MANIFOLD EXAMPLE (248sq.mt dwelling)

Below is an example of a 248sq.mt dwelling witha ventilation requirement of 123.4 l/s (444m3/h)

The ideal HRV selection would be for a 600m³/h unit.  Best practice being that the unit operates at 75% of total capacity when operating on high setting and 50% of fan capacity at low setting.  This is a key design criteria to maintain low velocity andnoise levels.

SYSTEM PRESSURE

Based on the airflow requirement and the schematic (Manifold 248 -schematic)

The air distribution system (duct) used has the main effect on system resistance.  With this example the quantities and layout is exactly the same for all 4 combinations.  However, the resistance in option 4 is nearly double that of option 1.  For a HRV unitto operate at its maximum efficiency the resistance has to be kept to the minimum.
 
1 -Primary duct 180mm Ø with 75mm Ø tributary ducts from manifold -System resistance 179Pa @ 17l/s
2 -Primary duct 180mm Ø with 63mm Ø tributary ducts from manifold -System resistance 247Pa @ 17l/s
3 -Primary duct 160mm Ø with 75mm Ø tributary ducts from manifold -System resistance 232Pa @ 17l/s
4 -Primary duct 160mm Ø with 63mm Ø tributary ducts from manifold -System resistance 300Pa @ 17l/s

VELOCITY

Based on the airflow requirement and the schematic (Manifold 248 -schematic).
 
1 -Normal mode (50% capacity of HRVunit) -Primary duct of 180mm Ø is 2.98m/s
2 -Normalmode -Tributary duct of 75mm Ø (based on 4l/s) is 0.91m/s
3 -Boost mode (75% capacity of HRVunit) -Primary duct of 180mm Ø is 4.94m/s
4 -Boost mode -Tributary duct of 75mm Ø (based on 17l/s) is 3.86m/s
5 -Normal mode (50% capacity of HRVunit) -Primary duct of 160mm Ø is 3.72m/s
6 -Normalmode -Tributary duct of 63mm Ø (based on 4l/s) is 1.33m/s
7 -Boost mode (75% capacity of HRVunit) -Primary duct of 160mm Ø is 6.17m/s
8 -Boost mode -Tributary duct of 63mm Ø (based on 17l/s) is 5.67m/s

BILL OF MATERIALS

The quantities remain the same -it is the size of duct (assuming quality is the same) that will effect the price.  There can be considerable price difference for different size ducting.  Also, manifolds differ considerably but for this exercise we can assume all manifolds to be acoustically treated and capable of handling 400m³/h per manifold.

Primary Ducts 12m of 180mm OR 160mm Ø pre insulated duct 7 no. 90º Bends -180mm OR 160mm Ø pre insulated duct 2 no. 180mm OR 160mm Ø pre insulated wall cowls 
Tributary Ducts 2 no. Manifold (Plenum boxes) 150m of 75mm OR 63mm Ø ducting  6 no. extract valves 9 no. supply valves 15 no. dampers (restrictors) to balance airflow at manifolds 15 no. valve adapters 30 no. air seals 50 no. bracket supports

Conclusion: Obviously, there is not only one way to design a ventilation system.  However, there are certain principals which need to be followed.  This exercise is intended to give you an idea of how the exact same manifold based layout can have different prices based on the size of duct but also significantly different system resistance.  The higher system resistance will impede the efficiency of the unit and use more power to deliver the required airflow.  The drawings below show the basis for the above billof materials and calculations.

The layout below shows the HRVunit fitted in the attic space above bedroom No.4.  The access hatch to the attic on the landing is 850mm x 850mm.  the attic space is floored up to and around the HRV unit for easy access to service and maintain the unit.  The blue lines are supply air and the red lines are extract



Customer Service

Contact Us

Curtaun,
Gort,
Co Galway
Tel.: +353 (0)91 633 800
Email: info@ventilationsupplies.ie

© A+ Ventilation Supplies 2017