Passive Solar Renovation

The other day we were driving home at about 5:30 – just after sunset – and could barely make out plumes of wood smoke exiting cowls on Heads Road and Cornfoot Street. The day had been sunny, but cool, as would be expected in July. Our curtains were still open, so we hurried along while remaining under 50 km/hr.

We parked, grabbed the bubs and groceries, and walked inside. Upon entering our old villa on Arawa Place, we were pleased to feel the warmth gifted us by the sun. The thermometer in the kitchen read 23 degrees Celsius.

By now, my wife is tired of hearing me say, “Wow, it’s so warm in here. I can’t believe all those houses had wood burners going.”

I chalk the difference up to legacy and sunlight.

 Before

 After

Unfortunately, Whanganui has been left with a legacy of thousands of homes built with seemingly no regard to the sun or even thermal comfort for that matter. Many of the dwellings I’ve audited during the last three months through Project HEAT share these characteristics: cold in winter and hot in summer.

Our home would have been the same before its passive solar renovation. As a matter of fact, we met a woman shortly after we bought the villa who told us, “I’ve been in that house before. I babysat there once. That’s the coldest house in New Zealand.”

While no longer the coldest home in the country, it is still far from the warmest. But on a sunny winter day, we find ourselves toasty warm inside long after dark, and with plenty of solar heated water – all free energy with no daily line charge!

The primary way we tapped into this free, abundant energy source required no specialist equipment and no specialist skills. As a matter of fact, the ‘solar collectors’ we used already exist in every home in the country: windows. The problem with most homes is that the windows are evenly distributed between the north, south, east and west.

On sunny winter days, only the northerly-facing windows have a positive energy balance. In other words, they gain more heat through sunlight energy during the day than they lose through radiation at night (if properly curtained, as you would). All of the other windows have negative energy balances even on the sunniest of winter days.

For us, the obvious solution was to ‘shift’ windows from southern exposure to northern exposure. While retaining roughly the same amount of total glazing, we were able to dramatically improve the solar gain of this old villa where – once upon a time – someone decided to put the toilet in the north corner.

 Before

After

Shifting the toilet to a more appropriate location was accompanied by opening up the north corner to create a bright, warm, cosy kitchen with French door access to abundant backyard vege gardens and an outdoor pizza oven. All of the work was done in accordance with the New Zealand Building Code, with special attention paid to weather-tightness and bracing.

At the same time, we insulated the ceilings as well as those walls that were opened up during the renovation. And finally, we added thermal mass inside of the building envelope to moderate and store solar thermal energy, but that, my friends, is a story for another day.

Sun Angles: Winter and Summer

Mid-way between the autumnal equinox and winter solstice we find ourselves in the unenviable position of short days and long nights, and looking forward to even shorter days and longer nights for some weeks to come. Despite this, our renovated, passive solar villa has been performing well – the indoor temperature has not dropped below 18 degrees in 2013. (More on this in subsequent columns.)

The scientific explanation for the change in day length is that the Earth’s axis is ‘leaning’ the Southern Hemisphere away from the sun slightly more each day until June 21^st. The way we perceive the sun in relationship to ourselves is that it rises a little further northeast and sets a little further northwest each day, as well as hanging lower in the sky at noon. Mind you, this is gradual. It takes 6 months for the ‘tilt’ to change from the sun’s highest point in the sky – and longest day of the year – and its lowest point in the sky.

A good eco-designer takes his of her lessons from nature. And nature takes his or her lessons largely from the sun. Using the transitive property, you can get the rest.

In the space below, I’ll explain two examples of good eco-design that take full advantage of the predictable behaviour of the sun: one biological and one physical.

 WBG, sold out quick-as.

If you were at Whanganui’s Saturday market for its last session before Christmas 2012, you may have been among the lucky few to have purchased The World’s Best Garlic. There is a lot that goes into growing The World’s Best Garlic besides humility. One important ingredient is timing. When I arrived in New Zealand five years ago I was told: “Plant garlic on the shortest day of the year and harvest it on the longest.” Generally speaking, this translates into June 21^st to December 21^st.

Please be aware, however, that this has nothing to due with full moons, cow poo vortexes, or Grecian Formula 44. It does have to due with soil temperature and gradually increasing sunlight day by day for half a year.

Also be aware that growing The World’s Best Garlic involves the right kind and amount of compost, mulch, and watering regimen, all of which are highly protected trade secrets.

The other example of good eco-design involves two examples of solar hot water that are dramatically different from one another but each serves its own users most appropriately. One system is set on an acute angle and one on an obtuse angle to the sky. In other words, one system is set up for maximum efficiency in the winter and one for maximum efficiency in the summer.

Solar hot water set for a winter sun. 

The solar hot water system on our home is set for a winter sun angle because we know that there are fewer total hours of daylight in winter, and that our insulated tank loses more heat each night in July than in January. There also tends to be more rain and clouds in winter, so we need to take advantage of every clear patch and fine day.

Even set at this high angle, our system can boil over any given day of the summer if we don’t use enough hot water. This ‘boiling’ water shoots down the gully trap as a safety feature to the system.

Solar hot water set for a summer sun. 

So who, you may ask, would set their solar hot water system for a summer angle when there are plenty of long, fine days. Answer: YMCA Central’s Raukawa Falls Adventure Camp. They get heaps of visitors all summer long, many of whom want a warm shower at the end of each day. But for much of the winter, the camp lays more or less dormant, and a back-up wood-fired hot water system can easily fill in when needed.

As spring follows winter, so form follows function…if the design is good.