stoughton high school · o chiller plant o chilled water distribution o chilled beam unit chiller...
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Stoughton High School
HVAC System: Basis of Design.1
Basis of Design Criteria
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o Occupant Thermal Comfort
o Indoor Air Quality
o Energy Efficiency / Environmental Impact
o System Noise
o First Cost / Return on Investment
o Maintenance
o Reliability
o LEED
HVAC: Energy Design Criteria
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• ASHRAE Standard 90.1
o Minimum Energy Criteria for Standard Construction
o ASHRAE Standard establishes a baseline system.
o High Performance and LEED Bldgs:
Design team develops a building which exceeds the
base line by 22%
o Building efficiency is measure with an energy model.
HVAC: System Options
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• Base Line: Variable Air Volume Air System (VAV)
o ASHRAE 90.1 minimum criteria
• System 1 (SD Basis of Design): Variable Refrigerant Flow System (VRF)
o Typically better than ASHRAE 90.1 by 25%~30%.
• System 2: Chilled Beam System
o Typically better than ASHRAE 90.1 by 25%~30%.
• System 3: High Performance VAV
o Typically better than ASHRAE 90.1 by 18%~23%.
VAV Box
VRF Fan Coil Unit
Chilled Beam Unit
VAV Box
Baseline HVAC System
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• Minimum Energy Requirement: ASHRAE 90.1
• Classrooms & Offices Heating / Cooling:
o Variable Air Volume Boxes for Zone Control (VAV)
o Package Roof Top Unit (RTU) with Gas Furnace Section.
VRF Description System
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• Classrooms & Offices Heating & Cooling:
o VRF Indoor Fan Coil Units
o VRF Outdoor Air Cooled Heat Pumps
o Refrigerant Pipe Distribution
o Heat Recovery System
Outdoor Unit
Indoor Unit
(Cooling Mode)
Indoor Unit
(Heating Mode)
Outdoor Unit
Indoor Unit Options
Overall System
VRF System Components
VRF Typical Classroom Layout
Terminal Cooling
Device Supply Air
Filtered Return
Exhaust Air
Outdoor Air
Control Damper
Perimeter Radiation or Radiant Ceiling Heating
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VRF System Summary
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• Pros:
o Comfort: Individual Room Control.
o Energy Efficient: Heat Recovery. Matches Cooling and Heating
o Quiet. Exceeds stringent noise criteria
o Distribution takes up little space due to minimum ductwork for ventilation
o Indoor Air Quality: Temperature control (VRF) is separated from ventilation air system.
With decoupled ventilation and temperature control, mold issues are minimized.
o Less expensive as compare to chilled beam and high performance VAV.
o Demand control ventilation
• Cons:
o Distributive Filters
o Distributive Condensate piping
Chilled Beam System Description
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• Classrooms & Offices Heating & Cooling:
o Chiller Plant
o Chilled Water Distribution
o Chilled Beam Unit
Chiller
Chilled
Water and
Hot Water
Distribution
Overall SystemChilled Beam Section
Chilled Beam in Ceiling
Chilled Beam Typical Classroom Layout
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Chilled Beam
Exhaust Air
Outdoor Air
Perimeter Heating
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Chilled Beam System Summary
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• Pros:
o Comfort: Individual Room Control.
o Energy Efficient: Heat Recovery. Matches Cooling and Heating
o Quiet. Exceeds stringent noise criteria
o Distribution takes up little space due to minimum ductwork for ventilation
o Indoor Air Quality: Temperature control (VRF) is separated from ventilation air system.
With decoupled ventilation and temperature control, mold issues are minimized.
• Cons:
o Condensate issue. Tight humidity control required. On humid days, air conditioning will turn off
with open windows or open classroom exterior doors.
o More expensive as compare to VRF.
o Demand control ventilation.
High Performance VAV System
Description System
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• Classrooms & Offices Heating & Cooling:
o Central Ductwork Distribution with Variable Air Volume Boxes for Zone Control (VAV)
o To achieve High Performance:
• Larger than average ductwork
• Custom Air Handler, AHU (Roof Top or Indoor)
• Optimization Control Strategy
• Water Cooled Chiller
• Cooling Tower
Custom Air Handling Unit Magnetic Bearing Water
Cooled Chiller
Cooling Tower
Overall System
High Performance VAV System Summary
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VAV Box w/reheat
Supply Air
Return Air
Perimeter Heating
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High Performance VAV System Summary
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• Pros:
o Central air filtration and condensate.
o Central compressors
• Cons:
o Comfort / Indoor Air Quality: Temperature control system and ventilation control are from the same
distribution source. Does not provide humidity control or mold control.
o Large than average ductwork required to meet noise criteria energy criteria. Takes up an additional
12” to 18” as compared the VRF and Chilled Beams.
o In order to out-perform ASHRAE 90.1 by 22%, Custom Air Handling Units are required.
o More expensive as compare to VRF. Approximately.
COMMON HVAC Components
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• Ventilation Source: Dedicated Outdoor Air System (DOA) with Heat Recovery
• Central Boiler Plant: High Efficient Condensing Boilers.
• Perimeter Heating
*Not common for High Performance VAV
DOA Diagram* Condensing Boiler DOA*
Perimeter Heating
Comparison Summary
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Function System 1 (SD Basis of Design)
Variable Refrigerant Volume (VRF)
System 2
Chilled Beam
System 3
High Performance VAV
Ventilation Ventilation provided by Dedicated Outdoor Air System
(DOA) with energy recovery
Same as System 1 Ventilation provided by mixing outside air and return air in the
VAV air handling unit.
Humidity
Control
Ventilation air pretreated by DOA to conditions that will
handle the moisture added by ventilation
Same as System 1 Humidity loads are addressed at air handler. Humidity
conditions may occur when outside air is cool and damp,
Control
System
A central DDC control system with web based control Same as System 1 Same as System 1
Pros • Comfort
• Energy Efficient:
• Quiet.
• Takes up little space
• Indoor Air Quality. Minimizes any mold issue
• Less expensive Vs. Chilled Beam
• Demand control ventilation
• Comfort
• Energy Efficient:
• Quiet.
• Takes up little space
• Indoor Air Quality. Minimizes any
mold issue
Central air filtration and condensate
Cons • Distributive Filters
• Distributive Condensate piping
• Condensate issue. Tight humidity
control ,Windows remain closed
• More expensive as compare to VRF.
• Demand control ventilation not
feasible
• Comfort / Indoor Air Quality: Temperature control system and
ventilation control are from the same distribution source. Does
not provide humidity control or mold control.
• Large than average ductwork required to meet noise criteria
energy criteria. Takes up an additional 12” to 18” as compared
the VRF and Chilled Beams.
• In order to out-perform ASHRAE 90.1 by 22%, Custom Air
Handling Units is required.
• More expensive as compare to VRF.
• Demand control ventilation not feasible.