Water-to-Air WSHP for U.S. Apartment Buildings | YUJU
Water-to-Air Water Source Heat Pumps for a 154-Unit U.S. Apartment Project
For a 154-apartment multifamily development in the United States, the proposed HVAC concept uses a two-pipe condenser-water loop served by a rooftop cooling tower and a gas boiler. Each apartment requires at least one self-contained water-to-air water source heat pump (WSHP) that can cool or heat its living space independently. Depending on the floor plan, the terminal may be installed in a vertical service closet or above a ceiling with supply ductwork.
Product appearance reference. Final cabinet construction, refrigerant, slide-out chassis and certified configurations require manufacturer confirmation.
How the Two-Pipe Water-Loop System Works
A common condenser-water supply and return network connects the apartment heat pumps. During cooling, each WSHP rejects heat from the occupied space into the water loop; the cooling tower removes excess heat. During heating, the unit extracts heat from the loop, with the boiler maintaining suitable loop conditions when required. A reversible refrigerant circuit allows individual apartments to respond to their own thermostat settings.
Unlike a chilled-water fan-coil system, the apartment terminal contains its own compressor and refrigeration circuit. The central plant regulates the shared water loop rather than delivering chilled water directly to a passive cooling coil.
Vertical Stack or Horizontal Ducted: Which Fits the Apartment?
| Installation | Typical application | Key design check |
|---|---|---|
| Vertical-stacked WSHP | Closets and vertical shafts with shared supply/return risers between floors | Removable slide-out chassis, flexible hoses, valve isolation, riser clearance and service access |
| Horizontal-ducted WSHP | Ceiling voids where conditioned air is delivered through ducts | Cabinet depth, access panel, condensate drainage, duct static pressure and sound transmission |
The project calls for capacities from approximately 0.75 to 3 Tons (2.6–10.6 kW nominal class), with at least one terminal per apartment and potentially two for larger layouts. A room-by-room cooling and heating load schedule is needed before final capacity and unit counts can be assigned.
Project Equipment Selection Checklist
| Item | Engineering target |
|---|---|
| Electrical supply | 208–230 V, single phase, 60 Hz |
| Air-moving system | Variable-speed ECM blower; performance verified at required external static pressure |
| Cooling water conditions | 85°F entering / 97°F leaving water at the stated design condition; verify capacity, flow and pressure drop |
| Water-side pressure | At least 250 psi required for the specified water-side assembly, including applicable valves, hoses and fittings |
| Control and protection | Microprocessor control, high/low refrigerant pressure protection, low-water-temperature protection, condensate overflow, low-voltage and anti-short-cycle functions |
| Room control | Compatible 24 V programmable/networked thermostat, with electric baseboard heat interlock where specified |
| Acoustics | NC 35 room noise target; review octave-band sound data and actual installation conditions |
| U.S. compliance | Verifiable ETL/NRTL listing for exact models; current applicable safety standard and AHRI performance certification where available |
Why Water Temperature and Pressure Must Be Verified
Boiler temperature is not automatically the WSHP entering-water temperature
One early project criterion specifies 140°F supply and 110°F return in heating mode, along with a minimum loop temperature of 65°F. Those values need to be reconciled before selecting equipment. A conventional boiler/tower WSHP loop generally operates at substantially lower temperatures than a 140°F boiler supply. The design team must confirm whether 140°F/110°F describes a separate boiler circuit, and whether a heat exchanger or mixing arrangement protects the apartment heat pumps.
Check the complete water connection assembly
A heat exchanger pressure rating alone does not establish the rating of an installed terminal. Valves, flexible connections, fittings and optional pumps must also be checked against the specified 250 psi requirement. Water flow, water-side pressure drop, strainers and service isolation are especially important in a multi-floor building.
Reference Data Are Not Yet Approved Equipment Submittals
Preliminary product materials reviewed for this application show packaged horizontal water-to-air units, including 1 Ton / 400 CFM, 2 Ton / 600–800 CFM and 3 Ton / 1,000 CFM reference configurations, with 0.3 in. w.g. external static pressure stated in the schedule. These are reference examples, not confirmed selections. The sample schedule identifies R454B and 277 V single-phase or 480 V three-phase electrical configurations, while a separate illustrated brochure mentions R410A. Neither establishes that an exact 208–230 V single-phase, 60 Hz, ETL-listed vertical-stack or horizontal model is available. The final product series, refrigerant, electrical configuration and certifications must be matched to the project requirements.
For each proposed model, the technical review should include capacity and efficiency at the specified entering-water conditions, airflow versus external static pressure, water flow and pressure drop, fan sound data, cabinet dimensions, service clearances, wiring diagrams, refrigerant data and certification identifiers. The applicable performance-rating framework for water-to-air heat pumps is ISO 13256-1.
YUJU Engineering and OEM Support
YUJU EnvironTech supports overseas HVAC purchasers and project teams by comparing manufacturer submittals, identifying configuration gaps, coordinating OEM requirements and preparing technical questions before pricing and approval. For this apartment application, the next step is to obtain verified 0.75–3 Ton model lists and installation drawings for both vertical-stack and horizontal-ducted units, followed by electrical, acoustic, hydraulic and certification review.
Project status: Equipment sourcing and technical evaluation. No final model approval, purchase, installation or measured operating result is implied.
Discuss your water-to-air WSHP project: YUJU EnvironTech — provide your apartment load schedule, water-loop design conditions, electrical service and installation constraints for a focused equipment review.
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