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

AC electricity meters are probably the most common type of meters modeled. They are tagged as ac-elec-meter. Haystack supports a model designed to scale from very simple meters (just a power and energy point) up to a comprehensive point list for three-phase power quality meters.

Electricity meter points are described by combining tags from the lists given below. The tags in each set are mutually exclusive. (For example, a power point cannot be both active and reactive.)

The primary measured quantities in an electical system are:

• power: typically measured in "kW"
• energy: typically measured in "kWh"
• volt: typically measured in "V"
• current: typically measured in "A"
• freq: typically measured in "Hz"
• pf: power factor

AC power measurements are further qualified by:

• active: typically measured in "kW" (assumed as default)
• reactive: typically measured in "kVAR"
• apparent: typically measured in "kVA"

Voltage and current measurements are further qualified by:

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

Three phase electicrical measurements are qualified by:

• phase: A, B, C, AB, BC, CA, N
• avg: for current, voltage, and power factor (assumed as default)
• total: for power and energy (assumed as default)

Energy exchange with the utility is qualified by:

• import: energy imported from the grid
• export: energy exported to the grid
• net: net exchange (assumed as default)

Active, Reactive, Apparent

As the name suggests, the voltage and current in alternating current (AC) electricity networks alternate polarity many times per second. Because instantaneous power is the product of voltage times current, it constantly fluctuates in an AC network. Three quantities describe the time-averaged nature of fluctuating AC power:

• active power, also known as real power, represents real work: a net transfer of energy from source to load. Active power represents the "normal" definition of power: the rate of energy transfer per unit time. The standard unit of active power is the Watt, "W"; the default Haystack unit is "kW".
• reactive power, also known as imaginary power, represents energy that circulates in an AC system without performing any real work. Its standard unit is the volt-ampere reactive, "VAR"; the default Haystack unit is "kVAR".
• apparent power is the combination of active and reactive power and represents the overall magnitude of energy movement. Its standard unit is the volt-ampere, "VA"; the default Haystack unit is "kVA".

If a power point does not have an active, reactive, or apparent tag, active power is assumed as the default.

Import, Export, Net

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

These measurements register power or energy transfer only in their associated direction and always have positive values.

• For instantaneous power measurements, import and export are mutually exclusive. One will report a positive value and the other will report zero.
• For energy measurements tallied over time, 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 electric power and energy.

• Positive net quantities indicate power or energy consumed.
• Negative net quantities indicate power or energy produced.

If a power or energy point does not have an import, export, or net tag, it is assumed by default to be a net quantity.

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.