Contingent Power Device for Residential Heating Systems

Description

BACKGROUND OF THE INVENTION

The present invention relates to the field of supplying contingent electrical power to systems when the primary electrical power source has failed, and specifically improves over the prior art for contingent electrical power provided to residential heating systems.

Residential heating systems typically employ a chemical fuel such as natural gas, propane, or heating oil to heat air (in the case of furnaces) or water (in the case of boilers) to warm the residence. One or more thermostats arranged in zones throughout a house or apartment building provide temperature measurements to direct the heating system which zones are below a temperature threshold and require warming. These systems require a nominal amount of high voltage AC electrical power for fuel ignition, thermostat management, zone circulator or fan operation, and sometimes an electronic system controller.

A failure in the supply of electrical power to a residential heating system will preclude its normal operation of supplying heat. Such failures may be caused by rolling brown-outs and black-outs from excessive consumer demand, and interruptions in the electricity supply grid caused by accidents, attacks on infrastructure, storms, excessive heat, floods, fires, and other natural disasters. In the event of such failures, the residence will typically retain use of the chemical fuel, however it cannot sustain home heating because of the electrical failure. It has been rare to address this need with a contingent power supply because of their cost and complexity. Several approaches to contingent power supplies are well known; these include portable power generators, portable power for transportation, uninterruptible power supplies, and renewable energy sources.

Portable power generators or backup generators for residential use are commonly based on fossil fuels such as gasoline or propane because these fuels are readily available and safely storable. However, they require combustion to operate, thereby increasing the release of carbon into the atmosphere. This also makes it difficult to situate and operate a power generator because its exhaust gas is toxic and must be operated outside of the residence, or the exhaust vented outside of the residence. Setting up a power generator in the event of an emergency could be a difficult, uncomfortable, and manual process. They are noisy devices, making them undesirable for extended use and annoying to neighbors and wildlife. Portable power generators are intended to be a master electric power replacement for the whole house, so they are scaled to provide more power than is necessary to achieve shelter-in-place during emergency situations, increasing their cost more than is necessary. They are also wasteful with fuel because they need to operate even when the electrical load demand is low.

Some forms of transportation, such as boats and recreational vehicles (RVs), have various devices that require AC power and hook up to an external main AC power source when docked or parked. While not hooked up to an external AC power source, they typically generate electricity from their motor. This is often a low voltage DC power source which can then be scaled up to household AC power levels with a power inverter. To provide AC power without the motor, boats and RVs may include a battery that can be charged from the motor or from the external AC source. A device known as an inverter/charger can handle all the operations of charging the battery and generating AC power from the battery. While convenient for vehicles, these devices are incomplete for residential use because they do not provide power for, and management of, thermostats throughout the house. Nor do they manage the timing of power distribution to multiple power loads when operating under battery power to avoid exceeding the capacity of the inverter and battery.

Uninterruptible power supplies (UPS) are rechargeable battery systems intended to provide perfectly continuous power to systems when an electrical failure occurs and are typically deployed to situations such as computer systems to prevent power interruptions from resetting expensive equipment and causing data corruption or loss of productivity. While it is possible to use a UPS for the purpose of maintaining power to a residential heating system, they are more complex and costly than is necessary because of the requirement to provide a high-quality continuous power supply, and generally are not scaled to the power level and duration requirements for residential heating. They also operate under the principle that the system under load must be fully operated at all times, even if that draws down their battery far faster than would be required to achieve shelter-in-place for the home.

Renewable power sources, such as wind turbines or solar panel generators, do not provide electricity generation at all times because the natural sources-wind and sun-are not always available, and therefore must also have a contingent power supply or draw energy from the power grid when they are not producing electricity, making them unsuitable for the purpose of guaranteeing contingent power availability during an emergency power failure.

SUMMARY OF THE INVENTION

The present invention is a contingent power supply for residential heating systems that extends the length of time available to operate from its rechargeable battery to provide a highly reliable and long-lasting shelter-in-place and damage prevention capability when a residence is subjected to an electric power supply disruption. Incorporating a rechargeable battery as the contingent power source, the present invention may be permanently installed inside the residence, alongside the residential heating system, and engaged automatically and easily tested to ensure proper operation.

The present invention is connected to an AC Power Source (1) that is usually part of the regional electricity distribution network; is connected to a Primary Load (11) which represents the residential heating system and zero or mode Secondary Loads (12) which represent secondary uses of electricity such as water pumps or refrigeration units; and is connected to one or more Thermostats (14) to provide low-voltage power to the thermostats and, when they are intelligent thermostats, to gather environmental data such as temperature, read other settings, and set override temperature thresholds. The present invention may also be connected to Control Applications (15) which enable a user or information system to obtain status information, initiate a test, and to configure settings.

The present invention incorporates a System Battery (4), Battery Charger (3), and AC Power Inverter (6) in order to provide a contingent AC power supply during times of residential power disruption and to charge the System Battery when the AC Power Source is normally available; a DC Power Supply (2) which converts the AC Power Source to low voltage DC power for the Battery Charger and other components; a System Controller (7) which can determine when to operate various switches and settings and to interact with user applications or other information processing systems; a Controller Power Supply (8) which can accept low voltage DC power from either the System Battery or DC Power Supply and provide continuous regulated DC power to the System Controller; a Thermostat Power Supply (13) which can accept low voltage DC power from either the System Battery or DC Power Supply and provide continuous low voltage AC power to thermostats; and a Primary Transfer Switch (9) and zero or more Secondary Transfer Switches (10) which perform an electrical relay function that connects the Primary Load and Second Loads to the AC Power Source or to the AC Power Inverter depending on AC Power Source availability or testing mode.

The present invention makes improvements over prior art through active power management of one or more loads, enabling a trade-off between comfort and battery discharge period while preserving household conditions that are survivable for a shelter-in-place situation, providing automatic engagement to prevent home damage, providing testable power management to instill confidence, providing thermostat management to optimize performance, all resulting in a device that is lower in cost and complexity and more amenable to consumer or technician installation and maintenance than prior art.

The present invention operates to engage its contingent power supply in an automated fashion, which is important because of situations such as a power failure while outside air is sufficiently cold to freeze interior pipes, leading to a rupture and flooding. If this situation occurred while residents are absent, such as during a vacation, a manually operated contingent power supply would not prevent damage.

Residential heating systems include a transformer to convert the external AC power source to a convenient lower voltage, typically 24 VAC, to provide power to the thermostats, enabling sufficient electrical power for the thermostat to close a circulation value or other heating zone controller. Many thermostats are intelligent devices which can track room temperature and set heating thresholds according to a preset schedule or more adaptable sensor inputs such as presence at home or in a room. However, these intelligent thermostats would not be aware of power failures to the heating system or how best to respond. Therefore, the present invention incorporates a thermostat power supply for operation under external AC power loss, and a means to communicate with thermostats for reading zone temperatures and overriding temperature settings to extend battery life.

The present invention is testable at any time. Where prior art contingent power supplies are used for residential heating systems, it may be difficult, costly, or inconvenient to test their readiness to operate properly during an emergency, in which case the homeowner cannot have confidence that their contingent power supply will operate properly during an emergency. For the purposes of operating under emergency conditions and enabling shelter-in-place, the resident must maintain very high trust that their contingent power supply will not fail when most needed.

The present invention is novel and unique relative to prior art because of the combination of active management of multiple loads to optimize battery life and prevent operating the power inverter and battery beyond their capacity, continuous thermostat power and thermostat management, automatic engagement, and convenient testability.

BRIEF DESCRIPTION OF DRAWINGS

Drawing 1 is an schematic representation of the components of the present invention, and is organized into four functional sections: a Power Management Section (2, 6, 8, and 13), a Battery Management section (3, 4, and 5), a Load Management Section (9 and 10), and a System Controller (7). Double-thick arrowed lines represent AC power from a source to a sink; solid single arrowed lines represent DC power from a source to a sink; and dotted lines represent control signals or other information flows. The dashed-line components (1, 11, 12, 14, and 15) represent external connections to the present invention.

The Power Management Section incorporates a DC Power Supply (2), AC Power Inverter (6), Controller Power Supply (8), and Thermostat Power Supply (13). These components work together to provide AC power to the Primary and Secondary Transfer Switches depending on the power availability of the AC Power Source, to provide low voltage DC power to the Battery Charger, to provide regulated DC power to the System Controller, and to provide low voltage AC power to Thermostats.

The Battery Management Section incorporates a Battery Charger (3), a Battery Manager (5), and a System Battery (4). When the AC Power Source is available, the Battery Management Section works together in a battery charging mode to recharge the System Battery and to maintain its charge level. When the AC Power Source is not available or when the present invention is performing a test, the Battery Management Section works together in a contingent power mode to provide DC power to the AC Inverter, Controller Power Supply, and Thermostat Power Supply. The Battery Manager must perform this mode switching function and to provide continuous measurement and reporting of the charge level of the System Battery.

The Load Management Section incorporates the Primary Transfer Switch (9) and zero or more Secondary Transfer Switches (10). Each Transfer Switch acts like an electrical relay, accepting a control signal from the System Controller which selects either the AC Power Source or the AC Power Inverter as input, and connecting the selected input to its load.

The System Controller (7) makes decisions about the conditions and timing of switching the Battery Manager between its battery charging mode and contingent power mode, the conditions and timing of switching the Transfer Switches, and may connect to a variety of Control Applications (15) such as a control panel, mobile app, cloud API, desktop app, or remote website.

DETAILED DESCRIPTION OF THE INVENTION

The present invention incorporates a Power Management Section (2, 6, 8, and 13), a Battery Management section (3, 4, and 5), a Load Management Section (9 and 10), and a System Controller (7) which work together to maintain a fully charged System Battery when operating under normal household power conditions, and to produce contingent AC power from the System Battery under power failure conditions or under a system test.

The System Battery (4) is a rechargeable battery or set of rechargeable batteries wired to act as a single battery. There are many kinds of rechargeable batteries having different chemistries and various material alternatives to construction, and exhibiting different operating characteristics such as rated voltage, voltage drop as a function of discharge or battery age, total charge capacity, degradation of charge capacity over time or number of charge cycles or operating temperature, optimized recharging protocol, potential for overheating or causing fire, environmental damage in the manufacture and disposal processes, and cost. Any of these rechargeable batteries, including future rechargeable batteries that are not presently known or in production, may be suitable for the present invention recognizing that certain tradeoffs may be acceptable for various situations.

The Battery Manager (5) incorporates an electrical switch that selects connection of the System Battery either to the Battery Charger or to the AC Power Inverter, Controller Power Supply, and the Thermostat Power Supply. It is possible for the Battery Manager to switch in an automatic fashion, for example engaging contingent power mode whenever the System Battery is fully charged, however for some implementations it would be preferable for the System Controller to be able to control the state of this switch in order to enter a testing mode or other performance optimizations. The Battery Manager also incorporates a battery charge measurement component which can report the level of battery charge to the System Controller. There are multiple approaches to measuring the charge level of a rechargeable battery with some tradeoff in benefits, cost, and performance, and any of these may be employed in the present invention depending on those criteria.

The Battery Charger (3) should be matched to the charging protocol of the System Battery. Electronic battery charging components are well known and an implementation of the Battery Charger could consist of a single module that performs the complete battery charging protocol, or multiple components that achieve the same. In some implementations the Battery Manager and Battery Charger may be an integrated component rather than two separate components.

The DC Power Supply (2) accepts the AC Power Source, typically 110 VAC or 220 VAC depending on the region of the world, and converts that to one or more DC lower voltage supplies as needed by the Battery Charger, Controller Power Supply, and Thermostat Power Supply. The AC Power Source can fail at any time; therefore, the DC Power Supply may fail to provide the lower voltage DC power to the other components. The major functions required are stepping down the high voltage AC Power Source to a lower level, AC-to-DC conversion, and regulating the DC level output. Several technologies for implementing the DC Power Supply are well known, such as a linear mode power supply consisting of a wired transformer coupled with diodes and linear regulators, or switching mode power supply which use some combination of inductors, capacitors, diodes, or electronic switches to create a regulated DC power level with a much greater efficiency (lower heat losses).

The Controller Power Supply (8) accepts the larger DC voltage output from the DC Power Supply and provides a regulated DC voltage into the System Controller, and can use the output of the Battery Manager as an alternative DC power input. The Controller Power Supply should be able to maintain a constant DC voltage level into the System Controller even if both DC Power Supply and Battery Manager outputs are unavailable for brief periods of transition, and can achieve this with a charge storage device such as a capacitor or battery, such that it effectively functions as an uninterruptible power supply to the System Controller. The Controller Power Supply monitors the voltage levels of the DC Power Supply and the Battery Manager's power output and battery level measurement, and reports these to the System Controller. An implementation of the Controller Power Supply could be fully integrated within the System Controller, or integrated within the DC Power Supply, or as a separate component.

The Thermostat Power Supply (13) is intended to replace the 24 VAC transformer that most residential heating systems provide to power Thermostats (14) and zone control elements. The Thermostat Power Supply accepts the larger DC voltage output from the DC Power Supply or can use the output of the Battery Manager as an alternative DC power input, such that it effectively functions as an uninterruptible power supply to the Thermostats. The technology for converting a DC voltage to an AC voltage at power supply levels is known as a power inverter, and many electronic implementations are well known. The Thermostat Power Supply should be able to maintain a constant AC voltage level into the Thermostats even if both DC Power Supply and Battery Manager outputs are unavailable for brief periods of transition, and can achieve this with a charge storage device such as a capacitor or battery. An implementation of the Thermostat Power Supply could be fully integrated within the DC Power Supply, or as a separate component.

The AC Power Inverter (6) accepts the DC voltage output from the Battery Manager and converts that to household power levels, typically 110 VAC or 220 VAC depending on region, and which are available to the Primary and Secondary Power Switches. AC Power Inverters are well known technologies and are widely available as fully integrated components or as subcomponents that can be integrated. The key operating characteristics of the AC Power Inverter are the DC input voltage, the AC output voltage, the nominal output current capacity, and temporary peak load current capacity. The key operating characteristics are used to select the implementation of the AC Power Inverter, and are dependent on the AC Power Source voltage level, the nominal and peak current drawn by the Primary Load and Secondary Loads, and the voltage and peak current capacity output of the Battery Manager.

The Primary Transfer Switch (9) and Secondary Transfer Switch (10) provide AC voltage outputs to the Primary Load (11) and Secondary Loads (12), respectively. The Transfer Switches will make a selection between the AC Power Source and the AC Power Inverter based on signals provided by the System Controller. There are typically two technologies used to implement Transfer Switches; Electromechanical Relays use metal switching contacts controlled by an electromagnet, and Solid-State Relays use transistors and electronic components to achieve the same result. Electromechanical Relays may make a slight sound while switching, and may have lower reliability over a wide range of environmental conditions or age. Solid State Relays will have larger current losses due to heat conversion, faster switching times, higher cost, and higher reliability over time and environmental conditions. One implementation of Transfer Switches is a Single-Pole Double-Throw relay where only the hot (black) AC Power Source line is switched and the neutral (white) AC Power Source line is directly connected to the AC Power Inverter, Primary Load, and Secondary Load; another implementation is a Double-Pole Double-Throw relay where both hot (black) and neutral (white) AC Power Source lines are switched to the Loads. The decision between these will be based on safety factors relating to system grounding, the design and capabilities of the AC Power Inverter, and cost. Either Electromechanical or Solid-State Relay technology may be used to implement Transfer Switches, depending on performance and cost requirements. An implementation of Transfer Switches may also include voltage level or current level measurement sensors, to provide the System Controller with more detailed operating information about the Loads and other high voltage AC power components.

The System Controller (7) takes signal inputs, including power supply status from the DC Power Supply and Battery Manager, battery charging level from the Battery Manager, information from Thermostats, and configuration settings from the Control Applications (15), and makes decisions about switching the Battery Manager and the Transfer Switches, and possibly sending control signals or configuration changes to the Thermostats. A typical implementation of a System Controller is a microcontroller, a CPU with input-output interface capabilities and integrated features like display drivers, serial communications ports, and radio communication capability including BlueTooth, WiFi, or cellular. Some microcontrollers may have a small operating capability at lower cost, an open-source example being Arduino, or may have much larger computing capabilities with a full operating system, an open-source example being Raspberry Pi. Any of these microcontrollers may be used to implement the System Controller with various trade-offs in capabilities, performance, integration convenience, and cost.

The Primary Load (11) typically refers to a residential heating system such as a boiler or furnace, where the AC Power Source is the household AC power as normally would be applied to the Primary Load, which is typically a dedicated AC power circuit with circuit breaker.

The present invention may be improved to support Secondary Loads (12) which are of secondary importance to the residential heating system and may be important for preventing damage or maintaining comfort. Examples of secondary loads include a basement sump pump, water well pump, electric water heater, refrigeration units, or freezer. Each secondary load would connect to a Secondary Transfer Switch. The System Controller may make decisions about allowing different Secondary Loads to receive power at various times. For example, enabling multiple Primary and Secondary Loads simultaneously would require a larger System Battery and AC Power Inverter, and may reduce the contingent power mode duration. A strategy that optimizes for the longest possible contingent power mode duration would only allow a single load to be permitted at one time. An improvement to the present invention incorporates current measurement devices on the input or output of each Transfer Switch such that optimized decisions about enabling Primary and Secondary Loads can be made based on actual current draw from the Loads.

In an implementation of the present invention, the System Controller gathers status and performance information and maintains a history of that information which can be used for analysis or improving future performance.

In an implementation of the present invention, the System Controller executes a test mode, where the AC Power Source is available as would be the normal condition, with the Battery Manager switched to contingent power mode and the Transfer Switches selecting the AC Power Inverter as inputs. The System Controller then monitors various system functions such as battery charge level over time, and terminates the test with a return to normal operation.

Under typical situations, a heating system includes one or more heating zones, each with a thermostat having its own thermometer and a temperature set-point that is adjusted to maintain a comfortable temperature in that zone, with corresponding heat distribution zones such as air ducts or hot water pipes. In a basic method of operation under contingent power mode, the System Controller may extend the duration of operation under the System Battery by switching the Primary Transfer Switch away from the AC Power Inverter, defining a duty cycle that favors reducing power to the loads. The house temperature is unlikely to rise to the thermostat set-point under these conditions, which is a tradeoff that can be adjusted. Blocking power to the Primary Load for longer periods will result in a colder zone temperature than the thermostat set-point but longer contingent power mode duration, which may be preferable to complete failure when operating under shelter-in-place emergency situations.

The System Controller may make more sensible decisions about the duty cycle controlling the Primary Transfer Switch depending on information inputs. In one improvement, the System Controller can monitor the current measurement signal for the Primary Load over time, and use this information to make assumptions about the recent duty cycle required to maintain the temperature set-point. In another improvement, the System Controller can track these measurements as a function of the time of day, because the temperature set-point is typically adjusted for different night-time and daytime levels. In another improvement, the System Controller can accept an outside temperature reading that may come from a local thermometer or from an Internet weather information source, and use that information to calculate how the Primary Load duty cycle can be adjusted based on the present outside temperature, or accounting for predictions of future temperatures.

In another improvement, the System Controller can access the temperature measurement, set-point, and possibly other information from the Thermostats, to make more optimized decisions about the Primary Load duty cycle. In one such implementation, a Thermostat may support a radio communication means such as BlueTooth which the System Controller can use to access this information directly from the Thermostat. In another implementation, the thermostat may have a wired or wireless connection to the Internet, enabling it to access Thermostat information through a Thermostat Application Programming Interface (API).

Nothing in this description of the present invention should preclude its use and enjoyment of its benefits when applied to other electricity powered systems such as air conditioners, heat pumps, and refrigeration units. In these cases, the capacity of the System Battery, Battery Charger, and Power Inverter may need to be increased over the amount required to operate a contingent power supply for chemical fuel-based heating systems, and other operating principles and advantages as described herein would still be relevant.