The other day I was looking at energy-efficient house designs.

Not having looked at off-the-shelf designs for quite a while, I expected to see plenty of houses integrating technologies that have been known for decades (and in some cases, centuries!); technologies like the use of wide eaves, northerly-facing windows (in our Southern Hemisphere), large thermal mass, solar-forced ventilation and so on. However I was amazed to see how few mainstream Australian builders appear to have any idea of these fundamentals of architecture.

Thinking about these aspects of energy-efficient house design reminds me of a building that I once constructed. Well, perhaps ‘building’ is a term with too much weight.

In fact it was a cat kennel.

Cat kennel? Yup – and the cat loved it. 

Designed specifically to provide a measure of solar winter heating, it comprised an insulated double storey timber dwelling, fronted top to bottom with a pane of glass. The cat didn’t have access to the lower storey – instead, that area was completely taken up by a 20-litre (5-gallon) steel drum, filled with water and painted black. The drum sat on some bricks, which were also painted black. The water and bricks gave the 1-metre high building substantial thermal mass.

The first storey was much simpler – a side opening through which the cat could enter and leave, a floor with ventilation openings around the edge connecting to the lower level, and of course that wall-to-wall, roof-to-floor northerly aspect front window.

During the cool sunny days, the water tank and bricks were heated by the sunshine flooding in through the window, aided by reflective aluminium building foil placed on the inside of the walls of the ground floor. Upstairs (well, there weren’t any stairs but you get the idea), the cat was directly heated by the sunshine. If you’ve ever seen the joy with which a cat finds a sunny spot inside a house, you’ll understand just how much this one enjoyed sitting in the upper section of her kennel.

But even as the sun fell towards the horizon and the shadows reached across the glass, she’d resolutely stay in place, the kennel staying measurable degrees Celsius warmer than ambient.

The design worked in a very simple manner: the air surrounding the hot water tank and bricks would rise through the vents around the edge of the floor, warming the upper compartment. As this air cooled, it would fall through other vent holes, before again being warmed. A convectional circulation of air ensued, keeping the living areas of the residence warm for up to five hours after sunset.

I originally fitted a lift-up panel to cover the front glass at night, reducing very substantially the amount of heat being lost through the window. This lowered panel also doubled as a reflector during daytime, being covered on its exposed surface with more building-insulation aluminium foil. However, I found that the chore of raising and lowering the front panel wasn’t worth it – the kennel stayed warm enough that the cat needed no persuasion at all to use it. For the same reasons – laziness and it was working, anyway – I discarded the idea of the ‘swing-stye’ café doors that I had intended to install once the cat had grown used to entering and exiting.

The kennel stayed in use until I moved house – I can’t actually remember what ended up happening to it.

One of the problems with my design was that it had been geared too much towards providing heat in winter – and not being actively cooled in summer. (Of course, if I’d been motivated enough to lift that front glass-covering panel each hot day then the insulated kennel – complete with all that thermal mass – would have stayed much cooler than it actually did.)

So if I build another one, I think I’ll go about it very differently. Especially in one area. For there is an aspect cutting edge house design that could now be incorporated at very low cost into a solar cat kennel – electronic control.

Why not, for example, fit down-draft active evaporative cooling towers to the kennel, perhaps using long lengths of insulated 4-inch storm water pipe as the towers? And the water spray to be pumped over the cooling medium at the top of the towers? Well, that could be electronically regulated in flow. Why not use an electrical solenoid to drive the open/close position of a flap that sets the kennel in either ‘heating’ or ‘cooling’ mode? Pushbutton digital temperature control and with inputs from sunshine and temperature sensors?

Sounds good…

But hold on! How much would such a complex and sophisticated electronic control system cost? And what would you use to do it? A full PC with analog-to-digital converter cards, output power relays – and a dedicated software program? Or what about an industrial-level PLC (programmable logic controller)? Nope – all much too expensive and complex.

What I’d use instead is the control electronics of a digital climate control system from a junked car.

It runs on a solar-friendly 12 volts, it has the relays and other output circuitry designed to vary fan speed (eg the fan output could be used to run at different speeds the water pump for the down-draft cool-tower), it has motors and controls to vary cooling duct flap positions, and it has built-in heating and cooling control logic – even a digital display and often an ambient temperature read-out as well!

And if you’re thinking of buildings larger than solar cat kennels, it’s a control system that also lends itself to a budget solar house application. For example, in a small dwelling you could use the original automotive climate control fan to circulate heated or cooled air. A relatively low speed but constant flow of air – like from a glass-covered wall solar heater. And the cooling tower water pump? It could be operated from the on/off output previously running the car’s air-conditioning compressor clutch.

Now you sure wouldn’t want to buy a new car climate control system for this application – it’d cost the earth. And you also wouldn’t want a wrecker orphan that you couldn’t find a wiring diagram for – but these issues aside, a car climate control should suit this type of application perfectly. Well, as perfectly as the price allows, anyway.

Hmm, a solar cat kennel with digital remote climate control… I know one feline who for sure would like that!