Welcome – The first post is as a response to Phil Warner – a proponent of the ‘solar roof’ renewable and sustainable home heating system first outlined in 1944 by James Bryant in Brisbane, Australia – outlines of discussions on solar roof follow – Phil has promised to contribute over the next few weeks.
Solar Roof – Random Postings and Thoughts:
The SolaRoof uses no dark insulation – no shade cloth or insulation beneath the
inner glazing. The SolaRoof is highly transparent to PAR and the glazing
temperature (which is our thermal energy exchange surface area) is always within
a couple of degrees of the TMTemp. In the winter there is very low loss during
the mid day thermal energy collection period, since there is no deltaT -very
little difference in temperature of the inner and outer glazing. So, all the
heat of condensation is sponged up by the large liquid thermal mass with a
temperature gain per sunny day that is small – say 2C to 4C only and losses on
cold winter night of 1 to 2C when we have a 30 inch bubble cavity. So, we have
low demand for conventional energy during the heating season.
Dual Solar – Thermal store houses:
1. Houses tend to be much better insulated than even dynamic foam buildings. They don’t gain nearly the energy in summer that a greenhouse does.
2. Modern house contstruction is based on, what? a 3 hour air exchange through heat recovery ventilators. Not a 90 second air change.
Now admitedly I’m comparing super efficient houses to standard greenhouse. But we’re looking at a performance gap of at least two orders of magnitude. While a completly active solar green house is a final destination, I don’t think we will achieve it in one step.
That said: The dual thermal store is a clever enough idea, that partitioning your thermal store makes sense, as it is a tricky retrofit.
Putting a pool under the greenhouse seems costly. In effect you are making either a swimming pool, or a full basement, combined with an earth roof.
Seems to me, you might be better off building on a lake.
Or building by a lake. While a swimming pool is expensive dugouts cost on the order of a buck or so per cubic meter. You need cooling only for the summer. What are the thermal characteristics of a 15 foot deep dugout covered with white silage film plastic? Remove the film in fall. Circulate water from the dugout over the top of the ice all winter long. By spring you have a pond that is mostly ice. Ponds here are heated by both sun and wind but even by the end of summer, the water is still only about 70F. Shielded from the sun, I bet it would be 50 degrees.
In winter then you need to scavenge heat. So you only need to incorporate one thermal store into the building. It can be smaller, and doesn’t need to be the entire subfloor.
In initial construction, there may be merit in NOT tightly integrating systems. Nick has a bunch of good articles on his web site of the concept of ‘solar closets’ well insulated structures that get water very very hot, using barrels of water for storage.
Perhaps this becomes the north wall. Building above ground is generally cheaper than building below.
One of the concepts I’ve been having trouble with in the dual store system is timing. You want one store of heat at a high temp for night time heating. You want one store at a low temp for day time cooling and dehumidification.
Using the water film cavity model, would someone walk me through the cycle? I’m having trouble figuring out when the cold store is rechilled, and the hot store re-warmed, AND dehumidification is still happening at the right times.
Basic frame and film for a green house runs on the order of $4 per square foot. Price with conventional sets of addons ranges from 7 to 12 bucks a square foot depending on how fancy you go. Heating/cooling costs vary by climate, but I’ve seen figures of 3-5 bucks per square foot per year. A neighbor of mine running two crops of seedlings per year in 7 40 x 150 green houses (42000 square feet) said his heating bill averaged $20,000 per month for his January-April crop. And that was when natural gas was 20 cents a therm.
However the largest single operating cost is labour. We have a coal generating station that offered free hot water (pick your temp from 140 F down to 40 F) to either fish or greenhouse operators. (The amount of hot water: 3 GW. Right now they use a 3 square mile lake to cool the water. It’s enough heat to heat over a square mile of double film greenhouse space even at our winter temps of -40.
While various people looked at the offer, they figured that it would cost too much to bring labour in. Greenhouse jobs pay $10/hour here — 2 bucks over minimum wage. You don’t drive far for a low wage job. The fish operation was closer to being viable — it had a higher value of product per man hour, and some processing could be moved to a nearby processing plant. But still it wasn’t good enough.
For Solar greenhouses to make a go economically, they have to be cost neutral with conventional greenhouses in no more than 5 years, and 3 would be better. That is, the energy savings at the end of 3 years needs to pay for the difference in construction costs. If my recollection of energy figures is correct, then 3 years energy is on the order of $12/square foot.
Can you make a solar system greenhouse that costs no more than $12 to $20 (3-5 years) more than the cost of a conventional greenhouse?
People in the horticulture business tend to be conservative. They have enough unknowns dealing with the interactions of plants and light and water and chemicals and bugs and weeds, and disease.
Bubble Windows Debate
James Farham from the A.N.U. physics dept. (http://physics.anu.edu.au/) advocates ‘bubble windows’ as part of a solar powered , eco home – here is a fascinating article he came up with.
* a bubble tube floating on the surface of a soap solution can generate bubbles with reasonable efficiency.
* a fan that can operate that bubble tube quietly
Would it be reasonable to make bubble-windows?
e.g. build a window like an acquarium. Make it as thick as the wall. Put 2″ of bubble solution in the bottom, float your bubble tube in it, and have a small fan that moves air from the top of the cavity through the bubble tube.
Most twin pane windows are little better than R2. You can make this a bit better by filling the interwindow space with argon, but everything I’ve read says the argon is gone (it ar-gone!) in 5 years.
A 6″ thick bubble filled space is something like R6, possibly more depending on who’s statistics/lies you believe.
In operation it has a very small heat store. So the system as a whole will be the average of indoor and outdoor temp, yes? This will mean that by the time temperatures outside get to -20 C, then the entire solution supply will freeze. Possibly a good idea for zone 5, not for zone 3.
Yes, this works well – any shop with a compassed air supply can also use such an
approach to building a self contained bubble window with less cost and thereby
investigate the R-value of bubbles. I did this type of experiment in London
years ago with friends at a an engineering firm. Yet I saw no follow up to
determine the R-value. I visited the national construction research agency of
the UK called BRE (Building Research Establishment) to discuss action on high
R-value windows – nothing happened to follow up. These public agencies around
the world are avoiding the determination that such very high insulation value
windows can be constructed – not with costly, exotic technology but with simple
liquid bubble methods that are low-cost and provide 10x more results than the
best of the high tech windows.
When do we find some Universities (mechanical engineering schools) who will
cooperate to generate the data and verify (multiple replications of results) the
insulation benefit. Automotive air blowers work good for this purpose. What is
this idea for a floating bubble generator pipe or duct?
I envision the bubble window of this type to use a blower with a snorkel to the
top of the window cavity. The bubble window will sit into the wall opening flush
to the outside wall but extending (in thickness of the cavity space) into the
room where there can be a built in reservoir in the lower part of the window.
Depending on design this soap liquid reservoir would be supported at its base on
the floor. In this way the liquid is away from the exterior cold, behind the
insulated wall and the bubble cavity is made thicker with an insulated framing
method to assure the effectiveness of the insulation at the edge of the bubble
window. Of course it is advantageous that this window is large to reduce the
effective cost per square foot of the system. If it is a window wall then it is
useful to implement a bubble re-circulation path for true control of bubble
regeneration and destruction.
The liquid reservoir – in its position within the room is where a conventional
radiator would be located and so is not taking away floor space while giving
additional effectiveness to the bubble window. And, not only can the bubble
window insulate, it can also incorporate a radiator element with connection to a
hydronic cooling/heating system that can maintain the bubble window reservoir at
a set cool (for the summer season) or warm (for the heating season) temperature
by connecting to the building heating/cooling.
I would love to see a floor to ceiling bubble window that provides much light
and is as super insulated as the best wall. This is using two single glazing
layers – so it is not technically difficult to build. Please, those who build,
report your results to encourage others!