| MASTERSPEC - EVALUATIONS | 06/03 (R 06/05) |
The following editing instructions relate directly to specific parts of the Section Text where they are referenced by the applicable Editing Instruction No. in the editor's notes:
Fan-coil units are cooling-only or heating-and-cooling units consisting of fans, coils, filters, piping specialties, and controls mounted on a common chassis. The cooling coil can be hydronic (chilled water) or direct expansion. Heating can be hydronic, steam, or electric coil. Units can be configured for concealed installations with no cabinets and with duct connections, or they can have finished cabinets for surface, semirecessed, and fully recessed mounting on ceilings or walls. Units are manufactured in several sizes and are classified according to the volume of air delivery. They can be equipped with several optional piping arrangements, controls, and accessories.
Configurations include horizontal, vertical, vertical-stacking, and low-height units, with finished exposed cabinets; and concealed units. Units are available in a vertical chassis with the fan and coil arranged vertically or in a horizontal chassis with the fan and coil arranged horizontally. Finished units are offered in a variety of standard and custom colors, and are suitable for installation in the occupied space configured for surface, semirecessed, and fully recessed mounting. Units are insulated with coated glass-fiber or closed-cell elastomeric foam insulation, and they can be fitted with disposable (standard) or cleanable filters.
Construction materials include painted sheet metal for most of the unit chassis; except where exposed to moisture, the chassis is galvanized steel. Condensate drain pans are available in plastic, stainless steel, or plastic-lined galvanized steel (materials vary among manufacturers), and they extend under the coil and valve connections. Exterior cabinets are primed and painted steel with factory finishes in standard or custom colors or prime coated for field painting.
Fans are forward curved, double inlet. Scrolls are made of galvanized or painted steel. Wheels are aluminum. Some small-capacity fan wheels may be made of a thermoplastic material.
Vertical stacking units are assembled with a vertical cabinet and hydronic piping approximating the building floor-to-floor height. Units contain piping risers for hot- and chilled-water distribution through the units for the full height of the building.
Two categories of fan-coil units are described in the Section Text. Each category is described in a separate Article. The categories are defined as follows:
The differences between the two categories of fan-coil units are summarized in the following table:
| FEATURES | FAN-COIL UNITS | DUCTED FAN-COIL UNITS |
|---|---|---|
| Airflow Range and Incremental Unit Sizes | 200 to 1200 cfm (94 to 566 L/s) in 200-cfm (94-L/s) increments | 800 to 4000 cfm (377 to 1890 L/s) in 400-cfm (188-L/s) increments |
| Unit Configuration | Blow or draw through | Draw through |
| Cabinet | Exposed or concealed | Concealed |
| Cabinet Orientation and Mounting | Horizontal or vertical; floor, wall, ceiling, or suspended; surface, semirecessed, recessed, or concealed; vertical stack concealed | Horizontal or vertical; floor mounted or suspended |
| Console Cabinet | Standard or low height | N/A |
| Fan Drive and Motor Configuration | Direct-drive, multispeed motor and fans mounted on removable fan board | Direct-drive, multispeed motor mounts in fan inlet; belt-drive, single-speed motor with adjustable sheave |
| Maximum External Fan Pressure Capability | 0.4-inch wg (99 Pa) | 2.0-inch wg (498 Pa) |
| Heating Coils | Hydronic, steam, or electric; combined hydronic coil with individual heating and cooling circuits. | Individual coils; hydronic, steam, or electric |
| Cooling Coils | Hydronic | Hydronic or DX |
| Maximum Filter Depth | 1 inch (25.4 mm) | 2 inches (50.8 mm) |
| Outdoor-Air Intake | Outdoor-air damper for maximum 25%, or 100% | Outdoor- and return-air mixing box with V-bank filter rack for up to 100% outdoor-air intake |
Direct- and belt-driven fans in ducted fan-coil units are capable of higher pressures than the fans used in fan-coil units. Fan-coil units can be connected to a separate discharge grille by a short straight duct or flexible connector but not through any significant length of duct.
Outdoor-air intakes for fan-coil units are located in wall boxes for vertical, wall-mounting units or in single, outdoor-air-intake ducts for horizontal units. The units include outdoor-air dampers but no return-air dampers. Outdoor-air dampers may open, but if the building is operating at a positive pressure, no outdoor air is supplied to the conditioned space. Mixing plenums offered with ducted fan-coil units may throttle the return air to ensure that the outdoor air is introduced into the conditioned space.
Fan-coil units equipped for heating and cooling may have a single coil containing separate circuits for each function (four-pipe units), or a single circuit for heating and cooling (two-pipe units). Heating may be provided by a separate coil with hot water, steam, or electric resistance.
Ducted fan-coil units have individual hydronic coils for heating and cooling (four-pipe units), or a single hydronic coil for heating and cooling (two-pipe units). Heating may be provided by a separate coil with steam or electric resistance.
Filters and internal construction of fan-coil units have been improved to aid compliance with ASHRAE 62. More easily cleaned foam insulation is available for thermal insulation. Filters that are more efficient and with greater holding capacity are available and condensate drain pans have been designed to ensure that condensate drains rapidly and completely. Considering the number of units and their close proximity to occupants, dirty units with moldy drain pans can be a major source of contamination.
Filter types typically available for fan-coil units and included in the Section Text are as follows:
| FILTER TYPE | ARRESTANCE PERCENTAGE ACCORDING TO ASHRAE 52.1 | MINIMUM EFFICIENCY REPORTING VALUE ACCORDING TO ASHRAE 52.2 |
|---|---|---|
| Washable Foam | 70 - 75 | 3 |
| Disposable, 1-Inch- (25-mm-) Thick, Coated Glass Fiber or Synthetic Media | 75 - 80 | 5 |
| Disposable, 1-Inch- (25-mm-) Thick, Pleated (Extended Surface) Cotton-Polyester Media | More than 90 | 7 |
Typical filter properties were taken from Table 3 in Ch. 24 of the 2000 ASHRAE HANDBOOK - HVAC Systems and Equipment. Disposable glass fiber and pleated surfaces are normally used in schools and commercial buildings. Data in Table 3 can be used to specify more stringent filter properties for rooms requiring higher levels of cleanliness. Verify the selection with the equipment supplier.
Thermostat features available with each type of fan-coil unit are as follows:
| Stages of Cooling | One |
| Stages of Electric Heating | Two or three |
| Coil Valve Control | Modulating or two position |
| Changeover | Manual or automatic |
| Fan Switch | Two or three speed |
| Deadband | Adjustable and nonadjustable |
| Mounting | Unit or remote |
| Programmable | Seven day, four periods each |
Commercial-style controls mounted and tested at the factory are available in many configurations. Descriptions of factory-mounted controls on fan-coil units are contained in the following two areas in the Section Text:
The Section Text allows the editor to delete the last category of these control descriptions in favor of specifying them in Division 23 Sections "Instrumentation and Control for HVAC" and "Sequence and Operations for HVAC Controls."
Fan-coil units are used to provide conditioning for individual or small rooms, usually on the building perimeter. The units may also be used for interior spaces and to condition rooms with cooling or heating load characteristics different from the surrounding rooms.
For individual zone control, consider a four-pipe hydronic system. To reduce piping costs, consider using individual two-pipe systems for each major exposure of the building. Two-pipe fan-coil units with electric heat are a low-cost alternative to four-pipe units but may use more energy.
Fan-coil units can be used in existing buildings; they require only supply, return, and condensate-drain piping, electrical power connections, and control wiring (if not integral controls). Tempered, ventilation air can be ducted to rooms containing fan-coil units to minimize penetrations in the outside walls of the building. This alternative may be attractive for historic buildings. Fan-coil units can also be used in multitenant buildings where flexibility in partition location is required to accommodate changing floor plans.
Fan-coil units might not allow the full use of the space along the outside wall because they project into the occupied room, and space must be allowed for air movement around the fan-coil units. Maintenance access is also a consideration for product selection and application.
The choice of heating media (electric, hydronic, or steam) for fan-coil units affects a project's energy economics, which usually favor hydronic or steam units. Hydronic and steam fan-coil units require a central system to support them. Compared to the costs of central systems (if central systems are not otherwise required), the first-cost benefits of electric heating are not insignificant and must be considered. The electric-heating coil alternative is expensive to operate under most fuel-rate structures but is often selected for ease of installation and resultant lower first cost. Where many intermittent heating-load applications exist, fan-coil units may be an energy-conservative advantage.
The choice of cooling media (chilled water or DX) for ducted fan-coil units also affects a project's energy economics. A large number of small inefficient air-cooled units may demand more electric energy than a water-cooled chiller system.
Fan-coil units operate at low discharge-air pressures, and thus low fan power input. This characteristic of fan-coil units is inherently energy conservative. However, the sum of a large number of small inefficient fan motors may exceed the power requirements of a single air-handling unit; motor and filter maintenance requirements dilute this benefit.
Economizer cycles, both air and water types, reduce cooling energy requirements and save energy.
Carbon dioxide sensors can save energy by reducing the energy required to heat and cool outdoor air when occupancy is less than peak design. Follow the ASHRAE 62 calculation procedure to establish the minimum outdoor-air quantities.
Model codes and standards, specifically ASHRAE 62, for indoor-air quality have indirectly required the addition of reheat coils for humidity control on fan-coil units that are conditioning large quantities of outdoor air for ventilation. This issue is especially important where the cooling-coil temperature is controlled to satisfy the room-temperature sensor. The coil is sized to cool the space at maximum summer conditions with full water flow. However, during most of the cooling season, cooling loads are considerably less than peak design conditions and the cooling-coil temperature is not low enough to dehumidify the combined space conditions and the outdoor air introduced for ventilation. To accomplish dehumidification, the supply air must be cooled and then reheated. However, ASHRAE/IESNA 90.1 limits simultaneous heating and cooling required by this dehumidification-reheat application. The following are exceptions that allow fan-coil units to reheat:
Closed-cell insulation with foil or matt facing is provided by some manufacturers to reduce the possibility of fibers from glass-fiber insulation being introduced into the conditioned space. In addition, the surface of closed-cell foam insulation is more cleanable than glass-fiber insulation. Regular cleaning may reduce the occurrence of mold growth in the units.
Plastic drain pans in some fan-coil units are removable for cleaning.
R-22 (HCFC-22) is the most popular refrigerant for fan-coil units equipped for direct-expansion cooling. However, R-22 contains CFC. In 2010, R-22 will be prohibited in new air-conditioning equipment. Its price will then probably begin to rise until 2020 when the production of R-22 must, by law, cease. Consider specifying CFC-free refrigerants such as R-407C, trade name Suva 9000 or Klea 66 ; or R-410A, trade name AZ-20, Suva 9100, or Puron.
ASHRAE 15, Safety Standard for Refrigeration Systems, defines fan-coil units with refrigerant coils as direct systems. Because refrigerant is piped through coils in the airstream supplied to the occupied space and because fan-coil units are installed in the occupied space, refrigerant leaks directly contaminate the occupied space. Although the possibility of contamination is a concern, the quantity of refrigerant usually does not exceed the density limit in ASHRAE 15 when using comfort air-conditioning packages. The limit for R-22 is 9.4 lb (4.26 kg) per 1000 sq. ft. (92.9 sq. m). This density is significantly above the usual requirement for standard air-conditioning systems. R-407C and R-410A should not be more restrictive than R-22.
LEED Rating: The LEED Rating System has been developed to guide owners of commercial buildings and Project team members on rating green and sustainable design practices. The Section Text contains requirements for air-conditioning equipment that can enable the design team to apply for credits that will contribute to a successful sustainable design, and possibly reward the Project team for successful completion of the Rating System.
"CFC Reduction in HVAC&R Equipment" is the third of three prerequisites in the Energy and Atmosphere (EA) category; prerequisites must be fulfilled to qualify for a LEED Rating. For a new building, new HVAC&R equipment must use CFC-free refrigerants. For an existing building, new HVAC&R equipment must use CFC-free refrigerants, and a phase-out plan must be submitted to convert existing HVAC&R equipment to CFC-free refrigerants by the end of the construction period.
Besides the prerequisite above, a credit is available in the EA category for "Ozone Depletion." This single-point credit is awarded if new HVAC&R equipment is HCFC free.
EA Prerequisite 2.0, "Minimum Energy Performance," also requires that direct-expansion-cooling fan-coil units have a minimum efficiency equal to ASHRAE/IESNA 90.1-1999.
Finally, EQ Prerequisite 1.0, "Minimum IAQ Performance," requires compliance with ASHRAE 62-1999 to establish minimum ventilation rates and filter selection criteria. EQ Credit 1.0, "Carbon Dioxide (CO2) Monitoring," requires the minimum outdoor air intake to be reset based on the concentration of carbon dioxide in the return air from the occupied space.
Fan-coil units installed in areas requiring seismic bracing must have bracing designed to applicable building codes. Local codes normally define design forces that must be resisted by mechanical systems. Seismic restraints should be designed by a professional engineer.
Ceiling-mounted and -suspended units represent the greatest seismic hazard. They must be restrained with rigid or cable restraints described in Division 23 Section "Vibration and Seismic Controls for HVAC Piping and Equipment." Floor-mounted units must be anchored to the floor. Wall-mounted units anchored to a wall should not require restraint.
See the Metric Appendix in the Evaluations in Division 23 Section "Common Work Results for HVAC" for SI (metric) pipe sizes.
Publication dates represent the editions on which the current Section Text is based. Standards are revised periodically, which may occur before this Section is updated again.
The following publications are useful in specifying fan-coil units. Other references may be needed for design purposes.
The list of manufacturers is neither a recommendation for the companies nor an endorsement of their products. Verify manufacturers' capability to comply with indicated requirements each time the Section Text is edited.
Airtherm A Mestek Company St. Louis, MO (314) 835-9911 www.airthermhvac.com Carrier Corporation Syracuse, NY (800) 227-7437; (315) 432-6000 www.carrier.com Engineered Air Ltd. Desoto, KS (913) 585-1071 www.engineeredair.com Environmental Technologies, Inc. Largo, FL (727) 541-3531 www.enviro-tec.com First Co. Dallas, TX (214) 388-5751 www.firstco.com International Environmental Corporation Oklahoma City, OK (405) 605-5000 www.iec-okc.com Marlo Coil Subsidiary of Engineered Support Systems, Inc. High Ridge, MO (636) 667-6600 www.marlocoil.com Marshall Engineered Products Co., LLC (MEPCO) Dunham-Bush, Inc. Harrisonburg, VA (800) 628-0192; (540) 434-0711 www.dunham-bush.com McQuay International Plymouth, MN (800) 377-1287; (612) 553-5330 www.mcquay.com Rosemex Saint Bruno, QC CANADA (450) 653-1002 www.rosemex.com Trane LaCrosse, WI (608) 787-2000 www.trane.com USA Coil & Air Malvern, PA (800) USA-COIL; (610) 296-9668 www.usacoil.com YORK International Corporation York, PA (717) 771-7890 www.york.com
When only a single unit or unit size is required on a particular project, a schedule is not necessary. However, if a given project requires several units of varying sizes, characteristics, and capacities, a schedule is preferred. It is the editor's option whether this schedule should appear in the Specifications or on the Drawings. Do not duplicate schedule information on both the Drawings and Specifications. If the editor wants to schedule particular units on the Drawings, the example below may be used as a guide.