...Hunt AIRFLOW dilution fans...

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AIRFLOW dilution and flue boost fans...

AIRFLOW dilution and flue boost fans are manufactured in the United Kingdom and distributed in Australia by Forbes and Hunt Boilers.

The range is available in standard form (HDF1 and GBDF series) typically used with atmospheric boilers and water heaters of around 75% efficiency.

In addition, an enhanced corrosion resistant version is available (SSDF series) incorporating stainless steel fan cases. These are ideally suited for installation into stainless steel ducting, higher efficiency boilers, or any boiler likely to produce condensation.

The key features of the product range include:

Flexibility to install into new or existing plant rooms

In line fan installation for the HDF1 series

Eliminates the need for more expensive larger diameter or external flues

Provides an alternative to the refurbishment of current flue installations

Efficient and quiet operation capable of overcoming system resistance in flue ducts

Inbuilt vane switch with position proving capability, that causes boiler shut down in the event of a fan failure

High levels of protection with the use of stainless steel on the SSDF series, and Aluzinc coated steel on the HDF1 and GBDF series

Fresh air added into the boiler's discharge flue duct which dilutes the flue gases, making them more suitable for disbursement at low levels

Other models also available

Choosing the Correct Dilution Fan

The fan selection depends on the airflow required to dilute the combustion products to a safe level and/or the pressure loss in the ductwork system that the fan has to overcome.

Note: The dilution calculations offered are based on reducing the CO2 content to 1% and should be used in conjunction with all requirements contained within AG5601/AG601 for Gas Installations.

To select the appropriate fan for your application follow these easy steps.

Step 1: Determine the Flow Rate required

The required volume flow rate of diluted flue gases necessary for a given boiler can be calculated as follows:

Flow Rate in Litres per Second (L/s) = 3.6 x rated input of boiler in kW

Step 2: Determine the Flue Pressure Resistance

Part 1 - Straight Section

First, you must determine the flue pressure resistance in all the straight sections of the ductwork.

Add up the total length of straight sections of ductwork. Multiply this total length by the pressure loss per metre of duct which you can determine from the following table.

(Note: If you have square duct instead of round, use the column for the next smaller round duct as an approximation, i.e. For 350 square duct you would use the figure for 300 round duct.)

 

Model GBDF3 in standard trim, suitable for natural gas flue arrangement

Model Model SSDF4 in standard trim, suitable for natural gas flue arrangement and higher efficiency boilers

 

 

Flue Pressure Resistance for Straight Sections (Pascals per metre)
Flue Diameter (mm)	175	200	250	300	350	400	500	600
100 L/sec	1.40	0.75	0.24	0.10	0.10	0.10	0.10	0.10
200 L/sec	5.00	3.20	0.90	0.36	0.17	0.10	0.10	0.10
300 L/sec	5.75	5.75	1.90	0.75	0.35	0.19	0.10	0.10
400 L/sec	12.0	10.0	3.40	1.30	0.60	0.32	0.10	0.10
500 L/sec	19.0	18.0	5.00	2.00	0.90	0.48	0.16	0.10
600 L/sec			7.00	2.80	1.30	0.70	0.22	0.10
700 L/sec			9.00	3.80	1.70	0.90	0.30	0.12
800 L/sec			11.0	5.00	2.20	1.20	0.37	0.15
900 L/sec			15.0	6.00	2.80	1.50	0.48	0.19
1000 L/sec			18.5	7.50	3.40	1.80	0.55	0.24
1200 L/sec				11.0	4.50	2.50	0.80	0.32
1400 L/sec				14.0	6.50	4.20	1.10	0.44