TORONTO DISTRICT SCHOOL BOARD
BAS Design Guidelines
Rev 1.3
May 5, 2021
TDSB BAS Design Guidelines Rev 1.3
INDEX
A. General Controls
B. Zone Controls
C. Boiler Plant
D. Glycol AHU Heating Loops
E. AHUs
F. Chillers
G. Cooling Centres
H. Pneumatic to DDC Upgrades
I. Domestic Hot Water
J. Shop Drawings Review
K. VFDs and Starters
L. Typical Controls Sequences – Boiler Plant
M. Typical Controls Sequences – AHU
N. Typical Controls Sequences – Zone Heating and Cooling
O. Typical Controls Schematics
TDSB BAS Design Guidelines Rev 1.3
A. General Controls
1. Mechanical drawings should contain:
1.1. Complete controls schematics and sequences are required on the mechanical drawings.
Provide comprehensive schematics and summaries for heating and cooling piping that is
part of the scope of the project.
1.2. Two outdoor air temperature sensors should exist for every building. Provide additional
sensors where required. If sensors already exist, do not provide new ones.
1.3. Provide valve and damper schedules when new valves or new actuators are installed as part
of the project with GPM, CV, Damper Size, Torque and other relevant information.
1.4. Provide equipment schedules for mechanical equipment that is part of the scope of the
project (e.g. exhaust fans, force flow heaters, unit heaters etc.)
1.5. Metric units should be displayed
2. Valves:
2.1. If there is a three-way control valve, include a note “See controls drawings for valve porting”
2.2. Control valves on air handling units or part of the boiler plant shall be provided with position
feedback status (AI). Control valves serving perimeter zones (e.g. perimeter heating, reheat
coils etc.) do not require feedback.
2.3. 3-way control valves shall be piped as mixing valves – pump is located after the 3-way valve
and pulls out of the common port. Do not pipe as diverting valves – pumps push water into
the common port.
2.4. Ensure porting is shown on 3-way valves – in heating applications ‘NO/A’ port comes from
the HW supply side and ‘NC/B’ port comes from the return side. ‘COM/AB’ port goes into
the pumps.
2.5. Pressure-independent valves should not be used.
3. Alarms:
3.1. A Low Heat Alarm shall be included with all new boiler plants. A low temperature aquastat
connected to the primary supply line and an outdoor air temperature thermostat shall be
wired together to the surveillance panel. If the outdoor air temperature drops below 5 °C
and the primary SWT drops below 40 °C, the alarm will trip. This alarm is not connected to
the BAS.
3.2. Whenever a new sump pump is installed, install a high-level sensor and connect it directly to
the alarm surveillance panel. Do not connect the sump system to the BAS.
3.3. A BAS Alarm output is required from the BAS to the surveillance panel to indicate if any
space temperature drops below 10 °C when the outdoor air temperature is below 5 °C.
3.4. A Surveillance Alarm input is required from the surveillance panel to indicate if the building
is armed.
4. Do not put on BAS:
4.1. Occupant adjustment of space temperature setpoints shall not be provided for any zones.
4.2. Occupancy override shall not be provided for any zones except gyms.
4.3. Devices controlled through BACnet are not acceptable unless special permission is obtained
from TDSB.
.1 BACnet is allowed for monitoring of specialized equipment, for example: large chiller
plants, VRF systems, dehumidification units and lighting systems. Essential control
points like Start/Stop, Status and Feedback will be obtained through hardwire points.
4.4. Water and gas meters are not required to be connected to the BAS.
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TDSB BAS Design Guidelines Rev 1.3
4.5. All life safety equipment (fire, smoke detection, NO2, CO, CH4 etc.) should not be connected
to the BAS. Where required, monitoring of these systems may be allowed with special
permission from TDSB.
5. Ensure controls requirements for related mechanical equipment (e.g. Boilers, RTUs etc.) are
reflected in the specifications.
6. Equipment status should always be a current sensor (AI: 4-20 mA) and not a current switch (DI).
All force flow heaters, unit heaters, pumps and fans controlled by the BAS require a status.
B. Zone Controls
1. Unless required to operate independently, control valves for force flow heaters or unit heaters
should be connected to the same output as the start/stop.
2. All exhaust fans require a start/stop and status. If a motorized damper is included with the fan,
only one DO shall be used to open the actuator and turn on the fan and open the damper.
Damper position status is not required.
3. All reheat coils shall be provided with discharge air temperature sensors.
4. For all zones where there are changes to the heating controls, remove any pneumatic valves and
replace with electronic DDC valves.
5. For unoccupied spaces such as mechanical rooms, storage rooms or individual washrooms,
stand-alone controls such as line-voltage thermostats with tamper-proof cover or self-controlled
valves are acceptable.
6. Electric duct heaters:
6.1. Must be interlocked with an airflow switch.
6.2. Provide supply air temperature and status.
6.3. Where possible, provide modulating control.
C. Heating Plant
1. Boilers:
1.1. BAS points for flow meters and flow switches should be avoided unless integral to the
design.
1.2. Essential points are Start/Stop, Status and Modulation. Hardware boiler alarms are not
required.
1.3. If the boiler does not have a local/remote switch (eg. on condensing boilers), the BAS will
wire a local/remote switch on the boiler Start/Stop BAS signal. When put in local, the switch
will open the contact forcing the boiler into local control.
2. Secondary Loop:
2.1. If there is a hot water secondary loop supplying AHUs, then incorporate the design as stated
in the ‘Glycol AHU Heating Loops’ section but replace the heat exchanger and 2-way valve
with a 3-way mixing valve to control the supply water temperature in the secondary loop.
3. Avoid use of multiple temperature sensors on sections of pipe with the same temperature (e.g.
individual return water temperatures to multiple boilers. One sensor should be placed on the
common return line.)
4. If there are no space temperature sensors in the building, include between 2 to 4 classroom
space temperature sensors dependent on the size of the school. Preferably place in corner
rooms distant from the boiler plant, northern side of the building and on different floors.
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TDSB BAS Design Guidelines Rev 1.3
D. Glycol AHU Heating Loops
1. If there is a glycol loop supplying one (1) AHU:
1.1. A heating valve should be on the hot water/steam side of the heat exchanger.
1.2. On the glycol side, there should be one constant volume pump which supplies glycol to the
AHU heating coil.
1.3. Provide a temperature sensor for glycol supply to the heating coil.
1.4. Do not provide VFDs, bypass valves, pressure sensors, backup pumps, return glycol sensors,
or water/steam sensors on the non-glycol side of the heat exchanger.
2. If there is a glycol loop supplying two (2) AHUs:
2.1. A heating valve should be on the hot water/steam side of the heat exchanger.
2.2. Provide two constant volume pumps (lead/standby).
2.3. Each AHU heating coil should have a 3-way valve controlling the flow to the AHU heating
coil.
2.4. Provide supply and return glycol temperature sensors.
2.5. Do not provide water temperature or steam sensors for the non-glycol side of the heat
exchanger. Do not provide VFDs, pressure sensors or bypass valves.
3. If there is a glycol loop supplying three (3) or more AHUs:
3.1. A heating valve should be on the hot water/steam side of the heat exchanger.
3.2. Provide two pumps with VFDs (lead/lag) and a differential pressure sensor.
3.3. Most heating coils should have 2-way valves. The AHU farthest from the HX should have a 3way valve to allow glycol to bypass under low flow conditions. If enough glycol can bypass,
do not provide a bypass valve.
3.4. Provide supply and return glycol temperature sensors.
3.5. Do not provide water or steam sensors for the non-glycol side of the heat exchanger.
E. AHUs
1. Dampers:
1.1. BAS shall have direct control over the economizer/mixed air dampers.
1.2. Unless mixed air dampers are required to modulate independently, all dampers should be
connected to one single analog output. Provide individual damper actuator feedbacks (AI).
1.3. For two-position dampers in 100% fresh air systems (Makeup Air Units), provide a single
point to start the fan. The signal shall open the dampers first and then the fan will then start
via a hard-wired interlock to a damper end-switch. Provide a damper open-status (DI) for
the intake damper and the exhaust damper, if applicable.
2. Additional sensors that are required:
2.1. Include an occupancy sensor for ERV units.
2.2. For systems with heat recovery or preheat in the fresh air intake duct, provide an averaging
temperature sensor between the pre-heating coil and the mixed air plenum.
3. Sensors that are not required:
3.1. Except for pool areas, humidity sensors are not required unless specifically requested by
TDSB.
3.2. If no dedicated heat exchanger is present, heating/cooling coil entering and leaving water
temperatures or steam pressure are not required.
3.3. Outdoor air temperature/intake temperature is not required for individual units.
3.4. Avoid the use of air flow sensors and flow switches unless integral to the design.
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TDSB BAS Design Guidelines Rev 1.3
4.
5.
6.
7.
3.5. Filter Status not required for any air filters.
3.6. No smoke detectors are required to be connected to the BAS.
3.7. Duct static pressure sensors are not required for constant volume units.
DX Cooling and Gas Heating:
4.1. DX Cooling compressors and gas burners require a status. This includes modulating gas
burners.
4.2. For packaged units that require a supply air temperature setpoint reset signal (i.e.
Engineered Air RTUs with CTRAC controllers), specify that the unit shall accept a separate
heating enable and cooling enable signal from the BAS. Heating and mechanical cooling
operation shall only be permitted when the respective enable signal from the BAS is
received. If the packaged unit only has modulating gas heating, a heating enable signal is
required.
4.3. If the BAS has control over the individual stages of heating or cooling, do not provide an
additional general heating enable/disable or cooling enable/disable.
4.4. For two-stage heating or cooling, provide BAS control and status over each individual stage.
If there are more than two heating or cooling stages, they are preferably controlled through
a reset signal as previously described.
Units Supplying Individual Zones:
5.1. For any AHUs supplying individual zones (Gyms, Auditoriums, Cafeterias, Libraries etc.)
served by pneumatically controlled perimeter heating, these pneumatic valves should be
replaced with electronic DDC valves and placed under BAS control.
5.2. For any AHUs supplying individual zones (Gyms, Auditoriums, Cafeterias, Libraries etc.),
include a space temperature and return air CO2 sensor. In addition to this, provide an
occupancy push button for gyms and occupancy sensors for auditoriums.
5.3. For AHUs supplying gyms with destratification fans, include the destratification fans on the
BAS.
Freezestats:
6.1. For units with fresh air, all water and glycol heating coils require a freezestat connected to
the BAS placed immediately after the heating coil. The freezestat should be interlocked with
the supply fan.
6.2. Hot water coils with mixed air dampers should have a manual reset freezestat.
6.3. 100% fresh air units and glycol coils should have an auto-reset freezestat.
6.4. For gas heating units, do not provide a freezestat.
For AHUs with an array of multiple supply or return fans:
7.1. Provide a single start/top for all the fans in the array
7.2. Provide individual statuses for the fans.
F. Chillers
1. Essential points for chiller plants are – start/stop, status, and supply water setpoint temperature
reset (AO). These points shall be hard-wired from the BAS.
2. For larger chiller plants, to monitor additional operating parameters, provide a BACnet interface
to chillers. This is not required for smaller plants.
3. Cooling tower fan operation should be under BAS control.
G. Emergency Cooling Centres
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TDSB BAS Design Guidelines Rev 1.3
1. Provide a keyswitch for the caretaker to initiate cooling operation.
2. Include a note on the drawings for:
2.1. AC unit OEM thermostat installation:
.1 Install at a height of 6’6” (2m) in gyms
.2 Set to 23 °C
.3 Lock keypad to ensure no settings are adjusted
.4 Set to only be Enabled/Disabled by BAS
.5 Install tamper proof guard
.6 Ensure it maintains settings during power outage and does not reset
2.2. AC unit OEM central controller installation:
.1 Install in mechanical room or storage room, preferably close to BAS panel.
.2 Install in a tamper proof enclosure
.3 Provide a lamacoid label saying “Do not adjust settings on this controller”
H. Pneumatic to DDC Upgrades
1. All obsolete BAS control modules must be replaced.
2. Provide a network architecture showing existing modules which can remain and existing
modules that require replacement.
3. All pneumatic valves and actuators must be replaced with electronic DDC valves and actuators.
3.1. For unoccupied spaces such as mechanical rooms, storage rooms or individual washrooms,
stand-alone controls such as line-voltage thermostats with tamper-proof cover or selfcontrolled valves are acceptable.
4. Provide comprehensive schematics for all systems reflecting current site conditions
5. Provide hot water heating, chilled water and ventilation system summaries where required.
6. Provide schedule for terminal equipment such as VAV boxes (min/max flows)
7. Provide floor plans showing the locations of all BAS devices (new and retained) and controlled
equipment
8. Provide separate demolition and new installation drawings
9. Removing entire compressed air system and exposed pneumatic piping is part of the scope.
9.1. This includes removing the air compressor and dryer.
9.2. Confirm if there are pneumatic safety devices (i.e. fire heads in AHUs) that will be impacted
by the demolition of the compressed air system.
9.3. Identify any miscellaneous pneumatic control devices not on BAS and replace with an
electronic equivalent.
10. All pneumatic thermostats must be removed. Provide stainless steel plates to cover openings
and make good.
11. All pneumatic lines must be capped during demolition work.
12. All new installed valves require sizing information including pipe size and design flow in a
schedule.
13. All new installed actuators require sizing information including duct size in a schedule.
14. Include itemized price for:
14.1. Isolation valves, strainers and balancing valves for each new control valve.
14.2. Flushing and chemical treatment of hot water heating and chilled water systems.
15. TAB:
15.1. VAV systems require air balancing.
15.2. Provide hydronic balancing wherever new balancing valves are provided.
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TDSB BAS Design Guidelines Rev 1.3
I. Domestic Hot Water
1. System should contain recirc pump start/stop (DO), pump status (AI) and DHW supply water
temperature (AI). Do not include any other points.
J. Shop Drawings Review
1. TDSB shall review the controls component of the tender package prior to tendering.
2. TDSB shall review contractor shop drawing submittals prior to final review and acceptance by
the consultant.
K. VFDs and Starters
1. Control Points
1.1. Unless stated otherwise, all VFDs shall have the following hardwired control points:
• VFD Start/Stop (BO)
• VFD Status (AI)
• VFD Speed Modulation (AO)
• VFD Speed Feedback (AI)
1.2. Additional points are not necessary (alarm, power, runtime etc.)
1.3. This applies whether it is variable volume or constant volume for both pumps and fans.
1.4. BACnet connection is not required for VFDs.
2. Pumps – Primary Loops
2.1. Pumps serving loops with equipment that have minimum water flow requirements (e.g.
boilers, chillers, cooling towers) shall be provided with magnetic starters and not VFDs or
ECMs.
3. Pumps – Secondary Loops
3.1. Variable Volume Pumps
.1 Low flow conditions can exist for systems with exclusive 2-way valves. To ensure this
does not happen, three methods can be used:
• Do not include control valves for UHs and FFHs to let them run wild
• Include some three-way valves to allow a minimum amount of water to bypass
• Include a bypass valve
One of these methods must be in place. Removing control valves from terminal devices
which pose a low risk of overheating is preferable.
.2 For variable volume flow applications in secondary loops, VFDs shall be used to control
pumps. A note on the drawings shall state: “Differential pressure sensors should be
installed across the supply/return lines in a serviceable location at the exit point of
boiler room. Final location to be confirmed by TDSB.”
3.2. Constant Volume Pumps
.1 VFDs are acceptable for constant volume pumps serving secondary loops, for example, a
loop with all three-way valves or pumping into a heat exchanger. The VFDs will be
programmed to a constant speed determined by the water balancer.
3.3. Sensor-less Pumps/Drives
.1 Sensor-less Pumps/Drives should not be used.
4. Fans
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TDSB BAS Design Guidelines Rev 1.3
4.1. VFDs shall be used for variable air volume applications, multi-speed fan applications or
where required by ASHRAE standards.
4.2. Fans in all other constant volume applications should be provided with a magnetic starter.
5. Starters shall be equipped with auxiliary contacts to satisfy interlocking and automatic control
requirements, “Hand-Off-Automatic” switches, pilot lights (green-On; red-Off), thermal
overloads, necessary fuses and control transformer (if required) for operation of all controls on
120V single phase.
L. Typical Controls Sequences – Boiler Plant
1. Heating Flag
1.1. The boiler plant shall be enabled when the heating flag is on. When the heating flag is on,
the graphics shall indicate that systems are in the winter mode. When the heating flag is
off, the graphics shall indicate that systems are in the summer mode.
1.2. The heating flag status shall be determined by the following conditions:
• Outdoor Air Temperature
• Month of the Year
• Lowest room space temperatures
1.3. The heating flag shall be programmed to operate as follows:
SHOULDER SEASON - MAY, JUNE, and SEPTEMBER:
Heating Flag
Occupied
Unoccupied
ON
OAT<10 °C or LTMP < 20 °C
OAT<4 °C or LTMP < 14 °C
OFF
OAT>12 °C and LTMP > 20.5 °C
OAT>6 °C and LTMP > 16 °C
SUMMER - JULY and AUGUST:
The Heating Flag is ‘OFF’.
WINTER - OCTOBER to APRIL:
Heating Flag
Occupied
Unoccupied
ON
OAT<13 °C or LTMP < 20 °C
OAT<8 °C or LTMP < 13 °C
OFF
OAT>15 °C and LTMP > 20.5 °C
OAT>10 °C and LTMP > 16 °C
2. Heating Plant Status Flag
2.1. The heating plant status flag determines whether air handling systems are allowed to
operate in the heating mode. The flag shall be on when all of the following conditions are
true:
• the primary heating supply water temperature is above 50 °C
• at least one heating pump status (serving air handlers) is on
3. Primary Heating Water Setpoint
3.1. The primary heating supply water temperature setpoint shall be 10 °C higher than the
secondary water temperature setpoint at all times. The minimum primary temperature
setpoint shall be 60 °C and the maximum shall be 82 °C.
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TDSB BAS Design Guidelines Rev 1.3
4. Boiler Control
4.1. For staging burners, the stages will enable based on the following schedule:
Stage
1
2
3
4
ON (SWT SP-SWT >)[°C]
5
4
3
2
OFF (SWT-SWT SP >)[°C]
5
4
3
2
Time Delay (min)
10
20
10
4.2. For modulating boilers, the boiler shall be enabled when the supply water temperature
drops 5°C (adjustable) below setpoint. During the initial 3 minutes (adjustable) of boiler
operation, the burner shall operate at low fire (0% command) and the P-I-D bias shall be
zero (error summing is disabled). Once this time has elapsed, modulation shall be controlled
by a P-I-D algorithm to maintain the supply water temperature setpoint. If at any time the
supply water temperature exceeds setpoint by more than 5 °C (adjustable) or exceeds 90 °C,
the boiler shall be disabled. The boiler modulation control shall be at minimum firing
position before the burner is shut off.
4.3. The lead boiler shall be alternated on the 1st and 16th day of each month. If three boilers
are present, the lead boiler shall be alternated on the 1st, 11th and 21st day of each month.
4.4. If the lead boiler is started and operating status is not detected within 10 minutes
(adjustable), then the lead boiler shall be regarded as “failed” and shall be removed from
the firing sequence. The lag boiler shall automatically be fired as the lead boiler. The start
command shall be maintained continuously on the failed boiler until a correct boiler status
is received. If this occurs, the boiler shall no longer be regarded as being failed and shall be
returned to operating as the lead boiler.
4.5. If the lead boiler has been operating continuously for 20 minutes (adjustable) or more and
the supply water temperature is still below setpoint, then the lag boiler shall be started.
4.6. The lead boiler circulation pump shall run continuously. If a lag boiler is required to operate,
then its respective circulation pump shall be started first. The lag boiler pump shall continue
to operate for a period of 3 minutes after the boiler is shut off.
4.7. Belly Pumps
.1 If the boiler is equipped with a belly pump to assist with boiler water destratification
and morning warm-up operation, then the belly pump shall be started when all of the
following conditions are true:
• The respective boiler is firing
• The primary return water temperature is below 55 °C
.2 The boiler belly pump shall stop when the pump has been running for at least 20
minutes and any of the following conditions are true:
• The respective boiler is off
• The primary return water temperature is above 65 °C and the pump has been
running for a minimum of 10 minutes
4.8. Primary (Unscheduled) Heating Water Pumps - The heating water pump providing
unscheduled heating water to the air handling systems shall start when any of the following
conditions is true:
• The outdoor air temperature is less than 1.5 °C.
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TDSB BAS Design Guidelines Rev 1.3
The heating plant status is on and any air handler (equipped with heating coils) fan
status is on.
All other times the pump shall be off.
4.9. Secondary Water Pumps
.1 When the heating flag is on, secondary pump control shall be enabled.
.2 The lead pump shall be alternated on the 1st and 16th day of each month.
.3 If the lead pump fails, the stand-by pump shall automatically start. If the lead pump
status is detected, then the stand-by pump shall stop.
.4 When the heating flag is off, all secondary pumps shall stop.
4.10. Secondary Heating Water (Perimeter Radiation)
.1 When the heating flag is on, the 3-way scheduled water control valve shall be
modulated to maintain the secondary supply water temperature setpoint.
.2 During occupied hours and the optimum heating start mode, the base secondary supply
water temperature shall be reset according to the outside air temperatures as follows:
•
MODE:
OCCUPIED
UNOCCUPIED
Outdoor Air (°C)
- 12
10
- 12
5
Supply Water (°C)
70
40
55
35
.3 During occupied hours and the optimum heating start mode, a variable offset between
7°C and 15°C (calculated by a P-I-D algorithm) shall be added to the base secondary
supply water temperature setpoint whenever the average classroom temperature is
below the occupied space heating setpoint temperature (20°C). The maximum
secondary water temperature shall not exceed 88°C at any time.
.4 During the unoccupied mode the 3-way control valve shall modulate to maintain the
lowest space temperature above the unoccupied space temperature setpoint (14°C).
The maximum secondary water temperature shall not exceed 60 °C at anytime.
.5 At any time when the 3-way valve is open to supply heat to the building, to protect the
boilers from thermal shock and flue gas condensation, the position of the 3-way valve
shall be proportionally modulated by a P-I-D algorithm to a minimum position (40%
adjustable) whenever the primary return water temperature falls below 50°C.
4.11. Optimum Heating Start
.1 The optimum heating start program shall start occupied operation of the 3-way heating
valve before the actual scheduled start of the occupied mode in order to raise the
lowest classroom space temperature to the occupied heating setpoint.
.2 The optimum heating start program shall commence a maximum of 3 hours (adjustable)
prior to the start of the scheduled occupancy time. The actual optimum start time each
day shall vary according to the outdoor air temperature, the coldest classroom
temperature and the measured heating plant capacity.
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TDSB BAS Design Guidelines Rev 1.3
M. Typical Controls Sequences – AHU
1. General
1.1. All setpoints shall be adjustable.
1.2. The unit shall receive a heating or cooling mode signal from the boiler plant and chiller
plants respectively.
1.3. The unit shall receive a heating fail signal from the boiler plant.
2. Occupancy Modes
2.1. Occupied Mode
.1 The unit will be in occupied mode based on a time of day schedule controlled by the
caretaker.
2.2. Night Setback
.1 Night setback shall be enabled when the associated space temperature drops below the
unoccupied space setpoint of 14 °C. The BAS shall cycle the AHU to maintain space
temperature at unoccupied setpoint. The mixed air dampers shall remain closed.
2.3. Optimal Heating Start
.1 The BAS shall enable the AHU up to 3 hours before occupancy to achieve occupied
setpoint when occupancy starts. The mixed air dampers shall be closed.
2.4. Occupancy Override
.1 For units supplying gyms, the BAS shall enable the unit for one hour if the local
pushbutton is pressed during unoccupied hours.
2.5. Occupancy Mild Setback
.1 For units supplying auditoriums, the BAS shall monitor space occupancy. If no occupancy
is detected for at least 10 minutes, the BAS shall disable the unit and cycle the fan to
maintain setback heating (-1.5 °C) and cooling (+1.5 °C) space temperature setpoints.
The mixed air dampers shall remain closed during occupancy setback.
3. System Start-up
3.1. The unit shall be enabled during occupied hours, night setback, optimal heating start or
occupancy override.
3.2. The BAS shall command the return fan on. Once status is confirmed and following a 1minute time delay, the BAS shall start the supply fan.
4. Fan Shutdown
4.1. The BAS shall shut down the fan under the following conditions:
• Unoccupied mode (night setback and optimal heating start are inactive)
• The building is unoccupied (i.e. the surveillance system is armed)
• Occupancy Mild Setback
• Freezestat trip. Supply Fan shuts down, return fan remains on.
• Heating Fail signal from boiler plant
• A low supply air temperature condition (see alarm conditions). The unit shuts down
and the heating valve is commanded 100% open. After 1 hour, the unit restarts and
the cycle is repeated if the condition is still present.
5. Fan Modulation
5.1. For variable volume air systems the BAS will modulate the fan to maintain the supply air
pressure at setpoint as determined by the air balancer.
6. Heating and Cooling Modes
6.1. Heating Mode
.1 When the boiler plant is enabled, the unit shall be in heating mode.
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TDSB BAS Design Guidelines Rev 1.3
6.2. Free Cooling Mode
.1 When the heating plant is disabled and the return air temperature is at least 2 °C below
the outdoor air temperature, the unit shall be in free cooling mode.
6.3. Mechanical Cooling Mode
.1 For DX Cooling, mechanical cooling mode will be enabled under the following
conditions:
• The heating plant is disabled
• The outdoor air temperature is above 19 °C.
• The space temperature is greater (+0.5°C) than the cooling setpoint (24 °C).
.2 For cooling through a chilled water coil, mechanical cooling will be enabled when the
chiller plant is on.
6.4. Emergency Cooling Mode
.1 The BAS shall enable emergency cooling when mechanical cooling is enabled for DX
cooling and the emergency cooling key-switch is activated during occupied hours.
7. Zone Temperature Demand
7.1. For units serving single zones, the zone temperature demand will be based on the space
temperature. For units serving multiple zones, the zone temperature demand will be based
on the return air temperature. The BAS shall calculate a Heating Demand % and a Cooling
Demand % from the zone through a PID algorithm. The zone temperature setpoints shall be
determined according to the following schedule:
Heating Setpoint
Cooling Setpoint
Free Cooling Setpoint
21 °C
24 °C
23 °C
8. Supply Air Temperature Setpoints
8.1. For units with modulating heating or cooling controls, the BAS shall adjust the supply air
temperature setpoints between the minimum and maximum value based on the zone
temperature demand. The BAS shall reset the supply air setpoint based on the system mode
according to the following schedule:
Mode
Heating
Minimum SAT SP (°C)
19 (16 for Gym/Auditorium/Café)
Maximum SAT SP (°C)
32 (unit as heat source)
24 (unit provides ventilation)
24
24
Free Cooling 16
Cooling
13
9. Heating
9.1. Heating Valve
.1 When the unit is running during heating mode, the BAS shall modulate the heating valve
to maintain supply air temperature at setpoint.
.2 When the unit is off during heating mode, the BAS shall modulate the valve to maintain
the mixed air temperature at 8 °C.
.3 The heating valve shall be commanded to 100% open when there is no heat available
from boiler plant or during low supply air temperature mode.
9.2. Face/Bypass Damper
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TDSB BAS Design Guidelines Rev 1.3
.1 When there is a heating valve and a face/bypass damper, the BAS will calculate a
heating PID value and modulate the heating valve and face/bypass damper according to
the following schedule:
Heating Demand (%)
0
50
100
Heating Valve Mod (%)
0
100
100
Face/Bypass Damper Mod (%)
0
0
100
.2
9.3. Gas Heating
.1 The BAS shall cycle the heating to maintain the space temperature at heating setpoint.
10. Cooling
10.1. Cooling Valve - During cooling mode when the supply fan is on, the cooling valve shall
modulate to maintain the supply air temperature at setpoint. All other times, the cooling
valve shall be closed.
10.2. DX Cooling - The BAS shall cycle the cooling to maintain space temperature at cooling
setpoint.
11. Mixed Air Dampers
11.1. “Mixed air dampers” refers to the combination of the fresh, return and exhaust air
dampers. Closed position means that the fresh air and exhaust air dampers are closed while
the return air damper is open. Open position means that the fresh air and exhaust air
dampers are open while the return air damper is closed.
11.2. Damper Close - The mixed air dampers shall close under the following conditions:
• The unit is off.
• The zone temperature is 2 °C below the heating setpoint during the heating season.
• The unit is unoccupied (including night setback and optimal heating start).
11.3. Fresh Air Percentage Calculation
.1 If |OAT-RAT|> 3 °C, the BAS shall calculate the fresh air % based on the following
formula:
Fresh Air % = (RAT-MAT)/(RAT-OAT) * 100
.2 If |OAT-RAT|< 3 °, the fresh air percentage shall be equal to the damper modulation %.
11.4. Fresh Air % Setpoint
.1 When controlling the fresh air % from the return air CO2 level, the fresh air setpoint
shall be calculated from the following schedule:
CO2 (ppm)
800
1000
Fresh Air % Heating
0
50
Fresh Air % Cooling/Free Cooling 0
75
.2 For non-CO2 applications, the fresh air % setpoint shall be set to a minimum value of
20%.
11.5. Mixed Air Temperature Setpoint
.1 The BAS shall calculate the mixed air temperature setpoint based on the following
formula:
MAT SP = RAT – Fresh Air % SP * (RAT-OAT)
.2 The minimum MAT SP shall be 12 °C.
11.6. Damper Modulation
12
TDSB BAS Design Guidelines Rev 1.3
.1 When the OAT is three degrees below the RAT, the BAS shall modulate the dampers to
maintain the mixed air temperature at setpoint.
.2 In other cases, the BAS will open the dampers to a fixed value based on the fresh air %
setpoint.
.3 During Free Cooling mode, the BAS shall modulate the dampers to maintain the mixed
air temperature at the lesser of either the mixed air temperature setpoint or the supply
air temperature setpoint.
12. Freezestat
12.1. If the freezestat trips, the BAS shall command the supply fan off and command the
heating valve to maintain a fixed plenum temperature. The return fan will continue to
operate.
13. Alarms
13.1. The BAS shall initiate alarms for the following conditions:
• Supply fan or return fan fail.
• Freezestat Trip
• CO2 levels are greater than 1500 ppm or less than 200 ppm
• Temperature Alarm – Space temperature < 10 °C
• Energy Cool Alarm – Space temperature < 22.5 °C when OAT > 21 °C
• Energy Heat Alarm – space temperature > 24 °C when OAT < 5 °C
• Supply Air Temperature Fail – OAT < 10C, SAT < 10 °C for a minimum of 3 minutes
and the supply fan running for a minimum of 5 minutes.
• Low Supply Air Temperature – OAT < 10 ° and SAT <10°C for 3 minutes and the
supply fan is running for 3 minutes.
• Mixed Air Temperature – MAT < 8°C for 3 minutes and the supply fan running for a
minimum of 5 minutes.
• Runtime Alarm – Fan status is on for more than 72 hours per week.
N. Typical Controls Sequences – Zone Heating and Cooling
1. Setpoints:
1.1. Space Heating setpoint will be 21 °C in occupied mode and 14 °C in unoccupied.
1.2. Space Cooling setpoint will be 24 °C in occupied mode. There will be no cooling in
unoccupied mode.
2. Controls:
2.1. The BAS will modulate the heating valve or cycle the heating to maintain space temperature
at heating setpoint.
2.2. The BAS will cycle the cooling to maintain space temperature at cooling setpoint
O. Typical Controls Schematics
13
TDSB BAS Design Guidelines Rev 1.3
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734
Toronto
District
School
Board
Facility Services Department
Design & Construction Division
15 Oakburn Cres. Toronto, Ontario M2N 2T5
t. 416-395-4588 / f. 416-395-9734