Sunday, May 26, 2013

Super Energy Efficient Lighting for Low Energy Buildings

There is a lighting revolution going on right now - just as there is a solar energy revolution and renewable energy revolution, and energy storage revolution!  I don't remember anyone predicting that after the information age began, we would be going through a major shift in energy and infrastructure.  And this is not to mention Passive House.  I feel like saying people building standard houses today will face some significant obsolescence issues within a few short years - namely in energy, IT, and lighting.  At first these seem like parts of the house one can easily change - but the energy aspect is a big one, and certain things are really hard to justify changing - like missing out on good solar exposure, major thermal bridges, and insulation values that don't cut it.

About the lighting:  Cree announced in December they have an LED that offers 200 lumens per watt (!).
Here's the press release:

If you are in the big box hardware stores, take a look at the LED offerings.  They are all hovering around 60 lumens per watt right now, if you get a good one.  Most are at 50 lumens per watt, often less.

How to get highly efficient lighting without spending too much?  Low Voltage distribution.
Watch the Video on What Is Lumencache:

It seems the thing to do is to separate the COB (chip on board - which is the actual LED chip) from the power supply.  This has two advantages:  purchase a single, centralized, high-efficiency, high-efficacy power supply; and then reduce the cost of the actual luminaires.  All those backward-compatible LED bulbs you can buy to replace the bulbs in your existing fixtures have the significant issue in their design that they have to have an on-board power supply, which is cheaply made to reduce costs and therefore, not that efficient. This also means the cost of those low performance power supplies is included in every bulb.  Eliminate this circuitry and you can improve the lighting.

So, we wire the house as per the Lumencache strategy, but there is another issue to handle.  LED's are pretty sensitive to voltages and current.  Say we have a living room with 12 LED luminaires, each one with nothing more than the COB in the luminaire.  We need to arrange these luminaires into groups that match the voltage and current output of the central LED driver system, or at least keep the demand within the range of output levels available at the central power source.

Welded Stainless Steel Floor - Waterproof

There are a few options for waterproof exterior decks/balconies.
  1. Use roofing on the deck - for small areas, a single EPDM membrane - black or white - over a wood frame.  I would think something needs to go on top of this to protect the membrane and make it more suitable to deck furniture and foot traffic - don't know what.  Regular built-up roofing is not my preference - I've been on this kind of balcony before and found the odour quite strong - so I assume the tar and rubber are off-gassing - anyway, it makes the space unpleasant.  I also would not do this over a deck which has had rigid insulation applied under the roofing membrane.  There is a mushy feeling underfoot, and a sense of doubt as to whether one can place furniture on the surface.
  2. Extruded aluminum deck:  These are generally powder coated extruded aluminum with either a rough or a smooth finish, such as available from Wahoo decks.  These work well, I think, but they are pricey at about $19/SF.  In our case, I couldn't find anyone local who imported them.
  3. Rubber membrane installed in a slanted scallop shape under the deck - it drains to one side - not an elegant solution, though cheap and simple.  Perhaps more suited to decks over soil, to carry water away from the house.
  4. The option we chose:  welded metal.
Welded stainless flashings not yet installed.
Why?  Cost of stainless is low right now - about $1.75/lb.  (it was about $4.55/lb ten years ago).  If you calculate the volume we are buying (1/8" thick plate is 18 cubic inches per sf), and multiply by the density of 0.3lb/cubic inch, you get the weight per sf.  Multiplying by price, we get about $9.45/SF - not too costly for smaller areas and it's an easy purchase from local sources.  I figured on a small area, I wanted to try this, and the thermal expansion issues would be minor - I expect this could be an issue on large expanses outdoors - the stainless steel has been in place a month or more now, and it is obvious that despite the high reflectivity, it does get quite warm in the hot sun - like a roof, so thermal expansion is something to keep in mind, as they do on steel roofs.  Stainless steel will also accept tons of abuse without any maintenance, feels solid underfoot, doesn't smell bad, and modifications can be made by welding to it....

I always wondered why people don't employ this solution in their projects for roofs and balcony floors, but even for interior floors.  What I found was that it was a fair bit of work, but not ridiculous, and the result is (I'm hoping) going to prove very practical and durable.  The steel frame in grey primer you see in the photos is regular structural steel, 3" deep C-channels welded to 6" deep hollow beams.  It is far stronger than it needs to be, but we ended up doubling up the joists from what is in the photos - It is a slightly difficult calculation to figure out the floor deflection as a diaphragm, and my rough numbers turned out to be close enough, but I didn't trust them, figuring the floor was supported on all sides.  The deflection of the diaphragm proved noticeable enough and it was simple to add additional joists so they ended up at 9" on centre, originally about 18" OC.  The floor feels very rigid now.  Originally, I thought I would have it plug welded from above and ground smooth, but the mag drill wouldn't stick well enough to the steel through the 1/8" stainless, so we mig-welded from below.  We tig-welded the seams from above (with some mig tacking from below) as the photos show - this is the reason for the tarp.

One thing I really like about stainless - I always feel it is easy to add to it with welding.  You needn't grind off the paint as you would have to with steel, and then re-paint after welding.  I knew I'd want to add some fittings, possibly cleats, hold-downs, etc.  This is easily done on exposed stainless.  The flashings were all welded on.  Most are 22ga, bent on site with a heavy brake - this proved tricky to weld to the 1/8" plate.  The flashing under the door was 14ga, fitted into a grove in the PVC door frame - it is just a window placed on the floor.

Distortion:  There was some distortion.  We had a 1/4"/ft (1 in 50) slope on the floor.  In some areas there was enough distortion to upset this slope and cause pooling - mainly on the long seam you can see near the 6" deep beam, where small sections were welded on.  I'm not too concerned, but we'll be working to correct this and see where it goes.

We used 304L for all the stainless - I'd done a little stainless tig-welding before, and I was familiar with the significant movement of carbon and chromium within the material in the heat-affected zone.  This causes non-stainless areas to appear near the weld afterwards - this is why you need to passivate the stainless after welding (dip into an acid bath to remove the surface areas of non-stainless material).  In our case we would not be giving acid baths to the stainless.  The 'L' in the material designation stands for 'Low carbon', which reduced post-weld corrosion quite a lot.  As it turned out, we did have some surface corrosion appearing on our project, but it was not due to the welds, which seemed to work well.  It was actually due to the use of wire-brushing with steel brushes.  We switched to stainless brushing after noticing this and all was well.

Welding was with both 308 and 309 rod - yes, welding regular steel to stainless is entirely fine and routinely done.

The reflection off the stainless is very bright - it is blinding, actually.  I was hoping this would be a good thing to raise the light incident on the deeply inset glass balcony door - but we did plan to have real wood-slat tiles or boards to block this reflection anyways.  I also plan to do some solar experiments on this balcony, so the reflective surface may be an interesting feature for this.  I've not seen anything on how to integrate this effect into the Passive House thermal modelling.  There are solar reflectors you can purchase that actually track the sun, and reflect it into a given window on the house, such as these:  This would be a significant energetic effect on the house - one that might be an attractive solution in some cases.  This one is really cute:
However, if this were part of a design, I would place the reflection-receiving windows high on the wall of the house reduce glare inside the building.

The experience with this has had me consider other metal flooring solutions:  A carbon steel sub-floor/finished floor in the basement (the beauty of this is that the subfloor is the finished floor, reducing labour and materials, and the floor plates - I'd use 4'x2' plates, screwed down - can be removed to gain access to the space beneath)......and also radiant stainless steel staircases (designed well, a radiant staircase can be good for both cooling and heating, since the stair is both a floor and a ceiling).

C3x5 (75mm deep, 7.5kg/m) C-channels welded to 3"x6" deep hollow steel tube beam - Beam wall was 3/16" or 1/4" thick.

Too bad we've not cleaned off the dark residues from the welding for the photo.  Need more photos of this part of the project.

Wednesday, May 15, 2013

Is Solar Thermal Too Expensive?

Recently we were invited to visit with Patrick Spearing and Suni Ball at Enerworks in Woodstock.  These guys do nothing but solar thermal.  We were pretty much blown away by their knowledge, professionalism, and by how much they taught us about solar thermal in one afternoon.  I'd like to recount some of the knowledge transfer as a way of note taking.

Narva Solar Thermal evacuated tubes and heat pipes

Solar Thermal Collectors:
Enerworks uses Narva glass tubes for their evacuated tubes.  Narva is long established as a UV-light glass tube manufacturer in Germany.  Making high quality tubes for evacuated solar thermal was a natural extension for them, and they've done some interesting things to address two critical issues:  Vacuum and stagnation.  Apparently you will find it very difficult to find any warranties on the vacuums of evacuated tubes.  This is because the borosilicate glass usually used is actually more permeable to helium than regular soda-lime glass.  Why use borosilicate glass, then?  I think it is because the clarity of the glass may be better than regular glass, and perhaps this is cheaper than manufacturing the low-iron soda-lime glass that Narva uses. Anyway, Narva tubes are evacuated to 10 to the -6 torr, (pretty deep vacuum), and the vacuum is guaranteed for 10 years, so this is a big deal.  The vacuum greatly improves the efficiency of the collector, and it also protects the materials inside the heat pipe from freezing.  In addition, the Narva tubes are single-wall, which makes them very robust.  The double-wall tubes are highly susceptible to breaking due to the long moment-arm that multiplies the stresses on the part of the tube that supports the whole inner glass wall.

The other thing is stagnation.  Somebody actually did a bunch of research and analysis and designed a heat pipe which self-limits at ____ temperature.  We asked how this was achieved, and the answer was thus:  by controlling all the physical factors affecting heat pipe design, one can actually make a heat pipe that self-limits its heat transfer and therefore its temperature.  These heat pipes are carefully manufactured to control:
  1. internal volume
  2. chemistry of working fluid
  3. volume/mass of working fluid
Without tight control of these parameters, there can easily be run-away temperatures and significant system stresses which can cause vapour-block, glycol break-down, etc.  It appears the Narva heat pipes contain a lot less working fluid than other heat pipes.  This one fact is sensible to me - it means they can completely vaporize their working fluid, which can limit the heat-pipe's upper temperatures, as well as reduce damage due to any freezing.  It also seems to me that heat-pipe technology is one area in which lower-cost and copycat products may be hard pressed to perform in.

Another Issue:  SRCC ratings for solar panels are somewhat skewed or inaccurate for solar evacuated tube panels.  They count the whole area of the panel without subtracting the spaces between the tubes.  Apparently the Solar KeyMark metric is much better to go by.

Will continue this another day as there is much more to tell.