Scenario 1. A building is served by a fan-coil system and a dedicated outdoor-air unit that cools the outdoor air to 70°F dry bulb during the cooling season, or heats the outdoor air to 68°F dry bulb during the heating season, before delivering the conditioned outdoor air directly to the individual spaces. (Note: In non-arid climates, this approach may not adequately dehumidify the outdoor air.)
■ When the outdoor dry-bulb temperature is greater than the cooling supply-air dry-bulb setpoint, the dedicated outdoor-air unit will cool the entering outdoor air to the cooling supply-air dry-bulb setpoint.
Table 4–5 Sample Scenarios Topic
Scenario 1 (page 46) Cool/Heat (Fixed Setpoints)
Scenario 2 (page 51) Dehumidify and Reheat/Heat (Fixed Setpoints) Scenario 3 (page 56) Dehumidify (Priority) or Cool/Heat (Optimized SADP) Scenario 4 (page 62) Dehumidify and Reheat/Heat (Optimized SADB))
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supply-air dry-bulb setpoint, the dedicated outdoor-air unit will heat the entering outdoor air to the heating supply-air dry-bulb setpoint.
This example will cover how to model the air-distribution system (steps 1–8), model the cooling and heating equipment (steps 9–
11), and assign the loads from the coils to the equipment (step 12).
1 Start by selecting Fan Coil as the system type.
2 On the Dedicated OA tab, select the type of dedicated ventilation unit to be modeled. In this example, the dedicated ventilation unit will supply air to spaces at a specific dry bulb. Therefore, Cool / Heat will be selected.
None – no dedicated ventilation unit
Cool / heat – a dedicated ventilation unit is used to cool the outdoor air to the user-input cooling dry bulb during the cooling season or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify (priority) or Cool / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (not reheated) during the cooling season or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify and Reheat / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (then reheat it to the user-input cooling dry bulb) during the cooling season or heat the outdoor air to the user-input heating dry bulb during the heating season.
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3 Select the control method for the unit. Because the dedicated ventilation cooling coil cools the outdoor air to the cooling supply-air dry bulb, or the dedicated ventilation heating coil heats the outdoor air to the heating supply-air dry bulb, Fixed Setpoints will be used.
4 Input the Cooling and Heating Design Setpoints. In this scenario, 70°F should be input for the cooling supply-air dry bulb, and 68°F for the heating supply-air dry bulb.
5 Select the schedule for the coils and fan in the dedicated outdoor-air unit.
Note: For additional information related to the other Control Methods, press F1 and click Control Method.
If the ventilation air is to be precooled, the Dedicated Ventilation Cooling Coil schedule defines the hours of available operation of the ventilation cooling coil. The optional ventilation cooling coil is available for any hour that this schedule reads 1 percent or greater.
If the ventilation air is to be preheated, the Dedicated Ventilation Heating Coil schedule defines the hours of available operation of the ventilation heating coil. The optional ventilation heating coil is available for any hour that this schedule reads 1 percent or greater.
The Optional ventilation fan schedule defines the hours that the ventilation unit can operate. If the Optional ventilation fan schedule reads 1 percent or greater, the fan is available that hour.
Note: If a custom schedule is created for the fan or coils, it is recommended to use values of 0 percent for hours off and 100 percent for hours available to run to avoid confusion.
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Dedicated outdoor-air systems 6 Select the dedicated
ventilation-deck location.
This tells TRACE 700 where to supply the preconditioned outdoor air. For this scenario, the outdoor air will be delivered directly to the spaces. As a result, Room Direct will be selected.
7 Select the level of the ventilation-deck location.
For this scenario, one large dedicated ventilation unit will condition the outdoor air for all of the rooms assigned to the fan-coil system, so the coils should be set at the System level.
outdoor air is mixed with the return air in the main unit(s).
Plenum – conditioned outdoor air is delivered to the plenum above the spaces.
Room Direct – conditioned outdoor air is delivered directly to the spaces. This can also be used to model the delivery of conditioned outdoor air to dual-duct VAV boxes where it mixes locally with recirculated return air.
System – The dedicated ventilation unit will be placed at the system level. It will pretreat the outdoor air for all of the rooms and zones assigned to the airside system. This is the most common choice for dedicated ventilation systems. The System Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Zone – Each zone (or room assigned directly to the system) will get a separate dedicated ventilation system. The Zone Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Room – Each room will get a separate dedicated ventilation system. The Room Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Same level as main cooling coil – The dedicated ventilation unit will be placed at the same level as the main cooling coil. The System Component Selection report should be used to size the dedicated ventilation unit.
Same level as main heating coil – The dedicated ventilation unit will be placed at the same level as the main heating coil. The System Component Selection report should be used to size the dedicated ventilation unit.
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8 On the Fans tab, input the fan type and the total static pressure for the primary fan (the fans in the fan-coil units) and the optional ventilation fan (the fan in the dedicated ventilation unit).
Next, define the cooling and heating plants represented by the fan-coil system and the rooftop air conditioner:
9 Add two new cooling plants and two new heating plants to the Configuration pane.
10Drag the appropriate icons from the Equipment Category section to define each plant.
11To finish defining this equipment, enter the information from Table 4–6 on page 4–51 on the appropriate equipment tab.
Finally, assign the coil loads of the air-distribution system to the proper cooling and heating plants:
12Drag each coil in the Unassigned Systems/
Coils pane to the appropriate plant in the Systems and Plants pane.
The illustration labeled After shows the completed assignments.
For cooling, use water-cooled chiller and air-cooled unitary.
For heating, use boiler and gas-fired heat exchanger.
Before…
After…
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Scenario 2. A building is served by a water-source heat pump (WSHP) system and a dedicated outdoor-air unit that delivers conditioned outdoor air to the individual heat pumps. During the cooling season, the dedicated outdoor-air unit dehumidifies the outdoor air to 55°F dew point and then reheats it to a “neutral”
70°F dry bulb. During the heating season, the dedicated unit heats the outdoor air to 68°F dry bulb.
■ When the outdoor dew point is greater than the cooling supply-air dew point setpoint, the dedicated outdoor-air unit will dehumidify the entering outdoor air to the cooling supply-air dew point setpoint, then reheat it to the cooling supply-air dry-bulb setpoint.
■ When the outdoor dew point is less than the cooling supply-air dew point setpoint and the outdoor dry-bulb temperature is greater than the cooling supply-air dry-bulb setpoint, the
dedicated outdoor-air unit will cool the entering outdoor air to the cooling supply-air dry-bulb setpoint.
■ When the outdoor dew point is less than the cooling supply-air dew point setpoint and the outdoor dry-bulb temperature is less than the cooling supply-air dry-bulb setpoint, the dedicated outdoor-air unit will heat the entering outdoor air to the heating supply-air dry-bulb setpoint.
This example will cover how to model the air-distribution system (steps 1–8), model the cooling and heating equipment (steps 9–
11), and assign the loads from the coils to the equipment (step 12).
Table 4–6 Equipment types
Cooling Equipment tab Heating Equipment tab Water-cooled chiller 2-stage centrifugal gas-fired hot water
boiler Air-cooled unitary split system
RAUC-20+ ton scroll
rooftop gas heat
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1 Start by selecting Water source heat pump as the system type.
2 On the Dedicated OA tab, select the type of dedicated ventilation unit to be modeled. In this example, the dedicated ventilation unit will supply low dew-point air reheated to a room- neutral dry bulb in cooling mode, and air at a specific dry bulb in heating mode.
Therefore, Dehumidify and Reheat / Heat will
be selected. None – no dedicated ventilation unit
Cool / heat – a dedicated ventilation unit is used to cool the outdoor air to the user-input cooling dry bulb during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify (priority) or Cool / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (not reheated) during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify and Reheat / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (then reheat it to the user-input cooling dry bulb) during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
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Dedicated outdoor-air systems 3 Select the control method
for the unit. Because the dedicated ventilation cooling coil dehumidifies the outdoor air to cooling supply-air dew point and reheats it to room neutral, or the dedicated ventilation heating coil heats the outdoor air to heating supply-air dry bulb, Fixed Setpoints will be used.
4 Input the Cooling and Heating Design Setpoints. In this scenario, 55°F should be input for the cooling supply-air dew point, 70°F for the cooling supply-air dry bulb, and 68°F for the heating supply-air dry bulb.
5 Select the schedule for the coils and fan in the dedicated outdoor-air unit.
Note: If a custom schedule is created for the fan or coils, it is recommended to use values of 0 percent for hours off and 100 percent for hours available to run to avoid confusion.
Note: For additional information related to the other Control Methods, press the F1 key and click Control Method.
If the ventilation air is to be precooled, the Dedicated Ventilation Cooling Coil schedule defines the hours of available operation of the ventilation cooling coil. The optional ventilation cooling coil is available for any hour that this schedule reads 1 percent or greater.
If the ventilation air is to be preheated, the Dedicated Ventilation Heating Coil schedule defines the hours of available operation of the ventilation heating coil. The optional ventilation heating coil is available for any hour that this schedule reads 1 percent or greater.
The Optional ventilation fan schedule defines the hours that the ventilation unit can operate. If the Optional ventilation fan schedule reads 1 percent or greater, the fan is available that hour.
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6 Select the dedicated ventilation deck location.
This tells TRACE 700 where to supply the preconditioned outdoor air. For this scenario, the outdoor air will be delivered to the heat pumps. As a result, Return/Outdoor Deck will be selected.
7 Select the level of the ventilation deck location.
For this scenario, one large dedicated ventilation unit will condition the outdoor air for all of the rooms assigned to the WSHP airside system, so the coils should be set at the System level.
Note: For additional details on Systems, refer to the System Type:
Characteristics in online Help.
Return/Outdoor Deck – conditioned outdoor air is mixed with the return air in the main unit(s).
Plenum – conditioned outdoor air is delivered to the plenum above the spaces.
Room Direct – conditioned outdoor air is delivered directly to the spaces. This can also be used to model the delivery of conditioned outdoor air to dual-duct VAV boxes where it mixes with conditioned recirculated return air.
System – The dedicated ventilation unit will be placed at the system level. It will pretreat the outdoor air for all of the rooms and zones assigned to the airside system. This is the most common choice for dedicated ventilation systems. The System Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Zone – Each zone (or room assigned directly to the system) will get a separate dedicated ventilation system. The Zone Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Room – Each room will get a separate dedicated ventilation system. The Room Checksums or System Component Selection reports should be used to size the dedicated ventilation unit.
Same level as main cooling coil – The dedicated ventilation unit will be placed at the same level as the main cooling coil. The System Component Selection report should be used to size the dedicated ventilation unit.
Same level as main heating coil – The dedicated ventilation unit will be placed at the same level as the main heating coil. The System Component Selection report should be used to size the dedicated ventilation unit.
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Dedicated outdoor-air systems 8 On the Fans tab, input
the fan type and the total static pressure for the primary fan (the fans in the WSHP units) and the optional ventilation fan (the fan in the dedicated ventilation unit).
Next, define the cooling and heating plants represented by the WSHP system and the rooftop air conditioner.
9 Add two new cooling plants and two new heating plants to the Configuration pane.
10Drag the appropriate icons from the Equipment Category section to define each plant.
11To finish defining this equipment, enter the information from Table 4–7 on page 4–56 on the appropriate equipment tab.
Finally, assign the coil loads of the air distribution system to the proper cooling and heating plants.
12Drag each coil in the Unassigned Systems/
Coils pane to the appropriate plant in the Systems and Plants pane.
The illustration labeled
“After” shows the completed assignments.
For cooling, use water-source heat pump and air-cooled unitary.
For heating, use boiler (for the WSHP system) and gas-fired heat exchanger.
Before…
After…
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Scenario 3. A building is served by a VAV air-handling system on each floor. A dedicated outdoor-air unit delivers conditioned outdoor air to the intake of each air handler. During the cooling season, the dedicated outdoor-air unit dehumidifies the outdoor air to 55°F dew point, but does not reheat it. During the heating season, the dedicated unit heats the outdoor air to 68°F dry bulb.
In addition, the system-level controller polls the humidity sensors located in each room and resets the dew point leaving the dedicated outdoor-air unit, to prevent the relative humidity in the worst-case room from rising above 60% while minimizing energy use.
■ The system controller determines the highest possible cooling supply-air dew point setpoint that still avoids the relative humidity from rising above the maximum upper limit (60%, in our example) in any room.
■ When the outdoor dew point is greater than the current cooling supply-air dew point setpoint, the dedicated outdoor-air unit will dehumidify the entering outdoor air to the cooling supply-air dew point setpoint.
■ When the outdoor dew point is less than the current supply-air dew point setpoint and the outdoor dry-bulb temperature is greater than the cooling supply-air dry-bulb setpoint, the
dedicated outdoor-air unit will cool the entering outdoor air to the cooling supply-air dry-bulb setpoint.
■ When the outdoor dew point is less than the current cooling supply-air dew point setpoint and the outdoor dry-bulb
temperature is less than the cooling supply-air dry-bulb setpoint, the dedicated outdoor-air unit will heat the entering outdoor air to the heating supply-air dry-bulb setpoint.
Table 4–7 Equipment types
Cooling Equipment tab Heating Equipment tab Water-source heat
pump water source HP–
high efficiency gas-fired hot water boiler
Air-cooled unitary split system RAUC-20+ ton scroll
rooftop gas heat
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(steps 1–8), model the cooling and heating equipment (steps 9–
11), and assign the loads from the coils to the equipment (step 12).
1 Start by selecting Variable Volume Reheat as the system type.
2 On the Dedicated OA tab, select the type of dedicated ventilation unit to be modeled. In this example, the dedicated ventilation unit will supply low dew-point air (not reheated) in cooling mode, and air at a specific dry bulb in heating mode.
Therefore, Dehumidify (priority) or Cool / Heat
will be selected. None – no dedicated ventilation unit
Cool / heat – a dedicated ventilation unit is used to cool the outdoor air to the user-input cooling dry bulb during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify (priority) or Cool / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (not reheated) during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
Dehumidify and Reheat / Heat – a dedicated ventilation unit is used to dehumidify the outdoor air to the user-input cooling dew point (then reheat it to the user-input cooling dry bulb) during the cooling season, or heat the outdoor air to the user-input heating dry bulb during the heating season.
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3 Select the control method for the unit. Because the dew point delivered by the dedicated ventilation
3 Select the control method for the unit. Because the dew point delivered by the dedicated ventilation