[Greenbuilding] Passive House Overheating

Matt Dirksen dirksengreen at gmail.com
Thu Aug 16 10:29:52 CDT 2012


Perhaps it depends on the beer? Imho, a single Dogfishead 60 Minute IPA
seems to create about 90 minutes of comfort down here in Maryland - at
least for the single user.

:)

(And thanks for the insight. I feel like humidity is the neglected step
child in the world of measuring issues within the home. Heat gets all the
attention, so it seems.)



On Thu, Aug 16, 2012 at 11:15 AM, John Straube <jfstraube at gmail.com> wrote:

>  Yes, you can distinguish sensible from latent (humidity) energy in the
> lab or carefully instrumented houses.
> No, it is not easy to measure in normal homes, but you can if you are
> careful and have numerous instruments.
>
> Systems that ventilate buildings with cool outdoor air are called
> "economizers" in commercial buildings.  They are used on many many modern
> buildings.  As they were being deployed it was noticed that you could not
> use temperature as a trigger for when to ventilate, because ventilation
> often brought in significant amounts of humidity which was adsorbed and
> stored in materials and furnishings.  When the AC turned on during warmer
> hours, it had to work much harder to remove this stored moisture, and
> comfort was compromised.  So they invented "enthalpy control" which only
> ventilates when the air outside has less energy in it, eg some combination
> of temperature and humidity.  Dont ventilate when it is 65F and raining, do
> ventilate when it is 70F and 40%RH.
>
> The folks at Florida Solar Energy Center and my colleague at BSC, Armin
> Rudd, have studied this effect in hot-humid climate housing and it is a
> really big deal.  Often the energy saved by window opening during summer is
> almost zero.
>
> As we get to super insulated homes, more and more of the AC energy
> required is to remove latent energy (control humidity).  This is a topic of
> active and intense research as normal AC systems dont do this: their ratio
> of sensible to latent heat is pretty much fixed.  We see lots of problem
> buildings with poor summer humidity control now that many new buildings
> have an enclosure is insulated and good window solar control is added.
> Many solve this with energy consuming dehumidifiers.
>
> In my own super insulated house, I have no over heating issues at all and
> I try to operate the windows very carefully, but humidity becomes a problem
> after 3 or 4 days of warm (over 80) humid  weather.  I am using a
> dehumidifier to limit RH peaks.  Next year I will be installing a variable
> capacity mini-split to do this more efficiently.
>
> And, I tried the getting a cold beer as a solution, but this was not quite
> good enough :)
>
>  Dr John Straube, P.Eng.
> www.BuildingScience.com
> On 12-08-16 10:57 AM, Alan Abrams wrote:
>
> this leads to a question...in a refrigerated system, can you effectively
> distinguish the energy required for reducing sensible heat from the energy
> to reduce latent heat?  The question arose on a project I am consulting on,
> in which the supposedly leading edge mechanical contractor designed an AC
> system that uses the dank, dark, and dismal 120 yr old basement as a return
> plenum.
>
>
>
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