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Tony Watkins

 ~ Vernacular Design 

Energy efficiency 2008 Print E-mail

ImageFirst you need to decide that your house will be a collector of energy rather than a user of energy.

A sustainable house produces a surplus of energy.









ImageThe following notes clarify some of the basic energy issues lest anyone is confused. Remember of course that energy efficiency is not the same as sustainability. In the UK they get really mixed up.

1) Solar landscape. A courtyard to the north with a heat-sink surface is an ideal solar collector. Keeping the wind out gives you control over the wind chill factor. The English farm-house was a U shape, while Chinese vernacular had a walled courtyard in front of a rectangular house. The heat sink comes free if you use a driveway or a paved footpath. Cats sleep on the footpath after the sun has gone down because they understand all this. Remember that frost can be caught in hollows. Even a slight southern slope will be much colder in the mornings than a slight northern slope. Trees are really important long before you begin to think about architecture. They create a micro-climate, provide shade when it is needed, and can protect you from wind. A swimming pool takes time to heat up and also time to cool down, just as the ocean does. The ocean is good news for New Zealand in tempering the effects of global warming. It is not rocket science to use your water storage tank in the same way. (I assume a house should collect water, so this heat sink comes free.)

2) Solar design. Face north and have a solid well insulated wall to the south. A kitchen facing east will be cheerful in the morning while one facing west will be too hot when you are cooking an evening meal. On the other hand bedrooms facing west will be warm when you go to bed. With solar design it is the floor of the house or perhaps a wall with some thermal mass which evens out the temperature through the day. The next move is to have a conservatory on the north to gather energy. This is only the process of taking a Trombe wall and making it big enough to grow vegetables in. Again the space comes free so this is a great way of saving money.

3) Remember that the 100mm skin house is a really stupid idea. If you ask the wrong question you will, of course, get the wrong answer. Solar design means something much more sophisticated than reducing life to dull, uniform mediocrity. The archive where you store your first edition Shakespeare and other family heirlooms needs a very high environmental standard. Keep out sweaty people out as well as your steaming shower. On the other hand who cares if the bathroom leaks? It is wet inside anyway. When you end up with a wide variety of environments they provide valuable design elements and the designer can balance one against another. This reduces the environmental cost of your house.

4) Solar water heating is just that. At its simplest you throw a coil of black pipe on the roof and have a hot shower. At a more sophisticated level it becomes complicated when the ordinary householder cannot purchase any decently designed unit. Sorting that out is the task of the NZIA and the big firms like Fisher and Paykel. The individual really cannot do it. There will only be real change when solar water heating becomes a designer item, like a refrigerator. Meanwhile remember that hot water goes uphill, so there is logic in putting your unit in the garden rather than on the roof.

5) Photovoltaics are different. They produce electricity. They do not like heat so putting them on the roof actually reduces their efficiency. Unlike solar water heating they need sunlight not heat. Be careful about overseas data. A few leaves can reduce the efficiency of some panels down to 20% or less which makes them very expensive. Go for amorphous silicone. It keeps its efficiency up, and is also effective at low sun angles. To understand this just check out a demonstration unit. You will be amazed.

6) Your next choices relate to the whole system. The panels will output DC so if you want AC you will need an inverter. If you are in a remote location you will probably choose 24V or 12V, with appliances available for both these options. Storage is the really big problem, and the real answers remain to be found. Any deep storage battery, even at 6V, is very heavy. As much as a person can lift and too much to carry in to a remote location. If you are in a grid location the theory is that you can use the grid for storage. When you are producing more than you are consuming you feed the surplus into the grid, and when your demand reverses you draw down from the grid. You stay on 240V AC for all this to happen easily.

7) You then need to choose between aggregated and disaggregated systems. All this means is that your pocket calculator has its own cell and its own storage system. Each power tool has its own charging unit. You avoid the problems of loss in DC cables, and the need for short runs. Spreading the risk of failure means reducing the risk. Updating components is generally the way to go rather than updating the system, as we discussed elsewhere.

8) The real problem again is that you cannot buy an off-the-shelf from the appliance store down the road. At the moment everyone is bombarded with theoretical information instead of simple solutions. Hopefully this will change soon.

9) When you have all this sorted out you go back to the beginning and start all over again making a choice between passive and active. Personally I would always opt for passive. The particular problem in New Zealand is that we get four climates in a day, and you need to be a particular kind of person to enjoy spending all day opening and closing vents and flicking switches.

10) With landscape solar passive means getting the big decisions right and then letting the rest look after itself. There are a few things you need to watch for like keeping summer sun out while letting winter sun in, but those are just part of any competent design.

11) With solar design passive means that a couple of times in a year you adjust the vents in your Trombe wall or conservatory. Where heat does need to get moved around the ideal is to use surplus heat to do that. This is the same idea as a water ram. Shift the hot air from under the roof down to a low level. It is a good idea to have a cool head and warm feet when you are working at a computer, so you need to reverse the natural temperature gradient. The hacienda in a Western film had it all worked out. The OM system in Japan makes for a very comfortable house even when it is snowing outside. Active means a few pumps to shift the air around. A refrigerator is a simple active system. We suck the heat out or the inside and spit it out the back. The foolishness is that we do not then use the heat for anything and it goes to waste.

12) With water heating passive means getting the panels down so that the cylinder does not need to be up in the sky.

13) With photovoltaics passive means, for example, not needing to track the sun. That is the logic of going down the amorphous route.

14) Having said all this it is important to remember that really simple active systems, like opening a window, are no more difficult than putting on a pullover. I do not want to sound too negative.

15) Beware of designers who do not look at the whole picture. Living in a sealed box is extremely dangerous. Insulation and double glazing can be killers. Beware of the various star rating systems. They may be great for your archive but they are not good for you. There is a lot of really bad advice floating around.

16) If you are now even more confused remember that taking one step in the right direction is better than being paralysed by the complexity of it all. In looking at the “Golden Home” design it became clear that a few simple changes could make an enormous difference to comfort, enjoyment and reduced running costs. When Councils and house designers fail to give you good advice you unfortunately have to be able to take the initiative. Your house is going to around a long time. Fifty years for a marquee, but five hundred years for sustainable architecture, as Kelvin said.

17) Designing for deconstruction and re-assembly, both-and design rather than either-or design, time-indexing, and a lot of the other things we discussed interact with all these decisions, but I will leave that for another note.

All this in response to a student question on 29 March 2008.


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