It is Heavy, It’s Thermal Mass

A decade and a half before Paul Simon’s innovative album Graceland (1986) exposed Western listeners to unique and original African sounds and rhythms, the incomparable Neil Diamond did the same with the lesser known album, Tap Root Manuscript (1970). Side two of the album is called “The African Trilogy (A Folk Ballet),” and includes two of my all-time favourite Neil Diamond songs: I Am the Lion, and Soolaimon.

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 Side one, however, is more likely to be memorable for most people due to a series of Top 40 (US) hits: Cracklin’ Rosie; Free Life; He Ain’t Heavy, He’s My Brother. The last of these hits – He Ain’t Heavy, He’s My Brother – was ‘recycled’ from The Hollies, whose version reached No. 1 in the UK Singles chart in 1969.

Like this well-known song, our Shacklock 501 is: a favourite feature of our home; it is ‘recycled’ from another dwelling; but critically, it is very heavy. And that is the point.

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Along with acting as a heating source for our home on cloudy, cold winter days, the 700-kilogram coal range/brick surround/concrete and tile hearth acts as a ‘heat sink’ on sunny winter days. In this respect, the combined heavy stuff that makes up the building code approved unit functions as ‘thermal mass.’

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From a purely physics perspective, everything that has mass can absorb heat. In the extreme, air has mass so it can absorb heat. But ‘light’ things like air gain heat quickly and lose it quickly. ‘Heavy’ things, on the other hand, absorb heat slowly and release it slowly.

Water is a good example of a substance that has significant thermal mass. One of the main reasons that Whanganui has such a wonderfully temperate climate is because the Tasman Sea is a giant heat sink. While Palmerston North experiences higher highs and lower lows than our fair city, we remain comfortably in between. That is one reason we all love living here.

When I teach eco-design, I make these general statements for people to wrap their heads around:

Water and anything that sinks in water has good thermal mass, but anything that floats in water acts more as insulation. The faster something sinks in water the more thermal mass it has, and the higher something floats in water the more insulation it probably provides. Think polystyrene. 

At its heart, a good song serves multiple functions: it moves people with its beat; it engages people with its lyrics; it rewards its writer with financial success.

Designing for multiple functions is at the heart of good eco-design. A clear example of this is the placement of the Shacklock 501 at the heart of our home.

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The 700 kilogram heating unit is situated approximately at the centre of our living spaces – lounge, kitchen, dining – so that the heat can radiate in all directions. While this may seem like common sense, a quick trip down Polson Street in Castlecliff may surprise you: at least four out of five chimneys are built on an exterior wall. Screen shot 2014-05-23 at 6.32.35 PM

As you can see from the photos, our Shacklock is built along an interior wall next to French doors that lead from our kitchen/dining to the lounge. Additionally, this location allows the sun to strike it three times during each winter day: morning, mid-day and afternoon.

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Like the Tasman Sea, the Shacklock’s thermal mass is a temperature moderator powered by sunlight energy. But, in the event of a day or two without sunshine, we can always load it with wood, which is really just sunlight one step removed.

Peace, Estwing