ASHRAE RP-1455 Advanced Control Sequences for HVAC Systems

Phase I: Air Distribution and Terminal Systems

Mark Hydeman, PE mhydeman@taylor-engineering.com

Brent Eubanks, PE beubanks@taylor-engineering.com

Taylor Engineering

Alameda, CA

What is RP-1455?

• Standardized control sequences.

• Best-in-class performance.

• Suitable for most built-up systems with

an EMCS.

What is RP-1455?

• Not intended for package units.

• Not intended for least-first-cost systems

(e.g. sensor points).

• National applicability (e.g. Title 24 or

ASHRAE Standard 62 ventilation rules)

What is RP-1455?

• Phase 1 addresses airside only.

• Possible Phase 2 for plant sequences.

• Derived from two dozen different sets of

sequences.

• Also includes fault detection and alarm

suppression based on NIST work.

Why RP-1455?

• Sequences are critical to performance.

• Sequences are hard to do well.

• Sequences are often neglected until the

end of CDs.

• Most sequences do similar things, but

everyone’s are slightly different.

Why RP-1455?

• Computers are stupid, so sequences

must be unambiguous.

Poor sequences

Control contractor confusion

Control contractor guessing

“Creative” interpretations

Unexpected results

How will RP-1455 be used?

• English-language sequences will be

published as an ASHRAE Guideline,

available for anyone’s use.

• ALC has implemented them for plug-

and-play.

• Other vendors are encouraged.

What does RP-1455 Cover?

• Sequences for VAV AHU serving

multiple zones, with various options.

• Terminal units: • VAV, cooling-only or reheat

• Dual-duct, with inlet or discharge sensors

• Series fan-powered, constant speed fan

• Parallel fan-powered, constant or variable fan

• Single Zone VAV AHU to be added

later, after field testing.

Points Lists, with Options

Control Diagrams

English Language Pseudocode

Control Graphs (illustrating pseudocode)

Plug-and-Play Variables, for ALC

What is Unusual in RP-1455?

• Dual-Maximum VAV box control

• Automatic Fault Detection and

Diagnostics (AFDD) for AHUs (only)

• Hierarchical Alarm Suppression

• Demand-Based Setpoint Reset by Trim

& Respond.

Dual Max VAV Control

Dual Max VAV Control

• Saves energy by minimizing reheat

• Heating Max CFM is lower than Cooling

Max CFM

• In heating, increase temperature first, then

airflow.

• Required by code in California, but still

not very common.

What is Unusual in RP-1455?

• Dual-Maximum VAV box control

• Automatic Fault Detection and

Diagnostics (AFDD) for AHUs (only)

• Hierarchical Alarm Suppression

• Demand-Based Setpoint Reset by Trim

& Respond.

AFDD: Automatic Fault

Detection & Diagnostics

• Based on research by House, Bushby

and Schein at NIST in 2000-2006.

• Only for air handlers (APAR). VAV box

FDD (VPACC) requires too much tuning.

• Finds fault and diagnosis by evaluating

equations (mostly energy balance).

AFDD Fault Conditions

AFDD Equations Depend on AHU

Operating State

AFDD Equations Depend on AHU

Operating State

• Dual-Maximum VAV box control

• Automatic Fault Detection and

Diagnostics (AFDD) for AHUs (only)

• Hierarchical Alarm Suppression

• Demand-Based Setpoint Reset by Trim

& Respond.

What is Unusual in RP-1455?

Hierarchical Alarm Suppression

• Nuisance alarms are a huge problem for

operators.

• If upstream equipment (e.g. AHU) and

downstream equipment (e.g. VAV

boxes) are both in alarm, this

suppresses downstream alarms.

Hierarchical Alarm Suppression

• Must define upstream/downstream

relationships for air, coolth, and heat.

• Upstream equipment passes “OK” token

to downstream equipment when it’s

working right. Until getting “OK”,

downstream alarms are suppressed.

• Dual-Maximum VAV box control

• Automatic Fault Detection and

Diagnostics (AFDD) for AHUs (only)

• Hierarchical Alarm Suppression

• Demand-Based Setpoint Reset by

Trim & Respond.

What is Unusual in RP-1455?

Demand-Based Reset of Setpoints by

Trim & Respond

• Used to reset e.g. static pressure or

supply air temperature setpoints based

on zone demand.

• Zones issue “requests” based on zone

temperature, or damper/valve position.

• Uses minimum energy to satisfy zones.

Demand-Based Reset of Setpoints by

Trim & Respond

• Every timecycle (user defined) setpoint

is reduced (“trim”).

• Then setpoint is increased (“respond”)

proportional to number of zone requests.

• Controlled variable experiences slow,

shallow cycles as demand changes.

Trim & Respond is More Stable and

Easier to Tune than PID

PID control based on valve position

T&R control based on valve position

Other Advantages of

Trim & Respond

• Trim slowly and respond quickly. (PID

goes up or down at the same rate.)

• Ignore requests to nullify rogue zones.

• Increase importance of a critical zone.

• Generate extra requests if far off of

setpoint.

Q&A

Please submit questions via the Chat

box • Look for menu at the top center of your

screen (it will expand down when you move

your mouse over it) and select Chat box

• Send questions to “All Panelists”