MVHR COMMISSIONING M/S TO L/S HELP PLEASE

[jimbob12345]

 

Hi everyone,  new to the forum, looking for some advice.

Trying to commission my MVHR using my cheaply made anemometer using a funnel, car door seals and an aquarium pipe to make a good seal on the ceiling and anemometer .

 

 

 

My Issue is that the device measures in M/S and I need L/S.

Ive had a scroll through the forum and have seen that most people have posted on graphs that they use about 1 M/S as around 7 L/S.

The issue is my anemometer has an internal radius of around 3.25 cm and 6.5cm diameter. 

Every online calculation i use is no where near 1 M/S per 7L/S.

 

I was just wondering where to go with this and how people came to there conclusions and calculations. 

 

Surely the calculation should be done on the anemometer internal hole and not the ducting size.

 

Thanks in advance 

[jimbob12345]

Just to add if i use the calculation of 3.3 l/s per 1 m/s I struggle to get near where I should be when the fans are on full flow, but I can feel alot of flow of air, hence why I'm curious about the calculation of the wind speed.

[jack]

I can't help much beyond agreeing with your 3.3 L/s calculation.

 

Can you give some examples of the numbers you're trying to meet?

[PeterW]

Vane anemometers are not reliable for low flows - they can’t really get over the initial start up “flow” required to get a good reading.

 

Your calcs are correct though - 3.3l/s in a 65mm dia duct is ~1m/s 

 

 

Decent calculator here 

 

[jimbob12345]

Thanks  so i have a titon 1.75 QPlus MVHR.

Its an average 3 bed house new build house.

Basically i took the front off the machine to find the outlet motor was smothered in thick thick mould Basically no longer functional.

I have lived here for a year and a half with no known issues.

So i managed to find my new home book pack and noticed on my commissioning forms that my address was written over tipex🤔.

This made me very suspicious,  so i purchased myself an add on touch screen display for the bedroom and noticed that the fans are only running at 18% idle speed and 85% humidity setting......

They had clearly never commissioned the system! The company that fitted it is no longer working and bellway had been a waste of time.

Being a vehicle technician im used to fixing other peoples co#k ups.

So i decided it woukd easier to clean the unit myself and commission it.

 

So i have recommissioned this morning using 3.32 l/s per 1 m/s.

 

I used my commissioning form i had.

 

On boost

 

8 l/s bathroom

6 l/s w/c

13 l/s kitchen

 

Inlets are looking good with an overall value of also 27 l/s  8.1m/s matched to the outlet.

 

My only Unknown is to achieve to boost figure my fans are running at 85% outlet and 56% inlet.

 

And to achieve a roughly 15 % drop for my balanced specified constant idle values my fans are 65% outlet and 45% inlet.

 

7 l/s bathroom

Etc etc

 

Should i look into why the motors are so far apart from eachother? Or is this completely irrelevant as the inlets will have much longer and 1 more pipe, so as long as this system is balanced and within specification it doesnt matter

[jimbob12345]

Also just to add, i live in the u.k and have set my humity to 60% not sure where to set this. The handheld units are saying around 50% around the rooms in the house. 

Obviously the 60% setting is in the machine on the outlet side.

So this 60% setting on the machine is keeping the house at around 50%, this does fluctuate alot as the mrs loves to hang washing from anything stationery in the house, to a point where im to scared to stay still for long periods of time.😆

Edited April 15, 2023 by jimbob12345

[jimbob12345]

Also the unit states it has an airflow of upto 76 l/s but im unsure if this is a combined efford from both inlet and out? 

If its just 1 way then im miles from this

[MikeSharp01]

2 hours ago, jimbob12345 said:

titon 1.75 QPlus MVHR

That's an obsolete unit now so perhaps worth stocking up on filters while there are still some about. The balance thing is ensuring you are not getting too greater  positive or negative pressure in the house. So as long as total extract l/s approximated to total supply l/s things are ok, some on here have advocated very slight positive pressure I dimly recall but controlling for that would be a fun project. The fan settings don't tell you much because the of the varying amount of work done in pulling equal amounts of air through different pipe setups as you say, although constant volume systems might have different outcomes - so balance is the thing to go on I guess. 

[JohnMo]

3 hours ago, MikeSharp01 said:

That's an obsolete unit now so perhaps worth stocking up on filters while there are still some about

Just buy one set of spare filters, do not though away the plastic frames, they just unclip from the old filter. Buy sheet filter material from RS components or similar.  Then use the removed old filter material as a template and cut from new sheet filter material. Clip the frames back together. You can then have one set of filters installed and a set ready to go. Way cheaper than buying complete filters.

 

Not sure where you have set your boost rates, should be 25% above normal rates.

 

How have you set your flow rates? What did you do?

[jimbob12345]

Thanks for the advice.

Well everything ive read says to commission the unit using the boost and these are the required specifications that are listed on manufacturers websites and on building regulations.

 

Said that bathrooms 8 l/s  kitchens 13 l/s and w/c 6 l/s, so i opened all the vents and slowly closed and reduced fan speed until i reached this setting. So my boost is now set at these rates.

 

I then adjusted the inlets to match the total outlets.

 

After this ive just reduced the boost by 15 % for my level 2 continuous mode.

 

Obviously i may well be wrong, its only what I could find

[JohnMo]

That could be why the fan speeds are high.

 

Basically start with all vents fully open. Leave the furthest away from unit fully open. Reduce or increase fan speed via the potentiometer for normal speed to get the flow correct at the furthest away vent. Then move to the next nearest, this time do not move the pot only move the vent.  Repeat. Once all vent extract done recheck and if any need adjustment, recheck all until none need moving.  Repeat fro supply.

 

Do the same for boost, but this time do not move the vents just the potentiometer.

 

The settings you are quoting should be the normal speed not the boost.

 

You want a supply rate of 11 l/s in a double bedroom and 5.5 in a single bedroom at normal settings.  Supply and boost should be the same flow rate overall.

[jimbob12345]

I did try this to start with but the problem i had was that the bathroom Is the closest and kitchen is furthest away.  I started in the kitchen and at 100% i could only reach  8 l/s but as the bathroom was closest that was extracting at around 18/s.

 

This is why i did it the other way round.

 

 

 

[JohnMo]

You may have to initially put the unit on boost and wind the boost to max.  The Titon units will not allow the normal to run faster than the boost. If you try to go past boost setting it seems like you are at max settings but you are not.

[jimbob12345]

Yes i put it into commissioning mode at manually ran both fans at 100%.

Thanks

[jimbob12345]

Ive also double checked building regs and it says those specs are for on boost,  not saying your wrong, just what im reading

[Temp]

22 hours ago, jimbob12345 said:

My Issue is that the device measures in M/S and I need L/S.

Ive had a scroll through the forum and have seen that most people have posted on graphs that they use about 1 M/S as around 7 L/S.

The issue is my anemometer has an internal radius of around 3.25 cm and 6.5cm diameter. 

Every online calculation i use is no where near 1 M/S per 7L/S.

 

m/s is a linear velocity.

L/s is a volume flow rate.

 

To convert between the two you first need to know the cross sectional area in m^2 (aka sqm) where you are measuring the velocity. In your case you are funnelling all of the air through the anemometer so that's the area you need.

 

The radius is 3.25 cm = 3.25 * 10^-2m.

So the area = Pi * (3.25 * 10^-2)^2 = 3.32 * 10^-3 m^2

 

The flow rate in cubic meters per second is then the velocity (in m/s) * the area (in m^2)

 

So let's say the velocity was 1 m/s...

 

The flow rate in cubic meters per second would be..

1 * 3.32 * 10^-3 = 3.32 * 10^-3 m^3/s

 

To convert that to L/s multiply by 1000 because 1m^3 = 1000L

 

So in your case with the funnel ..

 

1m/s = 3.32 L/s

Edited April 15, 2023 by Temp

[Temp]

If measuring the flow out of a pipe without the funnel take several velocity readings over the area of the pipe outlet and average them to give an average velocity. Then use the cross sectional area of the pipe in the calculation instead of the area of the anemometer. This is a little inaccurate because of the way you calculate the average velicity should be area weighted. There is more slow speed air around the edge than high speed air in the middle of the duct.

[Blooda]

Have you changed the filters?  When started to commission ours we found a big difference once we changed them, it had been running for about 6 months so the filters were quite a site.

 

On 15/04/2023 at 15:05, JohnMo said:

Just buy one set of spare filters, do not though away the plastic frames, they just unclip from the old filter. Buy sheet filter material from RS components or similar.  Then use the removed old filter material as a template and cut from new sheet filter material. Clip the frames back together. You can then have one set of filters installed and a set ready to go. Way cheaper than buying complete filters.

 

Not sure where you have set your boost rates, should be 25% above normal rates.

 

How have you set your flow rates? What did you do?

+ 1 :- The filters , here look like the ones in out Vent Axia, we have 4 set of frames lots and get the sewing machine out every so often, large sheet of about 2x1m for about a tenner from RS.    

[jimbob12345]

Hi thanks for all the replies, yes ive changed the filters. I have commissioned the unit now, i did use the internal radius of the anemometer in the end for my calculations.  

The fans, in particular the outlet seems to run at alot higher % than the inlet to balance the system,  but ive tried to stop over thinking about it as there is nothing i can do about it. Im not going to start playing with the pipe work or replacing motors, as long as i have the correct flow rate and its balanced im happy.

Thank you very much for the filter link, i will buy another caged set first so i can use the cage, gutted i only through it away a last week. Doh!

I would like to drop the fan speeds for the idle setting as they are abit noisy, but i dont want to go too low and cause an issue again.

Edited April 20, 2023 by jimbob12345

[Temp]

On 19/04/2023 at 13:45, Blooda said:

Have you changed the filters?  When started to commission ours we found a big difference once we changed them, it had been running for about 6 months so the filters were quite a site.

 

+ 1 :- The filters , here look like the ones in out Vent Axia, we have 4 set of frames lots and get the sewing machine out every so often, large sheet of about 2x1m for about a tenner from RS.    

 

It can be worth connecting your MVHR into an energy monitor plug. As the filter blocks up the current consumption increases, or at least it does on mine.

 

Our filters are quite a coarse foam similar to that used to filter aquariums.  I can wash them out with a garden hose or in a bucket of hot water. 

[Blooda]

41 minutes ago, Temp said:

 

It can be worth connecting your MVHR into an energy monitor plug. As the filter blocks up the current consumption increases, or at least it does on mine.

I have..... but it seems the one I bought is the most complicated piece of kit I have ever encountered  that and the fact the LCD / Polarisation seems to be focused so I have to look about 80 degrees upwards to get  a decent view, lying on the floor that my knees will let me get down but not so committal to let me get up 🤣   

 

"As the filter blocks up the current consumption increases" .... I agree .

 

So we are changing filters every 1 or 2 months.