Interesting article on GBA about radiant-in-floor heating.

GBA

The conclusion was:

Alex Wilson’s conclusion that a radiant floor heating system is “a great heating system for lousy houses.”

A good article although quite amazing that it missed the efficiency improvements that result from heat pumps (air or ground source) using large radiators. Hydronic (often related) also has some important advantages when it comes to energy storage (off peak electricity rates, PV solar, wood boiler, etc).

There is a lot of truth in this article. If you have a well insulated building, the floor temp will not be much warmer than room temp. Yes, folks who like lousy houses (e.g., 100 year old houses with an above floor HR heating system renovation) may believe that a 85F floor temp is very comfortable, but they will not be as comfortable with their HR system installation cost or their resulting utility bills as compared to a person using a HR heaing system in a new well insulated building.

The article does lose some credibility in referencing passive solar principles established in the late 1970s and stating that HR systems are incompatible with these principles. For example, “cool slabs can store more heat than warm slabs.” Besides being an untrue statement from a physics reality standpoint (warm slabs will continue to warm up and continue to store heat at exactly the same rate as cold slabs), using a HR system that is properly integrated with a passive solar design allows you to move the solar heat exactly where you want it without having any significant room temp swings like you will have with a traditional passive solar design. Regrettably, there are still many folks designing passive solar buildings using obsolete passive solar design rule of thumbs. There are also not very many folks who know how to properly integrate HR and PS heating systems.

Interesting if you read down to Dana's comments, the vast majority is Green Snobbery and misinformation.

We can't all afford to build and new house and most wouldn't build a Passive House even if they could. They have their own reason and fortunately are still "Free to Choose".
My house is sub 14 btu/sq.ft. and the floors are often just a couple of degrees above room temperature...I can feel the difference. When designing systems, both for old houses and new, I often site the various loads and the design temperatures for each.

The fact is more energy will be saved in renovation than can ever be saved in new residential construction and the combination of radiant floors and condensing boilers is a perfect way to make people comfortable and save fuel with one of the lowest carbon footprints per dollar invested anywhere.

Insulate and condensate.

The authors must assume that radiant floor heating is competing with insulation, but as Dana points out, it is more likely granite counter-tops et.al.

So where does one get current, up to date passive solar thumb rules?

When building a tight, well insulated house, does one put in the Pex just in case the heat pump doesn't perform to the homeowners expectations?

Posted By Lbear on 18 Apr 2014 02:35 PM
Interesting article on GBA about radiant-in-floor heating.

GBA

The conclusion was:

Alex Wilson’s conclusion that a radiant floor heating system is “a great heating system for lousy houses.”

Glib, catchy, but too silly to warrant serious comment. Obviously Building "Science" is "selling" the envelope. I say OOOO KKKK.

So where does one get current, up to date passive solar thumb rules?

How do they get out of date? Is the sun's output changing or something? I'm not sure what to make of the thumb rules for passive solar except to say I didn't find them of much use.
With the advent of much improved building envelopes, I believe nearly any home can become a passive solar with some attention paid to a few principles. Gone are the days when passive solars featured giant window walls of glass. Not sure if many of those worked in the first place.

When building a tight, well insulated house, does one put in the Pex just in case the heat pump doesn't perform to the homeowners expectations?

There is a lot more that could go wrong in the implementation of "tight and well insulated" than there is in the output of your heat pump.

With the advent of much improved building envelopes, I believe nearly any home can become a passive solar...

I agree, while the sun is shining. Beyond that, storing the heat and doing it without excessive under/overheating of the occupants is more difficult.

Glib, catchy, but too silly to warrant serious comment.

Oh really? Why? Got any specifics? I find the article to be substantially correct. If homes continue to improve, radiant in new construction may be increasingly relegated to special situations. Of course, we could always lobby for homes to be built leakier or more poorly insulated so that radiant made more sense. Sunrooms, for example. If you want to use your sunroom in Winter, there will be periods of no insolation in which the heating loads will be truly horrendous and radiant would keep the floor nice and warm.

With regard to my comment about obsolete passive solar rules of thumb, I will just paste some excerpts from our passive solar design software instructions.

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In short, passive solar heating involves:

1) Orienting the long axis of your house along the east-west direction so that there is a lot of wall area facing as due south as possible. If you live in the southern hemisphere, replace "south" with "north" in this previous sentence and throughout all of our calculator instructions.

2) Designing a roof overhang for BOTH your latitude and climate such that the windows on the south wall receive full sun during the cold winter months, are fully shaded during the hot summer months, and receive the appropriate amount of sun during the variable Spring and Fall months so as to minimize the need for supplemental heating while NEVER overheating the building. An often cited but misused "design rule of thumb" is to design a passive solar roof overhang using design solar altitude angles for full shade and full sun that are your latitude plus 18.5 degrees and your latitude minus 18.5 degrees, respectively.

3) Determining the south wall passive solar fenestration (i.e., south facing, vertically oriented, windows and doors containing glass) area that is necessary to provide the required amount of heat gain. An often cited but misused "design rule of thumb" is that passive solar buildings should have a total south wall passive solar fenestration area between 7% and 12% of the total building floor area.

4) Minimizing the window area in the other walls to reduce heat loss during the cold winter months and to reduce heat gain during the hot summer months. Even the worst wall assembly will have a much higher R-value (or much lower U-factor) than the best available window. As such, there are significant economic and energy efficiency benefits to minimizing the quantity and size of windows used in buildings.

5) Determining the correct amount of thermal mass needed to absorb, store, and slowly release the correct amount of heat gain during the daily passive solar heating cycle. An often cited but misused "design rule of thumb" is that for every square foot of south wall passive solar fenestration area in excess of the 7% "design rule of thumb", a passive solar building should have 5.5 square feet of 4 inch thick thermal mass material.

There are many passive solar companies that market their services based on using these overly simplistic and often grossly inaccurate "design rules of thumb" for above items 2), 3) and 5) and they also often charge exorbitant fees for their less-than-competent expertise and their defective passive solar house plans. Frankly, using "design rules of thumb" that may be grossly inaccurate is a very risky design approach that we believe should not be accepted or tolerated. We advise applying due diligence and avoiding companies who follow this practice if you want to ensure having a passive solar design that will keep your building occupants comfortable and happy without depleting your bank account.

Relative to the above item 2) "design rule of thumb", in addition to properly addressing your local latitude, it is also important that you properly address your local climate when designing your passive solar roof overhang as explained below:

Research what the average daily high temperatures are for your location/climate to select a date during the spring or summer months when the average daily high temperature reaches your desired indoor temperature. Use this calculator to determine the corresponding solar altitude angle at solar noon for this selected date. This solar altitude angle is called the Design Solar Altitude Angle for Full Shade and this is the date that your passive solar roof overhang will begin providing full shade to your passive solar fenestration (i.e., provide zero heat gain). If you typically have warm spring months, perhaps select an earlier date which will result in a lower Design Solar Altitude Angle for Full Shade which will begin providing full shade earlier and of longer duration during the spring and summer months. Conversely, if you typically have cool spring months, perhaps select a later date which will result in a higher Design Solar Altitude Angle for Full Shade which will begin providing full shade later and of shorter duration during the spring and summer months. In Rogue River, Oregon, the average daily high temperature reaches 68 degrees F on April 27 and the solar altitude angle is 61.2 degrees at solar noon on this date. Therefore, 61.2 degrees is an appropriate Design Solar Altitude Angle for Full Shade selection for our Rogue River, Oregon design example.

Research what the average daily high temperatures are for your location/climate to select a date during the fall or winter months when the average daily high temperature reaches your lowest temperature of the year. Use this calculator to determine the corresponding solar altitude angle at solar noon for this selected date. This solar altitude angle is called the Design Solar Altitude Angle for Full Sun and this is the date that your passive solar roof overhang will begin providing full sun to your passive solar fenestration (i.e., provide maximum solar heat gain). If you typically have cool fall months, perhaps select an earlier date which will result in a higher Design Solar Altitude Angle for Full Sun which will begin providing full sun earlier and of longer duration during the fall and winter months. Conversely, if you typically have warm fall months, perhaps select a later date which will result in a lower Design Solar Altitude Angle for Full Sun which will begin providing full sun later and of shorter duration during the fall and winter months. In Rogue River, Oregon, the average daily high temperature reaches an annual low of 44 degrees F on December 25 and the solar altitude angle is 24.2 degrees at solar noon on this date. Therefore, 24.2 degrees is an appropriate Design Solar Altitude Angle for Full Sun selection for our Rogue River, Oregon design example.

Relative to the above item 3) "design rule of thumb", there are many factors besides the actual fenestration area that have a significant effect on the passive solar heat gain. For example and perhaps most obviously, the amount of irradiance that actually enters the fenestration has a significant effect on the actual solar heat gain. The amount of irradiance that actually enters the fenestration depends on the building's local latitude, local atmospheric optical transparency quality, local climatic sunshine availability, local terrain obstacles, actual Solar Heat Gain Coefficient (SHGC) of the fenestration, and the actual hourly utilized fenestration area as governed by the actual passive solar roof overhang. And perhaps more importantly, the maximum amount of daily/monthly building solar heat gain should always be equal to or less than the daily/monthly building heat loss as determined by performing an actual building heat loss analysis. It should also be noted that this "design rule of thumb" has little significance if you have a well-designed and integrated passive solar heating and hydronic radiant floor heating system.

Relative to the above item 4) "design rule of thumb", there are many factors that can significantly affect thermal mass performance. For example, the maximum temperature that a thermal mass will reach during the daily irradiance time period depends on the initial temperature of the thermal mass, the daily irradiance magnitude (BTU/Day), the daily irradiance time period (Hours/Day), the absorptivity of the thermal mass material, the specific heat capacity of the thermal mass material, the actual mass of the thermal mass, and the exposed floor heat loss. The heat gain provided by a thermal mass during the night time hours depends on this maximum temperature, the surface area of the thermal mass, the emissivity of the thermal mass material, the R-value of the thermal mass material associated with the upward heat flux, the convective heat transfer coefficient of the surrounding air, the specific heat capacity of the thermal mass material, the actual mass of the thermal mass, and the exposed floor heat loss. A thermal mass will also release heat during the daily irradiance time period when the thermal mass temperature exceeds the room temperature. Consequently, the passive solar heat gain that occurs during the daily irradiance time period can result from both the irradiance that enters the building that is NOT absorbed by the thermal mass PLUS any heat gain that is released by the thermal mass during the daily irradiance time period. It should also be noted that this "design rule of thumb" has little significance if you have a well-designed and integrated passive solar heating and hydronic radiant floor heating system.

These "design rules of thumb" were likely originally developed by the passive solar design pioneers back in the 1960/70s before the widespread use of computers. These "design rules of thumb" may have worked reasonably well for the specific building locations and the construction materials/methods used at the time. However, there are also many reports of passive solar designs with seriously over-heated or under-heated buildings as a consequence of following these "design rules of thumb".

Fenestration. A $10 dollar word for window. From Latin. Takes some of the penache out of it, doesn't it?

If you want a clear explanation you will find it here.

http://tc45.ashraetcs.org/subcommittees_files/HOF_Fenestration_MinusShading.pdf

Now you will be better able to distinguish the meat from fat.

akes some of the penache out of it, doesn't it?

Maybe you meant 'panache'.

Now you will be better able to distinguish the meat from fat.

Was hoping maybe you would tell us what parts of the GBA article were 'meat' and 'fat', or at least glib, catchy and silly.

Actually, "fenestration" is a $10 dollar word for anything having glazing used for bringing sunshine into a building. This would include doors, skylights, and windows. "Glazing" is a $10 dollar word for glass, although there are also other glazing materials being developed that will likely replace glass in the future that transmit sunshine in a more controlled fashion, have much better thermal performance, and can also generate electrical power in the process.

This fenestration chapter is from the American Society Heating, Refrigeration, Air conditioning Engineers (ASHRAE) Fundamentals Handbook which covers the basic principles and data used in the HVAC&R industry. Mastering this content is the starting point for a good HVAC&R design engineer. We are active ASHRAE committee members and the equations used in this ASHRAE fenestration chapter and other chapters of this fundamental handbook are incorporated into the free DIY passive solar design software on our website.