Supply and Extract don't match up on paper

[John1001]

Hi,

 

I'm going to give self designing/installing a vent-axia kinetic unit myself a go. My house is a bungalow and fairly small so I figured the air flow calculations were easy enough to do:

 

1 Kitchen/diner (53m3) 13 l/s

1 Bathroom 8 l/s

1 Utility 8 l/s

------------

Extract 29 l/s

 

Bedroom(double) 11 l/s

Bedroom(double) 11 l/s

Bedroom(single) 5.5 l/s

Living room 4.8 l/s (based on room size)

------------

Supply 32.3 l/s

 

I see everyone's supply and extract calculations from BPC etc on the forum match up exactly. What room's supply or extract do I adjust to get these to match? Thanks

[JohnMo]

You need your volume of the house in m3 divide that by 2 to 3 to get your overall flow rate in m3/hr.

 

Just increase the extract rates to match the supply rates if required.

 

But living room flow look too low, it will end up a stuffy room, it should at least be the same or more as a double bedroom.

[Conor]

I had to more than double the extract flow rates to balance the supply. Your unit will balance the fan speeds anyway.

[John1001]

Thanks JohnMo

 

> You need your volume of the house in m3

House Vol. is 244m3

 

> divide that by 2 to 3 to get your overall flow rate in m3/hr

244m2 / 2.5 = 97.6m3/hr

 

Is that the minimum flow rate or the target flow rate?

 

The calculations have the actual flow rate at 138.6m3/h

 

Bedroom(double) 11 l/s

Bedroom(double) 11 l/s

Bedroom(single) 5.5 l/s

Living room 11 l/s

= 38.5l/s / 3.6 = 138.6m3/h

 

So 97.6m3/hr is the flow rate based on the size of the house (from what you said "You need your volume of the house in m3 divide that by 2 to 3 to get your overall flow rate in m3/hr.")

And 138.6m3/h is the required flow rate based on the regulations

 

Does it matter that these are so different. I assume I want to be hitting the regulation flow rate either way

 

 

 

EDIT

Actually if I divide by 2 instead of 2.5 it is 122 m3/hr, much closer to 138.6m3/h.

But what's the meaning behind that number "2 to 3" that I divided by?

Edited October 6, 2023 by John1001

[JohnMo]

24 minutes ago, John1001 said:

But what's the meaning behind that number "2 to 3" that I divided by

Give you one of the factors that affects flow rate. The other as you mentioned is 

 

25 minutes ago, John1001 said:

calculations have the actual flow rate at 138.6m3/h

So you choose the higher of the two flow rates, to set the min flow rate.

 

So you just need to increase extract to match supply and you have your target flow rates set.