Air Sampling and Industrial Hygiene Engineering - Chapter 7 pps

Mechanical design should also consider life-cycle operability, maintenance, and repair of the facility and real property–installed equipment, components, and systems.. 7.5 GENERAL PIPING

Indoor Air Quality and Environments

This chapter evaluates the operations and maintenance decisions that must be made for air monitoring appropriate for testing ventilation adequacy It includes a discussion of current air- monitoring instrumentation and methodology.

7.1 VENTILATION DESIGN GUIDE

Mechanical designs should be economical, maintainable, and energy efficient, with full consideration given to the functional requirements and planned life of the facility Mechanical design should also consider life-cycle operability, maintenance, and repair of the facility and real property–installed equipment, components, and systems Ease of access to components and systems in accordance with industry standards and safe work-ing practices is a design requirement

The best way to prevent IAQ problems is to have appropriate and effective engineer-ing controls in place to maintain the indoor air quality The followengineer-ing is an example of design criteria guidance that should be discussed throughout the design phase Various boxes throughout the chapter illustrate the real-world concerns from which this guidance was derived

7.2 EXAMPLE DESIGN CONDITIONS GUIDANCE

The following conditions should be used and will need to be investigated in designing the mechanical systems:

• Site Elevation: Equipment design elevation is {insert} feet (meters) above sea level Appropriate corrections should be made when calculating the capacity

of all mechanical equipment installed at this elevation

• Latitude: {insert} Deg N

• Heating Degree Days: {insert} annual

• Cooling Degree Days: {insert} annual

7.2.1 Outside Design Conditions

Winter:

{insert} °F (°C) for outside makeup air and infiltration loads

{insert} °F (°C) for air transmission loads

Summer:

{insert} °F (°C) dry bulb

{insert} °F (°C) maximum condensation wet bulb

7.2.2 Inside Design Conditions

Winter:

{insert} °F (°C) for occupied administration areas

{insert} °F (°C) for mechanical/electrical areas

Summer:

{insert} °F (°C) for occupied administration areas

{insert} °F (°C) for mechanical/electrical areas

7.3 MECHANICAL ROOM LAYOUT REQUIREMENTS

Mechanical equipment room layout should have ample floor space to accommodate routine maintenance of equipment and adequate headroom to accommodate specified equipment Ample space should be provided around equipment to allow unobstructed access for servicing and routine maintenance This space allotment should include ample areas for service and/or replacement of coils, tubes, motors, and other equipment Provisions for installation and future replacement of equipment should be coordinated with the architectural design The arrangement and selection of mechanical equipment should not interfere with complete removal of the largest piece of equipment without dis-mantling adjacent systems or structures Doors should be located to facilitate such service

7.4 ELECTRICAL EQUIPMENT/PANEL COORDINATION

Arrangement of all mechanical equipment and piping should be coordinated with electrical work to provide dedicated space for panels, conduit, and switches Clearance required by the NEC above and in front of electrical panels and devices should be pro-vided Mechanical equipment (pipes, ducts, etc.) should not be installed within space that

is dedicated to electrical switchboards and panel boards (see NFPA 70 Article 384-4) When

electrical equipment is located in a mechanical equipment room, dedicated electrical space including a proper safety envelope must be available

7.5 GENERAL PIPING REQUIREMENTS

As applicable, the following should be provided for all piping systems:

• All pumps, regardless of design service, should be nonoverloading during oper-ation so the pump can operate at any point on its characteristic pump curve

• Air vents should be installed on all high points in piping systems

Air vent location is critical to air actually being vented versus just moving to the next lower air pressure area of the piping Air and the odors associated with volatile compo-nents in the air accumulate in pipes when there is inadequate venting Ultimately this air

is then available to the building proper if there is an “escape route’’ from the piping Common escape routes are dry floor drains, through toilet waters, across sink traps and into sink drain-head spaces, and any breaks in piping

• Valves

—Vent and drain valves with hose-end connections should be provided on all mechanical systems

—Drain valves should be installed at low points and for equipment that must be dismantled for routine servicing

—Isolation valves, balancing valves, flow measuring devices, and pressure/ temperature test plugs should be provided at all heating and/or cooling ter-minal units

—Bypass piping with isolation valves should be provided around all nonredun-dant control and system regulating valves

• Pipe taps, suitable for use with either a 0.125 in (3.2 mm) outside diameter (OD) temperature or pressure probe, should be located at each pressure gauge

• Coils

—All coils should be provided with valved drain and air vent connections

—On air-handling units with multiple coils, isolation valves should be installed

on the supply piping and a balancing valve on the return piping of each coil

—A thermometer should be installed on the supply piping of each coil

—Temperature/pressure taps should be provided on the supply and return pip-ing of each coil

• Strainers should be provided with a valved blowdown connection and piped to

a floor drain

• All underground metallic lines, fittings, and valves, except for cast iron soil and storm drain piping systems, should be cathodically protected

• All exterior, underground nonmetallic piping should be buried with pipe detec-tion tape

These design criteria ensure that system components can be located and isolated for maintenance Areas where piping will be breached after isolation should be identified because in these areas exposure to workers and the environment from pipe contents is most likely during maintenance events Identification of these areas should then be keyed to general building ventilation systems, location of PPE, and provisions for emergency exit-ing of the buildexit-ing proper

7.6 ROOF-MOUNTED EQUIPMENT

Except for intake or relief penthouses, no mechanical equipment should be located on the roof of the facility

7.7 VIBRATION ISOLATION / EQUIPMENT PADS

Provide vibration-isolation devices on all floor-mounted and suspended mechanical equipment that could transmit noise and vibration to occupied areas All floor-mounted mechanical equipment should be provided with 6-in (152-mm) housekeeping pads Vibration isolation is also important to prevent the transmission of vibrations to nearby equipment, piping, and control systems The transmission of vibrations is an issue; sus-tained vibration of equipment may “shake loose’’ equipment components

7.8 INSTRUMENTATION

Sufficient instrumentation must be provided to aid maintenance personnel in balanc-ing and/or troubleshootbalanc-ing mechanical systems Durbalanc-ing design the followbalanc-ing systems should be assessed for instrumentation requirements:

• Media at each change in temperature point and at all mixing points in chilled water and air-handling systems

• Discharges of air handlers

• Chilled water-blending stations

• Chilled water zone return mains

Pressure gauges, thermometers, flow indicators, and sight glasses should be easily read from the adjacent floor The following design elements should be addressed:

• Isolation valves on each pressure gauge

• Thermometers with separable socket thermo-wells

The removal, repair, or cleaning of flow-measuring devices should be possible without having to shut down the entire system In order to accomplish integral system isolation, the following installations should be considered:

• A portable meter, with appropriate range, for each type of flow-measuring device installed

• Separate pressure gauges on both the suction end and the discharge end of pumps

The simple fact is that the easier a system is to maintain, the more likely that mainte-nance schedules will be followed and that prescribed maintemainte-nance will be effective

7.9 REDUNDANCY

Spare parts that are difficult to obtain or are manufacturer unique, and any special service tools, should be obtained and stored prior to system startup

7.10 EXTERIOR HEAT DISTRIBUTION SYSTEM

The heat distribution system for the structure extends from and includes the point of connection at the existing system to the service entrance

7.10.1 Determination of Existing Heat Distribution Systems

Generally, any new distribution systems will have to connect to existing distribution systems at the installation The first step for the designer is to determine what media are available at the installation The media distributed in these systems are as follows:

• High-temperature hot water (HTHW) (201–450°F [94–232°C])

• Low-temperature water (LTW) (150–200°F [66–93°C])

• Low-pressure steam (LPS) (up to 15 psig [103 kPa])

• High-pressure steam (HPS) (over 15 psig [103 kPa])

• Condensate return (up to 200°F [93°C])

7.10.2 Selection of Heat Distribution Systems

After the medium type has been determined, the heat distribution system type must then be selected There are four basic types of distribution systems that can be used:

1 Above ground (AG) (high and low profile)

2 Concrete shallow trench (CST)

3 Buried conduit (BC) (preapproved type)

4 Buried conduit (BC) (not preapproved type)

7.10.2.1 AG Systems

AG systems are the least expensive and lowest cost (for labor) maintenance sys-tems available However, aesthetic reasons may prevent the use of AG syssys-tems These systems are a good application in industrial areas where the entire piping systems are aboveground The AG system design should include the following:

• Detailed piping layouts

• Pipe support design (low- or high-profile type)

• Piping insulation selection

• Jacketing selection (to protect against moisture)

• Transition details to buried systems

• Vent, drain, and trap designs

7.10.2.2 CST Systems

CST systems are the preferred buried system These systems consist of concrete, at grade tunnels, that allow access along the entire route These systems can be used for all the listed media The CST design should include the following:

• Detailed piping layouts showing all support locations

• Clearances inside the trench system, insulation, and jacketing selection

• Concrete trench wall and floor design (cast-in-place)

• Concrete top design (precast or cast-in-place) complete with lifting devices

• All road crossings

• Grading to keep groundwater from ponding over the trench system

• Sealant types and locations

• System slope 1 in./20 ft [25 mm/6096 mm] minimum, to ensure the trench floor will drain to the valve manholes)

• Vent locations

All drains and traps must be located in the valve manholes Vents may be located in the trench system only if access is provided to them with manhole lids poured in the trench top

The use of manholes in these systems to provide housing for drains and traps must be evaluated concerning confined space entry provisions

7.10.2.3 Buried Conduit (preapproved type)

Due to many premature failures, buried conduit (preapproved type) is the last choice in buried distribution systems These systems consist of insulated steel carrier pipe enclosed in a drainable and dryable steel conduit These systems are not preferred except in an unusual situation that precludes the use of any other system (e.g., flood plain areas)

Manufacturer’s Responsibility

Buried conduit systems are transported to the site in factory assembled sections The manufacturer is responsible for the design of pipe supports, expansion compensation devices, end seals, insulation types, conduit design, and universal protection of the con-duit The manufacturer must submit expansion stress calculations for the designer to review compliance with project specifications

Designer’s Responsibility

The designer is responsible for all the general design considerations listed previously and should also include the design of the buried conduit system’s penetration into the con-crete valve manhole and the detailed routing of the system on the site

The use of manholes in these systems to provide housing for drains and traps must be evaluated concerning confined space entry provisions

7.10.2.4 Buried Conduit (not preapproved type)

BC systems (not preapproved type) consist of an insulated metallic or nonmetallic car-rier pipe covered by a nonmetallic conduit Due to the lower pressures and temperatures

of these media, these systems have proven effective

BC systems (not preapproved type) are similar to the preapproved buried conduit in that these systems are delivered to the site in factory assembled sections However, the designer

has less control with the not preapproved system The designer chooses the items listed for general design considerations, and, in addition, provides detailed piping layouts, insulation type and thickness, conduit selection, carrier pipe selection, and valve manhole entrances The use of manholes in these systems to provide housing for drains and traps must be evaluated concerning confined space entry provisions

7.10.3 Design of Heat Distribution Systems

The design of heat distribution systems includes, but is not limited to the following:

• Mechanical—expansion compensation, piping system design (fittings, valves, insulation), equipment selection, equipment sizing, and pipe sizing and routing

• Structural—reinforced concrete design, pipe supports, valve manhole design, and other miscellaneous structural designs

• Electrical—electrical service to equipment and controls, and universal protection (if required)

• Civil—excavation and backfill, grading, road crossings for buried systems, area drainage design, system plans and profiles, and site coordination to ensure sys-tem integrity (especially for CST) fits into the site properly

7.10.4 Existing System Capacity

The designer must determine if the system has adequate capacity to tie into the exist-ing heat distribution system The designer must also determine if the connectexist-ing points for the existing lines have adequate hydraulic capacity (are large enough) to satisfactorily han-dle the new loadings under variable operational scenarios

Each installation should have hydraulic analysis data to indicate what the new loading impact is on the existing system This information must be provided by the designer The designer must update the hydraulic analysis, while considering possible future expansion impacts, as part of any new system design

7.10.5 General Design Considerations

The following general design considerations should always be considered:

• Survey—A survey in the location of the distribution system must be done com-plete with soil borings and information on groundwater, soil types, and soil resis-tivity The survey data should be noted

• Utilities—A utility investigation must identify all existing utilities within a mini-mum utility corridor of 25 ft (7.6 m) of the new distribution system (including information on type, piping material, size, and depth) This investigation includes the engineering determination of where to connect the new distribution system to the existing system All new connections must be at or near existing system anchor points to avoid damage to the existing utility system

• Pipe sizing—All new pipes must be sized in accordance with prescribed engi-neering design procedures Minimum line sizes for any system should be 1.5 in (38 mm) (nominal) The use of better performing pipe materials for specific trench soils should be a consideration

• Expansion—Expansion compensation calculations are necessary to ensure the new lines are properly designed under the engineering allowable values for stresses, forces, and moments A computer finite element analysis program can be used to determine these values Only loops and bends are to be used for expansion com-pensation No expansion joints should be permitted in the design and installation

• Valve manholes—Concrete valve manholes must be completely designed includ-ing structural grated or concrete covers, internals (includinclud-ing valves, traps and drip legs), clearances, and reinforced concrete design

• Drainage—All valve manholes must either be gravity drained to an existing storm drain line with backflow protection or to a remote sump basin complete with duplex sump pumps, which discharge to an existing storm drain line or to grade

• Grading—Regardless of the system, grading must be designed to prevent groundwater from entering the valve manholes

• Plan/profile—Plans and profiles should be drawn for all systems showing, at a minimum:

—System routing and piping slope elevations

—System stationing

—All existing utility and other major interferences (depths if known)

—All adjacent roads and buildings clearly labeled

—Current types of surface conditions along the new utility corridor (asphalt, grass)

—Both new and existing grade contour lines (plan)

—Exact support locations for the new utility system

—Dimensioning (consistent English or metric units) to ensure accurate utility routing

7.10.6 Identification

Provide a brass name tag for each valve and temperature control device installed in all mechanical systems

All exposed or concealed piping in accessible spaces should be identified with color-coded bands and titles in accordance with American National Standards Institute (ANSI) Standard A13.1, Scheme for Identification of Piping Systems

• Pipes in buildings are categorized as pipes related to

—Fire protection systems

—Critical piping in essential and hazardous facilities

—All other piping

• All water pipes for fire protection systems in seismic zones 1, 2, 3, and 4 will be designed under the provisions of the current issue of the Standard for the Installation of Sprinkler Systems of the National Fire Protection Association (NFPA No 30) To avoid conflict with these NFPA recommendations, the criteria

in the following subsection are not applicable to piping expressly designed for fire protection

• Ductwork in buildings is categorized as

—Critical ductwork in essential and hazardous facilities

—All other ductwork

Consistent system identification provides a basis for future communication to mainte-nance and operations personnel, users of the system, and emergency providers

7.11 THERMAL INSULATION OF MECHANICAL SYSTEMS

This section contains requirements for the insulation of mechanical systems, including insulation of plumbing systems and equipment, roof storm drain system, hot water piping systems and equipment, chilled water piping and equipment, and the insulation of the duct systems

• Air-conditioning return ducts located in ceiling spaces used as return air plenums

do not require insulation

• Hot water and chilled water circulating pumps should not be insulated

• Provide reusable insulation covers at

—All check valves

—Control valves

—Strainers

—Filters

—Any other piping component requiring access for routine maintenance

• Insulation exposed to the weather or possible physical damage should be cov-ered by appropriate metal jackets All piping with metal jackets should be identi-fied on the drawings

The use of insulation must also be evaluated regarding the potential for leakage from piping and/or condensation, which renders insulation a potential site of biological amplification

7.12 PLUMBING SYSTEM

The plumbing system consists of the water supply distribution system; fixtures and fixture traps; soil, waste, and vent piping; storm water drainage; and acid and industrial waste disposal systems It extends from connections within the structure to a point 5 ft (1.5 m) outside the structure The design of all plumbing must comply with the most cur-rent National Standard Plumbing Code, unless otherwise stated

• Pipe materials for the domestic water system should be specified as nonferrous

• Underground water pipes must be installed below the recognized frost line or insulated to prevent freezing

—Service lines enter the building in an accessible location, and when entering through the floor, a displacement type water entrance should be provided

—When the incoming pressure of water supply exceeds the water pressure nec-essary for proper building operation by 10 psig (68.9 kPa), a pressure-reducing valve must be provided

7.12.1 Piping Run

Piping runs should be designed to minimize interference with ordinary movement of personnel and equipment

• The water supply piping is distributed throughout the building, with water mains generally running near the ceiling of the lowest floor

Neither water nor drainage piping should be located over electrical wiring or equip-ment unless adequate protection against water intrusion (including condensation) damage has been provided Insulation alone is not adequate protection against condensation

• Water and waste piping should not be located in exterior walls, attics, or other spaces wherever a danger of freezing exists Where piping is to be concealed in wall spaces or pipe chases, such spaces should be checked to insure that clear-ances are adequate to properly accommodate the piping Water piping should be designed for a maximum flow velocity of 8 ft/s

Pipe chases and collocation of piping must be evaluated for accessibility and the poten-tial for hosting contaminant repositories if leakage occurs Both biological and chemical risk should be evaluated, particularly for spaces where small leaks may go unnoticed

• Cross connections between water supply piping and waste, drain, vent, or sewer piping are prohibited

—Piping should be designed so that a negative pressure in the water supply pipe and/or a stopped-up waste, drain, vent, or sewer pipe will not cause backflow

of wastewater into the water supply piping

—Single check valves are not considered adequate protection against wastewater backflow

7.12.1.1 Back-Siphonage

The supply outlet connection to each fixture or appliance that is subject to back-siphonage of nonpotable liquids, solids, or gases must be protected in accordance with the National Standard Plumbing Code

Depending on the severity of the backflow situation, an air gap, atmospheric vacuum breaker, double check valve assembly, or reduced-pressure device may be required Severe backflow situations may include systems connected to boilers or converters containing gly-col mixtures, which should require a reduced-pressure device

• Air gaps will conform to the National Standard Plumbing Code

• Double-check valve assemblies, reduced-pressure assemblies, atmospheric (non-pressure) type vacuum breakers, and pressure type vacuum breakers will be tested, approved, and listed by the Foundation for Cross-Connection Control and Hydraulic Research

• Atmospheric type vacuum breakers, hose connection vacuum breakers, and back-flow preventers with intermediate atmospheric vents will be in accordance with American Society of Sanitary Engineering (ASSE) Standards 1001, 1011, and 1012

• Servicing stop valves should be installed in all water connections to all installed equipment items, as necessary for normal maintenance or replacement, and should be shown on the drawings, except when called for in project specifications

• Water conservation fixtures (low-flow type) conforming to the guide specifica-tions will be used for all toilets, urinals, lavatory faucets, and shower heads, except where the sewer system will not adequately dispose of the waste material

on the reduced amount of water

• Commercially available water hammer arresters should be provided at all quick closing valves, such as solenoid valves, and will be installed according to manu-facturers’ recommendations Vertical capped pipe columns are not permitted