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Possible Modifications based on Passive House Standard

by Chad Ludeman on April 15, 2008 · 7 comments

in Building Science,envelope,Green Programs,HVAC,Passive House

Since studying the Passive House standard of energy efficient design, we have been trying to determine what we can incorporate into our project without blowing the budget. Below are some of the ideas we have so far to improve the energy efficiency of the home after consulting the Passive House Standard.

Insulation

  1. Increase SIP wall panels to 6.5″ (R-25) thick from 4.5″ (R-17)
  2. Increase SIP ceiling panels to 10.25″ (R-43) thick from 8.25″ (R-32)
  3. Look into increasing insulation under the slab (currently ~R-14). If we keep our radiant heating system it may be beneficial to leave a hole in the insulation in the center of the slab in order to utilize the ground as a heat sink to maintain a more constant temperature in the slab. This needs further investigation.
  4. Investigate ways to further reduce thermal bridging with SIPs manufacturer
  5. Investigate whether we can afford bolstering the insulation of the walls on either side of the SIPs panels. A 1-2″ layer of foam board insulation on the exterior before the cladding is installed could boost our R-value by as much as 14 to bring us to R-39. A half inch of EPS foam board on the interior walls could replace drywall, adding another layer of insulation and allowing us to use an American Clay type of product to finish the walls that would also further improve the indoor air quality.
  6. Investigate a radiant barrier layer under the roofing material and above the SIPs.

Efficient Windows

  1. Investigate fiberglass windows with better U-values than the currently spec’ed Pella Proline series. See this window post for more info on options. Marvin Integrity is looking good right now as far as value but may still be a premium compared to the Pella’s.
  2. Replace the existing spec’ed sliding glass door with an energy star rated model.

Mechanical Ventilation with Heat Recovery

  1. Implement and HRV or ERV system as cost effectively as possible with minimal ducting.
  2. Investigate the possibility of using earth cooling tubes under the foundation that feed the HRV/ERV that will pre-heat or pre-cool the incoming air naturally prior to entering the home. The main issue here is the fear of condensation building up inside of the tubes under ground that could lead to mold formation.
  3. Investigate the possibility of incorporating a dehumidifying element into the HRV/ERV system that would allow us to eliminate a separate air conditioning system in the summer.

Efficient Heating System

  1. Radiant heating still seems to be the best way to go for our home as we will not be able to reach the full passive house standards in all other categories that could allow us to use the HRV/ERV system only with a post heating element. We also really like radiant heat and think it will be a great feature of the home.
  2. The heating source is still not nailed down as it depends on whether we will need air conditioning or not. If we do, then it may make sense to use a heat pump capable of cooling and heating the home and the water supply. If we do not need air conditioning then we will lean towards a gas, tankless unit with the option to add a solar thermal array.

As you can see, we don’t have all of the details nailed down yet. This will come in the next few weeks as we look at the budget in more detail and finalize the construction drawings. We may also look into hiring a consultant that is familiar with passive homes and efficient heating, cooling and ventilation systems for them.

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{ 7 comments… read them below or add one }

1 Charles April 15, 2008 at 5:08 pm

Polyurethane SIPs will get you significantly higher R values with only a little bit more money. 4.5″ panel is R26 – 6.5″ panel is R40. Check out Murus in Pennsylvania – http://www.murus.com

1-2″ of EPS will never, ever get you to R14. 1# density EPS (most common) is R3.6 per inch. 2# density is R4.2 per inch.

2 chad April 15, 2008 at 7:48 pm

Charles,

Thanks for correcting my error. I did not mean to specify EPS foam board. I am thinking more of the poly options that will allow R values near R-7.

Also, we did quote the Murus Poly SIPs but can not afford them on our budget.

3 Kevin D August 21, 2008 at 7:23 am

I built myself a superinsulated house with radiant floor heat. Since lighting and people essentially heat the house, the floors are rarely warm because the house needs very little heat. Therefore, I feel the extra cost of the boiler system wasn’t worth it.

Also with radiant floors, you may still need to install some sort of A/C, humidifier, and/or HEPA air filtration system. (Do I think you’ll need A/C? yep)

For a house this size and this open, I’d avoid ductwork (as you have) and consider a mini-PTAC (or two) for at least 4 reasons:

1. A/C essentially comes free.
2. Air to air heat pump cycle gives more btus/$ than natural gas or electric resistance. Natural gas prices
3. Ultra low first cost: $439 each.
4. Easy installation (similar to installing a window, in fact, the HVAC sub will never see your jobsite)

There’s a large selection out there, but I like the Amana:
http://tinyurl.com/6ov8e3

4 Kevin D August 21, 2008 at 7:37 am

Edit #3 above: “Natural gas prices will continue to rise quicker that electric prices”

Also, when photovoltaics become cheap enough for this house, they will be unable to assist in reducing your natural gas usage. (The simplest way to a zero energy home is with an all-electric home)

The best way to handle the back-up heat for DHW is probably just one resistance element in the top of the solar preheat tank.

5 Grant September 23, 2008 at 6:37 pm

For future 100K homes take a look at cement fiber board SIPs. While the SIP cost, itself, is higher they are immediately ready for coating on the interior and exterior. Many claim that the “as finished” costs actually end up lower with the CFB SIPs. In fact, an American Clay plaster can be directly applied to the CFB SIP interior with limited prep work. You cut out several steps and have the added benefit of higher thermal mass from the cement fiber board.

6 chad September 23, 2008 at 6:45 pm

Grant – Can you recommend a manufacturer? One within 250 – 500 miles of Philly?

7 Grant September 23, 2008 at 10:07 pm

I’m in Alabama and all the suppliers I’m looking at are in Florida.

It’s not a SIP, but the AllWall System uses Cement Fiber Board like an ICF form to pour concrete, and they will train you to make your own forms. The AllWall System seems Owner-Builder friendly.

I vaguely recall one of the Fiberboard SIP manufacturers also offering to allow local manufacturing.

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