PointPatterns

Overview

The ph.points lib defines standardized Xeto specs for the points commonly found on equipment. This chapter describes the patterns these specs follow so that points are modeled consistently across equipment and can be queried by their Xeto types.

Binary Run and Enable

The on/off state of equipment is modeled with RunPoint:

• RunCmd: commands equipment to run or stop running
• RunSensor: senses the actual on/off state of equipment

EnablePoint models a secondary interlock used in conjunction with a run point:

• EnableCmd: command that permits or prohibits equipment from running

Permission from an enable command may be required for a run command to take effect.

Binary Open and Close

The open/close state of two-position equipment, such as an actuator (e.g., for a damper or valve), a door, or a circuit breaker, is modeled with OpenPoint:

• OpenCmd: commands equipment to open or close
• OpenSensor: senses the actual open/close state of equipment

These generic points may be specialized for particular equipment, such as ActuatorOpenCmd and ActuatorOpenSensor for an actuator. Use the open/close pattern for two-position equipment, and the modulating pattern below for equipment whose position varies continuously from 0% to 100%.

Controlling Equipment Capacity

Equipment with more than simple on/off control varies its capacity either in discrete stages or by continuous modulation. The two may be combined when the capacity of individual stages is itself modulated.

Staged Capacity

Equipment with multiple discrete levels of capacity numbers its stages sequentially as integers 1, 2, 3, etc. using the stage tag. Each stage is commanded and sensed with its own run points, with the stage tag identifying the stage. For example, a two-stage heating coil is commanded with two HeatRunCmd points, one with stage 1 and one with stage 2. Each stage's actual on/off state is proven with a matching HeatRunSensor.

Modulating Capacity

ModulatingPoint models the variable capacity of equipment from 0% to 100%, such as valve position or motor speed:

• ModulatingCmd: commands equipment to operate at a percentage of capacity
• ModulatingSensor: senses the capacity at which equipment is operating

Command and Sensor Pairs

A command models the desired state of equipment, while a sensor models its actual state. When equipment provides feedback, both should be modeled as separate points. For example a fan is commanded on/off with FanRunCmd and its actual status is proven with FanRunSensor. Likewise a damper is commanded to a position with DamperModulatingCmd and its actual position is sensed with DamperModulatingSensor. Comparing the pair detects failures such as a fan commanded on that is not running.

Setpoints

A setpoint models a value that guides control, either as a limit that constrains a value or as the target that control drives a value toward. The same value may combine these roles, such as a VAV whose airflow has a target setpoint along with minimum and maximum airflow setpoints.

Heating and Cooling

The run, enable, and modulating patterns are specialized for heating and cooling equipment with the following specs:

• HeatRunCmd, CoolRunCmd: command heating or cooling equipment to run
• HeatRunSensor, CoolRunSensor: sense the on/off state of heating or cooling equipment
• HeatEnableCmd, CoolEnableCmd: permit or prohibit heating or cooling equipment from running
• HeatModulatingCmd, CoolModulatingCmd: modulate heating or cooling capacity
• HeatModulatingSensor, CoolModulatingSensor: sense heating or cooling capacity

Duplicate Points

An entity may have several points that would otherwise be modeled identically. Such points should be differentiated with one of the following mechanisms:

• a slot value on the same spec, when points form a numbered or enumerated series, such as the stage of a run command
• a more specific spec, when points differ in scope, such as ZoneAirTempOccHeatingSp versus ZoneAirTempUnoccHeatingSp
• a dis tag with a human display name, when points have no modeled distinction, such as redundant sensors of the same quantity

Examples

Basic Equip Operation

This example combines the patterns above: an enable command interlocked with a run command per the run and enable pattern, and the run command paired with a run sensor to prove the actual on/off state of the equipment. The generic point specs are used directly for any equip with simple on/off control. Here are the points for basic equip operation:

// equip enable command
id: @atlanta.equip.enable.cmd
enable
cmd
point
siteRef: @atlanta
equipRef: @equip
kind: "Bool"
tz: "New_York"
spec: @ph.points::EnableCmd

// equip run command
id: @atlanta.equip.run.cmd
run
cmd
point
siteRef: @atlanta
equipRef: @equip
kind: "Bool"
tz: "New_York"
spec: @ph.points::RunCmd

// equip run sensor
id: @atlanta.equip.run.sensor
run
sensor
point
siteRef: @atlanta
equipRef: @equip
kind: "Bool"
tz: "New_York"
spec: @ph.points::RunSensor

Staged Heating

This example combines the patterns above: the generic run and enable points specialized for heating, with each stage differentiated by its stage tag per the duplicate points guidance. The same point specs apply to any equip with staged heating, such as an AHU or a hot water boiler. Here are the points for two heating stages:

// stage 1 heat enable command
id: @atlanta.boiler.stage1.heat.enable.cmd
heat
enable
cmd
stage: 1
point
siteRef: @atlanta
equipRef: @boiler
kind: "Bool"
tz: "New_York"
spec: @ph.points::HeatEnableCmd

// stage 1 heat run command
id: @atlanta.boiler.stage1.heat.run.cmd
heat
run
cmd
stage: 1
point
siteRef: @atlanta
equipRef: @boiler
kind: "Bool"
tz: "New_York"
spec: @ph.points::HeatRunCmd

// stage 2 heat enable command
id: @atlanta.boiler.stage2.heat.enable.cmd
heat
enable
cmd
stage: 2
point
siteRef: @atlanta
equipRef: @boiler
kind: "Bool"
tz: "New_York"
spec: @ph.points::HeatEnableCmd

// stage 2 heat run command
id: @atlanta.boiler.stage2.heat.run.cmd
heat
run
cmd
stage: 2
point
siteRef: @atlanta
equipRef: @boiler
kind: "Bool"
tz: "New_York"
spec: @ph.points::HeatRunCmd

Modulated Cooling

This example combines the patterns above: the generic enable and modulating points specialized for cooling, and the modulating command paired with a modulating sensor to prove the capacity at which equipment is operating. Unlike staged heating, capacity varies continuously from 0% to 100%, so a single set of points models it without a stage tag. The same point specs apply to any equip with modulated cooling, such as an AHU or a chiller. Here are the points for modulated cooling:

// cool enable command
id: @atlanta.ahu.cool.enable.cmd
cool
enable
cmd
point
siteRef: @atlanta
equipRef: @ahu
kind: "Bool"
tz: "New_York"
spec: @ph.points::CoolEnableCmd

// cool modulating command
id: @atlanta.ahu.cool.modulating.cmd
cool
modulating
cmd
point
siteRef: @atlanta
equipRef: @ahu
kind: "Number"
unit: "%"
tz: "New_York"
spec: @ph.points::CoolModulatingCmd

// cool modulating sensor
id: @atlanta.ahu.cool.modulating.sensor
cool
modulating
sensor
point
siteRef: @atlanta
equipRef: @ahu
kind: "Number"
unit: "%"
tz: "New_York"
spec: @ph.points::CoolModulatingSensor

Equipment Points

These patterns are extended to specific equipment with specialized point specs, for example MotorRunCmd, FanRunSensor, and FanSpeedModulatingCmd. See the equipment chapters for the standardized points of each vertical:

• Motors: fans, pumps, and other motors
• AHUs: air handling units
• VAVs: variable air volume terminal units
• Zones: zone occupancy, hvac, air quality, and lighting