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 – WITHOUT HEAT EXCHANGER
The following sequence and supporting notes summary is also based on the equipment shown in the
Campus Chilled Water System Standard Detail #1, “Chilled Water Service – Building Entrance Piping
Diagram”, SK-1. This document is 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 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. 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;
building chilled water pumps, 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.
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
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 building chilled water distribution system, will be sensed and used to
control the speed of the Duty building 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) will be used by the
BAS for monitoring only.
D. CHILLED WATER SYSTEM ENABLE
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% (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 mins, 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.
3. The system shall be enabled for 1 hour minimum. After 1 hour if all the equipment chilled water
control valves have closed to 10% (10% hysteresis) or if other conditions used in place of direct
requests for other equipment served then the system will be disabled.
2
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
4. 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 distribute chilled water to the
building’s equipment. The goal is to reduce operating time and speed of the building pumps as
much as possible.
E. BUILDING PUMPING STARTING/STOPPING
1. The building chilled water system generally has two building pumps, CWP01 and CWP02, 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 (CWP01) is
designated the Duty pump, and the other (CWP02) 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.
2. The building chilled water pumps will operate in accordance with the University’s standard
Duty/Standby sequence with an exercise cycle.
3. The Duty pump shall be started at minimum speed if:
a. The OA temperature is > 52°F (only for systems where all equipment served has economizer
cooling). The OA temperature is not considered as a factor for pump enable for buildings
with equipment that has cooling needs that are not related to OA temperature (computer
room and other such rooms with internal loads). The primary OA temperature shall be the
base OPP OA sensor value from the network. The secondary OA temperature shall be the
building or other designated local OA value. Follow PSU OPP standard for conditions related
to use of OA temperature sensors.
b. And there are (3) cooling request. A cooling request is defined as a condition where the
requesting equipment’s control valve is 100% open and the controlled variable of the valve 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. The pump enable optimized setpoint block resets based on
any given valve controller with the highest number of requests (requests are not added from
various valve controllers).
c. If there is no control capability for request from the served equipment the pump will not be
started at the minimum speed unless required to in order to maintain the remote DP setpoint
(see that section). And when the pump is started to maintain the remote DP setpoint the
sequence below used to try to reestablish campus pressure operation alone will be utilized.
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) 5 minutes
(adj.).
e. Duty pump shall also be started if the network connection is lost for more than 10 mins. In
some applications the pumps 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
4. 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 (min pump speed). Both conditions must be met for 10 mins.
b. Or (when checked every (1) hr) if the campus DP1 is > than the pump enable setpoint for 15
minutes and the pump speed control PID output = 0 (min pump speed). Increase in DP-1 will
reduce required pump speed control PID output. Both conditions must be met for 10 mins.
F. PUMP SPEED CONTROL - OPTIMIZED DIFFERENTIAL PRESSURE RESET (TRIM AND
RESPOND)
3
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
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: Once pump is enabled the pump will start at min speed. The
optimized setpoint block for the DP2 setpoint shall modulate the pump VFD to its maximum
speed as required 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. Cooling requests are not accumulated for pump VFD speed DP2 reset until after pump has
started 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)
5 minutes (adj.).
c. Cooling requests are the same as described in the Building Pump Starting and Stopping
Section.
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
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. VFD speed control adjust to prevent recirculation: If building CHWS temperature (T3) is 2°F
greater than the campus CHWS temperature (T1) for an adjustable time, then the pump speed
will be reduced incrementally even though the actual building remote DP2 may be less than the
DP2 setpoint. The pump speed shall be reduced (with a ramp) by resetting the pump VFD
speed DP2 setpoint. This control logic is needed due to the conditions when campus pressure is
too low to support required campus chilled water supply flow into the building system. When the
controlled variable for the equipment control valves cannot be satisfied the valve will respond by
opening further and lowering the actual differential pressure at remote DP2. The basic pump
VFD speed control will respond by increasing the pump speed. The result will be over pumping
and higher building CHWS temperatures and therefore associated potential loss of
dehumidification capacity and wasted pump energy.
4. Pump (building chilled water) deadhead protection: If actual remote differential pressure at
DP2, with the Duty pump controlled to its minimum, is 3 psi > DP2 setpoint (for 15 minutes), then
4
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
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.
5. 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.
G. 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. The
optimized setpoint block for the T2 setpoint shall be reset from 54°F to 60°F using a time ramp if
there are no cooling requests. A cooling request will cause the T2 setpoint to be reset from 60°F
to 54°F using a time ramp.
4. 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 prior to starting pumps (see Building Pump Starting/Stopping
Section).
5. T2 setpoint shall be reset from 54°F to a lower limit of 52°F for buildings with all non-critical loads
or 48°F for buildings with critical loads if:
a. There are 3 or more cooling request for 5 minute (adj.).
b. If T2 (CHWR temperature) is reset below 54°F for more than 15 minutes 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
5
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
existing systems. T2 reset below 54°F should only be considered a temporary condition to
meet immediate required load.
H. 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 chilled water return
temperature, T2 setpoint. The optimized setpoint block for the T2 setpoint shall be reset from
54°F to 60°F using a time ramp if there are no cooling requests. A cooling request will cause the
T2 setpoint to be reset from 60°F to 54°F using a time ramp.
4. VFD speed DP2 setpoint, 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. There are 3 or more cooling request for 5 minute (adj.).
b. If T2 (CHWR temperature) is reset below 54°F for more than 15 minutes 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.
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 30 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. 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.
d. Duty and standby building pumps shall both operate at minimum speed for the first 2 minutes.
After that time the system they shall operate under otherwise normal control (with or without
pump operation)
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
6
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
c.
One chilled water valve at equipment served shall be open to 100% for 2 minute s (thru the
network)
4. Additional requirements when the building chilled water system was enabled for greater
than or equal to 1 hour during a consecutive 7 day period but pipe branches at the
equipment 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 central plant
locations 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 chilled water system (thru the network) in a chemical treatment
mode, where the duty building pump shall operate but without any campus chilled water flow. The
pump 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).
J.
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 .
K. 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.
I.
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)
7
Sequence of Operation
Campus Chilled Water Service Entrance
Without Heat Exchanger
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.
8