Wednesday, December 26, 2007

House Ventilation

Now that the insulation is in, the house has few ways for air to get inside or out. This is good because air will not infiltrate through holes in walls, floors, or duct seams in walls and crawl spaces. Air tightness makes heating and cooling more efficient since outside breezes won't blow air in.

The next steps address increasing tightness for heating and cooling energy efficiency, and whole house ventilation so that air exchange keeps air fresh and healthy.


Aside from sealing ducts and installing vapor barriers and weatherstripping, this house is tighter because of insulation characteristics and the characteristics of the heating/cooling system.

The insulation is predominantly blown-in insulation. We have used icynene insulation. Blown-in insulation does a better job of sealing stud cavities and ceiling joists than batt insulation, particularly when there is wiring in a wall or ceiling. Insulation, vapor barriers and weather stripping are not the only things impacting tightness - the heating and cooling system impacts house tightness as well.

Why does the Heating/Cooling System impact Airtightness?

Traditional heating and cooling is done with forced air (using hot air or frigid air). Large temperature extremes in heated or cooled air cause it to expand or contract - and since a house cannot contain this pressure, it breathes air in and out. It doesn't matter if the house is well sealed or not - air will be expelled or drawn in anyway.

For example, if a furnace heats air from 70F to 150F, this expands its volume by about 13%. If 1/10 the volume of the house is affected, this will displace 1.3% of the volume of the air in the house: it will force it out when heating, or suck it in during cooling, whether or not the house is tightly sealed. A 2500 square foot house would breath about 260 cubic feet of air each heating cycle!

This house's heating and cooling system uses low-temperature difference hydronic - so heating or cooling operates over longer periods of time Heating is done with lukewarm water (95F) and cooling is done with cool (not chilled) water. The result is that the air inside the building expands or contracts less, and the house doesn't breath as much as a forced-air heated or cooled house. Using smaller temperature variations reduces the amount of air breathed in and out.

By comparison, we might expect that if heating goes to only 85F (radiant floor), then the effect would be roughly 1/5 as much as above, or 50 cubic feet of air. So, by using lower termperature vairations in heating and cooling, the house breathes less, and the house truly is tighter.


One of the downsides of a tight house is that it doesn't leak air, you have to design in ventilation. This house's ventilation has summer and winter modes of operation. In either case, we strive to be energy effiicient - either using ventilation to cool the house in summer, or use heat recovery for winter ventilation.

Summer ventilation is accomplished by sucking (warm) air from the ceilings of the second story of the house and venting it outside. This is easy because the second story air return ducts are in the ceilings (see heating and cooling system design).
Cool fresh air is introduced into the first floor by means of an EarthTube. Since the air is both blown out and drawn in with low-power fans, air pressure in the house is near neutral. Whole-house ventilation is naturally achieved since summer heat causes air to rise, where it is ultimately vented out. Summer ventilation doesn't increase house cooling requirements because the EarthTube cools the incoming air.

During winter air inside the house is warmer and more humid than outside air. Straight ventilation would introduce uncomfortable cold drafts, and extra demands on the heating system. A heat recovery ventilator from FanTech is used to heat and humidify incoming air using the outgoing air stream. This air exchange is balanced, so that air pressure in the house is roughly the same as air pressure outside the house. Warm humid air is less likely to seek a path out through walls, windows and doors.

Finally, exhaust vents such as the kitchen hood, bathroom fans and fireplace should not have to fight a tightly sealed house. In our house the EarthTube (summer) and/or HRV inlet (winter) can be activated when the exhaust fans turn on, guaranteeing that air drawn into the house is coming in through desirable intakes.

Ventilation is an Art

Compared with Heating or Air Conditioning, Ventilation is unfamiliar territory in residential construction. As pointed out in a posting on the GreenerHouse Google Groups, it is so new that there are seminars to educate the public (not to mention contractors). The speaker, Judy Robertson, presented a talk "Putting the V back in HVAC" and pointed out that residential contractors are experienced with HAC - not HVAC! Some interesting bits from the seminar:
  • Green builders and homeowners are desparate to find residential HVACcontractors. Today's residential heating/air-conditioning contractors are not familiar with ventilation. Our HVAC contractor is a crossover contractor - they do part commercial and part residential. Several people asked me for our HVAC contractor's contact information.
  • The larger Fantech ventilation fans are quite noisy but can also move a lot of air, while the smaller Panasonic fans are whisper quiet by comparison. I intend to do a test run with the house ventilation fans to see how they fare.
  • Piping inlet air directly to desired rooms is important, because air flow rates for ventilation are a lot lower than those typical of forced air systems. Very important for bedrooms, since so much time is spent there. Check this in your house!
  • Heat recovery ventilators are less efficient with lower delta-T. It is important to duct exhaust air though conditioned space as much as possible prior to connection to the Heat Recovery Ventilator.
  • The amount of ventilation (air exchange) required for a building is a function of many things. ASHRAE has a minimum value based on square footage. The baseline air exchange rate we had chosen barely met this number.
There are air quality / energy tradeoffs between insufficient and excessive ventilation. If is was possible to automatically measure objective and subjective air quality, this would be easier.

Saturday, December 22, 2007


Framing, electrical and plumbing are complete. The house has been insulated. Insulation used in the house is a combination of radiant barrier, spray-in foam, rigid foam board, and fiberglass batts.

Radiant Barrier

This house makes use of CBF Ultra radiant barrier insulation almost everywhere:
  • under roof shingles
  • under floors
  • under stucco in exterior walls
  • inside walls, just behind drywall
  • inside basement walls, just behind finish
CBF Ultra was used because it has a foil barrier with bubbles on both sides. It can be embedded in a wall, in concrete, under stucco, etc. and will always have the air gap necessary for radiant barrier to work. Radiant barrier dramatically reduces radiant heat transfer. Radiant barrier on the outside of the house reduces heat gain during summer, while radiant barrier on the inside of the house reduces heat loss during the winter. Radiant barriers under heated floors reflect heat back up.

Radiant barrier behind stucco has an added benefit: it introduces an air gap between the building structure (sheathing, studs, beams) and the stucco. This air gap reduces heat conduction between the building structure and the outside, effectively increasing the insulation value of the walls. This little bit of insulation makes a big difference in the overall insulation value of the wall because the studs and structure have much lower thermal resistance than a foam-filled stud cavity.

For example, consider a 6 inch wall of R25, whose structure covers 10% of the wall area, and is about R6. The wall has an effective R value of R = 1/(0.9*25 + 0.1*6) = R19. If the bubble adds R3.8 everywhere, then the wall's effective R value becomes R = 1/(0.9*(1/(25+3.8)) + 0.1*(1/(6+3.8))) = R24. So adding 1/4 inch of bubble increased the real R value of the entire wall by 20%!

Radiant barrier was the first insulation installed in the second floor of the house, prior to new roof shingles, in mid-summer. The difference was immediate and noticeable. The temperature in the second story dropped 15F, and it was cooler upstairs than it was outside - with no other insulation in place!

Icycene blown-in insulation

The bulk of the insulation is blown-in Icynene. Blown-in insulation does a great job filling areas between wires and pipes, and has no problems filling odd cavities where standard batts of insulation would need to be crammed in (poor insulation) or leave voids (no insulation). Spray-in practically eliminates drafts through walls and ceilings, and thereby substantially reduces problems associated with vapor permeating walls with its resulting condensation.

Rigid Foam Insulation

Rigid foam insulation is used where few interferences exisit: under floors above crawl spaces, under tiles floors over slab, and as insulation in basement walls. Under wood floors in the joist spaces, 3" thickness Dow Thermax board with radiant barrier is used. Its radiant barrier reflects heat back up to the radiant floors. Thinner 1" thickness Dow Styrofoam blue board in combination with CBF Ultra radiant barrier is used over slab floors and behind basement walls.

Fiberglass Batts

Fiberglass batts are used to fill larger dead spaces that don't have wiring or plumbing in them, such as cavities under roof walls.

Saturday, September 15, 2007

Open Walls Tour

Today we hosted an "Open Walls" tour of the house. At this stage of construction, a lot of infrastructure is in place and viewable in the walls, under the floors or underground. Over the course of the next few weeks it will covered up and no longer visible.

The tour was a tremendous success, attended by over 50 people. It attracted many silicon valley engineers who are interested in more efficient heating, solar energy, and more efficient water usage. A few architects and at least one contractor (other than this project's general contractor) also attended. Alas, I was too busy to put out a guest book for people to sign.

The high points of the tour ...

The Heat Dissipation Loops in the Pit

The 12 foot deep pit was the major feature alongside the north side of the house.

  • The heat dissipation pipes for our cooling system were visible at the bottom, as were the aluminum heat spreaders both over and under the pipes.

Next, this pit will be partially filled in, and then the storm water dissipation and water storage pipes will be installed.

The Second Floor

The first tour group visitors came up to the second floor of the house at 2:30pm on a fairly sunny afternoon.

The abundant use of radiant barrier was plain to see. There was no other insulation installed yet. And yet it was immediately noticable that the temperature inside was actually very pleasant: it was not hot at all.

The radiant barrier fulfills several functions in the slanted roof: it serves as an insulation stop, so that insulation that is blown in will not go thought the wood roof shingles, it serves as a radiant barrier directly under the skip sheathing to which the wood shingle roof is attached, and it serves as an insect barrier, so that wasps or bees don't build a hive in the stud bays (we discovered a few when the walls were opened).

The Wine Cellar

Many wine cellars are designed with expensive refrigeration systems, and can keep wine at 55F so that bottles can mature over the course of 100 years. These refrigeration systems cost a lot of money to buy and operate.

My goal is to build a wine cellar that can hold decent wines at 60F, aging them over a period of 10 to 20 years, so I can enjoy them during my lifetime :-)

This cellar is designed to take advantage of relatively stable (60F) temperature at 12 feet of depth - which is the yearly average temperature of the San Francisco Bay Area. To do this well, the cellar is built deeper into the ground than the rest of the basement.

In spite of the lack of insulation, no door, and it being the end of the summer, the cellar temperature was 62F during the tour. I don't believe there will be any trouble achieving the target temperature of 60F.


There were some good discussions regarding the installed shower heat reclamation plumbing, the two examples of more efficient insulation and heating for the tile floor areas, and the frustrations with thrying to get greywater irrigation approved - even in this water conservation climate.

Visitors got to hear about (and critique) some of the planned experiments in heating and cooling. I welcome this feedback, and endeavour to produce data over time to show how well things actually work.

Tour Site Placards, as an online presentation. Some photos taken by a visitor.


I'd like to thank my wife Patti who took care of tasty refreshments for the visitors. I'd also like to thank my contractor Bernie and his staff for doing a great job presenting a clean and safe site, for last minute help putting up the informative signs and especially to Bernie for being available to answer many questions. Finally thanks to my friend Andy, a mechanical engineer, for answering questions for people who didn't quite catch the first tour but couldn't stay for the second.

Wednesday, September 12, 2007

Experiments in Building a Greener House

This blog records some "green" experiments built into our old house during a renovation.
The experiments include more efficient insulation, more efficient heating and cooling, and grey water. The main purpose is to show what works well, and when, based on measured data.
We also demonstrate that you don't need ultramodern architecture to have energy and water efficiency.