Cooker hood to mvhr extract plenums

[CC45]

@JSHarris I just followed them.  Dont they follow this site? Not an uncommon situation, we all seem to have different terms, I was brought up with gable ends of a house being called pine ends, still find it hard to remember to use gable ends.

[Jeremy Harris]

Just now, CC45 said:

@JSHarris I just followed them.  Dont they follow this site? Not an uncommon situation, we all seem to have different terms, I was brought up with gable ends of a house being called pine ends, still find it hard to remember to use gable ends.

 

 

I appreciate that, but a supplier using incorrect terminology like this just causes confusion.  The word plenum, in the context of air handling systems, is well-defined, and has never been applied to a terminal or vent, as fair as I know.  Even the disambiguation entry in Wikipedia seems to be clear on this.

 

 

[PeterW]

Odd one and I agree with @JSHarris - plenum is usually where pipes join although I've seen a Lindab outlet described as an Rectangular Extract Terminal Plenum so I've got no idea now ..!! 

[dpmiller]

The plenum being referred to here is a two- or three- pipe manifold acting as a header for the terminal.

 

Plenum generally implies a change in dimension or velocity too, in my experience. And that's exactly what these terminal *headers* do- taking a number of pipes and transforming the flow from them in speed, and direction, whilst changing size. A restricted terminal installed on one then offers resistance which brings damping/silencing into it also...

[Jeremy Harris]

I'm pretty sure that what is being referred to here is not a chamber of any sort, but a ceiling terminal.  By definition, a plenum is a chamber, it comes from the Latin, plenum spatius, meaning a full space.  To refer to an open terminal, that feeds air into or out of a room is wrong and misleading, especially so when there is a long-standing use of the term plenum in ventilation systems to refer to the chamber used to collect the ends of the ducts from each terminal before they are connected to some form of air handling unit.

Edited June 7, 2017 by JSHarris

[Bitpipe]

https://xkcd.com/386/

 

 

 

[RandAbuild]

Here's how I fixed our terminals - the plasterboard is cut around it, before the pipe is trimmed off prior to skimming.

 

The Airflex stuff from BPC is very good by the way - fits together well and is well made.

[Barney12]

18 hours ago, JSHarris said:

 

 

I appreciate that, but a supplier using incorrect terminology like this just causes confusion.  The word plenum, in the context of air handling systems, is well-defined, and has never been applied to a terminal or vent, as fair as I know.  Even the disambiguation entry in Wikipedia seems to be clear on this.

 

 

 

In fairness to BPC I don't think its them. Mine happened to arrive on a pallet today direct from Airflow. On the Airflow delivery note it clearly describes them as Plenum's.

[jack]

8 hours ago, Bitpipe said:

https://xkcd.com/386/

 

XKCD has a strip for everything (although that one covers most situations online!)

 

Good to see the plenum argument again.

[ryder72]

On 2017-6-6 at 08:27, PeterW said:

 

Good record hoods have two filters - first set in the hood itself where they catch the grease and muck and ideally these are stainless mesh so you can bung them in a dishwasher. Second filter is either just before or just after the fan and are activated charcoal to catch the smells. @ryder72 probably has some good examples. 

I have finally opted for a Gutmann hob with inside downdraft extractors. Following @JSHarris advise I have gone recirculating.

 

I am not convinced that the average extractor out there with a standard charcoal filter is generally good enough to adequately contain cooking smells not are the average filters up to the job on trapping grease. A number of high quality products are available but there is a massive amount of resistance to spending that amount of money.

 

We have specified plasma activated extractors a well. Niche German product. Rather expensive but its brilliant.

[ProDave]

THIS is a plenum, actually two of them.

 

[Jeremy Harris]

@ryder72, does anyone do a recirculating hood with something like ozone cooking odour treatment? 

 

We have a small, German made, ozone generator in the fridge, and that does a very good job of eliminating smells, and when I was experimenting with ozone generators for our water treatment system I found a great deal of information on using ozone to treat household odours, almost all of it from the US.  It would seem that injecting a very small amount of ozone into the cooker hood might be a very effective way of oxidising cooking odour molecules.

Edited June 7, 2017 by JSHarris

[Stones]

We touched on this before (using ozone as an odour eliminator) following your Chilli experiment.  I've still to invest in a generator to try it for myself.  On the to do list.  I suppose the main question would be how big an ozone generator would be required to remain within safe limits?

[Jeremy Harris]

12 minutes ago, Stones said:

We touched on this before (using ozone as an odour eliminator) following your Chilli experiment.  I've still to invest in a generator to try it for myself.  On the to do list.  I suppose the main question would be how big an ozone generator would be required to remain within safe limits?

 

Very small, I think.  The ones used in some public toilets are tiny, with an ozone plate that is only about 30mm x 15mm or so, and I think they are pulsed on and off.  I bought several different ozone generators when I was experimenting, and the 7g per hour (hopelessly optimistic Chinese rating!) ones use two plates, each around 100mm x 50mm.  These run very hot, and realistically produce around 2 or 3 g/hr, but that is massively more than would be needed to kill cooking smells, as when I ran a generator like this in a room, with a small fan blowing air over it, the air in the room became unbreathable pretty quickly.  It would makes your eyes sting, with a very strong smell of ozone after just a few minutes.  It was extremely effective at killing odours, though, quite amazingly so.  It did have the rather unpleasant side effect of killing all the insects and spiders in the room, too, which illustrates just how toxic ozone can be in quite modest concentrations.

 

However, there are 3.5 g/hr (again, optimistically rated) units available, and one of those, fitted on the room side of the filters and pulsed on and off to reduce the ozone level, might work well.  I'm convinced there's a lot of potential in using low doses of ozone in this way, as it is remarkably effective at oxidising odour molecules.

Edited June 7, 2017 by JSHarris

[ProDave]

If you want to see more mvhr ducting, I have just put another entry on my blog at www.willowburn.net look for the entry "MVHR ducting"

[ryder72]

1 hour ago, JSHarris said:

@ryder72, does anyone do a recirculating hood with something like ozone cooking odour treatment? 

 

We have a small, German made, ozone generator in the fridge, and that does a very good job of eliminating smells, and when I was experimenting with ozone generators for our water treatment system I found a great deal of information on using ozone to treat household odours, almost all of it from the US.  It would seem that injecting a very small amount of ozone into the cooker hood might be a very effective way of oxidising cooking odour molecules.

 

A couple of German manufacturers are experimenting with solutions. One uses what they call 'activated plasma' which in effect breaks down the odour causing molecule into its constituents, releasing CO2, H2, N2 and O2 in the air. I dont know the details of the technology and its mechanism. I have seen it work so I doubt its marketing gimmickry.

 

Another uses a system that ionises stale air over a filter to neutralise odours. I wasnt convinced that it was doing anything.

 

I dont know if either use ozone as part of the mechanism but it may well be how  it works. Does the ozone principle work by exchanging the third oxygen atom with the odour causing molecule to form something more stable and ozone in turn turning into a more stable O2 molecule?

 

[Jeremy Harris]

That's good news, as it sounds as if the "activated plasma" is an ozone generator - they are just "cold" plasma generators, that use corona discharge to create ozone from oxygen.

 

In essence, this works to kill odours because ozone is extremely reactive, and oxidises the larger odour molecules, mainly into CO₂ if they are organic (as most are).  There will be a small amount of nitrogen oxides produced, from the reaction with nitrogen in the air, but generally this is a pretty low concentration, as the ozone tends to be used up very quickly in oxidising the organic odour molecules.  As it's the reactive third oxygen atom from ozone that wants to attach itself to anything organic in order to create a more stable molecule, the remaining O₂ will carry one flowing through the unit.

 

I'm not surprised that the ionisation system isn't very effective, as I suspect that the effect will be drowned out by the high volume of air flowing through the unit.  Ionisers generally only work well in fairly still air.

[dogman]

I bought a SHARP Plasmacluster air purifier for our old house as it stank of rotting house. Not sure if its the same technology.  In a small bedroom it certainly removed the smell and made it feel fresher.

Often wondered if i could build it into the supply to the MVHR

 

[Jeremy Harris]

24 minutes ago, dogman said:

I bought a SHARP Plasmacluster air purifier for our old house as it stank of rotting house. Not sure if its the same technology.  In a small bedroom it certainly removed the smell and made it feel fresher.

Often wondered if i could build it into the supply to the MVHR

 

 

From what I've read in the past few minutes, I think that the Sharp unit is primarily an ioniser, but ionisers also produce a small amount of ozone as well, so it seems likely that there are two effects at work.  I can't see why a small unit couldn't be installed in the fresh air feed plenum, as long as it was set to produce only a low level of ozone.  Ozone is extremely corrosive, in that is will oxidise a lot of materials, including a few plastics, so a bit of research into the plastics used in the ducts and fittings might be a good idea before doing this.  As the concentration would be very low, I suspect this wouldn't be a problem even if the ducts and fittings weren't particularly ozone resistant.

[Jude1234]

Resurrcting this old thead. I need to choose an extractor for our kitchen, we are having MVHR. Have been advised to go for one with carbon filter and it will not be ducted to the outside.  I have looked and I cannot see unducted ones. Do I just geta normal one and it is fitted differently?

[joe90]

I just bought a rangemaster hood and that came with carbon filters, not sure this is standard!

[Gone West]

3 hours ago, Jude1234 said:

 I just get a normal one and it is fitted differently?

All the ones we looked at can be recirculatory but we had to buy the carbon filters separately for ours.