Dedicated Outdoor Air Systems

This specification covers factory-assembled dedicated outdoor air systems (DOAS) that draw 100% outdoor air, recover energy from the building exhaust, deep-cool and dehumidify the ventilation air to a controlled leaving dewpoint, reheat and temper the supply air as required, and deliver it to occupied spaces or to the inlets of a parallel sensible-conditioning system. Equipment covered includes the unit casing, the outdoor air and exhaust air fans, the air-to-air energy recovery section, the cooling and dehumidification section and its cooling source, the reheat section, the heating section, filtration, dampers, drain pans, and the factory controls that sequence dehumidification and reheat. Both indoor and outdoor (rooftop or grade-mounted) arrangements are addressed.

A DOAS exists to solve a single problem cleanly: ventilation air is a latent-load problem, and space conditioning is mostly a sensible-load problem, and the two do not track each other. A conventional mixed-air system tries to do both with one cooling coil, which forces a compromise — to wring enough moisture out of the outdoor air it must overcool the entire supply stream, then waste energy reheating it, and at part-load it often cannot dehumidify at all because the thermostat is satisfied before the coil gets cold enough. Decoupling the two loads resolves this. The DOAS takes responsibility for the entire latent load of the building (the moisture brought in by ventilation air and, by design intent, the internal moisture generated by occupants) by delivering air at a low, controlled dewpoint, and the parallel sensible system — variable refrigerant flow, fan coils, chilled beams, water-source heat pumps, or sensible-only zone equipment — then handles only the dry sensible load of each space without ever having to dehumidify. This is why DOAS units are designed and rated around moisture removal, and why the dewpoint of the supply air, not its dry-bulb temperature alone, is the controlling design parameter.

Because the DOAS conditions a full outdoor air stream year-round, two requirements dominate its design and this standard. First, air-to-air energy recovery is mandatory in most climates and at most ventilation rates under ASHRAE 90.1 — recovering energy from the exhaust stream is what makes conditioning 100% outdoor air economically viable, and the recovery device's effectiveness, frost behavior, and cross-leakage are central engineering decisions, not accessories. Second, achieving a low leaving dewpoint requires cooling the air well below the desired supply temperature and then reheating it; how that reheat is supplied (and whether it is recovered "free" reheat or purchased energy) is the second central decision. Equipment shall comply with AHRI 920 for performance rating of DX and heat-pump DOAS units, AHRI 1060 for air-to-air energy recovery ventilation equipment, AHRI 430 and AHRI 410 where central-station fans and coils are used, ASHRAE 62.1 for ventilation rates and air-stream classification, ASHRAE 90.1 for energy recovery and fan power, ASHRAE 55 for occupant comfort, the applicable AMCA fan and damper/louver standards, NFPA 90A for fire and smoke safety, and the applicable UL listing for electrical and refrigerant safety.

The boundary of work under this standard is the DOAS unit and its factory components, from the outdoor air intake and exhaust air connections to the supply air discharge connection. The supply and exhaust ductwork is covered by HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork; the diffusers, grilles, and registers that distribute DOAS air are covered by HVAC Air Distribution DevicesHVAC Air Distribution DevicesResolves to the current adopted revision.sync/hvac-air-distribution-devices; the parallel sensible terminal equipment is covered by its own standards; field refrigerant piping for split DX arrangements is covered by Refrigerant PipingRefrigerant PipingResolves to the current adopted revision.sync/refrigerant-piping; chilled water and hot water piping to coils is covered by the hydronic piping standard; and controls programming, graphics, and trending are covered by Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.

Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited. Where conflicts exist between referenced standards, the adopted energy and mechanical codes, the equipment manufacturer's instructions, or the contract documents, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

The Contractor shall submit the following for the Engineer's review and acceptance before equipment is ordered. Fabrication and procurement shall not proceed until action submittals have been reviewed and returned. Submittals shall be internally coordinated with the parallel sensible system and with the building automation system before any item is submitted.

• Manufacturer's product data for each DOAS unit, including model designation, an airflow schematic showing the sequence of energy recovery, cooling, reheat, heating, and filter sections, and the component schedule
• AHRI 920 certified performance ratings for DX and heat-pump units, including the integrated seasonal moisture removal efficiency (ISMRE2, or ISMRE270 where the unit reheats to a neutral leaving temperature with supplemental heat) and, for heat-pump units, the integrated seasonal coefficient of performance (ISCOP2)
• AHRI 1060 certified performance ratings for the energy recovery component, including sensible and latent effectiveness at 100% and 75% of rated airflow for both summer and winter conditions, the exhaust air transfer ratio (EATR), and the outdoor air correction factor (OACF)
• A psychrometric analysis for each unit plotting the air state points (entering outdoor air, after energy recovery, after the cooling/dehumidification coil, and supply air) at the cooling/dehumidification design condition, and the corresponding heating-season state points, with the leaving dewpoint and supply air temperature at each
• Capacity data at the cooling design condition and at the specified part-load (turndown) condition, demonstrating that the unit holds the leaving dewpoint setpoint at reduced ventilation flow and reduced load, where part-load dehumidification is required
• Fan performance curves at the design operating point per AHRI 430 / AMCA 210, with power and efficiency, and octave-band sound power levels per AMCA 300 for both supply discharge and casing radiation
• Coil selection data per AHRI 410 for cooling, reheat, and heating coils, with entering and leaving conditions, face velocity, rows, fin spacing, and air- and water-side pressure drop
• Filter section data with MERV rating certified per ASHRAE 52.2, initial and final resistance, and frame and seal construction
• Casing construction details, panel R-value, interior liner material, and, for outdoor units, the weatherproofing and finish system
• Energy recovery frost-control description (the method, the outdoor temperature at which it activates, and its effect on ventilation delivery during frost control)
• A controls points list and a written sequence of operation describing dehumidification control, reheat control, supply air temperature/dewpoint reset, energy recovery bypass and frost control, and the interface to the parallel sensible system and the Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system
• Electrical data: voltage, phase, minimum circuit ampacity, maximum overcurrent protection, and the refrigerant type and charge for DX and heat-pump units

The Contractor shall provide the following at or before substantial completion:

• Operation and maintenance manuals for each unit and all major components, organized with a table of contents
• As-built unit configuration and as-built controls points list reflecting any field modifications
• Factory test reports for each unit
• Startup and commissioning records, including the functional test of dehumidification, reheat, energy recovery frost control, and the interlock to the parallel sensible system
• Refrigerant charging records (DX and heat-pump units), documenting refrigerant type and total charge
• Energy recovery component maintenance data, including wheel drive belt and seal replacement intervals for rotary devices, and core cleaning procedure for fixed-plate devices
• Filter media installed at substantial completion with MERV certification and installation date tags
• Warranty documentation from the manufacturer and from any compressor and energy recovery sub-suppliers

DOAS units shall be manufactured by a company with a minimum of ten years of continuous experience designing and fabricating packaged ventilation and air-conditioning equipment, maintaining a quality management system, and able to provide replacement parts and factory service support for a minimum of fifteen years after the date of manufacture.

For each DOAS unit, the casing, fans, energy recovery section, cooling and dehumidification section, reheat and heating sections, filters, and dampers shall be provided as a coordinated factory assembly by or through the DOAS manufacturer. The interaction between the energy recovery device, the dehumidification coil, and the reheat source is what determines whether the unit actually holds its leaving dewpoint; resolving that interaction at the factory rather than assembling independent components in the field is the reason for the single-source requirement.

DX and heat-pump DOAS units shall be rated under the AHRI Certification Program for DX-Dedicated Outdoor Air System Units per AHRI 920, and published ISMRE2, ISMRE270 (where applicable), and ISCOP2 ratings shall bear the AHRI certification mark. Air-to-air energy recovery components shall be rated under the AHRI Certification Program for energy recovery ventilation equipment per AHRI 1060, and the published effectiveness, EATR, and OACF shall bear the AHRI certification mark. Where central-station fans and coils are used, ratings shall conform to AHRI 430 and AHRI 410. AHRI-certified ratings, not generic catalog values, shall be the basis of selection.

Each unit shall receive a factory functional run test before shipment, operating the refrigeration or heat-pump circuit (where integral), the fans, the energy recovery drive, and the dehumidification and reheat sequence, and confirming that the unit produces the specified leaving dewpoint at the test condition. A factory test report shall be submitted at closeout.

The complete DOAS assembly, including all electrical and (where integral) refrigerant components, shall be listed and labeled by a Nationally Recognized Testing Laboratory to UL 60335-2-40, or to UL 1995 where the Authority Having Jurisdiction continues to accept that listing for equipment manufactured before the transition date.

The unit shall be selected and rated for the design conditions at the installation site. The design outdoor air condition, the supply air leaving condition, and the exhaust air entering condition are as indicated on the mechanical schedules and the psychrometric process diagrams.

Because the DOAS conditions 100% outdoor air, it shall be selected at the project's dehumidification design condition — the design dewpoint or design wet-bulb condition from ASHRAE Fundamentals for the project location — and not merely at the cooling dry-bulb design. The dehumidification design condition, which typically pairs a moderate dry-bulb with a high coincident moisture content, is the condition that sizes the cooling coil and the reheat, and it is frequently more demanding for a DOAS than the peak dry-bulb hour.

The controlling leaving condition is the supply air dewpoint, because the DOAS is selected to absorb the building latent load. The leaving dewpoint setpoint shall be low enough that the DOAS supply air, after mixing with space air and absorbing the space moisture gains, holds the space relative humidity within the design range under ASHRAE 55. A leaving dewpoint of about 50°F to 55°F is typical for comfort applications; lower dewpoints are specified for spaces with strict humidity limits.

A neutral-supply DOAS delivers ventilation air at a temperature close to the space setpoint so it neither heats nor cools the space; the parallel sensible system carries the full space load. This is the most common and the most forgiving arrangement, because the parallel system and the DOAS never fight each other. A cold-supply (DOAS-to-space) arrangement intentionally delivers cool dry air to offset part of the space sensible load, which reduces the parallel system's capacity but requires careful diffuser selection to avoid drafts and requires that the parallel system not overcool and drive the space humidity back up. The cold-supply strategy decouples humidity control from the parallel system only if the DOAS dewpoint is held independent of its dry-bulb — which is exactly what the reheat section provides.

The following decisions define the unit. They are interdependent — the energy recovery type, the cooling source, the dehumidification and reheat method, and the supply strategy must be selected together — and they should be reviewed against the psychrometric analysis as a set.

Design outdoor (ventilation) airflow and exhaust airflow shall be as indicated on the mechanical schedules. The ventilation rate shall be established by the ASHRAE 62.1 ventilation rate procedure for the served spaces.

Air-to-air energy recovery is the feature that makes a DOAS practical. Conditioning a full outdoor air stream from a hot, humid summer condition or a cold, dry winter condition to the supply condition is a large load; recovering most of that load from the building exhaust, which is already near the space condition, cuts the cooling and heating capacity the unit must purchase by half or more. ASHRAE 90.1 requires exhaust air energy recovery for most ventilation systems based on the percentage of outdoor air and the design supply airflow, with a minimum enthalpy recovery ratio (the ratio of recovered enthalpy to the maximum available) of at least 50% at the design condition for the climate zone. Recovery shall be provided wherever required by the adopted energy code; the only DOAS units that omit it are those that fall below the code threshold or that qualify for a specific exception.

The first recovery decision is whether to recover latent energy (moisture) as well as sensible energy (temperature), and that decision turns on the application. Total-energy (enthalpy) devices — rotary enthalpy wheels and fixed-plate membrane cores — transfer both heat and moisture between the air streams. In a DOAS this is usually the right choice: in summer the enthalpy device pre-dries the incoming air using the drier exhaust, reducing the latent load on the cooling coil; in winter it returns moisture to the incoming air, reducing dry indoor conditions and the need for humidification. Sensible-only devices — heat pipes, sensible plates, sensible wheels, and runaround loops — transfer heat only. A sensible device is selected where moisture transfer is undesirable or prohibited: where the exhaust is contaminated and any cross-transfer to the supply is unacceptable, or where the design intent is to maximize the moisture removed by the cooling coil rather than recover it.

Rotary wheels and any device with a shared interface carry a small amount of air from the exhaust stream into the supply stream. AHRI 1060 quantifies this as the exhaust air transfer ratio (EATR) and the outdoor air correction factor (OACF). Where the exhaust is ASHRAE 62.1 Class 1 air (general comfort exhaust), a small EATR is acceptable. Where the exhaust contains Class 2 air, ASHRAE 62.1 limits the EATR to no more than 10% and requires that any transferred air be accounted for in the ventilation calculation; where the exhaust is Class 3 or Class 4, energy recovery that allows cross-transfer is prohibited and a sensible device with fully separated streams (heat pipe or runaround loop) shall be used. Rotary wheels intended for Class 1/Class 2 service shall include a purge sector, which uses a small pressure-driven flow to sweep carryover air back to the exhaust before the wheel rotates into the supply stream, reducing EATR.

In cold climates the warm, moist exhaust gives up its moisture as it is cooled by the incoming air, and that moisture can freeze on the recovery surface, blocking the exhaust path and destroying recovery. Every recovery device in a freezing climate shall have a defined frost-control strategy, and the strategy chosen affects the unit's ventilation delivery at the coldest hours. Wheels are frost-controlled by modulating wheel speed or by a timed defrost; fixed plates and heat pipes are frost-controlled by preheating the incoming air, by an exhaust-side bypass, or by recirculation. The frost-control method, its activation temperature, and its effect on ventilation flow during frost control shall be submitted.

A bypass damper around the recovery device shall be provided where the recovery would otherwise be active during economizer hours — when the outdoor air is already favorable and recovery would add unwanted heat — or where frost control or the energy code economizer provisions require the recovery to be bypassed. Bypass shall be controlled by the Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.

The cooling section of a DOAS does a different job than the cooling coil of a mixed-air unit: it is selected to drive the air to a low leaving dewpoint, which usually means cooling the air below the temperature the space actually wants. This is the core engineering of a DOAS. To reach a 50°F to 55°F leaving dewpoint at a humid design condition, the coil leaving dry-bulb must be at or below that dewpoint (the air leaves the coil at or near saturation), which is colder than a comfortable supply temperature. The air is then reheated to the desired supply temperature — but the moisture has already been removed and stays removed. AHRI 920 rates this behavior directly: its integrated seasonal moisture removal efficiency (ISMRE2, in pounds of moisture removed per kilowatt-hour) measures how efficiently the unit removes moisture across a range of conditions, and AHRI 920 testing is run to a 55°F leaving dewpoint reference.

The cooling source shall be selected to match the project's energy infrastructure and the unit type. Integrated DX (a packaged compressorized circuit within the unit) is the most common for standalone packaged DOAS because it makes "free" recovered reheat available from the condenser. A heat pump adds heating from the same circuit. A chilled water coil is used where a central chilled water plant exists and the DOAS is one of many loads on it; a chilled water DOAS must obtain its reheat from a separate source, since there is no condenser heat to recover.

Variable-capacity compressors are strongly preferred for DOAS because the latent load varies enormously across the year, and a single-stage compressor either dehumidifies fully or not at all. A variable-capacity circuit can hold the leaving dewpoint at part-load ventilation rates and at the many mild, humid hours when a fixed-stage unit would short-cycle and deliver wet air.

The DOAS shall hold the leaving dewpoint setpoint across the range of operating conditions, not only at the design hour. Many of the wettest hours of the year are mild — a rainy 70°F day at near-saturation carries a large latent load with almost no sensible load — and a unit that can only dehumidify at peak sensible conditions will deliver humid air during exactly those hours. The unit shall provide dehumidification down to the specified minimum turndown, by compressor staging or variable capacity, and the part-load performance shall be documented in the submittal.

Reheat is not optional comfort tuning on a DOAS — it is the mechanism that makes low-dewpoint dehumidification possible without delivering uncomfortably cold air, and on a neutral-supply unit it is a continuous part of normal operation. The decision is where the reheat energy comes from. Recovered reheat — hot-gas (refrigerant) reheat that takes heat rejected by the unit's own condenser, a wraparound heat pipe or runaround coil that precools the entering air and reuses that captured heat to rewarm the leaving air, or a passive dehumidification wheel — is "free" in the sense that it spends no purchased energy on reheat. Purchased reheat (a hot water or electric coil) is simpler but spends energy heating air that was just cooled, which the energy code restricts. Recovered reheat shall be used wherever the unit type allows it; purchased reheat shall be limited to applications where no recovered source is available or where the energy code permits it.

A wraparound device (heat pipe or runaround coil) deserves note because it improves dehumidification while it reheats: by precooling the entering air before the cooling coil, it lets the cooling coil reach a lower dewpoint for the same compressor capacity, and it then uses that captured heat to reheat the leaving air — typically lifting the supply from roughly 48°F to roughly 55°F — with no purchased energy and no controls. Its limitation is that a passive wraparound is largely self-regulating and cannot independently set the supply temperature; where precise leaving-temperature control is needed, modulating hot-gas reheat or a controlled wraparound is required.

In the heating season the DOAS shall temper the cold ventilation air so that it does not chill the spaces or the inlets of the parallel sensible system. With energy recovery active, much of the heating is recovered from the exhaust; the heating source supplies the remainder. For a neutral-supply unit, the heating section warms the air to near the space-neutral temperature; for a tempered-reset unit it may warm it further to offset part of the space heating load.

Heat-pump heating capacity falls as outdoor temperature falls, exactly when the heating load is greatest, so air-source heat-pump DOAS units in cold climates shall include auxiliary heat sized to carry the unit through the heating design condition and any heat-pump defrost cycles. Where a hot water coil is the heating source in a freezing climate, freeze protection shall be provided as specified under Casing, Fans, Coils, Filters.

The casing shall be double-wall construction throughout, because a DOAS handles cold, dehumidified air on the supply side and cold outdoor air on the entering side, and condensation will form on any cold single-wall panel. Panel insulation R-value shall be appropriate for the climate; cold-climate and outdoor units warrant higher-R panels to prevent exterior condensation and limit conduction loss.

Outdoor and rooftop units shall be provided with a factory weatherproof casing: pitched or sloped top panels, weather hoods and drainable louvers (rated per AMCA 500-L) over the outdoor air intake and exhaust, bird screens, a drainable base rail, gasketed access doors with hold-open hardware, and corrosion-resistant exterior hardware. The exterior finish shall be a two-coat corrosion-inhibiting and UV-resistant system.

Supply and exhaust fans shall be direct-drive plenum (plug) fans driven by electronically commutated (ECM) motors or by variable-frequency-driven premium-efficiency motors, so that airflow can be held constant as filters and the recovery device load, and so that fan power complies with ASHRAE 90.1. Fan and airflow performance shall be rated per AHRI 430 / AMCA 210. Fans shall be selected at the design airflow and external static pressure with capacity to maintain design airflow at the loaded-filter and frosted-recovery condition.

Cooling, reheat, and heating coils shall be rated and certified per AHRI 410, with tube and fin materials suited to the airstream. Because the cooling coil runs wet continuously and the entire airstream is outdoor air, coastal and corrosive-environment units shall use corrosion-resistant fin treatment.

Cooling coil face velocity shall be selected to limit moisture carryover off a continuously wet coil; a face velocity at or below 500 ft³/min per ft² (cfm/ft²) of coil face is recommended for DOAS, lower than a comparable mixed-air unit, because the DOAS coil is always operating wet at design.

A sloped, fully draining stainless steel drain pan shall be provided under the cooling coil and under any other condensing section. Because a DOAS coil runs wet continuously, standing water is both a Legionella risk and a corrosion risk; the pan shall fully drain and shall be Type 304 stainless steel minimum (Type 316 in coastal or chemical environments). A condensate trap with seal depth matched to the section's static pressure shall be provided so the trap is neither blown nor sucked dry.

Where a hot water heating or reheat coil is used in a freezing climate, freeze protection shall be provided, because the coil sees full design outdoor air with no warm return air to buffer it. Protection shall be a serpentine-element low-limit (freeze-stat) covering the coil face, glycol in the coil loop, or a face-and-bypass arrangement, as appropriate.

Final filtration shall be MERV 13 for occupied-space ventilation air unless the application requires higher efficiency, with a pre-filter to extend final-filter life. Filter frames shall seal positively to prevent bypass, which would void the rated efficiency.

The DOAS is a sequence machine: it must coordinate energy recovery, deep cooling, dehumidification, and reheat to hold a leaving dewpoint, and it must coordinate with the parallel sensible system so the two never undo each other's work. The unit shall be furnished with factory controls and a labeled terminal interface, and shall integrate with the Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system. Sequences should follow the intent of ASHRAE Guideline 36 where applicable.

The primary control loop shall sequence the cooling coil to maintain the leaving dewpoint (or leaving humidity ratio) setpoint, and shall sequence the reheat independently to maintain the supply dry-bulb setpoint. Holding these two loops independent is what lets the DOAS control humidity without coupling it to space temperature — the defining behavior of a decoupled-latent system.

Supply air temperature and dewpoint may be reset by the BAS based on outdoor conditions, space humidity, or the load on the parallel sensible system, to save reheat energy when the full dehumidification capacity is not needed. Reset logic shall be coordinated with the Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.

The DOAS and the parallel sensible system shall be interlocked through the BAS so that the parallel system does not satisfy space temperature in a way that drives space humidity up (overcooling that raises relative humidity), and so that the DOAS ventilation runs whenever the spaces are occupied. Occupancy scheduling, demand-controlled ventilation reset (where CO2 sensing is used), and the night/unoccupied mode shall be coordinated across both systems.

Each unit shall receive the manufacturer's standard production tests plus a functional run test confirming that the refrigeration or heat-pump circuit, fans, energy recovery drive, and the dehumidification-and-reheat sequence operate and that the unit produces the rated leaving dewpoint at the factory test condition. A drain-pan tightness test and an electrical continuity and insulation test shall be included. A factory test report shall be submitted at closeout.

After installation, the system shall be tested, adjusted, and balanced by an independent certified agency per Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current adopted revision.sync/testing-adjusting-and-balancing. The TAB agent shall set and document the design outdoor (ventilation) airflow and the exhaust airflow through the recovery device, and shall confirm that the supply-to-exhaust airflow ratio is within the range the energy recovery device was rated for, since EATR and effectiveness are airflow-ratio dependent. Functional testing shall verify that the unit holds the leaving dewpoint setpoint, that reheat maintains the supply temperature setpoint, that energy recovery frost control operates, and that the interlock to the parallel sensible system behaves as designed.

The unit shall be rigged and set per the manufacturer's instructions using furnished rigging points; cables shall not bear on casing panels. Rooftop units shall be set on a level, gasketed roof curb that matches the unit supply, exhaust, and intake openings; grade-mounted units shall be set on a level housekeeping pad. After setting, the unit shall be verified level so the drain pan slopes to drain. Vibration isolation shall be provided as required by the unit type and location.

Service clearances shall be maintained per the manufacturer's instructions for energy recovery wheel or core removal, coil pull, filter access, and compressor and control service, and for the airflow clearance at outdoor intakes and exhausts. Clearances shall be coordinated with the roof plan / mechanical equipment layout.

The outdoor air intake shall be located to draw clean air and shall comply with the ASHRAE 62.1 separation distances from exhaust outlets, plumbing vents, cooling towers, loading docks, and other contaminant sources. The DOAS conditions 100% outdoor air, so a poorly located intake contaminates the entire ventilation supply. The intake and the unit's own exhaust discharge shall be separated so the exhaust is not short-circuited back into the intake. Intake and exhaust locations are as indicated on the roof plan and the mechanical site plan.

The condensate drain shall be trapped with a seal depth matched to the unit static pressure, run to an approved point of disposal with continuous slope, and provided with a union for trap cleaning. Where the unit is in a freezing location, the condensate drain shall be protected from freezing.

Supply and exhaust ductwork shall connect through flexible connectors and shall be independently supported so duct weight is not carried by the casing. Ductwork construction shall conform to HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork, and supply ductwork carrying cold, dehumidified DOAS air shall be insulated and vapor-sealed per Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation to prevent external condensation.

Startup shall be performed by a factory-trained representative of the manufacturer. The startup sequence shall verify refrigerant charge (DX and heat-pump units), fan rotation and airflow, energy recovery drive operation and purge (where provided), the dehumidification-and-reheat sequence holding the leaving dewpoint, the heating sequence, the frost-control sequence, and the reporting of all BAS points. TAB per Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current adopted revision.sync/testing-adjusting-and-balancing and functional performance testing by the commissioning agent shall follow startup. Commissioning shall include a wet-condition test of dehumidification where the season permits, or a documented plan for deferred seasonal testing where it does not.

The manufacturer shall warrant the complete unit against defects in materials and workmanship from the date of substantial completion.

The compressor(s) in DX and heat-pump units shall carry an extended warranty, because compressor replacement is the most consequential failure on a packaged DOAS.

The energy recovery device — the wheel and its drive and seals, or the fixed-plate core, or the heat-pipe/runaround assembly — shall carry a warranty against defects and against loss of rated effectiveness from a defect.

The Contractor shall warrant the installation workmanship, including the curb and intake/exhaust connections, condensate, flexible connections, and controls terminations, for one year from substantial completion.

Spare filters shall be stored in sealed manufacturer's packaging labeled with the unit designation, MERV rating, and the installation date of the set in service. The O&M manual shall include the filter change schedule, the energy recovery maintenance schedule (wheel seal and belt inspection, or fixed-plate core cleaning), and the condensate trap cleaning procedure.