Network cabinet ventilation choices

[puntloos]

I have a dedicated network cabinet, with a service shaft right above it that goes all the way to the loft, and a dedicated MVHR extract. Normally the electrical gear will use maybe 200W, but it contains amplifiers for home cinema etc, theoretically taking it up to 2000W at full tilt. Your opinion on a few final choices here.

 

(not sure the picture helps, but it's the cab, power sockets, MVHR and shaft above)

 

A/ I have a secondary extract pipe that goes to the loft. I was thinking to attach a temperature controlled AC Infinity fan to it.

-> Will a fan disrupt the MVHR by e.g pulling air from the MVHR pipe? How to avoid this, or is it not a problem in practice?

 

B/ The shaft itself also has a decent amount of free space. 

-> How well will simple convection work? 

 

C/ My current plan for letting air into the cabinet is basically removing the bottom bit from the door

-> 20x762 gap? 50? 200x762?

-> If this gap is too big, worried about noise from cabinet to go into the room. Are there alternatives to consider?

 

 

 

 

[puntloos]

Anyone?

[Mike]

Not something I've tried to do domestically, but here are some thoughts. The initial one being that putting 2,000W into such a confined space may need an alternative solution, if it will really be that much.

 

On 10/12/2023 at 18:58, puntloos said:

A/ I have a secondary extract pipe that goes to the loft. I was thinking to attach a temperature controlled AC Infinity fan to it.

-> Will a fan disrupt the MVHR by e.g pulling air from the MVHR pipe? How to avoid this, or is it not a problem in practice?

The AC fan you mention runs at up to 205 CFM - that's 350m³/hr, albeit half speed may be enough to keep the temperature down. But that is going to disturb the operation of a regular MVHR system.

 

On 10/12/2023 at 18:58, puntloos said:

B/ The shaft itself also has a decent amount of free space. 

-> How well will simple convection work? 

It may be OK if free of obstructions, but if you're sucking 200m³/hr past it anyway...

 

On 10/12/2023 at 18:58, puntloos said:

C/ My current plan for letting air into the cabinet is basically removing the bottom bit from the door

-> 20x762 gap? 50? 200x762?

As a rule of thumb, an unobstructed 10mm gap below a door is good for up to 40m³/hour. So you'd be looking at a fair sized gap.

 

A dedicated air supply may be a better option - or perhaps fit a mini aircon unit instead of fans, which would work alongside the MVHR.

[puntloos]

1 hour ago, Mike said:

Not something I've tried to do domestically, but here are some thoughts. The initial one being that putting 2,000W into such a confined space may need an alternative solution, if it will really be that much.

 

The AC fan you mention runs at up to 205 CFM - that's 350m³/hr, albeit half speed may be enough to keep the temperature down. But that is going to disturb the operation of a regular MVHR system.

 

Indeed that's my worry. Do you agree that I should either permanently cut off, or at least temporarily cut off the MVHR if the fan starts making real wind?

Or are there some type of one-way points in air systems that will prevent air being sucked out of a MVHR pipe?

1 hour ago, Mike said:

It may be OK if free of obstructions, but if you're sucking 200m³/hr past it anyway...

 

As a rule of thumb, an unobstructed 10mm gap below a door is good for up to 40m³/hour. So you'd be looking at a fair sized gap.

Great to know, perhaps I should put down a big grate in that door somehow. Not try to make it sneaky..  - because you're saying it's going to need 50mm gap for 200m3

1 hour ago, Mike said:

 

A dedicated air supply may be a better option - or perhaps fit a mini aircon unit instead of fans, which would work alongside the MVHR.

Hmm tough to do at this point... I do have an aircon unit nearby (dedicated R32 fan coil unit for the room the cabinet is in)  but I was advised against using it to pull air from the cupboard, I forget why. 

[MikeGrahamT21]

I’m assuming you are considering how best the manage the environment in terms of humidity and temperature?

 

wattage of devices means very little, when we spec server rooms for new builds, we have to provide btu/hr outputs from the devices, the manufacturers of the equipment should be able to get this for you along with an operating humidity range, and maximum operating temperature.

 

having that info should make it easier to spec a solution 

Edited December 17, 2023 by MikeGrahamT21

[MikeGrahamT21]

4 minutes ago, puntloos said:

Great to know, perhaps I should put down a big grate in that door somehow. Not try to make it sneaky..  - because you're saying it's going to need 50mm gap for 200m3

Louvred door is probably an option here, and you will be wanting to attach a G3 grade filter medium to the back of it otherwise your AV kit will be rather dusty very soon

[puntloos]

44 minutes ago, MikeGrahamT21 said:

I’m assuming you are considering how best the manage the environment in terms of humidity and temperature?

 

wattage of devices means very little, when we spec server rooms for new builds, we have to provide btu/hr outputs from the devices, the manufacturers of the equipment should be able to get this for you along with an operating humidity range, and maximum operating temperature.

 

having that info should make it easier to spec a solution 

The room cabinet contains about 500W (peak) worth of network equipment (a switch powering a decent amount of POE stuff, router, broadband router, small NAS (75W)). But, next to that it houses my home cinema amplifiers. These are rated for 1750W total but that would be for "sine wave blasting continuous on all channels" - realistically I don't think they'll do more than 500W total during the loudest scenes. So 1000W 'continuous' would be my pessimistic-ish guess for a 2-hour (movie) slot. 

 

Currently we have perhaps a 100x100 gap still left in a 400x290 shaft

 

MVHR is a zehnder Q350

Edited December 17, 2023 by puntloos

[Mike]

10 minutes ago, puntloos said:

1000W 'continuous' would be my pessimistic-ish guess for a 2-hour (movie) slot.

Well that's clearly better than 2,000W.

 

59 minutes ago, puntloos said:

Do you agree that I should either permanently cut off, or at least temporarily cut off the MVHR if the fan starts making real wind?

Or are there some type of one-way points in air systems that will prevent air being sucked out of a MVHR pipe?

Maybe a motorised valve in the ductwork? I know that Atlantic make one in France - EAN 3416085437711 - so there must be similar available in the UK.

[puntloos]

52 minutes ago, Mike said:

Well that's clearly better than 2,000W.

It's all about how you count of course. Summing peak ratings gets me to 3000W but eg a 1000W subwoofer even when playing loudly very very rarely taps into that wattage hence my 1000W actual estimate. But yes, perhaps 1000W is more fair to work with.. 

 

Would you say that 100CFM is sufficient to carry away 1000W? 

52 minutes ago, Mike said:

Maybe a motorised valve in the ductwork? I know that Atlantic make one in France - EAN 3416085437711 - so there must be similar available in the UK.

 

My new problem with that is that at least the fan I suggested currently doesn't easily give off a signal that it's running, so I don't yet know how to tell such a buffer/valve to close up temporarily.

 

 

2 hours ago, MikeGrahamT21 said:

Louvred door is probably an option here, and you will be wanting to attach a G3 grade filter medium to the back of it otherwise your AV kit will be rather dusty very soon

 

One challenge I have is that the network cab is in a lived in room, so noise is a concern. I have one alternative which is that the 3" pipe I intended for extract is used for supply, and I could use the actual shaft as the extract, perhaps by installing a false ceiling and having a fan actually pull the air from cab into "above cab + shaft" ?

[Russdl]

@puntloos I wonder if you’re overthinking this regarding the MVHR aspect. The downdraft recirculating extractor on our hob can boost at up to 570m3/hr though more normally it’s around the 200-300m3/hr. I’ve not once considered its effect on the MVHR which is seldom above 100m3/hr and never noticed any problems.
 

With the extractor on a high setting it starts moving air internally around the house which becomes apparent if we’re cooking something pungent, with the extractor on a high setting and the kitchen door open, the smell will start spreading around the house indicative of all of the air in the house starting to move around heading towards the kitchen extractor. This is not an obvious airflow, only detectable as the smell spreads around. 
 

I would expect the same in your situation that with a high ventilation rate to keep your network cupboard cool the air within the house will slowly start recirculating through the cupboard. The MVHR will just get on with its thing, unperturbed. 

[Mike]

18 hours ago, puntloos said:

Would you say that 100CFM is sufficient to carry away 1000W?

I believe the formula for the required airflow in m³/hr = Watts x 3600 seconds / ((maximum permitted °C - ambient °C) x density of air (kg/m³) x specific heat capacity of air (J/kg.°C)

 

So taking 40°C as the maximum (a reasonable limit), and ambient as 22°C, then

 

1000W x 3600s / ((40°C - 22°C) x 1.225 kg/m³ x 1012 J/kg.°C) = 161m³/hr. Which is about 95CFM. So, to answer your question, yes if we ignore heat waves when the ambient temperature may go well above 22°C.

 

19 hours ago, puntloos said:

My new problem with that is that at least the fan I suggested currently doesn't easily give off a signal that it's running

There are no doubt other options, but the Shelly EM with a suitable clamp around the cable could be used to monitor the energy use. It also has an integrated 2A 230V relay that could be used to control a valve, though you / your electrician would need to study the manuals. Not yet used it myself, but I'm thinking of doing so to automatically switch on a kitchen hood if the hob or oven is switched on, though not sure when I'll get around to that.

 

14 hours ago, Russdl said:

The downdraft recirculating extractor on our hob can boost at up to 570m3/hr though more normally it’s around the 200-300m3/hr. I’ve not once considered its effect on the MVHR which is seldom above 100m3/hr and never noticed any problems.

I wouldn't expect a problem with recirculating, as the MVHR remains in balance, but this is external extract. However it would be interesting to get the thoughts of someone who ignored the normal advice and installed a kitchen hood with external extract (though they probably wouldn't run it for as long as a movie).

[Russdl]

1 hour ago, Mike said:

but this is external extract.

Missed that. Is that a good idea anyway?
 

Why not keep that excess heat inside, obviously there will be occasions when it’s not welcome but most of the time it would be. 

[Mike]

1 hour ago, Russdl said:

Why not keep that excess heat inside, obviously there will be occasions when it’s not welcome but most of the time it would be.

Good question!

 

It may be useful in the heating season (not necessarily, if the building is already heated enough), but the problem is handling it. The heat's generated in a confined space, which will rapidly heat up. As per the calculation above, I reckon that would mean extracting in the region of 161m³/hr of air from that one cabinet. Maybe the MVHR could add that much extract in boost mode, but that would boost extract from all over the house, which would tend to push up heat loss overall, while not extracting anything like enough from that one cabinet. So it becomes complicated...

 

Edited December 18, 2023 by Mike

[Russdl]

On 10/12/2023 at 17:58, puntloos said:

a dedicated network cabinet, with a service shaft right above it that goes all the way to the loft, and a dedicated MVHR extract

Delete the MVHR extract and surely the problem goes away doesn’t it?

If the chimney effect is not sufficient then I would have thought an extractor fan of some description would be sufficient to get the required airflow through the cabinet. 
 

I have no maths to back up that theory!

[puntloos]

13 hours ago, Mike said:

Good question!

 

It may be useful in the heating season (not necessarily, if the building is already heated enough), but the problem is handling it. The heat's generated in a confined space, which will rapidly heat up. As per the calculation above, I reckon that would mean extracting in the region of 161m³/hr of air from that one cabinet. Maybe the MVHR could add that much extract in boost mode, but that would boost extract from all over the house, which would tend to push up heat loss overall, while not extracting anything like enough from that one cabinet. So it becomes complicated...

 

Perhaps to be clear:

 

- I'm not extracting to the outside world, my extract goes to the loft (inside the thermal envelope, fully insulated), so indeed we're not losing the heat. So if you see the whole house as a "bubble" then indeed we're just moving air around. 

- We do have air conditioning (including in the loft) so true excess heat can be put outside 

 

My main worry was that if I have an MVHR extract and a standard fan extract into the same small space, air would be pulled from the MVHR pipe and 'confuse' the MVHR balancing. But indeed at the house level we're not fighting the MVHR.

 

Maybe the best approach is to just do the simple approach (both MVHR and extract) and should things go terrible some way, either close off MVHR completely, or indeed get some motorized valve...

Edited December 19, 2023 by puntloos

[Mike]

5 hours ago, puntloos said:

I'm not extracting to the outside world, my extract goes to the loft (inside the thermal envelope, fully insulated), so indeed we're not losing the heat. So if you see the whole house as a "bubble" then indeed we're just moving air around. 

- We do have air conditioning (including in the loft) so true excess heat can be put outside

A very useful clarification, and if the aircon can handle the excess heat that's also very good.

 

5 hours ago, puntloos said:

My main worry was that if I have an MVHR extract and a standard fan extract into the same small space, air would be pulled from the MVHR pipe and 'confuse' the MVHR balancing.

I'd say that was much less of a concern than with a separate external extract. The MVHR's extract fan will need to work a little harder as the air flow through extract vent in the cabinet goes into reverse & more has to be pulled through the other extract vents, but a Zehnder is doubtless clever enough to adjust for that automatically.

 

6 hours ago, puntloos said:

Maybe the best approach is to just do the simple approach (both MVHR and extract) and should things go terrible some way, either close off MVHR completely, or indeed get some motorized valve...

I agree :)

[puntloos]

Small final question:

 

I have the option of putting a ceiling into my cabinet, or have basically a direct shaft above the cabinet that would allow some air to just percolate up into the loft by itself (yes the powered fan extract pipe is really just a specific pipe in that same shaft). 

Should I:

 

1/ Leave the ceiling open, so indeed hot air goes up

2/ Close the ceiling and then put both MVHR and fan pipe in that ceiling

 

With #2 I somewhat lose the benefit of the direct riser (it's an additional way of venting heat and means the fan has to work less hard) but maybe there are benefits I haven't thought of?

[Russdl]

I vote for option 1 and keep the MVHR well out of

the equation. 

[Adrian Walker]

43 minutes ago, Russdl said:

I vote for option 1 and keep the MVHR well out of

the equation. 

Ditto

[Mike]

1 hour ago, puntloos said:

1/ Leave the ceiling open, so indeed hot air goes up

2/ Close the ceiling and then put both MVHR and fan pipe in that ceiling

From the ventilation aspect, provided you make provision to do 2 later, you could try 1 to start with and see how it goes. However from the fire control perspective it may be advisable / you may be required to have a ceiling, which is what I'd do anyway.