Distributed Climate-Control Systems and Methods with Distributed Protection against Refrigerant Loss

Abstract

Distributed Climate-Control Systems and Methods with Distributed Protection against Refrigerant Loss: the system includes a central condenser unit in combination with a distributed network of air handling units. Each air handler includes an evaporator, in which condensed refrigerant can undergo a phase change while absorbing heat of vaporization, plus a heat exchanger (e.g. a coil) which permits the heat absorption of the evaporator to be coupled to a forced airflow. Preferably the evaporator includes a metering device to provide variable refrigerant flow, and hence variable rates of heat transfer. The individual evaporators also include a sensor to detect ambient levels of the refrigerant, electrically operable cutoff valves which permit the evaporator to be isolated from both the liquid-phase and the gas-phase refrigerant flows. Local control logic is preferably connected to shut the cutoff valves whenever an ambient refrigerant concentration is found to exceed a tolerable level.

Description

BACKGROUND

The present application relates to distributed climate control systems, especially those which supply a condensed phase-change refrigerant compound to multiple evaporators in the same fluid system.

Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.

Consider, as an example of a distributed cooling system, a hotel having individual cooling units in the various guest rooms. Each cooling unit includes its own evaporator. A central condenser supplies liquid refrigerant—e.g. a halocarbon or other phase-change refrigerant—to all of the evaporators in a group. (The group might include a few guest rooms, or all guest rooms on one floor of the hotel, or all guest rooms on multiple floors of the hotel.) However, if one of the evaporators begins to leak, the whole system's refrigerant can potentially escape. If one of the evaporators suffers a catastrophic failure, all of the refrigerant in the system can potentially be discharged into one room. With conventional Freon-type refrigerants, this risks displacement of the oxygen, and hence poses a suffocation hazard. If flammable or toxic refrigerants are used, the safety hazard is increased.

Variable Refrigerant Flow (VRF) heating, ventilation, and air conditioning (HVAC) systems operate in conjunction with ANSI/ASHRAE Standard 15 and ANSI/ASHRAE Standard 34 safety standards. These standards specify requirements for the safe design, construction and application of refrigeration systems used in a wide variety of residential, commercial and industrial applications. However, these standards do not address loss of income, equipment concerns, reliability, comfort issues, and health/safety concerns relating to catastrophic refrigerant loss in a VRV/VRF system. Specifically, two points of failure are not addressed: (1) what happens when a contractor adds a refrigerant charge to the VRF system that is low on charge due to a leak; and (2) what could result from a catastrophic coil failure in a condition space like a hotel room, a hospital or daycare center.

If a VRF system has a catastrophic failure and loses all of its charge, all of the areas that are connected to that outdoor condenser will fail because the VRF system has lost the refrigerant charge and will be down until the faulty coil is repaired. For example, a hotel room has a VRF system that sustains a catastrophic failure and all 19 rooms on the fourth floor of a hotel are affected. The impacts of this catastrophic failure are a comfort issue, cost issue, and a safety/health issue because the hotel is down due to a refrigerant leak. It is critical for a contractor to find leaks when they are small before there is a catastrophic leak into a room where somebody could be fatally affected due to oxygen being displaced in the room. When 100 pounds of refrigerant is dumped into a single room, the oxygen in that room will be displaced and the refrigerant will inundate not only that room but the hallway outside of that room as well.

Not only is this a cost and comfort issue, this is a health and safety issue as refrigerant can cause asphyxiation and death if retained within an enclosed space. A small leak that goes undetected or not repaired for a period of time can grow to a larger leak.

The cost and downtime to find a refrigerant leak in a distributed system can be large. If the system is unpressurized, a repair contractor may have to look for signs of refrigerant having escaped (e.g. oil residue or exfoliation of metal), or may have to waste refrigerant on a partial recharge merely to use available leak detection tools. A further complication, in hotels, is that some guests may have a “Do Not Disturb” indication set.

Leak detectors and sensors are available for many common refrigerants. For refrigerant leakage monitoring, the actual refrigerant species is known, so it is not necessary to distinguish between that and similar species. One common technology is infrared absorption, where absorptions of specific wavelengths will be strongly affected by threshold concentrations of the refrigerant sought to be detected. This currently appears to be the most attractive technology for cheap durable installed leak detectors and sensors. However, many other technologies are possible, such as diode detectors and sensors, chemFETs, and FTIR.

Recently, flammable refrigerant gasses, such as propane, have attracted more interest. Such gasses can still provide a usable heat of vaporization, without corroding the metal tubing and without the greenhouse gas burden of chlorofluorocarbons.

The present application teaches, among other innovations, Distributed Climate-Control Systems in which one condenser (or multiple condensers) serves multiple evaporators (typically in multiple air handlers). Each air handler includes a refrigerant leak sensor plus cutoff valves which are automatically operated to isolate an evaporator from the refrigerant lines when some value of ambient refrigerant (leakage) is detected. This provides an early-warning system to isolate leakage problems and also launch an appropriate maintenance response.

The present application also teaches, among other innovations, methods for operation of a distributed climate-control system with distributed leak detection and response capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments and which are incorporated in the specification hereof by reference, wherein:

FIG. 1 schematically shows a complete distributed climate-control system.

FIG. 2 shows an example of a complete modular air handler unit which incorporates the above innovate teachings.

FIGS. 3A and 3B shows two examples of control modules which operate an air handler like that of FIG. 2, within a system like that of FIG. 1.

FIG. 4 shows an example of a condenser which is connected to multiple evaporators through one EEV and one solenoid valve at each evaporator.

FIG. 5 shows an example of a condenser which is connected to multiple evaporators through two solenoid valves at each evaporator.

FIGS. 6, 7, and 8 show more details of a single room unit, in three alternative implementations.

FIG. 9 shows an example of a multizone heat recovery system.

FIG. 10 shows an exemplary control module like those of FIGS. 3A and 3B using EEV and/or LEV.

FIGS. 11A and 11B show sample sensor configurations corresponding to FIGS. 3A and 10, respectively.

DETAILED DESCRIPTION OF SAMPLE EMBODIMENTS

The numerous innovative teachings of the present application will be described with particular reference to presently preferred embodiments (by way of example, and not of limitation). The present application describes several inventions, and none of the statements below should be taken as limiting the claims generally.

The present application discloses new approaches to configuration and control of distributed climate-control systems which include multiple separate evaporators. An important component of these systems is distributed leak detection.

Sample System Configuration

FIG. 1 schematically shows a system 0200 which includes a central condenser unit (outside heat exchanger OHE 0210) in combination with one inside heat exchanger (THE 0220) of the distributed network 0200 of air handling units. Each of the air handlers includes an evaporator, in which condensed refrigerant can undergo a phase change while absorbing heat of vaporization, and incorporates heat exchanger EEX 0222 (e.g. a coil) which permits the heat absorption of the evaporator to be coupled to a forced airflow path. (The forced airflow is typically driven by separate blower ECF 0223, but alternatively this blower could be integrated into the air handler if desired.) Preferably the evaporator includes a metering device 0221, shown here as an evaporator expansion valve (EEV), to provide variable flow of refrigerant, and hence a variable rate of heat transfer.

As taught by the present application, the individual ones of the evaporators also include additional unconventional elements. First, sensor HRS 0224 to detect ambient levels of the refrigerant is included; second, electrically operable cutoff valving 0231+0241 (RRV+RSV) is used to permit the evaporator to be isolated from both the liquid-phase and the gas-phase refrigerant flows; and third, local control logic (shown below) is preferably included with each of the evaporator units 0220, and is preferably programmed to shut the cutoff valves 0231+0241 whenever an ambient refrigerant concentration is found to exceed a tolerable level. (The tolerable level may be zero, or may be slightly higher in some cases.)

FIGS. 4 and 5 show two exemplary condenser configurations. In the example of FIG. 4, the condenser is connected to multiple evaporators through one EEV and one solenoid valve at each evaporator.

The exemplary condenser of FIG. 5 shows a condenser which is connected to multiple evaporators through two solenoid valves at each evaporator.

The exemplary single room unit of FIG. 6 uses metering EEVs or LEVs between the gas pipe and gas pipe thermistor TH23, and between the liquid pipe and liquid pipe thermistor TH22. In contrast, the exemplary single room unit of FIG. 7 uses solenoid valves where FIG. 6 uses EEVs or LEVs. In the sample embodiment of FIG. 8, either a solenoid or a metering device, but not both, is used between the gas pipe and gas pipe thermistor TH23, and no supplemental solenoid or metering device is used adjacent to the liquid pipe in place of the solenoid on FIG. 7's liquid pipe.

EEVs and LEVs are typically used as 100% shutoff valves. In each of FIGS. 6-8, the linear expansion valve connected immediately adjacent to liquid pipe thermistor TH22, on the pipe side, is preferably a manufacturer-installed metering device. This LEV can be programmed through software to add a sensor to detect refrigerant leaks, and this programmable LEV can operate as a shut valve or as a metering device.

The sample embodiment of FIG. 9 shows a multizone heat recovery system.

Sample Air Handler configuration

FIG. 2 shows an example of a complete modular air handler unit which incorporates the above innovative teachings. Note that a sensor for ambient gaseous refrigerant is included.

Sample Local Control Logic

FIGS. 3A and 3B show two examples of control modules which operate an air handler like that of FIG. 2, within a system like that of FIG. 1. Note that an electronic latching relation is preferably included, so that when the shutoff valve(s) have been activated, they cannot be accidentally inactivated.

FIG. 10 show an exemplary control module similar to that of FIGS. 3A and 3B, in which EEVs and/or LEVs are used instead of the solenoid valves of FIGS. 3A and 3B.

FIGS. 11A and 11B show examples of sensor pin configurations corresponding to FIGS. 3A and 10, respectively.

Triggering an Alarm Condition

Depending on the refrigerant used and the constraints of a particular installation, different alarm conditions can be triggered by different events in the disclosed system. Not all of these conditions have to be implemented in every installation, but it is worth noting that the disclosed systems allow these possibilities.

A. First, of course, detection of ambient refrigerant above a threshold value can be used to trigger an automatic shutoff as described above. When this occurs the response is not only local, but a signal from the air handler where trouble has been detected can be used to initiate exception handling in a central monitoring system.

B. The threshold value may be set to zero, so that any nonzero value will cause the cutoff valves to be operated. However, if the cutoff threshold value is set to be greater than zero, it may also be possible to set a lower value which will trigger a preliminary report. These preliminary reports can be useful for maintenance alerts, while not necessarily requiring drastic action.

C. A different consideration arises when the shutoff valves of one or more airhandlers have been activated, and yet the ambient refrigerant concentration has not returned to its baseline value. In this case the distributed sensing properties of the disclosed air handlers provide a new source of inputs to a higher-level control system (which may include a human operator).

Alarm Condition Handling

The simplest operation is to allow the local control logic (at the air handler) to activate the cutoff valves automatically, whenever an increased level of refrigerant is detected in the ambient, without any higher-level input. However, many modifications can be added to this basic control relation, as detailed below.

A secondary benefit of the localized leak detection is that human operators, and higher-level monitoring and control systems, now have access to a distributed network of leak detection sensors. This can be used to perform functions in addition to simple cutoff of a leaking coil. For instance, if the cutoff valves have been activated and refrigerant is still detected (after a few minutes), then not all leak sources have been isolated. In this case a further alarm condition can be triggered, to require, e.g., isolation of a section containing multiple air handlers.

With some refrigerants (especially those which are toxic or flammable), any trace of ambient refrigerant should trigger shutdown. However, in cases where the refrigerant is benign enough to allow a non-zero tolerable concentration, and the leak sensor is sensitive enough to detect ambient refrigerant levels below the tolerable concentration, it may be preferable to trigger shutdown only when the non-zero tolerable concentration has been detected.

Application: Hotels

Much of the above discussion relates specifically to hotel operation. However, it is important to realize that this is just one example of installations which can benefit from the disclosed inventions.

Application: Inpatient Health Care

Hospitals and other inpatient facilities place high demands on their infrastructure, since helpless patients can be critically vulnerable to defects in HVAC. Moreover, distributed climate control is particularly attractive for hospitals, where isolation of airflows can help to avoid diffusion of airborne pathogens. Wherever distributed climate control is needed, the disclosed inventions can provide improvement.

Application: Schools

Audible alarms and/or flashing lights can also be used to alert the teacher or other responsible personnel when there is a danger of refrigerant leakage.

Application: Military

Airflow isolation here can increase security against smoke and gas diffusion. Moreover, distributed climate control can help to provide additional support for blast isolation and intrusion barriers.

A further secondary benefit, unique to this class of applications, is survival of some evaporators when others have been compromised. When an air handler is not within the close defense perimeter, its shutoff valves can be activated to improve the chances that catastrophic refrigerant loss will not occur.

Application: Residential

Residential installations are particularly advantageous. First, the possibility of multiple zones being shut down is extremely repugnant to many customers. Second, residences are normally not constructed to the strict fire protection standards as commercial buildings, but fire is still a feared hazard. Thus the early warning and limited shutdown capabilities of the disclosed inventions are particularly advantageous here.

Use with Flammable Refrigerants

The disclosed system has been successfully demonstrated in an experimental prototype system which includes propane in the refrigerant (e.g. R290).

Advantages

The disclosed innovations, in various embodiments, provide one or more of at least the following advantages. However, not all of these advantages result from every one of the innovations disclosed, and this list of advantages does not limit the various claimed inventions.

• • Reduced environmental damage (risk) due to refrigerant leakage.
  • Reduced system downtimes due to leak.
  • Reduced cost and delay when leak repair is required.
  • Improved systemwide diagnosis of persistent leakages.
  • Reduced risk of occupant asphyxiation.
  • Reduced risk of fire, when flammable refrigerants are used.

According to some but not necessarily all embodiments, there is provided: A multi-location climate control system comprising: a condenser, which receives evaporated refrigerant from a refrigerant return connection, and condenses the evaporated refrigerant to a liquid flow of condensed refrigerant which is supplied to a refrigerant supply connection; and multiple air handler units in multiple locations, individually including an evaporator which is connected, through respective cutoff valves, to be supplied with condensed refrigerant and to discharge evaporated refrigerant, and a heat exchanger which thermally couples the heat absorption of the evaporator to a forced airflow path, and a refrigerant leak sensor which detects escaped refrigerant in the ambient air, and which is local to that air handler unit; and control logic which, under at least some circumstances, automatically activates the cutoff valve to cut off flow of condensed refrigerant into the respective evaporator, in dependence on the output of the leak sensor.

According to some but not necessarily all embodiments, there is provided: A multi-location climate control system comprising: a condenser, which receives evaporated refrigerant from a refrigerant return connection, and condenses the evaporated refrigerant to a liquid flow of condensed refrigerant which is supplied to a refrigerant supply connection; and multiple air handler units in multiple locations, individually including an evaporator which is connected, through respective cutoff valves, to be supplied with condensed refrigerant and to discharge evaporated refrigerant, and a respective metering device which regulates flow of refrigerant through that evaporator, and a heat exchanger coil which thermally couples the heat absorption of the evaporator to a forced airflow path, and a refrigerant leak sensor which detects escaped refrigerant in the ambient air, and which is local to that air handler unit; and local control logic which, under at least some circumstances, automatically activates the cutoff valve to cut off flow of condensed refrigerant into the respective evaporator, in dependence on the output of the leak sensor.

According to some but not necessarily all embodiments, there is provided: A multi-location cooling system comprising: multiple evaporators in multiple locations, ones of said evaporators being connected, through respective cutoff valves, to be supplied with refrigerant therethrough, and each respectively including a respective metering device which regulates flow of refrigerant through that evaporator, and each thermally coupled through a heat exchanger to a respective airflow path, and multiple refrigerant leak sensors, in multiple respective ones of the multiple locations; and control logic which, under at least some circumstances, automatically activates the cutoff valve for one of the evaporators when excess ambient refrigerant is detected by a corresponding one of the leak sensors.

According to some but not necessarily all embodiments, there is provided: A multi-location cooling system comprising multiple evaporators in multiple locations, ones of said evaporators being connected, through respective cutoff valves, to be supplied with refrigerant therethrough, and each respectively including a respective metering device which regulates flow of refrigerant through that evaporator, and each thermally coupled through a heat exchanger [coil] to a respective airflow path, and multiple refrigerant leak sensors, in multiple respective ones of the multiple locations; and control logic local to each location which contains a respective one of the evaporators which, under at least some circumstances, automatically activates the cutoff valve for one of the evaporators when excess ambient refrigerant is detected by a corresponding one of the leak sensors.

According to some but not necessarily all embodiments, there is provided: An air handler module, comprising: an evaporator, having a metering device which regulates flow of refrigerant through the evaporator, first and second refrigerant connections which connect the evaporator to receive a liquid flow of condensed refrigerant from a refrigerant supply connection and to supply evaporated refrigerant to a refrigerant return connection, one or more cutoff valves which, when activated, cut off the flow of refrigerant through the evaporator, and a heat exchanger which thermally couples the heat absorption of the evaporator to a forced airflow path; a refrigerant leak sensor which detects escaped refrigerant in the ambient air; and control logic which, when the refrigerant leak sensor detects an ambient refrigerant concentration above a minimum, automatically shuts the cutoff valves.

According to some but not necessarily all embodiments, there is provided: A multi-location climate control system comprising: a condenser, which receives evaporated refrigerant from a refrigerant return connection, and condenses the evaporated refrigerant to a liquid flow of condensed refrigerant which is supplied to a refrigerant supply connection; and multiple air handler units in multiple locations, individually including an evaporator which is connected, through respective cutoff valves, to be supplied with condensed refrigerant and to discharge evaporated refrigerant, and a heat exchanger which thermally couples the heat absorption of the evaporator to a forced airflow path, and a refrigerant leak detector which detects escaped refrigerant in the ambient air, and which is local to that air handler unit; and control logic which, under at least some circumstances, automatically activates the cutoff valve to cut off flow of condensed refrigerant into the respective evaporator, in dependence on the output of the leak detector.

According to some but not necessarily all embodiments, there is provided: distributed climate-control systems and methods with distributed protection against refrigerant loss, in which the system includes a central condenser unit in combination with a distributed network of air handling units. Each of the air handlers includes an evaporator, in which condensed refrigerant can undergo a phase change while absorbing heat of vaporization, plus a heat exchanger (e.g. a coil) which permits the heat absorption of the evaporator to be coupled to a forced airflow. Preferably the evaporator includes a metering device to provide variable flow of refrigerant, and hence variable rates of heat transfer. The individual evaporators also include a sensor to detect ambient levels of the refrigerant, electrically operable cutoff valves which permit the evaporator to be isolated from both the liquid-phase and the gas-phase refrigerant flows. Local control logic is preferably connected to shut the cutoff valves whenever an ambient refrigerant concentration is found to exceed a tolerable level.

Modifications and Variations

As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. It is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

For one example, a mechanical and/or electronic latch can be incorporated with the cutoff valves, to provide additional safety in case of a gross malfunction in the high-level system controls.

For another example, the condenser unit which is connected to supply a group of evaporator units may itself be a heat recovery unit, i.e. one which can provide bidirectional condensation between two refrigerant lines which are both capable of carrying liquid OR vapor. By substituting bidirectional units for the condenser and for each evaporator, heat can be ejected from or injected into each of the rooms as desired (subject to overall thermal balancing). This is a much more complicated system than that described above, but it is worth noting that the inventive concepts can be adapted to systems of this type too.

In some sample embodiments, the condenser can be a heat pump, and the evaporators can be reversibly operable as heat pumps.

In some sample embodiments, one or more sensors can be detectors. As used herein, detectors are typically used to detect whether or not a nonzero concentration is present, while sensors are typically used to determine the particular concentration. For example, where a detector might only report that some contaminant is present, a sensor might report that the concentration of the contaminant is 3 ppm.

For another example, some of the disclosed inventions can be included in a retrofitting kit, which permits cutoff valves, a leak sensor, and simple local control logic to be plumbed into the refrigerant connections of each evaporator in an existing multi-evaporator system.

Note that, in some cases, an operator may be given the capability to remotely override the automatic shutdown. Depending on the safety constraints of the particular refrigerant and the particular situation, it may sometimes be necessary to allow the operator to force a leaky unit to continue operation as an emergency or temporizing measure.

For another example, it is not strictly necessarily that the disclosed systems and methods by used only with refrigerants in which the liquid and vapor stages are sharply distinct. For example, carbon dioxide can also be used as the refrigerant, in which case the refrigeration cycle may extend into a supercritical portion of the refrigerant's phase diagram.

For another example, in climates where outside exhausting is a useful part of climate control, that function too can be managed along with control of evaporation rate. Similarly, many other functions can optionally be added in to the basic architecture described above.

For another example, the valves can optionally be implemented as EEV or LEV (linear expansion valve). This can be done in several ways:

1) The EEV or LEV valves can simply replace the solenoid valves in the above configurations.

2) A manufacturer can include an LEV in the air handler, with programming so that the LEV operates as a shutoff valve when refrigerant is sensed in the ambient air. In this case, such an air handler can be installed, along with just one LEV/EEV/solenoid valve, to provide a quick installation which implements the inventive principals above.

3) A system can be implemented with combinations of EEV/LEV and solenoid valves.

None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none of these claims are intended to invoke paragraph six of 35 USC section 112 unless the exact words “means for” are followed by a participle.

The claims as filed are intended to be as comprehensive as possible, and NO subject matter is intentionally relinquished, dedicated, or abandoned.

Claims

1. A multi-location climate control system comprising: a condenser, which receives evaporated refrigerant from a refrigerant return connection, and condenses the evaporated refrigerant to a liquid flow of condensed refrigerant which is supplied to a refrigerant supply connection; andmultiple air handler units in multiple locations, individually including an evaporator which is connected, through respective cutoff valves, to be supplied with condensed refrigerant and to discharge evaporated refrigerant, anda heat exchanger which thermally couples the heat absorption of the evaporator to a forced airflow path, anda refrigerant leak sensor which detects escaped refrigerant in the ambient air, and which is local to that air handler unit; and wherein the cutoff valves are also local to the same air handler unit; andcontrol logic which, under at least some circumstances, automatically activates the cutoff valve to cut off flow of condensed refrigerant into the respective evaporator, in dependence on the output of the leak sensor.

2. The system of claim 1, wherein each of the cutoff valves is integrated with a respective solenoid.

3. The system of claim 1, wherein each of the cutoff valves is an EEV.

4. The system of claim 1, wherein each of the cutoff valves is an LEV.

5. The system of claim 1, wherein at least two respective cutoff valves are connected to each evaporator, and are local to the same air handler unit which contains that evaporator.

6. The system of claim 1, wherein at least some ones of the evaporators are reversibly operable as heat recovery units, and wherein the condenser is also a reversible heat recovery unit.

7. The system of claim 1, wherein the refrigerant is a halocarbon.

8. The system of claim 1, wherein the refrigerant is flammable.

9. The system of claim 1, wherein individual ones of the air handlers further comprise a respective metering device which regulates flow of refrigerant through the respective evaporator in that same air handler, and wherein the metering device is operable to cut off refrigerant flow on one side of the evaporator.

10. The system of claim 1, wherein the metering device is not one of the two cutoff valves.

11. The system of claim 1, wherein the minimum value for the ambient refrigerant concentration is zero, and the control logic automatically shuts the cutoff valves whenever a nonzero value of ambient refrigerant concentration is detected.

12. The system of claim 1, wherein the heat exchanger is a coil.

13. The system of claim 1, wherein the control logic is local to each location which contains a respective one of the evaporators.

14-26. (canceled)

27. An air handler module, comprising: an evaporator, having a metering device which regulates flow of refrigerant through the evaporator,first and second refrigerant connections which connect the evaporator to receive a liquid flow of condensed refrigerant from a refrigerant supply connection and to supply evaporated refrigerant to a refrigerant return connection,one or more cutoff valves within the air handler module which, when activated, cut off the flow of refrigerant through the evaporator, anda heat exchanger which thermally couples the heat absorption of the evaporator to a forced airflow path;a refrigerant leak sensor which detects escaped refrigerant in the ambient air; andcontrol logic which, when the refrigerant leak sensor detects an ambient refrigerant concentration above a minimum, automatically shuts the cutoff valves.

28. The module of claim 27, wherein the minimum value for the ambient refrigerant concentration is zero, and the control logic automatically shuts the cutoff valves whenever a nonzero value of ambient refrigerant concentration is detected.

29. The module of claim 27, wherein the heat exchanger is a coil.

30. The module of claim 27, wherein the control logic is local to each location which contains a respective one of the evaporators.

31. The module of claim 27, wherein each of the cutoff valves is integrated with a respective solenoid.

32. The module of claim 27, wherein each of the cutoff valves is an EEV.

33-37. (canceled)

38. The module of claim 27, further comprising a respective metering device within the air handler module which regulates flow of refrigerant through that evaporator, and wherein the metering device is operable to cut off refrigerant flow on one side of the evaporator.

39-71. (canceled)