[personal profile] drscott
[Irrelevant note: my forearm started itching in the night, waking me up for half an hour until I got an icepack on it. Started itching again this morning. Annoying; no sign of skin disturbance.]

Most of my work (that paid) has been some form of global optimization, from optimizing parallel programs and schemes to automatically optimize parallel programs, to optimizing plan layouts in subdivision, to managing investments considering all tax and estate consequences and adverse events.

The new house in Palm Springs is no exception. Built in 2003, by the standards of the time it's well-insulated and efficient. At that time, electricity cost about 12 cents per kWh; currently the highest tiered rate (which we will easily reach using AC) is above 30c/kWh. The pricing scheme is hugely complicated and unpredictably micromanaged by an incompetent state legislature and regulators, and discriminates against large families as well as wasteful users. It does, however, result in such high marginal costs for larger houses that solar power, as currently subsidized, is more than competitive for the highest-tier rates.

The former owners were doing what most people do, shutting off AC in most of the house and using it sparingly in the areas they actually live in; this kept their bills down to $400/month or so, averaged year-round. In our usage with less than half the house cooled to 79-84 F, the power bill for the month of July would have been about $600 if we had been there full-time.

The problem of heating and cooling buildings is a complex global optimization problem. First note that what we want to optimize is not the temperature as shown by the thermostats (there are 6), but human comfort; if there is no one at home, there is no need to control anything (though furnishings can suffer from excess heat or extremely high or low humidity.) We want the house to know how many people are in what areas to determine how hard to work to condition the air. Also, comfort depends on many factors; temperature, humidity, moving air, radiation temperature (easily noticed in winter when it can feel cold at an apparently comfortable temperature because cold walls or windows soak up thermal radiation.) I am trying to give up hot coffee in the summer since a cup can make me uncomfortably warm for an hour when an iced coffee would not have.

The general problem of cooling can be solved using a variety of sources and sinks available in the environment. Groundwater, for example, is often at a reliable low temperature and can be use for cooling, either through a heat exchanger or indirectly by using it to cool a refrigerant. In the desert, evaporating water is an energy-efficient cooling method. [BTW. don't let anyone tell you that there's a water shortage and that evaporative cooling will make it worse; fossil fuel power plants use more water to produce the additional power needed for conventional AC than evaporative cooling uses. One source comments that use of evaporative cooling for a typical house results in additional water usage of about a shower per day, implying it would strain water resources; but since Southwestern homes typically use many times that amount on landscaping irrigation, and generation of additional electricity for conventional AC would use as much, additional water use is not really an issue.]

In a climate with wide swings in outdoor temperatures, simple ventilation and storage can provide most of the heating and cooling in many seasons; a whole-house fan and the house's heat storage capacity obviates the need for costly AC much of the time, but it requires constant monitoring of conditions and control of ventilation, and is most effective when outside conditions in the next 12-24 hours are known. A smart person can handle this, and until now, most whole-house fans have been controlled by a simple switch and the strategic opening and closing of windows.

There's huge room for improvement in the technology of AC. Manufacturers have improved conventional compression-cycle refrigeration AC a great deal since energy prices started to climb; SEERs (Seasonal Energy Efficiency Ratios) have climbed from 10 to 14-16 in two decades, cutting power used by a third.

But the original form of AC, used since ancient times in dry climates, passes hot, dry air over water to cool and humidify it; this is now called evaporative cooling. In its simplest form, a fan blows hot dry air over a medium soaked with water. Evaporating water cools the medium, which cools the air passing over it, which meanwhile picks up some moisture. In a desert climate, outside air at midday can be at 110 F and less than 10% humidity; the wet-bulb temperature (the temperature a thermometer registers when it is cooled by a soaked medium after air is blown over it) can be below 50 F. These simple evaporative coolers, known as "swamp coolers," were widely used in the desert Southwest until cheap AC units and the bad reputation of swamp coolers for high maintenance and growth of microorganisms in the medium led to their replacement by conventional refrigerative AC. There are times of year, also, when the humidity levels rise enough to reduce a swamp cooler's effectiveness, so that for some weeks of the year, the output is uncomfortably warm and humid.

More recent development of two-stage evaporative coolers resolves most of those issues. By using outside air in a first stage to cool one side of the medium, but exhausting the now-moister air and then drawing in more outside air to pass over the already-cooled moist medium on the other side, the air can be cooled more with less addition of humidity. This is not as efficient as a one-stage swamp cooler under ideal conditions for their use (because it uses more fan power to move more air), but works in a much wider range of conditions, and can cool a space for about 1/3 the cost of conventional AC (SEERs of 40 vs AC's 14). The fungus and microbial issues have been dealt with by a variety of automated purging and cleaning methods, though some disinfection and annual maintenance is still a good idea.

Many other factors influence comfort and can be tweaked to improve it; our house is not ideally oriented, with its long axis north-south and prime living areas facing west. The best designs for passive solar heating and cooling have the house laid out east-west, with a large southern overhang sized to allow in winter sun and keep out summer sun. We spend a lot of time opening and closing 15-20 shades on the east and west sides of the house as solar incidence changes. A set of automated shades with a smart controller which can respond to conditions would handle that for us.... [ultimately a window technology which can be controllably tuned to allow in or block light and heat will simplify this problem, but while this has been an area of research for some time, no cheap and practical windows of this type exist.]

[next: irrigation; outside lighting; music and TV distribution; security; evolution of the house computer; media servers; solar voltaic; LED lighting]

Date: 2010-08-11 08:50 pm (UTC)
From: [identity profile] joebehrsandiego.livejournal.com
Fascinating post, Curtis.

I like the "feel effect" of good evaporative cooling when the outside conditions allow for it. That's what we had, growing up in Rapid City in the '60s and 70s.

Please keep us posted on both your research & execution.

Date: 2010-08-11 09:14 pm (UTC)
From: [identity profile] billeyler.livejournal.com
For us, evaporative cooling is the way to go, although in the thick of the summer monsoon season (two weeks ago), it played havoc with the humidity levels in the house. More warped parquet floors and sticking cabinet doors.

Running only the fan without the water dries out the media and creates a somewhat fishy smell from the cooler. Not pleasant, even with a new cooler and new pad.

Although our water usage goes up significantly in the summer (mostly because of my watering the garden on the drip system), the electric bill stays fairly even all year, since the evap cooler is just a fan. We average about $78 a month in electricity in this 3500 square foot house. Danny keeps a schedule of our electric and gas use over the past 9 years.

You touched upon one of the other reasons for us moving to PS would be mentally (and a bit financially) difficult; the cost of refrigerated air.

Date: 2010-08-12 04:02 am (UTC)
From: [identity profile] dr-scott.livejournal.com
All of the pieces are not in place yet, but the two-stage system would solve the high humidity issue at a slightly higher running cost. What's needed is more suppliers and more development of the concept. In the meantime, you might consider watching the humidity and when it's getting up there, either not using the cooler at all (a bit of suffering) or adding a small conventional AC unit for emergency use -- it doesn't have to be high efficiency because you would only use it occasionally. I suspect you've thought of that...

What I'm eventually going for is an automated system that starts and stops its various components automatically to make the best use of ambient sources.

Date: 2010-08-11 09:22 pm (UTC)
From: [identity profile] ricksf.livejournal.com
Thanks Curtis for giving me some additional thought paths as we (my co-buyers and I) contemplate our own smaller home's HVAC issues. Starting with an aging 'whole house' A/C unit, a top of the line swamp cooler in good condition, unknown efficiency of the spa/pool gas heating system, we face different but globally similar issues. It is indeed a challenge.

Date: 2010-08-12 04:09 am (UTC)
From: [identity profile] dr-scott.livejournal.com
Pool heating is very expensive even with the most efficient gas system; many people never heat their pools now, but if you really do want to use the pool nearly year-round, a solar water heating system is a relatively cheap and simple add-on. The panels are made of black rubber tubing, no glass or concentrators, and can make the pool usable 70% of the year without any top-up heating.

As for AC, you guys should make a friend of the temperature/humidity/wet bulb chart, and use the swamp cooler as often as possible, switching to the aging central AC only when necessary. Its being old and inefficient won't matter much if it is only used a a small fraction of the time. Someone has to pay attention to the weather and manually switch over, though.

Date: 2010-08-12 08:09 am (UTC)
From: [identity profile] sunbeam-bears.livejournal.com
Growing up in Massachusetts, we were taught the benefits of using shades, When to open, when to shut. Basically opening and shutting shades where the sun is shining through, depending on the time of year. Wide open shades heated a room in winter, the same shades closed in summer kept a room cool. A constant musical chairs on a daily basis.
Here in Palm Springs we use our swamp cooler, and our A/C. But as you say, we have to pay attention to the weather. The south facing shades are always closed. The northwest shades get closed on occasion, as in, when I think of it.
Having a viable system that controlled A/C, Evap, and shades seems so simple an idea, it's a wonder someone isn't already making a ton of money building, and retro fitting.

Date: 2010-08-12 08:45 pm (UTC)
From: [identity profile] dr-scott.livejournal.com
There's convergence right now, with auto shade makers, lighting control people, thermostats, locks, and multimedia being set up for control via "scenes" (scenarios). This is for high-enders with unlimited budgets at the moment, but will trickle down, until every new house has some intelligence and people are used to it doing things automatically. You can roll-your-own as I am with control software and Z-wave-(etc)-enabled sensors and actuators, but it will take a lot of fiddling and a bit of custom scripting.

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