HVAC Systems by fjzhxb


									HVAC Systems
A. Design Conditions: Following are the temperature/humidity conditions to be used for the design of HVAC systems that serve “standard” buildings/spaces: Outdoor Air: 94 Degrees F. DB / 76 Degrees F. WB for cooling 79 Degrees F. WB for evaporative cooling -10 Degrees F. DB for heating Indoor Air: 75 Degrees F. DB / 50% RH for cooling 70 Degrees F. DB for heating

When a system that serves a “standard” building/space is provided with positive humidity control, the space humidity setpoint shall be limited as follows: Summer: Winter: Not less than 50% RH Not more than 30% RH

Examples of “nonstandard” spaces are central computer rooms, library rare book rooms, animal facilities and laboratories with special temperature/humidity requirements. In order to maintain a space relative humidity outside these limits specialized HVAC equipment and/or building construction is required. (See the Doors & Windows/Glazing and Walls/Partitions sections within these General Guidelines.) Design conditions for wind speed, direction and mean coincident dry bulb temperatures shall be obtained from the chapter entitled Climatic Design Information in the current edition of the ASHRAE Fundamentals Handbook. The most conservative data listed for Decatur, Illinois shall be used. B. Central Utilities: HVAC systems shall utilize central distributed chilled water, central distributed steam and central distributed electricity whenever these utilities are available. Lower pressure “Campus steam”, if available, (as opposed to higher pressure “Utility Steam”) shall be used as the source of heat for all HVAC systems within campus buildings that are served with steam from Abbott Power Plant through the central steam distribution system. If “Campus Steam” is not available (e.g. at more remote locations such as the Veterinary Medicine Complex and the furthest north reaches of campus) then “Utility Steam” may be utilized to serve building HVAC systems. The dedicated utilities that serve a new building (or portion thereof) shall be sized and configured as appropriate to serve potential load growth. C. Central HVAC Systems: Each building shall be served by a minimal number of central HVAC systems rather than numerous individual/package units such as fan coil units, window air conditioning units or DX “split systems”. Typically, each central system shall include an air handling unit, a return and/or exhaust fan or fans and air distribution/return/exhaust ductwork. D. Institutional Quality: HVAC equipment/systems shall be institutional as opposed to commercial grade (i.e. having a 25 year minimum life expectancy for dynamic system components such as motors, switches, pumps, valves, fans, dampers, compressors and burners, and a 50 year minimum life expectancy for static system components such as ductwork, piping, conduit, and wiring). E. System Size: The number of small systems (i.e. less than 5,000 CFM) shall be minimized. The installation of a smaller number of larger systems typically results in higher equipment quality and reduced maintenance requirements while providing more opportunity for the application of energy conserving features and control strategies.

F. System Configuration: HVAC systems shall be configured such that spaces with similar usage are served by a common system. As much as possible, spaces with dissimilar usage types or schedules shall not be served by the same system. Large lecture halls / public assembly areas shall be served by a dedicated HVAC system. The animal facilities within a laboratory building shall be served by a dedicated HVAC system. Areas that have special temperature and/or humidity requirements shall be served by dedicated systems. This allows the design of each system to be tailored to the specific needs of the areas being served. It also allows the implementation of specific control strategies (such as occupied/unoccupied modes and temperature resetting) for each system to conserve energy while satisfying the requirements of all of the spaces served by that system. G. Future Requirements: Each HVAC system shall be sized and configured so as to accommodate anticipated/potential changes in loads, layout, etc. (within practical limitations) as the use of the areas served changes in the future. H. Backup Equipment: A 100% backup or duplex unit shall be provided for each critical piece of HVAC equipment that is vulnerable to failure. I. Equipment Location: Each piece of motorized HVAC equipment shall be located within a mechanical equipment room with the exception of roof mounted exhaust fans, window air conditioners and specialized unitary equipment such as “Liebert” computer room units that are specifically designed to be located within the space being served. Location of motorized HVAC equipment above finished ceilings shall be avoided.

J. Energy Conservation: (See the Energy Conservation section within these General Guidelines for specific HVAC system guidelines and requirements related to energy conservation.) K. Sound Control: Sound control as it relates HVAC systems shall be given adequate priority. As mentioned elsewhere, the best way to control noise is to not create it in the first place. When focused attention is given to maximizing the efficiency of HVAC systems, noise is much less of an issue. The allowable HVAC-related background noise level for a given type of occupancy shall not exceed the guideline criteria provided in the chapter entitled “Sound and Vibration Control” in the current edition of the “ASHRAE Handbook, HVAC Applications”. L. Vibration Control: Most floor supported rotating HVAC equipment that is located within the lowest level of a building , with the exception of air distribution equipment and reciprocating equipment (e.g. air/refrigeration compressors and internal combustion engines) may and shall be installed with virtually no special provisions for vibration isolation between the equipment and its support system or associated hydronic piping. This equipment shall typically be “hard mounted” directly to a reinforced concrete housekeeping pad without the use of vibration isolation devices and “hard connected” to the piping systems they serve without the use of flexible pipe connectors. The use of flexible pipe connectors shall be minimized since they have proven to be leak/failure prone. An exception to these general rules may be necessary in facilities where equipment that is especially vibration sensitive (e.g. an electron microscope) is located at the lowest level of the building in close proximity to an equipment area. Rotating HVAC equipment that is supported from any ceiling or supported by any floor other than the lowest floor of the building shall be individually evaluated to determine if vibration isolation devices, inertia bases and/or flexible pipe connectors are needed to prevent unacceptable levels of vibration from being transmitted into the building structures. M. Terminal Zoning: HVAC systems shall be configured such that each occupied space can be controlled as a separate zone with regard to temperature and/or airflow. In other words, one terminal control unit (e.g. constant volume reheat coil or VAV unit with reheat coil) shall be provided for each occupied space.

N. Multizone Units: When a multizone air handling unit is utilized it shall be configured such that 100% of the airstream passes through the cooling coil prior to entering the reheat coil / bypass area in order to provide adequate humidity control. O. Fan Coil Units: Fan coil units shall not be installed, except as a last resort when it is not possible to serve an area by means of one or more central air distribution systems. In those instances where heating/cooling fan coil units are installed, they shall be “four pipe” units. P. Disallowed Equipment: The following types of HVAC equipment/systems shall not be installed in campus facilities: 1. “Rooftop” or similar packaged heating and/or cooling units 2. Residential furnaces / air conditioning systems 3. Heat pump type heating/cooling units 4. “Two-pipe” combination hydronic heating/cooling systems Q. Control Systems: (See the Energy Management / Environmental Control Systems section within these General Guidelines for specific control system guidelines and requirements.) R. Freeze Protection: Water, steam and condensate piping systems shall not be installed in locations where they could potentially become vulnerable to freezing (e.g. outdoors without sufficient earth cover, within unheated spaces, within building exterior walls or wall cavities, within exposed overhangs, within exposed exterior walkways, etc.) S. Humidification: Space humidification shall be avoided as much as possible due to the energy and maintenance costs as well as the indoor air quality problems associated with it. When required, it typically be provided by means of a steam reboiler type humidifier installed at the central station air handling unit that serves the area to be humidified. The makeup water to each humidifier shall be softened to reduce scaling within the humidifier. Steam from the campus wide central steam distribution system shall not be used in conjunction with a direct steam injection type humidifier. All steam from this system shall be condensed and the condensate returned to Abbott Power Plant through the central condensate return system.

T. Animal Facilities: (See the Animal Facilities section within these General Guidelines for specific HVAC system requirements related to animal facilities.) U. Wet Laboratories: (See the Wet Laboratories section within these General Guidelines for specific HVAC system requirements related to wet laboratories.)

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