Author Topic: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air  (Read 4436 times)

contrarian

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I agree ‘ventilation is an important issue and deserves more attention than it generally receives’.  A building super-insulated and super-airtight won’t support human habitation without the addition of air.  There are many constructional ways to achieve Passivhaus certification but only one ventilation solution – MVHR – which is the basic problem with Passivhaus.

You state with certainty that MVHR is necessary in the UK but this is far from proven.  I’m assuming your evidence is the Carbonlite Information Paper ‘Comparing energy use and CO2 emissions from natural ventilation and MVHR in a Passivhaus house’ that was contested by Arup within the RIBA Sustainability Group when published in 2009.  A very limited case was investigated in the paper, whereas Arup figures suggested that MVHR could not be justified on energy grounds in the South of England.  Most certainly the Carbonlite report cherry-picked the most favourable numbers to make its case, for example 87% heat recovery (and how long will that fan efficiency last?) rather than the PHPP default of 75%.  To my knowledge the AECB have produced nothing of certainty since?

Passivhaus is concerned with energy saving and comfort to the exclusion of the fact that homes are occupied by people of different lifestyles and culture.  We hear daily on the news how the culture of Germany differs from other parts of Europe.  Most certainly the home maintenance usual in Britain is at a remove from that usual in Germany.  The recent Good Homes Alliance report ‘Ventilation and good indoor air quality in new homes’ found that MVHR filters may need changing every three months1.  I suppose housing associations could have filter-change teams roaming the streets but for privately rented or owner occupied housing the likelihood of maintenance being adequate is zero.

Passivhaus exponents always argue that if the MVHR isn’t working problem, occupants can just open a window, and that mechanical ventilation is just like a boiler - it requires servicing.  If however a boiler isn’t working one feels cold but human perception of indoor air quality is a lot more fallible.  This is a worry – that at a time when allergenic illness is at an all time high and the basic causes are little understood2, we are proceeding with MVHR, a technology with so many problems.

My own particular interest is in retrofit which has far greater potential to help achieve the UK’s need for 80% carbon reduction than does new-build.  The Energy Saving Trust reported at Ecobuild3 that there have been problems with all the MVHR installations for Retrofit for the Future (the majority of their retrofits incorporated MVHR) including those attempting to achieve Passivhaus standard.  Your article is written as if we are within an ideal world, and Passivhaus certification standards most certainly are close to ideal.  But beyond control are the VOCs off-gassing into houses with largely unknown consequences for health.  As the NHBC points out, to outlaw the offending materials is at present impossible4 - dry air is the least of our worries - the design ventilation rate is a healthy and safety issue. 
     
In Scandinavia, where the science of indoor air quality was developed, at trade exhibitions there are prominent displays for duct cleaning equipment.  MVHR has ducting on the supply side of the system; the least gap in the insulation/ductwork will be a gathering point for condensation and pathogens that will be undisturbed for the lifetime of the building, because there is no likelihood in England that ductwork will ever be cleaned.

As Shaun Fitzgerald wrote just recently5 ‘…The Passivhaus standard’ involves the inclusion of a mechanical ventilation system.  I don’t understand what is passive about this’.  In the case of retrofit MVHR is a virtual non-starter because of the extreme difficulty of accommodating the ducting within existing 2-storey houses, which makes the Enerphit standard an irrelevance.  As the Institute of Sustainability FLASH reports suggest6 what is required is a hybrid system that will run passively most of the time but with fan-backup.  Passive stack has the advantage of ducting on the extract side only but given its limitations occasional fan power is required, however in the sheltered conditions of the south of England how many times a year will the fans run? 

There are passive systems with heat recovery: the BeDZed PSHR, the Lunos system in Germany, French-made ‘supply air’ windows, using secondary glazing to pre-warm incoming air, humidity/pressure controlled passive stack + heat recovery etc.  These may not have the supposed efficiency of MVHR but Enerphit is unaffordable anyway.  The only way to meet the 80% carbon reduction is to achieve 60% through physical measures – insulation etc – and enlist behaviour change amongst householders (plus renewables) to achieve the rest.  Householders will of course expect that the systems they are learning to use won’t be counter-intuitive - air should come from windows not out of a hole in the ceiling7.

MVHR is the market solution; it will make money for manufacturers who will be selling a lot of kit.  That doesn’t necessarily mean that the market solution is the right solution for people. Unfortunately the manufacturers’ trade organisations are such a forceful lobby, and because what was once the UK’s national and non-commercial building research centre has virtually ceased building research, alternative solutions are hard to test.  The only available test facilities are those owned by the manufacturers who have a vested interest in going mechanical.

I thought when the Passivhaus Trust was established that the intention was to adapt Passivhaus to UK requirements – climate and culture.  Instead the output of the Trust is in terms of ‘myth busting’ and promoting Professor Feist’s UK tour as if for a visiting rock star, is Passivhaus now the ‘only true faith’?  What you should be doing is promoting debate rather than acting as a mouthpiece for the mechanical equipment industry.  For example, are Passivhaus standards - adopted so far only by ardent enthusiasts - really appropriate for incorporation in the building regulations? 

We have a habit in this country of adopting skewed rather than holistic agendas that only later reveal unforeseen side effects.  The high-rise flats of the 1960s, built for speed but before long mouldy and uninhabitable, are a case in point.  50 years later the list of technical measures for inclusion within the Green Deal makes no mention of the words ‘domestic ventilation’8.  It’s all going to end very badly!


 1 Good Homes Alliance ‘Ventilation and good indoor air quality in new homes’ November 2011,  page 76.
2 NHBC ‘Mechanical ventilation with heat recovery in new homes’ January 2012, page 24.
3 Alex Stuart ‘Post occupancy evaluation and performance – first winter results’.
4 ibid 2 page 34.
5 Dr Shaun Fitzgerald ‘A help or hindrance – Dr Shaun Fitzgerald questions the use of PassivHaus design in the UK’ Architects Choice, March 2012 page 47.
6 Institute for Sustainability FLASH guide 7 ‘Improving the building services’ September 2011, page 7.
7 see Macintosh and Steemers ‘Ventilation strategies for urban housing lessons from a POE case study’.   Building Research and Information ( 2005) 33(1) pages 17 – 31.
8 Department of Energy and Climate Change ‘What measures does the Green Deal Cover?’ May 2011.

Mark Siddall

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #1 on: June 01, 2012, 12:06:32 AM »
Contrarian,

Firstly my I say that the key purpose of the article was to offer clarification with regard to the ventilation strategies and IAQ. Secondly with regard to MVHR the article was also developed to draw attention to the differences between quality assured design and the more common. Thirdly its purpose was to encourage debate about the very important and very interesting subject of IAQ and ventilation strategies. I thank you for taking engaging – whomever you are.

The “need” for MVHR: "You state with certainty that MVHR is necessary in the UK but this is far from proven." This statement is in correct. I state that for a house built to the Passivhaus standard, i.e. to achieve requirement of 15kWh/m2/yr or 10W/m2 peak load, then MVHR is required in the UK. This is not the same as stating that "MVHR is necessary in the UK." There is an important distinction.

Heat Recovery Efficiency: You refer to a Passivhaus "default" requirement for MVHR of 75%. I think that you are somewhat confused. This is not a default, rather it is a minimum requirement so as to help avoid the risk of thermal discomfort during the winter (When -10C outside the supply is to be over 16C; it is this dictates a minimum efficiency for the MVHR.)

For a worked example I’ll take two HRV systems. One has an efficiency, of say 87% whereas the other has an efficiency of about 75%. I've tested such a scenario using two such units on a Passivhaus modelled in PHPP and found that the house using the 75% efficient unit, would consume about 25% more energy. (If you were to address energy performance deficit incurred by the 75% efficient unit by improving the opaque thermal envelope alone you would need about 125mm more insulation!)  There are therefore considerable benefits in utilising the best available MVHR unit as it enables the U-values of the opaque and transparent fabric to be a little less stringent.  

By the way, I did not draw upon the AECB paper to which you refer rather I drew upon my own experience using PHPP. The potential of MVHR has been demonstrated in many southern European climates (I drew upon my experience from using PHPP, though i could equally refer to a Phd thesis by Jurgen Schnieders, papers by the Passivhaus Institute.)

Please make sure that you read the next edition of Green Building Magasine it will hopefully address many of the energy related concerns that you have. ;-)

Filters: With regard to building occupants; the German people are just as unfamiliar with MVHR as those from the UK. The frequency of filter changes will ultimately be determined by the site location and the occupants lifestyle. I agree that there are subtle though limited changes in behaviour that are required in this regard – changing a filter is not exactly rocket science! At this time we are in a learning and analysis phase. Reports of Passivhaus MVHR in Germany and Austria are good. Conjecture within the UK will not address the issues that you raise. What we need is some serious research to determine how UK residents adapt and whether any learning relates to teething troubles or something more concerning. This is taking place. Time will tell.

IAQ: I agree that human beings are not well suited to determining IAQ. For the purposes for rhetoric “at a time when allergenic illness is at an all time high and the basic causes are little understood” why are you so sure than natural ventilation is the answer? From the reading that I have done into IAQ there are few papers that suggest that natural ventilation addresses IAQ during the winter. (One reason being that people shut trickle vents when they feel a cold draft during the winter - bang goes the IAQ!)

Retrofit: I agree that retrofit is an important issue. I have not heard any negative reports regarding the MVHR units that were installed in the RftF three projects that I was involved in. Retrofits need to be considered on a case by case basis. In my opinion, for a range of reasons, EnerPHit may not always be the most practical or affordable option. Where opportunity allows however there is no reason for it not to be adopted. I can only agree with your concern regarding the Green Deal and any omission regarding IAQ.

Idea World: We certainly do not live in an ideal world. If we did we could ditch the need for quality assurance and design guidance that would be lovely. What I was seeking to do within the article was to highlight the fact that the Passivhaus standards places requirements upon the design and construction process that other national guidelines (in this case UK and Netherlands) fail to address. In this respect, for the design of MVHR systems, Passivhaus certainly points in the right direction.

Duct cleanliness: Certified Passivhaus Designers are trained in the importance of ensuring that the ductwork is in a suitably clean state prior to handover. The use of F7 and F8 filters on the supply side significantly reduce the risk of dust accumulation within the duct work. Inspections of the ductwork in the 20+ year old Passivhaus homes in Darmstadt have shown that they were not gathering dust. Unlike the American air conditioning systems Passivhaus MVHR is not subject to the same risks of pathogens etc. In part this is due to the airtightness requirements of the ductwork (<3% leakage). It is also due to the fact that the temperature of the ducts is maintained above the dew point – therefore not condensate can form that could theoretically lead to a issue.

Passive Stack: Will passive stack with fan back up really deliver the standards of IAQ that you also desire? Energy demand will increase by more than 50% relative to a Passivhaus if adequate IAQ is to be maintained. Also note that passive stack alone will not work with heat recovery. In the past have examined the BedZed type ventilation cowl (it is not pure stack as it also utilises wind pressures.) I found that allowing for deviation between the EN test standards and the Passivhaus test standard for MVHR, but excluding the thermal bridging incurred by the BedZed unit, that a good Passivhaus MVHR unit is more energy efficient AND is not subject to the vagaries of the whether or not the wind is blowing (leading to over or under ventilation.)

Behaviour change: It is interesting to see that you are in fact an advocate of behaviour change. Do you honestly believe that you can convince 60 million people to live at an average temperature of less than 18C? Brave of you! Would it prove easier to convince them to live at 20C and to change a filter once in a while?

Counter intuitive: Plenty of people accept the air coming from the dashboard in their car.

Market forces:  I am not interested in buying, selling or shipping product. I try remain open minded whilst also seeking to maintain critical awareness. I would like to say that after years of thinking and undertaking secondary research that I had found the perfect solution to the ventilation/IAQ dilemma. At this time, compared to all the other solutions that I’ve examined, MVHR appears to offer a most optimal solution so far.

Thermal Bypass: Of course one issue that has not been addressed is thermal bypass. The need to prevent the thermal envelope from being undermined by air movement cannot be over looked. Nor can the risk that poor standards of airtightness impose upon the building fabric (have you seen the damage that is can do to a roof space?) Recent coheating tests have show then Passivhaus buildings appear to be performing in accordance with the predictions, which is more than can be said for most standard UK buildings (which consume 40-60% more energy than predicted – not as a result of the end user but because of poor build/design quality.) If we are to achieve the desired reductions in CO2 emssions then this factor can not be over looked. And with improved airtightness comes the need to address ventilation strategy.

Bob Lowe of UCL did an intersting paper some time ago. In in terms of IAQ his work established that it was unlikely that an airtighness of less than 10 ach/h@50pa would provide adequate fresh air on a consistent basis. It is apparent that once the airtightness gets to about 5 ach/h@50pa that mechanical extract is required as nat vent can not do the job. Both 10 ach/h@50pa and 5 ach/h@50pa are way outside the standards of airtightness required for the preservation of the building fabric.

Macintosh and Steemers: This is a very interesting reference. I have read the paper also. One thing that has occurred to me after having read the paper is that the design of the heating/ventilation system is what I think of as a "split system" whereby the fresh air supply and the heat energy are supplied using different technologies (MVHR = fresh air, rads = heat). This does conceivably introduce some competing forces whereby people may choose to keep windows open for prolonged periods (and thus compromise the efficiency of the MVHR system) at the expense of increased heating also (heat load increases as ventilation heat losses are increased also.)

It is indeed important to note that the competing forces of comfort and window use is an issue (in terms of IAQ window use and ventilation may be considered to be distinct from one another - though from time to time, say when cooking, the two may overlap.) To my mind the findings of Macintosh and Steemers suggested that a more integrated means of supplying fresh air and heat may be beneficial - all air heating as may be used in Passivhaus homes (the alternative would be to somehow throttle back the supply temp of the rads). The heat supply in a Passivhaus is so low as to encourage much quicker behavioural reactions to redress issues associated with comfort. This means that short term purge ventilation - say to remove excess heat/humidity when cooking - is increasingly used to the intended purpose and does not conflict actual heating demand (with regard to behaviour the building acts as a soft educator to the occupant.)

One of anomaly that is currently inhibiting some designers from adopting the all air heating strategy at this time is uncertainty about the robustness of the weather data and it's influence upon peak load conditions. Time will tell whether this concern is entirely warranted.

The Passivhaus Trust has not had anything to do with the myth busting article that relates to this forum thread.

I find your cynicism regarding the visit of Prof Fiest somewhat disappointing - to me this does not suggest an open but critical mind. I am sure that you will appreicaite that there are few people with his experience of delivering, researching and monitoring the implications of ultra low energy buildings. It is in this context that the tour presents UK practioners etc. with the chance to hear and learn from his first hand experiences - challenges and successes. Should you choose to attend one of the events then I'm sure that your thought provoking scepticism would be appreciated, but please leave out the cynicism it does not assist a healthy debate.

By the way, what's your real name?
« Last Edit: June 02, 2012, 05:30:41 PM by Mark Siddall »

heinbloed

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #2 on: June 02, 2012, 06:30:55 PM »
The hot air of crematorys ....

Those who are interested in the issue and want to see a nation suffering under HRV systems and direct MV systems here:

http://brandpunt.kro.nl/seizoenen/2011/afleveringen/15-05-2011/fragmenten/verstikkende_ventilatie/

( the Dutch public TV station KRO on the issue)

The wheelbarrow at the beginning of the TV report (at 00:01:20) shows the medication needed by the population of 1 small street to combat the effects of sick building syndrom caused by the ventilation system in their homes.

If you need translation help let me know.

In short:
               1/2 million installed MHRV and MV systems installed in homes.
400.000 cases of premature admissions to hospices per year.
              From 150 recently researched MHRV systems by the ministry for infrastructure and environment not 1 (not one !) fullfilled strict Dutch regulations.
More people dy as a result from MHRV impacts than from house fires.
The statistical life time is reduced by MHRV systems.
The physical well being, the health as well.

The problem is known since 20 years, the construction mafia hindering changes in laws, the total ban on MHRV systems for homes.
The crux is the idea to save on home heating energy and CO2 emissions. Other meassures than MHRV systems to save on energy and CO2 emissions would be more expensive. The cheapest solution being the deadliest.

To calculate down the energy demand of buildings ( building energy rating) as anticipated by the industry to show their greenishness people are killed. This saves on CO2 taxes on concrete and materials. On strict reductions of direct emissions("We polute, yes, but we build energy saving homes....cheap, you know, affordable as you know ....")

Another sample where greenwashing kills for profits.


--------


Call me heinbloed, Mark Siddall.

 

 






Mark Siddall

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Passivhaus ventilation: It's not a lot of hot air
« Reply #3 on: June 03, 2012, 11:04:18 PM »
Hein,
The problems that are endemic to Holland are increasingly widely recognised, as are the successes in Germany and Austria. To my mind there is a fundamental issue; who says that the stringent Dutch regulations are based upon the correct assumptions? One would hope that they are well founded, but are they really appropriate?

Let me explain the reasoning for this line of questioning. I have read about a recent Dutch study - perhaps the one to which you refer (I refer refer to the one discussed in this paper http://tinyurl.com/6qz8hpa). Just as you note it compares delivered ventilation in the buildings to regulatory standards, but does not serve to determine or describe how these standards have been derived (what are the desired indoor CO2 levels, RH, VOCs etc) and whether or not the standards are indeed appropriate.

A recent study by REHVA (http://tinyurl.com/7w2x72s) shows that in Holland ventilation rates are very high as compared to other countries (roughly twice that of other nations). Is this really a sign of good indoor air quality? There is a strong argument that this level of ventilation constritutes over ventilation. Over ventilation results in lower indoor RH, thus less comfort, and greater risk of a suppressed immune system (according to research that is included in ASHRAE 55). I understand that high levels of ventilation also serve to increase the rate at which chemical reactions can occur - thus further impairing IAQ. The idea that "the solution to pollution is dilution" does not therefore hold true. (Whether or not the ventilation is natural or mechanical).

The key issue here is that the answer is not a simple one. It is not the case that 'MVHR is bad', or for that matter that natural ventilation is bad. Rather it is that poor ventilation specification (based upon say poor national or voluntary standards), poor design and poor implementation are bad. If we can agree on this premise then it is possible to begin a sensible discussion regarding the appropriateness of various strategies. It is also important to note that a rule for one ventilation strategy may not apply to another, even when seeking to achieve the same performance target (ventilation efficiency plays a part.)

Studies examining either ventilation strategy - natural or mechanical - show that without adequate QA they do not deliver the requisite performance. The one thing that I am clear about in my mind is that we need good standards of guidance and quality assurance throughout the design, construction and hand over/maintenance processes. At this time there is a paucity of adequate, scientifically derived, guidance and little in the way of adequate quality assurance standards (this applies to both mechanical and natural ventilation.)

Mark
« Last Edit: June 04, 2012, 09:15:04 AM by Mark Siddall »

Alan Clarke

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #4 on: June 03, 2012, 11:24:08 PM »
Oh for an independent building research organisation in this country!

I am getting the impression that ventilation in buildings is not as straightforward as everyone would like it to be. The variable ventilation rates experienced in so-called natural ventilation systems do not really seem to cause much problem in well insulated buildings - though there is clear evidence that discomfort from draughts leads to underventilation in cold weather. We do know the problems of high surface moisture and mould in poorly insulated houses, but in new build (or equivalent refurb) good insulation should avoid these issues.

In my experience the only way to get reliable ventilation rates is mechanical ventilation, either continuous extract or MVHR. Passive systems are just too vulnerable to varying stack and wind pressures - you'll get under ventilation in one condition and over ventilation in another. In a reasonably airtight building the fan will provide a consistent air flow rate - just what the regulations ordered. So why does anyone have a problem with this?

Clearly they do, and though there may be issues of noise - or just a feeling it's wrong - reports of ill health can't be dismissed.
One thing I had noticed in Dutch studies, and my own experience, is that minimum humidity levels tend to be lower. But humidity levels are also low in old houses that are draughty and heated to comfortable temperatures, so I think we know about humidity, and can detect this as an issue in itself.

So is it a new-build problem?  New houses will be consistently warm throughout the winter, and of course built with factory-fresh materials. This suggests there may be issues of offgassing - possibly from materials that are OK in cooler conditions, and can be dealt with in summer with the windows wide open. For instance timber - lovely and natural - comes complete with compounds such as terpenes evolved to defend trees against insects. So they may not be good for us either, but just to complicate things, recent research indicates that these chemicals produce worse ones when reacted with ozone - which isn't an internal pollutant, but comes in from outside - so increasing ventilation may just make things worse.

As I say, not as simple as we'd like.

Alan

Mark Siddall

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Passivhaus ventilation: It's not a lot of hot air
« Reply #5 on: June 04, 2012, 12:54:35 AM »
Here's a thought that may set the cat amongst the pigeons and some may even regard as paradoxical:

One thing that receives little attention is the fact that, in a building with a vastly reduced space heating demand (such as a Passivhaus building) the heating season is also deduced. There is therefore an increased potential for extending the use of natural ventilation whilst maintaining comfort (before having to batten down the hatches in order to maintain thermal comfort during the winter.) On this basis the occupant can therefore actually have their windows open for a larger proportion of the year!! (This is an argument that architect Prof Helmut Krapmeier has, justifiably I believe, made in the past.)

Recent feedback from an early occupier of a Passsivhaus home in the UK suggests that he now has much more control over the natural ventilation than in the leaky old homes of the past - a virtue of good airtightness. Couple these two factors together and you start to have a powerful combination. On this basis there is actually greater potential for successful window use/natural ventilation in a Passivhaus.

....There again, in built up areas, for reasons of acoustic privacy, it may be preferable for windows to be closed more often anyhow; regardless of whether or not you are in a super insulated building. And in this case at least there is controlled ventilation occurring.

Mark
« Last Edit: June 06, 2012, 10:50:46 PM by Mark Siddall »

Mark Siddall

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Passivhaus ventilation: It's not a lot of hot air
« Reply #6 on: June 04, 2012, 01:00:53 AM »
Alan,
It is certainly not simple is it. Thanks for pointing out the ozone issue - that is what I was alluding to albeit poorly.

Yes, I personally agree that in airtight homes mechanical ventilation is both advantageous and necessary. In fact a number of studies have shown that mechanical ventilation provides a more consistent and higher volume of air changes per hour than naturally ventilated buildings of a similar type (even when they in themselves have not been commissioned properly and therefore fail to comply with whichever design guidance or national standards!)

Mark
« Last Edit: June 04, 2012, 09:19:00 AM by Mark Siddall »

auchmill

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #7 on: September 23, 2012, 04:09:36 PM »
Doesn't the MVHR system result in a gradual, or not so gradual, heat loss?  e.g. a house with 3 shower rooms, unheated, having a temperature of say 16 oC, a warm kitchen of 21 oC a utility room of 16 oC and a warm study area of 22 oC have extract ducts.  This air is then used to heat incoming air to whatever, say 17 oC, or maybe less in winter when the external air temperature in near zero, which is then pumped into living areas which have a higher temperature, say 22 oC.  If this is right, then it doesn't seem a good idea to pour cold air into warm air.  This may not be important when the sun is shining and there's lots of solar gain, but in the evening it will surely result in the warm rooms becoming quite cool rather quickly.  Or do you turn the system off?

Look forward to someone enlightening me on this issue.  Thanks.

Mark Siddall

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #8 on: September 25, 2012, 10:43:43 PM »
Auchmill
Do you accept the premis that fresh air needs to be provided for the purposes of indoor air quality? If so you will accept that about 0.4 air changes per hour is required. Which fresh air is preferable outside air at 0C or 17C? With MVHR there is some heat loss but this is very limited compared to the alternative of direct ventilation (an 85-90% reduction can be achieved.)

Mark

Dave Howorth

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #9 on: September 26, 2012, 08:51:37 PM »
Doesn't the MVHR system result in a gradual, or not so gradual, heat loss?

The short answer is yes. That's one reason why heaters are frequently installed in the duct.

Quote
e.g. a house with 3 shower rooms, unheated, having a temperature of say 16 oC, a warm kitchen of 21 oC a utility room of 16 oC and a warm study area of 22 oC have extract ducts.

In practice, the shower rooms are likely to be warmer than average and the study is likely to have an air inlet rather than an extract duct, but the details don't really matter.

Quote
This air is then used to heat incoming air to whatever, say 17 oC, or maybe less in winter when the external air temperature in near zero, which is then pumped into living areas which have a higher temperature, say 22 oC.  If this is right, then it doesn't seem a good idea to pour cold air into warm air.  This may not be important when the sun is shining and there's lots of solar gain, but in the evening it will surely result in the warm rooms becoming quite cool rather quickly.  Or do you turn the system off?

You don't turn the system off, because as Mark says, the alternative is worse. But you do have to supply heat to the rooms to make up the difference. And it's a good idea not to place an unheated air inlet where it can blow over a chair or sofa, for example. Further heating of the air supply gets round both those problems but there are alternatives. Heating shower rooms to be warmer than average is another popular strategy.

auchmill

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #10 on: September 28, 2012, 11:45:14 AM »
Thanks for the replies.  I agree the heat losses will have to be made up in a Passivhaus just as in a conventional one.  And, yes, I accept ventilation is required, but I suppose an ancillary question is how much, when and in which rooms.  Is there actual empirical data on what is required?  There was a time when BC required a gale to blow through the attic and umpteen air changes per hour so that the energy companies didn't go out of business.  Now 0.4 is deemed adequate.

Since no house will be hermetically sealed there is always going to be air ingress, and also when people come and go opening doors and other normal activities.  Is this taken account of in real-life studies?

Dave Howorth

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Re: Mark Siddall: Passivhaus ventilation: It's not a lot of hot air
« Reply #11 on: September 28, 2012, 09:38:09 PM »
Thanks for the replies.  I agree the heat losses will have to be made up in a Passivhaus just as in a conventional one.  And, yes, I accept ventilation is required, but I suppose an ancillary question is how much, when and in which rooms.  Is there actual empirical data on what is required?  There was a time when BC required a gale to blow through the attic and umpteen air changes per hour so that the energy companies didn't go out of business.  Now 0.4 is deemed adequate.

Yes, there is empirical data, although not as much as would be ideal for dwellings. There's quite a lot for schools, I believe. If you search using "indoor air quality" (with the quotes) or feed that term to Google Scholar, you can find good links. Building Regs and suchlike are prescriptive about how much and in what rooms and whether inwards or outwards bound.

Quote
Since no house will be hermetically sealed there is always going to be air ingress, and also when people come and go opening doors and other normal activities.  Is this taken account of in real-life studies?

I think by definition, real-life studies are going to take this into account since, as you say, it does happen in real life.

 

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