Comments on: The Evolution of Passive House in North America

By: David Eakin

David Eakin — Thu, 11 Aug 2016 21:47:53 +0000

Kent – agree with all that
Kent – agree with all that you have said (I have extended family in Philly and live about 2 hrs West). My point was that there is no design criteria for those things deemed “comfort” (e.g., indoor air temps, indoor RH) but implementing solutions (as you described) will drive up energy use and reduce the apparent energy savings. So you could have a Passive House and still be uncomfortable unless you implement other countermeasures, that may drive energy use past the Passive House requirements. PS – in our area of the MidAtlantic I’m seeing more and more need for dehumidification PRIOR to AC – not just during shoulder months. Been following Matt Risinger’s Ultra-Aire/Therma-Stor blog info.

By: Kent Lessly, RA, CPHD

Kent Lessly, RA, CPHD — Thu, 04 Aug 2016 18:32:59 +0000

Hi David,
Hi David,

The design metrics for Passive House that you most frequently hear about are quantification of the energy performance and air-tightness necessary for achieving Passive House Certification.

However, the central design criteria for a Passive House is comfort. Everything revolves around that. So the beautiful thing about the Passive House design standard is that you won’t be making draconian sacrifices in comfort to achieve the predicted energy savings. You’ll also find that excellent indoor air quality is another important criteria that the standard adheres to. These are considered”soft criteria” as they are not enumerated specifically but taken into account in the modeling software and are achieved when a compliant design is achieved.

Ultimately, the temperature settings are up to the occupant and therefore, to a degree, so is the energy savings. But if you want to achieve the precise level of energy performance predicted by the Passive House Planning Package (PHPP – the energy modeling software for International Passive House design) those are the settings. 77 degrees F may seem a bit high in the context of standard construction here in the US, but with lower indoor humidity levels, it is very comfortable. This is especially true when the radiant temperature from the surrounding surfaces are within 7.2 degrees from each other as they are in a passive house.

Because of the airtight construction, indoor relative humidity is controlled in the winter by the fresh air ventilation system. The design standard seeks to achieve less than 1000 ppm of CO2 and 30% to 40% min. RH in the winter.

Summer humidity levels are often controlled with air conditioning. In areas with mixed climates and higher levels of humidity like here in Philadelphia, a dehumidifier is often required in the shoulder seasons and milder summer rainy days to maintain a comfortable level of RH. This is because AC is needed only a few months out of the year.

The optimal range of RH is 35% to 55%. As with temperature, it is the occupant that ultimately controls the RH.

By: David Eakin

David Eakin — Tue, 05 Jul 2016 00:23:52 +0000

John – Krigger/Dorsi
John – Krigger/Dorsi recommend less than 60% to preclude mold issues; several studies on what a minimum RH should be to preclude dry sinuses; Robert Bean’s site says that humans can tolerate a fairly wide range of RH depending on temperature. I just picked 45%-60% interior RH as a workable range. FWIW – one of the assumptions in the Passive House design parameters that is not easy to dig out is what the interior temps are supposed to be (lots of talk about energy use, emissions, and cost but not interior temps or assumed comfort). Found some data in a slide presentation talking to the North American climate diversity and needed changes to the PH standard: 68 degrees for Winter and 77 degrees for Summer – but I’m not sure if this is truly a set design factor in the software or just a working recommendation. Would like to hear more from folks with experience in PH design as to planned interior temp and RH ranges.

By: John Nicholas

John Nicholas — Mon, 04 Jul 2016 16:48:06 +0000

Do you have a citation for
Do you have a citation for the Healthy connection with around 50%?

By: Donald Endsley

Donald Endsley — Mon, 04 Jul 2016 10:51:40 +0000

John, ASHRAE 55 is mostly
John, ASHRAE 55 is mostly concerned with human comfort, not necessarily human health. A RH of 30-50 gives a high range of temperatures where humans are comfortable doing a high range of activities. Human health, especially due to respiratory issues, seems to be best at around 50% RH.

By: John Nicholas

John Nicholas — Sat, 02 Jul 2016 07:48:25 +0000

David, Why 45-60 on RH?
David, Why 45-60 on RH? ASHRAE 55 calls for 30 – 50. My home has been fairly constant the last 4 weeks at 40% +/- 2 with 75% RH Ambient. CZ 4 Mixed Humid and an ERV. Most folks are dialed in on the above 50% being a problem

I think part of the 40 year history is that the Passive Concept has be a niche market. Either highly motivated or DIY types. The activity in the multi-family area is a big boost. It will get exposure and those living in those apartments will not want much else when they buy a home.

By: David Eakin

David Eakin — Fri, 01 Jul 2016 20:30:15 +0000

The original standard could
The original standard could still work, with 2 changes. Add “maintaining an inside relative humidity between 45-60 percent” to the air quality section, and convert the Btu/square foot per year measurement to kwh/square foot per year (to address air conditioning/dehumidification load) in addition to heating load.
Now if only this standard would catch on with architects, builders and code enforcement officials – as well as the US Department of Energy. Of course it’s only been about 40 years and these things take time… What gets me is all the “opportunity costs” – all the millions of homes that have been built in 40 years that will still be around for 60 or more years – all with poor performance unless (expensively) retrofitted. So much easier (and less costly) to do it well initially.