Office of Physical Plant
Operations Division
Engineering Services
The Pennsylvania State University
Physical Plant Building
University Park, PA 16802-1118
SEQUENCE OF OPERATION SUMMARY
August 17, 2012
CAMPUS CHILLED WATER SERVICE ENTRANCE – WITH HEAT EXCHANGER (use this sequence
where all the campus chilled water flow is to the heat exchanger. If flow to heat exchanger and directly to
end equipment then utilize sequence for “without heat exchanger”, provide control valve for heat
exchanger and treat heat exchanger as any other equipment.
The following sequence and supporting notes summary is also based on the equipment shown in the
Campus Chilled Water System Standard Detail #2, “Chilled Water Service – Building Entrance Piping
Diagram”, SK-2. The “building system” refers to the portion of the system from the campus distribution
piping connection to the heat exchanger(s). The remaining portion of the system including the heat
exchanger and to all the equipment served with chilled water shall be referred to as the heat exchanger or
“HTX system”.
This document and schematic are both provided to the project design engineer as a basis of design. The
engineer is solely responsible for the final design. Further sequence details are expected to be provided
by the engineer and/or BAS provider. Engineer should modify design if required to meet specific project
requirements. Modifications could include, but not limited to, equipment, sensors, and sequence logic.
The design engineer shall also follow the PSU BAS standard specification and issue for this project.
Deviations from this or any other associated PSU standards shall be communicated to PSU in written
form and in sufficient time for review, discussion, and approval by PSU prior to final construction issue.
A. GENERAL
1. The building is served with chilled water from the campus chilled water system. A heat
exchanger(s) is provided to isolate the campus system from the building heat exchanger side
distribution system. The heat exchanger system may have a glycol and water solution in some
cases. In general the system is operated at a chilled water supply (CHWS) temperature range of
41°F - 44°F. There is however no fixed constant supply temperature. The plant is operated to
produce required chilled water with the minimal energy necessary. Operating the plant(s) using a
water side economizer process during “winter conditions” may result in a maximum (CHWS)
temperature of 48°F. Other plant conditions may also result in a typical maximum (CHWS)
temperature of 48°F. The designer should account for expected short time periods throughout
the year where the (CHWS) temperature shall exceed the stated maximum (CHWS) temperature
ranges and limits. The critical loads in the building need to be evaluated with regard to these
limitations (consult with PSU OPP for further detail). The building systems connected to the
campus chilled water system shall be designed to operate at a 12°F temperature differential
(minimum, ideally >16°F) between the supply and return when supplied with a (CHWS)
temperature of 42°F in the summer. The chilled water system in the building shall be controlled
to maintain the chilled water return (CHWR) temperature to a setpoint of 54°F or greater
(exceptions are made for critical loads, see following).
2. The chilled water system in the building consists of a piping connection between the campus
distribution system and the building system including but not limited to components such as;
Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
building chilled water pumps, heat exchanger water pumps, heat exchanger, water flow meter,
temperature sensors, pressure sensors, an air/dirt separator (project specific), an isolation valve,
a choke valve (temperature control), and check valves.
3. The purpose of the chilled water heat exchanger distribution system is to distribute chilled water
to air handling units (and other equipment such as fan coils, computer room AC, etc.) throughout
the building for the purpose of space cooling and process cooling as required. Campus chilled
water is available throughout the year (24/7), and as such, the chilled water system in this
building is designed to operate whenever necessary.
4. All setpoints and time limits etc. will be adjustable in the software logic, unless otherwise
indicated. In general use values indicated with exception of those that are indicated as being
project specific. Setpoints and time limits involved shall not be changed without specific review
and direction from PSU OPP.
5. In order for energy efficient operation of both the central plants and the building systems the
design and sequence of operations should minimize required campus chilled water flow and
maximize CHWR temperature as much as reasonably possible.
B. FLOW METER
1. Measurement of instantaneous building tonnage will be calculated by the building BAS using the
following inputs:
a. Campus chilled water supply flow from the campus chilled water flow meter
b. Campus chilled water supply temperature sensor, T1
c. Building chilled water return temperature sensor, T2
C. PRESSURE (summary, see other sections for sequences)
1. Campus differential pressure, DP1, between the campus chilled water supply and return will be
measured. For some specific buildings this value may be used by the campus chilled water
plant(s) for campus supply pump speed control. This DP1 value is also used for enable/disable
control of the building pump. DP1 will also be used as a safety shut-off isolation trigger.
2. Building differential pressure, DP2, which is the DP between the chilled water supply and return
at a remote location in the heat exchanger chilled water distribution system, will be sensed and
used to control the speed of the Duty heat exchanger chilled water pump. There may be multiple
remote DP sensors required.
3. Pressure P1, campus chilled water return pressure at building entrance, will be sensed and used
as a safety shut-off isolation trigger.
4. The campus chilled water supply pressure at building entrance will be calculated from the
campus DP and the campus chilled water return pressure. The value will be used for
comparisons with required specific building chilled water system pressure to assure that static
head is sufficient to maintain the fill pressure.
5. Pressures P2 and P3 (inlet and discharge of building pumps/pump bypass) and P4 and P5 (inlet
and outlet of load side of heat exchanger) will be used by the BAS for monitoring only.
D. HTX SYSTEM PUMP STARTING/STOPPING
1. Ideally all the building equipment provided with chilled water shall be capable of issuing cooling
requests for chilled water flow thru the BAS network. Where specific cooling requests from
equipment are impractical, then some other appropriate representative conditions for that
equipment will be used in place of specific requests to enable the system. In some applications
the system may be required to operate continuously due to process loads or other critical loads.
This issue should be resolved in the design phase and verified with PSU OPP.
2. For purposes of system enable only, if any equipment chilled water control valve in the
system is open > 20% for 10 minutes (or other condition used as a substitute request
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Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
where direct request is not practical), or if the network connection is lost for more than 10
minutes, then the following shall occur:
a. Duty HTX pump will start at minimum speed.
b. For conditions where equipment chilled water control valve is opened in response to chemical
treatment refer to Chemical Treatment Section of this sequence.
3. After 30 minutes min runtime if all the equipment chilled water control valves have closed to 10%
(10% hysteresis) or if other conditions used in place of direct requests indicate no load for other
equipment served, then the system will be disabled. If system does not have a system bypass
valve for low flow conditions, there shall be no min runtime requirement. After being stopped the
duty pump shall be off for a min of 10 minutes before being enabled.
4. The HTX chilled water system generally has two HTX pumps, CHWP03 and CHWP04 each sized
at 100% design flow rate. When required to operate, only one pump is required to provide the
required chilled water flow to satisfy the building cooling needs. One is designated the Duty
pump, and the other is designated the Standby pump. Each pump is provided with a VFD to
control the flow rate of the pump. Refer to PSU standards for the VFD and BAS interface
requirements.
5. The HTX chilled water pumps will operate in accordance with the University’s standard
Duty/Standby sequence with an exercise cycle. The specific details of this sequence are given
elsewhere.
E. HTX PUMP SPEED CONTROL - OPTIMIZED DIFFERENTIAL PRESSURE RESET (TRIM AND
RESPOND)
1. General: The objective is to minimize pump energy by always operating the pump(s) at the
lowest speed possible such that at least one cooling control valve is fully open and maintaining its
temperature control setpoint within an acceptable range. The minimum pump speed shall be
programmed at the VFD drive for (typ. 20% or 12 hz adj.) and also in the software as necessary.
The maximum pump speed shall be programmed at the VFD drive for (typ. 100% or 60 hz) and
also in the software as necessary. The system should be balanced for minimal pressure drop. If
design flow requirements are met at a pump speed less than 100% there should be no effort to
create a pressure drop so this design flow occurs at 100% speed. In that case the pump may
never have to operate at 100% (saving energy) but will have the capacity for greater flow.
2. Basic VFD speed control: The pump VFD speed DP2 setpoint shall modulate the pump VFD
speed to maintain a differential pressure setpoint that shall be automatically reset with a Trim and
Respond function as described below.
a. The pump VFD speed DP2 setpoint shall be recalculated every 5 minutes (adj.). The
incremental change per interval shall be based on the maximum cooling requests from any
one of the associated Primary or Terminal Application Controllers served by each pump
system.
b. A cooling request is defined as a condition where the requesting equipment’s control valve is
100% open and the controlled variable is off setpoint by 1°F (e.g. 1 cooling request). Each
additional 1°F from setpoint will generate an additional request. Therefore the further from
setpoint the greater the number of requests from that particular equipment.
c. All critical loads must have means of generating a cooling request.
d. The pump VFD speed DP2 setpoint shall be reset between a min and max setpoint (3-10 for
example) psi. The initial differential pressure setpoint shall be 3 psig (adj.). If network
communication is lost for more than 10 minutes, the setpoint shall be reset to 0.75 x
maximum DP2 setpoint and an alarm issued. The maximum DP2 setpoint is the pressure
required to provide full pump design flow (taking into account the design diversity of all the
connected load) to all control valves simultaneously while providing full design flow to the
“hydraulically most remote” load (some coordination between the design engineer, BAS
engineer and the TAB is expected). For a particular building this maximum value may need
to be set greater than 10 psi. The minimum value is an arbitrarily set number representing a
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Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
low value that will likely result in pump operation at min speed for optimal energy savings but
still high enough to maintain minimal flow after enable until DP has time to reset if required.
e. As cooling requests increase, the setpoint shall incrementally respond up by 0.5 psi per
request value, limited to 3 psi (adj.) per period (see above for time period), to the maximum
reset value.
f. With no cooling requests, the setpoint shall incrementally be trimmed down by 0.5 psi (adj.)
per period to the minimum reset value.
3. HTX Pump deadhead protection: If actual remote DP2, with the Duty pump controlled to its
minimum, is 3 psi > DP2 setpoint (for 15 minutes), then pump shall be turned off (for 15 minutes)
and an alarm issued. Further control logic may be necessary to insure that pump is operating in
accordance with manufacturer’s recommendations. If the system is provided with a HTX system
bypass valve then the valve shall be modulated open when above conditions are present.
4. Pump deadhead protection further explanation: The design engineer responsible for the project
needs to design and provide for all expected low flow conditions that the system will see over the
course of a typical year. In most cases the pump will not be capable of safe operation and able to
support all expected low flow needs. In most applications an additional smaller pump or
modulating system bypass valve (preferred choice typically) may be required for flows that are
too low for safe Duty pump operation. Both flow and associated required head combination must
be considered. The flow and head do not neatly follow the max condition system curve. For
example, some buildings may have a CRAC unit whose branch DP requires 15 psi, but with a
relatively very low flow, compared to the total system flow. In summary low system flow
conditions do not always also mean low head requirements (when branch DP is a large portion of
the overall DP total). In some case the Duty pump would not meet this condition without
operating in a region of the pump curve that would cause damage to the pump based on
manufacturer’s recommendations. Standard recommendation is that flow should be greater than
or equal to 0.20 multiplied by the gpm at the most efficient point on that particular pump operating
curve.
F. BUILDING CHILLED WATER SYSTEM ENABLE
1. For purposes of system enable, the same conditions that start the HTX Duty pump shall
enable the building system with the exception that HTX pump status must also be on: if
any equipment chilled water control valve in the system is open > 20% for 10 minutes (or
other condition used as a substitute request where direct request is not practical), or if the
network connection is lost for more than 10 minutes, then the following shall occur:
a. Isolation valve (CHWV-2) shall open.
b. And Choke valve (CHWV-1) shall modulate open to maintain (with a minimum position) the
chilled water return temperature setpoint (refer to CAMPUS CHILLED WATER VALVES
FLOW AND TEMPERATURE CONTROL).
c. For conditions where equipment chilled water control valve is opened in response to chemical
treatment refer to Chemical Treatment Section of this sequence.
2. If HTX system is not enabled or its pump status is off then building system will also be disabled.
3. After system is initially enabled and prior to starting building duty pump, system shall be operated
using only campus supply and return differential pressure to satisfy HTX load as indicated by
HTX chilled water supply temperature (T4). The goal is to reduce operating time and speed of
the building pumps as much as possible.
G. BUILDING PUMPING STARTING/STOPPING
1. The building chilled water system generally has two building pumps, CHWP01 and CHWP02,
each sized at 100% design flow rate. When required to operate, only one pump is required to
provide the required chilled water flow to satisfy the building cooling needs. One pump
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Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
2.
3.
4.
5.
(CHWP01) is designated the Duty pump, and the other (CHWP02) is designated the Standby
pump. Each pump is provided with a VFD to control the flow rate of the pump. Refer to PSU
standards for the VFD and BAS interface requirements.
The building chilled water pumps will operate in accordance with the University’s standard
Duty/Standby sequence with an exercise cycle.
The Duty pump shall be started at minimum speed to maintain HTX chilled water supply
temperature setpoint, T4 if:
a. T4 is 1°F above its setpoint for 5 minutes (adj.). The setpoint of T4 shall be a floating
setpoint typically 2°F (adj.) plus campus chilled water supply temperature, T1. Due to the
heat exchange processT4 setpoint must be a reasonable value above T1, if this value to
close to T1 then the result will be unachievable and the pump shall increase to its maximum
speed.
b. And the building system is enabled (building system is enabled if HTX is enabled)
c. And HTX pump status is on.
d. And the optimized setpoint block for T2 (choke valve control, see valve and temperature
control section also) has reset down to the its minimum (including override reset).
Duty pump shall also be started if the network connection is lost for more than 10 minutes.
Since the goal is to reduce operating time and speed of the building pumps as much as possible
there needs to be process to go back to campus pressure alone with building pumps off. Pump
shall remain on for a minimum runtime of 1 hr and continue on until:
a. DP1 is > 5psi above the value of DP1 when pump was most recently started and the pump
speed control PID output = 0 (pump at min speed). Both conditions must be met for 10
minutes.
b. Or (when checked every 1 hr) if T4 is within 2°F of setpoint for 15 minutes and the pump
speed control PID output < 50% then pump shall be stopped.
H. BUILDING PUMP SPEED CONTROL
1. General: The objective is to minimize pump energy by always operating the pump at the lowest
speed possible while maintaining its temperature control (T4) setpoint. The minimum pump speed
shall be programmed at the VFD drive for (typ. 20% or 12 hz adj.) and also in the software as
necessary. The maximum pump speed shall be programmed at the VFD drive for (typ. 100% or
60 hz) and also in the software as necessary. The system should be balanced for minimal
pressure drop. If design flow requirements are met at a pump speed less than 100% there
should be no effort to create a pressure drop so this design flow occurs at 100% speed. In that
case the pump may never have to operate at 100% (saving energy) but will have the capacity for
greater flow.
2. Basic VFD speed control: Once pump is enabled the pump will start at min speed. The pump
VFD speed PID shall modulate the pump VFD speed to its maximum as required to maintain HTX
chilled water supply temperature setpoint, T4 if.
a. Under normal conditions the optimized setpoint block for T2 (choke valve control, see valve
and temperature control section also) has reset down to the its minimum (including override
reset).
b. Network communication is lost, the speed shall be reset to 0.75 x maximum pump VFD
speed and alarm issued.
3. VFD speed control adjust to prevent recirculation: If building CHWS temperature (T3) is 2°F
(adj.) greater than the campus CHWS temperature (T1) for 2 minutes (adj.), then the pump speed
will be reduced incrementally (with a ramp) and an alarm issued, even though the PID output to
maintain T4 is requesting a higher speed. This control logic is needed due to the condition when
the campus pressure is too low to support required campus chilled water supply flow to the HTX,
then the basic pump VFD speed control will respond by increasing the pump speed. In this case
the flow is increased but much of it is recirculating through the check valve and not from the
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Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
campus in the proper amount. The result will be higher building CHWS temperatures and wasted
pump energy.
H. BUILDING PUMPS OFF - CAMPUS CHILLED WATER VALVES FLOW AND TEMPERATURE
CONTROL
1. When the building cooling is OFF, the choke valve, CHWV- 1 shall be at min position and the
isolation valve, CHWV-2 will be closed completely. The decision to leave the choke valve at min
position is based on experience that when both valves are closed, the water in this closed portion
of the system can become (at some locations) warm from the ambient conditions in a warm
mechanical room. The water expands and the pressure increases without any means of relief
unless a valve is left open.
2. When the building cooling is enabled (see building system enable section above), the isolation
valve, CHWV-2, will be open and CHWV-1, the choke valve, shall modulate with the constraints
of a minimum position to maintain T2 setpoint (54°F initial). A linear converter block shall reset
the minimum valve position from 20% to 10% as the campus chilled water DP ranges from 0 psi
to 10 psi. These values may be adjusted during the commissioning process based on particular
building conditions. This min position is required to avoid condition where the valve closes on low
(T2) reading and the stagnant water remains cool at T2 and therefore does not allow choke valve
to open again.
3. When the building chilled water pumps are off, CWHV-1 shall modulate as required from
minimum position to 100% open to maintain chilled water return temperature, T2 setpoint. If HTX
chilled water supply temperature setpoint, T4, is satisfied then CHWV-1 setpoint (T2) shall be
reset from 54°F to 60°F using a time ramp.
4. For conditions where HTX chilled water supply temperature setpoint, T4, is not satisfied, prior to
starting building Duty pump (due to limited campus flow chilled water flow) T2 setpoint shall be
reset from 54°F to a lower limit of 52°F for buildings without critical loads or 48°F for buildings
with critical loads if:
a. HTX chilled water supply temperature, T4, is 1°F above its setpoint for 5 minute (adj.).
b. If T2 (CHWR temperature) is reset below 54°F for more than 15 mins then a non-critical
alarm shall be issued. Lower CHWR temperatures reduce the efficiency of the central plant
chilled water production and increase pumping requirements for both the central system and
the building system. New construction shall be designed so that CHWR temperatures are
always above 54°F. PSU OPP has ongoing effort to increase CHWR temperatures in
existing systems. T2 reset below 54°F should only be considered a temporary condition to
meet immediate required load.
I.
BUILDING PUMPS ON - CAMPUS CHILLED WATER VALVES FLOW AND TEMPERATURE
CONTROL
1. When the building chilled water Duty pump is operating there is no minimum position for CHWV-1
(see Building Pump Starting/Stopping Section).
2. When Duty pump is started the pump shall be at min speed (see previous sections)
3. If Duty pump is operating at min speed for 10 minutes (adj.) and maintaining HTX chilled water
supply temperature setpoint, (T4) the T2 setpoint shall be reset from 54°F to 60°F.
4. For conditions where HTX chilled water supply temperature setpoint, T4, is not satisfied, prior to
increasing speed of building Duty pump from the minimum value, T2 setpoint shall be reset from
54°F to a lower limit of 52°F for buildings without critical loads or 48°F for buildings with critical
loads if:
a. HTX chilled water supply temperature, T4, is 1°F above its setpoint for 5 minute (adj.).
b. If T2 (CHWR temperature) is reset below 54°F for more than 15 mins then a non-critical
alarm shall be issued. Lower CHWR temperatures reduce the efficiency of the central plant
chilled water production and increase pumping requirements for both the central system and
6
Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
the building system. New construction shall be designed so that CHWR temperatures are
always above 54°F. PSU OPP has ongoing effort to increase CHWR temperatures in
existing systems. T2 reset below 54°F should only be considered a temporary condition to
meet immediate required load.
J.
BUILDING PUMP EXERCISE AND SYSTEM CHEMICAL TREATMENT
1. The objective of this sequence is to provide an opportunity for the chemical treatment process
administered at the central plant locations to distribute the chemicals to all the building system
components and filter the building chilled water on a timely basis. This will be scheduled during
typical unoccupied periods of the day and staggered so that no other buildings will be in the
exercise and chemical treatment mode at the same time (coordinate time schedule with PSU
OPP).
2. If the building chilled water system was enabled for less than 1 hour during a consecutive
7 day period then:
a. The system shall be enabled for 15 minutes (adj with a minimum of 15 minutes) or the
campus chilled water flow as measured by the main flow meter has accumulated a
determined gpm (this value would be established by coordination of the design engineer with
PSU OPP and based on system volume). For the same time or conditions the following shall
also be controlled as indicated.
b. CWV-1 and 2 shall be open 100%
c. Duty and standby building pumps shall operate at minimum speed for the first 2 minutes.
After that time the Duty pump shall continue to operate at minimum speed for the remainder
of the system enable (see 2.a above)
d. HTX pumps shall not be required to operate
3. If the building chilled water system was enabled for greater than or equal to 1 hour during
a consecutive 7 day period then:
a. Duty and standby building pumps shall operate (if not already on) at minimum speed for 2
minutes. After that time if the pump was not otherwise commanded on then the pumps shall
be off.
b. CHV-1 and 2 shall be under normal control
c. HTX pumps shall not be required to operate
K. BUILDING PUMP SYSTEM VALVE EXERCISE
1. The objective of this sequence is to exercise valves that may stay in one position for long periods
of time and then be unable to move properly when commanded.
2. CHV-1 (choke valve)
a. If CHV-1 is 0% for more 168 consecutive hrs, then cycle valve open to 30% and then
immediately return to normal operation.
b. If CHV-1 is 100% for more 168 consecutive hrs, then cycle valve to 80% open and then
immediately return to normal operation.
3. CHV-2 (isolation valve)
a. If CHV-2 is closed for more 168 consecutive hrs, then cycle valve open to 100% and then
return to normal operation. Open only after CHV-1 has closed to prevent unnecessary flow.
b. If CHV-2 is open for more 168 consecutive hrs, then cycle valve closed and then after 10
seconds (valve should not actually close with this short time period) immediately return to
normal operation. This short movement is required given that CWV-2 is 2-position type
valve, (open-closed) and preventing flow in an enabled system is to be avoided.
7
Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
L. HTX PUMP EXERCISE AND SYSTEM CHEMICAL TREATMENT
1. The objective of this sequence is to provide an opportunity for the chemical treatment process
administered at the pot feeder or glycol fill system to distribute the chemicals to all the HTX piping
system components and to filter the HTX chilled water on a timely basis. This will be scheduled
during typical unoccupied periods of the day and staggered to minimize campus electrical
demand charges (coordinate time schedule with PSU OPP).
2. If the HTX chilled water system was enabled for less than 1 hour during a consecutive 7
day period then:
a. The system shall be enabled for 30 minutes (adj with a minimum of 15 minutes). This time
value would be established by coordination of the design engineer with PSU OPP and based
on system volume. For the same time or conditions the following shall also be controlled as
indicated.
b. One half of the chilled water valves at equipment served shall be open to 50% (thru the
network) for one half the exercise time period and then these will close and the other valves
in the system shall be open 50% for the remainder of the exercise time period.
c. Duty and standby HTX pumps shall operate at minimum speed for the first 2 minutes. After
that time the system they shall operate under otherwise normal remote static pressure
setpoint control (with exception that the setpoint shall be at the upper range of the reset).
d. Building pumps shall not be required to operate
3. If the HTX chilled water system was enabled for greater than or equal to 1 hour during a
consecutive 7 day period then:
a. Duty and standby HTX pumps shall operate (if not already on) at minimum speed for 2
minutes. After that time if the pump was not otherwise commanded on then the pumps shall
be off.
b. One chilled water valve at equipment (or system bypass valve if available) served shall be
open to 100% for 2 minutes (thru the network)
c. Building pumps shall not be required to operate
4. Additional requirements when the HTX chilled water system was enabled for greater than
or equal to 1 hour during a consecutive 7 day period but pipe branches at the zone level
did not have adequate flow. The objective of this next portion of the sequence is to insure that
the chemical treatment process administered at the building is distributed to all the branches of
the system on a timely basis. At the equipment level controllers (for those served with chilled
water from this system) the time that the chilled water valve is open shall be accumulated. If the
valve was opened for 30 minutes or greater during a consecutive 7 day period than there is no
action, if not then the valves shall be opened 50% for 15 minutes (adj). If valve already open to
meet load take the higher of the PID request or the 50% value. This will enable the HTX system
(thru the network) in a chemical treatment mode, where the HTX Duty pump shall be on but the
building pumps and that system shall not be required to operate (building pumps off and no
campus chilled water flow). The HTX pumps will operate under normal speed control to maintain
remote DP setpoint (with exception that the setpoint shall be at the upper range of the reset).
The HTX system shall not try to maintain T4 setpoint either.
5. For control systems where above is not reasonable to implement:
a. Once a week the system shall be enabled for 30 minutes (adj with a minimum of 15 minutes).
This time value would be established by coordination of the design engineer with PSU OPP
and based on system volume. For the same time or conditions the following shall also be
controlled as indicated.
b. One half of the chilled water valves at equipment served shall be open to 50% (thru the
network) for one half the exercise time period and then these will close and the other valves
in the system shall be open 50% for the remainder of the exercise time period.
c. Duty and standby HTX pumps shall operate at minimum speed for the first 2 minutes. After
that time the system they shall operate under otherwise normal remote static pressure
setpoint control (with exception that the setpoint shall be at the upper range of the reset)
8
Sequence of Operation
Campus Chilled Water Service Entrance
With Heat Exchanger
Building pumps shall not be required to operate
M. CAMPUS CHILLED WATER VALVES SAFETY SHUT-OFF
1. If the campus differential pressure, DP2, is 0 psi or less for 30 seconds, the Duty building chilled
water pump will be stopped, the choke valve, CWV-1, and the isolation valve, CWV-2 will be
closed completely and an alarm will be issued. The valves will be released to reopen when the
differential pressure is re-established at 0.5 psi or greater for 30 seconds.
2. If the pressure sensed in the campus chilled water return pipe at P1 is 5 psi below the minimum
system pressure (determined during commissioning under various operating conditions) for 30
seconds, the Duty building pump will be stopped, the choke valve, CWV-1, and the isolation
valve, CWV-2 will be closed completely. The Duty pump shall be restarted and the valves will be
released to reopen when the system pressure is re-established for 30 seconds. An alarm will be
issued.
N. MISCELLANEOUS ALARMS & SYSTEM DIAGNOSTICS
1. Commissioning Alarms: The following monitoring and alarm functions shall initiate one of several
primary categories of commissioning “CCX” alarms displayed at the BAS workstation. At the
equipment controller level, each alarm within each category shall be labeled independently for
easy, diagnostic purposes. Primary Categories shall be as follows in bold:
a. Pump Control Fault (when the associated pump status is on)
1) Unstable PID loop: If any pump speed PID loop continues to cycle its output more than
40% of its range (adj.) 3 times (adj.) in any 60 minute internal.
2) “Excessive Pump Speed” Alarm: If the pump speed output remains above 95% for more
than 8 hours (adj.) accumulated per occupied period for at least 3 (adj.) consecutive
occupied periods.
3) Continuous Request Alarm: If one or more application controllers is sending continuous
cooling requests, and differential pressure has reset to maximum setpoint, and the
combined condition remains for more than 8 hours (adj.) continuously.
b. T2 (CHWR temperature) reset
1) If T2 (CHWR temperature) is reset below 54°F for more than 15 mins then a non-critical
alarm shall be issued. Lower CHWR temperatures reduce the efficiency of the central
plant chilled water production and increase pumping requirements for both the central
system and the building system. New construction shall be designed so that CHWR
temperatures are always above 54°F. PSU OPP has ongoing effort to increase CHWR
temperatures in existing systems. T2 reset below 54°F should only be considered a
temporary condition to meet immediate required load.
9