Thermostat with integrated submetering and control
A thermostat with voltage and current sensing capability is coupled directly to an HVAC unit and provides low latency failure detection and control using an on-board CPU. The thermostat can be configured to detect failure modes using current and voltage sensing and to make autonomous decisions to control the HVAC in response to such measurements.
1 . A thermostat for controlling HVAC equipment for a building, the thermostat comprising:
one or more control signal outputs configured to generate HVAC control signals, the HVAC control signals coupled to control inputs of a controller board of the HVAC equipment;
one or more temperature sensing inputs configured to sense temperature of a zone within the building controlled by the HVAC equipment;
a central processor configured to (1) control the HVAC equipment to keep the zone within the building within a temperature range based on set points stored within the thermostat and from data from the one or more temperature sensing inputs, and (2) compare a detected fan current to a baseline fan current, wherein a deviation of the detected fan current from the baseline fan current indicates one of: a tension of a fan belt is excessive or a degree to which a filter associated with an HVAC fan is clogged;
a first analog-to-digital converter that samples and converts a sensed voltage of the HVAC equipment into digital time series voltage data;
a second analog-to-digital converter that samples and converts a sensed current of the HVAC equipment into digital time series current data;
a digital signal processor that receives the digital time series voltage data and the digital time series current data and generates digital time series data representing real power (KW), reactive (KVAR) power, and total power (KVA) data; and a memory storing a first alarm rule, a second alarm rule, and the digital time series data,
wherein the first alarm rule causes the central processor to raise an alarm based on a level of percentage current imbalance of phases of an electrical supply powering the HVAC equipment, and the second alarm rule causes the central processor to raise an alarm when the KVA exceeds a predetermined threshold.
2 . The thermostat of claim 1 , wherein the central processor designates current data stored while a compressor is turned off as the detected fan current, and
wherein the baseline fan current is calculated by measurements taken at a time of installation.
3 . The thermostat of claim 1 , wherein the digital signal processor is configured to calculate and store, in the memory, time series data representing current drawn by the HVAC equipment, and the central processor is configured to designate current data stored while a compressor is turned off as the detected fan current.
4 . The thermostat of claim 1 , wherein the central processor calculates the percentage current imbalance of current of the phases of the electrical supply and applies the first alarm rule to the percentage current imbalance.
5 . The thermostat of claim 4 , wherein the digital signal processor calculates and stores, in the memory, time series data representing current drawn by the HVAC equipment, and the central processor designates current data stored while a compressor is turned off as the detected fan current.
6 . The thermostat of claim 4 , wherein the digital signal processor sums the real power (KW), the reactive power (KVAR), and the total power (KVA) data stored in the memory over a predetermined period of time and stores real power per hour (KWH), reactive power per hour (KVARH), and total power per hour (KVAH) in the memory.
7 . The thermostat of claim 4 , further comprising: a third alarm rule stored in the memory, wherein the third alarm rule causes the central processor to raise an alarm when the KVA exceeds a predetermined threshold when a compressor of the HVAC equipment is turned off.
8 . The thermostat of claim 4 , further comprising a third alarm rule stored in the memory, wherein the third alarm rule causes the central processor to raise an alarm when the KVA falls below a predetermined threshold when a compressor of the HVAC equipment is turned on.
9 . The thermostat of claim 4 , further comprising a third alarm rule stored in the memory, wherein the third alarm rule causes the central processor to raise an alarm when the KVA exceeds a predetermined threshold and issue commands to the HVAC equipment to shut down the HVAC equipment.
10 . The thermostat of claim 4 , further comprising a third alarm rule stored in the memory, wherein the third alarm rule causes the central processor to raise an alarm based on a level of percentage voltage imbalance of voltages of the phases of the electrical supply powering the HVAC equipment; wherein the central processor calculates the percentage voltage imbalance of the voltages of the phases of the electrical supply and applies the third alarm rule to the percentage voltage imbalance.
11 . The thermostat of claim 10 , wherein the first alarm rule and the third alarm rule send differing categories of alarm notifications based on the level of percentage voltage imbalance, and wherein the central processor operates to shut down the HVAC equipment if the percentage voltage imbalance exceeds a predetermined threshold.
12 . The thermostat of claim 4 , wherein the first alarm rule sends differing categories of alarm notifications based on the level of percentage current imbalance, and wherein the central processor operates to shut down the HVAC equipment if the percentage current imbalance exceeds a predetermined threshold.
13 . A thermostat for controlling HVAC equipment for a building, the thermostat comprising:
one or more control signal outputs configured to generate HVAC control signals, the HVAC control signals coupled to control inputs of a controller board of the HVAC equipment;
a central processor configured to compare a detected fan current to a baseline fan current, wherein a deviation of the detected fan current from the baseline fan current indicates one of: a tension of a fan belt is excessive or a degree to which a filter associated with an HVAC fan is clogged;
a first analog-to-digital converter that samples and converts a sensed voltage of the HVAC equipment into digital time series voltage data;
a second analog-to-digital converter that samples and converts a sensed current of the HVAC equipment into digital time series current data;
a digital signal processor that receives the digital time series voltage data and the digital time series current data and generates digital time series data representing real power (KW), reactive (KVAR) power, and total power (KVA) data; and
a memory storing a first alarm rule, a second alarm rule, and the digital time series data,
wherein the first alarm rule causes the central processor to raise an alarm based on a level of percentage current imbalance of phases of an electrical supply powering the HVAC equipment, and the second alarm rule causes the central processor to raise an alarm when the KVA falls below a predetermined threshold when a compressor of the HVAC equipment is turned on.
14 . The thermostat of claim 13 , further comprising:
the memory storing a third alarm rule that causes the central processor to raise an alarm based on a level of percentage voltage imbalance of the voltages of phases of an electrical supply powering the HVAC equipment, wherein the central processor is configured to calculate a percentage voltage imbalance of the voltages of the phases of the electrical supply and to apply the first alarm rule to the calculated percentage voltage imbalance.
15 . The thermostat of claim 13 , further comprising:
one or more temperature sensing inputs configured to sense temperature of a zone within the building controlled by the HVAC equipment wherein the central processor is configured to control the HVAC equipment to keep the zone within the building within a temperature range based on set points stored within the thermostat and from data from the one or more temperature sensing inputs.
16 . A thermostat for controlling HVAC equipment for a building, the thermostat comprising:
one or more control signal outputs configured to generate HVAC control signals, the HVAC control signals coupled to control inputs of a controller board of the HVAC equipment;
a central processor configured to compare a detected fan current to a baseline fan current, wherein a deviation of the detected fan current from the baseline fan current indicates one of: a tension of a fan belt is excessive, the fan belt is loose, the fan belt is broken, or a degree to which a filter associated with an HVAC fan is clogged;
a first analog-to-digital converter that samples and converts a sensed voltage of the HVAC equipment into digital time series voltage data;
a second analog-to-digital converter that samples and converts a sensed current of the HVAC equipment into digital time series current data;
a digital signal processor that receives the digital time series voltage data and the digital time series current data and generates digital time series data representing real power (KW), reactive (KVAR) power, and total power (KVA) data; and
a memory storing a first alarm rule, a second alarm rule, and the digital time series data,
wherein the first alarm rule causes the central processor to raise an alarm based on a level of percentage current imbalance of phases of an electrical supply powering the HVAC equipment,
wherein the second alarm rule causes the central processor to raise an alarm based on a level of percentage voltage imbalance of voltages of the phases of the electrical supply powering the HVAC equipment, and
wherein the central processor calculates the percentage voltage imbalance of the voltages of the phases of the electrical supply and applies the second alarm rule to the percentage voltage imbalance.
17 . The thermostat of claim 16 , wherein the deviation of the detected fan current from the baseline fan current indicates one of: the fan belt is loose, or the fan belt is broken, and the deviation associated with the indication that the fan belt is loose is less than the deviation associated with the indication that the fan belt is broken.
18 . The thermostat of claim 17 , further comprising an alarm signal output configured to be triggered based on detecting the deviation associated with the indication that the fan belt is broken, wherein the alarm signal output is further configured to enact one or more of steps of shutting down the HVAC, requesting maintenance, or requesting equipment.