Airtightness

zeupater

Hi

The site you referenced has single room options for circumstances where outside wall mounting isn't possible ... for example (from manufacturers installation manual) ...

"The Vent-Axia HR100R is a remote mounting unit to provide balanced ventilation with up to 70% heat recovery for applications where there is no immediate access to an external wall. The HR100R is ideal for installations involving internal bathrooms and meets building regulation requirements for this application."

... installation would be a little more complex and you might need to create outside access through the roof or a gable end as opposed to simply replacing an existing through the wall extractor, but it is possible & the unit cost is far more realistic for what it actually does, particularly so considering it's targetting humidity at a major source point before it drifts around the rest of the home ...

HTH - Z

Coastalwatch

zeupater said:

Hi

The site you referenced has single room options for circumstances where outside wall mounting isn't possible ... for example (from manufacturers installation manual) ...

"The Vent-Axia HR100R is a remote mounting unit to provide balanced ventilation with up to 70% heat recovery for applications where there is no immediate access to an external wall. The HR100R is ideal for installations involving internal bathrooms and meets building regulation requirements for this application."

... installation would be a little more complex and you might need to create outside access through the roof or a gable end as opposed to simply replacing an existing through the wall extractor, but it is possible & the unit cost is far more realistic for what it actually does, particularly so considering it's targetting humidity at a major source point before it drifts around the rest of the home ...

HTH - Z

Thanks for posting the links Zeup it really does seem to offer the majority of us a means of achieving a sensible alternative. Without giving serious thought to the matter a full system has always been out of the question for us but the units shown in your link make perfect sense. Not unlike your suggestion of combining ASHP's and PV all those years ago.

DougMLancs

Ditto, I like the look of those single units 👍

zeupater

Coastalwatch said:

zeupater said:

Hi

The site you referenced has single room options for circumstances where outside wall mounting isn't possible ... for example (from manufacturers installation manual) ...

"The Vent-Axia HR100R is a remote mounting unit to provide balanced ventilation with up to 70% heat recovery for applications where there is no immediate access to an external wall. The HR100R is ideal for installations involving internal bathrooms and meets building regulation requirements for this application."

... installation would be a little more complex and you might need to create outside access through the roof or a gable end as opposed to simply replacing an existing through the wall extractor, but it is possible & the unit cost is far more realistic for what it actually does, particularly so considering it's targetting humidity at a major source point before it drifts around the rest of the home ...

HTH - Z

Thanks for posting the links Zeup it really does seem to offer the majority of us a means of achieving a sensible alternative. Without giving serious thought to the matter a full system has always been out of the question for us but the units shown in your link make perfect sense. Not unlike your suggestion of combining ASHP's and PV all those years ago.

Hi

Yes, it really comes down to only being able to think at a level slightly above the one dimensional abilities of those who set the rules ....

I put the issue down to someone coming up with a solution to a wrongly perceived problem ... for example, in this case it's issues caused by airtightness and the perceived single solution, however the problem is that there are actually two issues to address, humidity control to avoid damp & health problems, and, of course, preventing the occupants from suffocating through lack of oxygen.

Of course, although these can be seen as issues with a single solution (ie ventilation) there are obviously different approaches that can be applied. You can address winter humidity in a closed environment with a dehumidification system which then leaves the separate air quality/oxygen levels to address, however, this depends more on occupancy per m3 of living space than a direct relationship to property volume related air changes ... effectively, if you've already addressed moisture and air quality related to dampness, you're only left with air quality related to the mix of gasses present (ie O2/CO2 etc by unit volume) & the removal of contaminants (dust/bacteria/VOCs etc), which in itself has various approaches ... we use filters with plasma/ionisation to improve air quality, therefore for us it really only comes down to maintaining a healthy gas ratio in the air we breath ...

So, the question now comes down to how much do we breath & what proportion of the oxygen to we consume - well that's pretty simple, it's ~11cum/day with ~25% O2 extraction per breath per person, so the logical air changes could be classified as ~5cum/day/person equivalent for short periods (overnight for a few days) in very cold conditions, to somewhere ~15cum/day/person maximum to recover to atmospheric equilibrium, all depending on household living volume of course .... what would this mean for an average sized home (~1100sqft/250m3) to maintain air quality with 2 occupants at 15cum/day each, if fully airtight and used filters, ionisation & dehumidification?  ... well that's be based on somewhere around 0.12 air changes per day ((15(m3)x2(people)/250(m3)), so 0.005 air changes/hour ...

Wouldn't this really low figure logically suggest that the huge difference to recommended air changes are simply related to extraction of humidity and it's related issues rather than ensuring air gas ratios are maintained ....

.... the issue therefore comes back to one dimensional sequential thought processes ... there's moisture, ... moisture causes damp, damp causes mold, which in turn causes both structural decay & breathing problems - so the 'only' answer 'has' to be humidity extraction and air replacement at a given rate ... therefore the 'only' solution is to codify & mandate this rate to the exclusion of alternate remedies ... then comes along the complication of energy efficiency ... well that's easy, yet another single solution to a problem caused by reliance on a single solution ... leave everything as is & just recover a proportion of the heat from the extracted air! .....

To anyone with any form of ability to think logically, the first thought must be 'who on earth made this kind of solution up and how is it that anyone allowed such rubbish to remain codified into building & environmental policies?' ... well, whatever colour of politics anyone bends towards, it's all our fault as we're the ones that choose clueless representatives that ultimately employ the clueless 'experts' that don't have the ability to think & process thought in a multi-dimensional way ... there are alternative solution which are open to consideration & some of us are actually employing them now.

HTH - Z                 

michaels

I always wonder if it is worth just having some sort of filtered (and heated) air intake to improve air quality in two ways, filtering out pollen etc and making sure the air in the house is exchanged in the manner of your choosing, the slight positive pressure resulting would mean that all those failed draught proofing areas would be out rather than in so wouldn't feel like cold draughts.

Presumably any incoming winter air is also relatively dry assuming it is cold as then it can't be holding much moisture?

paul991

theres thishttps://www.i-sells.co.uk/nuaire-drimaster-eco-hall-control-diffuser-positive-input-ventilation-unit?msclkid=b82e6318c93412f421c4004a1a94f607&utm_source=bing&utm_medium=cpc&utm_campaign=SHOPPING TOP SELLERS (Dekstop)&utm_term=4578916187452664&utm_content=NUADRI-ECO-HC but if you have the heater version it will use more power  , has  a 400watt heater fitted

zeupater

Hi michaels

The issue is that positive air ventilation is still performing forced extraction thus increasing the rate at which the property leaks heat, it's just that positive air pressure is replacing an extractor based negative pressure.

Having said that, I do tend to agree that perceived comfort levels should improve with positive air systems if the incoming air is pre-heated, but there's still the additional energy & cost to run the system, which would likely be far greater than running a dehumidifier which has no effect on internal/external pressure differentials. The added benefit of dehumidification is that not only the majority of the energy being consumed is converted to heat within the property, but there's also latent heat energy released from condensation, so the system effectively has an over par electrical efficiency, in many cases likely providing a COP closer to 2 than 1, whereas all forms of extraction, positive or negative pressure and whether the heat is recovered or not, would provide various degrees ranging from a negative COP to one significantly below 1.0, the only logical exception would be an extraction solution based on a combined heat recovery/heat pump setup to mitigate extraction heat losses so as to raise the overall COP above par ...

HTH - Z   

paul991

https://www.houzz.co.uk/magazine/how-to-retrofit-healthy-ventilation-into-your-home-stsetivw-vs~132528720 is  an article that explains  not all mvhr units are fitted to fully insulated properties but the cost seems to be excessive unless you have a bad damp problem

waqasahmed

paul991 said:

https://www.houzz.co.uk/magazine/how-to-retrofit-healthy-ventilation-into-your-home-stsetivw-vs~132528720 is  an article that explains  not all mvhr units are fitted to fully insulated properties but the cost seems to be excessive unless you have a bad damp problem

It also appears that an MVHR is worth it regardless of air tightness, however it's obviously better the more air tight your property is. That's especially the case when you're trying to achieve PassivHaus standards 

https://www.enhabit.uk.com/2020/07/08/is-mvhr-suitable-for-all-homes/

zeupater

waqasahmed said:

paul991 said:

https://www.houzz.co.uk/magazine/how-to-retrofit-healthy-ventilation-into-your-home-stsetivw-vs~132528720 is  an article that explains  not all mvhr units are fitted to fully insulated properties but the cost seems to be excessive unless you have a bad damp problem

It also appears that an MVHR is worth it regardless of air tightness, however it's obviously better the more air tight your property is. That's especially the case when you're trying to achieve PassivHaus standards 

https://www.enhabit.uk.com/2020/07/08/is-mvhr-suitable-for-all-homes/

Hi

The issue is that heat recovery ventilation is essentially pressure neutral, especially so in single room solutions whereas any form of forced extraction causes a negative (or positive) pressure differential.

The article referenced discusses the difference in carbon emissions (/efficiency losses) between natural ventilation & heat recovery as calculated by SAP and effectively questions the validity of the SAP methodology, including a the chart showing emissions by frequency of air changes .... however, what they've essentially missed is that all data points are calculated at an internal/external pressure differential of 50 pascals, which in real money is a force of 5kg/m2 acting on all of internal/external surface walls, ceilings etc and that this force is always acting on these surfaces, because that's what the air change calculation & test methodology says.

This circles back to the issue of test vs real world conditions raised in the post on 20/10 and whether a pressure differential of 5kg/m2 would be considered typical on an an annual basis, as opposed to that for for the heating season only ... after all, what's the real effect on emissions when the windows are open in the summer, there's no heating/cooling & it's pretty breezy outside - I'd suggest absolutely none & this is the kind of issue that causes SAP to overestimate heat requirements in older properties ....

HTH - Z