Meters

Overview

The general problems addressed by the meter ontology are:

• modeling meters
• modeling submeters and their relationships
• modeling the flow of energy
• modeling equip and point loads on meters

Meters

Meters are modeled as equip entities with the meter tag along with the phenomenon measured. The following meter subtypes are defined:

• ac-elec-meter
• dc-elec-meter
• flow-meter

Flow meters should always be tagged with the substance they are metering. Common examples include:

• naturalGas meter
• domestic water meter
• chilled water meter
• steam meter

All meters must additionally define exactly one of these two tags:

• siteMeter: marker applied to the main site level meter
• submeterOf: Ref to parent meter

Electric Meters

Haystack models AC and DC electric meters using ac-elec-meter and dc-elec-meter. There is support to model these meters and their points for simple use cases (e.g., just a demand and energy point) and complex use cases (e.g., three-phase AC power quality meters). For a common application involving electric utility data see the provided example.

Electricity meter points are described by combining tags from the lists given below. The tags in each set are mutually exclusive. For example, a point cannot have two primary quantities, or have both the volt and power tags.

DC electrical measurements are described using a combination of the types of tags below:

1. elec marker tag
2. Primary quantity
3. dc marker tag
4. Direction (if applicable)

AC electrical measurements are described using a combination of the types of tags below:

1. elec marker tag
2. Primary quantity
3. ac marker tag
4. Characteristic of the primary quantity
5. Direction (if applicable)
6. Location

Note: The primary quantity freq does not use tags to distinguish a characteristic, direction, or location.

Primary Quantities for AC and DC measurements

Both ac-elec-meter and dc-elec-meter support measurements of the following electrical primary quantities:

• power: Average electric power over one or several alternating current (AC) cycles or instantaneous DC electric power. Measured in "kW", "kVAR", or "kVA" units for ac measurements depending on the characteristic active, reactive, or apparent, respectively. Measured in "kW" units for dc measurements.
• demand: Average electric power over a defined time interval (e.g., 5, 15, or 30 minutes). Measured in the same units that are used for power measurements.
• energy: Integral of electric power over time. Measured in "kWh", "kVARh", or "kVAh" units for ac measurements depending on the characteristic active, reactive, or apparent, respectively. Measured in "kWh" units for dc measurements.
• volt: Effective voltage. Root mean square (RMS) voltage is assumed for ac measurements. Measured in "V" units.
• current: Effective current. Root mean square (RMS) current is assumed for ac measurements. Measured in "A" units.

The following primary quantities apply only to AC electrical measurements:

• freq: The number of cycles per second in an alternating current (AC) sinusoidal waveform. Measured in "Hz" units.
• pf: The ratio of active power to apparent power. Measured with numbers in the range of -1.0 to 1.0 or 0.0 to 1.0 with a special unit called pf, which is effectively unitless and used for data visualization.

Some electric meters log interval-based data, demand or energy, using a monotonically increasing value in time. The difference of these values between two intervals is used to determine the actual value for an interval. Haystack distinguishes data logged this way using the hisTotalized tag on the point entity.

Directions for AC and DC measurements

Some electric meters track and report electricity imported from the electric grid separately from electricity exported to the electric grid. The tags import and export differentiate these phenomenons. More broadly, export indicates electricity flowing toward the grid (in the direction of the siteMeter), and import indicates electricity flowing toward the load.

These measurements register electricity transfer, involving the primary quantities current, power, demand, and energy only, in their associated direction and always have positive values.

• For instantaneous measurements (i.e., current and power), import and export are mutually exclusive. One will report a positive value and the other will report zero.
• For interval-based measurements (i.e., demand and energy), it is possible that both import and export may report a positive quantity for that interval, which means that some energy flowed in each direction during that interval.

The net tag indicates the difference between import and export:

net = import - export

Haystack uses the load convention for net electricity flow.

• Positive net quantities indicates electricity consumed.
• Negative net quantities indicates electricity produced.

Note: Direction related tags do not apply to angle, imbalance, and thd characteristics used to describe current and voltage.

Characteristics of AC Measurements

AC power, demand, and energy measurements are further qualified by characteristics:

• active: Describes real work being performed. Haystack's standard unit of active power and active demand is "kW". Haystack's standard unit of active energy is "kWh".
• reactive: Describes electricity circulated in an AC electrical system that does not result in real work being performed. Haystack's standard unit of reactive power and reactive demand is "kVAR". Haystack's standard unit of reactive energy is "kVARh".
• apparent: Describes the overall magnitude of energy movement. Haystack's standard unit of apparent power and apparent demand is "kVA". Haystack's standard unit of apparent energy is "kVAh".

AC voltage and current measurements are further qualified by the following characteristics:

• magnitude: magnitude (assumed as default)
• angle: phase angle, typically measured in "deg"
• imbalance: imbalance, measured in "%"
• thd: total harmonic distortion, measured in "%"

Similarly AC power factor measurements are further qualified using a pfScope choice:

• pfTrue: True power factor
• pfDisplacement: Displacement power factor
• pfDistortion: Distortion power factor

Note: The primary quantity freq does not have characteristic related tags.

Locations for AC Measurements

Generic tags are used to describe three types of ac electrical measurements that do not involve aggregation of multiple measurements:

• elecLine: for electrical line measurements "L1", "L2", and "L3"
• elecLineToLine: for electrical line-to-line measurements "L1-L2", "L2-L3", and "L3-L1"
• elecLineToNeutral: for electrical line-to-neutral measurements "L1-N", "L2-N", and "L3-N"

Non-aggregated ac electrical measurement locations are qualified by:

• lineVolt: elecLineToLine
• phaseVolt: elecLineToNeutral
• lineCurrent: elecLine
• phaseCurrent: elecLineToLine
• linePower: elecLineToLine
• phasePower: elecLine
• linePf: elecLineToLine
• phasePf: elecLine
• lineEnergy: elecLineToLine
• phaseEnergy: elecLine
• ground: for electrical current measurement of the electrical ground conductor
• neutral: for electrical current measurement of the electrical neutral conductor

Aggregated three-phase ac electrical measurement locations are qualified by:

• lineAvg: When applied to a point entity with the current tag, indicates the average of the values for the current primary quantity characteristic at all locations defined in elecLine. When applied to point entities with the volt, power, pf, or energy tags, indicates the average of the values for the primary quantity's characteristic at all locations defined in elecLineToLine.
• phaseAvg: When applied to a point entity with the volt tag, indicates the average of the values for the volt primary quantity characteristic at all locations defined in elecLineToNeutral. When applied to a point entity with the current tag, indicates the average of the values for the current primary quantity characteristic at all locations defined in elecLineToLine. When applied to point entities with the power, pf, or energy tags, indicates the average of the values for the primary quantity's characteristic at all locations defined in elecLine.
• total: Applies only to point entities with power, demand, or energy tags. Indicates the sum of the values for the primary quantity's characteristic at all locations defined in elecLine.

Aggregated split-phase ac electrical measurement locations are qualified by:

• lineAvg: When applied to a point entity with the current tag, indicates the average of the values for the current primary quantity characteristic at the "L1" and "L2" locations defined in elecLine.
• phaseAvg: When applied to a point entity with the volt tag, indicates the average of the values for the volt primary quantity characteristic at the "L1-N" and "L2-N" locations defined in elecLineToNeutral. When applied to point entities with the power, pf, or energy tags, indicates the average of the values for the primary quantity's characteristic at the "L1" and "L2" locations defined in elecLine.
• total: Applies only to point entities with power, demand, or energy tags. Indicates the sum of the values for the primary quantity's characteristic at the "L1" and "L2" locations defined in elecLine.

Only one tag indicating the location of a measurement should be applied to a point entity. The total tag takes precedence when applicable to allow for common queries between three-phase and split-phase AC electrical systems. For example, in a split-phase ac electrical system the total tag should be applied to a point entity instead of linePower to indicate the L1-L2 power measurement.

Note: The primary quantity freq does not have location related tags.

An Example Utility Application

Many electric utilities commonly use three AC electricity measurements for computing a monthly bill:

1. Peak active demand (kW)
2. Total energy consumption (kWh)
3. Peak apparent demand (kVA)

It might be desired to monitor these data points using a granular interval (e.g., 5 minutes) on a siteMeter to better understand or help validate these metrics used by the electric utility for billing. In some cases the electric utility might offer this interval data. Otherwise customer owned electric metering may be used to obtain it.

At a site with a 3-phase electric utility service, these data points would be modeled as follows:

1. For peak active demand - a point with the tags ac, total, active, import, and demand
2. For total energy consumption - a point with the tags ac, total, active, import, and energy
3. For peak apparent demand - a point with the tags ac, total, apparent, import, and demand

Also, all three of these data points should have a hisMode tag with a value of consumption applied to indicate they model interval based data.

Flow Meters and Thermal Meters

Flow meters measure flow rate and total volume of fluids. Thermal meters (sometimes called BTU meters) also use temperature sensors and can provide power and energy calculations. Points for flow meters include:

• flow: rate of volume flowing through the meter per unit time
• volume: total volume consumption of the meter
• power: energy consumed per unit time such as "BTU/h"
• energy: energy consumption such as "BTU"

Note that thermal meters should use the same power and energy tags as elec meters.

Flow meters must always be tagged with the fluid they are metering. For example a natural gas meter must be tagged with naturalGas. If a meter measures flow/volume then add the flow tag. If the meter measures power/energy then add the thermal tag.

Examples:

// Natural gas meter
id: @gasMeter
naturalGas
flow
meter
equip

// Steam thermal meter
id: @steamMeter
steam
thermal
flow
meter
equip

Energy Flow to Loads

We use the suite of <phenomenon>Ref tags to model the relationship of energy flows from the meters to their load. Commonly used relationship tags include:

• elecRef: model flow of electricity
• naturalGasRef: model flow of natural gas
• chilledWaterRef: model flow of chilled water for cooling
• hotWaterRef: model flow of hot water for heating
• steamRef: model flow of steam for heating

These tags are placed on the loads and reference their upstream meter. For example, a boiler would use the naturalGasRef to reference its upstream meter as follows:

id: @gasMeter
naturalGas
flow
meter
equip

id: @boiler
steam
boiler
equip
naturalGasRef: @gasMeter

Example Model

Let's illustrate a more complete example using a "tree" of meters and loads:

Main Elec Meter
 +- Luminaire (equip load)
 +- HVAC Elec Submeter
     +- RTU-1 (equip load)
         +- Fan (point load)
         +- DischargeTemp (not a load)
     +- RTU-2 (equip load)
         +- Fan (point load)
         +- DischargeTemp (not a load)

The entities and their tags would look like this:

id:@A, dis: "Main Elec Meter", ac, elec, meter, siteMeter, equip
       dis: "Main Elec Meter Demand", equipRef @A, elec, power, unit:"kW", sensor, point, ...
       dis: "Main Elec Meter Consumption", equipRef:@A, elec, energy, unit:"kWh", sensor, point, ...

id:@B, dis: "Luminaire", equip, elecRef:@A, luminaire

id:@C, dis: "HVAC Elec Submeter", ac, elec, meter, submeterOf:@A, equip
       dis: "HVAC Elec Submeter Demand", equipRef:@C, elec, power, unit:"kW", sensor, point, ...
       dis: "HVAC Elec Submeter Consumption", equipRef:@C, elec, energy, unit:"kWh", sensor, point, ...

id:@D, dis: "RTU-1", equip, elecRef:@C, ahu
       dis: "RTU-1 Fan", equipRef:@D, elecRef:@C, fan, cmd, point, ...
       dis: "RTU-1 DA Temp", equipRef:@D, discharge, air, temp, sensor, point, ...
id:@E, dis: "RTU-2", equip, elecRef:@C, ahu
       dis: "RTU-2 Fan", equipRef:@E, elecRef:@C, fan, cmd, point, ...
       dis: "RTU-2 DA Temp", equipRef:@E, discharge, air, temp, sensor, point, ...

In the example above we have a top-level main electrical meter with the id @A. Note it is tagged as ac-elec-meter to model an AC electric meter. It is also tagged as siteMeter to indicate its the main site-level meter. It has two associated points for power (kW) and energy (kWh).

Next, since we don't have a lighting submeter, the lighting load references the main meter directly via its elecRef tag.

After that, we have an HVAC submeter with the id @C. Note it is tagged as ac-elec-meter also. But it is not a siteMeter; instead it is associated as a submeter of the main meter using the submeterOf tag. You can model submeter trees of arbitrary depth (submeters of submeters). It also has two points for kW and kWh.

Lastly, we have three electrical equipment loads defined. The two RTUs are associated with HVAC submeter via elecRef which references the HVAC submeter via id. We also tag one or more points under the equipment that are meaningful for the load. Motors would often be tagged as loads since they draw energy, but sensors would typically not be considered loads.