A 4-pipe heat pump can serve separate chilled-water and hot-water circuits, with simultaneous heating and cooling available on the applicable EXINDA configuration. The selection task is to match these operating modes and the minimum stable output to the building's actual loads.
EXINDA supports commercial air-to-water heat pump selection for North American HVAC consultants, contractors and distribution partners. This guide explains how to turn questions about operating modes and turndown into a clear equipment selection and commissioning brief.
Which 4-pipe heat pump operating modes are available?
The EXINDA configuration described here has separate cooling and heating water heat exchangers. Each has a dedicated function.
| Mode | Cooling water heat exchanger | Heating water heat exchanger |
|---|---|---|
| Cooling only | Produces chilled water | No active hot-water production |
| Heating only | No active chilled-water production | Produces hot water |
| Simultaneous cooling and heating | Produces chilled water | Produces hot water |
This design does not switch both water heat exchangers into cooling or both into heating. Match these three operating modes to the intended project before comparing capacities.
First distinguish water circuits from refrigerant circuits
A water circuit carries chilled or hot water to the building. A refrigerant circuit transfers energy within the heat pump. They are different parts of the system.
When a specification asks whether “both circuits can heat,” label which circuits it means. Use a hydraulic schematic for the chilled-water and hot-water connections, and the equipment documentation for refrigerant-circuit operation. This avoids selecting equipment on an ambiguous description.
Match simultaneous operation to overlapping loads
Start with the periods when the building needs cooling and heating together. For example, internal zones may need cooling while perimeter zones need heating. Record the two loads during the same period, rather than adding peaks that occur at different times.
Provide entering and leaving water temperatures, design flows and outdoor conditions. In simultaneous operation, evaluate the cooling and heating outputs as a paired operating point. Separate heating-only and cooling-only ratings do not automatically describe simultaneous performance.
Also define what should happen when one demand falls away. The equipment selection and control sequence should cover cooling-dominant, heating-dominant and overlapping demand, using the operating envelope of the selected configuration.
Understand module and circuit turndown
Turndown compares a stated maximum capacity with the minimum stable capacity on the same basis:
Turndown ratio = stated maximum capacity ÷ minimum stable capacity.
A complete module may combine compressor modulation with refrigerant-circuit staging. Its minimum output can therefore differ from the minimum output expressed as a percentage of an individual circuit's rating.
| Equipment level | What to request |
|---|---|
| Individual refrigerant circuit | Minimum stable output and the capacity basis for that circuit |
| Complete module | Minimum stable module output and the active-circuit arrangement |
| Multiple-module plant | Minimum output with the intended module and circuit staging sequence |
Review these figures in the required heating, cooling or simultaneous mode and at the relevant conditions. Do not use compressor speed alone as a substitute for delivered-capacity data.
Use minimum output to assess low-load operation
Compare the lowest sustained building load with the minimum stable output of the smallest intended active equipment combination. If output exceeds demand, review module staging, active water volume, zoning and temperature-control settings together.
Installing additional modules does not automatically improve low-load performance. The plant must be able to stage them appropriately, while maintaining the required water circulation and respecting minimum run and off times.
EXINDA can review the selected module's capacity information alongside the proposed sequence, helping the project team define a suitable operating arrangement.
Verify the selected sequence during commissioning
- Check cooling-only and heating-only operation against the documented sequence.
- Where conditions allow, establish simultaneous demand and record water temperatures and flows on both sides.
- Reduce demand and observe the intended capacity reduction and circuit or module staging.
- Observe demand transitions, water-temperature control, run times and any alarms.
- Record the final settings and results for the installation and service teams.
If site conditions do not permit a particular mode test, record that test as outstanding and arrange it when the required conditions are available.
Frequently asked questions
Does four-pipe mean both water heat exchangers can heat?
No. The configuration described here uses dedicated cooling and heating water heat exchangers. It provides cooling only, heating only or simultaneous cooling and heating.
Is circuit turndown the same as module turndown?
No. Each uses a different capacity basis. Request the minimum stable output at the circuit, module and plant levels relevant to the selection.
Does a large turndown ratio guarantee no cycling?
No. Compare minimum output with the actual load and review water volume, controls and staging together.
Request an EXINDA operating-mode and part-load review
Send the project location, heating and cooling loads, overlapping and minimum demand, water temperatures, electrical supply and proposed module arrangement to info@exindagroup.com. EXINDA can review the applicable configuration and identify the performance and control information needed for selection.
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