Garden Recording/Mixing Room in Surrey, UK - Build Diary

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endorka
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#61

Postby endorka » Mon, 2023-Feb-13, 20:50

BeardMusic wrote:Source of the postWhat I planning is to have the outlet/inlet grill on the actual boxes themselves, if you imagine on the pic below, as the end of the boxes fall roughly in the center of the room (front and back) this seems to be a good placement for them room-wise. Left one (rear) will be over the sofa at the rear of the room (Setting up the room facing the long dimension) and the right one (front) will be over the mix desk

The end of the boxes falling roughly into the centre of the room is a good plan. Why is the duct from the outer leaf to to those boxes going into the middle of the silencers though? It should enter the silencer at the opposite end to where the silencer vents into the room.

If possible, the silencer inlet should not be on the same plane as the silencer outlet. So if the outlet is going into the room at the bottom of the silencer, having the inlet on a side would give more attenuation than having it on the top of the silencer. The size of your silencer should make this less of an issue though if it can't be done.

What are the boxes on the outer leaf for?

Nominally, yes. It is worth noting that the grilles will only have a certain percentage of their area free for air though, as part of it will be covered with fins or similar. So for example you may need a 200 x 200mm grill to get a free area equivalent to your 150mm diameter duct.

OK. not sure how to calculate this, as I siad I was planning on just having 150mm outlet/inlets on the boxes in the room. I could make them 200mm wide if that helps.

The free area should be specified on the datasheet for the grille. If it's not, ask the supplier if they have it. If they don't I'd look for another grill that has this information. Here's a good example of free areas of various grill sizes:
Capture2.PNG


So for those grilles, the 200mm wide choice would give a free area a bit more than duct with a 150mm diameter. The 150mm wide grill would be less. Alternatively, Glenn has recently posted a good design for an in room plenum with grill that would allow the silencer outlet to be 150mm across. The plenum would then have the 200mm wide grill.

As I said, there will very rarely be more than 2/3 people in the room at one time. I do want it comfortable for the odd time I may have the band in there (4 of us in total). Looking at the specs for the TD 500 (https://www.justfans.co.uk/silent-500150-p-1906.html) That you suggested, I was pretty happy with it. Do you think I should go more powerful?

To answer this we'll first have to estimate the static pressure of your entire ventilation system at the required rate of air flow. Static pressure measures the resistance of the system to having air pushed through it. It's analogous in some ways to sucking water through a straw; easier through a thick straw than a thin one. Same with ducts; thinner ducts have higher static pressure. Longer ducts have higher static pressure, like a long straw would.

You should include the combined static pressure of filter, silencers, ducts, grilles, plenum boxes, and anything else you might have in the air path. Elbow joins and turns in the duct increase the static pressure more than straight runs. Most of this can be found in datasheets for those products. For example, the following shows the static pressure of several different sized G2 filter boxes at certain flow rates. I think the one I have came with a curve of static pressures at different flow rates.
Capture1.PNG


The silencers, well, there is a calculation that approximates it, probably :D

Get as much of this data as you can and I'll help you with the calculation. Based on my own experience with the 500-150 fan, it might be enough. Or it might not. I would not commit to it without verifying first without estimating the static pressure of your system.

If you'd rather just get on with the job ASAP without all those sums I'd keep the option open for the next fan up the series, just in case.

Cheers,
Jennifer



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#62

Postby endorka » Tue, 2023-Feb-14, 06:29

Here's another showing the pressure loss curves (what I've been referring to as "static pressure") of two 90 degree duct bends, one normal, one high efficiency. So for example, to get 6 air changes per hour in my control room requires an air flow rate of 50 l/s (litres per second). At this rate, the standard bend would give about 16 Pascals of pressure loss. The high efficiency bend would give 7.5 Pascals.
Capture.PNG


All the components in your system will have similar curves as they generate greater resistance (pressure loss) at higher air flow rates.



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Garden Recording/Mixing Room in Surrey, UK - Build Diary

#63

Postby gullfo » Tue, 2023-Feb-14, 11:24

one thing a single forced air system provides (beside using vav units for zoning :-) ) is the ability to cross-link the supply and return lines to balance the overall pressure by regulating how much is directly transferred when there are pressure changes or as a general overall adjustment. in a multiple fan system - most times this is not an option. i mention this because in a single system, esp dedicated to a small studio, efficiency is somewhat less important because then you're focused on noise reduction and low speed etc and not just achieving the flow rate and related balance. this is where an HRV/ERV unit with dual fans can benefit because you have essentially a single system to balance and get the desired flow rates, filter maintenance access, and energy efficiencies etc.



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Garden Recording/Mixing Room in Surrey, UK - Build Diary

#64

Postby BeardMusic » Sat, 2023-Feb-18, 14:46

Quick update on the build before I come back to the silencer boxes...

Day 503 - Finally managed to get the 2nd layer of OSB on all external walls. Again doing stuff on my own so, it's slow progress. Cutting out the windows in position was tricky. But as you can see, the roof is now also complete.

IMG_20230214_142146.jpg


IMG_20230214_095457.jpg


IMG_20230213_152409.jpg


Next steps for the main build is to wrap the room and install the external windows.



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#65

Postby BeardMusic » Sat, 2023-Feb-25, 09:24

Thanks for the replies! Sorry for delay, so busy at work this week :(

endorka wrote:Source of the post
BeardMusic wrote:Source of the postWhat I planning is to have the outlet/inlet grill on the actual boxes themselves, if you imagine on the pic below, as the end of the boxes fall roughly in the center of the room (front and back) this seems to be a good placement for them room-wise. Left one (rear) will be over the sofa at the rear of the room (Setting up the room facing the long dimension) and the right one (front) will be over the mix desk


The end of the boxes falling roughly into the centre of the room is a good plan. Why is the duct from the outer leaf to to those boxes going into the middle of the silencers though? It should enter the silencer at the opposite end to where the silencer vents into the room.

If possible, the silencer inlet should not be on the same plane as the silencer outlet. So if the outlet is going into the room at the bottom of the silencer, having the inlet on a side would give more attenuation than having it on the top of the silencer. The size of your silencer should make this less of an issue though if it can't be done.

What are the boxes on the outer leaf for?


Apologies, as I said, they were old pictures just to show you the location; the old images were showing the original plan of four boxes. here are some updated images that hopefully show the final location/design of the dual boxes:

final Boxes_1.jpg


final Boxes_2_no joists.jpg


final Boxes_3_close.jpg



Showing how boxes fit with outer joists.
final Boxes_4_close_with joists.jpg



These images hopefully give you an idea of where the vent holes are in the middle of the room.
final Boxes_5_underneath.jpg

final Boxes_6_underneath_left.jpg



Nominally, yes. It is worth noting that the grilles will only have a certain percentage of their area free for air though, as part of it will be covered with fins or similar. So for example you may need a 200 x 200mm grill to get a free area equivalent to your 150mm diameter duct.


OK. not sure how to calculate this, as I siad I was planning on just having 150mm outlet/inlets on the boxes in the room. I could make them 200mm wide if that helps.


The free area should be specified on the datasheet for the grille. If it's not, ask the supplier if they have it. If they don't I'd look for another grill that has this information. Here's a good example of free areas of various grill sizes:Capture2.PNG

So for those grilles, the 200mm wide choice would give a free area a bit more than duct with a 150mm diameter. The 150mm wide grill would be less. Alternatively, Glenn has recently posted a good design for an in room plenum with grill that would allow the silencer outlet to be 150mm across. The plenum would then have the 200mm wide grill.


Thanks. Looking at the grilles on Just Fans they don't appear to have 'free area' on the datasheets. However, as I am connecting the inner outlet/inlet grilles directly under the boxes I have found these ones and hopefully they do not impede the flow too much although there is a datasheet here but I'm not sure what to look for is it the pressure loss?

https://www.justfans.co.uk/adjustable-c ... -3781.html (internal grilles)
Looks like they come in 150mm 160mm and 200mm
Screenshot 2023-02-25 at 12.00.34.png


Tech data here: https://www.justfans.co.uk/pub/KUV.pdf
Screenshot 2023-02-25 at 12.02.52.png



For the External grilles, I'm looking at these: https://www.justfans.co.uk/metal-extern ... p-316.html
Screenshot 2023-02-25 at 12.05.05.png


Data sheet: https://www.justfans.co.uk/pub/GrillCirc.pdf (Pressure loss data 2nd page)
Screenshot 2023-02-25 at 12.07.18.png


I'm not clear on how these grilles connect to the ducting, I assume there is an adaptor... this flanged spigot only goes to 125mm, hmmm. : https://www.justfans.co.uk/flanged-spig ... -4526.html


Obviously we need to also factor in the filter from the fresh air supply.

As I said, there will very rarely be more than 2/3 people in the room at one time. I do want it comfortable for the odd time I may have the band in there (4 of us in total). Looking at the specs for the TD 500 (https://www.justfans.co.uk/silent-500150-p-1906.html) That you suggested, I was pretty happy with it. Do you think I should go more powerful?


To answer this we'll first have to estimate the static pressure of your entire ventilation system at the required rate of air flow. Static pressure measures the resistance of the system to having air pushed through it. It's analogous in some ways to sucking water through a straw; easier through a thick straw than a thin one. Same with ducts; thinner ducts have higher static pressure. Longer ducts have higher static pressure, like a long straw would.


Yep, I see. I've just realised that my external joists of 170mm high are going to cause a problem with the installation of the fan as it is 220mm high. I'm going to have to make a box or something that extends below the soffits outside to allow room. this means that the 500 fan is already too big, so would be great to make sure that one works as going bigger in the sand size means bigger in the dimensions too.


You should include the combined static pressure of filter, silencers, ducts, grilles, plenum boxes, and anything else you might have in the air path. Elbow joins and turns in the duct increase the static pressure more than straight runs. Most of this can be found in datasheets for those products. For example, the following shows the static pressure of several different sized G2 filter boxes at certain flow rates. I think the one I have came with a curve of static pressures at different flow rates. Capture1.PNG

The silencers, well, there is a calculation that approximates it, probably :D

Get as much of this data as you can and I'll help you with the calculation. Based on my own experience with the 500-150 fan, it might be enough. Or it might not. I would not commit to it without verifying first without estimating the static pressure of your system.

If you'd rather just get on with the job ASAP without all those sums I'd keep the option open for the next fan up the series, just in case.


As I mentioned, physical restrictions might mean that I can only go with the 500 fan.

No huge hurry with calculations as I'm not going to be building the boxes until I build the inner room and ceiling, but I do want to start ordering the equipment soon. Good news is that I have just acquired the liner from Tom though!

As always, thanks for all your help/advice.


Need to crack on with the external build and get ordering Materials for the inner layer. lots to do and so little time...


Cheers, Sam.



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#66

Postby endorka » Sun, 2023-Mar-05, 20:14

BeardMusic wrote:Source of the postApologies, as I said, they were old pictures just to show you the location; the old images were showing the original plan of four boxes. here are some updated images that hopefully show the final location/design of the dual boxes:


Looks good. I think you mentioned before you have a structurally approved way of dealing with the joist that is fouling on the silencer?

One port on those silencers is on the top, the other is on the bottom, so they are both on the same plane. All things being equal you'll get better isolation if this can be avoided. The bottom port must be on the bottom, so the only way I can think of this is to have the top port being on one of the short sides. That looks like it would foul on the side of your structure though. You could avoid this by building a "chimney" coming out the top of the silencer that the flex tube would go into the side of. It would mean a lot of extra work though. and since your silencers are so long I can't say if it would offer any significant benefit.

Looking at the grilles on Just Fans they don't appear to have 'free area' on the datasheets. However, as I am connecting the inner outlet/inlet grilles directly under the boxes I have found these ones and hopefully they do not impede the flow too much although there is a datasheet here but I'm not sure what to look for is it the pressure loss?


Pressure loss is what you are looking for but I can't see a table for it in the datasheet. You could always email them and ask for this?

For the External grilles, I'm looking at these: https://www.justfans.co.uk/metal-extern ... p-316.html
Screenshot 2023-02-25 at 12.05.05.png


Those look decent, they have a fly screen which is very important. The datasheet allows you to calculate pressure loss for a given flow rate. I can't remember what you are aiming for, but at 50 l/s for the 200mm one it's about 15 Pascals per grille.

I'm not clear on how these grilles connect to the ducting, I assume there is an adaptor... this flanged spigot only goes to 125mm, hmmm. : https://www.justfans.co.uk/flanged-spig ... -4526.html

That looks likely. If you can't find all the supplies on that website, there is another good one I have used here;

https://www.i-sells.co.uk/



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#67

Postby endorka » Sun, 2023-Mar-05, 20:31

Here's how I calculated the pressure loss for one of my silencers: take special care of the different measurement units involved!

Silencer box flow calculations using the equivalent duct length method:
Cross section area of silencer is 18*20 = 360cm2
Equivalent diameter is 21.41cm = 8.43"

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is: Duct Diameter x 60

8.43” x 60 = 506” or 42’ for each 90 degree turn

x 8 for each silencer = 336 feet of straight duct

Using the engineeringtoolbox.com friction or head loss calculator this results in;
https://www.engineeringtoolbox.com/duct ... d_444.html

Friction Loss (inH2O): 0.0618
Friction Loss (inH2O/100 ft): 0.0184
Air velocity (ft/min): 282
Air velocity (ft/sec): 4.7



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#68

Postby gullfo » Mon, 2023-Mar-06, 12:22

nice Jen! also you can reference the materials online for their roughness coefficient and/or "straight duct" performance - e.g. https://www.jm.com/content/dam/jm/globa ... 0Chart.pdf to find the friction loss. since i use a lot of duct board for attenuators and plenums etc, this is one of the go-to charts :-)



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#69

Postby BeardMusic » Wed, 2023-Mar-29, 18:06

endorka wrote:Source of the post Here's how I calculated the pressure loss for one of my silencers: take special care of the different measurement units involved!

Silencer box flow calculations using the equivalent duct length method:
Cross section area of silencer is 18*20 = 360cm2
Equivalent diameter is 21.41cm = 8.43"

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is: Duct Diameter x 60

8.43” x 60 = 506” or 42’ for each 90 degree turn

x 8 for each silencer = 336 feet of straight duct

Using the engineeringtoolbox.com friction or head loss calculator this results in;
https://www.engineeringtoolbox.com/duct ... d_444.html

Friction Loss (inH2O): 0.0618
Friction Loss (inH2O/100 ft): 0.0184
Air velocity (ft/min): 282
Air velocity (ft/sec): 4.7



Thanks Jennifer!

Really appreciate your inputs (and yours Glenn)

tbh, looking at your figures is making my head swim. I spent some more time looking for pressure loss info and asked a guy at the site, but it's a bit beyond my brain at present. Even looking at you calculations for pressure loss above I'm not any clearer on how much the flow is reduced.

I have emailed the guys at just fans to see if they can suggest a rough pressure loss for my shopping list:

1x https://www.justfans.co.uk/silent-500150-p-1906.html
1x https://www.justfans.co.uk/acoustic-alu ... -p-71.html - using about a 2 meters from vent box into the filter then into fan then exhaust grille
1x https://www.justfans.co.uk/duct-mounted ... -2946.html
2x https://www.justfans.co.uk/adjustable-c ... -3781.html (will be used on the internal face of the vent boxes inside the room; inlet/outlet)
2x https://www.justfans.co.uk/metal-extern ... p-316.html (These will be used for the external inlet/outlet in soffits)

Will wait to see if they can come back with something.

As I mentioned before, physical limitations mean even fitting the T500/150 is going to be a struggle and the bigger one much harder. I'm off next week and really want to get on with the boxes and fan set up. Based on my cross section calculations being more than recommended for 5 people, and that I'm rarely, if ever, going to have 5 in the room, it's likely that I'm going to proceed and hope for the best.

One thing I could do is use 200mm outlet/inlets in the room boxes to help a bit.

I'll advise if they come back with something helpful. For now I really need to start cracking on with the inside walls and the 100 other jobs to do :)



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#70

Postby endorka » Thu, 2023-Mar-30, 13:13

Yes, converting between the different units used is tricky. If you remind me of the cross sectional area of your silencer path I'll do the calculation of the silencers for you.

Cheers,
Jennifer



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#71

Postby BeardMusic » Fri, 2023-Mar-31, 04:30

endorka wrote:Yes, converting between the different units used is tricky. If you remind me of the cross sectional area of your silencer path I'll do the calculation of the silencers for you.

Cheers,
Jennifer


Hi Jennifer, that's very kind, as always.

Just fans have come back with datasheets for all components, so hopefully that helps (we already had 2 of them):

ac8.3_duct-mounted-filter-boxes (1).pdf
(379.38 KiB) Downloaded 226 times
ac8.3_duct-mounted-filter-boxes (1).pdf
(379.38 KiB) Downloaded 226 times

AAC13 Pleated Panel Filters.pdf
(65.59 KiB) Downloaded 210 times
AAC13 Pleated Panel Filters.pdf
(65.59 KiB) Downloaded 210 times

KUV.pdf
(723.85 KiB) Downloaded 206 times
KUV.pdf
(723.85 KiB) Downloaded 206 times

GrillCirc.pdf
(346.69 KiB) Downloaded 211 times
GrillCirc.pdf
(346.69 KiB) Downloaded 211 times

EN_TD-SILENT.pdf
(3.93 MiB) Downloaded 195 times
EN_TD-SILENT.pdf
(3.93 MiB) Downloaded 195 times


my calculated cross section: 197 x 161 = 24,633 mm2 ~= 246 cm2


Let me know if you need any additional info,

Cheers,

Sam.



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#72

Postby endorka » Fri, 2023-Mar-31, 13:57

Silencer box flow calculations using the equivalent duct length method:
Cross section area of silencer is 197 x 161 = 24,633 mm2 ~= 246 cm2
Equivalent diameter is 19.4cm = 7.64"

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is: Duct Diameter x 60

7.64” x 60 = 458” or 38’ for each 90 degree turn

x 20 for each silencer = 764 feet of straight duct

Airflow: use Rod Gervais recommendation of 75 cfm for five people in the room.

Using the engineeringtoolbox.com friction or head loss calculator this results in;
https://www.engineeringtoolbox.com/duct ... d_444.html

Friction Loss (inH2O): 0.112 = 28 Pa
Friction Loss (inH2O/100 ft): 0.0147
Air velocity (ft/min): 236
Air velocity (ft/sec): 3.9299999999999997

Each silencer will therefore have a theoretical friction loss of 28 Pa when airflow is 75 cfm.
Velocity at the register is less than 300 ft/min so that is good too.

Total friction loss for both silencers is 56 Pa.

Cheers,
Jennifer



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#73

Postby endorka » Fri, 2023-Mar-31, 16:13

Air flow rate in different units used in the various datasheets:

75 cfm = 0.035 m^3/s = 127 m^3/h = 36 l/s

The duct mounted filter box datasheet does not have a specification for that rate, but based on a similar product with a G4 filter I'd estimate 20 Pa.

Ceiling valve: unknown

External grille:
150mm diameter grill @ 36 l/s = ~25 Pa
200mm diameter grill @ 36 l/s = ~7 Pa

If you use the 150mm grilles that will be 50 Pa
If you use the 200mm grilles that will be 14 Pa

If you have short duct runs and avoid sharp bends where possible you'll not add too much to this. It looks like you'll have two 90 degree betnds so let's add 30 Pa to account for this.

We have a total static pressure (excluding duct runs & ceiling valves) at 75 cfm of:
Silencers + filter + grilles + ductwork

150mm grilles: 56 + 20 + 50 + 30 = 156 Pa
Applying this to the graph in the fan datasheet gives the following airflows:

Fan Lo speed: 20 m3/h
Fan Med speed: 120 m3/h
Fan Hi speed: 350 m3/h


200mm grilles: 56 + 20 + 14 + 30 = 120 Pa
Applying this to the graph in the fan datasheet gives the following airflows:

Fan Lo speed: 150 m3/h
Fan Med speed: 260 m3/h
Fan Hi speed: 410 m3/h

Summary

Your target air flow of 75 cfm is equivalent to 127 m^3/h, so in theory you'll get around that with:

- 150mm external grilles running the fan at medium speed, or;
- 200mm external grilles with the fan at low speed.

Running the fan at low speed with the 150mm system should theoretically provide enough airflow for one person.

Whatever grille size you go for, I would say there is enough headroom in the system to allow for errors in those calculations that may have overestimated the airflows.

This is the extent of my knowledge, and the system seems balanced around those points. If you run the fan faster you will get more airflow, but probably not as much as those calculations show as the static pressure will increase with the greater airflow from the fan, and the entire system will resist with a higher static pressure as a consequence. Presumably there are dynamic calculations one can apply to determine this more accurate, but they are not known to me :D

Cheers!
Jennifer



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#74

Postby endorka » Sat, 2023-Apr-01, 04:18

I found a 200mm ceiling valve similar to the one you have specified. The datasheet says each unit will offer ~6 Pa of resistance at 36 l/s. This would add an additional 12 Pa to the above figures, probably not much in the scheme of things.
https://www.i-sells.co.uk/200mm-white-c ... -(ducmw204)?ref=ViewProduct
1000xWHITE-COATED-200MM-METAL-CEILING-EXTRACT-VALVE-MW204-DATASHEET.jpg


Two of the 150mm version would add about 40 Pa of resistance, which would create a significant airflow reduction. If used with the the "200mm grilles" calculation as above, it would give this system a lower performance than the "15t0mm grilles" calculation. If you used the 150mm internal valves with the 150mm external grilles, it would be worse still.

In your shoes I'd definitely use the 200mm internal valves, and the 200mm external grilles if space allowed.

Cheers,
Jennifer



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#75

Postby BeardMusic » Sat, 2023-Apr-01, 11:48

Thanks Jennifer!


I can get fit the 200mm Grilles internally on the boxes and external grilles but issue is the ducting:

This may be a silly question but is that with 200mm Ducting? Issue is that I can only get a max size of 170mm width ducting as the roof joists are only 170mm wide. I could squash the ducting but I'm not sure that is a good idea.

However, they only do 160mm or 200mm Ducting. so 160mm is going to be what I have to go with... :(

So, would using 200mm grilles internal and external with the 150mm ducting be better than 150mm Grilles with 150mm ducting? Logic says yes, but that could be wrong logic. lol




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