Thermal Mass Anyone?

| 3/9/2011 3:41:38 PM

Tags: energy, energy efficiency, homes,

Thermal Battery Pour 

Any net zero-energy home (one that actually produces at least as much energy annually as it consumes) needs two things. The first is the sun, providing passive solar energy.

Needing the sun for energy is why some Passive House retrofit homes leave me baffled. In his lecture at The Cooper Union in NYC, Wolfgang Feist said that southern exposure is helpful in achieving Passive House energy efficiency requirements, but not essential. Not all homes you wish to renovate have a decent southern exposure.

But here’s the problem with that position. In its simplest form, we are discussing the heat you create for your home and how well the house is able to retain that heat. In a home without southern exposure (to provide external energy from the sun for passive solar heat and/or solar electric), you rely solely on the home’s insulation and on energy created by internal heat sources (like a heating unit or your family).

So let’s say you have two homes that are super insulated to the same degree. One home has negligible external heat or electric gain and the other has south-facing windows that allow passive solar heat gain and electric solar panels, which together provide anywhere from 50% to 100% of the home’s energy needs. Obviously, the passive solar home has a much better chance of being net zero energy or more, because it’s using external energy.

The second necessity is retaining maximum heat. That is simple enough with a house that has no southern exposure: super insulate it. In a home with southern exposure there is an additional requirement. How do you store the excess energy coming into your home for when you need it? With electric solar panels, if you have net metering, it is easy. The excess energy is fed to the electric grid. The electricity you use and the excess electricity you produce is tallied up at the end of the year; you pay or receive a settlement amount.

donald eyermann
3/29/2013 11:01:12 PM

The biggest issue with conventional homes and even net zero homes is that they only work on the interior heating/cooling of the air and are completely passive with regard to the structure. We have completely rethought the way we build homes. We are a manufacturing entity producing alternative technology AICF (Asymmetrical externally Insulated interior Concrete thermal mass Form) in both Foundation Panels and Wall Panels, which by US Oak Ridge National Lab research quantified the eficiency at 2.46 compared to 1.00 = a conventional wood stud home used as the basis of extensive research. That is an up to 246% more energy efficient basic structure; then we add near surface geothermal direct cooling with solar radiant heat absorption & storage system; built within the structure. This is to initiate Pro-Active thermal compensation for heat loss/gain by the sturcture. That is why all our insulation is on the outside, not within the wall envelope. Thus the interior air is less impinged upon by the exterior environment. Then we add a counterflow thermal exchange duct-in-duct Fresh Air system featuring "strategic uptake" to achieve conditioning and cleaner interior air, fo a much healthier environment inside the home. Then we take that one step further and full integrate solar, wind and even the use of electric vehicles (both primary transport & recreating/work vehicles) into the household energy system (V2H) to achieve an overarching "Natural Energy Management Strategy"... when you combine this together you can achieve the next step above a net zero house... you can achieve a net Positive Energy Lifestyle & that's our URL

john kosmer
3/19/2011 1:21:55 PM

Gardner_3 For my original Kosmer Solar House Project we used two layers of 2 inch thick polyisocyanurate foam core inuslation (closed cell insulation) with foil on each side. The two layers were staggered and taped at the joints. The two layers were installed over a high tech pool liner to prevent water and humidity migration or wicking. The liner was installed over tyvek that was as a sacrificial material to walk on during installation. The tyvek was laid over a one foot depth of round gravel with a three foot depth of round gravel (about one foot in width) used around the perimeter (directly under the position of the walls.) That is roughly R–26 in insulation value. On the next project house, I will use three layers of 2 inch thick insulation under the slab and along the perimeter vertical edge of the slab. I especially have concerns of heat dissipating along the insulated perimeter vertical edge because the slab because it is closer to a colder ground that the ground under the central portion of the slab. The extra cost for those additional materials and labor (including digging 2 inches deeper) is marginal when added to the cost of the entire house. That is roughly R-39 in insulation value.

john kosmer
3/19/2011 12:50:35 PM

Zane. Yes. But earth bag or straw-bale only addresses half the problem. It addresses the super insulated aspect of the house. Hopefully, you can orient the long side of the home south and have good southern exposure. The correct ratio of windows to south the wall exposure (25-35% glazing) will allow you to address the second part of the problem, bringing it an external source of energy (light turned into heat) for the slab to absorb. If you have poor southern exposure and are only going to build a super insulated home, then 4-6” of concrete my be more appropriate, especially if you intend to embed radiant floor heat in it. Either way, a concrete slab is the way to go in the twenty first century. Basements are an archaic idea that have out lived their usefulness, but that’s another story.

ed burham
3/19/2011 8:08:16 AM

I have lived on concrete slabs most of my life. They are great when properly designed, meaning well insulated, and either channels for air flow of hydronic tubing embedded in them. Rot, water, vermin and fire proof, as well as being part of the heating and cooling system.

3/18/2011 8:41:01 PM

The slab is well insulated ? What does that mean? 2 inches? 4 or 12inches of foam between the slab and the ground? Isnt that the most important aspect even more important than slab thickness?

suzanne horvath
3/18/2011 12:11:31 PM

Would this be a good base for an earth-bag or straw-bale house?

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