GARCIA GALUSKA DESOUSA Consulting Engineers

Transcription

1 L#57295/Page 1/July 21, 2017 HVAC SYSTEMS NARRATIVE REPORT The following is the HVAC system narrative, which defines the scope of work and capacities of the HVAC system as well as the Basis of Design. While there are several different HVAC system options that are suitable for the proposed Renovation and Addition Option, the proposed HVAC system described below represents highly energy efficient, moderate first cost HVAC system options that provide a high level of thermal comfort and indoor air quality that has demonstrated to have a low overall life cycle cost in comparison to other system options and are compatible with the existing building s architectural and structural features. As part of the project s future design development, we recommend that a building energy model and life cycle cost analysis of a minimum of three HVAC system options should be performed. 1. CODES All work installed under Section shall comply with the all town, state, county, and federal codes, laws, statutes, and authorities having jurisdiction. 2. DESIGN INTENT The work of Section is shown on the drawings and specifications. All work is new and consists of furnishing all materials, equipment, labor, transportation, facilities, and all operations and adjustments required for the complete and operating installation of the Heating, Ventilating and Air Conditioning work and all items incidental thereto, including commissioning and testing. Mechanical systems shall function to deliver the performance levels to maintain space comfort within specifications set forth by ASHRAE Standard (note: Central AHU humidification system is not in the project scope, humidification control shall be accomplished through use of the energy recovery), ventilation requirements within ASHRAE , energy efficiency within ASHRAE and IECC Data center temperature and humidity levels shall be designed within ASHRAE TC recommended range (64.4 deg F to 80.4 deg F with a humidity level less than 60% RH) and Town record vaults shall be designed to maintain temperature and humidity conditions per the Owner s Design Criteria and/or Massachusetts Archives Performance Guidelines for Safes and Vaults. 3. BASIS OF DESIGN: (MASS CODE) Massachusetts Code values are listed herein based on local weather data values as determined from ASHRAE 2011 Handbook weather data. Outside: Winter 7 F, Summer 88 F DB 73 F WB Inside: 70 F +/- 2 (adj.) deg F for heating and 75 F +/-2 (adj.) deg F(55% RH) for cooling. Unoccupied temperature setback will be provided to maintain 60 F DB during heating season and 80 F DB during cooling season. Outside air is provided in accordance with ASHRAE Standard and IBC Mechanical Code (IMC 2015) requirements as a minimum. All occupied areas will be designed to maintain a level less than 850 PPM carbon dioxide. TEL FAX info@g-g-d.com

2 L#57295/Page 2/July 21, SYSTEM DESCRIPTION HVAC Option #1: Boiler/Chiller w/ Hot/Chilled Water/Energy Recovery Air Handling Units, Full Economizer, 4-Pipe Induction Unit System The existing Town Hall and Addition Renovation will be served by two (2) 500 MBH condensing boilers and a single 55 ton chiller. Each boiler will have a variable speed in-line pump feeding an insulated hot water supply and return piping system. The chiller will have a variable speed in-line pump feeding an insulated chilled water supply and return piping system. The piping from both the chilled water system and hot water system will be distributed to central station air handling units. Each AHU must have a full sized outside air duct connected to a large louver for the code required economizer cycle with a second similar duct and louver for relief air. Induction Units with hot/chilled water coils and ducted supply ventilation air will be used to zone individual rooms and groups of rooms to provide better temperature control. Return air ductwork will run from each room or zone back to the two air handler units. HVAC Option#1 System Summary: Requires a dedicated mechanical room with access to the exterior for louvers for AHUs Requires a mechanical room for boilers, expansion tanks, pumps, buffer tanks, air separators and glycol feed tank(s). A single 55 ton chiller will be located outside at grade Cooling System Chilled water pumps (primary/standby with VFDs), piping, associated insulation, valving and accessories. Two (2) 500 MBH condensing boilers Heating Hot water pumps (primary/standby with VFDs), piping, associated insulation, valving and accessories. Central station air handling units consisting of: o One (1) Chilled water/hot water air handling/ energy recovery/economizer unit at 2,500 CFM to serve the building office areas and o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 1,500 CFM to serve the Main meeting room o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 1,000 CFM to serve the Secondary meeting room o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 6,000 CFM to serve the Auditorium o Associated supply, return/exhaust ductwork, insulation, dampers, and air distribution devices. Louvers for AHU and EFs Induction Units will zone each office/room or group of rooms based on exposure and usage Induction Unit system requires about 24 of ceiling plenum space for ductwork and other mechanical equipment HVAC Option #2: Boiler/Chiller w/ Hot/Chilled Water/Energy Recovery Air Handling Units, 4-Pipe Full Economizer, Fancoil Unit System The new Town Hall will be served by two (2) 500 MBH condensing boilers and a single 40 ton chiller. Each boiler will have a variable speed in-line pump feeding an insulated hot water supply and return piping system. The chiller will have a variable speed in-line pump feeding an insulated chilled water supply and return piping system. The piping from both the chilled water system and hot water system will be distributed to central station air handling units. Each AHU shall have a full sized outside air duct connected to a large louver for the code required economizer cycle with a second similar duct and louver for relief air. Fancoils with a dual

3 L#57295/Page 3/July 21, 2017 temperature water coil will be used to zone individual rooms and groups of rooms to provide better temperature control. Supply and return air ductwork will run to each room or zone to provide code required ventilation. HVAC Option #2 System Summary: Requires a dedicated mechanical room with access to the exterior for large louvers for AHUs Requires a mechanical room for boilers, expansion tanks, pumps, buffer tanks, air separators and glycol feed tank(s). A single 55 ton chiller will be located outside at grade Cooling System Chilled water pumps (primary/standby with VFDs), piping, associated insulation, valving and accessories. Two (2) 500 MBH condensing boilers Heating Hot water pumps (primary/standby with VFDs), piping, associated insulation, valving and accessories. Central station air handling units consisting of: o One (1) Chilled water/hot water air handling/ energy recovery/economizer unit at 2,500 CFM to serve the building office areas and o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 1,500 CFM to serve the Main meeting room o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 1,000 CFM to serve the Secondary meeting room o One (1) Chilled water/hot water/energy recovery/economizer air handling unit at 6,000 CFM to serve the Auditorium o Associated supply, return/exhaust ductwork, insulation, dampers, and air distribution devices. Louvers for AHU and EFs Fancoils will zone each room or group of rooms based on exposure and usage Requires about 18 * of ceiling plenum space for ductwork and other mechanical equipment. *This assumes fan coil units shall be wall mounted or floor mounted console style units. Horizontal ceiling suspended fan coil units would require approx. 24 in. ceiling cavity space. Small boiler/pump room on ground floor Mechanical rooms on ground floor. HVAC Option #3: Boiler w/ Hot Water/DX/Energy Recovery Air Handling Units, Full Economizer, VRF System The new Town Hall will be served by (2) two 250 MBH condensing boilers. Each boiler will have a variable speed in-line pump feeding an insulated hot water supply and return piping system. The piping from the hot water system will be distributed to central station air handling units. Each AHU must have a full sized outside air duct connected to a large louver for the code required economizer cycle with a second similar duct and louver for relief air. Each of the AHUs shall have a dedicated split system condensing unit for cooling. Variable refrigerant flor (VRF) ductless cooling units (DCUs) with refrigerant piping and condensate piping will run throughout the building and connect to an outdoor 30 ton VRF air cooled heat pump unit. Supply and return air ductwork will run to each room or zone to provide code required ventilation. HVAC Option #3 System Summary: Requires a dedicated mechanical room with access to the exterior for large louvers for AHUs

4 L#57295/Page 4/July 21, 2017 Requires a mechanical room for boilers, expansion tank, pumps, air separator and glycol feed tank(s). Four (4) Condensing units (1@10 Ton, 1@3 ton, 1@5 ton, and 1@7.5 tons) will be located outside at grade. One (1) 30 ton (2 15 Ton Modules) condenser/vrf unit will be located outside at grade. Refrigerant liquid and refrigerant suction piping based on manufacturer s recommendations from VRF unit to DCUs Two (2) 250 MBH condensing boilers Heating Hot water pumps (primary/standby with VFDs), piping, associated insulation, valving and accessories. Central station air handling units systems consisting of: o One (1) Split DX(direct expansion)/hot water air handling/ energy recovery/economizer unit at 3,000 CFM to serve the building office areas o One (1) Split DX(direct expansion)/hot water/energy recovery/economizer air handling unit at 1,500 CFM to serve the Main meeting room o One (1) Split DX(direct expansion)/hot water/energy recovery/economizer air handling unit at 1,000 CFM to serve the Secondary meeting room o One (1) Split DX(direct expansion)/hot water/energy recovery/economizer air handling o unit at 3,500 CFM to serve the Auditorium Associated supply, return/exhaust ductwork, insulation, dampers, and air distribution devices. Louvers for AHU and EFs DCUs will zone each room or group of rooms based on exposure and usage Requires about 18 * of ceiling plenum space for ductwork and other mechanical equipment. *This assumes VRF fan coil units shall be wall mounted style units. Horizontal ceiling suspended fan coil units would require approx. 24 in. ceiling cavity space. HVAC Option #4: Geothermal System A high efficiency geothermal system could be paired with any of the three options listed above. The geothermal system would eliminate the requirement for Chiller and Condensing equipment described in the option above, and central indoor heat pump equipment would be provided. The geothermal system would require a well filed piping and pump distribution system to support the HVAC system cooling and heating plant requirements. Geothermal systems could be Open Vertical Standing Colum Wall or Closed Loop design. Closed loops typically require a larger quantity of wells but the wells have a reduced depth and have smaller diameter piping. Open loop well quantity sixteen (16) 500 ft deep each. Closed loop well quantity estimated at three (3) wells at depth of approx ft deep each Geothermal condensing water supply and return piping, pumps, valving and accessories are required. Refer to Pros/Cons list for all HVAC design options.

5 L#57295/Page 5/July 21, 2017 Building Management System: A new building energy management system (EMS) shall be installed for all HVAC system options. The EMS shall be an open protocol BACNet compatible building energy management system. The building EMS shall control building HVAC systems and shall store the information in a webaccessible database. The EMS will be capable to automatically distribute alarms and building information to support problem identification, maintenance and continued achievement of performance goals over the life of the systems. Typical components which the project shall require alarms, and monitoring include: would be Boilers, Air Handlers, Chillers, split system AC units, etc. Miscellaneous HVAC Systems: 5. DEMOLITION 1. In-line or roof exhaust fans shall be provided to serve the areas of the building that require separate dedicated exhaust systems utilizing exhaust air fans, ductwork and associated controls, i.e. Janitors Closets, Utility Rooms, etc. 2. All exterior stairways, entrances, and vestibules will be provided with hot water cabinet unit heaters. 3. Ancillary spaces will be heated by fin tube radiation, radiant heating panels, and/or convectors. 4. All corridors will be ventilated by the HVAC system that serves the adjacent area in which the corridor is located. Ventilation will be provided to ensure sufficient outdoor ventilation and make-up air is provided to offset the building exhaust air to maintain proper building pressurization. 5. Unit heaters will be provided to serve Mechanical and Utility Room areas. 6. Ductless high efficiency split system AC units shall be provided for the IT Server and Elevator Machine Room. All existing building HVAC systems shall be demolished, removed from the site and disposed of in a legal manner by the Contractor. Demolition activities shall be performed in a Phased manner as direct by the Project Architect. 6. TESTING REQUIREMENTS The mechanical contractor shall provide testing of the following systems with the Owner and Owner s representative present: Boiler plant system Air handling unit systems including all rooftop units, indoor air handling systems and exhaust air systems Terminal heating and cooling devices Automatic temperature control and building energy management system Testing reports shall be submitted to the engineer for review and approval before providing to the Owner.

6 L#57295/Page 6/July 21, OPERATION AND MAINTENANCE MANUALS AND OWNER TRAINING: When the project is completed, the Mechanical Contractor shall provide operation and maintenance manuals to the Owner. Operator training and users project documents are required for O&M staff to properly maintain the facility. These documents include the O&M Manual, As-built Drawings, and a Systems Manual (System Manual shall be developed by the CxA). Outside service providers and qualified, licensed and trained town staff will provide preventative maintenance and necessary repairs. Maintenance supervision and some actions will be performed by town staff, and require detailed training on the HVAC systems. Training will include the education of multiple members of staff, as chosen by the owner, in the proper use of the monitoring system. The project mechanical specifications will outline this requirement and will require the video recording of M/E/P systems training sessions. Basic level of maintenance typically includes changing of filters and visual inspection of equipment. Advanced level of maintenance typically includes seasonal changing between heating and cooling systems, visual inspection of the equipment, checking refrigerant levels in the chiller, and cleaning the boiler etc. The above is a sample of typical maintenance items. The end user shall decide what will be done in house and what will be contacted out. The end user should also review all maintenance contracts to verify the bill of goods. 8. RECORD DRAWINGS AND CONTROL DOCUMENTS: When the project is completed, an as-built set of drawings, showing all mechanical system requirements from contract and addendum items, will be provided to the Owner. 9. COMMISSIONING The project s HVAC systems shall be fully commissioned in accordance with project Commissioning specifications. 10. ENERGY EFFICIENCY GOALS: The project design shall meet and exceed the following minimum requirements: 1) LEED v4 - Minimum Efficiency Guidelines 2) MA 780CMR 8th Edition Ch.13 Energy Efficiency IECC ) ASHRAE Standard

7 L#57295/Page 7/July 21, 2017 COHASSETT TOWNHALL RENOVATION/ADDITION HVAC SYSTEM OPTION COMPARISON OPTION 1 PROS CONS ACTIVE CHILLED BEAM/ INDUCTION UNITS Superior thermal comfort conditions. Superior thermal comfort control as individual unit with associated controls will be provided for each zone. Low maintenance costs. Primary maintenance done at air handling unit. Fewer systems for heating/cooling Relatively quiet: No fans within space. Higher first cost. Moderate automatic temperature controls cost. Condensate drain maintenance (for AC). Maintenance of equipment is in occupied area. Distribution ductwork system is required resulting in additional architectural features (e.g. ceiling space, soffits, etc.). Chilled water pumps and associated VFD s required increase capital investment, maintenance, and operating costs. OPTION 2 PROS CONS VARIABLE WATER FLOW SYSTEM (CHILLED WATER) Superior thermal comfort conditions. Superior thermal comfort control as individual unit with associated controls will be provided for each zone. Lower operating costs than VRF system. All new equipment results in increased system life expectancy. Does not require distribution ductwork system. Refrigerant is self-contained in outdoor equipment. Lower ceiling plenum height required than induction units. Moderate first cost. High maintenance costs for quantity of units and factory authorized service is required for VRW system. Higher noise levels than induction due to fan motor located within occupied zone. High automatic temperature controls cost. Quarterly filter changes per unit. Condensate drain maintenance (for AC). Maintenance of equipment is in occupied area. Wall mounted evaporators do not provide direct ventilation to the space. Space humidity monitoring is critical to avoid condensation at the evaporator units (natural ventilation). Chilled water pumps and associated VFD s required increase capital investment, maintenance, and operating costs.

8 L#57295/Page 8/July 21, 2017 OPTION 3 PROS CONS VARIABLE REFRIGERANT FLOW (VRF) AIR CONDITIONING OPTION 4 GEOTHERMAL SYSTEM Superior thermal comfort conditions. Superior thermal comfort control as individual unit with associated controls will be provided for each zone. All new equipment results in increased system life expectancy. Distribution ductwork system only required for ventilation. Lower ceiling plenum height required than induction units. PROS Geothermal systems could be designed to serve as the heating and cooling plants for Option 1,2 and/or 3 listed above. Geothermal systems have very high operating efficiencies and lower operational costs. Geothermal system reduces carbon footprint of building. Extended system service life, due to lack of outdoor chiller/condensing equipment. Greatly reduced outdoor sound levels from HVAC equipment, due to elimination of large chiller/condensing unit(s) Moderate first cost. High operating costs due to air conditioning, ventilation fans, and electric heat (VRF units). High maintenance costs for quantity of units and factory authorized service is required for VRF system. Highest noise levels of 3 options due to compressor and fan motor located within occupied zone. High automatic temperature controls cost. Quarterly filter changes per unit. Condensate drain maintenance (for AC). Maintenance of equipment is in occupied area. Wall mounted evaporators do not provide direct ventilation to the space. Space humidity monitoring is critical to avoid condensation at the evaporator units (particularly when used with natural ventilation). Refrigerant piping is located inside building with potential of leaks. ASHRAE 15 provisions must be met. Manufacturer provided equipment controls to integrate to the Building Management System (BMS). CONS Highest First Cost - Geothermal systems have a higher first installed cost, primarily due to well field drilling, excavation and piping costs. Geothermal systems require some additional maintenance and system monitoring. Open loop type wells typically have higher maintenance costs than closed loop systems. Potentially higher electricity costs due to heating via electricity in winter. However, a supplemental high efficiency hot water boiler plant can be integrated into the system design for heating system redundancy and flexible fuel pricing. Higher automatic temperature controls cost.

9 L#57295/Page 9/July 21, 2017 Refrigerant piping is located inside building with potential of leaks. ASHRAE 15 provisions must be met. Requires sufficient site for wells