Ventilation Strategy?

PROJECT K

Hi all, currently in the process of completing a low energy (technically but not certified passive) house - at roof level now. Even though i have completed the PHPP with MHRV and everything is specified and detailed to my early grave i am increasingly wary of ducted air supply from heat recovery units.

While I am an engineer by profession, I am not in any way an expert in these systems but i believe that there will be potential long term issues in maintaining/cleaning ductwork and there does appear to be some movement away from ducted MHRV in Europe. Manufacturers/supliers claim ducts wont get dirty due to filters but that simply isnt true - even if filters are regularly changed ducts will be subject to dust and potential bacteria build up (at least for older systems). I have inspected two buildings, less than 5 years old and if you could see what they were breathing in!!! (okay these were very poorly installed systems but it does warrant a rethink...)

I am therefore leaning more towards Demand Control ventilation, either with humidity controlled inlets or possibly decentralised MHRV in selected rooms. Just wondering is there anyone who shares my concerns out there (or not!) and have any experience (good or bad) in either of these latter two systems? The DCV is very appealing to me due to its simplicity and low cost but as the extract fan runs continuously without heat recovery, there will be a slight trade off in energy saving compared to ducted MHRV. The decentralised MHRV option appears to offer the best of both with ***claimed***:rolleyes: efficiency of circa 90-91%

All comments welcome!

Thanks...

4Sticks

Google Amersvort Amsterdam to see your concerns are well founded. Unless expertly designed and installed avoid HRV. It can damage your health.

Edit

for example

and this too

glashanator

I too am coming to this stage...

I know there is/was some ancient machinery in MHVR used out there in the last 3 to 5 years in some systems. But thinking/hoping the technology has moved on immensely.

If you go for airtightness and achieve it, and if MHVR is not adequate, then what is?

beyondpassive

My view, established over 4 years of monitoring low energy buildings, is that heat recovery is a necessity. However it is critical that the system is designed and the installer is reputable. I generally would only specify 4 systems and nominate only 4 or maybe 5 installers. I insist on metal spiral ducts and a summer bypass mode. Yes there is a management issue with ventilation, as there is for any mechanical system. Build in a maintainance schedule into your plumbers annual service visit and buy up spare filters.

4Sticks

And what "strategy" for the cases where the end users will not be known to you?
The Dutch experience sounds a stark warning.

PROJECT K

glashanator wrote: »

I too am coming to this stage...

I know there is/was some ancient machinery in MHVR used out there in the last 3 to 5 years in some systems. But thinking/hoping the technology has moved on immensely.

If you go for airtightness and achieve it, and if MHVR is not adequate, then what is?

Thanks glashanator - i have no issue with the machinery technology (in reputable manufacturers units) or the principal of heat recovery. My concern is the physical condition of the supply air ducts (post installation if not installed properly) or at some point during the lifetime/occupancy of the building. Dust gets everywhere - regularly maintained filters or not. Bacteria will thrive in warm air supply ducts if it gets any chance to initiate (granted this is unlikely but i would err on the side of caution in our humid climate!). In your typical semi-D with short duct runs and compact distribution network this is less of an issue - but i have seen monstrous "passive" houses with duct runs in excess of 15-18m - the longer the duct the greater the risk of contaminates...and the more difficult it will be to maintain/clean (unless you leave inspection opes in ceiling)

@beyondpassive - i agree that heat recovery is ideal, in fact necessary for the 'holy grail' of passive certification/compliance and is required to make significant reductions in heat loss. However, is it worth striving for this extreme level of thermal performance at the risk of air quality? The decentralised option is becoming more appealing to me as it would appear to tick all the boxes...DCV relying on humidity controlled inlets only can suffer from less than adequate ventilation.

@4sticks - thanks for the docs, i came across them before during my research but had lost them, good to review again! And yes the less we rely on maintenance and taking this responsibility away from the homeowner/occupants the better! I would hate to think what the cost would be for an annual clean out of the ductwork!!! (and how effective it would be)

beyondpassive

Decentralised heat recovery and demand control are two seperate systems. If you're moving a lot of air through smooth or metal ducts, you have an inert environment for mould and bacteria. The exhaust side is more humid, but in reality you dont have to worry too much about that side as it dumps to outside. You can put most heat exchagers in a dishwasher and you can get ducts cleaned out on a 6 or 8 year maintainance cycle. So design the ducts like a water slide, nice and smooth and fast.

4Sticks

There is much evidence to contradict you bp wrt real world experiences with MVHR - sorry.

It is important to note that the current 2009 iteration of TGD F provides only for hole - in - wall ( crude )* and MVHR ( sophistacted )* approaches . It is silent on DCV ( the sensible compromise)*.
Meaning that a certifying professional is burdened with demonstrating compliance without reliance on this TGD.

* my view / opinion

beyondpassive

4Sticks wrote: »

There is much evidence to contradict you bp wrt real world experiences with MVHR - sorry.

from Holland in 2006 or cowboy installers?

4Sticks wrote: »

It is important to note that the current 2009 iteration of TGD F provides only for hole - in - wall ( crude )* and MVHR ( sophistacted )* approaches . It is silent on DCV ( the sensible compromise)*.
Meaning that a certifying professional is burdened with demonstrating compliance without reliance on this TGD.

Part F compliance should be formost in design of MHRV or DCV, but this would generally be by way of a deemed to satify calculation rather than Prime facia though TGD F.

4Sticks

beyondpassive wrote: »

from Holland in 2006 or cowboy installers?

from UK 2013

in the wider world there would seem to be every possibility that, where MVHR systems are not designed, installed and operated correctly, house occupants may take radical steps in response to problems with their indoor environment – such as turning the MVHR system off.

Source

Assessment of MVHR systems (NF52) by NHBC

(google it )

4Sticks

beyondpassive wrote: »

deemed to satify calculation

1. to satisfy who?
2. carried out by who?
3. to what standard or Code ?

oconnb3

i have a dormer 14 yrs old, no thought went in to insulation or airtightness got an energy heat loss surey done recently air blow test was 7.5 not great. Now thinking of retrofitting up stairs airtightness and insulation taking it apart as much as possible. Have going to pump wall cavity with Walltite (expensive) will insulate and airtight cavity wall. Ventilation is where i don't know much about MVHR or Demand Control...... any advice welcome i will have access to walls and floors for ducting if need be