Great web-site for Green Building

I have 2 new favorite web-sites! The first is Functional Fenestration as I mentioned in my last post. The second is Green Building Advisor.com. We are now pending on a house with an enormous vaulted ceiling and it sounds like re-insulating it will be expensive and difficult. While trying to research the issue I came across this excellent article re building a properly-insulated cathedral ceiling. And from there I discovered the rest of the site. I’m home!

We’re pending! My new favorite web-site

We made an offer on a short-sale and the seller accepted. So we’re now ‘pending’ approval from the bank! After all these years we’re closer than we’ve ever been before to owning a house.

Also, I was just reviewing some of the brochures I’ve collected over the years and realized that one of the automated window systems had a web-site URL which I had never visited. NEW FAVORITE!

Functional Fenestration has a wide assortment of window automators and specifically calls-out their use in Passive Solar Design and automated ventilation.

New ‘smart’ thermostats

The introduction of the new ‘Nest’ smart thermostat made me take a new look at my previous post re the RCS TR60 unit.  (I also have to congratulate them on the ‘nest’ name/domain, it fits perfectly with a home-improvement product.)

 
The RCS TR60 is still available through Smarthome.com but it costs even more than the ‘Nest’ and is considerably less fancy.  Browsing the Smarthome.com ‘HVAC > Automation’ section, however, I also see several cheaper models from RCS.  What’s different about them?
 
 
 
The RCS TR16 thermostat is about $60 less than the TR-60 and appears to use X10 commands over ethernet cabling.  Both are labeled ‘RS-485 communications’ but look totally different.  More significantly, I don’t think this TR16 model includes the ‘SmartVent’ feature that I so desperately want. I did a quick scan of the installation manual and saw mention of a remote temperature sensor, but no fan schedule or smart ventilation.

 

There’s an even cheaper RCS TS60 which looks identical to the TR60.  The quick description says nothing about a remote temperature sensor, much less ‘Smartvent’.
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Finally, there’s the new Nest smart thermostat.  It’s beautiful!  The company was founded by former Apple Co employees and it shows in the elegant design and operation.  The only control is a dial wrapped discretely around the outside of the round display, which you can twist side-to-side and push (towards the wall?) to do a SELECT.

Still no ‘smart’ ventilation option, but I’ve emailed them about it so who knows…

Besides it’s attractive interface and ease-of-use, the primary advantages of the Nest are:

• automatic scheduling based on first week’s manual usage

• automatic networking over wi-fi
• remote control through web-site and smartphone
• future expandability?

Study of passive/overnight cooling

Interesting article from Home Energy magazine where they compared the ability of 3 heavily-insulated houses to remain cool during a hot summer, without using A/C.
Home Energy – Battle of the Walls: Peak Reduction
Their conclusion seems to be that heavily-insulated houses like these (R-28 walls) are dependent on thermal mass to maintain the indoor temperatures.

At the entry-level uninsulated end of the housing spectrum, the first priority obviously has to be insulation. But at some point the priority ‘crosses over’ to internal thermal mass.

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Home Energy magazine is interesting — it’s got a handful of free online articles and the rest are behind a subscription paywall.  $75/yr doesn’t seem like much for the apparent quality of the articles but I’m not ready to pull the trigger just yet…

Virtual 3D ‘sun’ in closed home-theatre?

Just playing around with an idea: Since the future home theatre/music room will have few (if any) windows, would it be possible to add faux ‘skylights’ across the ceiling with a virtual sun? I’m thinking here of a 3D pane of glass with an LED ‘sun’ that could track the position of the actual sun outside.  Silly, I know, and probably not worth the cost or effort, but HOW COOL would that be?

Adding LED lighting is simple enough, the trick is trying to make it appear as if it’s further away than just the ceiling.

A quick search online has led me to the Wikipedia page on ‘parallax barrier’ which is a common technique for ‘autostereoscopy’, i.e., glasses-free 3D.

Is a solar chimney unnecessary?

This is going to be a quick post:

I’ve been getting a lot of feedback (on a ‘green’ building forum) to my idea of building a comprehensive solar chimney to both heat and ventilate a house. The consensus seems to be that it’s overkill in San Diego! The climate is so mild that the money for building the ‘chimney’ would be better spent on insulation.

Then, maybe afterwards, I should replace the existing heater (and A/C, if applicable) with a smaller more-efficient ‘mini-split’ heat pump.

Follow-up discussion of latest solar chimney experiments

Getting a chance to read through those latest university experiments I last posted about.  I read the Japanese one first.  They didn’t really set out to measure a residential solar chimney, unfortunately.  Instead they were focused on measuring how well a ‘sodium sulfate decahydrate’ phase-change material (salt that melts at the right temperature) would work as a thermal mass.  They were hoping it would heat up enough to melt and then continue releasing heat well into the evening; it did.  Really, the most interesting part to me was their conclusion where they said it was difficult to separate the effect of the ‘stack effect’ (heat) from that of the outside wind in generating airflow through their contraption.

The Singapore paper, in contrast, was definitely focused on residential use.  They even suggest using the solar chimney for drying your freshly-cleaned clothes!  Hmm, more tweaking to my design…

• Their first conclusion is that you need a big air-gap, much bigger than you would want for a trombe wall.  For their particular design and a gap of 0.1 meters they measured ‘airflow’ of 0.025 Kg/s (mass flow-rate).  Opening the gap increased the flowrate to 0.035 Kg/s at a gap of 0.6 m — about a 50% improvement.
• There was a point of rapidly diminishing returns for increasing the gap size.  Increasing it to a full 1.0 m only gained another 20% in flowrate, and increasing to 1.5 m only a further 5%.  At this point they measured reverse-flow, i.e., cold air getting sucked into the outlet.
• They quote the ideal/optimized ratio of gap-to-height for Trombe walls as 1/10.
• Their optimized ratios for ventilation were nearer to 1/2.  For instance a 1 m high chimney worked best with a 0.8 m gap, a 2 m high chimney with a 1.0 m gap, and a 3 m high chimney with a 1.5 m gap.
• From the graphs it appears that the optimized ratio is not very sensitive, i.e., you can use a smaller gap and still get most of the effect.
• They make the general observation that increased ‘inlet width’ (bigger vents) reduce pressure losses and improve flowrate.
• The flowrate increases proportionally with height, i.e., the 3m high chimney had 3x the flowrate of the 1 m high.

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Finally, in thinking about my proposed design I have some new concerns:

• Will the output of the chimney be too hot to vent directly into the house during the winter?  If so I would want to pipe it in through the A/C ductwork, i.e., to diffuse it.
• How much moisture or condensation will build-up inside the chimney?  I may need to monitor that, too, and have a way for the system to purge the wet air before cycling back to heating mode.