Methods and apparatuses for detecting faults in HVAC systems based on load level patterns
Methods and systems are described for detecting a wide variety of fault conditions in a HVAC system based on analysis of current and historical energy consumption patterns, and on comparison with energy consumption patterns of other similarly situated RTUs. Energy consumption comparisons are preferably made in regard to a normalized load ratio or NLR or more preferably to a daily maximum normalized load ratio or MDNLR, which provide more robust and reliable bases for comparison of faulty and fault-free RTUs, and hence for generalized fault detection, than other previously known metrics or criteria.
1. A system for detecting one or more fault conditions in at least one HVAC unit in a plurality of HVAC units, the system comprising:
at least a first sensor configured to acquire first energy consumption data pertaining to the operation of the at least one HVAC unit;
at least a second sensor configured to acquire second energy consumption data pertaining to the operation of one or more similarly situated HVAC units; and
a processor operative to:
receive the first energy consumption data from the at least first sensor and the second energy consumption data from the at least second sensor;
determine, from the first energy consumption data, a first average energy consumption value corresponding to each of a plurality of time segments over particular predetermined time periods of the operation of the at least one HVAC unit;
determine first arithmetic ratios of the determined first average energy consumption values relative to a known or estimated first maximum average energy consumption value for the at least one HVAC unit to obtain first normalized load values corresponding to the each of the plurality of time segments in the predetermined time periods;
determine first maximum normalized load values among the normalized load values within each of the predetermined time periods;
determine, from the second energy consumption data, second average energy consumption values of the similarly situated HVAC units corresponding to each of the plurality of time segments over the predetermined time periods;
determine second arithmetic ratios of the determined second average energy consumption values relative to known or estimated second maximum average energy consumption values for the similarly situated HVAC units to obtain second normalized load values corresponding to each of the plurality of time segments in the predetermined time periods;
determine second maximum normalized load values among the second normalized load values within each of the predetermined time periods;
compare the first maximum normalized load values to the second maximum normalized load values by taking a fourth arithmetic ratio of the particular predetermined time period's first maximum normalized load value relative to the second maximum normalized load value for the same predetermined time period, wherein a compressor failure fault condition may be indicated when the fourth arithmetic ratio is outside a compressor fault threshold range; and
when the comparison of the first and the second maximum normalized load values meets one or more fault thresholds, automatically report the fault conditions in the at least one HVAC unit.
2. The system according to claim 1 , wherein the particular predetermined time periods are approximately 24 hours.
3. The system according to claim 1 , wherein the each of the plurality of time segments are approximately in a range between 10 and 60 minutes.
4. The system according to claim 1 , wherein the compressor fault threshold range is less than 0.75 or greater than 1.5.
5. The system according to claim 1 , wherein an economizer fault condition may be indicated when the fourth arithmetic ratio is above an economizer fault threshold value and the outside air temperature is either below a lower temperature value or above an upper temperature value, wherein the lower temperature value is less than the upper temperature value.