I recently spent some time living in a passively cooled and heat building (ie, using passive, interior thermal mass). Night temperatures were consistently around 70F and day temps were around 90F (ie, the problem was more heat than cold, but both were issues). The building had uninsulated concrete walls. Some observations:

Forced ventilation at night (to cool the concrete down) and a sealed room during the day (to minimize heat gain) worked best. An automated, indoor/outdoor comparison thermostat to control the fan would have been convenient and slightly more effective.

Shading (trees, overhangs, tinted windows) was critical in reducing daytime heat gain. White walls and air sealing (it was poor) were also important. Exterior insulation would have helped.

Interior circulation (a ceiling fan) was critical in improving heat transfer to/from the air and concrete.

The system was comfortable enough (all interior passive thermal mass systems require living with temp swings) with low average humidity levels (say 60%). At high humidity levels, the nighttime cooling supplied by the concrete caused excessive humidity (even condensation) and was not as comfortable.

Passive internal thermal mass was clearly a negative (less comfortable, more energy use) when used with air conditioning. It caused slow response, condensation, variations in comfort (at the same air temp) and interfered with the strategy of only running the A/C as needed (ie, while occupied and only during the hottest times).

Overall, I found passive (not counting the fans) interior thermal mass to be cheap and simple but comfort was only fair or "better than nothing".

The building had uninsulated concrete walls

What about the lid? If it is an insolation-intensive environment, the roof is important.

Forced ventilation at night

My first choice would be for passive ventilation at night, using the residual heat from the day to drive a stack effect.

Having uninsulated concrete walls was the problem...unless they were several feet thick. Having inadequate ceiling/roof insulation would be a problem too. Ideally you want lots of insulation on exterior side of wall and no insulation on the interior side. This will tend to keep the inside of the building at a relatively constant average temp both day and night. The magnitude of this average temp and any daily variation are largely governed by the irradiance aperture and the thermal mass design. It takes a little engineering to get the design right for each specific building location/climate. Unfortunately, this is hardly ever done.

I agree, insulation, more mass and better air sealing would have kept the temperature more constant. Grooved concrete on the wall would also help (it would minimize the air/concrete differential needed to move heat). Stack effect ventilation could save the small amount of fan energy used.

I don't think there is an easy solution to the biggest issue of humidity and condensation. Running a dehumidifier during the day could work, but wasn't an option at night (since the unbalanced thermal situation required nighttime ventilation). Same for the incompatibility with part-time A/C use.

My "do it better" conclusion - some combination of external mass, insulation, air sealing and active AC/dehumidification. With enough of the first 3, the cost of the last one is insignificant, even if left on 24 hrs/day.

Grooved concrete on the wall would also help (it would minimize the air/concrete differential needed to move heat)

To increase surface area? How deep on the grooves? Would they end up being like "fins"?

Just to be clear, it is internal thermal mass (that is well insulated from outdoor temp) that is required to achieve a relatively constant and comfortable indoor temp both day and night, and in both winter (passive solar heating) and summer (passive cooling). External mass provides little benefit. To successfully design a building that uses passive solar heating or passive cooling you need to accurately know and manage the BTUs associated with:

1) The heat loss of the building.

2) The maximum instantaneous clear sky solar heat gain.

3) The average monthly climatic solar heat gain.

4) The heat absorbed/released by the internal thermal mass during the irradiance period.

5) The heat absorbed/released by the internal thermal mass after the irradiance period.

Passive solar heating can be readily accomplished and significantly reduce supplemental heating requirements in any climate/location where there is at least a couple hours of irradiance each day. Fortunately, this is the situation in much of the US lower 48.

Passive cooling is best accomplished in a climate/location where summer humidity is low and where night time temps are significantly below the design indoor temp. Fortunately, this is the situation in much of the western US. If you are in a location where the day and night time temps are always well above your design indoor temp, you will not be able to achieve this design indoor temp using passive cooling.

Comfort level relative to humidity is not a problem that can be successfully addressed via passive cooling other than by being in climate/location and having a successful design that keeps the indoor temp below say 75 deg F. Again, this may or may not be possible depending on the specific climate/location.

The data is quite clear that external mass does work. Some studies show it to be less effective than internal mass, but that depends on how much you are willing to let the internal temperature vary. With little or no variation (ie, maximum comfort), internal thermal mass is pretty much worthless (ie, it under-performs external mass). Underground buildings are an example of external thermal mass.

I should also point out that once you start opening and closing windows twice a day, the system isn't exactly "passive" (external mass doesn't need this).

Here is what I was thinking for ribbed concrete:

http://www.westbrookblock.com/?page_id=46

Well, we don't have any problem achieving a 68-72 deg F design temp and keeping daily temp variation under +/- 2 deg F only using internal thermal mass...but we carefully engineer the BTUs in our designs. Underground buildings are an example where outdoor temp has been removed and replaced with ground temp relative to wall heat transfer. I would say manually or automatically opening/closing windows is a more "passive" approach than using forced ventilation and room fans.

Do you have a WEL instrumented house that is accessible online?

Not sure what you mean by WEL instrumented? Our integrated hydronic radiant floor heating and passive solar designs are instrumented for floor temp, indoor temp, outdoor temp, supply temp and return temp, and these temps can be monitored via the internet which is useful for a variety of purposes. We don't normally instrument or provide internet monitoring capability for our purely passive solar designs as there is no reason to do that.

More info at http://www.welserver.com/

these temps can be monitored via the internet

OK, please provide an Internet link to what you have to support "temp variation under +/- 2 deg F only using internal thermal mass.". It's a vague statement, but under some conditions, any house will achieve that and under others, it violates the rules of physics.

Thanks for this info. This WEL instrumentation system costs about $500 and appears to only do simple temp sensor internet monitoring. We (or really our customers) prefer using a UL listed home automation system for providing full HVAC internet connectivity and remote control. If the customer desires a burglar and fire system we recommend the HAI Omni system for accomplishing this and the home automation. If you are just interested in simple temp sensor internet monitoring, you can purchase an Arduino micro controller with an ethernet shield for about $50 for temp sensor internet monitoring. 2-way HVAC internet connectivity using an Arduino is also possible but requires some micro controller knowledge and good programming skills.

Actually, our passive solar designs vigorously follow and adhere to all the principals of physics (heat transfer, solar radiation and thermodynamics). That was really my point and what actually needs to be done to successfully design passive solar buildings. Unfortunately, there are very few passive solar "experts" capable of doing this.  Adding internal thermal mass to a building increases the thermal capacitance of the building. Increasing the thermal capacitance of a building makes it more difficult to change the inside temp of the building...which can be good or bad depending on what your design objectives. For example, having high thermal capacitance is not good for rapid temp setback recovery.  If you maximize the thermal capacitance of a building and minimize the heat loss/gain through the building envelope, the internal thermal mass temp and indoor temp will tend to stay one and the same. So as a passive solar building designer, your goal is to carefully size and control the temp of this internal thermal mass by knowing and managing the BTUs as described previously and minimize the heat loss/gain through the building envelope.

As you know, there are two ways to minimize the heat loss/gain through the building envelope: minimize delta T (this is your underground building approach) or maximize insulation R-value (the more conventional approach). We prefer to spend as many days above ground as possible...

Yes, adding external thermal mass will increase the R-value and reduce the heat loss/gain through the building envelope, but you will have to add many inches of external concrete (as compared to other forms of insulation) to significantly increase the R-value. Yes, adding external thermal mass will also increase the thermal capacitance of the building too, but controlling the temp of external thermal mass is problematic do the large variations in outdoor temp.

It is far easier to control the temp of an internal thermal mass system. When you get aggressive about capturing irradiance, you also need to start using an active internal thermal mass system (i.e., internal thermal mass augmented to allow controlling and moving the BTUs via a hydronic system).

So no online data to support your claims? A WEL will monitor anything you can put a sensor on and appears to be the standard for Internet accessible energy monitoring.

Yes, it appears a WEL will monitor temp sensors placed in an accurately temperature controlled chicken egg incubator too. Frankly, it appears more like a FaceBook approach for showcasing than a vigorous approach for accessing actual building performance. However, this is the first I have heard about this and I don’t know much about it. Is there an independent agency that actually validates the WEL results and, if so, how much does it cost?

We are not making any claims other than that a disciplined approach based on sound engineering principals should be used to design passive solar buildings. Your original post just struck me as being somewhat ignorant in that you made a general statement about passive solar performance based on just spending some time in a building without providing any details about the building’s construction, climate/location, or passive solar design elements. If you and your customers are happy with your results, you should continue doing whatever it is that you are doing.

We are not making any claims other than that a disciplined approach based on sound engineering principals should be used to design passive solar buildings.

One only has to read your earlier comments to see that your claims go far beyond this.

Umm, jonr, kinda hard to complain about lack of speciificity when you don't tell us where you were, how the attic is insulated and, most importantly, what "comfort" means to you. Borst is telling you that he can keep the combination of mass and radiant heat within +/- 2 degrees. Why is that hard to believe? While that approach isn't entirely passive, it most certainly is green, In a climate with daily extremes above and below "comfortable," you still use less conventional hvac because thermal lag reduces delta t -- delaying heating or cooling to more favorable ambient conditions. I've shown you test homes using set-ahead AC strategies that kept the AC off all day. While the daily swing might not meet jonr comfort standards, that would be an individual thing, eh?