Transfer grilles above doors

[markocosic]

Any recommendations for air transfer grilles above doors that are light blocking/ sound deadening/suitable for 63 mm CLS and plasterboard stud walls?

 

I've decided that the bedrooms are not well with coupled to the hall for the mvhr to be happy without there being a sock to hang the door open. 🙂

[Marvin]

5 hours ago, markocosic said:

Any recommendations for air transfer grilles above doors that are light blocking/ sound deadening/suitable for 63 mm CLS and plasterboard stud walls?

 

I've decided that the bedrooms are not well with coupled to the hall for the mvhr to be happy without there being a sock to hang the door open. 🙂

That's a challenge. We just have a gap under the doors.

 

Light reducing is possible but sound as well I haven't heard of.

 

How much free air do you need?

Edited September 30, 2022 by Marvin

[ProDave]

As well as a gap under the door I left a gap above the door, and no door stop bead at the top, just down the two sides.

[markocosic]

I'm not sure @Marvin

 

It isn't something that I've given too much thought to previously; but now that window closed season is here and I have a lodger that I didn't have before so the door is shut; it's something that needs attention.

 

Drivers for airflow are:

 

- Moisture removal

- CO2 removal

- Heat transfer

 

Bedroom 1 is 3.2 x 3.6 x 2.3 metres. 26.5 m³ (small)

Bedroom 2 is 3.2 x 2.6 x 2.3 metres. 19 m³ (smaller)

Bedroom 3 is 2.3 x 1.8 x 2.3 metres. 9.5 m³ (harry potter)

 

 

I think CO2 is the annoying one. My wife is more sensitive to it than I am.

 

 

 

 

 

There's an app for that:

https://www.engineeringtoolbox.com/pollution-concentration-rooms-d_692.html

 

 

 

 

 

 

 

So we need 2.5 air changes per hour in the largest of the bedrooms to keep CO2 to 2000 ppm or 6 air changes per hour to keep it to 1000 ppm.

 

2.5 * 26.5 = ~65 m3/hr or ~1.1 m3/minute or 18 L/sec

6 * 26.5 = ~160 m3/hr or ~2.5 m3/minute or 45L/sec

 

This suggests an "occupancy method" of 20 cubic feet per minute per person or 0.55 m3/minute per person:

https://continentalfan.com/general-ventilation-how-much-airflow-do-we-need-to-ventilate/

 

That pretty much tallies with the 2.5 ACH for two people above.

 

And fits with this reference to 10L/sec per person for commercial buildings.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/945754/S0973_Ventilation_Actions_Summary_16122020_V2.pdf

 

Sleeping...probably involves less CO2...so a ventilation rate that gives 2000 ppm for active duty would give 1000 ppm for sleeping duty.

 

There's a page for that too:

 

https://www.engineeringtoolbox.com/co2-persons-d_691.html

 

Sleeping should be 0.013 to 0.02 per person not 0.05 which gives about 2 ACH or 15 Litres/sec or 0.9 m³/min or 54 m³/hr per double bedroom:

 

 

 

That's...quite a lot

 

MVHR is this:

 

https://www.titon.com/uk/products/hrv-2-q-plus/

 

So likely needs to run at 40-50% overnight if serving just the upstairs bedrooms. (which it is)

 

In answer to the door grille: 15 litres/sec. One and a half paint buckets.

 

If door gap 0.8 metres wide and 0.01 metres tall area is 0.008 m² so velocity for 0.015 m³/sec would be 2 m/sec or so. Breezy! Is my maths right here? Top and sides leaking a bit (depending on how badly the door fits) will add a fair bit more as length is longer.

 

2 cm door undercut brings that to 1 m/sec Or you trick of leaving off the top door stop bead and having 1 below / 1 above. Assuming forced fresh air input to drive that air change.

 

 

More Google sanity checking. Yanks use forced air heating/cooling so they need a return air path for the heating/cooling air. (which presumably means fewer concerns on CO2 as if the heating/cooling flow is adequate the CO2 should work out too)

 

https://www.energyvanguard.com/blog/can-door-undercuts-work-as-return-air-pathways/

https://www.energyvanguard.com/blog/easy-retrofit-return-air-bedrooms

 

Talking similar orders of magnitude. 

 

2 cm off the bottom of the doors...or a 20 cfm / 15L/sec / 0.5 m3/hr grille with a decent pressure drop.

[JohnMo]

Not sure if something is wrong with the calculation, but passivhaus, build regs specify between 0.3 and 0.5 ACH.

 

A real example - My bedroom has an ACH rate of around 0.5, with 2 adults and dog with door closed and 10mm door undercut 838mm wide, CO2 will slowly increase to around 1000ppm overnight.  With door open it sits no higher than about 700ppm.

[markocosic]

Sze.

 

Passivhaus builds tend to be decently sized.

 

0.5 ACH works fine for out LT apartment: (double bedroom 6 x 4 x 3 metres = 72 m³)

 

 

That's the equivalent of 1.35 ACH in a 26.5 m3 room AND you've got that much more volume to dilute into over the 8 hour period.

[JohnMo]

Sorry I am lost.

[markocosic]

Size.

 

1 ACH in a shoebox is a lot less fresh air than 1 ACH in a warehouse.

 

A fixed amount of CO2 fills a shoebox faster than a warehouse.

 

Passivhaus projects tend to be high end. High end projects are bigger. They set the ACH based on an assumed "stocking density" of humans per cubic metre. If the density is higher the ACH need to be higher. 

Edited September 30, 2022 by markocosic

[JohnMo]

Just use the fresh air row under passivhaus as reference

 

 

[gregh]

@markocosic did you ever find a useful product/solution here? Assuming the grilles would also need to be fire rated? Ie. Sort of makes bedroom fire doors useless if a fire can just jump through the duct!

[markocosic]

Hi,

 

On 20/02/2023 at 14:00, gregh said:

@markocosic did you ever find a useful product/solution here? Assuming the grilles would also need to be fire rated? Ie. Sort of makes bedroom fire doors useless if a fire can just jump through the duct!

 

I put this to one side of a while but I'll need a solution before say Christmas. 

 

Did you do my homework in the interim by any chance? 🙂