Heat recovery
Run-around coil heat recovery is long-established technology in Finland. What Windis adds is the control: Windis Zero holds the run-around loop at an operating point where heat recovery delivers what the coils were sized for, even as conditions change.
Size it in Windis Select- Adaptive power optimisation as an add-on feature
- Zero IQ
- Pipe sizes by water flow
- DN20–DN100
- Fieldbus protocols as standard, plus I/O
- 4
- Regardless of the air handling unit's manufacturer
- Any make
What run-around coil heat recovery is
In run-around coil heat recovery, also called liquid-coupled recovery, the air handling unit has its own coil on the extract side and on the supply side, with a liquid circulating between them. Extract air gives up its heat to the liquid, the liquid carries it to the supply side, and supply air is warmed before it is blown into the space. The two airstreams never meet.
Windis Zero is a patented control system for that run-around loop. It is installed either in a new air handling unit or in an existing one, and it works regardless of the unit's make. The only requirement is that the unit has run-around coil heat recovery.
What the control can achieve
The highest efficiency a recovery coil can reach is decided when it is sized: coil size, flow velocity and the design data settle it. In use that point is easily lost, because outdoor temperature, airflow and load vary while constant flow control settles on a single compromise value. Windis Zero's job is to keep efficiency close to the design value even then. It does not raise efficiency above the design value; it prevents it from drifting below it during operation.
The benefit always depends on the site's airflows, temperatures and operating hours, so no fixed saving percentage is stated on this page. A site-specific estimate is made from the design data.
Where Windis Zero is used
- New-build projects where the air handling unit is being designed now
- Renovations where the air handling unit is not being replaced
- Systems with more than one extract-air coil
- Sites that also want supply air cooled in summer
When Windis Zero is chosen
Windis Zero suits any site whose air handling unit has run-around coil heat recovery.
New build
With a new air handling unit.
The control and the run-around loop are designed in from the start, so the loop's components arrive on site as one factory-built package.
Renovation
Into an existing unit, without replacing it.
Windis Zero connects to an existing air handling unit regardless of its make, so heat-recovery control can be improved without changing the unit. The controller is built into the package, so the building management system needs no software changes.
Several extract-air coils
When heat is recovered from more than one coil.
The delivery includes two-way control valves as standard, which measure the liquid flow from each extract-air coil separately.
Supply air cooling
When supply air is also to be cooled in summer.
An integrated changeover valve lets the same recovery coil cool the supply air, which removes the need for a separate cooling coil and its control system. If the recovery and cooling circuits use different liquids, an intermediate heat exchanger is included in the delivery.
Windis Zero and Windis Zero IQ
The family has two parts. Windis Zero is the control system and the factory-built run-around loop. Windis Zero IQ is a feature added to it.
Windis Zero
The control system for run-around coil heat recovery and the factory-built loop: pump, valves, sensors, expansion and filling unit and insulated piping. On-site work is limited to connecting the package to the air handling unit and to the building management system.
Windis Zero IQ
Adaptive power optimisation. Constant flow control sets the liquid flow from one design value and hits the optimum only in the conditions that value was calculated for. Zero IQ continuously seeks the operating point at which heat recovery transfers the highest power at each moment.
Choosing the solution by situation
Scroll the table sideways
| Situation | Solution | Why |
|---|---|---|
| New air handling unit | Windis Zero | Control and run-around loop designed in from the start |
| Renovation, unit not replaced | Windis Zero | Connects to an existing unit regardless of its make |
| System with several extract-air coils | Windis Zero | Two-way control valves measure each coil's liquid flow separately |
| Supply air cooled in summer | Windis Zero | A changeover valve puts the same coil into cooling duty |
| Conditions vary a great deal | Windis Zero IQ | Adaptive power optimisation on top of Windis Zero |
Windis Zero IQ is a feature of Windis Zero. In varying operating conditions, adaptive optimisation typically recovers roughly 5 to 10 per cent more energy than constant flow control.
What the delivery contains
- Control
- A pre-programmed Windis controller connected to the building management system. The same controller as in Windis air curtains.
- Run-around loop
- Circulation pump and variable frequency drive, three-way changeover valve, three-way energy valve, water-side temperature and pressure sensors, expansion and filling unit and insulated piping.
- Interfaces
- Modbus RTU, Modbus TCP, BACnet MSTP and BACnet IP, plus I/O (run permission, cooling permission and setpoint 0–10 V, alarm).
The full scope of delivery and the pipe-size table are on the Windis Zero product page.
What sizing is based on
Heat recovery is sized from the air handling unit's design data. At least these affect the sizing of the run-around loop:
- Supply and extract airflows
- Outdoor and indoor air temperatures, and extract air humidity
- Size and design values of the recovery coils
- Type and concentration of the liquid
- Water flow, which settles the pipe size within DN20 to DN100
- Number of extract-air coils
- Whether supply air cooling is needed from the same coil
Site-specific sizing is done in Windis Select. It calculates the values from the design data entered and produces the sizing report, the functional description and the schematic for the design documents.
Technical platform and building management
Windis Zero has the same controller and the same way of connecting as Windis air curtains, with no add-on modules or separate licences.
Integrated energy metering
The metering separates recovered energy from cooling energy, so both appear in the building management system as their own figures.
Air bubble detection
The energy valve raises an alarm if air bubbles are detected in the circuit. Bubbles weaken heat transfer in the coil.
Interfaces as standard
Modbus RTU, Modbus TCP, BACnet MSTP, BACnet IP and I/O.
Renovation without software changes
The controller is built into the package, so a renovation needs no software changes in the building management system.
Technical brochure, installation instructions and schematics: Documents
Frequently asked questions
What is Windis Zero?
Windis Zero is a patented control system for run-around coil heat recovery in an air handling unit. Besides the controller, the delivery includes a factory-built run-around loop with its pump, valves and sensors.
Does Windis Zero work with any air handling unit?
Yes, the system works regardless of the unit's make. The only requirement is that the unit has run-around coil heat recovery.
Can Windis Zero be installed in an old unit?
It can. In a renovation, heat-recovery control can be renewed without replacing the air handling unit. Because the controller is built into the package, the building management system needs no software changes.
Does Windis Zero raise the efficiency of heat recovery?
The coil's sizing sets the ceiling for what heat recovery can reach at all. Windis Zero does not lift efficiency above that ceiling; it keeps operation close to it even when outdoor temperature, airflow and load vary.
How much does Windis Zero save?
The benefit depends on the site's airflows, temperatures and operating hours, so there is no single percentage that applies everywhere. An estimate is made from the site's design data.
What does Windis Zero IQ do?
Zero IQ continuously seeks the operating point at which heat recovery transfers the highest power at each moment. No design parameters are set, and installation requires no flow calculation or balancing. In varying operating conditions this typically recovers roughly 5 to 10 per cent more energy than constant flow control.
Can the same coil be used to cool supply air?
Yes. An integrated changeover valve puts the same recovery coil into cooling duty, which removes the need for a separate cooling coil and its control system. If the circuits use different liquids, an intermediate heat exchanger is included in the delivery.
How is Windis Zero connected to the building management system?
The controller is delivered pre-programmed. The interfaces are Modbus RTU, Modbus TCP, BACnet MSTP, BACnet IP and I/O, which carries run permission, cooling permission and setpoint 0–10 V as well as the alarm.
What decides the pipe size?
The pipe size is chosen by water flow within DN20 to DN100. The table of water flow against pipe size is on the Windis Zero product page.
Size your project in Windis Select
Enter the air handling unit's design data and Select calculates the values and produces the documents for the design. Help with the sizing is available directly from Windis.