6.3.3 Air Systems | Chicago Public Schools

Indoor Air Handlers

Modular Indoor Air Handlers (AHU) shall have a full perimeter galvanized steel base rail with base rail height as required to meet deflection requirements and to accommodate condensate trap (air conditioning and steam) height requirements. Casing shall be constructed of insulated, double wall panels, including the roof, walls and floor. Access doors shall be provided to allow full access to the interior of the unit for cleaning, parts replacement and maintenance. Access doors shall be hinged with vision safety glass and surface mounted handles. Doors shall open against pressure. Doors opening with pressure, including those provided with safety latches/pressure breaks, shall not be used. Unit shall include factory-mounted Marine LED lights that are water and dust resistant in all areas of unit access/fan sections, wired to an external unit switch, and powered from a circuit separate from the unit to allow for operation when the unit is in the off position.

Verify that the unit has proper clearance for outdoor air intake, exhaust air discharge, maintenance access for potential pulling of coils, filters, fans and proper cleaning.

Code requires no fresh air intake below 10'-0" above finish grade for building ventilation systems.

Fan Section: Fans shall be direct drive type (avoid belts where possible) with electrically commutated motors or variable frequency drives. Plug/plenum type fans preferred; Class II minimum. Fan arrays require project specific CPS approval. Where fan arrays are to be considered, backdraft dampers per fan shall be provided or blank off plates, and each fan shall include individual fan status monitored by the BAS.
Coil Section: Cooling coils casing and drain pan shall be stainless steel. Heating coil casing shall be galvanized steel. Coils shall be provided in their own casing frame and be able to slide out for repair or replacement. Coils/ fins shall be accessible for cleaning/repair from both sides. Access sections shall be provided upstream and downstream of each coil. No casing, piping or other elements shall block the finned area of the coil. Refer to Specifications for full coil requirements. Maximum airflow velocity through cooling coils shall be 450 FPM. Heating coils maximum airflow velocity shall not exceed 650 FPM.
Filtration Section: Unit shall include full filter racks with side loading filters. Refer to Section 6.2.4 Filtration for requirements.
Damper Section: Unit shall include a separate section for air mixing, with dampers for modulating or return, exhaust and outdoor air. Provide a separate actuator per damper. Provide an air blender as required to minimize stratification. If air blender is not provided, provide adequate space for air mixing so that stratification does not occur. Dampers and associated actuators shall be designed in accordance with the BAS specifications. Control dampers shall be ultra-low leak type. Exhaust and outside air dampers shall include insulated frames and blades.
Air Leakage: Positive pressure sections - maximum of 1% at +6” WC. Negative pressure sections - maximum of 1% at -6”WC.
Floor Deflection: Maximum of L/300 at the greater of +/- 6”WC or unit associated fan dead head condition.
Walls and Roof Deflection: Maximum of L/200 at the greater of +/- 6”WC or unit associated fan dead head condition.
Unit Controls: Unit controls shall be field installed in accordance with the BAS plans and specifications
Electrical Accessories: The unit motor starter/VFD/EC motor panel and disconnect may be factory mounted on the exterior of the casing in a NEMA enclosure (NEMA rating based on code/installation location). Where VFD is located inside the unit or EC motors are used, a remote display/control panel shall be provided to allow the commissioning agent to view/adjust the fan functions without shutting down the unit or disturbing the airstream. Disconnect shall be wired in the field. All units shall include unit mounted 120v convenience receptacle on the supply and return fan (when provided) sections, wired independent of the unit power. Unit lighting shall be wired independent of the unit power.
Monitoring for Variable Air Volume Systems: Provide a direct outdoor airflow measuring station per the CPS BAS Specification. Accuracy shall be the more stringent of LEED and the CPS BAS Specification. Provide a measurement device capable of measuring the minimum outdoor air intake flow with an accuracy of +/-10% of the design minimum outdoor airflow rate. An alarm shall indicate when the outdoor airflow value varies by 15% or more from the outdoor airflow setpoint.
Monitoring for Constant-Volume Systems: Balance outdoor airflow to the design minimum outdoor airflow rate defined by the greater of ASHRAE 62.1 – 2010 and or the Chicago Building Code higher. Install a current transducer on the supply fan, an airflow switch, or similar monitoring device.
Fan Tracking: Typically, fan tracking of the supply versus return fan based on T&B generated fan curves in the field is utilized. Provide direct measurement supply/return/exhaust airflow stations in lieu of fan tracking when requested by CPS.
Energy Recovery: Where required by Code or to meet project energy goals, provide total energy wheels (molecular sieve type desiccant with aluminum wheel, sensible & latent) with VFD or EC motor. Provide wheel bypass in both airstreams.

Exterior Air Handlers

Casing shall be constructed of insulated, double wall panels, including the sloped roof, walls and floor. Access doors shall be provided to allow full access to the interior of the unit for cleaning, parts replacement and maintenance. Access doors shall be hinged with vision safety glass and surface mounted handles. Doors shall open against pressure. Doors opening with pressure including those provided with safety latches/pressure breaks shall not be used. Unit shall include factory-mounted Marine LED lights that are water and dust resistant in all areas of unit access/fan sections, wired to external unit switch, and powered from a circuit separate from the unit to allow for operation when the unit is the off position.

Aluminum construction shall be allowed with CPS approval where weight is a concern. Roof of unit shall be sloped for proper drainage.

Units shall be located sufficiently away from the edge of the building for safety and visibility issues (minimum 10’-0”). Where 10’-0” or greater cannot be maintained, obtain approval from CPS on a project/unit specific basis to utilize safety guard rails. Provide site line study for approval by CPS. Access harness tie down solutions shall not be utilized. Any unit mounted greater than 30” above roof level shall be reviewed with CPS for proper access to the unit. A structural platform may be required and shall be coordinated with the Structural Engineer or Record.

Verify that the unit has proper clearance for outdoor air intake, exhaust air discharge, maintenance access for potential pulling of coils, fans, wheels and proper cleaning.

Code requires no fresh air intake below 10'-0" above finish grade for building ventilation systems.

Fan Section: Fans shall be direct drive type (avoid belts where possible) with electrically commutated motors or variable frequency drives. Plug/plenum type fans preferred; Class II minimum. Fan arrays require project specific CPS approval. Where fan arrays shall be considered, backdraft dampers per fan shall be provided or blank off plates, and each fan shall include individual fan status shall be monitored by the BAS.
Coil Section: Cooling coils casing and drain pan shall be stainless steel. Heating coil casing shall be galvanized steel. Coils shall be provided in their own casing frame and be able to slide out for repair or replacement. Coils/ fins shall be accessible for cleaning/repair from both sides. Access sections shall be provided upstream and downstream of each coil. No casing, piping or other elements shall block the finned area of the coil. Provide piping bump out (same construction as casing) with access door for piping coil connections/risers/coil trim (typically 2’ deep by the length of the coil section). Refer to Specifications for full coil requirements. Maximum airflow velocity through cooling coils shall be 450 FPM. Heating coils maximum airflow velocity shall not exceed 650 FPM.
Gas Burner and Heat Exchanger: Unit shall be indirect fired type with capacity as scheduled, installed downstream of the supply fan. Standard controls shall include a full modulating main gas valve/train with a turndown ratio of at least 7:1 for units less than 400 MBH and 10:1 for any larger units.
Refrigerant Cooling Coil or Heat Pump Coil: Direct expansion coil shall be copper tubes expanded into aluminum fins and shall not be less than three rows in depth, or include more than twelve fins per inch. Coil shall include a 304 stainless steel drain pan, stacked if necessary based on coil size. Provide a condensate drain, with P-trap, to the nearest roof drain.
Compressors: Units shall include a minimum of 2 compressors. Compressors shall be heavy duty suction cooled, hermetic scroll type. One of the compressors shall be digital scroll type and include hot gas bypass. Each compressor shall have an independent refrigeration circuit completely piped, tested, dehydrated, and fully charged with oil and refrigerant. Inverter duty compressors may be utilized to meet project energy goals. The combination of all new and existing base building HVAC&R equipment shall comply with the LEED ozone depletion and climate change formula.
Condenser Section: Units shall include a minimum of 2 condenser fans (low sound type, electronically commutated motor type as required to meet energy goals). Condenser coils shall be a seamless copper tube, expanded into aluminum fins or aluminum micro channel type. Provide removable hail guards over condenser surface and field installed cottonwood screens over condenser section air intake areas.
Filtration Section: Unit shall include full filter racks with side loading filters. Refer to Section 6.2.4 for requirements.
Damper Section: Unit shall include a separate section for air mixing, with dampers for modulating or return, exhaust and outdoor air. Provide a separate actuator per damper. Provide an air blender as required to minimize stratification. If air blender is not provided, provide adequate space for air mixing so that stratification does not occur. Dampers and associated actuators shall be designed in accordance with the BAS specifications. Control dampers shall be ultra-low leak type. Exhaust and outside air dampers shall include insulated frames and blades.
Air Leakage: Positive pressure sections - maximum of 1% at +6” WC. Negative pressure sections - maximum of 1% at -6”WC.
Floor Deflection: Maximum of L/300 at the greater of +/- 6”WC or unit associated fan deadhead condition.
Walls and Roof Deflection: Maximum of L/200 at the greater of +/- 6”WC or unit associated fan deadhead condition.
Unit Controls: Unit controls shall be field installed (hydronic, electric heat and steam units) or factory installed (direct expansion and gas furnace units) in accordance with the BAS plans and Specifications.
Electrical Accessories: The unit motor starter/VFD/EC motor panel and disconnect can be factory mounted on the exterior of the casing in a NEMA 3R enclosure. Where VFD is located inside the unit or EC motors are used, a remote display/control panel shall be provided to allow the commissioning agent to view/adjust the fan functions without shutting down the unit or disturbing the airstream. Disconnect to be wired in the field. All units shall include a unit mounted 120v GFIC convenience receptacle on the supply and return fan section, wired independent of the unit power.
Monitoring for Variable Air Volume Systems: Provide a direct outdoor airflow measuring station per the CPS BAS specification. Accuracy shall be the more stringent of LEED and the CPS BAS specification. An alarm shall indicate when the outdoor airflow value varies by 15% or more from the outdoor airflow setpoint.
Monitoring for Constant-Volume Systems: Balance outdoor airflow to the design minimum outdoor airflow rate defined by the greater of ASHRAE 62.1 – 2010 and the Chicago Building Code. Install a current transducer on the supply fan, an airflow switch, or similar monitoring device.
Fan Tracking: Typically, fan tracking of the supply versus return fan based on T&B generated fan curves in the field is utilized. Provide direct measurement supply/return/exhaust airflow stations in lieu of fan tracking when requested by CPS.
Energy Recovery: Where required by Code or to meet project energy goals, provide total energy wheels (molecular sieve type desiccant with aluminum wheel, sensible & latent) with VFD or EC motor. Provide wheel bypass in both airstreams.

Specialty Air Handling Equipment

Pool Dehumidification Unit
All Aquatic Centers shall include a properly designed Dehumidification Air Handler that follows Specification Section 23 84 17. These units can be either indoors with outdoor condenser/condensing unit section or roof mounted. Provide a minimum of two refrigerant circuits. Select refrigerant circuits so that the total pounds of refrigerant in any circuit is less than 100 lbs or as required by Code to avoid the City of Chicago Fireman Dump Valve requirement. The unit selection, and source of heating and cooling, shall be made by the EOR based on what is available from the facility central plant systems, utilities and based on the overall usage of the space and other systems needed within. Typically, pool units are not connected to the facility chilled water system.

Indoor units: shall include: compressor(s), evaporator (dehumidifying coil), heat (hot water or steam), condenser refrigerant hot gas/reheat coil, remote condenser/dry cooler, compressor heat recovery for pool water pre heat, supply air blower(s), return/exhaust air blower(s), filtration, exhaust to outside air energy recovery heat pipe system (or energy recovery method of equal efficiency), mixing/economizer sections, blower motor(s), motor starters/VFDs/ EC motors, and controls.

Rooftop Units: shall be supplied with a remote or integral (preferred) air-cooled condenser/dry cooler. The unit shall include: compressor(s), evaporator (dehumidifying coil), heat (modulating gas or electric), condenser refrigerant hot gas/reheat coil, condenser/dry cooler, compressor heat recovery for pool water pre heat, supply air blower(s), return/exhaust air blower(s), filtration, exhaust to outside air energy recovery heat pipe system (or energy recovery method of equal efficiency), mixing/economizer sections, blower motor(s), motor starters /VFDs/EC motors, and controls.

Dust Collection Systems
All shop areas (carpentry, metal works, masonry, some theatre prop shops, project specific consult with CPS) which will generate either excessive levels of dust shall include a variable speed collection system maintaining a set negative pressure setpoint in the ductwork. This system shall be designed to provide point-of-use connection to the elements/equipment producing the particulate. The collection of these shall be done by equipment located on the exterior of the building. The location of the equipment shall be closely coordinated with all trades to maintain ease of access for maintenance, sound levels in surrounding areas, removal of particulate and proper distance to areas of air intake and public spaces. Provide an enclosure for sound/vision/security around the unit. Coordinate with architectural drawings. Refer to CPS Specification Section 23 35 13 for system specifics and requirements. Coordinate exhaust system design with space conditioning/make up air design so that space operates under negative pressure when in operation (either 10% greater exhaust to supply or space to ambient operates at -0.05”WC.

Automotive/Truck Exhaust Collection Systems
All automotive spaces teaching/repair areas shall include a variable speed automotive exhaust system. This system shall be designed to provide point-of-use connections to the vehicle exhaust discharge. The location of the equipment shall be closely coordinated with all trades to maintain ease of access for maintenance, sound levels in surrounding areas, removal of fumes and proper distance to areas of air intake and public spaces. Refer to CPS Specification Section 23 35 13 for system specifics and requirements. Coordinate exhaust system design with space conditioning/make up air design so that space operates under negative pressure when in operation (either 10% greater exhaust to supply or space to ambient operates at -0.05”WC. Provide CO / NO2 sensors in space.

Makerspace Exhaust Systems
All physical (messy) Makerspaces shall operate under negative (constant volume supply and exhaust systems by balanced 10% greater exhaust than supply, variable volume /on/off exhaust systems by differential pressure (space relative to adjacent corridor or ambient). Initial setpoint shall be -0.05”WC. Provide a dedicated exhaust fan per laser cutter. Interlock the fan to the exhaust fan. When a BAS exists in the building, the BAS shall monitor the laser cutter status and fan status. Provide a dedicated exhaust fan for the 3D printer area and locate general exhaust diffusers above the 3D printer area. Provide an interlock exhaust fan for all 3D printers. When any 3D printer is ON, the exhaust fan shall be ON. When a BAS exists in the building, the BAS shall monitor the 3D printers status (current sensor) and fan status.

Energy Recovery Systems
The use of energy recovery systems may be required to meet Energy Conservation Code and project energy goal requirements. The types of system used shall be allowable by all local Codes. These systems are used to recover heating or cooling load from the exhaust air and transfer it to the incoming outdoor air. Review the individual project conditions and make a recommendation to CPS for type and application. CPS review and approval required before proceeding. Refer to CPS Specification Section 23 72 00 for system specifics and requirements.

Kitchen Make-up Air Units
Kitchens with exhaust hoods or general exhaust systems shall include a dedicated Kitchen Make-up Air Unit (MAU) or air transfer/supply from the unit serving the Cafeteria/Servery. The Kitchen shall operate under negative pressure relative to adjacent Cafeteria/Servery. Cafeteria/Servery spaces shall operate under negative pressure relative to adjacent academic/corridor spaces. Kitchen spaces shall be maintained at no greater than 80°F in summer and no lower than 70°F in winter. Refer to CPS Specification Section 23 74 23 for system specifics and requirements.

Radon Mitigation (Buildings with basements, crawl spaces, unexcavated areas)
Provide radon mitigation system as necessary to maintain a radon level less than 4 pCi/L from regularly occupied spaces at or below grade. Radon gas itself may be removed with activated carbon, but in HVAC systems, this method is too costly for the benefit derived. Reduction of radon emissions at the source by sealing entry points or depressurizing the source location like sub-slab ventilation are the accepted methods of reducing exposure to radon.