Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/20536—Modifications to facilitate cooling, ventilating, or heating for racks or cabinets of standardised dimensions, e.g. electronic racks for aircraft or telecommunication equipment
  • H05K7/20627—Liquid coolant without phase change
  • H05K7/20654—Liquid coolant without phase change within rooms for removing heat from cabinets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• This invention relates to a heat exchange system for maintaining, within a specified range, the temperature of apparatus in a cabinet, and more particularly, to a system that uses the ground for stabilizing the temperature of electrical and mechanical telephone equipment that is mounted within a cabinet and in which recirculated air transfers heat directly between the telephone equipment and a ground loop, and the like.
• Electric resistance heat although able to provide sufficient auxiliary heat within the cabinet to prevent freezing, suffers from a number of drawbacks. Electric resistance heat is very inefficient and expensive because electricity is used " directly for heat rather than as a source to move or to transfer that heat, such as through a heat pump. This inefficiency contributes to a poor load factor at the power plant, higher levels of pollution to the atmosphere and higher operating costs for the user.
• Forced air systems which use the air as the primary cooling medium also suffer from a number of problems. In these systems, heating is still provided through electrical resistance heaters, with their attendant problems, as mentioned above. Additionally, forced air convective cooling by means of fans that blow outside air across the equipment introduces airborne contaminants into these systems which can adversely affect many types of equipment. Acidity of this contained matter can cause electrical breakdowns, and dust buildup can reduce effective heat transfer. Adding outside filters reduces these airborne containments but increases maintenance costs and can restrict airflow as filters clog and reduce cooling capacity. Frequent maintenance is also required at high cost to the user.
• a secondary set of problems related to the forced air method include high ambient noise levels outside of the cabinet due to fan rotation and this contributes to noise pollution as well as possibly violating local noise ordinances. These fans, moreover, aggravate high temperature conditions on very hot days by increasing the temperature of the air that is drawn into the cabinet through the heat added by the fan apparatus. These very high temperature conditions tend to accelerate component failure. Still another method involves the use of an indirect exchange cooling process in which one fan is interior to the space within a cabinet and a second fan is coupled with an air-based heat exchanger outside the cabinet. This method uses closed air circulation within the cabinet, transferring heat to a tube assembly that has additional surface area outside the cabinet. Outside of the cabinet, either through natural or forced convection, heat dissipation occurs.
• This method solves the interior air contamination problem but does not provide effective cooling during high internal loading coupled with high outside temperatures.
• This condition requires excessively large heat exchange surface areas and external fans which are expensive. Operating costs for this system can also be excessively high. Exposure, moreover, of e heat exchanger to outdoor climatic conditions can reduce affective life.
• Air conditioners can effectively cool equipment and do enable isolation of outdoor air from indoor air. Further in this regard, air conditioners fail to perform efficiently on peak cooling days that coincide with very high equipment heat output. During these peak demand periods, cooling efficiencies are very low, with resulting higher operating costs. Air conditioners also create other related problems. Outdoor air, as the primary cooling medium still can introduce containments into filters adding to maintenance costs. Noise pollution is greater than with simple fans because they are augmented with compressor noises. Additionally, a power failure can render the cooling system inoperative and for certain critical applications where equipment must run on battery backup such as telephony equipment, the results could be catastrophic. Air source heat pumps as cooling systems certainly reduce the electric heat inefficiencies but suffer from all the other drawbacks of a conventional refrigerant based cooling systems.
• a ground source heat pump system which uses the earth as the primary medium overcomes some of the noise and filter maintenance issues, because the heat exchange does not require interaction with the outside air.
• the power failure problem as cited in connection with air source heat pumps remains unresolved.
• a further serious drawback of a ground source heat pump system is its requirement to dissipate compressor heat underground during the cooling cycle. Compressors generate a great deal of heat, and this heat adds to the burden that the system (of which the compressor is a part) must dissipate.
• a related problem in the heating mode is the requirement for antifreeze within the ground source heat exchanger loop system. This antifreeze is required to prevent fluid freezing caused by the low refrigerant temperatures developed within a ground source heat pump during the heating mode. The antifreeze, moreover, can reduce heat transfer effectiveness both during the heating and cooling modes.
• All three refrigerant based systems moreover, operate in the cooling mode with air coils below the dewpoint of air. This creates a dehu idification condition in which the system requires water removal. Large volumes of water require large dry wells (at a cost) and pose the threat of water spillage on the equipment if the drainage system fails. This is particularly hazardous to electronic equipment which is prone to fail through electrical shorting if water covers the connections. All three refrigerant based systems also require a reasonable physical space either within the cabinet or outside in order to function. This physical space outside the cabinet is normally aesthetically unpleasant and in some cases is too close to property boundaries, therefore requiring awkward placement of the cabinet. Interior space is normally at a premium within the cabinet, thus large compressor based heating and cooling systems placed within the cabinet waste cabinet space.
• All three refrigerant based systems further require several large rotating motors to turn compressors and fans. These motors normally produce some level of electro-magnetic energy which can, when in close proximity to certain electronic components cause malfunctions due to induced electrical noise. This interference is normally proportional to both the size of the field producing equipment and proximity to the operating electronics. Special shielding can be introduced but it adds to the cost and complicates air flow design.
• these three refrigerant based cooling systems also require nonbenign compounds that impose at least some environmental hazards in order to work. Refrigerant leaks are possible with each of these systems, particularly when equipment is vandalized or poorly maintained, and the negative impact on the environment in terms of ozone depletion could be significant if large numbers of these systems leaked refrigerant.
• an illustrative embodiment of the invention provides for direct heat exchange between recirculated air in a telephone equipment cabinet and the fluid in a fluid- to-ground heat exchanger.
• This ground loop allows heat in the circulating fluid to be dissipated or absorbed within the earth from the fluid circulated through the loop.
• the fluid will absorb heat from the ground and transfer that heat through a heat exchanger within the equipment cabinet directly to the recirculating air within the cabinet.
• a low power, direct current activated flow control assembly provides for this circulation and an air-to-fluid heat exchanger combined with a fan assembly, recirculates the air within the housing.
• the fan assembly also can be of a variable speed in order to match the air flow to the thermal load imposed on the system.
• a control system regulates operation of the heat stabilization apparatus.
• This invention takes advantage of the fact that the average annual temperature at 10 to 25 feet below the earth's surface tends to be slightly higher than the average annual temperature for a particular region. Albany, New York, for instance has a typical temperature range of -20 to 100°F. Neither of these extremes are coupled to the ground at depths below 15 feet. Thus, the earth as a heat exchange source or sink is stable at temperatures considerably below ° air temperature within the equipment cabinet.
• both heating and cooling operations are controlled by a thermostat that regulates the interior temperature of the cabinet.
• the control system for the present invention permits a broader range of acceptable temperatures for successful equipment operation.
• This unique feature makes direct heat exchange both practical and cost effective, when compared with more complicated heat pump apparatus. 0
• the use of the direct fluid-to-ground heat exchanger, coupled with the air-to-fluid heat exchanger eliminates refrigerant from the circuit, thereby avoiding one of the major environmental concerns related to space conditioning today.
• water or if necessary, 5 water mixed with potassium acetate as an anti-freeze compound, is used as the circulating fluid because of its environmental acceptability and to insure that no temperature within the fluid circuit will go below the fluid's freezing temperature. Ordinary water, of course, 0 does enhance the overall efficiency of heat exchange relative to other fluids.
• the power requirements are very low in comparison to compressor based systems. Additionally, circulators and 5 fans are readily available with direct current (DC) motors, whereas compressors are typically not DC driven. This allows for simple, low wattage direct battery support for continued temperature stabilization during power failure to enable critical applications such as telephony equipment to Q continue operation within acceptable temperature limits until normal power service is restored.
• DC direct current
• the equipment can readily fit within the conditioned cabinet, virtually eliminating the outside noise 5 pollution problem.
• Recirculating the air within the cabinet moreover, also eliminates the requirement for outdoor filters, again dramatically reducing the high maintenance costs of air based systems. It is not possible to make cabinets of this character completely air tight.
• air recirculation is adequately established if the external air flow into the cabinet is limited through the usual precautions, for instance, of neoprene gaskets on each cabinet door in order to isolate the air being recirculated within the cabinet from outside air.
• a typical cabinet that has a recirculating air system suitable for use with the invention is described in Northern Telecom Inc. 's "Product/Service Information" leaflet 5600.1 16/11-91, Issue 1, dated November 15, 1991.
• the air to circulating fluid heat exchange will normally operate just above the dewpoint of air. This will greatly reduce the effects of condensation and virtually eliminate the problem of spillage from overflowing condensate pans, thereby eliminating the potential for an electrical failure that could develop as a consequence of condensate accumulation.
• the low power circulators and fan do not generate the level of electromagnetic interference, or electrical signal noise, that could cause problems with respect to the housed equipment, in comparison with the much higher levels of electrical noise levels generated by compressors and large fan assemblies that have characterized the prior art.
• the structure that exemplifies the invention is subject to a number of different embodiments.
• the invention for example is best used in those applications that transfer thermal loads of 5 tons, or less, (one ton equals 12,000 British thermal units per hour).
• the invention is admirably suited to electrical equipment thermal stabilization, because equipment of this nature typically creates thermal loads of 1/2 ton to 5 tons.
• the invention can be used to transfer greater thermal loads and for this purpose the novel apparatus that comprises the invention can be coupled with more conventional heat pump equipment in a hybrid, or combination design to accommodate larger equipment heat transfer requirements. Note, however, in these hybrid and combination systems, that the benefits of the invention do alleviate the undesirable features of these prior systems, at least to the extent that some of the thermal load is stabilized through apparatus that characterizes the invention.
• the invention also is adaptable to a plurality of piping fields, or ground loops, buried in the earth. Each of these loops can be selectively connected to the fluid-to-air heat exchanger within the equipment cabinet. Switching ground loops in this manner reduces the potential for thermal saturation in the soil in the vicinity of each of these loops and a typical system for performing this function is described in Thomas F. O'Connell United States Patent No. 4,360,056, granted November 23, 1982, for "Geokinetic Energy Conversion.”
• Fig. 1 is a perspective view of an equipment cabinet that illustrates features of the invention, with a portion of the top cover removed in broken section;
• Fig. 2 is a schematic diagram of a ground loop heat exchanger, for use with the cabinet shown in Fig. 1; and Fig. 3 is a perspective view of a typical air flow assembly for use with the cabinet shown in Fig. 1.
• FIG. 1 shows a generally rectangular equipment cabinet 10 for housing electrical equipment 11, e.g. telephone apparatus.
• the cabinet 10 is essentially air tight, except for air vents 12 and 12' formed in top 14 of the cabinet 10.
• a generally rectangular housing 15 is joined to the top 14 of the cabinet 10 to form a void space 16 between the top of the housing 15 and the cabinet top 14 for air recirculation within the cabinet and housing combination, as described subsequently in more complete detail.
• an air-to-fluid heat exchanger 17 is secured to the housing 15.
• a flow control assembly 20 also is secured within the housing 15, between one end of the air- to-fluid heat exchanger and a side wall of the housing.
• a control box ,1 also is nested within the housing
• control box 21 contains a thermostat, or temperature sensing apparatus and suitable electrical circuits to activate the flow control assembly 20 in order to regulate the flow of fluid through the air-to- fluid heat exchanger 17 as described subsequently in more complete detail.
• a fan assembly 22 also is secured to the housing 15 and positioned over the air vent 12' for i e purpose of recirculating air through the interior of the equipment cabinet 10 and the void space 16.
• FIG. 3 shows the structural details of the fan assembly 22.
• a pair of fan impellers 23, 24 each are driven respectively, by low power direct electrical current motors 25, 26.
• variable speed fans might be preferred, although a fan speed control circuit is not shown in the drawing.
• Power for these motors is supplied either from a conventional rectified power supply (not shown ; n the drawing) or, in the case of a power failure, from battery 27 (Fig. 1) which is switched to the low power direct current motors 25, 26 through the operation of an appropriate emergency circuit in the control box 21.
• a conventional rectified power supply not shown ; n the drawing
• battery 27 Fig. 1
• Fig. 2 shows an illustrative ground loop 32, which may be formed of polyethylene tubing.
• the ground loop 32 enables a working fluid, preferably water, to flow in a closed circuit, and without change of physical state, from a depth in earth 33 at which the earth's temperature remains within an acceptable temperature range.
• the tubing that comprises the subterranean portion of the loop 32 is laid out within a drill borehole to optimize heat transfer with the earth and to create turbulent flow in the tubing to improve overall heat transfer potential.
• the lower, or deeper part, of the subterranean portion of the loop 32 is encased in grouting material 34 to establish a better thermal contact and to eliminate aquifer contamination.
• the upper portion of the loop 32 that is close to the earth's surface is enclosed in dirt, drill cuttings 35 and the like.
• the ground loop heat exchanger is connected to the flow control assembly 20 through appropriate ground loop couplings 18 and 19. The water, moveover, follows a flow path from the loop 32 through the flow control assembly 20, air-to-fluid heat exchanger 17 and back to the ground loop.
• a sensor (not shown in Fig. 1) responds to a temperature increase that exceeds a predetermined set point (e.g. 90°F) by energizing the motors 25 and 26 which drive fan impellers 23, 24 (Fig. 3) within the fan assembly 22 (Fig. 1) .
• a predetermined set point e.g. 90°F
• the impellers draw recirculating air from the interior of the cabinet 10 through the air vent 12 into the void space 16.
• the air from the vent 12 flows in the direction of arrows 34, 35 through the air side of the air-to-fluid heat exchanger 17.
• the hot air from the cabinet 10 transfer this heat to the cooler water on the water side of the heat exchanger.
• a set point switch in 5 the control box 21 once more energizes the fan assembly 22 to draw cold recirculating air of the heat exchanger 17.
• the appropriate circuit within the control box 21 causes the flow control assembly to pump relatively warmer water from the ground loop 32 (Fig. 2) in 0 order to enable the water to heat the air within the heat exchanger 17. This warmed air then is pumped in the manner described above, back into the interior of the cabinet 10 in order to keep the temperature of the electrical equipment 11 at or above the desired level for efficient operation.
• the invention consequently, also provides for the activation only of the flow control 0 assembly 20 to maintain warmer fluid flow from the subterranean ground loop throughout the system, thereby preventing freezing, burst piping and the like in these circumstances.
• a circuit within the control box 21 responds by switching not only its own operation but also that of the low power fan motors 25, 26 (Fig. 3) and the flow control assembly 20 (Fig. 1) to the battery 27.
• the housing 15 and the temperature stabilizing equipment within the housing can be attached as a unit ' to existing equipment cabinets 10 in order to improve the thermal stability of these cabinets.
• a temperature stabilization apparatus that largely overcomes the noise, contamination, electrical background signals, and environmental problems that have characterized the prior art.
• the invention also provides a more efficient and cost- effective temperature stabilization device than that which heretofore has been available.

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• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Microelectronics & Electronic Packaging (AREA)

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• 1993
  • 1993-04-23 AU AU41129/93A patent/AU4112993A/en not_active Abandoned
  • 1993-04-23 EP EP93910744A patent/EP0640246A4/de not_active Withdrawn
  • 1993-04-23 WO PCT/US1993/003821 patent/WO1993023875A1/en not_active Application Discontinuation
  • 1993-04-23 CA CA 2135762 patent/CA2135762A1/en not_active Abandoned

Non-Patent Citations (2)

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