EP0640246A1

EP0640246A1 - Temperature stabilization apparatus

Info

Publication number: EP0640246A1
Application number: EP93910744A
Authority: EP
Inventors: Thomas F. O'connell
Original assignee: GEOTECH ENERGY CONVERSION Corp
Current assignee: GEOTECH ENERGY CONVERSION Corp
Priority date: 1992-05-15
Filing date: 1993-04-23
Publication date: 1995-03-01
Also published as: WO1993023875A1; EP0640246A4; AU4112993A; CA2135762A1

Abstract

An illustrative embodiment of the invention provides a temperature stabilization apparatus for a closed equipment cabinet (10) in order to maintain the equipment (11) in the cabinet within predetermined temperature limits. A subterranean ground loop (32) is coupled to a heat exchanger (17) in which a portion of the ground loop is buried within the earth (33) to a depth at which the earth's temperature remains within predetermined limits. The heat exchanger (17) transfers heat between recirculated air (30, 31, 34, 35) within the cabinet and the earth (33) to provide the needed temperature stability for equipment within the cabinet. Water, in which its physicial state does not change, is the preferred working fluid for the ground loop.

Description

TEMPERATURE STABILIZATION APPARATUS

TECHNICAL FIELD

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.

BACKGROUND ART

There is a need to stabilize the temperature of equipment, and particularly electrical and mechanical telephone and power equipment, within an acceptable temperature range in order to maintain the equipment at proper performance levels. Operating equipment that is subjected to extreme temperatures tends frequently to fail, resulting in increased maintenance costs and excessive out- of-service time. Equipment of this nature does not normally require the comfort temperature range (70 to 75°F) that is required by human beings, but more typically can successfully operate in temperature ranges of 35 to 110°F. Further in this same regard, high humidity conditions in excess of 70%, considered uncomfortable for humans, are normally not a problem for electrical and mechanical equipment of this character.

Various methods have been employed to provide controlled heating and cooling within the aforementioned equipment temperature range, but all of these techniques have serious problems.

For example, some systems have employed electric heating, forced air cooling, and refrigerant based cooling systems. Although each of these methods provides either heating or cooling, or both, each method is subject to a number of inherent limitations.

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.

Additionally, high temperature air on very hot days reduces the cooling effectiveness. This natural temperature fluctuation can create a thermal shock condition for the equipment or under sustained high temperature this indirect cooling system becomes a marginally effective means for cooling the equipment. Λis can cause a rapid reduction in equipment life.

Conventional 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. Further, during a power failure, emergency battery to keep the electrical equipment operational could require a great deal of capacity as well as complicated power inverters that may generate a considerable amount of electrical noise to permit heating or cooling to continue. 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. However, 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. Consequently, this added compressor heat contributes to the ground's thermal state and can lead to thermal saturation unless very large (and costly) ground heat exchangers are used. 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 are normally of fixed capacity in their ability to cool. Unfortunately, equipment within a cabinet can represent various levels of thermal loading and therefore can vary considerably in the cooling capacity that is required. Fixed capacity systems typically handle peak conditions well but become very inefficient as loads are reduced. Cycling losses due to frequent starts and stops contribute to the inefficiencies and add to the operating costs. Additionally, cooling equipment life is shortened.

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.

Further, 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.

SUMMARY OF THE INVENTION

To overcome these, and other inadequacies of the prior art, 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. Alternatively, if the temperature of the telephone equipment is to be increased, 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.

In accordance with the invention, both heating and cooling operations are controlled by a thermostat that regulates the interior temperature of the cabinet. Unlike conventional temperature control required for human comfort, 5 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. Preferably, 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.

In accordance with another aspect of the invention 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.

In accordance with a further aspect of the invention, 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. Some migration into the cabinet of atmospheric air and entrained contaminants ordinarily can be expected, depending on ambient air conditions. For practical purposes, and for the purposes of this invention, 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.

In accordance with yet another aspect of the invention, because there is no change in state for the fluid used in connection with the invention, the additional heat generated by the compressors in heat pumps that have been used in the past is eliminated, thereby reducing the thermal saturation that can occur with heat pumps that have been applied to ground loop systems. This adds to the overall improved performance of the ground loop design. Related to this, the normally unacceptable temperature swings developed with the ground source heat exchanger during heat transfer, though outside human comfort ranges, remain within the tolerances of most operating equipment.

In accordance with another aspect of the invention, 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.

In accordance with another aspect of the invention, 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. This virtually eliminates the requirement for electrical shielding. 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). Thus, 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.

Further, 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."

These, and other features of the invention are apparent through the following detailed description of modes for carrying out the invention, when taken with the figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

MODES FOR CARRYING OUT THE INVENTION

^{For a} more complete appreciation of the invention, attention is invited to Fig. 1 which 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.

In accordance with a salient characteristic of the invention, 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. Within the void space 16, 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

15 between one end of the flow control assembly 20 and a transversely disposed side of the housing 15. Although not shown in the drawing, the 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.

Attention now is invited to Fig. 3 which shows the structural details of the fan assembly 22. As sL wn, a pair of fan impellers 23, 24 each are driven respectively, by low power direct electrical current motors 25, 26. For some operations, 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. As illustrated in the Fig. 3 schematic, the fans 23, 24, when activated, draw air from the direction of the air-to-fluid heat exchanger 17, in the direction of arrows 30, 31, and discharge this recirculated air in the direction of arrows 28, 29 through the air vent 12' (Fig. 1) in the cabinet top 14 in order to force this air through the second vent and into the interior of the equipment cabinet 10.

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. Ideally 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.

In operation, as heat accumulates within the cabinet 10 (Fig. 1) through the operation of the electrical equipment 11, 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) . When activated, 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. Within the 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. This cooled air then is drawn by the action of the fans in the direction of the arrows 30, 31 into the fan impellers 23, 24 (Fig. 3), respectively, in order to permit the fans to discharge this cooled air into the interior of the cabinet 10 through the air vent 12' for the purpose of cooling the electrical equipment within the cabinet. At the same time that the circuit within the ° control box 21 activates the fan assembly, the circuit within the control box also activates the flow control assembly 20. When so activated, the flow control assembly 20 pumps water from the ground loop 32 (Fig. 2) through the water side of the heat exchanger 17. In this manner, cool 5 water from the ground loop 32 absorbs heat from the air that the fan assembly 22 (Fig. 1) drew through the heat exchanger 17. The warmer water then flows through the ground loop 32 into the earth 33 where the heat is discharged to the cooler earth, thereby cooling the water. The cooled water then 0 completes its travel through the loop 32, the flow control assembly 20 and the heat exchanger 17.

In a similar manner, as the temperature of the air within the equipment cabinet falls below some predetermined lower limit (e.g., 40°F) , a set point switch (not shown) in 5 the control box 21 once more energizes the fan assembly 22 to draw cold recirculating air of the heat exchanger 17. At the same time, the appropriate circuit (not shown) 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. 5 During extended periods of non-operation for the electrical equipment 11 in the cabinet 10, a condition may exist that could cause the fluid within the above-surface piping to freeze. 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.

Should conventional sources of electrical power 5 fail, 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.

It is important to note that in accordance with another feature of the invention 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.

INDUSTRIAL APPLICABILITY

Thus, there is provided in accordance with the principles of the invention, a temperature stabilization apparatus that largely overcomes the noise, contamination, electrical background signals, and environmental problems that have characterized the prior art. At the same time, the invention also provides a more efficient and cost- effective temperature stabilization device than that which heretofore has been available.

Other aspects of the invention will be apparent to those of ordinary skill in the art.

Claims

CLAIMS What is claimed is:

1. A temperature stabilization apparatus for a closed equipment cabinet for maintaining equipment in the cabinet within predetermined temperature limits, comprising a housing, an air-to-fluid heat exchanger within the housing, a flow control within the housing and coupled to the heat exchanger for pumping fluid through the heat exchanger, a fan within the housing for recirculating air through the heat exchanger, and a control circuit within the housing for selectively activating said flow control and said fan as the temperature of the recirculated air within the equipment cabinet exceeds the predetermined limits.

2. A temperature stabilization apparatus according to Claim 1, further comprising a subterranean ground loop coupled to the heat exchanger in which a portion of the ground loop is buried within the earth to a depth at which the earth's temperature remains within the predetermined temperature limits.

3. A temperature stabilization apparatus according to Claim 2, further comprising a plurality of ground loops, each of said loops being selectively coupled to the heat exchanger to prevent thermal saturation of the earth in the vicinity of each of the ground loops.

4. A temperature stabilization apparatus for maintaining equipment within predetermined temperature limits comprising a cabinet, said cabinet having a void space that communicates with the interior of said cabinet, an air-to-fluid heat exchanger within said void space, a flow control within said void space coupled to the heat exchanger for pumping fluid through the heat exchanger, a fan within said void space for recirculating air through the heat exchanger, and a control circuit for selectively activating said flow control and said fan as the temperature of the recirculated air within the equipment cabinet exceeds predetermined temperature limits.

5. A temperature stabilization apparatus according to Claim 4, further comprising a subterranean ground loop coupled to the heat exchanger in which a portion of the ground loop is buried within the earth to a depth at which the earth's temperature remains within the predetermined temperature limits.

6. A temperature stabilization apparatus according to Claim 5, further comprising a plurality of ground loops, each of said loops being selectively coupled to the heat exchanger to prevent thermal saturation of the earth in the vicinity of each of the ground loops.

7. A temperature stabilization apparatus according to Claim 4, wherein said apparatus further comprises water within said air-to-fluid heat exchanger, said flow control and said ground loop.

8. A temperature stabilization apparatus according to Claim 7, further comprising telephone equipment within said cabinet for temperature stabilization by the apparatus.

9. A temperature stabilization apparatus according to Claim 7, further comprising electrical power distribution equipment within said cabinet for temperature stabilization by the apparatus.

10. A temperature stabilization apparatus according to Claim 4, wherein said control circuit further comprises circuit means for selectively activating said flow control and deactivating said fan to prevent said fluid from freezing.

11. A temperature stabilization apparatus for use in combination with another temperature stabilization system for maintaining equipment within predetermined temperature limits comprising a cabinet, said cabinet having a void space that communicates with the interior of the cabinet, an air-to-fluid heat exchanger within said void space, a flow control within said void space coupled to the heat exchanger for pumping fluid through the heat exchanger, a fan within said void space for recirculating air through the heat exchanger, and a control circuit for selectively activating said flow control and said fan as the temperature of the recirculated air within the equipment cabinet exceeds either of the predetermined temperature limits in conjunction with the other temperature stabilization system.

12. A temperature stabilization apparatus according to Claim 11, further comprising a subterranean ground loop coupled to the heat exchanger in which a portion of the ground loop is buried within the earth to a depth at which the earth's temperature remains within the predetermined temperature limits.