Category Archives: design

solar water heater

Passive Water Heaters

The last topic I’m going to cover in this series on passive design is passive water use. Heating water consumes a considerable chunk of the energy that the typical house uses, so if you can cut your active water heating it can pay off both in terms of cutting energy use and cutting your bills.

While passive solar water heating systems are less efficient than their active counterparts, they tend to be cheaper, reliable, and long lasting. There are two basic types of passive water heaters, the integral collector-storage passive system or a thermosyphon system.

Integral Collector-Storage  (ICS) Passive Water Heater

An ICS system works best in more moderate climates, where the temperature rarely falls below freezing.  The ICS system has exposed pipes, so above freezing temperatures are necessary to keep the pipes from freezing and ruining the system.  The ICS system is made up of an insulated storage tank, a solar collection tank and the pipes that connect them. The solar collection tank is used to heat water in batches using solar energy. Once heated, the water passes into the insulated storage tank, and cool water fills the solar collection tank again.

Thermosyphon Passive Water Heater

A thermosyphon consists of a tank, pipes and a solar circulator. In this case instead of the sun heating a large tank of water, the sun heats winding pipes of water. Cool water flows from the high positioned tank into the lower circulator where it is heated. Warm water flows from the circulator back into the tank due to natural convection caused by the temperature gradient.  An indirect thermosyphon that uses glycol fluid in the circulator loop can be used in colder climates if the piping is adequately insulated.

If you’re interested in building your own passive water heater, you can find some good information here.

photo: “Solar Water Heater boiler” by gmourits CCBY


Passive Cooling through Ventilation

Our ancestors came from hot climates, so we’ve been working on keeping the shelters we live in cool for ages.  There are a number of different ways to accomplish this, and today I’m going to write specifically about ventilation. Moving air is incredibly effective at cooling – especially at cooling people -because it helps sweat or other water evaporate. Think about it, have you ever been sweaty and stood in front of a fan? You cool off quickly, even to the point of getting a chill as the moving air evaporates your sweat.

Here are four methods of ventilation that are used around the world to help keep our homes and other buildings cool.

Cross Ventilation

Cross ventilation relies on wind moving through a space. You’re probably already familiar with the fact that if you open two windows across the room from each other, you are going to get a better breeze through a space than if you only open windows on one side of a room. Because of this, open floor plans can be great for passive cooling through ventilation. An important factor to note is that the two openings – the inlet and the outlet – should be of equal size, or the outlet should be larger for optimal air flow.

Stack Ventilation

Have you ever noticed the slated window on the top level of a house? This is a gable vent, for stack ventilation. Hot air rises and escapes through these openings. As it does so, it causes a pressure difference between indoors and outdoors, and this causes cool air to be drawn into a house through vents strategically placed near to the ground.

gable ventilation

Untitled” by Wonderlane, CC BY


Some Indian architecture makes use of a lattice screen called a jaali (or jali). The Jaali will often be placed lower to the ground to allow cool air to enter a room, and the lattice screen provides diffused light, while also providing privacy. They are quite beautiful as well.

jaali for ventilation

Jaali” by Nagarjan Kandukuru, CC BY


Traditional Persian architecture often makes use of a structure known as a windcatcher (other names include shish-khan, a badgir, or a malqaf). When used effectively, windcatchers are able to cool a room enough to keep water at near freezing temperatures throughout the summer months. A windcatcher is a raised tower structure, typically on the roof of a building. It may have 4 or 8 sides, and has openings on 1, all 4, or all 8 sides, depending on typical air patterns in a location.   A windcatcher can work in three different ways. It can, as it’s name suggests, catch wind and direct it downwards into a room. It can also function as a solar chimney, allowing hot air to escape, cause a pressure gradient, and pull in cool air. In a climate that has a diurnal cycle – hot days and cold nights – this is especially useful. When paired with good building materials such as adobe, a windcatcher can keep the inside of a building quite cool. Thirdly, it can be paired with an underground canal. The windcatcher will pull warm air upwards, and with properly placed inlets, pull air in along the ground-cooled water. The water will cool the air, and the now cooled air will be pulled throughout the structure.

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Passive Cooling

There are a number of simple ways you can use passive design to keep your already constructed building cooler during the hot summer months, as well as some really cool building techniques that can be incorporated into construction to keep a building cool.  Today I’m going to cover the simple, already constructed building methods.


Passive heating is all about trapping the heat from the sun inside your building. Likewise, passive cooling is about keeping that heat out. In the posts about passive lighting and passive heating, I talked about how important southern facing windows are to letting light and heat into a building, but what do you do with those windows during the summer? Using an awning on your southern windows can be a great solution. The angle of the awning will keep out the harsher rays of the sun in the summer, and in the winter, when the sun is angled lower in the sky, the light and heat will still be able to come in under the awning.

Shade Trees

Planting a deciduous shade tree in your southern yard can help keep your home or building cool as well. In the summer months, the leafy tree will provide shade for your southern windows, and if the tree is tall enough, for the roof as well.  In the winter, the tree will drop its leaves and let the light and heat pass through.


Using thick curtains on southern and western facing window during the day can also keep keep a room or building cool by keeping the sun out, in the evening when the harshness of the rays have lessened, you can open the curtains again to let in the light.

Air Flow

Get that air moving. Open up windows on all sides of the building, and keep interior doors open as well to help allow the air to pass through the building.

Next week I’ll get into some of the ways that we can use construction to help get the air moving, and keep it cool in the first place.

Are you looking for an introduction to passive design? You can find it here.

Oh, hey, Building Earth has a facebook page now.  Keep up to date on posts and other interesting green news by liking us!

Passive Heating do-it-now

Ok, maybe you don’t have any big renovations planned for your home, but you still want to make your living space more heat energy efficient. Let’s go back to the second goal in passive heating:  Seal up your building so the heat doesn’t escape. Here are some simple things you can do to seal up your home and keep it warm without burning so much gas this winter.


The thing about warm air is that it can escape through really tiny holes and cracks, so we want to do our best to fill them all in. Start by checking your windows, where the frame of the window comes in contact with the wooden sill. Is it sealed? If not, use caulk all the way around to fill in and block any potential leaks. Now look at the junction between the glass and the window frame and do the same. You can find clear caulk especially made for windows for this project.

Window Plastic

To add an extra layer of sealant, (or if you live in an apartment and can’t get permission to caulk your windows,) go with the old standby of window plastic. Wipe down the sill well, and make sure it is dry before putting down the double sided tape to help ensure a good seal.

Weather Stripping

Doors are the other prime leak location. Especially older wooden doors whose wood has begun to weather and warp. You can help stop up those possible leaks by putting weather stripping on the edges of the door. A draft guard along the bottom edge works well to block leaks too. Make sure you measure your door and the gaps between the door and the jam to ensure you get the appropriate size weather stripping and draft guard. You want the weather stripping to be slightly thicker than the gap it is filling to get a good seal. So there you have it, three simple ways to make your house better at passive heating. The great news is, these three things can also help keep your house cool during the summer as well. And we’ll have more on that coming up.

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Are you looking for an introduction to passive design? You can find it here.

Oh, hey, Building Earth has a facebook page now.  Keep up to date on posts and other interesting green news by liking us!


passive heating

Pre-construction passive heating

Since my post on passive lighting got a little unwieldy (900+ words! Who has time for that?) I decided to break this post in two in hopes of avoiding another monster post. So today I’ll be covering passive heating from the perspective of what should be done before or during construction of a building.

I know, I know, it’s the beginning of July, and probably the last thing you want to think about is keeping your house warm. But it might be better to think about this sort of thing now than in the middle of January when you open your heating bill. In fact, you might still be recovering from the number those polar vortex heating bills did on your budget this past winter. So I propose that it’s always a good time to think about how you can more efficiently (and cost effectively!) heat your home.

Passive heating ultimately comes down to two goals:

  1. Capture heat from the sun.
  2. Seal up your building so the heat doesn’t escape.

Just like with passive lighting, before construction begins is the best time to start thinking about passive heating. Some forethought on position and building materials can save all sorts of heat energy down the line.


The goal when siting a building for passive heating is to put the broad side of the building in direct sunlight. Here in the northern hemisphere, that means the south side of the building should be the broadest side. The west side is also a good choice because the afternoon sun is stronger and hotter than the morning sun.

Windows, Walls, and Floors, oh my

So, now that you’ve set up the position of your building to soak up the sun, you need to get that heat from the outside in. This can be done by putting nice big windows on the sunny side of your building. Some types of window glass are better at allowing heat to pass through them than others. For passive heating, look for a solar heat gain coefficient (SHGC) of 0.6 or higher.

And once the heat is inside, you want to hold it there. Flooring and wall materials such as concrete and tile are great at holding onto heat (this is called a solar mass). So put a tile flour under your big southern window.  And build that southern wall with bricks or concrete blocks.

Side note: In our neighborhood in Detroit, we often saw that flowers planted beside a brick building were among the first to pop up in the spring – the bricks held onto enough solar heat to convince those seeds to germinate a bit earlier!


Insulate. Insulate. Insulate.

Insulate more than the minimum recommendation. Insulate on the outside of the thermal mass (because you want to keep that heat inside!). Remember, heat rises and wants to dissipate into cold air, so insulate your roof especially well, and your north wall too.

So there you have it, three main areas of consideration when it comes to construction and passive heating. If you’re planning on getting your house re-roofed this summer, take some extra time to check the quality of your roof insulation, and add some more!

Are you looking for an introduction to passive design? You can find it here.

Oh, hey, Building Earth has a facebook page now.  Keep up to date on posts and other interesting green news by liking us!