- UNC-Chapel Hill’s standard HVAC system is a fully ducted, centralized, variable volume custom air handling unit serving VAV terminal units with hot water reheat coils.
- HVAC systems should be of heavy commercial/industrial quality construction. Design the system to provide a reliable service life of at least 30 years.
- HVAC should be conservatively sized such that it can maintain proper temperature and humidity levels without having to operate at the top end of its design envelope.
- The equipment shall be outfitted with the necessary sensors and components such that it can self-monitor and provide the necessary information for easy diagnosis of problems.
- The systems must be flexible enough to accommodate space renovations that will occur during its life.
- The systems should strive to centralize and locate points of routine maintenance such that building downtime, occupant interruption, and maintenance time is minimized.
- Recirculation of air from break rooms, mechanical rooms and print/copy rooms is not permitted.
- Heat recovery methods shall be utilized unless proven to be not cost effective by a life cycle cost analysis. Careful coordination with the Architect during schematic design is necessary to provide chases to combine exhaust systems which aid in the incorporation of heat recovery systems.
- Design the system to provide positive pressurization to the building, minimizing infiltration.
- The system shall be fully ducted on both the supply and return side.
- Ductwork shall be externally insulated metal ductwork. Duct liner or exposed insulation anywhere in the system is not permitted.
- The use of non-centralized fan powered devices such as fan powered terminal units and fan coil units are typically prohibited in occupied spaces. In certain situations and when approved by UNC Engineering Services, institutional grade fan coils, may be considered when served by outside air makeup units.
- The University encourages innovative design, but deviation from these standards must be approved by the Engineering Services.
- Design HVAC systems which provide air change effectiveness greater than or equal to 0.9, as calculated by ASHRAE 129-1997.
- Air handling equipment including air handling units, exhaust fans, and terminal units shall be shown to scale on the floor plans. HVAC plans (ductwork) at the Construction Document phase (or Later) shall be shown as “double lined” unless duct diameters are less than 10″.
- The use of discontinued or soon to be discontinued equipment is not permitted.
- For centralized HVAC systems serving DLAM, labs, and other critical areas, provide a minimum of two (2), manifolded AHUs per system to assure continuous HVAC service during AHU outages. Provide isolation dampers, to isolate each AHU during maintenance.
- Pressure relief: Specify pressure relief doors, when fans are capable of damaging ducts and equipment casings.
- Cooling equipment larger than 30,000 BTU must be floor mounted.
Server and IT Rooms
Provide independent cooling separate from the central HVAC system.
Sources of water leaks must not be located over server and IT equipment.
Typically institutional grade fan coils are provided for cooling. When possible mount fan coils low on a wall as the first choice or outside of the room. All possibilities of leaking water onto the telecom equipment must be eliminated. When provided in the telecom room, provide an auxiliary drain pan with auxiliary float switch. Chilled water piping should stub through the wall and directly into the fan coil valve enclosure. Any leaks or dripping shall be contained within the fan coil enclosure and/or drain pans.
Provide floor-mounted vertical, up-flow fan coils. Fan coils above the ceiling are prohibited.
For spaces with a considerably different thermal loading schedule than the majority of the building, provide an independent HVAC system. This typically applies to spaces with high process loads or spaces with substantially different occupancy schedules.
The designer should note this submittal requirement is for UNC review and the HVAC zoning plan does not necessarily need to be included in the final construction drawings.
- Indoor Summer Conditions: 75 °F, 50% RH max.
- Indoor Winter Conditions: 70 °F, 30% RH min.
- Mechanical Room Conditions: 50-83 °F, 50% RH max.
- Air handlers providing ventilation air shall be designed with a preheat coil, regardless of outside air percentage or the calculated mixed air temperature.
- Specify that coils shall completely fill unit casing. Do not overlap coils.
- Specify continuous thickness, minimum 0.035 inches, including return bends.
- Specify leak testing at 315 psig minimum.
- Spray Coil Systems are not permitted.
- Specify for maximum air velocity not to exceed 500 feet per minute.
- Cooling coils that will have peak demand during the winter shall be sized for 50 °F supply water.
Chilled Water Coils (requirements in addition to General Requirements)
- Refer to UNC Chilled Water Design Guidelines for supply and return water temperature requirements.
- Mechanical schedules for cooling coils shall indicate chilled water velocity in the coil tubes at design conditions.
- Specify stainless steel coil casings, frames, supports, attachment hardware and intermediate troughs for the cooling section. For custom AHUs, fasteners attached to stainless components shall be 400 series stainless steel or equivalent performance and zinc plated fasteners are prohibited.
- Specify for maximum air velocity not to exceed 450 feet per minute.
- Size coils for a maximum of eight rows at 10 fins per inch.
- Specify coils with water velocity between 4 and 6 feet per second at full load (design) conditions.
- Specify copper tubes with minimum thickness of 0.035 inches and aluminum fins with minimum thickness of 0.0095 inches.
- Specify 16 gauge stainless steel drain pans and stainless steel intermediate troughs. Cross break pan to drain connection. Drain pans shall be sloped and pitched to allow proper drainage.
Drain pans shall extend at least 6″ on the downstream side of cooling coils.
Do not install cooling units above ceilings. Where this is unavoidable, or where units are installed in other concealed locations, provide auxiliary drain pans in addition to drain pans provided with the unit. Provide capped drain plug on pan. Provide water detection system(s) in auxiliary pan which shuts unit down and closes the chilled water valve to the coil on detection of water. Do not install auxiliary drain pans in a manner which interferes with service access to the unit. Do not locate units above rigid type ceiling that would require dismantling of ceiling for access to the unit.
Specify an auxiliary drain pan under the entire air handler when it’s installed over occupied spaces.
For walk-in AHUs, specify aluminum grating over all drain pan sections. Specify pitched and triple sloped drain pans.
Condensate traps shall be sized so that water shall never stand in drain pans even with loaded filters.
Cooling condensate pumps should be avoided. Provide gravity drains when feasible.
Do not route condensate drain lines to storm sewer system or to building exterior.
Provide a cleanout at the bottom of the trap and one for rodding straight into the drain pan. Slope drain lines ¼” per foot.
The total trap height shall be a minimum of 1.5 times the maximum negative differential at that location + 1″.
Specify on the coil schedule the minimum height above the trap over-flow (dimension A) and below the trap overflow (dimension B). For draw through AHUs, the “A” dimension shall be at least local maximum static pressure plus 1″ and the B dimension shall be at least half the local maximum static pressure.
For AHUs specify base rail heights adequate to allow for trap installation. For draw through units 3″ greater than twice the maximum fan-suction pressure. For blow through units specify the minimum base rail height 3″ greater than the max fan discharge pressure.
Duct-mounted humidifiers are preferred for applications in variable volume systems; or mount in the AHU before the cooling coil. Ease of access is critical.
For duct-mounted humidifiers, specify welded stainless steel ductwork from the humidifier downstream for a distance of 1.5 times the absorption distance of the humidifier. Provide a minimum of 3″ deep; double sloped, stainless steel, drain pan integral to the duct extending the entire length of the humidifier section. Provide a drain with trap. Drain to a conspicuous location. Steam humidifier dispersion tubes shall be insulated.
Provide a minimum of 10″ x 10″ sweat-free windows for viewing humidifier operation.