10435 Downsville Pike Hagerstown MD 21740 301-766-2800 Addendum 2 TO: All Prospective Offerors FROM: Lisa C. Freeman, CPM, Supervisor of Purchasing REF: Bid #2016-56 Kitchen Renovation at E. Russell Hicks Middle School BID DUE DATE: Thursday May 5, 2016 at 2:00 pm local time Please note the following changes/clarifications to Bid #2016-56 BIDDER QUESTIONS April 29, 2016 2.1 Q: On Sheet AD1.1, Kitchen Ceiling New Work Notes, #9 states, Infill existing duct opening (louver to remain) with insulated metal panel. Please provide specification or description of insulated metal panel referred to in above. A: The insulated panel shall be double wall galvanized steel with a minimum insulating value of R-13. Connection to existing louver shall be weather tight. 2.2 Q: There are a number of spec sections (05400-light gage framing, 09250-plaster and gypsum board, 09400- fiberglass reinforced plastic panels) that appear to be not applicable to this project. Please confirm my assumption is correct. A: All sections listed are applicable for the project. 2.3 There are a number of spec sections that appear to be missing (concrete, structural steel, insulated metal panel, food service, mechanical, plumbing, sprinkler, electrical) but do apply to this project. Please clarify by identifying what product is intended or provide specs. A: All specifications are on the drawings. In addition, coordinate the installation requirements and BMS with RTU specification, which is attached to this addendum. Contractors shall use Control Systems, Inc., of Hagerstown for the controls scope on this project, as they are the sole source controls contractor used by WCPS. 2.4 Q: Is the sprinkler modification required since we are not adding any walls or modifying drastically? A: Sprinkler modifications are required to accommodate new ceiling elevation and fixture locations. 2.5 Q:Will the hood require a dry chemical fire sprinkler system? A: No. 2.6 Q: What is the current roof type? Is it under warranty? A: Roof warranty documents are attached to this addendum. 2.7 Q: Please clarify the type and manufacturer of the new light fixtures that are to be used for the new work portion of this project. A: New light fixtures shall be Lithonia #2TL4-40L-FW-A12-EZ1-LP840. Addendum 2 Bid #2016-56 END OF ADDENDUM
SECTION 15737 PACKAGED ROOFTOP AIR CONDITIONING UNITS PART 1 GENERAL 1.1 RELATED DOCUMENTS A. Drawings and general provisions of the Contract, including General and Supplementary Conditions and Division 01 specifications, apply to this section, and the other sections of Division 23. 1.2 SUMMARY A. Section Includes: 1. Packaged rooftop air conditioning unit. 2. Roof curb. 1.3 REFERENCES (Unless otherwise noted, references apply to latest editions. ) A. Air-Conditioning Heating, and Refrigeration Institute: 1. ARI 210/240 Unitary Air-Conditioning and Air-Source Heat Pump Equipment. 2. ARI 270 - Sound Rating of Outdoor Unitary Equipment. 3. ARI 340/360 - Commercial and Industrial Unitary Air-Conditioning and Heat Pump Equipment. B. American National Standards Institute: 1. ANSI Z21.47b/CSA 2.3b and ANSI Z83.8/CSA 2.6, Safety Standard Gas-Fired Furnaces. 2. ANSI/AHRI Standard 340/360 performance rating of commercial and industrial unitary air-conditioning and heat pump equipment. C. Air Movement and Control Association International, Inc.: 1. AMCA 500 - Test Methods for Louvers, Dampers, and Shutters. D. American Society of Heating, Refrigerating and Air-Conditioning Engineers: 1. ASHRAE 52.1 - Gravimetric and Dust-Spot Procedures for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter. 2. ASHRAE 62 - Ventilation for acceptable Indoor Air Quality. 3. ASHRAE 90.1 - Energy Standard for Buildings except Low-Rise Residential Buildings. E. ASTM International: 1. ASTM B117 - Standard Practice for Operating Salt Spray (Fog) Apparatus. F. National Electrical Manufacturers Association: PACKAGED ROOFTOP AIR CONDITIONING UNITS
1. NEMA 250 - Enclosures for Electrical Equipment (1000 Volts Maximum). 2. NEMA MG 1 - Motors and Generators. G. National Fire Protection Association: 1. NFPA 54 - National Fuel Gas Code. 2. NFPA 90A - Standard for the Installation of Air Conditioning and Ventilating Systems. H. Underwriters Laboratories: 1. UL Standard 1995/CSA C22.2 No. 236, Safety Standard for Heating and Cooling Equipment. 1.4 DEFINITIONS A. Energy Efficiency Ratio (EER) - Ratio of net cooling capacity in Btuh to total rate of electric input in watts under designated operating conditions. B. Integrated energy efficiency ratio (IEER) single number figure of merit expressing cooling part load EER efficiency for commercial unitary air conditioning and heat pump equipment on the basis of weighted operations of various load capacities for the equipment. 1.5 SUBMITTALS A. Shop Drawings: Indicate air handling unit dimensions, performance data, lifting points, piping connections, roof curb data, and attachments. B. Product Data: Submit data indicating: 1. Cooling and heating capacities. 2. Dimensions. 3. Weights. 4. Rough-in connections and connection requirements. 5. Duct connections. 6. Electrical requirements with electrical characteristics and connection requirements. 7. Controls: Provide the following items: a. A detailed description of the programmed sequence. b. Control interface (BACNet, ModBus, LonWorks, hardwired, etc). c. List of all available control points (points that can be changed by the central control system remotely). d. List of all available monitoring points (points that can be viewed by the central control system remotely). e. Provide a description for each point in non-coded language. f. Provide the address or name of the point or SNVT (Standard Network Variable Type). g. Indicate the read/write capability for each point. 8. Accessories. C. Test Reports: Submit results of factory test at time of unit shipment. D. Manufacturer's Installation Instructions: Submit assembly, support details, connection requirements, and include start-up instructions. PACKAGED ROOFTOP AIR CONDITIONING UNITS
E. Manufacturer's Certificate: Certify products meet or exceed specified requirements. 1.6 CLOSEOUT SUBMITTALS A. Division 01 Section Execution and Closeout Requirements : Closeout Procedures. B. Project Record Documents: Record actual locations of controls installed remotely from units. C. Operation and Maintenance Data: Submit manufacturer's descriptive literature, operating instructions, installation instructions, and maintenance and repair data. 1.7 QUALITY ASSURANCE A. Cooling Capacity: Rate in accordance with ARI 340/360. B. Sound Rating: Measure in accordance with ARI 270. C. Insulation and adhesives: Meet requirements of NFPA 90A. D. Minimum heating efficiency: 80 percent. E. Performance Requirements: Conform to minimum EER prescribed by ASHRAE 90.1 when tested in accordance with ARI 340/360. F. Outside Air Damper Leakage: Test in accordance with AMCA 500. G. Perform Work in accordance with all applicable codes, standards, and local authorities having jurisdiction requirements. 1.8 QUALIFICATIONS A. Manufacturer: Company specializing in manufacturing products specified in this section with minimum three years documented experience. B. Installer: Company specializing in performing Work of this section with minimum three years experience. 1.9 DELIVERY, STORAGE, AND HANDLING A. Accept units on site. Inspect for damage. B. Protect units from damage by storing off roof until roof mounting curbs are in place. 1.10 COORDINATION A. Coordinate installation of roof curbs with roof structure, roof deck and roof membrane installation. B. Coordinate all controls with BMS contractor to ensure proper communication between the central control system and the unit as required by the contract documents. Provide a list of all available points (non-coded language description) to the BMS contractor. Ensure RTU can accept all required control points from BMS and that the BMS can read all required monitoring points. Ensure that the controls interface between the packaged RTU controls and the BMS is operational. PACKAGED ROOFTOP AIR CONDITIONING UNITS
C. Coordinate with Engineer regarding control sequence. Any deviation of the programmed controls from the specified controls should be clarified in writing and provided to the Engineer and Commissioning Agent (CxA) for review. D. Contractor is responsible for providing all control devices shown on the ATC diagram or points list in the contract documents unless otherwise specified. Prior approval by the Engineer is required, in writing, to change this requirement. If there are issues regarding these devices they should be documented in writing and provided to the Engineer (and CxA) for review. 1.11 WARRANTY A. Manufacturer shall provide a limited parts only warranty for a period of 12 months from the date of equipment startup or 18 months from the date of original equipment shipment from the factory, whichever is less. Warranty shall cover material and workmanship that prove defective, within the specified warranty period, provided manufacturer s written instructions for Installation, Operation, and maintenance have been followed. Warranty excludes parts associated with routine maintenance, such as belts and filters. B. Furnish five year manufacturer s warranty for compressors. C. Furnish five year manufacturers warranty for heat exchangers. 1.12 EXTRA MATERIALS A. Furnish one set of fan belts for each unit. B. Furnish one set of filters for each unit. PART 2 PRODUCTS 2.1 Manufacturer A. Unit shall be as manufactured by AAON, comparable products as manufactured by Trane, Venmar or Mammoth shall be submitted for approval as a comparable product. 2.2 General Description A. Packaged rooftop unit shall include compressors, evaporator coils, filters, supply fans, dampers, air-cooled condenser coils, condenser fans, reheat coil, gas heaters, exhaust fans, and unit controls. B. Unit shall be factory assembled and tested including leak testing of the DX coils, pressure testing of the refrigeration circuit, and run testing of the completed unit. Run test report shall be supplied with the unit in the service compartment s literature pocket. C. Unit shall have decals and tags to indicate lifting and rigging, service areas and caution areas for safety and to assist service personnel. D. Unit components shall be labeled, including refrigeration system components and electrical and controls components. E. Estimated sound power levels (db) shall be shown on the equipment schedule. PACKAGED ROOFTOP AIR CONDITIONING UNITS
F. Installation, Operation, and Maintenance manual shall be supplied within the unit. G. Laminated color-coded wiring diagram shall match factory installed wiring and shall be affixed to the interior of the control compartment s hinged access door. H. Unit nameplate shall be provided in two locations on the unit, affixed to the exterior of the unit and affixed to the interior of the control compartment s hinged access door. 2.3 Construction A. All cabinet walls, access doors, and roof shall be fabricated of double wall, impact resistant, rigid polyurethane foam panels. B. Unit insulation shall have a minimum thermal resistance R-value of 13. Foam insulation shall have a minimum density of 2 pounds/cubic foot and shall be tested in accordance with ASTM D1929-11 for a minimum flash ignition temperature of 610 F. C. Unit construction shall be double wall with G90 galvanized steel on both sides and a thermal break. Double wall construction with a thermal break prevents moisture accumulation on the insulation, provides a cleanable interior, prevents heat transfer through the panel, and prevents exterior condensation on the panel. D. Unit shall be designed to reduce air leakage and infiltration through the cabinet. Cabinet leakage shall not exceed 1% of total airflow when tested at 3 times the minimum external static pressure provided in AHRI Standard 340/360. Panel deflection shall not exceed L/240 ratio at 125% of design static pressure, at a maximum 8 inches of positive or negative static pressure, to reduce air leakage. Deflection shall be measured at the midpoint of the panel height and width. Continuous sealing shall be included between panels and between access doors and openings to reduce air leakage. Piping and electrical conduit through cabinet panels shall include sealing to reduce air leakage. E. Roof of the air tunnel shall be sloped to provide complete drainage. Cabinet shall have rain break overhangs above access doors. F. Access to filters, dampers, cooling coils, reheat coil, heaters, exhaust fans, compressors, and electrical and controls components shall be through hinged access doors with quarter turn, zinc cast, lockable handles. Full length stainless steel piano hinges shall be included on the doors. G. Exterior paint finish shall be capable of withstanding at least 2,500 hours, with no visible corrosive effects, when tested in a salt spray and fog atmosphere in accordance with ASTM B 117-95 test procedure. H. Units with cooling coils shall include double sloped 304 stainless steel drain pans. I. Unit shall be provided with base discharge and return air openings. All openings through the base pan of the unit shall have upturned flanges of at least 1/2 inch in height around the opening. J. Unit shall include lifting lugs on the top of the unit. K. Unit base pan shall be provided with 1/2 inch thick foam insulation. PACKAGED ROOFTOP AIR CONDITIONING UNITS
2.4 Electrical A. Unit shall be provided with dual point power connection with terminal blocks. Disconnect shall be provided and installed in the field. Cooling shall be powered by one point of power and the other shall power the remainder of the unit. B. Unit shall be provided with phase and brown out protection which shuts down all motors in the unit if the electrical phases are more than 10% out of balance on voltage, the voltage is more than 10% under design voltage or on phase reversal. 2.5 Supply Fans A. Unit shall include direct drive, unhoused, backward curved, plenum supply fans. B. Blowers and motors shall be dynamically balance and mounted on rubber isolators. C. Motors shall be premium efficiency ODP with ball bearings rated for 200,000 hours service with external lubrication points. D. Variable frequency drives shall be factory wired and mounted in the unit. Fan motors shall be premium efficiency. 2.6 Exhaust Fans A. Exhaust dampers shall be sized for 100% relief. B. Fans and motors shall be dynamically balanced. C. Motors shall be premium efficiency ODP with ball bearings rated for 200,000 hours service with external lubrication points. D. Access to exhaust fans shall be through double wall, hinged access doors with quarter turn lockable handles. E. Unit shall include belt driven, unhoused, backward curved, plenum exhaust fans. F. Variable frequency drives shall be factory wired and mounted in the unit. Fan motors shall be premium efficiency. 2.7 Cooling Coils A. Coils shall be designed for use with R-410A refrigerant and constructed of copper tubes with aluminum fins mechanically bonded to the tubes and galvanized steel end casings. Fin design shall be sine wave rippled. B. Coils shall have interlaced circuitry and shall be standard capacity. C. Coils shall be hydrogen or helium leak tested. D. Coils shall be furnished with factory installed expansion valves. 2.8 Refrigeration System A. Unit shall be factory charged with R-410A refrigerant. PACKAGED ROOFTOP AIR CONDITIONING UNITS
B. Compressors shall be scroll type with thermal overload protection and carry a 5 year non-prorated warranty, from the date of original equipment shipment from the factory. C. Compressors shall be mounted in an isolated service compartment which can be accessed without affecting unit operation. Lockable hinged compressor access doors shall be fabricated of double wall, rigid polyurethane foam injected panels to prevent the transmission of noise outside the cabinet. D. Compressors shall be isolated from the base pan with the compressor manufacturer s recommended rubber vibration isolators, to reduce any transmission of noise from the compressors into the building area. E. Each refrigeration circuit shall be equipped with expansion valve type refrigerant flow control. F. Each refrigeration circuit shall be equipped with automatic reset low pressure and manual reset high pressure refrigerant safety controls, Schrader type service fittings on both the high pressure and low pressure sides and a factory installed replaceable core liquid line filter driers. G. Unit shall include a variable capacity scroll compressor on the lead refrigeration circuit which shall be capable of modulation from 10-100% of its capacity. H. Lead refrigeration circuit shall be provided with hot gas reheat coil, modulating valves, electronic controller, supply air temperature sensor and a control signal terminal which allow the unit to have a dehumidification mode of operation, which includes supply air temperature control to prevent supply air temperature swings and overcooling of the space. I. Each refrigeration circuit shall include adjustable compressor lockouts. 2.9 Air-Cooled Condenser A. Condenser fans shall be a vertical discharge, axial flow, direct drive fans. B. Coils shall be designed for use with R-410A refrigerant. Coils shall be multi-pass and fabricated from aluminum microchannel tubes. C. Coils shall be designed for a minimum of 10 F of refrigerant sub-cooling. D. Coils shall be hydrogen or helium leak tested. E. Condenser fans shall be VFD driven variable speed for condenser head pressure control. Factory provided and factory programmed VFDs shall continuously modulate the fan air flow to maintain head pressure at acceptable levels. Cooling operation shall be allowed down to 35 F with adjustable compressor lockouts. 2.10 Gas Heating A. Stainless steel heat exchanger furnace shall carry a 25 year non-prorated warranty, from the date of original equipment shipment from the factory. B. Gas furnace shall consist of stainless steel heat exchangers with multiple concavities, an induced draft blower and an electronic pressure switch to lockout the gas valve until the combustion chamber is purged and combustion airflow is established. PACKAGED ROOFTOP AIR CONDITIONING UNITS
C. Furnace shall include a gas ignition system consisting of an electronic igniter to a pilot system, which will be continuous when the heater is operating, but will shut off the pilot when heating is not required. D. Unit shall include a single gas connection and have gas supply piping entrances in the unit base for through-the-curb gas piping and in the outside cabinet wall for across the roof gas piping. E. Natural gas furnace shall be equipped with modulating gas valves, adjustable speed combustion blowers, stainless steel tubular heat exchangers, and electronic controller. Combustion blowers and gas valves shall be capable of modulation. Electronic controller includes a factory wired, field installed supply air temperature sensor. Sensor shall be field installed in the supply air ductwork. Supply air temperature setpoint shall be adjustable on the electronic controller within the controls compartment. The turndown of the heat exchanger shall be a minimum of 10:1. 2.11 Filters A. Unit shall include 2 inch thick, pleated panel filters with an ASHRAE efficiency of 30% and MERV rating of 8, upstream of the cooling coil. B. Unit shall include 0-100% economizer consisting of a motor operated outside air damper and return air damper assembly constructed of extruded aluminum, hollow core, airfoil blades with rubber edge seals and aluminum end seals. Damper blades shall be gear driven and designed to have no more than 20 cfm of leakage per sq ft. at 4 in. w.g. air pressure differential across the damper. Low leakage dampers shall be Class 2 AMCA certified, in accordance with AMCA Standard 511. Damper assembly shall be controlled by spring return DDC actuator. Unit shall include outside air opening bird screen, outside air hood, and barometric relief dampers. C. Provide a factory installed clogged filter switch can magnahelic gauge. 2.12 Controls A. RTU shall be provided to match existing control strategy in the rest of the building. B. Current building control is by Schneider Electric IA Series. No third party integration shall be permitted. C. The RTU shall be provided with a standard thermostat interface for connection to the BMS. D. The BMS Contractor shall furnish all temperature sensors, damper actuators, and other controls necessary to properly condition the space. E. Airflow monitor shall be factory installed or provided by the BAS Contractor. 4-20 MA or 0-5 VDC signal shall be available to the BAS for damper control. F. Direct Expansion (DX) system safeties shall be by unit manufacturer. 2.13 Accessories A. Unit shall be provided with a safety shutdown terminal block for field installation of a smoke detector which shuts off the unit's control circuit. PACKAGED ROOFTOP AIR CONDITIONING UNITS
2.14 2.03 Curbs A. Curbs shall to be fully gasketed between the curb top and unit bottom with the curb providing full perimeter support, cross structure support and air seal for the unit. Curb gasket shall be furnished within the control compartment of the rooftop unit to be mounted on the curb immediately before mounting of the rooftop unit. B. Solid bottom curb shall be factory assembled and fully lined with 1 inch neoprene coated fiberglass insulation and include a wood nailer strip. PART 3 EXECUTION 3.1 EXAMINATION A. Verify roof curbs are installed and dimensions are as instructed by manufacturer. 3.2 INSTALLATION A. Roof Curb: 1. Assemble roof curb. 2. Install roof curb level. 3. Coordinate curb installation and flashing with Division 07 Section: Roof Accessories : 4. Install units on roof curb providing watertight enclosure to protect ductwork and utility services. 5. Install gasket material between unit base and roof curb. 6. Unless otherwise indicated, fill all voids between curbs and ductwork with heavy density rigid board insulation of thickness to match height of roof curb. B. Install flexible connections between unit and inlet and discharge ductwork. Install metal bands of connectors parallel with minimum 3 inch (25 mm) flex between ductwork and fan while running. Refer to Division 23 Section: HVAC Air Distribution. C. Install condensate piping with trap and route from drain pan to nearest roof drain. Refer to Division 23 Section: Pipes and Tubes for HVAC Piping and Equipment. D. Install components furnished loose for field mounting. E. Install electrical devices furnished loose for field mounting. F. Install control wiring between unit and field installed accessories. G. Remove from roof and dispose off-site panels removed from units during installation of economizer and dampers. H. Locate remote panels as indicated on the Contract Drawings. I. Install Work in accordance with all applicable codes, standards, and local authorities having jurisdiction. J. All wiring within the AHU, where inside a control panel, shall be installed in UL approved conduit or raceway. PACKAGED ROOFTOP AIR CONDITIONING UNITS
3.3 INSTALLATION - NATURAL GAS HEATING SECTION A. Connect natural gas piping in accordance with NFPA 54. B. Connect natural gas piping to unit, full size of unit gas train inlet. Arrange piping with clearances for burner service. C. Install natural gas valves and piping accessories above roof as indicated on the Contract Documents. 3.4 MANUFACTURER'S FIELD SERVICES A. Furnish initial start-up and shutdown during first year of operation, including routine servicing and checkout. B. Provide technical support to ensure the communication interface between the RTU and the BMS is operational. 3.5 CLEANING A. Vacuum clean coils and inside of cabinets. B. Install temporary filters during construction period. Replace with permanent filters at Substantial Completion. 3.6 DEMONSTRATION A. Engage a factory authorized service representative to train owner s maintenance personnel to adjust, operate and maintain systems. 1. Train Owner s maintenance personnel on procedures and schedules for starting up and shutting down, trouble shooting, servicing and maintaining air handling units. 2. Review data in maintenance manuals. 3. Schedule training with owner with at least seven (7) days advance notice. 3.7 Sequence of Operation A. Supply Fan Control 1. The supply fan runs continuously and is constant volume. The supply fan is maintained by minimum on and off timers. B. Heating Mode 1. The heating mode will be enabled when the return air temperature falls below the return air heating setpoint minus hysteresis. During the heating mode, the controller will modulate the 10:1 turndown gas heater to maintain the return air heating setpoint. The heating mode will remain active until the return air temperature rises above the return air heating setpoint plus hysteresis. C. Cooling Mode 1. The cooling mode will be enabled when the return air temperature rises above the return air cooling setpoint plus hysteresis and the outside air temperature is above the cooling lockout temperature setpoint. During the cooling mode, the DDC controller will modulate the digital scroll compressor and stage the standard PACKAGED ROOFTOP AIR CONDITIONING UNITS
scroll compressor cooling to maintain the return air cooling setpoint. The cooling mode will remain active until the return air temperature falls below the return air cooling setpoint minus hysteresis. Cooling stages are maintained by adjustable minimum on, off, stage up and stage down timers. D. Dehumidification Mode 1. The dehumidification mode will be enabled anytime the return air dewpoint rises above the return air dehumidification setpoint plus hysteresis. During the dehumidification mode, the DDC controller will modulate and stage cooling to maintain the return air dewpoint at the return air dehumidification setpoint. The dehumidification mode will remain active until the return air dewpoint falls below the return air dehumidification setpoint minus hysteresis. The dehumidification mode will be cancelled if the return air temperature falls below the return air heating setpoint. Reheat will be modulated to maintain the return air cooling setpoint minus 1 F. E. Economizer Mode 1. Economizer cooling will be enabled when the outside air enthalpy drops below the return air enthalpy. When the DDC controller is in the cooling mode, the economizer will be used as the first stage of cooling. The economizer will modulate between its minimum and maximum positions to maintain the space temperature at the space cooling setpoint. Cooling stages can be activated to supplement the economizer once the economizer has reached its maximum position and more cooling is required to achieve the space cooling setpoint. Once supplemental cooling stages have been activated, the economizer output signal is held at its maximum position until cooling stages are no longer needed and then can resume normal modulation. Cooling stages are no longer needed when the economizer control loop has reached its minimum position. F. Constant Outside Airflow 1. The outside air damper is modulated to maintain a minimum outside airflow (CFM). Economizer Mode can override the damper open but cannot reduce the minimum airflow. The controller shall monitor kitchen exhaust hood activity and increase the minimum outside airflow setpoint whenever the kitchen exhaust hood is active. G. Building Static Pressure Control 1. The exhaust fan is modulated to maintain building static pressure at the building static pressure setpoint whenever the supply fan is active. H. Supply Fan Status 1. The supply fan status input must be CLOSED for mechanical heating or cooling to operate. If this input opens during normal operation, all mechanical heating and cooling outputs will be deactivated within 10 seconds and an alarm will be generated. I. Emergency Shutdown 1. The emergency shutdown input must be CLOSED for normal operation. If this input is OPEN, no outputs on the controller will be activated. If this input opens during normal operation, all of the controller outputs will be deactivated within 10 seconds and an alarm will be generated. PACKAGED ROOFTOP AIR CONDITIONING UNITS
J. Dirty Filter 1. If the main filter status input closes during supply fan operation, an alarm will be generated indicating the filters need to be changed. K. Freeze Protection 1. If the supply air temperature falls below the freeze protection limit (default 40ºF) and the freeze protection timer expires (default 10 minutes), all outputs will be deactivated and an alarm will be generated. Normal operation will be restored when the supply air temperature rises above the freeze protection limit by 5ºF. L. Suction Pressure Protection 1. Suction pressure is used to unload the cooling and dehumidification PID loops to protect against coil freezing. Unloading occurs when the suction pressure drops to 100 psi (32ºF). With multiple stage units, this process will stage down on/off compressor stages and if staged down to one compressor will turn that compressor off if the suction pressure remains under 90 psi (26ºF) for up to 5 minutes. The compressor must remain off for 5 minutes before allowed to restart. A low suction pressure alarm will be generated. M. Head Pressure Control 1. A discharge pressure transducer will be monitored on each compressor or refrigerant circuit. The condenser fan signal is modulated to maintain the head pressure setpoint (365 psi/110 F condensing pressure/temperature) during the cooling and dehumidification modes. The condenser signal range is from an adjustable minimum setpoint to maximum (100%). If the maximum head pressure should climb to over 500 psi (133 F), the condenser signal will be forced to 100% until the head pressure falls by 150 psi. N. Adjustable Setpoints 1. Head Pressure 2. Throttling Range 3. Minimum Fan Signal O. Unoccupied Mode 1. The supply fan and exhaust fan are off, and the outside air damper is closed. The space sensor will be used to determine unoccupied mode demands. Heating, cooling or dehumidification will occur when the space temperature/dewpoint rises or falls outside the unoccupied setbacks. During unoccupied demands, the supply fan will energize and the space will be controlled to maintain the space temperature/dewpoint at the unoccupied setbacks. The outside air damper will remain closed, and the exhaust fan will remain off. END OF SECTION PACKAGED ROOFTOP AIR CONDITIONING UNITS