How Double Flow Ventilators Work:
Principle of how Double Flow Ventilators work:
Flow-controlled fans:
Flow-controlled fans are still the most common fans on the market.
They use a constant rotational speed: modulation of the airflow rate is only done via the unit's settings during commissioning or via a control box.
They provide a lower airflow rate in case of increased air resistance, for example due to clogged filters.
.The airflow rate is not automatically adjusted. A good commissioning with flow measurement is therefore essential to adjust the setting of the extract fan and the supply fan.
In practical terms, when an installer commissions a regulated airflow double flow ventilation system, he must, to avoid any disappointment linked to a loss of thermal and sanitary performance:
- Implement balancing solutions for the network (self-regulating vents - the simplest solution with fans with regulated flow rates -and/or flow reducer ring or adjustable vents) to compensate for the differences in length and elbow between each duct for the insufflation network and the extraction network.
- Adjust the power of the exhaust fan according to the ratio between its capacity and the sum of the flow rates at the theoretical exhaust outlets, then check that the sum of the flow rates measured at the outlets corresponds well. If not, he must increase or decrease the fan power until the desired result is obtained.
- Adjust the power of the insufflation fan so as to obtain the same flow rate as for the extract units by carrying out the same adjustment and measurement manipulations.
Constant airflow fans
A constant airflow fan will deliver the airflow set on the machine whatever the sizing of the installation and the associated pressure drops(within the limit of a network of sufficient quality).
If the air resistance increases (increase in pressure drop that normally with a standard flow regulated fan would decrease the airflow to the vents), the fan motor will automatically spin faster to always get the same pre-set amount of air.
Of course, the constant flow fan motor will operate in the opposite direction if there is a reduction in air resistance (the motor will spin slower).
Constant flow fans therefore automatically change their speed to ensure that the airflow rate remains the same and that the internal air quality remains optimal.
Constant pressure fans
Constant pressure fans are mostly used in the case of hygro-variable double flow ventilation systems.
Once the system is commissioned, the principle for this fan is to decrease or increase its rotation speed according to the opening or closing of the hygro vents until the set pressure is reached again.
These are the same types of fans used for Single flow ventilation hygro A or hygro B.
Hygro-variable double flow ventilation systems have little interest because they combine the installation constraints of a classic double flow CMV (installation cost and network passage) but without benefiting from the indoor air quality, a major advantage that a double flow CMV is supposed to provide.
Why install constant airflow fans?
In a dwelling using balanced double flow ventilation (double flow CMV), two fans provide ventilation (fresh air supply fan / stale air extraction fan).
Constant airflow fans ensure a balance between the extraction fan and the insufflation fan.
If not, the fans will most certainly not have the same airflow rates (Poor commissioning, clogged filters or network, wind action, thermal draught, opening and closing of doors...).
There are then the following 2 cases:
- The fresh air supply flow rate is greater than the extracted stale air flow rate: we obtain a overpressure of the dwelling. This causes heat from the dwelling to be exhausted to the outside via air leakage from the building structure.
- The extracted stale air flow rate is greater than the fresh air supply flow rate: this results in a depression of the dwelling. As a result, cold outside air is drawn into the dwelling via air leaks in the building structure. .
This would result in an immediate loss of thermal efficiency of the dwelling.
The loss of efficiency will be more significant as the two airflows are not identical within the heat exchanger. In this case, the efficiency of the heat exchanger is degraded.
The commissioning of a constant flow rate double flow CMV is much simpler to carry out.
Once the set flow rates have been set on the machine, all that is required is to balance the extract network and then the supply network using adjustable vents and/or flow reducers and a flow meter.
Even if the air network is badly balanced, the overall air renewal is ensured.
How do the standard constant flow fans and those developed and patented by BRINK work?
Comparative between a standard constant flow fan and the constant flow fan developed by BRINK:
| Standard constant flow fans | Brink constant flow fan | |
|---|---|---|
Principle:For centrifugal fan impellers with forward curved blades (inclined in the direction of impeller rotation), it is relatively simple to calculate the fan flow rate on the basis of torque (N.m Newton meter) and rotational speed (rpm). The torque of such fans increases proportionally to the square of the rotational speed (rpm). This results in a power curve to which we can define, for each point, a pressure. The combination of this pressure and the rotational speed of the fan motor then allows us to determine the airflow.
Benefits:
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Principle:All BRINK ranges are equipped with backward inclined centrifugal fans (inclined in the opposite direction of rotation). Unlike forward inclined fans, the torque of these fans does not increase proportionally to the square of the speed of rotation. As a result, we cannot determine the pressure and thus the associated airflow. The use of these fans requires the application of an alternative solution to calculate the airflow. Solutions have been found and patented by Brink Climate Systems:
Benefits:
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