M907 - BUILDING 1 PRESSURIZATION CONTROL SEQUENCES - AHU-21.pdf

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Project Number

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Project Title

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Approved: Project Manager

Cincinnati V.A Medical Center

U.S. Department of Veterans Affairs

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ARCHITECT/ENGINEER OF RECORDCONSULTANT

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CONSTRUCTION

DOCUMENTS

FULLY SPRINKLEREDKEVIN HENDERSONPROJECT NO. STATE COA FIRM NO.

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BUILDING 1 PRESSURIZATION

CONTROL SEQUENCES - AHU-21

10/23/25 GSE WJS

REMEDIATE TEMPERATURE

CONTROLS

M907

539-21-108

CINCINNATI, OHIO

2020-05099 01528

SCALE: NONE

AHU-21 CONTROLS - EXISTING CONTROL DIAGRAM

EXISTING SEQUENCES

AHU-21 SEQUENCE OF OPERATIONS

1. GENERAL

A. UNIT IS NORMALLY STARTED AND STOPPED BY THE DCP OR REMOTELY AT THE ECC. H-

O-A SWITCH WILL BE KEPT IN THE "AUTO" POSITION. "HAND" AND "OFF" POSITIONS WILL BE

USED ONLY FOR MAINTENANCE.

B. WHEN THE UNIT IS "OFF", FOR ANY REASON, OUTSIDE AIR DAMPERS D-1 & D-5, RELIEF

AIR DAMPERS D-3 & D-4, RETURN AIR SMOKE DAMPER SD-1 AND SUPPLY AIR SMOKE

DAMPERS SD-2, SD-3, SD-4 AND SD-5 WILL BE FULLY CLOSED, RETURN AIR DAMPER D-2

WILL BE FULLY OPEN, AND SUPPLY AND RETURN FANS WILL BE OFF.

C. WHEN THE UNIT IS "ON", ISOLATION SMOKE DAMPERS SD-1, SD-2, SD-3, SD-4 AND SD-5

WILL OPEN, AND ONCE PROVED OPEN, SUPPLY AND RETURN FANS WILL START, AND D-1,

D-2, D-3, D-4 AND D-5 WILL MODULATE IN ACCORDANCE WITH THE FOLLOWING SEQUENCE.

2. TEMPERATURE CONTROL

A. SUPPLY AIR TEMPERATURE, SENSED BY T-7 PRIMARY/T-11 SECONDARY (DEPENDING

ON WHICH SUPPLY FAN IS OPERATING), WILL BE MAINTAINED AT SETPOINT OF 55 DEG. F.

(SEE DISCHARGE AIR RESET SEQUENCE BELOW) VIA DCP BY MODULATING COOLING COIL

VALVE V-1 OR ECONOMIZER DAMPERS D-1, D-2, D-3, D-4 AND D-5 OR PREHEAT COIL VALVE

V-2, IN SEQUENCE. SEPARATE CONTROL LOOPS WILL BE UTILIZED FOR EACH

ECONOMIZER COOLING, MECHANICAL COOLING, AND HEATING FUNCTION.

B. REHEAT COILS 1-RH21A AND 1-RH21B - VALVES V-5 AND V-6 WILL MODULATE TO

MAINTAIN DISCHARGE AIR TEMPERATURE SET POINTS BASED ON A RESET SCHEDULE OF

95 DEG. DISCHARGE AIR TEMPERATURE SENSED BY T-1 AND T-8 AT 0 DEG. OUTSIDE AIR

TEMPERATURE AND 80 DEG DISCHARGE AIR TEMPERATURE AT 60 DEG OUTSIDE AIR

TEMPERATURE.

3. ENTHALPY ECONOMIZER CONTROL

A. OUTSIDE AIR TEMPERATURE AND HUMIDITY, AND RETURN AIR TEMPERATURE AND

HUMIDITY WILL BE MEASURED, AND THE ENTHALPY OF EACH DETERMINED. IF THE

ENTHALPY OF THE OUTSIDE AIR IS LESS THAN THE ENTHALPY OF THE RETURN AIR, THE

ECONOMIZER WILL BE ENABLED. WHEN THE OUTSIDE AIR ENTHALPY IS HIGHER THAN THE

RETURN AIR ENTHALPY AND MECHANICAL COOLING IS AVAILABLE, THE ECONOMIZER WILL

BE DISABLED.

4. ECONOMIZER CYCLE

A. DURING THE "ECONOMIZER" CYCLE, THE AMOUNT OF OUTSIDE AIR AND RELIEF AIR

WILL BE INCREASED AS REQUIRED TO MAINTAIN THE UNIT DISCHARGE AIR TEMPERATURE

SETPOINT, AS SENSED BY T-7 OR T-11. PROVIDE A MIXED AIR SENSOR AND LOW LIMIT

CONTROL (T-5) SET AT 50 DEGREES F. TO PREVENT OVER-OPENING OF THE ECONOMIZER

OUTSIDE AIR DAMPERS. ALL CONTROL SETPOINTS WILL BE FULLY ADJUSTABLE TO MEET

JOB CONDITIONS.

5. MINIMUM OUTSIDE AIR

A. MINIMUM OUTSIDE AIR WILL BE PROVIDED PER 5.2 AND 5.3 BELOW BY OPENING AND

MODULATING MINIMUM OUTSIDE AIR DAMPERS D-1 TO MAINTAIN THE MINIMUM OUTSIDE

AIR SET POINT (SEE AHU SCHEDULE) AS MEASURED BY OUTSIDE AIR FLOW SIGNAL VPS-4.

THE RETURN AIR DAMPERS D-2 WILL OPEN FULL AND RELIEF AIR DAMPERS D-3 AND D-4

WILL REMAIN CLOSED. THIS CONDITION WILL BE MAINTAINED EXCEPT DURING THE

"ECONOMIZER" CYCLE.

B. WHEN 1-SF21A OPERATES, MINIMUM OUTSIDE AIR SET POINT 1 WILL BE MAINTAINED.

C. WHEN 1-SF21B OPERATES, DAMPERS WILL MODULATE AS DETERMINED BY A SPACE

MOUNTED CO2 SENSOR. THE CONTROL WILL BE LINEAR WITH AIR FLOW AT SET POINT 1

AT 800 PPM AND AT SET POINT 2 AT 1000 PPM.

6. AIR FLOW CONTROL

A. 1 1-SF21A - THE SUPPLY AIR FLOW WILL BE CONTROLLED BY THE DCP MODULATING

THE SUPPLY FAN VARIABLE SPEED MOTOR CONTROLLER (VSMC) TO MAINTIAN 1.0" OF

DUCT STATIC PRESSURE (FIELD ADJUSTABLE), SENSED BY SPS-1, SPS-2, SPS-6 AND SPS-7

LOCATED 2/3 DISTANCE DOWN THE SUPPLY DUCTS.

B. 1-SF21B - THE SUPPLY AIR FLOW WILL BE CONTROLLED BY THE DCP MODULATING THE

SUPPLY FAN VARIABLE SPEED MOTOR CONTROLLER (VSMC) TO MAINTAIN SPACE

TEMPERATURE IN THE AUDITORIUM AS SENSED BY T-10. IF THE SPACE FALLS OR RISES

MORE THAN 2 DEGREES F. FROM THE SETPOINT, THE FAN SPEED WILL BE INCREASED

SLOWLY UNTIL THE SPACE IS WITHIN 1.5 DEGREES F. OF SETPOINT. WHEN THE OUTSIDE

AIR TEMPERATURE IS BELOW 60 DEGREES F., THE FAN WILL REMAIN AT 50 PERCENT AIR

FLOW.

C. THE DCP, USING TOTAL SUPPLY AIR, OUTSIDE AIR AND RETURN AIR FLOW SIGNALS

(VPS-1, VPS-2, VPS-3, VPS-4 AND VPS-5), WILL RESET THE RETURN AIR FAN VARIABLE

SPEED MOTOR CONTROLLER (VSMC) TO MAINTAIN A CONSTANT AIR FLOW DIFFERENCE

BETWEEN THE SUPPLY AIR AND THE RETURN AIR EQUAL TO MINIMUM OUTSIDE AIR (SEE 5

ABOVE).

D. VARIABLE SPEED MOTOR CONTROLLERS WILL RESPOND TO START/STOP COMMANDS

AND ALL SAFETIES (FREEZE, SMOKE, ETC.) WHETHER IN THE AUTOMATIC OR BYPASS

MODES.

E. THE DCP, USING HIGH PRESSURE SENSORS SPS-3 AND SPS-5 LOCATED AT THE SUPPLY

FAN DISCHARGES, WILL PREVENT THE SUPPLY FANS FROM DEVELOPING OVER 3 INCHES

AND 4 INCHES RESPECTIVELY, OF POSITIVE STATIC PRESSURE (FIELD ADJUSTABLE). IF

STATIC PRESSURE AT SPS-3 OR SPS-5 EXCEEDS THEIR ASSOCIATED PRESSURE,

THE SUPPLY AND RETURN FANS WILL STOP. 6.6 THE DCP, USING HIGH PRESSURE SENSOR

SPS-4 LOCATED AT THE RETURN FAN INLET, WILL PREVENT THE RETURN FAN FROM

DEVELOPING OVER 3 INCHES OF NEGATIVE STATIC PRESSURE (FIELD ADJUSTABLE). IF

STATIC PRESSURE AT SPS-4 EXCEEDS 3 INCHES OF NEGATIVE PRESSURE, THE SUPPLY

AND RETURN FANS WILL STOP.

7. HUMIDITY CONTROL

A. WHEN THE DCP IS NOT CALLING FOR HUMIDITY, SENSED BY RETURN AIR HUMIDITY

SENSOR H-1, 2-WAY "ON-OFF" CONTROL VALVE V-3 WILL REMAIN CLOSED. WHEN THE DCP

IS CALLING FOR HUMIDITY, V-3 WILL REMAIN OPEN.

B. RETURN AIR HUMIDITY, SENSED BY H-1, WILL BE MAINTAINED AT SETPOINT (30% RH,

ADJUSTABLE) VIA DCP BY MODULATING HUMIDIFIER CONTROL VALVE V-4 TO MAINTAIN

THE DESIRED HUMIDITY. THE DCP WILL OVERRIDE THIS CONTROL TO MAINTAIN A

MAXIMUM HUMIDITY LEVEL OF 80% AS SENSED BY H-2 AND H-3. DCP WILL CLOSE VALVE

V-3 WHENEVER THE SUPPLY FAN IS OFF. VALVE V-4 WILL BE INTERLOCKED WITH A FLOAT

SWITCH TO KEEP THE HUMIDIFIER OFF IF THE HEADER IS FLOODED.

C. UPON A CALL FOR HUMIDITY, THE ON-OFF SOLENOID VALVE V-7 WILL OPEN TO

PRESSURIZE THE CONDENSATE RETURN FROM THE HUMIDIFICATION HEADER.

D. ON-OFF CONTROL VALVE V-3 WILL REMAIN CLOSED WHENEVER THE OUTSIDE AIR

TEMPERATURE IS ABOVE 55 DEG. F.

8. FREEZE PROTECTION

A. IF THE AIR TEMPERATURE AS SENSED BY T-3 FALLS BELOW 40 DEGF, AN ALARM SIGNAL

WILL INDICATE AT THE DCP AND ECC. IF THIS TEMPERATURE FALLS BELOW 35 DEG.F, THE

SUPPLY AND RETURN FANS WILL SHUT DOWN AND A CRITICAL ALARM WILL INDICATE AT

THE DCP AND ECC.

9. AUTOMATIC SHUTDOWN / RESTART

A. WHEN SMOKE IS DETECTED BY ANY OF THE DUCT SMOKE DETECTORS (DSD-1 THRU

DSD-5), THE SUPPLY AND RETURN AIR FANS WILL SHUT "OFF", ISOLATION SMOKE

DAMPERS SD-1, SD-2, SD-3, SD-4 AND SD-5 WILL CLOSE, AN ALARM SIGNAL WILL BE

TRANSMITTED TO THE FIRE ALARM SYSTEM, AND AN ALARM SIGNAL WILL INDICATE AT THE

DCP AND ECC. EXHAUST FANS SERVING AREA OF THE SUPPLY FAN WILL CONTINUE TO

RUN, SMOKE DAMPERS WILL OPEN AND SUPPLY AND RETURN FANS WILL RESTART WHEN

THE FIRE ALARM CIRCUIT IS RESET.

10. EMERGENCY CONSTANT SPEED OPERATION

A. UPON FAILURE OF THE INDIVIDUAL FAN VSMC, THE ASSOCIATED SUPPLY AND RETURN

FANS WILL BE STARTED/STOPPED MANUALLY AT THE DCP OR THE ECC THROUGH THE BY-

PASS STARTER. FANS WILL THEN BE OPERATED AT CONSTANT SPEED.

11. SUPPLY FAN ISOLATION

A. WHENEVER SUPPLY FAN SF-21A OR SF-21B IS NOT RUNNING, FOR ANY REASON,

CORRESPONDING ISOLATION SMOKE DAMPERS ID-1 OR ID-2 WILL BE CLOSED.

12. DEMAND CONTROL VENTILATION

A. MODULATE OUTSIDE AIR, RETURN AIR AND AND RELIEF AIR DAMPERS IN RESPONSE TO

DEMAND CONTROL VENTILATION CONTROL SEQUENCES PROVIDED IN VA PROJECT

NUMBER 539-13-105.

13. RELIEF AIR DAMPER CONTROL

A. THE RELIEF AIR DAMPER SHALL BE MODULATED AS REQUIRED TO MAINTAIN A

BUILDING STATIC PRESSURE OF 0.05 IN WG (ADJ.) RELATIVE TO THE OUTSIDE AIR

PRESSURE.

B. WHEN THE AIR HANDLER IS OFF, THE RELIEF AIR DAMPER SHALL BE CLOSED.

SCOPE OF WORK

A. COMMISSION AHU TO VERIFY IT IS OPERATING PER THE WRITTEN SEQUENCE OF

OPERATIONS.

B. RECALIBRATE ALL PRESSURE TRANSDUCERS.

C. PROVIDE PREVENTATIVE MAINTENANCE ON ALL DAMPERS AND ACTUATORS. CLEAN,

LUBRICATE AND ENSURE SMOOTH OPERATION OF DAMPERS AND ACTUATUORS. VERIFY

DAMPER IS CLOSING AND SEALING SHUT. REPORT ANY WORN DAMPER SEALS AND/OR

MALFUNCTIONING ACTUATORS TO THE VA.

D. CLEAN AND CALIBRATE ALL AIR FLOW MONITORING STATIONS.

E. REVISE CONTROL SEQUENCES TO INCLUDE THE FOLLOWING:

a. DISCHARGE AIR RESET

• THE AIR HANDLING UNIT CONTROLS WILL PROVIDE DISCHARGE AIR TEMPERATURE

CONTROL BASED ON ZONE DEMAND DEVIATION FROM SETPOINT. ALL ZONES WITH

DDC CONTROLS WILL BE SAMPLED AND THE ZONE FURTHEST FROM SETPOINT

WILL GOVERN. AS THE DEVIATION FROM SETPOINT DECREASES, THE DISCHARGE

AIR WILL BE RESET. 55 DEG. F AND 62 DEG. F WILL BE THE LOW AND HIGH RESET

LIMITS, RESPECTIVELY. ALL CONTROL SETPOINTS (INCLUDING HIGH AND LOW SET

POINTS FOR DISCHARGE AIR TEMPERATURE) WILL BE FULLY ADJUSTABLE TO MEET

JOB CONDITIONS.

b. NIGHT SET BACK

• THE AIR HANDLING UNIT (ASSOCIATED SUPPLY AND RETURN FANS) WILL BE ABLE

TO BE SCHEDULED FOR OCCUPIED/UNOCCUPIED 7-DAY AND HOLIDAY OPERATION.

DURING THE OCCUPIED MODE, THE TEMPERATURE CONTROLS WILL FUNCTION AS

SPECIFIED,DURING UNOCCUPIED MODE THE AIR HANDLING UNIT CONTROLS WILL

FUNCTION AS SPECIFIED EXCEPT THE OUTSIDE AIR DAMPERS WILL REMAIN

CLOSED. THE CONTROLS WILL CYCLE THE UNIT TO MAINTAIN A REDUCED SPACE

TEMPERATURE OF 60 DEGREES F.

• INITIAL SCHEDULE - UNIT WILL OPERATE MONDAY THRU FRIDAY 6:00 AM TO 10:00

PM, SATURDAY 10:00 AM TO 3:00 PM. UNIT WILL BE OFF AFTER SCHEDULED HOURS,

SUNDAY AND ALL LEGAL HOLIDAYS. COORDINATE EXACT SCHEDULE WITH COR.

• COOLING SETUP CONTROL AND COOL DOWN - DURING THE UNOCCUPIED TIME, IF

THE SPACE TEMPERATURE RISES ABOVE 82 DEGREES F. THE UNIT WILL CYCLE ON

TO COOL THE SPACE DOWN TO 79 DEGREES F. AND THEN TURN OFF. OUTSIDE AIR

WILL BE USED FOR COOLING FIRST UNLESS THE ECONOMIZER IS LOCKED OUT. AN

OPTIMAL START PROGRAM WILL START THE UNIT IN ADVANCE OF OCCUPIED TIME

TO ENSURE PROPER SPACE TEMPERATURES AT OCCUPANCY TIME. DURING SET

UP OR COOL DOWN OPERATION IF THE ECONOMIZER IS INACTIVE, THE OUTSIDE

AIR DAMPERS WILL REMAIN CLOSED.

• MORNING WARM-UP AND INITIAL START - AIR HANDLING SYSTEM WILL ENTER A

MORNING WARM-UP MODE IN ADVANCE OF THE OCCUPIED TIME VIA AN OPTIMAL

START SEQUENCE, THE OUTSIDE AIR DAMPERS WILL REMAIN COMPLETELY

CLOSED AND THE RETURN DAMPERS WILL REMAIN FULLY OPEN. THIS MODE WILL

CONTINUE UNTIL THE RETURN TEMPERATURE RISES ABOVE 68 DEGREES F., AT

WHICH TIME THE ECONOMIZER DAMPERS WILL BE POSITIONED TO MINIMUM.

ECONOMIZER DAMPER CONTROL WILL BE DELAYED TWO MINUTES DURING

START-UP TO PREVENT CABINET HEAT FROM FALSE LOADING THE SYSTEM.

• DURING UNOCCUPIED MODE, WHEN AN OVERRIDE BUTTON AT T-10 IS PRESSED IN

THE AUDITORIUM, THE UNIT WILL CYCLE TO OCCUPIED MODE FOR 2 HOURS. WHEN

ANY OTHER OVERRIDE BUTTON IS PRESSED, THE UNIT WILL CYCLE TO OCCUPIED

MODE FOR 1 HOUR.

F. MODIFY RELIEF AIR DAMPER CONTROL FOR MAX SPACE PRESSURE PER SHEET M900.

GENERAL NOTES

1. DIAGRAM AND SEQUENCE OF OPERATION IS INFORMATION FROM ORIGINAL SHOP

DRAWINGS AND IS FOR REFERENCE ONLY.

# DESCRIPTION DATE

1 ADDENDUM 4 01-12-2026