Curious how a water-source heat pump works and whether it fits a home or building? This guide explains the refrigeration cycle, the water loop that moves heat, and how systems achieve efficient heating and cooling. It also covers costs, maintenance, and design choices that influence comfort and energy use. The goal is to demystify how water-source heat pumps operate so owners, managers, and renovators can make informed decisions.
How A Water-Source Heat Pump Works
A water-source heat pump (WSHP) is a compact unit that heats and cools by moving heat to or from a circulating water loop. Instead of burning fuel, it transfers heat using a refrigeration cycle and electricity for the compressor and fans.
The Refrigeration Cycle In Plain Terms
Inside each WSHP, a closed refrigerant loop contains a compressor, reversing valve, expansion device, and two heat exchangers: an air coil and a water coil. Refrigerant absorbs heat at the evaporator and releases heat at the condenser.
In cooling mode, indoor air passes over the cold air coil where refrigerant absorbs heat and moisture. The compressor raises the refrigerant’s temperature and pressure, and the water coil then rejects that heat into the building’s water loop.
In heating mode, the reversing valve flips the roles. Refrigerant pulls heat from the tempered water loop at the water coil and releases it into the room air at the air coil. Even relatively cool water contains usable heat.
The Water Loop That Balances The Building
WSHPs connect to a circulating water loop that typically runs between about 60°F and 90°F. Each room’s heat pump adds or removes heat as needed. When the loop gets too warm, a cooling tower or fluid cooler rejects heat. When the loop gets too cool, a boiler or heat pump adds heat.
This loop acts like a thermal marketplace. Rooms in cooling dump heat into the loop, helping warm rooms that need heating. The result is zoned comfort with simultaneous heating and cooling across a building.
Controls And Modulation
Modern WSHPs often use variable-speed compressors and ECM fans to match capacity to the load. Loop pumps can be variable-speed, with pressure-independent control valves keeping each unit’s flow steady while saving pumping energy.
Loop temperature setpoints are commonly reset based on demand. For instance, the system can float toward 75–80°F when many zones call for cooling, improving efficiency and heat recovery.
Closed-Loop, Open-Loop, And Geothermal Variations
“Water-source” describes how the heat pump connects to water, but there are multiple ways to create the loop. Each variation affects efficiency, cost, and maintenance.
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Closed-Loop With Cooling Tower And Boiler
A closed hydronic loop runs through the building. A cooling tower or dry fluid cooler rejects excess heat in warm weather; a boiler adds heat in cold weather. This is common in offices and multifamily buildings.
- Pros: Proven, scalable, good zoning, relatively simple permitting.
- Cons: Tower requires water treatment; boiler adds emissions unless electric or heat pump–based.
Open-Loop Using Wells Or Surface Water
Open-loop draws groundwater or lake water through a heat exchanger and discharges it after use. The heat pump sees very stable water temperatures, boosting efficiency.
- Pros: High performance due to steady water temperature; lower tower/boiler needs.
- Cons: Water quality management, potential scaling/fouling, permitting, and discharge compliance.
Ground-Source (Geothermal) WSHP
A ground heat exchanger (vertical bores or horizontal trenches) maintains loop temperature naturally. The ground provides a neutral heat source/sink year-round.
- Pros: Excellent efficiency, reduced reliance on boilers/towers, strong comfort in extreme weather.
- Cons: Higher upfront cost; drilling space and geology considerations.
Hybrid And Heat-Recovery Options
Hybrid loops combine a fluid cooler with a high-efficiency condensing boiler or a heat-recovery chiller. In mixed-use buildings, rejected heat from cooling can be captured for heating or hot water, improving overall efficiency.
Efficiency Metrics And Performance In Real Buildings
WSHP efficiency is reported using EER (cooling) and COP (heating). Ratings often follow ISO 13256-1 for water-source performance, with typical rating conditions near 86°F entering water for cooling and 68°F for heating.
Because WSHPs exchange heat with water, their efficiency depends strongly on entering water temperature (EWT). Lower EWT helps cooling; higher EWT helps heating. Part-load operation with variable-speed components can raise seasonal efficiency.
| Entering Water Temp (°F) | Cooling EER (Range) | Heating COP (Range) | Notes |
|---|---|---|---|
| 60 | 22–28 | 3.2–3.8 | Great for cooling; heating COP modest due to cooler source |
| 70 | 18–22 | 3.6–4.5 | Balanced loop temp for shoulder seasons |
| 80 | 15–18 | 4.2–5.0 | Better for heating; cooling EER starts to drop |
| 90 | 13–16 | 4.8–5.5 | High EWT favors heating; tower may be needed for cooling |
Representative packaged WSHPs commonly fall around 14–22 EER for cooling and 3.5–5.0 COP for heating, depending on EWT, fan power, and compressor type. High-performance, variable-speed models often lead at part load.
In buildings with diverse zones, heat rejected by cooling zones often serves heating zones via the loop, yielding system-level efficiency that exceeds any single unit’s rating.
Benefits And Tradeoffs Compared To Other HVAC Options
WSHPs are frequently compared with air-source heat pumps (ASHP), variable refrigerant flow (VRF), rooftop units with gas heat, and ground-source systems. Key differences involve source temperature, zoning, refrigerant distribution, and maintenance.
| Option | Advantages | Drawbacks | Typical Efficiency |
|---|---|---|---|
| Water-Source Heat Pump (WSHP) | Zoned comfort, simultaneous heat/cool, good year-round efficiency, moderate refrigerant charge per unit | Needs loop, tower/boiler or geo; water treatment; more components overall | ~14–22 EER cool; 3.5–5.0 COP heat (EWT-dependent) |
| Air-Source Heat Pump (ASHP) | Simple install, no water loop, wide product range | Efficiency drops in extreme cold/heat; outdoor units exposed to weather | SEER2/HSPF2 vary; COP 1.5–3.5 in cold climates |
| VRF | Excellent modulation; long refrigerant piping; detailed zoning | Large refrigerant volumes; careful design for safety; defrost in cold | High seasonal efficiency; performance weather-dependent |
| Rooftop Unit + Gas Heat | Low first cost; simple replacement | Combustion emissions; less heat recovery; duct losses | Varies widely; typically lower than WSHP or VRF |
| Ground-Source Heat Pump | Top-tier efficiency; stable source temp; low operating cost | Highest first cost; drilling space and geology limits | Often >20 EER cool; >4–5 COP heat |
Bottom line: WSHPs shine in multifamily, schools, hotels, and offices where zoning, heat recovery, and indoor equipment are priorities.
Design And Sizing Essentials
Right-sizing and proper loop design determine comfort and efficiency. Oversizing can increase cycling and noise; undersizing risks poor comfort at peaks.
Load, Airflow, And Capacity
One refrigeration ton equals 12,000 Btu/h. Many WSHPs are applied at about 350–450 CFM per ton, with external static pressure matched to ductwork. Correct dehumidification calls for sensible heat ratios tuned to climate and occupancy.
Water Flow And Piping
Typical WSHP flow rates are 2.0–3.0 gpm per ton, with about a 10°F delta-T. Reverse-return piping or pressure-independent control valves help balancing. Include strainers, air separators, isolation valves, and flexible connectors.
Variable primary pumping with ECM pumps and differential pressure control saves energy. Maintain minimum flow through operating units to protect compressors.
Loop Temperature Strategy
Common loop ranges are 60–90°F. Use tower enable above a high setpoint (for example, 85°F) and boiler enable below a low setpoint (for example, 65°F). Reset strategies minimize unnecessary tower or boiler operation.
Water Treatment And Materials
Closed loops still need treatment to prevent corrosion, scaling, and biofilm. Maintain inhibitor levels, monitor pH, and test conductivity. For towers, follow industry best practices for Legionella risk management and drift control.
Freeze Protection And Glycol
Where loop temperatures risk dropping near freezing, add propylene glycol (commonly 20–30%) and account for reduced heat capacity and higher pumping power. Verify unit compatibility with glycol solutions.
Ventilation And Humidity Control
WSHPs condition zone air; they are often paired with a Dedicated Outdoor Air System (DOAS) to supply filtered, dehumidified ventilation air meeting ASHRAE 62.1/62.2 guidelines. This division improves indoor air quality and comfort.
Acoustics And Vibration
Terminal WSHPs can achieve low sound levels with lined cabinets, flexible duct connectors, and isolation pads. Place units outside bedrooms when possible and specify appropriate sound performance data.
Installation Steps And Cost Ranges In The U.S.
Costs vary with building type, location, and whether a tower/boiler, well, or geoexchange is used. The following steps and ranges are typical guidance, not bids.
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Typical Installation Steps
- Site assessment, load calculations, and system selection (closed-loop, open-loop, or geothermal).
- Loop design, pump sizing, water treatment plan, and controls specification.
- Piping, valving, and equipment layout; structural and acoustic considerations.
- Install WSHP units, loop piping, towers/boilers or geo field, and DOAS if used.
- Flushing, chemical cleaning, fill and purge, test-and-balance of water and air.
- Controls integration, commissioning, verification of safety and performance.
Cost Ranges
| Application | Equipment Cost ($/Ton) | Installed Cost ($/Ton) | Notes |
|---|---|---|---|
| Closed-Loop WSHP With Tower/Boiler (Light Commercial/Multifamily) | $1,200–$2,500 | $6,000–$12,000 | Includes loop, pumps, WSHPs; wide range by market and complexity |
| Open-Loop (Well/Lake) WSHP | $1,200–$2,500 | $4,000–$8,000 + wells/intake/discharge | Wells or intake/discharge can add $20,000–$50,000+ |
| Ground-Source (Geothermal) WSHP | $1,500–$3,000 | $10,000–$20,000 | Includes borefield/trenches; site geology drives cost |
| In-Unit WSHP Replacement (Condo/Apartment) | $3,500–$6,500 per unit | Varies | Excludes building loop work; add for controls/electrical |
Tip: Factor ongoing water treatment, tower service, and filter changes when comparing lifecycle costs to other HVAC systems.
Operation, Maintenance, And Troubleshooting
WSHPs reward consistent maintenance with long service life. Many units last 20–25 years, while towers and boilers have their own lifespans and service needs.
Preventive Maintenance Schedule
| Task | Frequency | Why It Matters |
|---|---|---|
| Replace/clean air filters | Monthly to quarterly | Protects coils, sustains airflow and efficiency |
| Inspect and clean coils | Semiannually | Improves heat transfer and dehumidification |
| Check condensate drains/pans | Cooling season | Prevents leaks and microbial growth |
| Verify refrigerant charge and sensors | Annually | Correct charge and accurate controls maintain COP/EER |
| Pump, valve, and actuator checks | Annually | Ensures proper flow and quiet operation |
| Water treatment testing | Monthly/quarterly | Controls corrosion, scale, and biofilm |
| Cooling tower service | Seasonal | Legionella management, basin cleaning, drift control |
| Glycol concentration test | Annually (if used) | Maintains freeze protection and heat transfer |
Common Issues And Quick Checks
- Poor cooling: Check dirty filters, fouled coils, low water flow, or high loop temperature. Confirm tower operation.
- Poor heating: Verify loop temperature; check boiler enable, flow, and thermostat settings.
- Noisy unit: Inspect fan balance, loose mounts, or excessive external static pressure.
- Short cycling: Oversized unit or control deadband too tight; verify refrigerant charge and sensors.
- Condensate leaks: Clear drain lines, ensure proper trap and slope.
Domestic Hot Water And Heat Recovery Opportunities
WSHP systems offer compelling heat-recovery options that improve total building efficiency and cut operating costs.
Desuperheaters And Water-To-Water Heat Pumps
Some units include desuperheaters that capture compressor waste heat to preheat domestic hot water (DHW). Dedicated water-to-water heat pumps on the loop can produce 120–140°F DHW efficiently, particularly when other zones are cooling.
Heat-Recovery Chillers
In larger buildings, a heat-recovery chiller can reject condenser heat into the space heating loop or DHW, reducing or eliminating boiler runtime during shoulder seasons.
Load Diversity Pays Off
Mixed-use buildings with kitchens, gyms, offices, and apartments see diverse heating and cooling loads. Capturing internal heat gains and redirecting them to spaces or water that need heat maximizes the benefit of the WSHP loop.
Comfort, Noise, And Indoor Air Quality Considerations
Comfort depends on steady temperature, humidity, and low noise. WSHPs can deliver all three when applied properly.
To manage humidity, size coils for latent removal and use a DOAS to deliver dry, filtered outdoor air. In humid climates, consider reheat strategies to avoid overcooling while controlling RH.
For noise, specify low-sone fans, line cabinets, and isolate vibration. Closet-mounted units near sleeping areas need careful acoustic design and duct layout.
Closed loops have low aerosol risk, but cooling towers require documented water treatment and maintenance to manage Legionella. Maintain access for cleaning and testing.
Codes, Incentives, And Certifications
Compliance and incentives can meaningfully impact project cost and feasibility. Always verify current local and federal programs.
Energy codes: WSHP designs typically follow ASHRAE 90.1 (commercial) or IECC provisions. Loop setpoint control, pump power limits, and heat recovery may be required by code or earn credits.
Tax credits: Ground-source heat pumps qualify for a federal tax credit of up to 30% of eligible costs for homeowners (Section 25D) and a similar credit for businesses (Section 48), subject to rules and timelines.
Other incentives: Commercial buildings may qualify for 179D deductions for energy-efficient designs. New homes can qualify for 45L credits when meeting program criteria. Utilities often provide rebates for high-efficiency equipment and controls.
Certification: Look for AHRI-certified ratings for WSHP performance and listings that reference ISO 13256-1 test procedures. For towers and boilers, follow relevant standards and manufacturer guidance.
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Practical Tips To Improve Performance
- Keep the loop in range: Use intelligent tower/boiler enable points and reset strategies to reduce energy use.
- Right-size terminal units: Avoid oversizing; specification should reflect realistic internal gains and ventilation loads.
- Use variable-speed where it matters: ECM fans, variable-speed compressors, and VFD pumps often pay back quickly.
- Commission thoroughly: Flush, purge, and balance the loop; verify every unit’s airflow and water flow.
- Maintain water quality: Proactive treatment prevents scale and corrosion that erode efficiency.
- Plan for service: Provide access panels, unions, and isolation valves for fast maintenance.
When A Water-Source Heat Pump Makes The Most Sense
WSHPs fit best in buildings that need zoned control, simultaneous heating and cooling, and indoor equipment. Multifamily, hotels, schools, and offices often benefit from the loop’s heat sharing and from placing equipment indoors for longevity and aesthetics.
For single-family homes, a ground-source heat pump is the common water-source approach. In multifamily, replacing aging in-unit WSHPs can be a straightforward way to improve comfort and efficiency without major duct changes.
Future-Proofing And Refrigerants
HFCs are phasing down under federal policy, pushing HVAC toward lower global warming potential refrigerants. Manufacturers are transitioning from R-410A to options like R-454B or R-32. When selecting equipment, consider service readiness and code compliance for next-generation refrigerants.
FAQs: How Does A Water-Source Heat Pump Work?
Does A WSHP Still Work In Very Cold Weather?
Yes. Because WSHPs exchange heat with water, not frigid outdoor air, they maintain reliable output. A boiler, geo field, or heat-recovery device keeps the loop within range in cold snaps.
What Kind Of Energy Savings Are Typical?
Compared with electric resistance heat or older systems, WSHPs can reduce HVAC energy use by 20–40%, depending on loop design, controls, and climate. Savings vary by building and maintenance quality.
How Is A WSHP Different From Geothermal?
“Water-source” describes using water as the heat exchange medium. Geothermal is one type of water-source system that uses the ground as the source/sink. Many WSHPs use a tower/boiler loop instead.
Do WSHPs Provide Hot Water?
WSHPs can support domestic hot water with desuperheaters or dedicated water-to-water heat pumps using the same loop, often at high efficiency when cooling loads are present.
What Maintenance Is Most Critical?
Filter changes, coil cleaning, and water treatment have the biggest impact. For open loops and towers, diligent scale and biofilm control protects heat transfer and health.
How Long Do WSHP Units Last?
Many packaged WSHPs run 20–25 years with proper care. Cooling towers, boilers, and pumps have separate lifespans; plan capital replacements accordingly.
Are WSHPs Good For Retrofits?
Often yes, especially in buildings that already have a water loop. In-unit replacements can upgrade efficiency and comfort with minimal architectural impact.
Key Takeaways
- A water-source heat pump moves heat rather than generating it, using a refrigeration cycle tied to a tempered water loop.
- Loop devices like cooling towers, boilers, or geothermal fields keep water temperatures in an efficient range.
- Well-designed WSHP systems deliver zoned comfort, enable heat recovery, and can cut HVAC energy use substantially.
- Success depends on right-sizing, water treatment, and commissioning, plus intelligent controls and regular maintenance.
How to Get the Best HVAC Prices
- Firstly, keep in mind that installation quality is always the most important thing for residential HVAC project. So never sacrifice contractor quality for a lower price.
- Secondly, remember to look up the latest rebates as we talked above.
- Thirdly, ask for at least 3 bids before you make the decision. You can click here to get 3 free estimates from your local contractors, and this estimate already takes rebates and tax credit into consideration and filter unqualified contractors automatically.
Lastly, once you chose the right contractor, remember to use the tactics from this guide: Homeowners Tactics When Negotiating with HVAC Dealer to get the final best price.
