HVAC design guide for large owner maintained

multi-wing facility

5.1Introduction

  1. The primary objective of these standards is to achieve consistency in the mechanical design. These guidelines are general and are supplemented by the applicable codes, standards, and guides referenced in this manual.
  2. As a minimum, all new and renovated construction will conform to the 2009 International Mechanical Code (IMC) and the 2009 International Plumbing Code (IPC).
  3. Additional standards listed in Appendix Section of this report can be referenced if appropriate for a specific project. This will have to be determined by designer on a project by project basis.
  4. A design narrative with specific project criteria is to be developed so that project design requirements can be available in a written format to all reviewing parties. Commercial specifications along with detailed design drawings are required to be incorporated in all final construction bid packages. Final mechanical as-builts will be produced during the construction phase.
  5. New construction energy consumption shall be at least 30% less than ASHRAE 90.1 2007 standards. Renovation project energy consumption shall be at least 20% less than ASHRAE 90.1 2007 standards.
  6. Endeavor to reduce energy consumption by 50% below ASHRAE 90.1 2007 standards if Life Cycle Cost justified.

5.5Mechanical Equipment Selection – General

A.All energy consuming equipment shall be selected on minimum capacity, physical size, configuration, special features AND the lowest Life Cycle Costs

B.A description of equipment is required to be indicated on the equipment list drawings. The engineer is required to locate and describe one manufacture’s model that meets design requirements. The following guidelines are required:

  1. Indicate the manufacturer’s catalog number and performance information.
  2. Provide additional specifications to describe complicated equipment.
  3. Use performance data that will ensure a quality product and the lowest Life Cycle Cost.
  4. Key mechanical items numbers to the plans and details.
  5. Manufacturer’s actual performance data is required for capacity equipment.
  6. All equipment assemblies requiring line electrical power will have a local disconnect provided by electrical contractor or manufacturer. Coordinate with electrical engineer exact requirements per each piece of equipment.

5.6VENTILATION:

  • Ventilation systems shall include a 100% outside air capacity economizer.
  • Variable volume, temperature and pressure ventilation systems are typically required using pressure independent VAV boxes.
  • Constant volume applications will incorporate pressure independent VAV boxes.
  • Pressure independent VAV boxes will be used on exhaust side for spaces requiring pressure control.
  • Full time 100% outside air systems will require a minimum 50% heat recovery package.

FANS & Air Handling Units (AHU):

  • Fans will be selected and sized to minimize noise in order to minimize the need for sound attenuation.
  • In fan systems totaling 10 HP or more, capacity will be adjusted using Variable Frequency Drives (VFD). Use OWNER standard VFD specifications and instructions.
  • Fan motors 1 HP and larger will be premium efficiency 1800 RPM unless a different speed is approved by OWNER. Size motors so that they operate at about 80% load at maximum anticipated airflow.
  • If fan HP requirement is ≥10 HP for any single purpose, use multiple direct drive plug fans in a wall type configuration (Huntair, Trane, Aaon or approved equal) rather than one large fan.
  • Packaged Roof Top AHUs will have a minimum R-13 insulation value.
  • Note: Aaon manufactures AHUs and packaged units with variable speed compressors, variable speed multiple fan walls and minimum R-13 insulation. All at a similar price to competitors with conventional features.

AIR FILTERS:

  • Owner has studied air filters and determined the lowest LCC product for each application. An approved equal would produce an equal or lower LCC to the specified filters.
  • Size filter banks so that only 2’x 2’ and 1’x 2’ filters are used and air velocities should be no greater than 4500 FPM.
  • Use 4” deep MERV 8 high capacity filters in typical applications.
  • Use 22” deep MERV 13 bag filters if needed to acquire LEED points.
  • Areas requiring higher efficiency air filters shall use 4” deep MERV 8 high capacity prefilters and 22” deep MERV 15 final filters. It is also acceptable to use 12” deep rigid filters that provides the lowest total cost of ownership as determined by the BetterBricks Air Filter Comparison Calculator.

HEAT EXCHANGE COILS:

  • Heat exchange coils should be designed for 14 degree F cooling and 20 degree F heating temperature differentials.

DUCTWORK

  • Do not use more than 4 feet of flexible ductwork unless it is necessary in retrofit applications.
  • Do not expose fiberglass to the ventilation system air stream or to occupied space.
  • Use full radius or splitter vane elbows only.
  • Select duct velocities to meet N.C. requirements of each occupied space.
  • Do not use opposed blade damper registers in occupied spaces. Locate balancing dampers next to the connection to the main branch or terminal box to minimize noise levels in occupied spaces. Insure that these dampers are accessible.
  • For return and exhaust ductwork, select a pressure rating that will avoid damage to ductwork in event of sudden smoke/fire damper closure during fan operation.
  • Protect ductwork from overpressure due to the sudden closing of dampers. Provide accessible, well-sealed pressure relief doors or panels that can be closed and sealed with out special tools or new parts after they blow open.

DAMPERS:

  • Construct damper blades of minimum 14 gauge galvanized steel and damper frames of minimum 16 gauge galvanized steel. Provide opposed blade action with stainless steel compressible jamb seals and extruded blade edge seals suitable for 0 degrees F to 250 degrees F. Blades shall rotate on stainless steel sleeve bearings. Damper blade lengths shall not exceed 60 inches. Leakage rate shall not exceed 5 CFM/square foot at 1-inch water gage and 9 CFM/square foot at 4 inches water gage. Leakage and pressure ratings shall be based on AMCA Publication 500.
  • Damper shafts shall have at least one flat facet at the point of connection to the actuator.
  • Provide a grooved scribe running parallel to the blades on the end of each damper shaft.
  • Outside, Return and Relief air dampers shall be independently driven and controlled.
  • Large damper assemblies shall be made of individually driven sections that are small enough to ensure reliable operation and uniform closure across the entire damper assembly when operated by a single actuator.

HVAC ACTUATORS:

  • Generally, actuators shall use 24 VAC power, analog control (or floating point control with position feedback) and mount around a rotating shaft to modulate dampers and valves.
  • Provide actuators with at least 150% of the required device torque.
  • Damper actuators shall be operated and controlled independently so that if one damper segment or actuator becomes inoperable, the others remain operable.
  • When adequate control air is available, use pneumatic actuators for large valves. Two stacked electric actuators may be used with OWNER approval for large valves.
  • Mount electric actuators horizontally to hot water valves.

ACTUATED VALVES:

  • Modulating 2-way control valves shall be pressure independent.
  • 3-way valves shall not typically be used. A 2-way controlled bypass may be used to maintain a minimum water flow.
  • Pressure independent flow control valves will not generally need circuit setters or dedicated strainers.
  • Two-position valves shall be of a rotating type and may be ball, shoe or butterfly depending on size and application.
  • Valves 2.5” and smaller shall be stainless steel, brass or bronze.
  • Valve stems shall have at least one flat facet at the point of connection to the actuator.

CHILLERS:

  • In general, variable speed chilled water systems will be used for cooling applications.
  • Lowest total cost of chiller ownership will be the primary criteria for purchase so anticipated energy consumption will be used in conjunction with the installed cost and anticipated O&M costs to determine the “best bid”.
  • Typically, variable speed compressors will produce the lowest total cost of ownership.
  • OWNER will provide a chiller selection tool characterized for the specific needs of the project. The mechanical designer will assist in creating a load profile for this tool.
  • Air Cooled chillers <200 tons will be considered if LCC justified.
  • Hybrid systems using indirect evaporative cooling, direct evaporative cooling and/or refrigerated cooling may be considered to reduce life cycle costs (LCC).
  • Small DX units may be allowed for small process loads such as data centers or labs.
  • If practical, cooling equipment should be provided in sizes and configurations so that hot gas bypass is never needed.
  • Reciprocating compressors are not allowed.

PUMPS:

  • Generally, variable speed pumps will be selected for N+1 operation such that all but one pump can operate at 60 HZ and produce 100% design flow. For example, three chilled water pumps might be installed and sized so that two pumps must run at 100% speed in order to maintain design flow. Typically all three pumps will operate in parallel at reduced speed to produce design flow. Pump selection and sequence of operation must be optimized to minimize energy consumption.

MOTORS:

  • All electric motors ≥ 1 HP shall be premium efficiency

5.9HVAC Design Conditions

A.Unless otherwise specified by the design engineer, the following guidelines are established HVAC design conditions at OWNER:

  1. Outdoor summer conditions: 96°F dry bulb, 60°F wet bulb (Reference ASHRAE weather data tables). These conditions are to be used when not designing for a specific indoor humidity.
  2. Outdoor summer conditions: 83°F dry bulb, 65°F wet bulb (Reference ASHRAE weather data tables). These conditions are to be used when designing for a specific indoor humidity and dehumidification or humidity control is in the design criteria.
  3. Outdoor winter conditions: 13°F dry bulb (Reference ASHRAE weather data tables).
  4. Pressurize all structures to minimize infiltration.
  5. The minimum outside air required to provide ventilation for each zone is determined by ASHRAE Standard 62.1-2007, Ventilation for Acceptable Indoor Air Quality.
  6. Design heating water system with 140°F maximum supply temperature and a minimum 20°F drop. Use condensing boilers and control return water temperature to range from 70°F to 120°F.
  7. Design chilled water systems with a minimum of 40°F and maximum of 45°F and a 10°F drop.
  8. Indoor office design conditions per owner energy policy:
  9. Occupied cooling = 78°F. Never set below 76°F.
  10. Occupied heating = 68°F
  11. Unoccupied cooling = 85°F
  12. Unoccupied heating = 55°F

5.10Evaporative Air Conditioning Design

A.Evaporative cooling is the primary cooling application for warehouses, shops not requiring close temperature controls, non-residential kitchens, and makeup air ventilation units. Evaporative cooling can also be considered as a source of cooling for offices and labs. The following are established guidelines for evaporative cooling:

  1. Operating efficiency for adiabatic cooling equipment is a minimum of 70 percent.
  2. Base the system installed capacity on the condition space peak cooling load and not an arbitrary air change air flow rate
  3. State adiabatic cooler specifications in terms of air capacity, the air entering dry and wet bulb temperatures and leaving dry bulb temperature.
  4. Indirect Evaporative coolers may be used for office and lab applications in order to meet energy efficiency requirements. These units must be installed in similar fashion to refrigerant units with return and exhaust air.
  5. When evaporative coolers are installed as supplemental cooling in an air handling unit, it is required to be installed downstream from the chilled water coil and controlled to operate as a first stage of cooling whenever the outside air dew point is below the highest allowable space dew point.
  6. Consider air duct design, location of coolers, and reliefs of the higher rate air supply (for two speed configuration) to ensure a satisfactory operating system.
  7. Specify drip pad coolers on small installations.
  8. Specify high efficiency rigid media coolers with stainless steel water sumps on medium and large size systems.
  9. For energy conservation, specify the lightest color available from the manufacturer for exterior finish coat of cabinet.
  10. Specify two speed or variable speed motors.
  11. Provide and detail a bleed, overflow and drain on the piping diagram for each piece of evaporative equipment. Set the bleed amount for 1 gallon per 1000 CFM. Discharge the bleed line to the sanitary sewer.
  12. Detail a system for thoroughly draining supply water piping subject to freezing.
  13. Include a slide damper in the design of small evaporative units.

5.11Refrigerated Air Conditioning Systems

A.The following are established guidelines for refrigeration systems:

  1. Design refrigeration systems to meet the requirements of the international mechanical code (IMC).
  2. Design refrigeration systems to meet the requirements of ASHRAE Standard 90.1-2007, energy standard for buildings except low rise residential buildings.
  3. Whenever possible include 100% OA economizers in HVAC system.
  4. Specify air conditioning and refrigeration institutecertified water coils. Size coils for 450 feet per minute maximum face velocity.
  5. Choose refrigerants to comply with the minimum coefficient of performance ratings as listed in ASHRAE 90.1.
  6. When a refrigeration machinery room is required design the room to meet the requirements of the UMC.
  7. Install air vents on all high points on chilled water lines.
  8. Minimizing LCC may require water cooling towers but it may be cost effective to use air cooled condensers for chillers smaller than 200 tons. Consider Smardt air cooled chillers.
  9. Specify hail guards for all exposed condenser coils.
  10. Select air cooled condensers for a 105°F entering air temperature and consider water spray systems to help meet energy efficiency requirements.
  11. Small condensers at grade level should be mounted on concrete pad or rails at least 6 inches above grade.

5.12Exhaust System Design

B.The design guidelines for typical exhaust systems include the following:

  1. Establish exhaust requirements per ASHRAE Standard 62.1-2007.
  2. Exhaust toilet rooms, darkrooms, battery rooms and any other areas that contain noxious, harmful, or objectionable fumes.
  3. Areas being exhausted are required to be balanced so a slight negative pressure exists.
  4. Exhaust refrigeration machinery rooms to meet the requirements of the UMC.
  5. Use sight proof and non-adjustable louvers.
  6. Use special exhaust grilles and door louvers in darkrooms to prevent passage of light.

5.13Local Exhaust Ventilation

A.Clearly define the source of all exhaust air and provide clean tempered air into the space to replace exhaust air.

B.Design hoods and calculate exhaust requirements based on similar applications found in the ACGIH, American conference of governmental industrial hygienists industrial ventilation manual.

C.Local exhaust ventilation systems are to be installed per manufacturer’s requirements and guidelines set in ACGIH.

D.Coordinate layout requirements of fume hoods with architect. Locate fume hood faces 10 feet or more from the closest air supply or exhaust point but not along normal traffic routes. A fume hood should not be located where the room air currents are greater than 50 feet per minute.

E.Fume hood full open air face velocity settings can be between 80 and 100 feet per minute. Generally, a face velocity of 100 feet per minute is satisfactory if the quality of supply air distribution is adequate. OWNER may accept 50 FPM face velocities based upon agreement with the users and designers. Regulated carcinogens and radiological hoods require higher face velocities.

F.Install fume hoods with an airflow indicator: a vanometer, differential pressure gauge or variable air volume control system.

G.Exhaust systems handling particles require minimum transport velocities be maintained throughout the system.

H.Exhaust systems handling vapors or gases duct velocities of 2000-3000 feet per minute usually result in a good balance.

I.Calculate exhaust requirements for closed type glove boxes for 50 CFM per box.

J.Exhaust vacuum pump-oil mist to the outside or to the building exhaust system.

K.HEPA systems used in radiological applications are to be installed per manufacturer’s recommendations.

5.14Exhaust Fans

A.The design guidelines for typical exhaust fans include the following:

  1. Roof exhausters for general room exhaust are required to be aluminum, roof mounted, curb type, centrifugal, integral weather cover, bird screen, back-draft damper, electrical disconnect.
  2. Exhaust fans that serve acid, corrosive or fume hoods are required to be utility and epoxy coated. Design fumes at an exit velocity of 3000 feet per minute. Extend exhaust stacks at least 10 feet above roof level or air intakes that are within 50 feet. Do not install weather cap on stacks that discharge hazardous chemicals.
  3. Coordinate design of exhaust stacks with structural and electrical to ensure proper stack support and lightning protection.

5.15Ductwork Design

A.The design guidelines for duct design include the following:

  1. Design supply ductwork using equal friction or static regain method.
  2. Design return air and exhaust duct on approximately 0.05 inches of water column loss per 100 feet of duct. Ensure the proper air quantities will be returned from even the most remote opening.
  3. Coordinate ductwork layout with the architect to minimize penetrations through firewalls and smoke barriers. At these penetrations, fire or fire/smoke dampers with access doors are required.
  4. Duct work is required to be constructed and installed in accordance with UMC or SMACNA, sheet metal and air conditioning contractors’ national association.
  5. Consider the requirement for a return air fan when the return duct resistance exceeds 0.25 inches of water.
  6. Provide means of balancing system. Consider dampers, flow measuring stations, temperature and pressure test connections, gauges and flow sensors.
  7. Draw duct work to scale. Thoroughly dimension the duct on the drawings. Clearly show register size, equipment list number, cubic feet per minute, and pressure drop. Show all turning vanes in elbows, transitions, duct liners, and air proportioning vanes.
  8. Diffuser size and cubic feet per minute are required to be shown on plan drawings for each type and size of diffuser. A diffuser or return air device with no volume control may be referred to as a grille. Install balancing dampers at trunk, not in room.
  9. Ductwork will require to be constructed and installed accordingly to the following pressure classifications:
  1. From the fan to the VAV box: 4” w.g. positive
  2. Downstream of the VAV box: 1” w.g. positive
  3. Return air: 1” w.g. positive or negative
  4. Lab exhaust: 4” w.g. negative
  5. Restroom and general exhaust: 2” w.g. negative
  1. For pressures less than negative 4” w.c., greater than positive 10” w.c. and highly corrosive duct refer to SMACNA Round Industrial Duct Construction Standards of SMACNA Rectangular Duct Construction Standards.
  2. Fire and Smoke dampers are to be specified for dynamic closure to shut off against airflow at a minimum of 2375 feet per minute and 4 inches of water.

5.16Equipment on Roof

A.It is preferred to locate air intakes and exhausts on roof and orient them to minimize adverse wind effects. All outside air intakes are to be at least 10 feet from flues, sewer vents, and exhausts.