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Water and Ground Source Heat Pump System Design Guide

A water or ground source heat pump should not be selected by building area alone.

A reliable system must match the building load, source-water or ground-loop conditions, required outlet-water temperature, circulation flow, hydraulic resistance, domestic hot water demand, electrical supply, and control strategy.

Even when the heat pump itself is correctly selected, a project can still suffer from insufficient heating, excessive electricity use, unstable operation, or frequent alarms if the groundwater flow is inadequate, the ground loop is undersized, the circulation pumps consume too much power, or the terminal units require higher water temperatures than expected.

This guide is intended for project owners, HVAC contractors, distributors, consultants, and procurement teams. It explains the information required before requesting quotations and provides a practical framework for comparing different system proposals.

Variable Frequency Water& Ground SourceIntegrated Heat Pump

What Matters Most When Buying a Water or Ground Source Heat Pump System?

Before comparing equipment prices, buyers should answer nine questions.

Procurement priorityQuestion to answerInformation the supplier should provide
Source feasibilityCan the site provide a reliable water source or accommodate a ground loop?Well test, geological information, thermal response data, or source-side design conditions
Capacity at project conditionsHow much heating or cooling capacity remains at the actual source and load temperatures?Capacity, input power, and efficiency at the specified operating condition
Total system efficiencyDoes the published COP include circulation pumps? How much power will the well pump use?Unit performance table, pump selection, and annual energy estimate
Multiple operating modesHow will space heating, cooling, and domestic hot water be prioritized?Operating-mode matrix, DHW tank design, and control sequence
Ground-loop or well sizeHow many boreholes, how much pipe, or how much water flow will be required?Load calculation, borefield simulation, or well-system design
Terminal compatibilityCan the unit operate with underfloor heating, fan coils, radiators, or air handling units?Required supply and return water temperatures and flow rates
Hidden project costsDoes the quotation include pumps, heat exchangers, tanks, valves, and commissioning?A clear supply scope and exclusion list
Maintenance requirementsHow will water quality, filtration, scaling, and remote monitoring be managed?Water-quality limits, maintenance instructions, and control specifications
Responsibility for performanceWho designs and verifies the heat source, heat pump, hydraulics, and controls?Responsibility matrix, commissioning procedure, and acceptance criteria

A low equipment price has limited value if the source system, pumps, controls, or commissioning requirements are excluded.

Water Source vs. Ground Source Heat Pump Systems

The U.S. Department of Energy describes a geothermal heat pump system as having an underground heat collector, a heat pump, and a building distribution system. The underground heat exchanger may be installed vertically or horizontally.

The DOE also notes that, in many areas of the United States, temperatures at a depth of about 30 feet, or 9 metres, remain relatively stable at approximately 10–15°C. Local ground temperature and geological data must still be used for actual design. U.S. Department of Energy: Geothermal Heat Pumps

Commercial systems generally use one of the following source configurations.

Closed-Loop Ground Source System

A closed-loop system circulates water or an antifreeze solution through pipes buried in the ground. The circulating fluid does not directly mix with groundwater.

Common arrangements include:

Vertical systems require less land, but drilling costs can be high. Horizontal systems may cost less to install where sufficient land is available, but their performance is more affected by soil moisture, burial depth, rainfall, and seasonal ground-temperature changes.

Open-Loop Groundwater System

An open-loop system pumps groundwater from a production well, passes it through an isolation heat exchanger or heat pump, and then discharges or reinjects it.

This arrangement may reduce the amount of buried pipe required, but the project must confirm:

ASHRAE points out that groundwater heat pump systems may require fouling protection when the water quality is poor. Pumping energy can also become excessive when the aquifer is deep or the water system is poorly designed. ASHRAE Handbook, Chapter 35

Legal requirements vary by location. In the United States, for example, wells used to return heat pump water underground may fall under the EPA’s Class V Underground Injection Control program. Other countries and regions may require separate drilling, water abstraction, discharge, reinjection, or environmental permits. U.S. EPA: Class V Injection Wells

Engineered Water Loop or Surface-Water System

Some projects can use a building water loop, lake, pond, river, mine water, wastewater source, or another engineered water circuit.

The presence of water does not automatically make it a suitable heat source.

The project still needs to verify:

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Step 1: Calculate the Real Building Load

Do Not Select the Heat Pump by Floor Area Alone

A watts-per-square-metre estimate can support an early budget, but it is not sufficient for final equipment selection.

The design team should calculate or confirm:

A hotel, apartment building, school, office, and villa can have completely different load patterns even when their floor areas are similar.

Calculate Domestic Hot Water Separately

Domestic hot water should not simply be added to the space-heating load.

The DHW calculation should include:

If the system gives DHW priority, the designer should also determine how long space heating can be interrupted while the storage tank is being reheated.

Step 2: Confirm the Source Before Selecting the Heat Pump

What Is Required for a Vertical Ground Loop?

A vertical borefield design normally requires:

For larger systems, uncertain geological conditions, or projects with high drilling costs, the design team should evaluate whether a thermal response test is justified.

A thermal response test can help determine the site’s effective ground conductivity and borehole resistance. This reduces the risk of installing an unnecessarily large borefield or an undersized field that cannot maintain acceptable loop temperatures.

What Is Required for a Horizontal Ground Loop?

Horizontal-loop design should consider:

Dry soil and wet soil can have very different heat-transfer performance. A fixed pipe length per kilowatt should therefore be treated as a budget estimate, not as a final design rule.

Why “Metres of Borehole per Kilowatt” Is Not a Final Design Method

Ground-loop length is affected by both peak load and long-term energy balance.

If a cooling-dominated building rejects much more heat into the ground than it extracts each year, the ground temperature may rise over time. A strongly heating-dominated project may gradually reduce the ground temperature.

ASHRAE explains that ground heat exchanger design should consider loads over different time scales, including peak loads and annual ground-load imbalance. ASHRAE Ground Source Heat Pump Design Guidance

Ground-loop length should therefore be calculated from project-specific data rather than copied from another installation.

Step 3: Compare Heat Pumps at the Project Operating Condition

COP Must Always Be Read Together With Its Rating Condition

Heat pump COP is not a fixed value. It changes with source-side entering temperature and load-side leaving temperature.

Common rating conditions include:

In heating mode, a lower source temperature and a higher outlet-water temperature generally increase the required temperature lift. This can reduce both heating capacity and COP.

For a commercial quotation, ask the supplier to provide:

  1. Heating capacity at the minimum design source temperature
  2. Cooling capacity at the maximum design source temperature
  3. Input power at the required outlet-water temperature
  4. COP or cooling efficiency at the same condition
  5. Required source-side flow
  6. Required load-side flow
  7. Pressure drop through both heat exchangers
  8. Maximum input current
  9. Part-load performance
  10. Operating limits

ISO 13256-2 covers the testing and rating of water-to-water and brine-to-water heat pumps. AHRI’s geothermal and water-source heat pump certification program also verifies ratings such as heating capacity, cooling capacity, COP, and EER for products within its program scope. AHRI Geothermal and Water-Source Heat Pump Program

This does not mean that every heat pump carries AHRI certification. The buyer should verify the rating standard and certification status of the specific product being offered.

What Does “Up to 60°C Outlet Water” Mean?

A maximum outlet-water temperature describes an operating limit. It does not prove that the unit will retain its nominal capacity or published COP at 60°C.

For a high-temperature radiator or DHW application, request the following data at the required high-water-temperature condition:

A unit capable of reaching 60°C may still be more efficient when operating at 35–45°C.

Step 4: Calculate Source-Side and Load-Side Flow

For a clean-water circuit, preliminary flow can be calculated as:

For a clean-water circuit, preliminary flow can be calculated as

If glycol or another antifreeze fluid is used, the calculation must be corrected using the actual density and specific heat at the selected concentration and operating temperature.

Heating Flow Calculation Example

Assume that a project requires 24 kW of heating and the heat pump has a COP of 4.0 at the project condition.

The approximate compressor input is:

24÷6=6kW

The source must provide approximately:

24-6=18kW

If the source-side temperature difference is 3 K, the preliminary clean-water flow is:

18÷（1.163×3）=5.16m³/h

If the load-side temperature difference is 5 K, the preliminary load-side flow is:

24÷（1.163×5）=4.13m³/h

This example shows why source flow should not automatically be calculated from the delivered heating capacity. Part of the delivered heat comes from the compressor’s electrical input.

Final pump selection must also consider:

The same principle applies in cooling mode, except that the source system must reject both the building cooling load and the compressor heat.

Step 5: Match the Heat Pump to the Terminal Water Temperature

The terminal-water temperature directly affects heat pump performance.

Underfloor Heating

Underfloor heating normally uses relatively low water temperatures and is well suited to heat pump operation.

The design should still verify:

Fan Coils and Air Handling Units

Coil capacity must be checked at the actual supply and return water temperatures.

A coil selected for a conventional boiler or chiller may not provide the required capacity when connected to a lower-temperature heat pump system. A larger coil surface, higher airflow, or different water flow may be required.

Radiators

Existing radiators may have been selected for boiler water temperatures of 70°C or higher. Before replacing the boiler with a heat pump, calculate the radiator output at the proposed 45°C, 50°C, or 55°C supply temperature.

Possible improvements include:

Chilled-Water Terminals

Cooling design should confirm:

Step 6: Design the Complete Hydraulic System

The heat pump is only one component of the complete installation.

Depending on the project, the hydraulic system may also require:

Does the System Need a Buffer Tank?

A buffer tank should be evaluated when:

Buffer-tank volume should be calculated from minimum run time, minimum system load, permitted water-temperature change, and existing system volume.

How Does Antifreeze Affect the System?

Antifreeze provides freeze protection, but it also reduces heat capacity and increases fluid viscosity and pumping resistance.

Confirm:

IGSHPA currently identifies CSA/ANSI/IGSHPA C448:2025 as its current design and installation standard. Its previous 2017 standard has been sunset for current design work. IGSHPA Standards

Every project must also comply with the codes and environmental requirements of the installation location.

Step 7: Include Pumping Energy in the Efficiency Calculation

Comparing heat pump COP alone can overestimate the efficiency of the complete system.

Total electrical consumption may include:

For annual comparison, use a system seasonal performance factor:

For a clean-water circuit, preliminary flow can be calculated as

A groundwater source may offer a favourable temperature, but a deep well with high pumping head can reduce or eliminate that advantage.

The supplier should therefore state whether the published COP includes any internal pumps and identify all external pump power separately.

Step 8: Decide the Number of Heat Pumps and the Backup Strategy

A single large unit may have a lower initial equipment cost. Multiple units in parallel can offer:

Depending on the importance of the building, the project may use:

The electric heater capacity, activation conditions, and electrical demand must be included in both the design and the operating-cost calculation.

Step 9: Define the Heating, Cooling, and DHW Control Sequence

A heat pump that supports heating, cooling, and domestic hot water does not necessarily provide full rated capacity to all three loads at the same time.

Before procurement, confirm:

If the building requires simultaneous heating, cooling, and hot water, ask for a hydraulic schematic and operating-mode matrix. Do not rely on a general “three functions” statement.

Step 10: Compare Total Installed Cost and Lifecycle Cost

A complete project budget may include:

Use the same building load, operating hours, and energy prices when comparing proposals.

The lifecycle comparison should include:

  1. Heat pump cost
  2. Borefield or well-system cost
  3. Annual compressor electricity
  4. Annual pumping electricity
  5. Auxiliary heating consumption
  6. Filtration and water-treatment costs
  7. Cleaning and inspection costs
  8. Expected major equipment replacement

Payback depends on climate, load profile, energy prices, drilling costs, and local incentives. A payback period from another project should not be applied without recalculation.

Ground Source and Water Source System Comparison

ItemVertical ground loopHorizontal ground loopOpen-loop groundwater
Land requirementRelatively lowHighRelatively low
Site investigationGeology and thermal propertiesSoil, moisture, and available landWell yield, groundwater level, and water quality
Main source investmentDrilling and groutingExcavation and pipe installationProduction well, reinjection or discharge, and well pumps
Main operating riskInsufficient loop length or long-term thermal imbalanceSeasonal ground and moisture variationFalling water level, scaling, blockage, or poor reinjection
Pumping energyDepends on loop and header resistanceDepends on pipe length and circuit designStrongly affected by well depth and reinjection pressure
Water-quality exposureLowLowHigh
Typical permit issuesDrilling and underground constructionExcavation and land-use rulesWater abstraction, discharge, and reinjection
Suitable applicationsLimited land and long-term operationLow-rise sites with available landSites with a verified and legally usable water source

No source type is suitable for every project. The final decision should be based on site conditions, system risk, and lifecycle cost.

What Should Be Checked During Commissioning?

Ground-Loop System

The handover package should include:

Groundwater System

The handover package should include:

Heat Pump System

Commissioning measurements should include:

A record showing that the heat pump can start is not sufficient evidence that the system achieves its design performance.

CASSKY All-in-One Water and Ground Source Heat Pump

The CASSKY All-in-One Water / Ground Source Heat Pump is an indoor water-to-water heat pump platform designed for connection to a qualified water source or an engineered closed ground loop.

Depending on the selected model and hydraulic design, the system can support:

The series is intended for villas, apartments, and light commercial buildings.

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Current Series Selection Data

ParameterCurrent reference value
Heating capacity6–30 kW
Cooling capacity5–26 kW
Maximum heating outlet waterUp to 60°C
Minimum cooling outlet waterDown to 7°C
Reference heating COPUp to 4.8 at B0/W35
Reference cooling EERUp to 5.2 at W30/W7
Source sideGround loop or qualified water loop
Power supply220–240 V single phase or 380–415 V three phase, depending on model
Control communicationRS485 / Modbus RTU options can be discussed
Remote functionsSupported configurations can provide 4G monitoring and control

These values are intended for preliminary product screening. Capacity, efficiency, water-temperature limits, electrical supply, communication, and internal hydraulic components vary by model and rating condition.

Before procurement, request the model-specific datasheet, performance table, hydraulic diagram, controller manual, and confirmed supply scope.

Why Project Data Matters

A 20 kW heating requirement does not automatically mean that a nominal 20 kW heat pump is suitable.

CASSKY selection should be based on the capacity available at the project’s actual:

This prevents a nominal rating at one favourable condition from being used for a more demanding application without correction.

Information Required for CASSKY Project Selection

For a preliminary model recommendation, provide:

Based on this information, CASSKY can review the candidate model, unit quantity, operating condition, and additional information required for system design.

RFQ Checklist for Comparing Suppliers

Send the same project information to every supplier so that quotations can be compared on the same basis.

Project Information

Require Each Supplier to State

This format prevents suppliers from quoting different rating conditions or leaving major system components outside the stated price.

Frequently Asked Questions

Can the Same Heat Pump Be Used for Water Source and Ground Source Projects?

Some water-to-water heat pumps can operate with either a qualified water source or a closed ground loop. The selected model must cover the project’s actual entering-water temperature, flow, and fluid type. Changing the source may also change capacity, efficiency, pump selection, and protection settings.

Does Every Ground Source Heat Pump Project Require Borehole Drilling?

No. A horizontal ground loop can be used where sufficient land is available. A closed-loop pond or lake system may also be possible where the water body, environmental conditions, and local regulations are suitable. Vertical boreholes are commonly used when land is limited.

Can a Heat Pump Be Selected by Building Area?

Building area can support an early estimate, but final selection requires heating load, cooling load, DHW demand, terminal-water temperature, source temperature, and operating schedule.

How Much Ground Loop Is Required?

There is no universal loop length per kilowatt. The required length depends on ground conductivity, borehole resistance, peak load, annual energy balance, borehole spacing, and permitted loop temperature.

Can Groundwater Flow Directly Through the Heat Pump?

It may be technically possible when water quality meets the heat exchanger requirements. Many commercial projects use an isolation heat exchanger between the groundwater and the closed heat pump circuit to reduce scaling, corrosion, and maintenance risk.

Can a Ground Source Heat Pump Produce Domestic Hot Water?

Yes, when the selected model and hydraulic design support DHW production. The design must include the required water temperature, storage volume, recovery time, hygiene requirements, mode priority, and auxiliary heating strategy.

Does 60°C Outlet Water Make the Heat Pump Suitable for Every Radiator System?

No. The buyer must check heating capacity, COP, source-temperature limits, and radiator output at the proposed operating temperature. Reaching 60°C does not mean the unit retains its nominal capacity or efficiency at that condition.

Does a Higher COP Always Mean Lower System Electricity Consumption?

No. Published COP normally describes the heat pump at a defined test boundary. Total system consumption also includes well pumps, ground-loop pumps, load pumps, terminal fans, controls, and auxiliary heaters.

Can the Ground Loop Provide Free Cooling?

Free or passive cooling may be possible when the source temperature is low enough and the terminal system is suitable. The design must also manage indoor humidity, condensation, heat exchanger approach temperature, pumping energy, and long-term ground heat balance.

Should the Ground Loop Be Sized for the Peak Load?

Peak capacity is only one design factor. The borefield also needs to account for monthly loads, annual heat extraction and rejection, long-term ground-temperature change, and the permitted entering-water temperature range.

References

  1. U.S. Department of Energy — Geothermal Heat Pumps
  2. ASHRAE Handbook — Chapter 35: Ground-Source Heat Pumps and Geothermal Energy
  3. International Ground Source Heat Pump Association — Standards
  4. AHRI — Geothermal and Water-Source Heat Pump Certification Program
  5. U.S. Environmental Protection Agency — Class V Injection Wells
  6. CASSKY — All-in-One Water / Ground Source Heat Pump

This guide supports preliminary system selection and procurement. Final ground-loop, groundwater, hydraulic, electrical, and control design should be completed or reviewed by qualified professionals according to local regulations.