BASICS OF THE THERMAL COMFORT PERFORMANCE OF

BUILDINGS

by James Fricker, B.MechE, F.AIRAH, M.EngAust, CPEng http://fricker.net.au

Does warming a glass of softdrink

make CO2 bubble out of the water?

A puzzle...

Same for the

oceans!

For every tonne of CO2 in the atmosphere, there are 50 tonnes dissolved in our oceans. As oceans warm, CO2 comes out of solution (into the atmosphere), and as oceans cool they absorb CO2 back from the atmosphere! Does CO2 increase cause ocean warming, or the reverse?Could cloud cover decrease cause ocean temperature increase, and not CO2?

EMBODIED ENERGY - SOME BASICS

What is embodied energy?

Embodied Energy is the energy consumed by all of the processes associated with the production of a product, including the production (or extraction) of its raw materials.

How is embodied energy related to carbon dioxide emissions?

CO2 emissions are highly correlated with the energy consumed in manufacturing. On average 0.1 tonne of CO2 is produced per gigajoule of embodied energy.

Thus energy conservation is generally a carbon emission reduction, helping the minimisation of global warming (if CO2 is the cause!)

But what if the investment in energy conservation is not recovered by energy savings? Answer: It actually accelerates fossil fuel depletion.

Thermal INSULATION –

Is more always better?

$$$ Cost vs. $$$ Saved

Embodied Energy

Environmental impact

Thermal MASS –

Is heavy always better?

$$$ Cost vs. $$$ Saved

Embodied Energy

Environmental impact

Embodied energy of building materials

COMFORT is an individual human perception,

mainly affected by

- air temperature

- radiation

- breeze

- humidity

- noise

- the individual’s health, activity, and clothing

~ Mild Climate (Melbourne spring or autumn) ~

~ Cold Climate (Melbourne winter) ~

Heavy mass building: smooths temperature – slow to warm up, slow to cool down. Large energy storage, large energy shifts.

Light mass building: large temperature swings – fast to warm up, fast to cool down. Small energy storage, small energy shifts.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Low insulation and light mass: rapid temperature swings, aircon and heating desired, except for the few hours where temperature is mild. High heating and cooling energy.

Low insulation and heavy mass: slow temperature swings following climate (this is fine if climate is mild, but in a cold climate, significant need for heating = high heating energy.)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

High insulation and light mass: fast temperature swings following climate, but easily matched with aircon or heating. Great for transient occupancy. Low heating and cooling energy.

High insulation and heavy mass: slow temperature swings following climate (this is fine if climate is mild, but in a cold climate, still need for heating). Best for continuous occupancy.

WE HAVE THERMAL MASS, SO WHY DO WE NEED INSULATION?

If the building is heated or cooled by fossil fuels, insulation reduces the energy requirement. (The BCA thinking)

Thermal mass will delay thermal response, but if the desired indoor temperature is different to the outdoor temperature, heating or cooling are desired, hence insulation is useful.

BUT A SIDE EFFECT OF IMPROVED INSULATION…

Unfortunately a common effect of better insulation is that because air conditioning and heating running costs are reduced, occupants can now affordably extend the service running hours.

Or worse still, now that there is good insulation, an air conditioner may be installed for the first time.

Both of these can have significant impact on the desired energy conservation by insulation.

But are those high R-values really necessary?

THE DIMINISHING VALUE OF ADDED INSULATION

The heat transfer through a roof or wall that becomes a summer cooling load on air conditioning is reduced by added insulation.

The initial insulation that is added causes the most dramatic reduction in cooling load and A/C running costs.

But every extra bit of insulation that is then added has diminishing benefit.

The reducing financial benefit of further added insulation reflects the diminishing benefit on embodied energy grounds.

SUMMARY

Conserve fossil fuels as they are non-renewable, so design buildings well.

HEAVY MASS building construction dramatically reduces daily temperature swings, increasing the likelihood of thermal comfort.

But heavy mass buildings also need appropriate insulation in cold climates, to reduce heating energy.

Mass can help with diurnal variation, but is negligible in seasonal variation. (Unless building is underground!)

Insulation (and all building materials) have environmental impact, so there is negative benefit with excess insulation.

As the esteemed Dr Yarbrough wrote in 2005:

“The increase in embodied energy that results from the addition of materials to a structure must be included in estimates of the impact of a conservation effort on the national energy use…

The evaluation of competing energy conservation projects should include embodied energy to obtain the true impact on the national energy budget.”

ACKNOWLEDGEMENTS

For their generous help, the author gives special thanks to

Dr David Yarbrough of R&D Services (U.S.A.), thermal expert

Dr Steve Moller of Sustainable Built Environments (Melbourne), engineer

Thank you for your attention

JAMES M FRICKER PTY LTD54 Felix CrescentRingwood North 3134http://fricker.net.aufricker@optusnet.com.au

Aerogel™, the ultimate thermal insulator