Sequences of Operation for Common HVAC Systems

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PAGE

I. PURPOSE ..................................................................................................................... 1

II. SCOPE .......................................................................................................................... 2

III. CONTENTS OF THIS PACKAGE ............................................................................. 2

Using the Sequences in this Package .............................................................................. 3

IV. USERS OF A CONTROL SEQUENCE ...................................................................... 5

V. APPROACHES TO SPECIFYING A SEQUENCE .................................................. 6

Structure of a Sequence of Operation: Modes vs. Components...................................... 6

Levelof Detail: Operation vs. Algorithms...................................................................... 8

IV. SEQUENCES OF CONTROL

A. CONSTANT VOLUME AIR HANDLING UNITS

1. Supply Fan

a. CV 1A1 Chilled Water Coil, HW Coil, DCV........................... 9

b. CV 1B1 Chilled Water Coil, 2-Stage Heat, Economizer ........ 15

c. CV 1C1 DX Coil, HW Coil, Economizer ............................... 21

d. CV 1D1 DX Coil, 2-Stage Heat No Economizer..................... 27

2. Supply and Return Fans

a. CV 2A1 Chilled Water Coil, HW Coil, Economizer

OA Flow Control ..................................................................... 32

b. CV 2B1 Chilled Water Coil, 2-Stage Heat, Economizer ........ 38

c. CV 2C1 DX Coil, HW Coil, Economizer ............................... 44

d. CV 2D1 DX Coil, 2-Stage Heat, Economizer ........................ 51

3. Fan Coil Units

a. FC 1A Fan Coil Unit................................................................. 57

October 2005 ASHRAE 2005 Page i


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B. VARIABLE VOLUME AIR HANDLING UNITS

1. Supply Fans

a. Chilled Water Coil, HW Coil, Economizer

1) VAV 1A1 Duct Static Reset, SA Temp

Reset on Cooling Demand, No Space

Pressure Control, Demand Controlled

Ventilation, Differential Dry Bulb

Economizer ............................................................... 61

b. DX Coil, 2-Stage Heat, Economizer

1) VAV 1D1 Fixed Duct Static Setpoint,

Constant SA, No Space Pressure Control,

Measured Minimum Airflow, No

Economizer ............................................................... 67

2. Supply and Return Fans

a. Chilled Water Coil, Hot Water Coil, Economizer


Reset on Cooling Demand, Space Static

controlled with EA Damper & Return Fan,

Demand Controlled Ventilation, Differential

Enthalpy Economizer................................................... 72

2) VAV 2A2 Duct Static Reset, Constant SA,

Airflow Tracking Measured Minimum

Airflow, Differential Dry Bulb Economizer..................................................................................... 79

b. Chilled Water Coil, 4-Stage Heat, Economizer

1) VAV 2B1 Fixed Duct Static Setpoint, SA

Temp Reset on Cooling Demand, Space

Static controlled with EA Damper & Return

Fan, Minimum damper position for Min OA

Airflow, Differential Dry Bulb Economizer..................................................................................... 85

2) VAV 2B2 Duct Static Reset, SA Temp



Min OA controlled with Plenum Pressure,Differential Enthalpy Economizer ............................ 91

c. 4 Stage DX Coil, Hot Water Coil, Economizer

1) VAV 2C1 Duct Static Reset, SA Temp



Measured Minimum Airflow, Fixed Dry

Bulb Economizer......................................................... 97

October 2005 ASHRAE 2005 Page ii


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2) VAV 2C2 Fixed Duct Static Setpoint,

Constant SA Temperature, Space Static


Min OA controlled with Plenum Pressure,

Differential Dry Bulb Economizer ........................... 103

d. 4 Stage DX Coil, 4-Stage Heat, Economizer


Constant SA Temperature, Static controlled

with EA Damper & Return Fan, Measured

Minimum Airflow, Differential Dry Bulb

Economizer ............................................................... 109

2) VAV 2D2 Fixed Duct Static Setpoint, SA

Temp Reset on Cooling Demand, Fan

Tracking, Measured Minimum Airflow,

Differential Dry Bulb Economizer ........................... 115

3. Supply, Return and OA Injection Fans

a. Chilled Water coil, Hot Water Coil, Economizer

1) VAV 3A1 Fixed Duct Static Setpoint,

Constant SA Temperature, Space Static


Min OA controlled with Plenum Pressure,

Differential Dry Bulb Economizer ............................ 121

b. 4-Stage DX Coil, Hot Water Coil, Economizer

1) VAV 3C1 Fixed Duct Static Setpoint, SA

Temp Reset on Cooling Demand, Exhaust

Damper/Return Fan, Min OA ControlledWith Injection Fan, Differential Enthalpy

Economizer ............................................................... 127

2) VAV 3C2 Fixed Duct Static Setpoint, SA

Temp Reset on Cooling Demand, Fan

Tracking, Min OA Controlled With

Injection Fan, Differential Dry BulbEconomizer ............................................................... 133

4. Supply and Relief Fans

a. Chilled Water Coil, Hot Water Coil, Economizer1) VAV 4A1 Duct Static Reset, SA Temp


controlled with EA Damper & Relief Fan,

Demand Controlled Ventilation, Differential

Dry Bulb Economizer ............................................... 139

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b. Chilled Water Coil, 4-Stage Heat, Economizer

1) VAV 4B1 Duct Static Reset, SA Temp



Measured Minimum Airflow, Dry Bulb

Economizer ............................................................... 145

c. 4-Stage DX Coil, Hot Water Coil, Economizer




Measured Minimum Airflow, Dry Bulb

Economizer ............................................................... 151

d. 4-Stage DX Coil, 4-Stage Heat, Economizer


Constant SA Temperature, Exhaust

Damper/Return Fan, Min OA controlled

with Plenum Pressure, Differential Dry Bulb

Economizer ............................................................... 158

5. Supply Fans, Relief Fans, and OA Injection Fans

a. Chilled Water Coil, Hot Water Coil, Economizer


Reset on Cooling Demand, Exhaust

Damper/Return Fan, Min OA Controlled

With Injection Fan, Differential Dry BulbEconomizer.................................................................. 164

b. Stage DX Coil, Hot Water Coil, Economizer


Reset on Cooling Demand, Exhaust

Damper/Return Fan, Min OA Controlled

With Injection Fan, Differential Dry BulbEconomizer ............................................................... 170

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I. PURPOSE

This document is intended to establish a common set of sequences for control of common HVAC

systems. It is expected that this set will be extended and modified both by ASHRAE and by users

to fit a variety of needs. A set of industry-accepted sequences will:

Provide a common language of terms and choices to consider in HVAC systems,

increase effectiveness of HVAC designers in specifying DDC systems,

improve the quality of specifications produced,

facilitate communication between specifiers and contractors,

increase efficiency of the contractors in the construction and commissioning process,

improve the functionality and energy efficiency of the DDC systems delivered, and

increase the understanding and familiarity with the operation of DDC/HVAC systems among

the building owners and operators.

Considering this set of purposes, the intended users include HVAC designers, control contractors,

commissioning agents, and building owners, operators, and maintenance technicians. Each user

is important, but the HVAC designer is the primary user; all the other users are obliged to work

with what the HVAC designer delivers.

This resource will aid HVAC designer in the development of control sequences by providing an

accurate, consistent, and well-organized starting point. It provides:

an effective specification format,

a common sequence that is frequently applicable or easily customizable to match a specific

application, and

a peer-reviewed specification of that sequence.

It does notsave the designer from:

deciding how the HVAC system must operate,

correctly applying codes and standards, or

designing to meet the end user's goals.

The designers retain all the responsibility implied by their role in the construction process.

II. SCOPE

This resource offers commonly accepted sequences for a variety of air handling units and

terminal units. There is no attempt here to cover every kind of HVAC unit. In some cases,

alternative sequences are presented; there is no attempt to cover all of the useable options.

In addition to the sequences, this document offers suggestions for development and customizing

sequences of operation for a specific project. The examples presented here are well-founded

sequences for each type of equipment and leave the advanced or very special control schemes to

the consulting engineers and control contractors to provide as value added. These control

sequences are written for implementation using a DDC system.

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III. CONTENTS OF THIS PACKAGE

The control sequences in this document are presented with other parts of a control specification,

including a control schematic, object list, and mode table. These parts are needed to fully

communicate the operation and installation of the control system. The material in this document

represents a common application that should be tailored to match the actual system and the

operational requirements. Publishing a control sequence that does not match the system or meet

the users efficiency or operational requirements, while vastly entertaining to the contractors

field personnel, adds little to the construction effort.

The control schematic is a diagram of the system showing the relationships between equipment

and control components. The input/outputs to DDC are shown, as are any hardwired interlocks.

Often the control schematic is included in the contract drawings. Wherever the control schematic

appears, it is a key to communicating the system and the associated controls.

The object list defines the physical and virtual (software) points required for operation and

monitoring of the system. There are many formats in use for the object list. Some contain more

information than others. The format used in this document is best suited less complicated

projects.

The type of point is listed. Point types include analog inputs, binary inputs, pulse inputs, binary

outputs, and analog outputs. The specific implementation of the programming may dictate

additional virtual points not shown on the object list. For this reason, the designer may not be

able to list all of the virtual points. Also defined in the object list are trending, alarm, and

reporting graphic display requirements. In some more complex projects, it is preferred to

describe these functions in the text of the sequence rather than as entries in the object list. In this

package, the object list indicates which points are assigned alarms and the alarm thresholds.

Some alarms are tied to the system status. For example, when the air handler is in the unoccupied

mode, the supply air temperature may not need to be alarmed or different alarm limits may apply.Alarm thresholds can be established to track setpoints that are dynamically reset.

Each graphic upon which a point should appear is listed. Points can be assigned to more than one

graphic screen. Similarly, each trend log that should display a points data is listed. Points are

often assigned to multiple trend logs. Both graphic displays and trend logs may be created and

changed as needed as part of normal operations, but it is important to identify which points will

be made available for reporting even though they may not be initially assigned to a specific graphor trend log.

Any standard or custom reports that the point is assigned to are listed in the notes column. Any

other special requirements are listed in the notes column as well.

These sequences also include a mode table. The mode table summarizes the complete sequence of

operation indicating the states (open, closed, modulated to maintain 55F) that are expected when

the system is in different modes of operation (cooling, heating, fire, warm-up and others). Each

row in the table corresponds to a mechanical component in the system. Each column corresponds

to one of the operating modes of the system. Each cell in the table tells what the particular

component does in that mode. The table presents no new information. It briefly restates

information already delivered in the full-text sequence. As such, a specifier using a mode table

must take pains to ensure the table is consistent with the text. For users of the specification, the

clean, organized format of a table answers many questions more quickly and surely than re-



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reading the text. This applies to control programmers, commissioning agents, building operators,

and even the designer who needs to check the completeness of their own work.

Using the Sequences in this Package

In using the sequences in this publication, a thorough understanding of the actual system to be

controlled and the requirements of the user are required. With this information in hand, select a

system similar to the actual system and custom tailor the sequence to meet the goals and

requirements of the project. Some specific items to review are the location and quantity of smoke

detectors and other sensors.

Different codes have differing requirements. Some codes require detectors in the supply, and

some codes require detectors on the return. Many codes require both supply and return detection

over 15,000 cfm. Freeze protection is an important consideration from an equipment design and

control standpoint. Attention should be given to assuring that the freeze protection design is

appropriate to the climate. Duct static pressure safeties may be needed if, for example, there is a

fire damper located in the main ductwork that, when closed, would cause the duct static to rise

past the ducts pressure rating. Note that static pressure safeties do not react fast enough to

prevent duct damage if a large damper closes rapidly. The number of heating and or cooling

stages shown on the control diagram, sequences and object list should match the equipment.

The control sequences should be reviewed for compliance with any energy codes in effect for the

project. The owner should be involved in the review of the control sequences to assure they

conform to the facility standards and requirements.

Cutting and pasting the sequences in this manual with little or no thought will most likely result

in a system that does not fully meet anyones needs.

To simplify locating a control sequence that is applicable to a specific system, the sequences aregiven a designation. There are three broad heading categories: Constant Volume Air Handling

Units, Variable Volume Air Handling Units, and Terminal Units. For the air handling units

within each category, the sequences are given a unique number that corresponds to fan and coil

configuration of the unit.



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The designation of the control sequences is by equipment type. For example:

2 B X - 1 2 3 4 5

Economizer Type

1 None

2 Differential dry bulb

3 Dry bulb

4 Differential enthalpy

Minimum Outside Air Control

1 Fixed minimum damper

Position

2 Demand controlled ventilation

3 Measured OA flow

4 Based on inlet plenum pressure

5 Injection fanSpace Pressure Control

0 None

1 Exhaust damper/return fan

2 Fan tracking

3 Exhaust damper/relief fan

X Not applicable

Supply Air Temperature Algorithm

1 Fixed SA setpoint

2 SA varies to meet space setpoint

3 SA setpoint reset based on space temperature

4 SA temperature reset based on OA temperature5 SA reset on OA and cooling demand

S Controlled on space temperature

Supply Duct Static Pressure Control

1 Fixed static setpoint

2 Duct static reset based on VAV box demand

X Not applicable

Sequence Number 1, 2, 3, etc.

Coil Type

A Chilled water coil, heating water coil

B Chilled water coil, staged heat

C DX coil, heating water coilD DX coil, staged heat

Fan Type

1 Supply fan

2 Supply and return fans

3 Supply, return and injection fans

4 Supply and relief fans

5 Supply, relief and injection fans



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IV. USERS OF A CONTROL SEQUENCE

When preparing a control sequence, the author should keep in mind its multiple uses. The

following users depend on the sequence for the purposes described below. These are listed in

approximately chronological order, not in order of importance.

A. HVAC Designers. The designer should use the control sequence to assure that the

equipment is capable of carrying out the various steps without causing damage to the

equipment. Additionally, the sequence should be reviewed for compliance with indoor

air quality, comfort, energy conservation, and life safety requirements in relation to the

specific mechanical equipment. Integrating control system and the mechanical system

form the earliest stages of design will result in improved system operation and lower

construction costs.

B. Authorities Having Jurisdiction (typically Fire Departments and Building Departments)

may review the sequence as part of the permit process. They review the sequence to see

that the operation of the equipment complies with the minimum requirements set forth in

the energy conservation, mechanical, and life safety codes.

C. Control Contractors, including the Technicians and Programmers. These people

implement the specified sequence of operation. The control program will typically

include many details not specified in the sequence, such as hysteresis settings, alarm

delays, minimum on/off times, etc., but the end result must be that the equipment

operates as specified. Any settings not specified are left to the discretion of the

programmer, so it is important to include critical setpoints, interlocks, and safety settings

in the control sequence.

D. Commissioning Agents and Construction Project Managers. Part of acceptance testing is

ensuring the installed system operates as specified. Everyone involved in acceptancedepends on a clear sequence to support the decisions.

E. Building Operators. An operators job includes verifying and maintaining correct

operation of the equipment. This leads to frequent questions about what the building is

supposed to do. Operators also need to adjust setpoints, alarm limits, and other operating

parameters. To do this, they need to understand the effects of each adjustable number.

Operators count on finding this information in the sequence of operation.

F. Maintenance Technicians. During the operating life of the building, if a system does not

perform correctly, the person troubleshooting the problem must understand how the

system is supposed to work in order to identify the part that is not working. A well-

written sequence of operation is essential for commissioning and can be an invaluable aidto troubleshooting.

The sequence should be complete, that is, it should cover all modes of operation: occupied,

unoccupied, warm-up, cool-down, and emergency modes, including safety trip, fire, and smoke

modes. In a perfect world, the system will do exactly what the sequence describes, so prepare

carefully, you should get what you ask for.



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V. APPROACHES TO SPECIFYING A SEQUENCE

There are many valid approaches to describing a sequence. Those in this package all follow one style, but

a specifier needs to choose a style best accomplishes the goals of the project. Two aspects of that style

are discussed here.

Structure of a Sequence of Operation: Modes vs. Components

There are two basic methods of organizing a sequence of operation: by operating mode or by component.

In a sequence that is structured by operating mode, the major paragraphs each describe a single mode

such as occupied, unoccupied, and morning startup. The paragraph for one mode specifies operation of

every component of the system in that particular mode. As an example, here is a partial sequence for a

unit ventilator organized by operating mode:

The occupancy mode (Occupied or Unoccupied) shall be determined by the equipmentschedule. The start time shall be adjusted by an optimum start routine that starts the unit at

the latest possible time that insures the space temperature will be at the occupied setpointat the time of occupancy.

A. OCCUPIED MODE:1. The unit fan shall be energized.2. The heating coil valve, mixed air dampers, and cooling coil valve shall

modulate in sequence to maintain space temperature at the heating or coolingsetpoint. Simultaneous heating and cooling, including economizer cooling,shall not be allowed. When the outdoor air temperature is greater than thereturn air temperature, the OA dampers shall close to minimum position.

3. The OA damper shall not close below the minimum position required foroutdoor air ventilation.

B. UNOCCUPIED MODE1. The unit fan shall be de-energized unless activated by the optimum start

routine.2. The heating coil valve, mixed air dampers, and cooling coil valve shall close

completely unless activated by the optimum start routine. During optimumstart, the heating coil valve, mixed air dampers, and cooling coil valve shallmodulate in sequence to maintain space temperature at the heating or coolingsetpoint. Simultaneous heating and cooling, including economizer cooling,shall not be allowed. When the outdoor air temperature is greater than thespace temperature the OA dampers shall close to minimum position.

3. The OA damper shall be allowed to close completely. No minimum ventilationis required.

C. OPTIMUM START1.

In a sequence that is structured by component, the major paragraphs each describe a single component.

The paragraph for one component tells how it works in each operating mode. Here is a partial sequence

for the same unit ventilator, arranged by component:

A. RUN CONDITIONS: The unit shall be energized and the fan shall run under either ofthe following conditions:1. The space is occupied, as determined by the equipment schedule.



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2. An optimum start routine indicates the unit must run to bring the spacetemperature to the occupied setpoint by the time of occupancy.

B. OA DAMPER:

1. Economizer operation shall be enabled during occupied or optimum startconditions if the outdoor air temperature is less than the space temperature.When economizer operation is enabled, the OA damper shall modulate tomaintain the space at the cooling setpoint.

2. During occupied periods, the OA damper shall not close below the minimumposition required for outdoor air ventilation.

3. The OA damper shall close to its minimum position (if occupied) or closecompletely (during optimum start) whenever the heating coil is energized orwhenever the outdoor air temperature is greater than the space temperature.

4. The OA damper shall close completely whenever the freezestat trips.

C. COOLING COIL:1. During occupied or optimum start conditions, the cooling coil shall modulate to

maintain the space at the cooling setpoint. If economizer operation is enabled,the cooling coil shall not be enabled until the OA damper is at least 90% open.2. ...

Done correctly, both formats provide the same information. Sequences that are organized by operating

mode are generally easier to understand, because they describe how the entire system will operate under a

given set of conditions. The drawback to this format is that it can be difficult to program a controller

from this sequence, as details about how each component should operate are scattered throughout the

sequence. Sequences that are organized by component may be easier for a programmer to use because

most control programs are structured by component. Similarly, many technicians find the component

structure more useful as a troubleshooting tool because they are generally troubleshooting a specific

component. The question, why is the heating valve open, is easier to answer if all information aboutthe heating valve is contained in one section.

The decision of which format to use should primarily be determined by the intended use of the sequence.

If the intent is to explain operating concepts and highlight differences between the operating modes, the

sequence should be organized by operating mode. If the intent is to provide specific programminginstructions and to provide maintenance documentation, the component approach should be used. As a

secondary consideration, if the designer needs to provide sequences for multiple variations of a piece of

equipment (ex: unit ventilators with hot water heat, gas heat, or electric heat) the component approach

may be easier to produce since only the affected component needs to be rewritten.

Since the purpose of this document is to describe control sequences commonly used in HVAC systems,

the sequences will be arranged by operating mode. Sequences arranged by component shall be

considered the equivalent of the sequences in this document and are equally acceptable, provided they

implement the same control actions. Regardless of which format is used for the sequence text, the

completed sequence should include an object list, mode table, and control schematic.



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Level of Detail: Operation vs. Algorithms

A specifier also has to decide how much detail to write. Some specifications call out the calculations that

a DDC system must implement. Others indicate the required mechanical conditions and responses

without discussing calculations. The following examples illustrate the difference.

The chilled water valve and OA damper shall modulate in sequence to maintain thedischarge temperature at the setpoint."

"A PI feedback loop shall control the discharge temperature. As the PI output goes from 0to 40%, the OA damper shall modulate from minimum to fully open. As the PID outputgoes from 50 to 100%, the valve shall modulate from closed to fully open."

The first example allows any control program that achieves the desired mechanical result. The second

specifies exactly what control algorithm will be used. When the specification contains more detail, the

specifier takes more responsibility for the control system design, leaving the contractors with less

flexibility and less risk.

As in any aspect of specification, the goal is to allow all the flexibility that bidders need to mosteffectively meet the project goals, while ruling out products and practices that dont satisfy the needs.

The designer needs to choose the level of detail that maximizes chances of success on the project.

Although the level of detail is not directly related to the format, most operating mode sequences tend to

be concept oriented (ex: Heating coil valve, mixed air dampers, and cooling coil valve shall modulate in

sequence.), while the component approach is more likely to provide programming specifics (ex: The

cooling coil shall not be enabled until the OA damper is at least 90% open.)



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Sequences of Operation for Common HVAC SystemsCV Air Handler Supply Fan, Chilled Water Coil, HW Coil, Demand Controlled Ventilation

SECTION I DESCRIPTION OF EQUIPMENT

Sequence Designation: CV 1A1-XSX21

Quick Summary

SA Temp Control Reset Based on Space Temperature

Space Pressure Control None

Minimum OA Control Demand Controlled Ventilation

Humidification Yes

Dehumidification No

Economizer No Economizer

Morning Pre-Cooling Mechanical Cooling

A. OVERVIEW

This sequence of control describes the direct digital control (DDC) requirements for a simple

constant volume air handling system. These air handling units are typically in the 2,000 to

7,000 cfm range (4 to 12-ton) serving a single zone with a single exposure.

B. THINGS TO CONSIDER BEFORE APPLYING THIS SEQUENCE

This sequence uses Demand Control ventilation with a space CO2 sensor. There is no

measurement of outside air flow rate. The minimum OA flow rate is established by the

required outdoor air flow at design occupancy (Vot) and the required outdoor air flow with no

occupants (Vat). These two air flow rates must be shown in the contract documents.

ASHRAE Standard 62.1 describes these values in greater detail. The damper positions

corresponding to these two airflow rates are set by the balance contractor. The CO2

concentrations corresponding to the ambient level and the steady state concentration at the

design occupancy must also be shown. These values may be found in the ASHRAE 62.1

Handbook.

There is no outside air economizer in this unit. This is typical of units having a hydronic

(waterside) economizer, a humidified space or in certain climate zones. Relief air (if

required) needs to be provided since this unit has no relief provisions. ASHRAE Standard

90.1 requires economizers in many applications. See examples of units with economizer in

this section if this is a desired option. A return air damper or a manual balance damper may

be required in the return depending on the system layout and the outside air quantity.

Heating water coils are shown with normally open valves and cooling coils with normallyclosed valves. This convention is typical in cold climates and may be different in warm

climates. Actuators that fail in the current position may be considered for some applications

instead of the fail open/closed type. Edit the control drawing to reflect the actual system.

The humidifier may require hard-wired interlocks for airflow and high duct humidity. If the

equipment requires these interlocks, they should be shown on the system schematic.

No dehumidification sequence is provided. De humidification requires reheat capability

which is not included in this unit.



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The location and quantity of duct smoke detectors is regulated by code. Verify code

requirements and revise the system schematic accordingly.

An outside air temperature sensor is shown. This value may be available through the

network. Revise the system schematic if this sensor is not required.

C. SYSTEM SCHEMATIC



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D. CONTROL SYSTEM OBJECT LIST2

Tag Object Name Type Alarm Graphic Trend Notes

A-1 AHU-1 Space Temperature AI 60/801

AHU1 5 min Report 1A-2 AHU-1 CO2 Level AI 18001 AHU1 5 min Report 1

A-3 AHU-1 Supply Air Temperature AI 40/1001 AHU1 5 min Report 1

A-4 AHU-1 SA Humidity Level AI 801 AHU1 5 min Report 1

A-5 AHU-1 Humidifier Modulate AO

A-6 AHU-1 Supply Fan Status BI Fail AHU1 COV Report 1

A-7 AHU-1 Supply Fan Start/Stop BO AHU1 COV

A-8 AHU-1 CW Coil Valve Modulate AO AHU1 5 min

A-9 AHU-1 RA Humidity Level AI 20/701 AHU1 5 min Report 1

A-10 AHU-1 Low Temp Alarm BI Yes AHU1 COV Report 1

A-11 AHU-1 Return Air Temperature AI AHU1 5 min Report 1

A-12 AHU-1 HW Coil Valve Modulate AO AHU1 5 min

A-13 AHU-1 Mixed Air Temperature AI 35/1001 AHU1 5 min Report 1

A-14 AHU-1 Min OA Damper AO AHU1 5 min

A-15 AHU-1 Outside Air Temperature AI AHU1 5 min

A-16 AHU-1 Runtime AV 10,000 AHU1 5 min

A-17 AHU-1 Supply Air Setpoint AV AHU1 5 min Report 1

A-18 AHU-1 Supply Air Setpoint High AV AHU1

A-19 AHU-1 Supply Air Setpoint Low AV

A-20 AHU-1 Occ Space Setpoint AV AHU1

A-21 AHU-1 RA Humidity Setpoint AV

A-22 AHU-1 Unoccupied Space TempSetpoint

AV AHU1

A-23 AHU-1 Unocc SA Setpoint AV

A-24 AHU-1 Return Air CO2 Setpoint AV

A-25 AHU-1 OA Low Temp Protection

Setpoint

A-26 AHU-1 MA Low Temp

Protection Setpoint1 Lockout alarm when unit is de-energized. Provide 15-minute startup delay prior to enabling

alarm2 Not all virtual points are shown. Provide all points required for software operation.

SECTION II SEQUENCE OF OPERATION

The occupancy mode (Occupied or Unoccupied) shall be determined through a user-adjustable, graphical,

seven-day schedule with a holiday schedule.

Whenever the supply fan is de-energized, as sensed by the status switch, the outside and exhaust air

dampers shall be closed and the return air damper shall be open, the heating and cooling valves shall be

closed or positioned as described below and the humidifier shall be locked out.



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A. OCCUPIED MODE

1. The supply fan shall be energized.

2. There shall be separate heating and cooling space temperature setpoints with a 5F

deadband between the heating and cooling

3. The heating coil valve and cooling coil valve shall modulate in sequence to maintain

supply air temperature setpoint. There shall be a deadband between heating and cooling.

4. Minimum Outside Air: The minimum OA flow rate is established by the required

outdoor air flow with no occupants (Vat) and the required outdoor air flow at design

occupancy (Vot). The damper positions corresponding to these two airflow rates shall be

set in conjunction with the balance contractor. The OA damper shall modulate between

the no occupants position and the design occupancy position as the space CO2

concentration varies from 400 ppm (ambient) to 1,500 ppm (adjustable).

5. Supply air temperature setpoint shall be reset based on space temperature according to

the following reset schedule:

Supply Air

Temperature Setpoint

Space

Temperature

55F Setpoint +2F

85F Setpoint -2F

All parameters shall be independently adjustable.

6. The humidifier shall modulate to maintain return air humidity setpoint of 30%

(adjustable), subject to the duct high limit setpoint of 90% (adjustable). Humidificationshall be locked out whenever the fan is de-energized or the duct humidity exceeds the

high limit setpoint.

7. The software shall prevent:

a. The heating setpoint from exceeding the cooling setpoint minus 5F (i.e. the

minimum deadband shall be 5F);

b. The unoccupied heating setpoint from exceeding the occupied heating setpoint;

and the unoccupied cooling setpoint from being less than the occupied cooling

setpoint.

B. UNOCCUPIED MODE

1. Unoccupied Off: The supply fan shall be de-energized except when operation is called

for as described below. Outside air dampers and exhaust dampers shall be closed and

return air damper open. Heating and cooling valves shall be closed and humidifier

locked out.

2. Unoccupied OFF Coil Protection: When the supply fan is de-energized and the outside

air temperature is below the Outside Air Low Temperature Protection Setpoint of 35F

(adjustable) and the mixed air temperature is less than the Mixed Air Low Temperature

Protection Setpoint of 45F (adjustable), OR the Low Temperature Limit trips, then the



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heating coil valve shall cycle to maintain mixed air temperature protection setpoint of

45F.

When the outside air temperature is above the Outside Air Low Temperature Protection

Setpoint of 35F + deadband, or the mixed air temperature is greater than the Mixed Air

Low Temperature Protection Setpoint of 45F + deadband; the heating and cooling coil

valve shall be closed.

3. Unoccupied Setback: The supply fan shall cycle on with the outside and exhaust

dampers closed when the space temperature drops below the unoccupied space

temperature setpoint of 65F (adjustable). When the fan is energized, the heating shall

modulate to maintain supply air temperature setpoint of 95F (adjustable).

5. Morning Warm-up: If the space temperature is below the occupied temperature setpoint

and the outside air temperature is below 40F Morning Warm-up shall be initiated by the

optimum start program. The outside air and exhaust air dampers shall be closed and

return air damper open during the morning warm-up cycle. If the space temperature isbelow setpoint, the unit shall warm the space to setpoint by raising the unit supply

temperature to 95F (adjustable) until the space temperature equals the occupied space

temperature setpoint. If the space reaches the occupied space temperature setpoint before

occupancy, the system shuts off. If occupancy occurs before the space reaches the

heating setpoint, the system switches to occupied mode. Morning warm-up shall occur

only once in a day.

6. Morning Pre-cooling: If the space temperature is above the occupied space temperature

setpoint and the outside air temperature is above 70F, Morning Pre-Cooling shall be

initiated by the optimum start program. The outside air and exhaust air dampers shall be

closed during the Morning Pre-Cool cycle. The unit shall cool the space to setpoint by

lowering the unit supply air temperature setpoint to 55F until the space temperatureequals the occupied space temperature setpoint. If the space reaches the occupied space

temperature setpoint before occupancy, the system shuts off. If occupancy occurs before

the space temperature reaches the occupied space temperature setpoint, the system

switches to occupied mode. Morning Pre-Cool shall occur only once per day.

C. SAFETY SHUTDOWNS

1. Duct smoke detection, space smoke detection, and low temperature limit trips shall de-

energize the supply fan and close the outside air dampers. Manual reset of the tripped

device shall be required to restart the system.

2. When the OA temperature is below the Outside Air Low Temperature Protection Setpoint35F (adjustable) and the air handler has shut down in alarm, the heating and cooling

valves shall cycle as described previously in the unoccupied off coil protection mode.



18/180


SECTION III CONTROL MODE SUMMARY

Unoccupied

Device Occupied Off Setback Warm-

up

Pre-cooling Safeties

S Fan On Off Cycles On On Off

OA

Damper

Modulate to

maintain CO2

setpoint subject

to min position

Closed Closed Closed Closed Closed

HW

Valve

Modulate in

sequence with

CW valve

Cycle if OAT

< 35,

otherwise

closed

Modulate Modulate Closed Cycle if OAT


19/180

Sequences of Operation for Common HVAC SystemsCV Air Handler Supply Fan, Chilled Water Coil, Staged Heat, Economizer


Sequence Designation: CV 1B1-XSX12

Quick Summary

SA Temp Control Varies to Maintain Space Temp Setpoint


Minimum OA Control Fixed Minimum Position

Humidification None

Dehumidification None

Economizer Dry Bulb Differential Temperature

Morning Pre-Cooling Economizer Cooling

A. OVERVIEW

This sequence of control describes the direct digital control requirements for a simple constant

volume air handling system. These air handling units are typically in the 2,000 to 7,000 cfm

range (4 to 12-ton), serving a single zone with a single exposure.

B. THINGS TO CONSIDER BEFORE APPLYING THIS SEQUENCE:

There is no measurement of outside air volume. The minimum outside air flow rate is

established by the outside air damper minimum position set by the balance contractor. The

maximum outside air flowrate is determined by the outside air intake configuration.

A fixed minimum outside air volume is provided. This is useful in facilities with a consistent

number of people in the facility or a fixed exhaust requirement.

There are no humidification or de-humidification cycles.

In humid regions an enthalpy-based economizer may be desired.

Pumped coils may be desired for low temperature protection and turbulent flow through the

coil tubes. Pumped cooling coils lower the chilled water Delta T that may adversely affect

the chillers. Additional freeze protection strategies may be needed depending on climate.

A single space temperature setpoint controls the unit. This applies to units serving a single

space or units serving multiple spaces that have similar exposures and internal loads.

Cooling coils are shown with normally closed valves. This convention is typical in coldclimates and may be different in warm climates. Actuators that fail in the current position

may be considered for some applications instead of the fail open/closed type. Edit the control

drawing to reflect the actual system.

The location and quantity of duct smoke detectors is regulated by code. Verify coderequirements and revise the system schematic accordingly.





20/180


When operating in economizer mode, the return and exhaust air paths will be required to

handle up to 100% of the system airflow as circulated only by the pressure differential

between the space and outside, unless an alternative path is defined for relief air. To avoid

over pressurization of the space, the return air, exhaust air and/or relief air duct work and

accessories must be sized appropriately.

C. SYSTEM SCHEMATIC



21/180


D. CONTROL SYSTEM 02

Tag Object Name Type Alarm Graphic Trend NotesA-1 AHU-1 Space Temperature AI 65/801 AHU1 5 min Report 1


A-3 AHU-1 Supply Fan Status BI Fail AHU1 COV

A-4 AHU-1 Supply Fan Start/Stop BO AHU1 COV Report 1

A-5 AHU-1 CW Coil Valve Modulate AO AHU1 5 min



A-8 AHU-1 Stage 2 Heat Start/Stop BO AHU1 COV Report 1

A-9 AHU-1 Stage 1 Heat Start/Stop BO AHU1 COV Report 1

A-10 AHU-1 Mixed Air Temperature AI 35/1001 AHU1 5 min Report 1

A-11 AHU-1 Mixed Air Dampers AO AHU1 5 min


A-13 AHU-1 Run Time AV 10,000 AHU1 5 min


A-15 AHU-1 Mixed Air Low Temp

Setpoint

AV

A-16 AHU-1 Unoccupied Space Temp

Setpoint

AV AHU-1

A-17 AHU-1 Heating Interstage

Differential

AV

A-18 AHU-1 OA Damper Min Position AV

A-19 AHU-1 Warm-up OA Temp

Setpoint

AV

A-20 AHU-1 Pre-Cool OA Temp

Setpoint

AV

1 Lockout alarm when unit is de-energized. Provide 15-minute startup delay prior to enabling




seven-day schedule with holiday schedule.


dampers shall be closed and the return air damper shall be open, the cooling valve shall be closed or

positioned as described below, heating shall be de-energized or staging as described below.



22/180


A. OCCUPIED MODE


2. The outside air damper shall open to the predetermined minimum position. The OAdamper shall not close below the minimum position required for outside air ventilation.

This position shall be set in conjunction with the balance contractor.



4. The heating shall stage and the mixed air dampers and cooling coil valve shall modulate

in sequence to maintain space temperature setpoint. Provide deadband between heating

and economizer cooling setpoints. Heating shall stage off-low-high. High shall not be

energized unless low has been energized for at least 5 minutes or the supply air

temperature is more than 15F below setpoint. Provide a 2F (adjustable) inter-stage

differential for heating.

5. Economizer cooling is enabled whenever the outside air dry bulb is less than the return

air dry bulb minus differential. When the outside air dry bulb is greater than the return

air dry bulb, economizer cooling is disabled. When economizer cooling is enabled,

mixed air dampers will modulate to maintain space temperature setpoint. There shall be

a mixed air low limit function to modulate the mixed air dampers closed to prevent the

mixed air temperature from dropping below the mixed air low limit setpoint of 45F

(adjustable).

6. The heat stages shall be energized only when the supply fan is energized; the heaters

internal air flow and high temperature safeties are satisfied.






setpoint.

B. UNOCCUPIED MODE

1. Unoccupied Off: The supply fan shall be de-energized except when operation is calledfor as described below. Outside air dampers and exhaust dampers shall be closed and

return air damper open.


air temperature is below the Outside Air Low Temperature Protection Setpoint of 35 F


Protection Setpoint of 45F, OR the Low Temperature Limit trips, then open the cooling

coil valve 100%.





23/180


Low Temperature Protection Setpoint of 45F + deadband; the cooling coil valve shall be

closed.


dampers closed and return damper open when the space temperature drops below the

unoccupied space temperature setpoint of 65F (adjustable). When the fan is energized,

the heating shall stage off-low-high until the space temperature equals the unoccupied

space temperature setpoint.

4. Morning Warm-up: If the space temperature is below the occupied temperature setpoint

and the outside air temperature is below 40F (adjustable) Morning Warm-up shall be

initiated by the optimum start program. If the space temperature is below the occupied

space temperature setpoint, the supply fan shall energize, the outside and exhaust

dampers shall remain closed, the return air damper open, and the heating coil shall stage

off-low-high until the space temperature equals the occupied space temperature setpoint.If the space reaches the occupied space temperature setpoint before occupancy, the

system shuts off. If occupancy occurs before the space reaches the heating setpoint, thesystem switches to occupied mode. Morning warm-up shall occur only once in a day.

5. Morning Pre-cooling: Pre-cooling shall occur only during the summer months of May

through September. If space temperature exceeds the pre-cooling space temperature

setpoint, and the outside air temperature is below 60F, Morning Pre-cooling may begin.

The unit shall start in the morning pre-cool mode as determined by an optimum start

program at the latest possible time to have the space at the Pre-cooling space temperature

setpoint at occupancy time. The outside air, return and exhaust air dampers shall

modulate to provide 55F (adjustable) supply air until the space temperature falls below

the pre-cooling space temperature setpoint. Heating shall be disabled. If the space

reaches the pre-cooling setpoint before occupancy, the system shuts off. If occupancy

occurs before the space reaches the pre-cooling setpoint, the system switches to occupiedmode. Morning Pre-cooling shall occur only once in a day.

C. SAFETY SHUTDOWNS


energize the supply fan and close the outside air and exhaust air dampers. Manual reset

of the tripped device shall be required to restart the system.

2. When the OA temperature is below the outside air low temperature protection setpoint,

35F (adjustable), and the air handler has shut down in alarm, the heating and coolingvalves shall cycle as described in unoccupied mode.



24/180



UnoccupiedDevice Occupied Off Setback Warm

-up

Pre-Cooling Safeties

S fan On Off Cycles On On Off

OA

damper

Fixed min.

position

modulates when

economizer mode

is enabled.

Closed Closed Closed Closed or

modulates when

economizer

mode is

enabled.

Closed

RA

damper

Track opposite of

OA Damper

Open Open Open Open or tracks

opposite OA

damper

Open

EA

damper

Track OA

Damper

Closed Closed Closed Closed or tracks

OA damper

Closed

Heat Stage Off-Low-Hi

in sequence with

dampers and CW

valve

Off Stage Stage Off Off

CW

valve

Modulate in

sequence with

heat and dampers

Open If OAT


25/180

Sequences of Operation for Common HVAC SystemsCV Air Handler Supply Fan, DX Coil, HW Coil, Economizer


Sequence Designation: CV 1C1-XSX12

Quick Summary

SA Temp Control: Varies to Meet Space Setpoint

Space Pressure Control: None

Minimum OA Control: Fixed Minimum Position

Humidification: None

Dehumidification: None

Economizer: Dry Bulb Differential Temp Return Air


A. OVERVIEW


volume air handling system. These air handlers are typically in the 2,000 to 7,000 cfm range

(4 to 12-ton), serving a single zone with a single exposure.


There is no measurement of outside air volume. The minimum outside air flow rate is

established by the outside air damper minimum position set by the balance contractor. The

maximum outside air flowrate is determined by the outside air intake configuration.


number of people in the facility.



coil tubes. Additional freeze protection strategies may be needed depending on climate.


Control interlock wiring between the condensing unit and the evaporator should be identified

on the system schematic if the manufacturer requires it.

Heating water coils are shown with normally open valves. This convention is typical in cold

climates and may be different in warm climates. Actuators that fail in the current positionmay be considered for some applications instead of the fail open/closed type. Edit the control

drawing to reflect the actual system.

This sequence does not have an optimum start requirement. Optimum start can save energy

by starting equipment at the latest possible time to have the space at the occupied temperature

setpoint at the time of occupancy.





26/180


When operating in economizer mode, the return and exhaust air paths will be required to

handle up to 100% of the system airflow as circulated only by the pressure differential

between the space and outside, unless an alternative path is defined for relief air. To avoid

over pressurization of the space, the return air, exhaust air and/or relief air duct work and

accessories must be sized appropriately.



C. SYSTEM SCHEMATIC



27/180




A-1 AHU-1 Space Temperature AI 60/801 AHU1 5 min Report 1


A-3 AHU-1 Supply Fan Status BI Fail AHU1 COV

A-4 AHU-1 Supply Fan Start/Stop BO AHU1 COV

A-5 AHU-1 Cool Stage 1 Start/Stop BO AHU1 COV

A-6 AHU-1 Cool Stage 2 Start/Stop BO COV



A-9 AHU-1 HW Coil Valve Modulate AO AHU1 5 min

A-10 AHU-1 Mixed Air Temperature AI 35/1001 AHU1 5 min

A-11 AHU-1 Mixed Air Dampers AO AHU1 5 min


A-13 AHU-1 Runtime AV 10,000 AHU1 5 min

A-14 AHU-1 Occ Space Temperature

Setpoint

AV AHU1

A-15 AHU-1 Mixed Air Low Temp

Protection Setpoint

AV

A-16 AHU-1 Unoccupied Space Temp

Setpoint

AV AHU-1 5 min

A-17 AHU-1 Morning Warm-up SA

Temp Setpoint

AV

A-18 AHU-1 DX Cooling Lockout OA

Temp Setpoint for DX Cooling

Lockout

AV

A-19 AHU-1 OA Damper Min Position AV AHU-1 5 min

A-20 AHU-1 Warm-up OA Temp

Setpoint

AV

A-21 AHU-1 OA Low Temp Protection

Setpoint

AV


alarm2

Not all virtual points are shown. Provide all points required for software operation.


The occupancy mode (Occupied or Unoccupied) shall be determined through a user-adjustable, seven-day

schedule. Whenever the supply fan is de-energized, as sensed by the status switch, the outside and

exhaust air dampers shall be closed and the return air damper shall be open, the heating valve shall be

closed or positioned as described below. DX Cooling shall be de-energized.



28/180


A. OCCUPIED MODE


2. The outside air damper shall open to the predetermined minimum position. The outside

air damper shall not close below the minimum position required for outside air

ventilation. This position shall be set in conjunction with the balance contractor.



4. The heating coil valve and mixed air dampers shall modulate and the DX cooling shall

stage in sequence to maintain occupied space temperature setpoint. The DX unit shall

stage up or down if a steady temperature error exceeds 2F (adjustable). Provide

deadband between heating and economizer cooling setpoints.

5. Economizer cooling is enabled whenever the outside air dry bulb is less than the return

air dry bulb minus differential and the space temperature is above setpoint. When the

outside air dry bulb is greater than the return air dry bulb, economizer cooling is disabled.When the economizer cooling mode is enabled, the mixed air dampers shall modulate to

maintain the occupied space temperature setpoint. There shall be a mixed air low limit

function to modulate the mixed air dampers closed to prevent the mixed air temperature

from dropping below the mixed air low limit setpoint of 45F (adjustable).

6. DX Cooling:

a. If the outside air temperature is greater than the DX lock-out temperature and the

system is not in morning warm-up, DX cooling shall be enabled.

b. DX operation shall observe the following timing constraints:1) When a cooling stage is called to run, it will run for at least the DX

minimum on-time.

2) When a cooling stage cycles off, it will remain off for at least the DX

minimum off-time.

c. DX operation shall observe the following performance constraints

1) Under a steady partial load, if the system cycles, the cycling must be

limited to a single stage, while the others stay on or off.

2) Under a steady partial load, if the system stabilizes, the space

temperature error must be less than the DX temperature deadband.

d. Safety trips and loss of fan status shall override the time delays and de-energize

all cooling stages.






setpoint.



29/180


B. UNOCCUPIED MODE


for as described below. Outside air dampers and exhaust dampers shall be closed and

return air damper open.




Protection Setpoint of 45F (adjustable), OR the Low Temperature Limit trips, then the

heating coil valve shall cycle to maintain mixed air temperature of 45F (adjustable).



Low Temperature Protection Setpoint of 45F + deadband; the heating coil valve shall be

closed.


dampers closed and return damper open when the space temperature drops below the

unoccupied space temperature setpoint of 65F (adjustable). When the fan is energized,

the heating valve shall modulate to maintain supply air temperature setpoint of 95F

(adjustable).

4. Morning Warm-up: If the space is below the occupied temperature setpoint and the

outside air temperature is below 40F (adjustable) Morning Warm-up shall be initiated at

a predetermined time. The outside air dampers shall be closed during the morning

warm-up cycle. If the space temperature is below occupied space temperature setpoint,

the supply fan shall energize, the outside air and exhaust air dampers shall remain closed,

return air damper open, and the unit shall warm the space to setpoint by raising the unitsupply temperature to 95F (adjustable) until the space temperature equals the occupied

space temperature setpoint. If the space reaches the occupied space temperature setpoint

before occupancy, the system shuts off. If occupancy occurs before the space reaches the

heating setpoint, the system switches to occupied mode. Morning warm-up shall occur

only once in a day.

5. Morning Pre-cooling: Pre-cooling shall occur only during the summer months of May

through September. If space temperature exceeds the pre-cooling space temperature

setpoint, and the outside air temperature is below 60F, Morning pre-cooling may begin.


program at the latest possible time to have the space at the pre-cooling space temperature

setpoint at occupancy time. The outside air, return and exhaust air dampers shallmodulate to provide 55F (adjustable) supply air until the space temperature falls below

the pre-cooling space temperature setpoint. Heating and mechanical cooling shall be

disabled. If the space reaches the pre-cooling setpoint before occupancy, the system

shuts off. If occupancy occurs before the space reaches the pre-cooling setpoint, the

system switches to occupied mode. Morning Pre-cooling shall occur only once in a day.



30/180


C. SAFETY SHUTDOWNS


energize the supply fan and close the outside air and exhaust air dampers. Manual reset

of the tripped device shall be required to restart the system.

2. When the OA temperature is below the Outside Air Low Temperature Protection Setpoint

35F (adjustable) and the air handler has shut down in alarm, the heating and cooling

valves shall cycle as described in unoccupied mode.


Unoccupied

SafetiesDevice Occupied

Off Night

Setback

Warm-up Pre-Cooling

S Fan On Off Cycles On On Off

OA

Damper

Fixed Min position,

or Economizer

enabled

Closed Closed Closed Closed or

Economizer

enabled

Closed

RADamper

Track opposite of OAdamper

Open Open Open Trackopposite of

OA damper

Open

EA

Damper

Track OA damper Closed Closed Closed Track OA

damper

Closed

HW

Valve

Modulate in

sequence

with dampers and

DX

Cycle if

OAT < 35,

otherwise

closed

Modulate Modulate Off Cycle if

OAT < 35,

otherwise

closed

DX

Cooling

Stage Off-Low-Hi in

sequence with

dampers and heat

Off Off Off Closed Off



31/180

Sequences of Operation for Common HVAC SystemsCV Air Handler Supply Fan, DX Coil, Staged Heat, No Economizer


Sequence Designation: CV 1D1-XSX11

Quick Summary

SA Temp Control Varies to Maintain Space Temp Setpoint


Minimum OA Control Fixed Minimum Position

Humidification None

Dehumidification None

Economizer None

Morning Pre-Cooling Mechanical Cooling

A. OVERVIEW





There is no measurement of outside air volume. Outside airflow rate is set as the minimum

damper position by the balance contractor.


number of people in the facility or with fixed exhaust air requirements.

There is no outside air economizer in this unit. This is typical of units having a hydronic

(waterside) economizer, a humidified space or in certain climate zones. Relief air (if

required) needs to be provided since this unit has no relief provisions. ASHRAE Standard

90.1 requires economizers in many applications. See examples of units with economizer in

this section if this is a desired option. There are no humidification or de-humidification

cycles. A return air damper or a manual balance damper may be required in the return

depending on the system layout and the outside air quantity.

Morning pre-cooling with DX relies on the increased efficiency of the system when the

outside (condensing) temperatures are low. Different climate regions may effect the

economics morning pre-cooling using DX.

Control interlock wiring between the condensing unit and the evaporator should be identified

on the drawing if the manufacturer requires it.

Two stages of heating and cooling are shown. The system schematic and object list should be

modified to reflect the actual number of stages in the equipment.

Since there is no economizer cycle, DX cooling may be required to operate when the outside

temperature is low. If so, the condenser must be designed for low ambient operation.





32/180




C. SYSTEM SCHEMATIC



33/180




A-1 AHU-1 Space Temperature AI 60/801 AHU1 5 min Report 1A-2 AHU-1 Supply Air Temperature AI 40/1001 AHU1 5 min Report 1A-3 AHU-1 Return Air Temperature AI AHU1 5 min Report 1A-4 AHU-1 Supply Fan Status BI Yes AHU1 COV

A-5 AHU-1. Supply Fan Start/Stop BO AHU1 COV

A-6 AHU-1 Cool Stage 1 Start/Stop BO AHU1 COV

A-7 AHU-1 Cool Stage 2 Start/Stop BO


A-9 AHU-1 Heat Stage 2 Start/Stop BO AHU1 COV

A-10 AHU-1 Heat Stage 1 Start/Stop BO AHU1 COV

A-11 AHU-1 Mixed Air Temperature AI 35/1001 AHU1 5 minA-12 AHU-1 Min OA Damper BO AHU1 5 minA-13 AHU-1 Outside Air

Temperature

AI AHU1 5 minA-14 AHU 1 Runtime AV 10,000 AHU1

A-15 AHU-1 Space Setpoint AV AHU1


A-18 AHU-1 Mixed Air Setpoint AV

A-19 AHU-1 Unoccupied Setpoint AV

A-20 AHU-1 Unocc SA Setpoint AV

A-21 AHU-1 Morning Pre-Cool

Setpoint

AV





34/180






dampers shall be closed and the return air damper shall be open, DX cooling and all heating stages shall

be de-energized.

A. OCCUPIED MODE


2. The heating and the DX cooling shall stage in sequence to maintain space temperature

setpoint of 73F (adjustable). Heating shall stage off-low-high. High shall not be

energized unless low has been energized for at least 5 minutes or the space air

temperature is more than 8F (adjustable) below setpoint. Provide a 2F (adjustable)inter-stage differential for heating. DX cooling shall be enabled on a call for cooling,

only when supply fan status has been proven and whenever the heating is not active. The

DX unit shall stage up or down if a steady temperature error exceeds 2F (adjustable). If

the system cycles under a steady load, the controller shall be adjusted to limit cycling to a

single stage. Provide deadband between heating and cooling setpoints. There shall be an

adjustable on-off timer for each DX stage to prevent short cycling.



4. The OA damper shall be open to the minimum position required for outside air

ventilation. This position shall be set in conjunction with the balance contractor.

5. The heat stages shall be energized only when the supply fan is energized; the heaters

internal air flow and high temperature safeties are satisfied.

6. The outside and exhaust air dampers shall close and the return air damper shall open

when the unit is de-energized.




b. The unoccupied heating setpoint from exceeding occupied heating setpoint; and

unoccupied cooling setpoint from being less than the occupied cooling setpoint.

B. UNOCCUPIED MODE


for as described below. Outside air dampers and exhaust dampers shall be closed.


dampers closed when the space temperature drops below the unoccupied setpoint of 65F

(adjustable). When the fan is energized, the heating shall stage to maintain supply air

temperature setpoint of 95F (adjustable).



35/180


3. Morning Warm-up: If the space is below the occupied temperature setpoint and the

outdoor air temperature is below 40F (adjustable) Morning Warm-up shall be initiated

by the optimum start program. The optimum start program shall start the unit at the latest

possible time to reach the desired occupied space temperature setpoint at occupancy time

If the average space temperature is below the occupied space temperature setpoint, the

supply fan shall energize, the outside and exhaust dampers shall remain closed and the

heating coil shall stage to maintain supply air temperature setpoint of 95F (adjustable)

until the space temperature equals the occupied space temperature setpoint. If the space

reaches the occupied space temperature setpoint before occupancy, the system shuts off.

If occupancy occurs before the space reaches the heating setpoint, the system switches to

occupied mode. Morning warm-up shall occur only once in a day.

4. Morning Pre-cooling: If space temperature exceeds Pre-cooling space temperature

setpoint, and the outside air temperature is below 60F, Morning Pre-cooling may begin.


program at the latest possible time to have the space at the occupied setpoint at

occupancy time. The outside air damper shall be closed during the morning cool-down

cycle. The heating valve shall be closed. The unit shall cool the space with DX cooling

by lowering the unit supply temperature to 50F (adjustable) until the space temperature

falls below the pre-cooling space temperature setpoint. If the space reaches the pre-

cooling setpoint before occupancy, the system shuts off. If occupancy occurs before the

space reaches the pre-cooling setpoint, the system switches to occupied mode. Morning

cool-down shall occur only once in a day.

C. SAFETY SHUTDOWNS

Duct smoke detection, space smoke detection, and low temperature limit trips shall de-energize

the supply fan and close the outside air and exhaust air dampers. Manual reset of the tripped

device shall be required to restart the system.


Unoccupied

Device Occupied Off Night

Setback

Warm-

up

Pre-

Cooling

Safeties

S fan On Off Cycles On On Off

OA damper Open to minimum position Closed Closed Closed Open Closed

RA damper Closed to the minimum setting Open Open Open Closed Open

EA damper Open to minimum position Closed Closed Closed Open Closed

Heat Stage Off-Low-Hi in sequence

with dampers and DX

Off Stage Stage Off Off

DX

Cooling

Stage Off-Low-Hi in sequence

with dampers and heat

Off Off Off Closed Off



36/180

Sequences of Operation for Common HVAC SystemsCV Air Handler Supply Fan, Return Fan, Chilled Water Coil, HW Coil, Economizer


Sequence Designation: CV 2A1-XSX32

Quick Summary

SA Temp Control: Supply Air temperature reset

Space Pressure Control: None

Minimum OA Control: Active Flow Control

Humidification: None

Dehumidification: None

Economizer: Dry Bulb Differential Temp return Air


A. OVERVIEW






number of people in the facility or a fixed exhaust air requirement. The outside air volume is

actively measured and controlled.



coil tubes. Pumped cooling coils lower the chilled water Delta T that may adversely affect

the chillers. Additional freeze protection strategies may be needed depending on climate.


Heating water coils are shown with normally open valves and cooling coils with normallyclosed valves. This convention is typical in cold climates and may be different in warm

climates. Actuators that fail in the current position may be considered for some non-critical

applications instead of the fail open/closed type. Edit the control drawing to reflect the actual

system.

The location and quantity of duct smoke detectors is regulated by code. Verify coderequirements and revise the system schematic accordingly.



If the minimum OA volume is larger than the zone exhaust and exfiltration air volume a

defined path for the relief air is needed.



37/180


C. SYSTEM SCHEMATIC



38/180


D. CONTROL SYSTEM OBJECT LIST 2


A-1 AHU-1 Space Temperature AI 60/801

AHU1 5 min

Report 1A-2 AHU-1 Supply Air Temperature AI 40/1001 AHU1 5 min Report 1A-3 AHU-1 Supply Fan Status BI Fail AHU1 COVA-4 AHU-1 Supply Fan Start/Stop BO AHU1 COVA-5 AHU-1 CW Coil Valve Modulate AO AHU1 COVA-6 AHU-1 Low Temp Alarm BI Yes AHU1 COV Report 1A-7 AHU-1 HW Coil Valve Modulate AO AHU1 5 minA-8 AHU-1 Mixed Air Temperature AI 35/1001 AHU1 5 minA-9 AHU-1 Minimum OA Air Flow AI AHU1 5 minA-10 AHU-1 Minimum OA Damper

Modulate

AO

A-11 AHU-1 Mixed Air DamperModulate

AO


A-13 AHU-1 Return Fan Start/Stop DO

A-14 AHU-1Return Fan Status BI Fail AHU1 COV

A-15 AHU-1Return Air Temperature AI AHU1 5 min

A-16 AHU-1 Occ Space Temperature

Setpoint

AV AHU1

A-17 AHU-1 Unoccupied Space


AV

A-18 AHU-1 Supply Air Temp

Setpoint

AV AHU1

A-19 AHU-1 OA Min Flow Setpoint AV AHU1 Report

A-20 AHU-1 Outside Air Low

Temperature Protection Setpoint

AV AHU1 Report

A-21 AHU-1 Mixed Air Low

Temperature Protection Setpoint

AV AHU1 Report

A-22 AHU-1 Morning Warm-up OA


AV

A-23 AHU-1 Morning Pre-Cool OA

Temp Setpoint

AV

A-24 AHU-1 Run Time AV 10,000 AHU11 Lockout alarm when unit is de-energized. Provide 15-minute startup delay prior to enabling







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Whenever the supply fan is de-energized, as sensed by the status switch, the return fan shall be de-

energized and the maximum and minimum outside and exhaust air dampers shall be closed and the return

air damper shall be open, the heating and cooling valves shall be closed or positioned as described below.

A. OCCUPIED MODE

1. The supply fan and return fan shall be energized.

2. The minimum outside air damper shall slowly modulate open until the minimum outside

air flow setpoint is achieved.



4. The heating coil valve, mixed air dampers, and cooling coil valve shall modulate in

sequence to maintain supply air temperature setpoint. Supply air temperature setpoint

shall be reset based on space temperature according to the following reset schedule (Allparameters shall be independently adjustable.):

Supply Air


Space Temperature

55 F Setpoint +2 F

75 F Setpoint -2 F

All parameters independently adjustable

5. Economizer cooling is enabled whenever the outside air dry less than the return air dry

bulb. When the outside air dry bulb is greater than the return air dry bulb plus deadband,

economizer cooling is disabled. Provide deadband to prevent heating coil operation

whenever economizer cooling is enabled. There shall be a mixed air low limit function tomodulate the mixed air dampers closed to prevent the mixed air temperature from

dropping below the mixed air low limit setpoint of 45F (adjustable).


a. The heating setpoint from exceeding the cooling setpoint minus 5F (i.e., the




setpoint.

B. UNOCCUPIED MODE

1. Unoccupied Off: The supply fan and return fan shall be de-energized except when

operation is called for as described below. Minimum and maximum outside air dampers

and exhaust dampers shall be closed and return air damper shall be open.

2. Unoccupied OFF Coil Protection: When the supply fan is de-energized and the outdoor



Protection Setpoint of 45F (adjustable), OR the Low Temperature Limit trips; then the



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heating coil valve shall cycle to maintain mixed air temperature of 45F (adjustable) and

the chilled water valve shall be open.


Setpoint of 35F + deadband (adjustable), or the mixed air temperature is greater than the

Mixed Air Low Temperature Protection Setpoint of 45F + deadband; the heating and

cooling coil valves shall be closed.

Date post:	04-Jun-2018
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Sequences of Operation for Common HVAC Systems

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