condensation in extract manifold?

[woodman]

This is a problem I've never heard of, just wondering if anybody else has come across it? 

Newly installed MVHR is a NUAIR XBOX 95, distribution is by 75mm  semi rigid ducting. All ducting and manifolds are mounted in  the loft, beneath about 300mm of rockwool insulation. 

Whilst adding additional lagging to the MVHR external air intake and exhaust ducts, I've noticed a lot of condensate inside the extract manifold. Perhaps sufficient  to continue to accumulate and run along the 75mm ducts and potentially drip from the extract vents if left long enough. (The manifolds are home made, wooden, so will probably need to purchase a steel exhaust manifold)

I think this is probably caused by hot, humid air from the family bathroom (following a shower being taken)  meeting amd mixing with cooler air in the manifold being extracted from other (unused) bathrooms in the house.  The manifold is below the loft insulation, so is  adequately insulated but will clearly be below the temperature of air extracted during a shower, so I would think that condensation is inevitable?

I'm proposing to add a condensate drain to the manifold, and link this to the existing MVHR drain,  using an additional trap.

Has anybody else experienced this?

[JFDIY]

I was going to suggest a condensate drain, you'd have to make sure all sides slope to one point.

 

That said there must be some areas of stagnant air to allow the moisture to drop out on a cold surface withing the manifold. 

 

Either insulate to prevent the cold spots or can you add in some fillets or even baffles to the internal shape to get the air moving across the surfaces?

 

Perhaps a block of foam inside would shift the airflow and might even attenuate a bit of noise?

[Ed Davies]

9 hours ago, woodman said:

I think this is probably caused by hot, humid air from the family bathroom (following a shower being taken)  meeting amd mixing with cooler air in the manifold being extracted from other (unused) bathrooms in the house.  The manifold is below the loft insulation, so is  adequately insulated but will clearly be below the temperature of air extracted during a shower, so I would think that condensation is inevitable?

 

In principle, yes, if you mix two quantities of 100% RH air at different temperatures than the resultant mixture will have an RH greater than 100% so condensation is likely. But it'd be really weird, and a bit concerning, for the RH in the rest of the house to be anywhere near 100% so in practice I can't see why this sort of mixing is likely to result in much condensation.

 

It's not that there are lot of actual water droplets being extracted from the bathroom, is it? E.g., is the extract directly over the shower?