Thermal and Solar Heating & Cooling in an Earthship Style Eco Home

Okay, so we’re gonna have a look at the six Earthship principles.

We’re just going to cover principle one here –  solar angles we’ve discussed previously at the meeting of the eco home.

You can grab that from this presentation –  I’ll drop it in the appendix at the bottom this is available on the website, and it’s live on on Google Drive – I’ve published it as a web page as well.

So, let’s have a look at solar heating – also known as solar gain or passive, you might have come across a term passive have seen passive house designs if you’ve been investigating eco homes at all.

It’s fairly simple – so looking at this slide sunlight enters the building during the day the floor walls etcetera absorb energy and get hotter during the day.

This stored energy is then useful during colder hours such as the nighttime winters etc – they’ll be radiating that heat back when the temperature of the air in th eroom is lower than that of the floors, then they’ll start releasing that energy into the room.

The problem in Taiwan, I know, usually is too much heat okay for about eight or ten months of the year! So we’ll look at ways of reducing energy from the Sun later such as roof overhangs cable awnings shades blinds curtains etc.

We’ve got in the model for the Eco village some bamboo and trees to show how shade from those effects where the Sun comes into the building or onto the walls of the building as well

A quick question to think about if you’ve if you’ve never touched on this subject before is which materials would be better for absorbing energy? Stone Metal Water Air?

Air and water being fluids that you can move about right from place to place….water being much denser than air so capable of storing much more energy.

Stone and metal are solids, dense, will store a lot of energy.  Pound-for-pound what’s better?  Stone, or if you can get Rammed Earth that’s effectively as dense as stone.  Compared to metal that you have to mine – yeah there’s a lot of a lot of expense with metal so you might decide to choose stone if you’re gonna use that as some kind of energy storage or heat sink in your building.

So thinking about why those materials are better for absorbing energy in certain situations pros and cons of each is useful.

There’s a couple of links here for one on solar gain on Wikipedia and one about solar chimneys that’s old tech – very cool, solar chimneys 😉

So, on to Thermal Cooling – also known as a convection engine.

When you look through the Earthship books, literature, and Earthship websites they call it a convection engine here and there.

We can use heat to cool buildings – hot air rises – as we all know if you put energy into air it will become less dense.

It will expand, so hot air being less dense than cooler air, the cool air will sink, the hot air will rise, and we can use a simple vent in the roof to allow the hot air to escape.

These are gravity operated – you can pull them open with a simple rope.

You could have a solar chimney on the outside of the building doing this as well.

Earthships typically with a lot of glass at the front are probably heating up that floor and gray water plant at the front enough to to give you some some decent convection up through the roof.

When we put a simple vent in the roof we can allow the hot air to escape that way and of course as that goes up inside the building and escapes through the vent in the roof, fresh air is going to get drawn in through the ventilation pipe which runs through the earth Bank at the back of the building.

As the air comes through that pipe from the outside it’s cooled by the temperature stored in the earth.  Or, more accurately, the earth bank is heated by the warm air being drawn through the vent pipe?  Maybe 😉

Underground is gonna be lower generally than the temperature outside in the summer – almost definitely in the Sun unless we have a really bad day.

So the heat in the air in the pipe is going to warm up the the stainless steel or whatever you’re using in in the ducting in the pipe itself – the metal in the ducting will pass that heat then through to the the earth in the earth bank.

Obviously there’s a lot of mass in that earth bank so that Earth Bank will absorb a lot of energy from from warm air coming through it from the outside before you significantly warm up that earth bank.

The hot air going up out of the roof vent creates a flow with the warm air coming through the pipe through the earth Bank being cooled and released into the room, then warming up at the front of the building and going up out of the roof.

Solar chimneys again – take a look at that old effective tech.

Wen you look at this diagram this slide here you might see a solar chimney on the outside of the building on the outside wall here the ones that you see in the desert really old tech had just just stone a lot of the time you could make them out of sheet metal.

I suppose anything that’s going to heat up while in the Sun.  Then the vent would go out through the front wall and into the solar chimney a really simple thing to do.

Let’s have a look at the next slide so here we’ve got some data from ResearchGate now this was in Nicosia yes Nicosia Cyprus not sure what their humidity is like compared to Taiwan but yeah looking at their temperatures in the summer – this is somewhere around 35 40 something like that ambient temperatures.

The spiky pink line – that’ll be daily ambient temperatures by the looks of it, so air temperature I suppose the temperature around us, and this zero meters here this will be ground level I suppose, ground level temperatures.

So the Green Line is the temperature under the ground at a depth of one meter and you can see you’re already getting a significant drop from surface temperature here just by going down a meter.

So if surface temperature here is about 42 degrees come down from 42 degrees we’re getting a temperature underground at a meter of about 26, 27 degrees by the looks of this.

So you’re still getting a drop from from 40 say down to 25 26 so you’re still dropping 15 degrees 25 might not be quite comfortable in the house.

But it’s still gonna knock a lot off your energy bill if you run in some kind of HVAC system heating ventilation air conditioning system, it’s gonna chip quite a bit off your energy bills.

The sweet spot to me if I remember rightly from looking at this graph I think – it’s the orange line here that I’m tracing out now two meters orange line here you go to two meters deep – maybe from about eighteen degrees centigrade or Celsius up to about 25 degrees Celsius.

So that’s already a much more stable range of temperatures 18 to 25 Celsius, at 2 meters.  In terms of construction or excavation that’s probably not too difficult to get down to two meters.  You start getting down to four meters you’re definitely gonna need some much more heavy-duty excavating equipment – shutters etc.

You don’t want to be up in it if it collapses right!  So, trenches for for that kind of depth are much more difficult to construct – but two meters yeah it’s probably doable without adding too much expense to that part of the project, and you get a really good seven degree variation in temperature.

But the interesting thing about this is there’s a lag – the lower down you go in in the ground the more time it takes for for the Sun to heat that ground up.

So it’s a meter there the Green Line shows it well outdoor temperatures here are about forty or ground temperatures here at zero meters on the blue line are about 42 degrees – then you look at the Green Line the curve is lagging behind it as the ground takes time to warm up.

So even though at a meter depth you still get more variation in the ground temperature – it’s still only around 25/26 because the ground hasn’t warmed up yet.

It’s taking time to catch up with the summer, to warm the ground up.

If you go into the orange lines – the orange line two meters here then it’s down at about 20 that’s still gonna take another 60 days or so looking at looking at the graph here from about 200 days to about 275 days.

It’s gonna take another two months or so until the ground temperature at two meters, with all the energy from from that summer heat has made its way down, so 25 degrees on the orange line here in the summer might be might be really nice to have that coming into the building.

You’re dropping down from ground temperatures at forty two, daily ambient temperatures up near thirty somewhere, 20 degrees might be very pleasant so yeah that seems to be the sweet spot.

You can have a look for more online for that in terms of thermal performance.

This graph I’ll try and break this down – you’ve got time of day from midnight here running through to midday, and then to midnight again.

And this is showing the temperature spike at the warmest time of the day – the red area, and the reddish pink area at the top of the chart here is showing high temperatures.  So… I’m assuming this is for the highest point here would be the highest temperature in the summer about 40 degrees C.

And I’m assuming this is 6 a.m. as this is usually the coldest time of day, just before the Sun comes up.  So this is gonna be the lowest temperature in the winter at minus 30.  So you can see they’ve got a huge temperature difference here even in the summer.

They’re probably getting down to 15 degrees or something in the summer by the looks of it.  Anyway – there’s a big big temperature difference so you can still see with the amount of temperature variation they get from 40 degrees plus centigrade down to minus 30 centigrade – this blue line is no fuel at all, that’s just the building with sunlight, air vents in the roof, air ducts bringing air through the earth bank in the bank and it’s staying around 21 degrees in the summer, something like that.

So to go from no fuel which is the blue line to the Comfort line which is the orange line above it it’s a very small increase in energy to get from 21 to 22 degrees C.  Compared to heating your house from it’s freezing, or cooling it from 40 degrees down to 22 C. 

So that gives you an idea of not just how little energy they use but how stable that line is throughout the year.  That’s a really stable line for temperature variation.

If you put the concrete box that I’m in- if put that room out in the Sun and out in the freezing cold the temperature in here it’s going to be very very similar to the temperature out there without some serious energy input such as air conditioning and so on.

So, that little rant over – that’s a really good graph to look at it for temperature stability and that’s about it for thermal cooling. 

You can have a look at solar chimneys and we’ll get into shading and cable awnings and stuff like that in the next presentation!

By |2019-02-06T16:18:05+00:00July 22nd, 2016|Latest Articles|