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LEV testing - undersized systems
Not every LEV problem is a decline from a good starting point. Some systems never worked properly - they were undersized from day one, too small for the job they were installed to do. This is a different problem from a system that has faded, and it shows different signs. Recognising an undersized system matters, because no amount of maintenance fixes a design that was never big enough.
The short answer
An undersized LEV is one that was too small for its job from the start - not a system that has declined, but one that never had the capacity to control the exposure properly. The signs are telling: it has never captured well even when new and clean, it struggles across all its hoods at once rather than at one failing point, adding demand on it makes everything worse, and maintenance never brings it up to the mark because there is nothing to restore it to. Testing catches this by measuring the system against what the process actually needs, revealing a shortfall that is designed-in rather than developed - a problem no fan repair or filter change can solve, because the system was never big enough.
A different kind of problem
Most LEV problems are declines: a system that worked well when installed loses performance over time as a fan wears, a filter loads or a duct leaks. But there is a different, less-discussed problem - a system that never worked properly in the first place because it was undersized from the start. Such a system was specified or installed too small for the job: not enough airflow, hoods too small or too few, ductwork or fan inadequate for the demand of the processes it serves. It did not fade from a good starting point; it never had a good starting point to fade from.
This distinction matters because the two problems call for completely different responses. A declined system can be restored - fix the fault and it returns to the performance it once had. An undersized system cannot be restored, because there is no good performance in its past to return to; the shortfall is designed-in, not developed. So recognising that a system is undersized rather than declined is important: it tells you the problem is fundamental to the design, not a maintenance issue, and that the fix is not repair but a change to the system's capacity. Treating an undersized system as if it just needs maintenance wastes effort on a problem maintenance cannot solve.
It never worked well
The clearest sign of an undersized system is that it never captured well, even when it was new and clean. A declined system has a history of working properly before it dropped off; an undersized one does not. If the extraction has struggled to control the contaminant from the day it was commissioned - if there has always been dust escaping, a smell that was never fully drawn away, a sense that it was never quite enough - that points to a system that was too small from the start rather than one that has degraded. The absence of a period of good performance is the tell.
This can be obscured by the assumption that the extraction must be adequate because it was installed for the purpose. But installation for a purpose does not guarantee adequacy for it - a system can be specified or fitted too small, and then it never does the job however well it is maintained. So a useful question when a system seems to underperform is whether it ever performed well. If the honest answer is that it has always struggled, the problem is likely capacity, not decline - and the commissioning data, if it exists, may confirm the system fell short even when new. A system with no history of adequate performance was probably never sized to deliver it.
It struggles everywhere at once
Another sign distinguishes undersizing from decline: how the shortfall is spread. A declined system usually has a specific failing point - one hood that has lost capture because of a local fault, a fan that has worn, a filter that has loaded - while the rest may still work. An undersized system, by contrast, tends to struggle across all its hoods at once, because the problem is not a local fault but a global lack of capacity: the whole system simply does not move enough air for the demand placed on it, so every point is starved together rather than one point failing.
This system-wide character is a strong clue. If every extraction point is marginal or inadequate at the same time, with no single failing component to blame, that pattern fits a capacity problem rather than a fault. It shows up especially when demand rises: an undersized system that copes marginally when only some hoods are in use falls apart when all of them are - because the total airflow it can produce is shared among the points, and there simply is not enough to go round when demand peaks. Adding a hood or running more processes makes everything worse, because it draws on a capacity that was already stretched. A system that fails globally under demand, not locally through a fault, is a system that was never big enough.
Maintenance won't fix it
The defining feature of an undersized system is that maintenance never brings it up to the mark. Change the filter, service the fan, clean the ducts - and it still does not control the exposure adequately, because none of these adds capacity. Maintenance restores a system to its own best performance, but if that best was never enough, restoring it changes nothing. So a system that stays inadequate however diligently it is maintained, with no fault to find and fix, is very likely undersized - the maintenance is doing its job, but the job was never the problem.
This is where testing against actual need is what catches the issue. A thorough examination does not just check whether a system is performing as it did before; it measures the system against what the process genuinely requires to control the contaminant - the capture velocity and airflow the hazard demands. An undersized system fails that comparison even when it is in perfect condition, because the shortfall is against the requirement, not against its own past. That is how testing distinguishes undersizing from decline: a declined system falls short of its own benchmark, while an undersized one falls short of the need itself, in good condition and all. Recognising that tells you the answer is not another repair but a system with the capacity the job actually requires.
The takeaway
Some LEV problems are not declines but undersizing - a system too small for its job from day one, that never had the capacity to control the exposure. The signs distinguish it from a faded system: it never captured well even when new and clean, it struggles across all its hoods at once rather than at one failing point, it falls apart when demand rises, and maintenance never brings it up to the mark because there is nothing good in its past to restore it to.
Testing catches this by measuring the system against what the process actually needs, not just against its own history - so an undersized system fails even in perfect condition, revealing a shortfall that is designed-in rather than developed. That recognition matters, because it changes the answer entirely: an undersized system is not fixed by a fan repair or a filter change but by giving it the capacity the job requires. No amount of maintenance fixes a design that was never big enough - and knowing the difference is what stops effort being wasted on the wrong solution.
Questions
A system too small for its job from the start - not enough airflow, hoods too small or too few, ductwork or fan inadequate for the demand. It never had the capacity to control the exposure properly, so unlike a declined system it never had good performance to fade from.
A declined system worked well once and lost performance, so it can be restored by fixing the fault. An undersized system never worked well, so there is nothing to restore it to - the shortfall is designed-in, not developed. The two call for completely different responses: repair versus added capacity.
It never captured well even when new and clean; it struggles across all its hoods at once rather than at one failing point; it falls apart when demand rises because there is not enough airflow to go round; and maintenance never brings it up to the mark, because none of it adds capacity.
Because the problem is global, not local. A declined system has a specific failing component; an undersized one simply does not move enough air for the demand, so every point is starved together. Running more processes or adding a hood makes everything worse, drawing on a capacity that was already stretched.
Because maintenance restores a system to its own best performance, and if that best was never enough, restoring it changes nothing. Changing filters, servicing the fan and cleaning ducts add no capacity. A system that stays inadequate however well it is maintained, with no fault to find, is very likely undersized.
By measuring the system against what the process actually needs - the capture velocity and airflow the hazard demands - not just against its own past. An undersized system fails that comparison even in perfect condition, because it falls short of the requirement itself rather than of its own benchmark.
Our thorough examination measures your LEV against what the process actually needs - revealing whether a struggling system has declined and can be repaired, or was undersized from the start and needs real capacity.
