Abstract:
A method for operating a ducted fumehood with increased energy efficiency, wherein the method includes passing exhaust air from the ducted fumehood through a heat exchanger, and passing other air through the heat exchanger, so as transfer heat content from the exhaust air to the other air, or to transfer heat content from the other air to the exhaust air, so as to temperature-condition the other air.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
     This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/281,592, filed Nov. 19, 2009 by Francois Hauville for MODULAR FILTRATION ASSEMBLY, which patent application is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to air filtration systems in general, and more particularly to air filtration systems for purging hazardous substances from the air. 
     BACKGROUND OF THE INVENTION 
     Air filtration systems are used in many situations to purge unwanted substances from the air. Such filtration systems generally exist in a variety of forms, depending upon their function. 
     One type of air filtration system in common use, e.g., in laboratories, comprises a fumehood, fumehood is a protected enclosure for isolating a benchtop workspace from the ambient air of a laboratory, in order that dangerous substances may be handled safely within the fumehood without endangering nearby personnel. 
     Fumehoods may be ducted or ductless. With a ducted fumehood, the exhaust air from the fumehood is directed into building ductwork which leads to the outside atmosphere, with a filter being disposed intermediate the ductwork between the fumehood and the outside atmosphere. With a ductless fumehood, the exhaust air from the fumehood is directed into a filter which is attached directly to the fumehood, with the filter purging hazardous substances from the exhaust air before the exhaust air is directed back into the ambient air of the laboratory. 
     Ducted fumehoods offer certain advantages, e.g., multiple fumehoods can be exhausted through a single filter, their fixed location (a consequence of the fixed ductwork within a building) make them easy to oversee and administer, etc. However, ducted fumehoods also suffer from the disadvantage that the ambient air of the laboratory is exhausted through the fumehood to the outside atmosphere. As a result, heated air is lost from the laboratory during the winter, and cooled air is lost from the laboratory during the summer, thereby driving up energy costs. Ductless fumehoods do not suffer from this disadvantage, since they return the filtered exhaust air back to the ambient air of the laboratory. However, ductless fumehoods suffer from the disadvantage that each fumehood requires its own filter, which can complicate logistical issues such as filter monitoring, filter replacement, etc. 
     The present invention is directed to ducted fumehoods, and more particularly to a novel method and apparatus for operating ducted fumehoods with increased energy efficiency. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel method and apparatus for operating ducted fumehoods with increased energy efficiency. 
     More particularly, the present invention provides a novel method and apparatus for transferring heat content between the exhaust air of a fumehood and other air so as to temperature-condition that other air. 
     In one preferred form of the invention, there is provided a method for operating a ducted fumehood with increased energy efficiency, wherein the method comprises: 
     passing exhaust air from the ducted fumehood through a heat exchanger, and passing other air through the heat exchanger, so as transfer heat content from the exhaust air to the other air, or to transfer heat content from the other air to the exhaust air, so as to temperature-condition the other air. 
     In another form of the invention, there is provided apparatus for operating a ducted fumehood with increased energy efficiency, wherein the apparatus comprises: 
     a heat exchanger configured to receive exhaust air from the ducted fumehood, and to receive other air, so as to transfer heat content from the exhaust air to the other air, or to transfer heat content from the other air to the exhaust air, so as to temperature-condition the other air. 
     And in another form of the invention, there is provided a system comprising: 
     a ducted fumehood; 
     a heat exchanger configured to receive exhaust air from the ducted fumehood, and to receive other air, so as to transfer heat content from the exhaust air to the other air, or to transfer heat content from the other air to the exhaust air, so as to temperature-condition the other air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
         FIG. 1  is a schematic view showing a ducted fumehood; 
         FIG. 2  is a schematic view showing, among other things, a ducted fumehood, a rooftop filter, and ductwork connecting the ducted fumehood to the rooftop filter; 
         FIG. 3  is a schematic view showing the novel method and apparatus of the present invention, wherein a heat exchanger is used to transfer heat content between the exhaust air of a fumehood and other air so as temperature-condition that other air, whereby to temperature-condition the ambient air of the laboratory; 
         FIG. 4  is a schematic view showing details of a preferred form of the system of  FIG. 3 ; 
         FIG. 5  is a schematic view showing one preferred form of the present invention, wherein the heat exchanger comprises a reversible heat pump, and further wherein the reversible heat pump is configured to recover heat from the exhaust air of the fumehood and return the recovered heat to the ambient air of the laboratory; and 
         FIG. 6  is a schematic view showing the same system as  FIG. 5 , except that the reversible heat pump is configured to transfer heat content from other air to the exhaust air of the fumehood so as to temperature-condition that other air, whereby to temperature-condition the ambient air of the laboratory. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Looking first at  FIG. 1 , there is shown a typical ducted fumehood  5 . Ducted fumehood  5  generally comprises an enclosed workspace  10  accessed by a front door  15 , with front door  15  engaging a sash  20  when the enclosed workspace is “sealed”. An air inlet  25  admits ambient air from the laboratory into enclosed workspace  10 , and an air outlet  30  removes exhaust air from enclosed workspace  10 . The exhaust air from air outlet  30  is passed into ductwork  35 , which in turn leads to a filter (not shown in  FIG. 1 ) where the exhaust air is filtered before being vented to the outside atmosphere. 
     More particularly, and looking now at  FIG. 2 , the exhaust air from ducted fumehood  5  is passed through ductwork  35  to a filter  40 , where the exhaust air is filtered to remove hazardous substances from the exhaust air (thereby rendering the exhaust air safe) before the exhaust air is vented to the outside atmosphere. A suction fan  45  is provided downstream of filter  40  so as to draw the exhaust air out of fumehood  5  and through filter  40 . In addition, an exhaust fan  50  ( FIG. 1 ) is preferably also provided at the air outlet  30  of fumehood  5  so as to ensure that the enclosed workspace  10  of fumehood  5  is kept at a negative pressure differential relative to the ambient air of the laboratory, in order to ensure that any air within the enclosed workspace passes through filter  40  before being vented to the outside atmosphere. 
     In a typical installation, ducted fumehood  5  is located in a laboratory within a building, and filter  40  is disposed on the roof  55  ( FIG. 2 ) of that building, with ductwork  35  connecting the output of ducted fumehood  5  to the input of filter  40 , and with the output of filter  40  being vented to the outside atmosphere. Furthermore, in a typical installation, a plurality of fumehoods  5  are connected to the rooftop filter  40 ; however, in the figures, only one ducted fumehood  5  is shown connected to filter  40  in order to simplify the description. 
     It will be appreciated that, in relatively temperate climates, the room temperature of the laboratory (within which the fumehood is disposed) will be fairly close to the temperature of the outside atmosphere. In this situation, there will be relatively little energy loss from venting the temperature-conditioned air of the laboratory to the outside atmosphere and replacing the temperature-conditioned air of the laboratory with the non-temperature-conditioned air of the outside atmosphere. 
     However, in other climates, e.g., the continental United States and Europe, there is often a substantial difference between the temperature of the ambient air of the laboratory and the temperature of the outside atmosphere. In this situation, there can be a relatively significant energy loss from venting the temperature-conditioned air of the laboratory to the outside atmosphere and replacing the temperature-conditioned air of the laboratory with the non-temperature-conditioned air of the outside atmosphere. 
     By way of example but not limitation, in the continental United States and Europe, during winter, the temperature of the ambient air in the laboratory might be 22 degrees C. and the temperature of the outside air might be 0 degrees C. Correspondingly, during summer, the temperature of the air inside the laboratory might be 22 degrees C. and the temperature of the outside atmosphere might be 32 degrees C. In these circumstances, venting the “conditioned” air from inside the laboratory to the outside atmosphere can be highly energy inefficient, since additional energy is required in order to “condition” the new air (drawn from the outside atmosphere) before it is supplied to the laboratory. 
     Thus, in winter, venting heated laboratory air to the outside atmosphere “wastes” the heat content of the conditioned laboratory air and, in summer, venting the cooled laboratory air to the outside atmosphere “wastes” the “cool content” of the conditioned laboratory air. 
     By way of example but not limitation, in the continental United States and in Europe, it is common for each vented fumehood to add approximately $6,000-$8,000 to the cost of temperature conditioning (i.e., heating or cooling) the ambient air of the laboratory. 
     The present invention provides an extremely efficient and cost-effective means for transferring heat content between the exhaust air of a fumehood and other air so as to temperature-condition that other air. 
     More particularly, and looking now at  FIG. 3 , in accordance with the present invention, a heat exchanger  100  is disposed between the output of filter  40  and the input to suction fan  45 , i.e., before final venting of the exhaust air to the outside atmosphere. More particularly, heat exchanger  100  comprises a filtered air line  102  passing through the heat exchanger and a fresh air line  103  also passing through the heat exchanger. Filtered air line  102  and fresh air line  103  do not communicate with one another, i.e., the contents of the filtered air line do not mix with the contents of the fresh air line. However, filtered air line  102  and fresh air line  103  do permit the transfer of heat energy from one air line to the other air line. 
     More particularly, and still looking now at  FIG. 3 , filtered air line  102  comprises a first input line  105  which is connected to the output of filter  40 , and a first output line  110  which is connected to the input of suction fan  45 . Fresh air line  103  comprises a second input line  115  which draws fresh air from the outside atmosphere and a second output line  120  which supplies fresh air to the interior of the building. A blower fan  125  is connected to second input line  115  so as to draw fresh air into second input; line  115  and blow it out second output line  120 . 
     Heat exchanger  100  transfers heat content between the heat exchanger&#39;s filtered air line  102  and the heat exchanger&#39;s fresh air line  103  so as to temperature condition (i.e., either warm or cool) the fresh air prior to introducing that fresh air into the building. In other words, heat exchanger  100  transfers heat energy between filtered air line  102  and fresh air line  103  so as to reduce the temperature differential between filtered air line  102  and fresh air line  103 , whereby to temperature-condition the outside air before it is introduced into the laboratory. 
     As noted above, the heat exchanger&#39;s filtered air line  102  and the heat exchanger&#39;s fresh air line  103  do not communicate with one another, i.e., the contents of the filtered air line do not mix with the contents of the fresh air line. However, filtered air line  102  and fresh air line  103  do permit the transfer of heat energy from one air line to the other air line. To this end, and looking now at  FIG. 4 , in one form of the present invention, heat exchanger  100  preferably comprises a first heat exchanger element  130  interposed in the airflow of filtered air line  102 , and a second heat exchanger element  135  interposed in the airflow of fresh air line  103 , with first heat exchanger element  130  being connected to second heat exchanger element  135  by means of a fluid line  140 . In this construction, first heat exchanger element  130  transfers heat content between the heat exchanger&#39;s filtered air line  102  and the heat exchanger&#39;s fresh air line  103 , whereby to temperature condition the fresh air before the fresh air enters the building. 
     It should be noted that it is generally preferable to position the heat exchanger after the filter, rather than before the filter, so that harmful substances can be removed from the exhaust air of the fumehood before those harmful substances reach the heat exchanger. This will, protect the heat exchanger from any damage that could occur due to contact with harmful substances contained in the exhaust air. Thus it will be appreciated that the filter will serve two purposes: first, to remove unwanted substances from the exhaust air so that those unwanted substances are not vented to the outside atmosphere, and second, to protect the heat exchanger from contact with harmful substances. 
     In one preferred form of the present invention, heat exchanger  100  comprises a reversible heat pump  100 A. More particularly, and looking now at  FIGS. 5  and  6 , the reversible heat pump  100 A comprises the first heat exchanger element  130  disposed in the airflow of filtered air line  102 , and the second heat exchanger element  135  disposed in the airflow of fresh air line  103 . A compressor  145  circulates refrigerant through a refrigerant line  140 . More particularly, refrigerant line  140  passes by first heat exchanger element  130  so as to exchange heat therewith and passes by second heat exchanger element  135  so as to exchange heat therewith. The reversible heat pump  100 A also comprises a reversing valve  150  for reversing the flow of refrigerant through refrigerant line  140 . Reversible heat pump  100 A preferably also comprises a pair of thermal expansion valves  155  and a pair of bypass valves  160  in refrigerant line  140 . 
       FIGS. 5 and 6  illustrate operation of the reversible heat pump assembly  100 A during heating and cooling modes, respectively. 
     More particularly, in  FIG. 5 , reversing valve  150  is set to extract heat content from the filtered air line  102  and transfer that heat content to the fresh air line  103 , whereby to heat fresh air line  103 . 
     In  FIG. 6 , reversing valve  150  is set to extract heat content from fresh air line  103  and transfer that heat content to filtered air line  102 , whereby to cool fresh air line  103 . 
     Significantly, because the reversible heat pump  100 A is designed to transfer heat content to and from filtered air line  102 , and because filtered air line  102  contains air which has a temperature which is very close to room temperature, the reversible heat pump is always working off air that is approximately 22 degrees C. This makes for very efficient energy recapture from the filtered air line, and allows for the use of smaller and more efficient reversible heat pumps. It is believed that as much as 90% of the thermal energy in the filtered air line can be recaptured through the use of a reversible heat pump. 
     MODIFICATIONS 
     It is to be understood that the present invention is by no means limited to the particular constructions herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the invention.