Earth angel Passivhaus goes mainstream residential - AIRAH

Page created by Manuel Vargas
 
CONTINUE READING
Earth angel Passivhaus goes mainstream residential - AIRAH
FEBRUARY–MARCH 2021 · VOLUME 20.1
                                                    RRP $14.95
                                               PRINT POST APPROVAL
                                             NUMBER PP352532/00001

Earth angel
Passivhaus goes
mainstream residential.
Earth angel Passivhaus goes mainstream residential - AIRAH
F E AT U R E

     How to push
     the envelope
     Over the past decades, the US has transformed its
     approach to airtightness and ventilation. Building physics
     luminary Max Sherman talks to Sean Maxwell, AM.AIRAH,
     about the journey, and the lessons Australia could learn.

     Max Sherman is an ASHRAE fellow and                  of space conditioning energy is due          buildings if they aren’t designed properly.
     distinguished retired senior scientist               to air leakage in a traditionally leaky      So yes, dedicated and properly designed
     at the Lawrence Berkeley National                    home. Most ventilation in a leaky home       ventilation is essential for healthy indoor
     Laboratory in the US. Over many years his            actually comes from air leakage, which is    air quality and it has to be done right.
     research has informed our fundamental                why those homes did not have designed
     understanding of building energy                     ventilation systems. With such air leakage   SM: When you “ventilate right,” is
     efficiency and occupant health. Sherman              also comes uncomfortable draughts,           there a basic formula to do that?
     was keynote speaker at the AIRAH                     moisture intrusion, and degradation of       MS: One of the points in my talk was
     Building Physics Virtual Forum last year,            insulation. It’s a real risk to a building   that there are many steps along the way
     and Sean Maxwell, AM.AIRAH, took                     and its occupants.                           to ventilating right. What is acceptable
     the opportunity to ask Sherman about                                                              as a code minimum might be different
     a range of issues relating to ventilation            SM: So “building tight” must not
                                                                                                       than what is considered best practice.
     and building envelope physics.                       be that hard if most US state codes
                                                                                                       What is best for a project will depend
                                                          require some airtightness and
     Sean Maxwell: Max, your talk                                                                      on how much influence you have on
                                                          even blower door testing. Right?
                                                                                                       the design and what kind of budget is
     at the AIRAH Building Physics
                                                          MS: After you know how to do it, it’s        available. But there are almost always
     Forum was titled “Build Tight
                                                          not hard, but getting that knowledge         steps you can take along the way.
     and Ventilate Right. It’ll Be
                                                          is not easy. The industry has a
     Okay.” It sounds like you trying                                                                  SM: For our codes and standards,
                                                          sometimes‑painful learning curve to
     to reassure your Aussie friends?                                                                  should acceptable solutions to
                                                          change practices to where it is easy.
     Max Sherman: Australia can learn from                                                             requirements for ventilation
     the American experience by informing                 SM: But can there be a                       vary by climate zone?
     regulation with building science. The US             tightness problem too?
                                                                                                       MS: Minimum requirements for
     certainly hasn’t done everything right,              MS: Absolutely. Too tight can be             ventilation (as in m3/hr) do not
     but Australia can learn from what we did             unhealthy and also cause building            vary by climate. You always need
     right and where we fell short.                       management problems that one                 proper ventilation. But the optimal
                                                          must be aware of. You can’t assume,          solutions may change by climate,
     SM: Why has so much of your
                                                          for example, that people are going to        for example, because of infiltration
     research been devoted to
                                                          just be there to open windows when           impacts or costs to condition outdoor
     understanding and addressing air
                                                          it makes sense to; some contaminants         air. Furthermore, one needs to
     leakage? Why is it such a problem?
                                                          aren’t properly diluted when it’s            look at moisture as a contaminant,
     MS: Well, energy is what gets one’s                  too tight. Ventilation systems can have      which means that a moisture design
     attention first, because a third to a half           trouble working correctly in ultra-tight     may be necessary in some climates.

22   F EB R UA RY– M A RCH 2021   •   ECO L I B R I U M
Earth angel Passivhaus goes mainstream residential - AIRAH
Max Sherman

                                               Sean Maxwell, AM.AIRAH

SM: California requires                      SM: Can something as simple
ASHRAE 62.2. What are                        as a continuously running
some of the basic features                   exhaust actually achieve
of that standard?                            adequate indoor air quality?
MS: One requirement is that local            MS: Yes, and it’s the most
exhaust such as kitchens and baths           common method we use.
must go directly outside. Intermittent       In my talk I spoke about a recent
ventilation is good for singular events      study of new homes in California
like cooking or a shower, but it’s not all   and compared it to a similar
you need. ASHRAE 62.2 also requires          study from 10 years prior.
continuous whole-dwelling ventilation,
                                             One important thing to note
which is useful for extracting pollutants
that build or release gradually over         was that when we started the
time, such as VOCs and moisture and          study, most houses in the
emissions from occupants and their           group had their ventilation
activities.                                  systems disabled because of
                                             noise, or not knowing what the
SM: Are there inexpensive ways               random switch on the wall was
to provide adequate ventilation?             controlling. We had to make sure
                                             all the houses had their systems
MS: Yes, the cheapest solution is the        running, then we measured
“double duty” bath fan. If you don’t         contaminants.
already require exhaust fans in the
wet rooms, you should, because these         Most of the houses were of
are the rooms that are responsible for       moderate air tightness of
the most internal moisture generation        3 to 6 [m3hr-1m-2]. But with
and often other contaminants as well.        their simple systems running,
California requires ASHRAE Standard          basic markers of IAQ like
62.2. A continuously running Energy          formaldehyde and particulates
Star bath fan, which has an added            were improved compared to
cost of maybe AU$100 over standard           the homes built 10 years prior
construction, can meet the minimum.          with no continuous ventilation.
Again, a basic ventilation system is         It didn’t take much to make
better than no system at all.                a positive change.
Earth angel Passivhaus goes mainstream residential - AIRAH
FE ATURE

     SM: Regarding building tight,                        If you had exactly the right amount           step of the way. The reason for this is that
     would you have any idea where                        of infiltration to serve as ventilation,      no one, traditionally, does a moisture
     we could set benchmarks to start                     you’d have the exact same amount of           design. Things worked historically and
     requiring ventilation? I’ve heard                    moist outdoor air entering through            when only minor tweaks were made,
     the number 7 ACH50 as a limit                        infiltration as you would indoor air          they kept on working. If big changes
     below which you need mechanical                      leaving through exfiltration. The exit        are contemplated, one must design
     ventilation. Is that a good limit?                   point with exhaust ventilation is             for moisture as well.
                                                          obviously the fan itself. But if the
     MS: The 7 ACH50 tightness limit was                                                                We did have huge problems in our
                                                          infiltration coming in is not a problem in
     a rule of thumb from a bygone age.                                                                 hot‑humid climates, which are not gone
                                                          a leaky house with no ventilation, it won’t
     We now have the tools to do it better                                                              yet. One of the biggest contributors we
                                                          be a problem with exhaust ventilation.
     and it’s not that hard. If you separate                                                            had was vinyl wallpaper. It was popular
     the tightness requirement from the                   You could have a problem if you had           for many years but is impermeable and
     ventilation requirement, the job                     a poorly constructed building and             so moisture condensed on the back side
     becomes much easier. The tightness                   system in the first place, of course.         and rotted the plasterboard. Of course,
     requirement may start out lenient but                                                              any vapour retarder on the inside of
     then tighten as the industry learns to               SM: So the indoor air that was                the plasterboard can be problematic if
     do it easily. The limit itself may depend            leaving through the building                  moist air can get behind it.
     on the energy benefit of tightening and              envelope is now leaving through
     thus on climate and energy costs.                    the exhaust fan. But the outdoor              SM: How do you handle
                                                          air infiltrating through the                  that mix of problems?
     Underlying all these points is that                  envelope was doing that already?
     there needs to be a way of determining                                                             MS: The right thing to do in an air
     minimum acceptable ventilation.                      MS: Right, the moisture impact of             conditioned home in such a climate
     Having that allows the determination                 adding continuous mechanical exhaust          is to have an air barrier and a vapour
     of optimal strategies for airtightness,              is quite small. In fact, tightening and       barrier on the outside of the insulation.
     energy, moisture, etc. I am obviously                adding a fan will generally be an             Even if there is no insulation, the
     partial to ASHRAE, but both the                      improvement on the moisture front,            barrier needs to be on the outside so
     Europeans and east Asians have some                  but one can always think up pathological      the condensed water can drain in a
     of their own ventilation standards.                  cases. The time to look carefully is          controllable manner. This is especially
     I don’t think those apply as well to                 when one is adding ventilation to a           true when the outdoor dew point spends
     Australia given that those two were                  severely under-ventilated building.           a lot of the time above maybe 20°C.
     optimised for their climates and                     Now sometimes in the field we                 SM: This goes back to the
     construction types (e.g., the European               occasionally do see a problem, but when       question about make-up air for
     one requires room-by-room ventilation).
                                                          we look into those, the exhaust fan was a     simple exhaust-only ventilation
     There are lots of changes to consider                minor contributor. The more important         systems, and whether it’s a
     at once, but treating the building as a              contributor is usually the improper           problem in hot humid climates.
     system is really the only way to make sure           use of vapour-impermeable layers.             If you concentrate on sealing the
     you don’t have unintended consequences               People do sometimes blame the last straw,     exterior weather‑resistive barrier
     that could doom any advancement.                     which is often the ventilation.               in the house, can you reduce the
                                                                                                        risk of leaks carrying moisture
     SM: The cheap and simple double-                     SM: What design and construction              through insulated wall assemblies?
     duty bath fan solution sounds ideal                  guidance is there to help
     for homes in colder or mild climates.                with these problems?                          MS: A tight envelope helps reduce
                                                                                                        the moisture problems, but only if
     MS: It’s the most common system that                 MS: A lot of problems that were at first      the tightness is on the outside of
     meets ASHRAE 62.2 for those climates,                attributed to ventilation were really         any moisture-sensitive materials:
     and our research shows that it’s effective           problems in designing the building            plasterboard, untreated wood, etc.
     enough to be a reasonable code or                    envelope. That does not happen much           If you caulk and seal all the plasterboard
     standard requirement.                                anymore, but it was a big deal for a while.   to make it really tight, but still let
                                                          Building Science Corporation has a lot        outdoor air get to its (cold) backside,
     SM: Is there any danger to using                     of very good publications on how do the       the plasterboard will rot from the
     that solution in a hot humid                         building envelope correctly. If you have      wall cavity inward – maybe the studs
     climate like Louisiana (negative                     not had a chance to look at their stuff you   too. Moisture retarders need to be
     pressure, pulling humid air through                  might want to. Spring for one of their        on the warm side of the wall and if
     cooled building assemblies)?                         builder guides (e.g., hot‑humid climates)     the air‑tightness layer is the same,
     MS: I have to laugh. Not because it                  and it might be worth your while.             then it must be as well.
     isn’t a good question, but because a lot             SM: OK, so the industry has                   SM: Can an air conditioning
     of us worried about this exact problem
                                                          been seeking solutions to these               system help with controlling
     for a long time. In fact, for a few years
                                                          problems for some time already?               the humidity indoors?
     there was a prohibition in using that
     system in those climates. But skipping               MS: Moisture problems in humid                MS: Yes, that can help because it
     ahead to the answer – no it’s not a real             climates have dogged the transition to        supplies “free” moisture removal.
     problem. Here’s why …                                high-performance buildings at every           One important thing to note, however,

24   F EB R UA RY– M A RCH 2021   •   ECO L I B R I U M
Earth angel Passivhaus goes mainstream residential - AIRAH
FE ATURE

is that as air conditioner size gets smaller   our political example. We do, however,
with improved buildings, the amount            have climates and building types quite
of latent extraction we used to count          similar to Australia and have been
on to keep the inside dry goes away.           working the technology side a bit longer.
This both extends the moisture problems        My advice would be to steal our best
to less severe climates and also increases     ideas and then use them better.
the need to do a dedicated moisture
design … which could necessitate               SM: A few of your slides in your
additional or different equipment.             talk referred to good intentions
                                               but missed opportunities.
SM: Can modern AC systems                      “Beware the Bleeding Edge”
with a “dry mode” reliably help                it said. Any advice to take away?
remove humidity, or is it not wise
to count on those as a strategy?               MS: Going too far too fast often leads
                                               to unintended consequences. It is really
MS: We have a variety of                       good to have a segment of the industry
air conditioning equipment that                that wants to do this as long as everyone
has enhanced dehumidification                  understands there are going to be
capabilities. Depending on the                 setbacks. The more setbacks there are,
technology it can be complete or               the faster we all learn how to progress –
partial. Such equipment can be                 but of course that means someone may
helpful in reducing indoor humidity,           get the bad end of the stick.
but one must determine if the latent
capacity is sufficient and one must            Another issue is optimisation versus
have a suitable control strategy.              resilience. Many over-optimised
                                               systems do not survive contact with
Energy-recovery ventilators can reduce         real life. For example, if a key filter that
the latent capacity needed from such           is supposed to be changed annually
equipment and save operating costs,            gets clogged with insects every month
but they are not a solution by themselves.     during the summer, the system won’t
                                               work half the year. This is a real story.
SM: In the US you have the
Home Ventilating Institute (HVI)               For the majority of buildings,
to give respectable performance                it is probably a good idea to favour
ratings for ventilation systems.               simple and robust compared to
We don’t have that here.                       complicated and brittle.
Any advice for us? Is it worth                 To say it another way, Australia may
setting up some performance                    make progress faster by taking baby
rating capacity here for ourselves,            steps quickly than by taking big leaps
or should Aussie products be                   it might regret. ❚
sent to America for testing?
MS: Certified rating of equipment is a
good way to make sure all manufacturers                   Would you like
can have a level playing field to compete                 to know more?
in. HVI principally serves North
American customers, but manufacturers               Access to Max Sherman’s keynote
from around the world have their                 presentation and other recordings from
products rated by them. The testing does          the Building Physics Virtual Forum are
not have to be done in the US.                  available to registered delegates or can be
                                                      purchased via bit.ly/3mpVkS9.
I would encourage you to discuss
setting up what Australia needs with              Sean Maxwell, AM.AIRAH, is technical
HVI, before striking out on your own.               manager for Pro Clima Australia and
You would get a lot more product                      one of the members of AIRAH’s
availability if the manufacturers                Building Physics Special Technical Group.
could use their usual test methods.              If you would like to find out more about
                                                      the STG and get involved, go to
SM: From an American                                 www.airah.org.au/buildingphysics
perspective, what advice would
                                                   For guidance on designing building
you give to Australia’s evolving
                                                  envelopes, Sherman recommends the
energy-efficiency landscape?
                                                      Building Science Corporation.
MS: The US as a whole is not very good                 Go to buildingscience.com/
at restraining its carbon footprint,                book‑categories/builders-guides
so I would not recommend following
You can also read