HRV Systems and Air Flow rates??

delfagio · 28-07-2015 11:12am #1

Just wondering if someone could shed a bit of expert light on this one for me.

How are air flow rates for HRV calculated. Is there a specific amount of air that should be replaced in the house every hour and if so how is this calculated? Is it per person in the house or per volume of air in the house. Are there allowances made for say if a gathering of 30people at a party etc.?

Say for example my house is 200m2 between ground floor and 1st floor with an Airtightness of 1m3/hr/m2.

Also as my house is a story and a half, the small attic is within my airtight envelope due to the construction I went with. Is this also taken into the volume of air to be changed? Or is this neglected as it wouldn't be habitable space??

I will be running through this with my HRV supplier before final commissioning but just want to be able to have it straight in my own head first.

Been an engineer means that part of my brain always likes/needs to know all the in's and out's and calculations rather than just knowing something is there and working and not fully understanding HOW it works.

Thanks all for your help

runawaybishop · 28-07-2015 11:26am

delfagio wrote: »

Just wondering if someone could shed a bit of expert light on this one for me.

How are air flow rates for HRV calculated. Is there a specific amount of air that should be replaced in the house every hour and if so how is this calculated? Is it per person in the house or per volume of air in the house. Are there allowances made for say if a gathering of 30people at a party etc.?

Say for example my house is 200m2 between ground floor and 1st floor with an Airtightness of 1m3/hr/m2.

Also as my house is a story and a half, the small attic is within my airtight envelope due to the construction I went with. Is this also taken into the volume of air to be changed? Or is this neglected as it wouldn't be habitable space??

I will be running through this with my HRV supplier before final commissioning but just want to be able to have it straight in my own head first.

Been an engineer means that part of my brain always likes/needs to know all the in's and out's and calculations rather than just knowing something is there and working and not fully understanding HOW it works.

Thanks all for your help

Very roughly -1/3 of the air changed an hour. Calc your cubic area and knock off 10% for furnishings. You system running at a low setting should meet this.

Include the attic.

delfagio · 28-07-2015 8:17pm

Thanks runawaybishop for that,

I had looked it up there today also in Part F Ventilation section of the Building Regulations.

But if say the house is designed for say even 4-5people at 4liters/second. What happens if there is 20people over for a whole day at a family gathering. Does this mean there wouldn't be enough air supply???

Great I will include the attic, this will be included in the Blower Door test so makes sense it's added into HRV Calculations.

Outkast_IRE · 28-07-2015 8:22pm

delfagio wrote: »

Thanks runawaybishop for that,

I had looked it up there today also in Part F Ventilation section of the Building Regulations.

But if say the house is designed for say even 4-5people at 4liters/second. What happens if there is 20people over for a whole day at a family gathering. Does this mean there wouldn't be enough air supply???

Great I will include the attic, this will be included in the Blower Door test so makes sense it's added into HRV Calculations.

You can simply open a window or some control panels have a boost button.

delfagio · 28-07-2015 8:54pm

Cheers Outkast, yea true it wouldn't do any harm to open the Windows, most HRV suppliers do say to do this.

As I mentioned in my post above, my attic space is within my thermal envelope, should I get an air supply feed installed at one gable end and an air extract duct at the other gable end?? I know the space isn't habitable as it's just storage, but to prevent the air been stuffy? I will have to run this past the HRV supplier to check as we hadn't thought about it at the time of design

runawaybishop · 28-07-2015 8:58pm

delfagio wrote: »

Cheers Outkast, yea true it wouldn't do any harm to open the Windows, most HRV suppliers do say to do this.

As I mentioned in my post above, my attic space is within my thermal envelope, should I get an air supply feed installed at one gable end and an air extract duct at the other gable end?? I know the space isn't habitable as it's just storage, but to prevent the air been stuffy? I will have to run this past the HRV supplier to check as we hadn't thought about it at the time of design

Should probably have a extract to exhaust stale air up there. Does your system have a co2 sensor? It should have a boost anyway to increase the exchange rate. Can't say I've noticed issues when I have a lot of guests over but you may need to run faster, especially if anyone is smoking.

delfagio · 28-07-2015 9:10pm

Yea the system does have boost switches at all ensuites and bathroom and main localised boost switch in utility beside kitchen.

Not sure if it has a CO2 sensor, I must check this with supplier, it will be connected somehow to the fire alarm system so that it will shut off if the fire alarm is set off due to a fire occurring heaven forbid.

Will look into getting an extract vent in attic space with supplier thanks

HRV Systems and Air Flow rates??

Comments