NOTE This standard covers factory-assembled, unitary water-source heat pump equipment rated below 135,000 Btuh and the shared building water loop that interconnects the units. (1.1)

NOTE A water-source heat pump moves heat between the conditioned space and a common circulating water loop rather than to outdoor air at each unit. In cooling, the unit rejects heat into the loop; in heating, it extracts heat from the loop. Because every unit shares one loop, a building can reject heat from sunny-side zones into the loop while shadow-side zones simultaneously draw heat from it, recovering energy internally before the loop conditioning equipment must add or reject any. (1.2)

NOTE The water-loop heat pump (WLHP) system is the dominant commercial application of this equipment and is the primary subject of this standard. (1.3)

NOTE In a water-loop system the circulating water is maintained within a moderate band, typically 60 °F to 90 °F, by a boiler that adds heat when the loop falls below its low limit and a cooling tower or closed-circuit fluid cooler that rejects heat when the loop rises above its high limit. The loop itself is a building recirculating loop, not a connection to the earth or groundwater. (1.4)

NOTE Ground-source (geothermal) closed-loop, bore-field, and open-well systems are excluded; those systems share the same unit hardware but add earth-coupling design not covered here. (1.9)

NOTE Ground-source systems introduce bore-field thermal sizing, well flow, and low-temperature brine operation that change unit selection and loop design substantially. The unit hardware overlaps, but the loop engineering does not, so they are out of scope. Detailed hydronic distribution piping beyond the unit connections is likewise a coordination note only here; see the project plumbing and hydronic documents. (1.10)

NOTE Standalone loop-rejection and loop-heating equipment design is cross-referenced, not specified in full. (1.11)

NOTE Cooling towers and fluid coolers are addressed as loop heat-rejection equipment under Cooling Towers. Where this standard sets loop-side requirements it does so to coordinate the WSHP units with that equipment, not to replace it. (1.12)

NOTE Each unit model furnished shall carry a current AHRI 600-2023 certified rating; ratings published only by the manufacturer and not independently certified shall not be accepted. (4.2)

NOTE AHRI third-party certification confirms that the published cooling capacity, heating capacity, EER, and COP have been verified independently rather than self-declared. Requiring an active certification listing protects the owner from optimistic catalog ratings and is the single most effective quality gate for this equipment class. (4.3)

NOTE ANSI/AHRI 600-2023 is the current controlling rating standard and supersedes the legacy ARI 320, AHRI 325, and AHRI 330 family. (5.1)

NOTE AHRI 600-2023 (I-P) was approved September 2023 and consolidates the older water-loop, ground-water, and ground-loop rating standards into one document. It establishes capacity and efficiency at defined entering-water and entering-air conditions using ASHRAE 37 as its laboratory test method. Specifying superseded ARI 320 or AHRI 325/330 certification confuses manufacturers and delays submittals. (5.2)

NOTE DOE federal minimum efficiency standards at 10 CFR 431, Subpart F set the regulatory floor and reference ISO 13256-1:1998 as their test basis. (5.3)

NOTE The federal test procedure incorporates ISO 13256-1, while AHRI 600-2023 uses ASHRAE 37. The two are functionally equivalent at the 86 °F water-loop cooling rating point but diverge at ground-loop conditions. Cite ANSI/AHRI 600-2023 as the primary performance reference and treat the DOE values as the minimum efficiency floor below which equipment may not be furnished. (5.4)

NOTE Rated capacity and efficiency shall be established at the ANSI/AHRI 600-2023 standard rating conditions unless the project schedule states otherwise. (5.5)

NOTE The AHRI 600-2023 standard rating point for cooling is 86 °F entering water temperature, 2.25 gpm/ton source flow, and 80 °F dry-bulb / 67 °F wet-bulb entering air. For heating it is 68 °F entering water temperature, 2.25 gpm/ton source flow, and 70 °F dry-bulb entering air. These are laboratory reference conditions; they are not the project design conditions and capacity must always be reconfirmed at the actual design EWT. (5.6)

NOTE Selected units shall meet the scheduled cooling and heating capacity at the project design entering-water temperatures, not merely at the AHRI rating point. (5.7)

NOTE A unit selected at the 86 °F cooling rating point can fall short of its scheduled capacity at a 90 °F loop peak, because cooling capacity drops as entering water gets warmer. Confirming capacity at the actual high-limit loop temperature is the most common selection error this standard guards against. Heating capacity is typically 80 % to 110 % of cooling capacity at rated conditions and likewise shifts with loop temperature. (5.8)

NOTE Cooling efficiency (EER) and heating efficiency (COP) shall equal or exceed the values scheduled, and in no case shall fall below the federal minimum and the applicable ASHRAE 90.1 minimum. (5.9)

NOTE The DOE federal floor at 10 CFR 431 is 12.2 EER for units below 17,000 Btuh and 13.0 EER for units from 17,000 to 135,000 Btuh, both with a 4.3 COP minimum for heating. ASHRAE 90.1-2022 sets the same floor for code compliance. ENERGY STAR and owner high-efficiency tiers run well above this; select the tier from the schedule, not from the floor. (5.10)

NOTE The unit mounting orientation shall be selected to suit the architectural layout and the available service access. (6.1)

NOTE Vertical (closet or chase) units stack supply and return in a single cabinet and suit perimeter closets in hotels and apartments. Horizontal units mount above the ceiling and suit office and corridor plenums. Console units are low-profile floor-standing perimeter units for under-window placement. Through-the-wall units serve a single room from an exterior wall. The choice is driven by the architecture, not by the mechanical system, so it must be coordinated against the architectural drawings. (6.2)

NOTE The unit type shall match the load-side distribution medium for the zone served. (6.3)

NOTE Water-to-air units deliver conditioned air and serve the great majority of zone applications. Water-to-water units deliver hydronic heating or cooling water and serve radiant panels, chilled beams, or secondary hydronic loops. Selecting the wrong type strands the distribution system, so confirm it against the zone's terminal devices. (6.4)

NOTE Each unit's cooling and heating capacity shall be established by a block or zone load calculation, not by floor area rule of thumb. (6.5)

NOTE Capacity is set by an ACCA Manual J or equivalent block load for the zone. Typical hotel and apartment units fall in the 0.75 to 2 ton range; the equipment class spans 0.5 ton (6,000 Btuh) to 11.25 ton (135,000 Btuh) per unit. (6.6)

NOTE A dedicated outdoor air system (DOAS) should be provided to handle ventilation and latent load where the WSHP units handle sensible zone load. (6.7)

NOTE WSHP units are most effective sizing for sensible zone load while a separate DOAS unit delivers tempered, dehumidified outdoor air to satisfy ASHRAE 62.1 ventilation and the building's latent load. This pairing is increasingly the default in commercial and multifamily design and should be coordinated with the ventilation documents. Standalone cooling-tower and fluid-cooler selection for the loop is addressed in Cooling Towers. (6.8)

NOTE The refrigerant circuit shall be factory-sealed, factory-charged, and leak-tested by the manufacturer; no field refrigerant work shall be required for a standard installation. (7.1)

NOTE WSHP units ship as sealed hermetic packages. Keeping field refrigerant work out of the standard installation preserves the certified charge and avoids the leak risk and skilled-labor cost of field brazing the refrigerant side. (7.2)

NOTE The refrigerant type shall be confirmed against the HFC phase-down schedule applicable at the project location before equipment is ordered. (7.3)

NOTE R-410A remains common across the installed base, but lower-GWP refrigerants such as R-32 and R-454B are replacing it in newer product lines. Several jurisdictions, including California under the AIM Act phase-down, restrict sales of higher-GWP equipment on a published timeline. Ordering R-410A equipment without checking the local schedule risks a unit that cannot legally be sold or installed when it arrives. (7.4)

NOTE Where multiple units share an enclosed space, the total refrigerant charge shall be evaluated against ASHRAE 15 and the building code for machinery-room classification and leak-detection requirements. (7.5)

NOTE ASHRAE 15 and IBC refrigeration provisions set charge limits per occupied volume and trigger machinery-room ventilation and refrigerant-detection alarms above defined thresholds. Multiple units in one mechanical room or chase can aggregate enough charge to cross those thresholds, so the analysis must be done rather than assumed away. (7.6)

NOTE The system shall be a two-pipe water-loop arrangement with the boiler and heat-rejection equipment connected to a common loop. (8.1)

NOTE A reverse-return two-pipe loop is the most common arrangement because it self-balances and is forgiving of field variation. A direct-return two-pipe loop costs less to install but requires careful balancing valve selection at each unit. The choice trades first cost against balancing effort. (8.2)

NOTE The loop shall be maintained within its design temperature band by automatic control of the boiler and the heat-rejection equipment. (8.4)

NOTE The standard water-loop band is 60 °F to 90 °F. Common design setpoints are a 65 °F low limit that energizes the boiler and an 85 °F high limit that energizes the cooling tower or fluid cooler. A dead band between the two prevents simultaneous heating and rejection. (8.5)

NOTE A loop temperature reset or setpoint schedule shall be included in the contract documents so the controls contractor has a defined basis of control. (8.6)

NOTE Omitting the boiler and cooling-tower setpoint basis from the documents is a chronic source of RFIs, because the controls contractor finds no setpoint to program. Stating the low limit, high limit, and any reset strategy in the specification closes that gap before it becomes a field question. (8.7)

NOTE The loop fluid shall be plain water for loops maintained above the freezing range; a propylene glycol solution shall be provided only where loop or ambient conditions can approach freezing. (8.8)

NOTE A building recirculating loop held at 60 °F or above needs no freeze protection and runs on plain water, which preserves capacity and pumping efficiency. Propylene glycol is reserved for hybrid arrangements where some portion of the loop can approach or fall below 32 °F; glycol reduces capacity and increases pumping head, so it is not added without cause. (8.9)

NOTE The boiler and heat-rejection equipment shall be sized against the simultaneous loop load using a diversity factor, not the sum of every unit's peak. (8.10)

NOTE In a mixed-use building, heating and cooling zones rarely peak together, and the loop recovers heat internally. Sizing the boiler and tower for 100 % simultaneous load grossly oversizes both. A diversity factor of 60 % to 75 % is typical for mixed-use buildings. (8.11)

NOTE Each unit shall be provided with a balancing valve so that it receives its design loop flow. (8.13)

NOTE Without a balancing provision at each unit, the loop short-circuits to the path of least resistance and starves units at the hydraulic extremes. (8.14)

NOTE Each unit on a two-pipe loop shall be provided with a two-position automatic shutoff valve that closes when the compressor is off, per ASHRAE 90.1 Section 6.5.7. (9.1)

NOTE When a unit's compressor cycles off, leaving its loop circuit open lets water circulate through it for no benefit, wasting pump energy continuously across every idle unit. ASHRAE 90.1 Section 6.5.7 requires an automatic valve that isolates the off unit. Omitting it is both an energy-code violation and a permanent parasitic loss. (9.2)

NOTE The submittal shall identify whether the two-position valve is factory-mounted by the unit manufacturer or field-mounted, and that responsibility shall be assigned in the contract documents. (9.4)

NOTE The valve can ship factory-mounted on the unit or be field-installed in the loop drop. Either is acceptable, but the documents must state which, or the valve falls between scopes and is omitted. Confirming factory-versus-field mounting on the submittal prevents that gap. (9.5)

NOTE Each unit shall be furnished with controls compatible with the project's control architecture. (10.1)

NOTE A standalone thermostat suits a simple installation. A unit-mounted BACnet or Modbus controller allows point-level monitoring and is the norm for managed commercial and hospitality buildings. Full BAS integration adds demand-controlled loop temperature reset and central scheduling. (10.2)

NOTE A desuperheater for domestic hot water heat recovery shall be provided only where the connection to the plumbing system is coordinated and shown. (10.4)

NOTE Many units offer a desuperheater that recovers compressor heat to preheat domestic hot water. The option is wasted if the connection port is left capped because the plumbing tie-in was never coordinated. Resolve the connection in design, or do not specify the option. (10.5)

NOTE Each unit shall meet a scheduled maximum NC level in the occupied space, stated at the scheduled airflow and external static pressure. (11.1)

NOTE Sound is critical in hotels and residences, where guestroom and bedroom NC targets of 25 to 35 are typical, while commercial office space tolerates NC 35 to 45. A bare NC number without the airflow and static-pressure test conditions is ambiguous and generates RFIs. (11.2)

NOTE Electrical characteristics and branch-circuit protection shall comply with NFPA 70 (NEC) Article 440 for hermetic refrigerant motor-compressors. (12.1)

NOTE NEC Article 440 governs minimum circuit ampacity and maximum overcurrent protection for the hermetic compressor in each unit. Branch circuits and disconnects shall be sized from the unit nameplate minimum circuit ampacity and maximum overcurrent protection, not from running amps. (12.2)

NOTE Units shall be installed in accordance with the manufacturer's published instructions and with the service clearances shown on the approved submittal. (13.1)

NOTE Closet and chase installations are the most clearance-constrained. Units squeezed in without the filter-pull and compressor-access clearance the manufacturer requires become expensive to service for the life of the building. (13.2)

NOTE After installation, the entering and leaving water temperature and water flow at each unit shall be measured and shall fall within 5 % of the design conditions. (14.1)

NOTE Field verification confirms that the loop actually delivers the design flow and temperature to each unit, which is what makes the certified capacity real on the project. A 5 % tolerance band on water temperature and flow is the practical acceptance criterion; units outside it indicate a balancing or sizing problem to resolve before acceptance. (14.2)

NOTE The manufacturer shall warrant each unit against defects in materials and workmanship for the period stated below from the date of Substantial Completion. (16.1)

NOTE A one-year whole-unit warranty is the industry baseline. Extended compressor coverage of five years is widely available and commonly specified for equipment that is difficult to access after occupancy, such as ceiling-mounted units above finished spaces. (16.2)