Howdy. I have been reading some on the German initiated Passive House Standards. Most examples I have seen are in heating dominated climates. Are the principles the same for cooling dominated climates (specifically SW Texas, between Austin & San Antonio, 78655 ... I got "chastised" for not specifying location on another post ). Can you expect to achieve the energy use guidelines/limits in a hot climate?

Thanks in advance.

A few years ago I saw a Passivhaus study that was orientated at Mediterranean (actually Europe outside DE) climates. It did country by country (city by city) studies on how Passivhaus might be applied. From memory, it was called Passive On or something similar. I could not find it with a quick google search, however.......except for the UK results.

You may find it if you browse. From memory, some places like Seville needed active cooling to keep comfort levels. The study also did not address latent very well IIRC.

Bruce
(who watches his speed VERY carefully when driving through Martindale, TX)

Weren't the basic energy usage standards (for both heating and cooling) derived from some fundamental underlying concept involving only the air needed for exchange to heat/cool the house?

One thing that might be done is to use a heat pump water heater, but only during the cooling season. It would take excess indoor heat and concentrate it into the hot water system.

There are also simple cooling loops utilizing no compressors, just fluid circulated around a buried loop which can be installed before the foundation is backfilled. It can be used to precool incoming air.

Earth tubes might be useful, and of course, insulating, shading and sealing to reduce the heat load as much as possible.

Posted By Bruce Frey on 24 Oct 2011 12:10 AM
A few years ago I saw a Passivhaus study that was orientated at Mediterranean (actually Europe outside DE) climates. It did country by country (city by city) studies on how Passivhaus might be applied. From memory, it was called Passive On or something similar. I could not find it with a quick google search, however.......except for the UK results.

You may find it if you browse. From memory, some places like Seville needed active cooling to keep comfort levels. The study also did not address latent very well IIRC.

Bruce
(who watches his speed VERY carefully when driving through Martindale, TX)

I'll do a little more targeted Googling ... thanks for the info. And yes, in Martindale, America 55 mph does not mean 56 mph . Coincidently, bruce in Martindale

Posted By ICFHybrid on 24 Oct 2011 09:35 AM
Weren't the basic energy usage standards (for both heating and cooling) derived from some fundamental underlying concept involving only the air needed for exchange to heat/cool the house?

One thing that might be done is to use a heat pump water heater, but only during the cooling season. It would take excess indoor heat and concentrate it into the hot water system.

There are also simple cooling loops utilizing no compressors, just fluid circulated around a buried loop which can be installed before the foundation is backfilled. It can be used to precool incoming air.

Earth tubes might be useful, and of course, insulating, shading and sealing to reduce the heat load as much as possible.

Thanks for the thoughts. My experience with earth tubes, in an friends house, was not positive. It always smelled musty. They might work better in a dry climate ... I suspect/guess.

I think we need to keep in mind that this location (zip 78655) is almost exactly the same latitude as Cairo, Egypt, so dealing with the heat is a big issue. Designing a low-energy consumption house is a trick in that climate. Passive House is one approach, but I would also consider a more active approach. The solar insolation at that location is 5.21 kWh/m^2/year on a flat plate collector tilted at the latitude and facing south. Best orientation for PV panels at that zip code is 185 deg azimuth, and a tilt of 25 deg. (slightly flatter than the latitude), but collection is surprisingly not strongly dependent on orientation. PVWatts gives an estimated yearly energy collection of 1334 kWh per kW DC rated installed power for that best case fixed panel orientation.

Of course, active solar requires access to the sun, and a good house design in that area should try to include shade trees (and pecans certainly grow well along the San Marcos river). Perhaps consider PV panels on a detached garage, or pedestal mounted.

The economics for active solar depend strongly on what subsidies are available from the local utility (maybe utilities in that area), but the federal government offers a 30% subsidy through the income tax system. In some areas local utilities offer larger subsidies than the federal govt., but those tend to change over time.

In my case, which is an extremely different climate, I found the payback for going to super high insulation levels was much longer than for solar PV that included the subsidy effect (http://www.residentialenergylaboratory.com/costs.html). The economics for going completely to Passive House standards did not look attractive in my situation, while active solar looked better. The 2012 IECC code should give you a guideline for insulation levels that might be a "reasonable" starting point. You might trade off active solar versus Passive House insulation levels and other options by computing payback times for your situation.

San Antonio<==>Austin is on the cool edge of US zone 2 (if "cool" is the right word, although those are two of the cooled cities in TX by another definition), and quite comparable in climate to Lafayette, LA, where a PassiveHouse house was certified last year:

http://www.jetsongreen.com/2010/07/small-passive-house-in-lafayette.html

http://www.passivehouse.us/project_detail.php?id=1038

There's merit to the notion that the last 20-30% reduction in energy use to take it all the way to the PassiveHouse standard may actually be more expensive than supporting that reduced load with PV-powered ductless air-source heat pumps though. It takes a sharp pencil and a real design to figure out where the exact crossover is.
Ground mounted PV works, if you're maxing out the shading at the house.

A big issue in 78655 (and in Lafayette LA) not perfectly addressed by the Passivehouse standard is the high latent-cooling loads of the Gulf coast states. (Austin's dew point averages are slightly higher than Cairo Egypt's). Mechanical dehumidification is necessary in the gulf-coast states to keep the indoor air healthy, so allowing somewhat higher than PassiveHouse sensible-loads and using a mini-split to deal with cooling/heating/dehumidification with sufficient PV to make up for the power draw isn't necessarily a terrible thing. You can't get ANY dehumidification to speak of out of earth tubes at the deep subsoil temps in that area, and sucking in ~73F-dew-point midsummer air into an 80F room results in a stultifying mold-inducing 80% relative humidity.

I couldn't find averages for Lafayette, La., but Baton Rouge is just down the road. Looks like the morning humidity for Austin in October is closer to Cairo than Baton Rouge, but the afternoon humidity is closer to Baton Rouge. I think of Cairo as being in the (ultra-dry) Sahara Desert, but it is also not far from the Mediterranian Sea, so looks like it does have some humidity to deal with.

October averages
Austin Cairo Baton Rouge
Avg. Morning Relative Humidity 82% 81% 89%
Avg. Afternoon Relative Humidity 54% 40% 50%

from http://www.myforecast.com/bin/climate.m?city=60268&metric=false (and similar)

Weatherspark is your friend:

http://weatherspark.com/#!dashboard;a=Egypt/Cairo

http://weatherspark.com/#!dashboard;a=USA/LA/Lafayette

http://weatherspark.com/#!dashboard;a=USA/TX/Austin

The relative humidity numbers are useless without the outdoor temperature, since it's relative to that temperature.  The dew-point is the measure of the absolute-humidity, not relative humidity, and the INTERIOR temperature and the outdoor dew point is how to calculate what happens when you ventilate the cooler interior with outdoor air.  (Enable the Weatherspark dew point graphs, and look at the monthy/seasonal averages. Use the cursor to eyeball the historical or even daily means.)

Cairo, Austin & Lafayette are hot, and can still be pretty damned dry in terms of outdoor relative humidity, even at fairly high dew points.

Vancouver BC &  Amsterdam NL are relatively cool and quite rainy by comparision, but have much drier air (lower dew points) on average- ventilation with outdoor air in those areas rarely raises the indoor relative humidity.

Rather than scanning a psychrometic graph until your cross-eyed, use an online calculator to determine what the RH will be for the air of a reasonable conditioned space temp would be at any particular dew point temp:

http://www.sugartech.co.za/psychro/index.php

70F dew-point air is a mold-inducing 73% RH at 80F indoor temps.

60F dew-point air is a reasonable 51% RH at 80F indoor temps, but a somewhat-humid 60% RH @ 75F.

Outdoor air with 55F dew points or lower is what it takes to dehumidify a home with reasonably low ventilation rates. In Austin that would only be the case on average from about November-first to April Fools Day, but in Seattle or Carbondale CO it's 365 days per year, save for the occasional outlier days.

Sorry for the delayed response. Thanks for the WeatherSpark link. I thought that it was interesting to compare the dew points, per your suggestion, dana1. I pasted in below a comparison of dew points for Austin, TX, Lafayette LA, and Cairo, Egypt. The tables always get messed up in format when posted, but these results show Austin to be slightly more humid than Cairo in the summer, and slightly less humid than Lafayette. Interestingly to me, looking at the winter lows for dew points, Austin is dryer than either Lafayette (no surprise) or Cairo (surprise to me). The dew points during the summer for all three locations suggest that a significant amount of water vapor needs to be removed for indoor comfort. Compared to these three locations, Athens, Greece, a reference city for southern Europe, is much dryer with summer high values for dew point of 63 F for max, and 51 F for min.

All dew points in degrees F
Summer Winter
Max High DP Max Low DP Min High DP Min Low DP
Austin, TX, USA 74 66 46 29
Lafayette, LA, USA 77 71 50 35
Cairo Egypt 73 63 48 37

"Interestingly to me, looking at the winter lows for dew points, Austin is dryer than either Lafayette (no surprise) or Cairo (surprise to me). "

Cairo is never downwind from a cold (==dry) continental air mass. When the wind is out of the north in Cairo it's moderated in temp & humidity by the Mediterranean, whereas a NWW wind in Austin can be coming from Yukon or Alaska without benefit of a large water mass. To get a similarly cool dry air mass in Cairo would have to come out of the NE all the way from the from the central Asian steppes, but that would take a highly unusual, (or nearly impossible) weather system to sustain. When the wind comes from the west (sahara) or south or southwest (sahal) it's always coming from a relatively warm area, where the temps aren't low enough to wring much moisture out via precipitation.

The prevailing winds in Athens are downwind of the Alps/Balkans, where the adiabatic cooling at altitude precipitates the moisture out. It's also further north than you might think (39 degrees north, about the same as Baltimore or Colorado Springs), despite a very warm-temperate climate, comparable to that of San Jose (which is about 37 degrees north.)

Weatherspark IS a very nice resource, eh? It makes estimating design temps for just about any location possible in a heartbeat.

That's funny...I came here because of that Weatherspark link, but I learned something about passive housing standards. I'd like to add that up here in Maine, we have some interesting data: Average temps in July are 80'. It's been a lot warmer than that the last two summers, meaning less overall power bills. Up here, we have a lot of windows to open!

Another point that the media isn't talking about much is the amount of work that the weather is providing for out of work folks. Not only is the new 'in' thing up here green building and construction, but the weather's allowing for year-round work, unheard of up here. "New building standards helping keep Portland contractors in business", WMTW, Maine. Who knows, this whole 'hippie' movement could actually become mainstream!

This is an article done on my personal home in Austin. We are building Passive Homes all over Austin now, and the principles are the same just flipped upside down. Passive house in the south is about trying to create homes that cool themselves as much as possible, instead of heat themselves.

http://www.greenbuildingadvisor.com/blogs/dept/green-building-news/aiming-passive-house-texas

Posted By nicholasblaise on 18 Jul 2013 07:36 AM
This is an article done on my personal home in Austin. We are building Passive Homes all over Austin now, and the principles are the same just flipped upside down. Passive house in the south is about trying to create homes that cool themselves as much as possible, instead of heat themselves.

http://www.greenbuildingadvisor.com/blogs/dept/green-building-news/aiming-passive-house-texas

As the original poster, living 35 miles south of Austin, this is very informative. Thanks! I will be following your blog or whatever that is :)

Austin's building code requirements for "Net-Zero-Energy ready" on new housing has created a whole new generation of better-builders in the 'hood, eh?

Getting to PassiveHouse is a bit tougher standard to meet than Net Zero but still far cheaper in Austin than in the much colder climates of the upper midwest or northeast. At the crashing cost of photovolaic solar and the innovative accounting/compensation "Value of Solar Tariff" approach in Austin (rather than rough-justice "run the meter backward" net metering ), getting to Net Zero in Austin-proper is getting cheaper and more cost-effective every day. Whether other utilities can adopt a similar compensation profile within their business model remains to be seen (I've read San Antonio is giving it a shot, with mixed success), but Texas has some of the most innovative and evolving power utility structures in the US, and may end up leading the way for high penetration of distributed power generation, showing the rest of the country how it's done! (Your utility WILL vary!)

See:

http://rabagoenergy.com/files/value-of-solar-rate.pdf

http://www.greentechmedia.com/articles/read/can-a-value-of-solar-tariff-replace-net-energy-metering

The rationale behind Minnesota's recently expanded PV subsidy was based largely on Austin Energy's value-of-solar studies used for formulating their compensation for rooftop solar. The value of PV to the grid operator and rate payers is usually much higher than a net-metered residential retail rate, due to the lowering of peak grid load & current on the main transmission infrastructure. The more distributed power generation you have out there (particularly PEAK power) the less you need to invest in grid capacity upgrades. At some penetration of PV the local-grid volatility gets more difficult to manage, but very few places are in that situation yet, and the technology to deal with it already exists, and is falling in price.

The financial crossover between going for PassiveHouse vs. Net Zero is a fuzzy one, but for sure getting both the peak & average load of a house down has value, to both the owner/occupants and the grid operators.

There is no better standard insulation than FOAM. www.buysipsonline.com