions may change depending on the nature of the refrigerated goods. 
   The flow chart of  FIGS. 2A and 2B  illustrates a program that can be executed by the system controller  26  in order to carry out the above described control functions. Accordingly, at a block  100 , the conditions detected by the sensors described above are read. 
   The system controller  26 , at a block  102 , computes pertinent variables including the optimum dew point temperature for the anteroom  14 . The psychometric chart, if desired, can be employed for this purpose. For example, given the set point dry bulb temperature and relative humidity of the freezer  12  and the relative humidity of the anteroom  14 , the optimum dew point temperature for the anteroom  14  can be determined. For this purpose, a line, which may be referred to as the squall line, may be used. This line is tangent to the saturation curve of the psychometric chart and passes through the line indicated by the set point dry bulb temperature or relative humidity of the freezer  12 . The optimum dew point temperature for the anteroom  14  can be determined from the point where the relative humidity line corresponding to the relative humidity of the anteroom  14  or the dry bulb line corresponding to the dry bulb temperature of the anteroom  14  crosses this squall line. 
   The set point dew point temperature for the anteroom  14  should be no higher than this optimum dew point temperature because, if the actual dew point temperature of the anteroom  14  is higher than this optimum dew point temperature, then frost, ice, and water conditions can result. The set point dew point temperature, for example, may be set equal to the optimum dew point temperature for the anteroom  14 . 
   At a block  104 , the system controller  26  notes the traffic direction, if any, that is given priority. This priority is defined by the user and can be stored in memory. According to the example given above, vehicles moving from the freezer  12  to the anteroom  14  may be given priority over vehicles moving from the anteroom  14  to the freezer  12 . If the system controller  26  determines at a block  106  that the user has not assigned a priority to either traffic direction, the system controller  26  determines at a block  108  that the traffic will be controlled on a first come, first served basis. 
   If the system controller  26  determines at the block  106  that the user has assigned priority to one of the traffic directions, or after the system controller  26  determines at the block  108  that the traffic will be controlled on a first come, first served basis, the system controller  26  determines at a block  110  whether the door  10  is open. If the door  10  is open, the system controller  26  determines at a block  112  whether at least one of the manual door switches  36  and  38  has been operated. If neither of the manual door switches  36  and  38  has been operated, the system controller  26  determines at a block  114  whether the current time is a time when the volume of traffic is normally high. 
   If the system controller  26  determines at a block  110  that the door  10  is not open, or if the current time is a time when the volume of traffic is normally high, or if at least one of the manual door switches  36  and  38  has been operated, the system controller  26  determines at a block  116  whether a vehicle is detected. If a vehicle is not detected at the block  116 , program flow proceeds through point B. If the current time is not a time when the volume of traffic is normally high as determined at the block  114 , the system controller  26  determines at a block  118  whether a vehicle is detected. 
   If a vehicle is detected at either of the blocks  116  and  118 , the system controller  26  determines at a block  120  whether there is traffic approaching the door  10  in both the freezer  12  and the anteroom  14 . If traffic in only one of the freezer  12  and the anteroom  14  is approaching the door  10 , the traffic light in the traffic room is turned to green and the traffic light in the non-traffic room is turned to red at a block  122 . However, if traffic in both of the freezer  12  and the anteroom  14  is approaching the door  10 , the traffic lights in the freezer  12  and the anteroom  14  are controlled at a block  124  based on the priority set by either the block  104  or the block  108 . 
   After the traffic lights are controlled at the block  122  or the block  124 , the system controller  26  updates the traffic volume data at a block  126 . This data is used to model the time based traffic volume that is used by the block  114  as discussed above. Program flow then proceeds through point B. 
   If no vehicle is detected as determined at the block  116  or the block  118 , or after the system controller  26  updates the traffic volume data at a block  126 , the system controller  26  determines at a block  128  whether the actual dew point temperature in the anteroom  14  is above its set point. 
   If the actual dew point temperature in the anteroom  14  is not above its set point, a block  130  causes the door  10  to be closed if the door is not open due to traffic or operation of at least one of the manual door switches  36  and  38 , and a block  132  checks the feedback that the door  10  is closed. If the door  10  is closed, program flow proceeds through point C. If the actual dew point temperature in the anteroom  14  is above its set point, a determination is made at a block  134  as to whether the door  10  is open. If the door  10  is not open, a block  136  causes the door  10  to be opened, and a block  138  checks to make sure that the door  10  is opened. If the door  10  in fact did not open as determined at the block  138 , or if the door  10  did not close as determined at the block  132 , a block  140  causes an alarm to be given, turns the traffic light on each side of the door  10  to red, calls the operator, and terminates program flow. 
   If the door  10  is determined to be open by the block  134  or the block  138 , the deviation of the actual dew point temperature in the anteroom  14  from its set point is computed at a block  142 , and a test is made at a block  144  to determine if the deviation is greater than a predetermined amount A. If the deviation is greater than a predetermined amount A, a block  146  causes the transfer fans to be energized to bring more air from the freezer  12  into the anteroom  14 , and program flow thereafter proceeds through point C. If the deviation is not greater than a predetermined amount A, the open door is sufficient to return the actual dew point temperature in the anteroom  14  to its set point. Therefore, a block  148  causes the transfer fans, if on, to be de-energized, and program flow thereafter proceeds through point C. 
   After the block  146  causes the transfer fans to be energized, or after the block  148  causes the transfer fans, if on, to be de-energized, or if the door is closed at tested by the block  132 , a determination is made at a block  150  as to whether the actual dry bulb temperature in the anteroom  14  is below its set point. 
   If the actual dry bulb temperature in the anteroom  14  is not below its set point, a block  152  flags the fan and coil unit  52  in the anteroom  14  to operate so as to cool the anteroom  14 . If the actual dry bulb temperature in the anteroom  14  is below its set point, the deviation of the actual dry bulb temperature in the anteroom  14  from its set point is computed at a block  154 , and a test is made at a block  156  to determine if the deviation is greater than a predetermined level  1 . If the deviation is not greater than the predetermined level  1 , a block  158  flags the fan and coil unit  52  in the anteroom  14  to operate so as to heat the anteroom  14 . However, if the deviation is greater than the predetermined level  1 , a block  160  flags the coil evaporator pressure regulator relay of the fan and coil unit  52  in the anteroom  14  to operate so as to increase suction pressure and increases the fan speed of the fan and coil unit  52 . 
   After a delay following the block  152  flagging the fan and coil unit  52  in the anteroom  14  to operate so as to cool the anteroom  14 , or after the block  158  flags the fan and coil unit  52  in the anteroom  14  to operate so as to heat the anteroom  14 , or after the block  160  flags the coil evaporator pressure regulator relay of the fan and coil unit  52  in the anteroom  14  to operate so as to increase suction pressure and increases the fan speed of the fan and coil unit  52 , a determination is made at a block  162  as to whether frost has built up on the lower jam of the door  10 . 
   If frost has built up on the lower jam of the door  10 , a block  164  flags the fan and coil unit  52  in the anteroom  14  to operate so as to heat the anteroom  14 . The fan speed will increase as a function of the deviation from the set point. If additional heat is required, the EPR valve will be set to deliver a higher surface temperature to increase the temperature of the air exiting the fan outlet  56 . After the block  164  flags the fan and coil unit  52  in the anteroom  14  to operate so as to heat the anteroom  14 , or if frost has not built up on the lower jam of the door  10 , a determination is made at a block  166  as to whether frost has built up on the top jam of the door  10  or on the evaporator coil of the fan and coil unit  62 . 
   If frost has built up on the top jam of the door  10  or on the evaporator coil of the fan and coil unit  62 , a block  168  flags the speed of the fan of the fan and coil unit  62  to increase and/or flags the coil evaporator pressure regulator relay of the fan and coil unit  62  to operate so as to increase suction pressure. 
   If frost has not built up on the top jam of the door  10  or on the evaporator coil of the fan and coil unit  62 , a test is made at a block  170  to determine if any of the fan coil units have been flagged on. If so, a block  172  flags the fan coils off. 
   After a block  168  flags the speed of the fan of the fan and coil unit  62  to increase and/or flags the coil evaporator pressure regulator relay of the fan and coil unit  62  to operate so as to increase suction pressure, or after the block  170  determines that the fan coils have not been flagged on, or after the block  172  flags the fan coils off, program flow returns to the beginning of the algorithm shown in  FIGS. 2A and 2B . 
   Modifications of the present invention will occur to those practicing in the art of the present invention. For example, as described above, fans and/or doors are used to control air flow between the freezer  12  and the anteroom  14 . Additionally or alternatively, other devices can be used to air flow between the freezer  12  and the anteroom  14 . 
   Accordingly, the description of the present invention is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which are within the scope of the appended claims is reserved.