Passive House

Tenet 1-Super Insulation

Cozy memories are often wrapped in a favorite blanket, perhaps The one that Grandmother crocheted is  - it’s so warm!

But it’s not warm. The person wrapped inside is warm; the blanket’s role is to slow the loss of that warmth to the surrounding environment. The body has produced heat by burning calories which is kept close to the source through Grandmother’s kindness.

Another trivia question:

Q-What is a calorie?

A-A measure of heat.

The calorie we are familiar with when assessing the menu is actually a ‘kilo-calorie’ which is the amount of heat required to raise the temperature of one kilogram of water 1 degree Centigrade. (The ‘small’ calorie, which is rarely used outside the chemistry lab, is heat sufficient to raise 1 gram of water 1 degree Centigrade.)

That’s the warmth that grandma’s blanket is retaining. The food consumed is turned into energy for swimming, running, thinking or watching a movie wrapped in a crocheted blanket. One of the by-products of those calories is body heat: heat in=heat out. Burning calories is a fit description.

But if a nutritional calorie is heat, How would that even be measured? By setting food on fire and measuring the heat output? Actually-yes. That’s exactly how it is done, using a

device called a bomb-calorimeter. There’s a combustion chamber (the bomb) that contains oxygen and is surrounded by water. Your cheeseburger is lit up and the resulting change in water temperature measured.

Heat can be measured several different ways: calories, joules, watts, and British Thermal Units (BTU’s). They all can be translated into work or a certain amount of ‘power’. Human bodies, horses, steam engines, electric motors and gasoline engines are all capable of producing ‘power’. Power over time equals energy.

A BTU is a somewhat dated power rating, but is still popular in some industries. Its metric is the amount of heat required to raise the temperature of a pound of water 1 degree Farenheit and is roughly equivalent to the heat produced by a kitchen match.

A person sitting, watching a movie, produces about 300 BTU’s of heat in an hour, which is dissipated into the room. Wrapped in a blanket, however, the dissipation is dramatically slowed.

The same is true for a building, but rather than calories, the energy comes in the form of electricity, natural gas, wood, coal that is directly or indirectly used to create heat (or cooling).

the benefit of insulation is two-fold: one is to reduce energy used, resulting in cost-savings to the Owner, the other is reducing the carbon released by the production, delivery and use of  energy.

The insulation lets you enjoy more of what you paid for. The slower energy is lost to the outdoors, the longer when can get our money’s worth in comfortable spaces to live and work.

Judicious stewards of energy would then want to be able to establish a metric with which to compare insulations and, as a result, be confident in establishing expected energy use.

The R value has become the most popular  the metric for evaluating insulation qualities. Plywood, brick, drywall, all have R values as do all construction materials, These can be totted up and incorporated in the total insulation value of an assembly.

The R value is derived from its lesser know cousin the U value which directly measures the rate that heat passes through a material-a lower number is a better.

More specifically a U values measures how many BTU’s of heat are lost in an hour across a surface area of one square foot where the difference in temperature on either side of the insulation (inside to outside) is so many degrees Fahrenheit. In text BTU’s per hour per square foot per difference in degrees (between inside and outside)

In equation form:

U= BTU/hr·ft2· △ ◦F

different metrics can be used, of course, with Watts, square meters and degree difference in Centigrade or Kelvin. The point is that these units can be measured with that knowledge made useful in evaluating insulating materials or heating needs.

We talk in terms of heat since heat is an expression of energy whereas cold is seen as the absence of heat. A heat pump, for instance can move heat inside or outside resulting in heating  or cooling respectively.

Humans have a tendency to prefer the cleanliness of integers and identify with the time tested adage, “if something is good, more of it is better. , so the fussy, fractional, dimishing U value was inverted to create the pure R value, i.e. a U value of 0.1 (1/10) is the same as an R value of 10 (10/1)

In considering the variables in this equation, it’s evident that we can reduce energy use in several different ways.

BTU’s are energy costs.

Hours? 60 minutes-Not much can be done about that.

The area of exterior surface is a potent variable, though. Just ask Capt Robert Scott. In his race to reach the south pole, he chose ponies instead of dogs to pull the sleds, hoping that their larger size would make for faster progress. The larger surface area, however, compared to the compact body of a sled dog, resulted in faster heat loss which was one of the contributing factors in the death of everyone in the expedition as the ponies internal systems couldn’t keep up with the heat loss across their comparably bigger surface area.

The difference in temperatures is a consideration, too. It sets what effort is needed to maintain a particular temperature. On the Titanic, Jack needed to produce a certain amount of heat for his body to continue to function. The extremely cold water of the North Atlantic required Jack’s body to generate extraordinary amounts of heat to maintain a survivable body temperature. (Spoiler alert- He wasn’t able to) If the Titanic had sunk in the Bahamas, Jack might still be with us.

There are many types of insulation, both in material and form, that can accommodate almost any construction condition, with science searching for better/less expensive products constantly.

Insulation has been with us for millennia with more types being tested regularly. In the equation of the Passive House it is the perhaps the most potent weapon in the designer’s arsenal. But the demands of Passive House stretch beyond the blanket in which the project is wrapped.

Next time - Gone with the Wind redux