Testo 405i setup

[Deniance]

Can anyone give me some tips on setting up the testo 405i for comissioning mvhr?

 

I thought I set my unit up correctly and was supplying 20 litres per second into my 4 rooms (5 l/s per room )

 

had a bit of condensation on the window in one room so tried to make it a few more litres per second in that room to deal with it

 

anyways, i wasn’t getting the 5l/s per room that I did last week so I tried to setup again

 

Except this time I can’t get the figures right

 

i made a 100mm tube like in the pictures but if I use it this way I get a reading, if I flip the tube the other way so the probe is further away I get a different reading

 

also I disconnected one pipe from the mvhr unit and used the testo to set exactly 21 l/s coming out of the mvhr, then I put duct back on and went around expecting to get 5 l/s in each of the 4 rooms 

 

except now I’m getting 8 l/s in each room (32 l/s in total)!

 

So this is where I’m getting stuck, measure unit to produce 21 l/s, but then Total of all supply outlets is 32 l/s? 
 

is it because it’s windy outside or batteries low?

[JohnMo]

Have set the correct pipe diameter into the Testo?

[Gone West]

9 hours ago, Deniance said:

 

is it because it’s windy outside

Almost definitely, we had to stop if it was windy because the readings were too variable.

[Deniance]

So managed to get some time today to fiddle with the flow rates

 

charged phone, new batteries in testo 

 

took the supply to the house off and put probe and piece of duct into the mvhr and managed to get the unit to feed 20.8 l/s, so then I went to the 4 supply grilles and managed to get each one equal except they totalled 22l/s!

 

I was expecting less as you should lose some to the ducting and the length of ducting?

 

so I repeated it again and same result, slightly higher total of all grilles compared to why the unit is producing

 

but then I discovered that the flow rate differs if you move the probe inside the duct!

 

so I had the probe set in the middle of the duct, but if you pull the probe out until one of the little sensors is close to the edge of the duct the readings change a lot!

 

so centre of duct I got 20.8

 

just off centre I was getting near 25!

 

but head is scrambled now, don’t know what one is right or whether to measure both and take an average!?

[S2D2]

20 minutes ago, Deniance said:

 

so centre of duct I got 20.8

 

just off centre I was getting near 25!

Spin the whole duct 180 degrees and see what the reading is for the off centre position. Sounds like you have highly non-uniform flow due to a bend near the outlet or something. The longer pipe will help redistribute to a uniform flow, hence why turning the pipe around changes the value.

 

Interesting issue to watch out for when calibrating perhaps.

[Deniance]

36 minutes ago, S2D2 said:

Spin the whole duct 180 degrees and see what the reading is for the off centre position. Sounds like you have highly non-uniform flow due to a bend near the outlet or something. The longer pipe will help redistribute to a uniform flow, hence why turning the pipe around changes the value.

 

Interesting issue to watch out for when calibrating perhaps.

Yeah that photo is wrong, I’ve spun the duct so probe is further away from the action so to speak, it gives more stable readings further away I’ll give it another go tomorrow if I get time , I watched a video where a guy measured a 16 inch duct and takes readings a few times as he pulls the probe out then takes averages, so maybe that’s what I got to do even though it’s only in a 100mm duct

[dpmiller]

you're overthinking. Having spent more than ten years measuring flows in fume cupboards, Biological safey cabinets, and various laminar flow units, I can confirm that airflow is just-about impossible to read repeatably...

 

Flow in any tube/ duct is irregular and as @S2D2says the longer the straight length before the probe the better. You can use egg-crate to try and straighten/ laminarise the flow, but it's all over kill.

Probe in the centre of the duct, fix it there, take readings. Done...

[Deniance]

Glad you’ve said that because it’s driving me mad, been up and down stairs about a million times!!

 

I’ll give it one more go later

 

the pulling the probe back a few mm really does put the values up though 

 

if I put it in centre of duct with the damping settings on the testo you can get a stable reading, and if you pull it back about 15mm which makes one sensor close to the edge and one sensor dead centre you get a higher reading and that is also stable 

[Blooda]

On 03/11/2023 at 22:58, Deniance said:

also I disconnected one pipe from the mvhr unit and used the testo to set exactly 21 l/s coming out of the mvhr, then I put duct back on and went around expecting to get 5 l/s in each of the 4 rooms 

 

 

No need to disconnect, We drilled a 10mm Hole in the supply and extract pipes and to use the Same Testo 405i  as you.   This meant we could easily balance the system [extract and supply].  A bit of aluminium tape was enough to seal it during commissioning.  There is an average reading on the settings, so you can get a sort of average where you pull the probe out slowly.  

 

sort of like this, [I cannot find the video I saw originally, which was for a round duct.

 

Measuring In-Duct Airflow with the Testo 405i - YouTube

 

Most important thing is get the extract and supply balanced.  The individual outlets can be near enough.    As @dpmiller said almost impossible to get a static reading in airflow.  

 

[Gone West]

11 hours ago, Deniance said:

but then I discovered that the flow rate differs if you move the probe inside the duct!

I fixed the probe to be in the centre of the duct and didn't move it as I took the measurements, so I was always comparing like with like.

[Deniance]

2 hours ago, Blooda said:

 

No need to disconnect, We drilled a 10mm Hole in the supply and extract pipes and to use the Same Testo 405i  as you.   This meant we could easily balance the system [extract and supply].  A bit of aluminium tape was enough to seal it during commissioning.  There is an average reading on the settings, so you can get a sort of average where you pull the probe out slowly.  

 

sort of like this, [I cannot find the video I saw originally, which was for a round duct.

 

Measuring In-Duct Airflow with the Testo 405i - YouTube

 

Most important thing is get the extract and supply balanced.  The individual outlets can be near enough.    As @dpmiller said almost impossible to get a static reading in airflow.  

 

My Brookvent unit is push fit when it leaves the unit, so I can wiggle the bit of flexi duct out revealing the hole , I then pop a 300mm piece of 125mm pipe in there that has a stuffing gland for the probe , so this is air produced by the unit after the filter , I can’t do the same for the extract as it’s too tight, but tonight I will go outside to the exhaust and measure that as that will be after the filter , this way I can get both supply and exhaust direct at the machine after filters and get them super balanced! The exhaust is straight out the wall after the machine so is as short as possible 

[Deniance]

[Deniance]

[Deniance]

These are the 2 positions I used, one gives 21 l/s and the horizontal one gives 25 l/s and it’s repeatable 

 

I went for the lower one in the end as it made the machine a tiny bit quieter when running

[Arudge]

On 07/11/2023 at 06:57, dpmiller said:

 I can confirm that airflow is just-about impossible to read repeatably...

 

Flow in any tube/ duct is irregular and as @S2D2says the longer the straight length before the probe the better. 

I had a long conversation with a civil engineer last night regarding this, he came to the same conclusion. He went on to say that a vane type anemometer would work better, in his opinion the sampling area was too small and too many currents in the pipe for a hot wire anemometer, he'd also be inclined the reduce the pipe diameter to smooth out the flow.