Two-Stage Evaporative Cooling Project

[Originally published June 5, 2016, at]

Two-Stage Evaporative Cooler from OASys
Two-Stage Evaporative Cooler from OASys

[This follows up on the previous post, This is Not My Beautiful House. Taken from “The Globally Optimized House: AC,” written August 11, 2010.]

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.

This house in Palm Springs is no exception. Built in 2003, by the standards of the time it was well-insulated and efficient. At the time it was built, electricity cost about 12 cents per kWh; currently the highest tiered rate 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. With less than half the house cooled to 79-84 F, the power bill for the month of July was normally about $600. Many Palm Springs houses are only occupied during the winter season, from November to May or so, when cooling needs are minimal. But year-round occupancy calls for more efforts to save on AC.

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 approached using a variety of sources and sinks available in the environment. Groundwater, for example, is often at a reliable low temperature and can be used for cooling, either through a heat exchanger or indirectly by using it as a heat sink for a conventional AC compressor. 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.]

Craning in Evaporative Coolers
Craning in Evaporative Coolers

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. Very expensive new AC units have reached SEERs of 25, for another third saving, but diminishing returns have set in.

The original form of cooling, 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 air from a swamp cooler 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 of old-style swamp coolers 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; this house was 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. There were 15-20 shades on the east and west sides of the house to adjust as solar incidence changes. A set of automated shades with a smart controller which can respond to conditions would handle that…. [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.]

[Updating with a bit from Green Building Advisor, “Saving Energy With an Evaporative Cooler:”]

Whatever happened to the OASys?

Many articles on evaporative coolers mention the OASys, an energy-efficient appliance that was developed by engineers at the Davis Energy Group in Davis, California. Unfortunately, the OASys is no longer available.

For a while, the OASys was being manufactured by Speakman. After a while the production of the unit was moved to a factory in India. Because of poor sales, however, manufacturing was discontinued. The remaining units were shipped to a warehouse in Nevada, where a warehouse fire destroyed the entire inventory.

The end of an historical era

A few years ago I had a conversation about evaporative coolers with John Proctor, the president of Proctor Engineering Group in San Rafael, California. Proctor, a nationally known air conditioning expert, told me that evaporative coolers deserve wider use. “The problems with direct evaporative coolers are overblown,” notes Proctor. “I lived in an evaporatively cooled home in Colorado for many years and was extremely happy with it. It worked well. I’m befuddled by the fact that more people don’t use evaporative coolers.”

Like most GBA readers, Proctor is a strong advocate for the use of energy-efficient HVAC equipment, so his love of evaporative coolers isn’t too surprising. Although energy-efficiency advocates have been singing the praises of evaporative coolers for years, the tide seems to have turned away from these devices. Evaporative coolers are fading away.

A reporter for The Arizona Republic, Ryan Randazzo, described the trend in a 2010 article titled “Once-Common Evaporative Coolers Are Disappearing from Phoenix-Area Homes.” Randazzo wrote, “Now the metal boxes atop homes are rare, done in by a combination of cheap and increasingly energy-efficient air-conditioning and the time and expense of maintaining the coolers. Arizonans steadily have moved away from using the sometimes noisy, always drippy evaporative coolers, even though they may reduce energy bills.”

According to Randazzo, almost every Phoenix home had an evaporative cooler in 1940. In 1984, nearly half of all Phoenix residents still had one. By 2010, however, less than 10% of Phoenix homeowners had an evaporative cooler. “Most residents who still use them are either extremely cost-conscious, handy at fixing the units, or both,” Randazzo reported.

Randazzo continued, “New housing developments are limiting coolers’ use on roofs. And people are just happy to use an air-conditioner that rarely needs repairs vs. a cooler that needs rooftop service at least twice annually.”

Randazzo interviewed Mike Donley, president of Donley Service Center. Donley explained that “most people just tired of climbing on the roof in the spring to clean and activate their cooler, and getting up there again in the fall to clean it and seal it off. … ‘Coolers are a do-it-yourself project,’ Donley said. … ‘I hate to say this, but if you are going to [pay to] have us service it twice a year, you are better off buying a high-efficiency AC system,’ Donley said.”

So unless a manufacturer steps forward with a two-stage cooler that doesn’t require maintenance at all (which is possible; an automated device could clean itself, as ours did in part), people will think of it as too much trouble and move to use less efficient, overly drying AC.

Control Board
Control Board
The Air2O units had a microcontroller board to automate the cleaning cycles and run the different fans, valves, and pumps. This was a key weakness, since the software on the board was burned into an EEPROM — we were promised an update but that was never delivered. Engineering had shrunk to one key engineer, and the company went out of business soon after. The unit was constructed of sheet metal and some low-cost Chinese parts, including a motor that failed and had to be replaced at our expense. I bought a supply of colorful plug fuses since they burned out fairly often. After six months it was running smoothly and other than shutting down for winter and starting up again for summer, the units weren’t a lot of work to keep running.

This project wasn’t terribly expensive and eliminated 80% of the power used for AC, keeping most of the project house cool and comfortable at very low cost. But the next owner didn’t understand how the units worked and relied on the conventional AC units. Until the units are mass-produced by a consumer products company that designs them for ease of use, they won’t be practical for most people.

Some technical manuals and files from the Speakman Oasys – Air2O – CRS-2500 project:

Spec Sheet CRS-2500

Air2O Owner’s Manual

Air2O Installer’s Guide

Air2O CRS-2500 Specification Manual 20110101

PalmSprings [Excel document on evaporative cooling potential in Palm Springs, CA]

This is Not My Beautiful House

[Originally published June 5, 2016, at]

When I went to work at BBN Labs (a DARPA research shop, like a B-grade Xerox PARC or Bell Labs) in 1984 as a freshly-minted MIT graduate, my office was small and barren, with a desk, a VT-100 terminal, and a classic Mac. But it was still the age of the private office, and I’m thankful I never had to deal with the cubicle, or worse, the bullpen of today — I would never have been able to program with the noise and distractions.

The engineer next door had a leather couch and an oriental rug in his office, and art and geeky knick-knacks on shelves all around. Sometime during the first week, the headhunter / HR contractor who had recruited me stopped by. “Don’t get too comfortable. I mean, don’t spend a lot of time decorating.”

I didn’t know quite what he was getting at — interpreting it as philosophical advice, or perhaps practical because he had just seen the overdecorated office next door. Everything changes and ends, so best be prepared to move on as soon as you think you’ve arrived at your destination? Always have your bug-out bag packed and ready? But later I realized he meant he knew the Labs were splitting, with the part I was working for to be spun off to commercialize the BBN Butterfly multiprocessor. And in a few months we were in a new building next door, so decorating my office would have been a waste of time.

And so it is with houses. Last year we bought a large ten-year-old house for retirement. But this has me thinking of what the headhunter told me — and why I’ve spent so much time moving and fixing up places, hoping this time it would be Just Right….

College Avenue House
College Avenue House

By the time I started work at BBN I had been a landlord for five years, looking after a turn-of-the-century mansion that had been split up into four units during the Depression. It was my first venture into real estate investment — a grand three-story house on College Avenue between Tufts University and Davis Square, Somerville. I knew the Red Line subway extension would be coming to Davis Square, and at $70K the building was a good bet. I imagined doing all sorts of renovation, but while we lived in the ground floor apartment and I did do a lot of small upgrades for energy conservation and the like, I was too young and distracted to do anything major like finish the enormous attic into another glorious apartment as I had intended. And knowing what I know now, I realize I would have been stymied by the NIMBYs nearby anyway….

We had friends gutting and renovating houses in (crime-ridden, cheap) San Francisco (which is no longer cheap.) One time we were staying at their house while they had stripped their own bathroom down to the studs — which meant using a fully-exposed toilet. “Pretend there’s still a wall there.” The things we did when we were young and hungry…

I was getting into microcomputers and compilers and AI, which is how I ended up at BBN doing multiprocessor LISP for the SCI (Strategic Computing Initiative), which was supposed to be a government-funded response to the Japanese AI scare. Neither country cracked the problem, then both pulled the funding plug when no practical results happened — lots of money and effort went down the drain. This drying up of interest and collapse in AI research starting around 1986 is now called The AI Winter… which also crashed my next employer, Symbolics, when the beancounters decided to direct all researchers to buy Sun machines with Lisp compilers instead.

So because I had an absorbing job, I lost interest in the house projects, and it seemed like a good idea to free myself to move around by selling it. We got $350K for it; since we had borrowed all but $14K downpayment, that meant a profit of over $250K on a $15K investment, by the wonders of leverage and good luck. And the rents had largely paid for our own house expenses along the way, as rent controls ended, interest rates dropped, the subway opened, and investment started to flow back into the neighborhood, which today is highly desirable — Zillow thinks the building is worth $1.8 million now, 25x what we paid in 1978. Those conditions are unlikely to ever be repeated.

I entered a PhD program in computer science at Northeastern studying things like denotational semantics with Mitch Wand. A year of that was enough, and I moved to Vancouver to get away from the various unpleasantnesses of that era — escaping to a tiny apartment in a highrise tower in the West End.

First Bowen house framing stage
First Bowen house framing stage – 1992

I bought a big piece of land on Bowen Island and spent the next five years subdividing it, attacked by the Islands Trust and the antidevelopment faction on the island — which as it turned out, is retirement home to many Canadian bureaucrats. You really haven’t lived until people at a public meeting gang up to attack you as “an American developer.” The photo is of the first house being built in my subdivision, not by me — I never built my own house there, since I realized I wasn’t wanted.

Sunnyvale Eichler - 2007
Sunnyvale Eichler – 2007

I fought them to a draw and got out alive, though just barely. I ended up in California, where I picked up a new partner and bought an Eichler in Sunnyvale (photo above). That was my first real success at renovation — we updated the kitchen and baths, much of it “just enough” updating — for example, the 1969 bathrooms just needed new drop-in sinks and faucets to seem fresh, so I could do a lot of the work myself. We paid the dangerously-high sum of $600K for the house in 2000 and sold it for $1.2 million in 2007. Now Zillow claims it’s worth $1.7, showing how inflated values are in Silicon Valley….

View from Upper Market SF House
View from Upper Market SF House

We eventually ended up in the city of San Francisco itself, renting the top floor unit of a new building on upper Market Street. The developer built the largest building he could legally, and what he thought would sell — two condos in a five-story building, with the garage and entries in the middle floor.

The builder/developer made a few mistakes. First mistake: badly judging the market, which collapsed as he was finishing the project in 2008. Second mistake: the steel-framed center of the building didn’t settle, but the back end did, leaving our living room with an inch-high bulge running across the floor. Third mistake: the slate-tiled roof deck, planned hot tub and the garden box, which he never finished installing (but did fill with dirt.) The roof deck leaked. And leaked. And leaked — he rebuilt parts of it several times, while areas inside the house were soaked and had to be replaced. While it would be grand to sit in one’s rooftop hot tub watching the city lights and sipping Chardonnay, the reality never quite justified the trouble.

Market St Kitchen - Green Marble Counters!
Market St Kitchen – Green Marble Counters!

Meanwhile, the green marble countertops in the kitchen were probably chosen as a selling point — luxury! Green! Marble! But were horrible, since the slightest hint of acid — a lime, champagne, anything — etched the marble in ugly gray spots and rings. Despite our precautions, parts of it looked terrible in less than a year, and the owner had to bring in a refinisher to redo it and seal it again.

Nighttime View from Market St House
Nighttime View from Market St House

One last view from the Market Street place. The effect of the views eventually wore off, and we were left with the high rent, the leaks, the cold wind and fog that made the roof deck less than pleasant most of the time, and the steep walk up and down the hill to the gym.

Sevilla Great Hall - 2010
Sevilla Great Hall – 2010

Finally, we bought a big place in far south canyon Palm Springs. It came decorated in a sort of post-modern Beetlejuice style, not quite our taste but well-done. At over 6,000 sq. ft. it was a lot more house than we needed, but we were thinking one of our parents (or both?) might end up living with us, and of course we wanted room for guests. Neither of those really happened, so half the house was generally closed off.

The place had three dishwashers, three refrigerators, four water heaters, and six AC units. I replaced most of the ceiling lights with LED units, and since the AC bills were in the hundreds (and could easily have been in the thousands!), I looked into two-stage evaporative cooling.

Craning in Evaporative Coolers
Craning in Evaporative Coolers

Here you see one of the evaporative coolers being craned to the roof, where it was installed near the existing HVAC unit to share ducting. The concept of evaporative cooling takes advantage of the cooling effect of evaporation; the desert air is usually very dry, and under the right conditions evaporation can drive a surface down to near freezing temperature (the dew point is the theoretical limit, and that is often very cold — as I write it is 94 degrees outside, but the dew point is 37 degrees F.)

Normal evaporative coolers just run outside air over wet materials to cool and add moisture before sending it into the house. A two-stage cooler uses that effect to cool water, then expels the first stage air outside. The cold water is then sent to the next stage to chill outside air which is further cooled by running it over moist materials, but since the air is already cooled it gets a bit cooler and does not pick up so much moisture. The result is cool, clean, slightly moist air, perfect for a home in the desert. Running both units, we were able to cool the parts of the house we used most down to comfortable levels using less than 20% of the power used for AC, since all that was needed was a few showers a day worth of water and two big fans.

Control Board
Control Board

Unfortunately this super-advanced cooler was made by a pioneering company, and I soon had arrows in my back. No one knew how to install it, so I had to design the ducts myself. The computer control program would occasionally glitch, requiring a system reboot — cut the power and restart. When it was running, the air was much nicer than what you get from AC, but you had to understand how to open doors and windows just so to balance the system — air was being blown in cool and had to escape, so choice of open windows to distribute the coolth was an art.

It was no great strain for me to run it, but when our plans changed again and I was left alone in the house, it made no sense to keep the house for several more years. We put it up for sale. No one understood the coolers, since unlike solar panels virtually no one has ever seen one — the cheaper one-stage coolers, known as “swamp coolers” locally, have a reputation for being high-maintenance and the choice of people too poor to afford real AC. So that was no help at all in marketing the house, and I doubt the new owner ever used the instructions I left for him.

The Morrison, Phase 2 Construction
The Morrison, Phase 2 Construction – 2012

While waiting for that to sell, I put a deposit down on a unit to be built at The Morrison, a trendy modern development of detached houses on tiny lots, each with a small pool. One of the few developments that kept selling through the recession, and now a model for many copycat developments in Palm Springs. Above is a view of the construction site from our partly-furnished new house.

Finished Pool - 2013
Finished Pool – 2013

So again we had to move and set up a new place — change all the lighting to LED, buy new furniture, decorate. It always seems to be me that has the time and opportunity, so I do it. And years pass, and other things I could be focusing on don’t get done….

“Don’t get too comfortable. Don’t spend a lot of effort decorating,” as my HR guy told me long ago. Unless that’s what you want to do — specialization allows most of us to concentrate on what we’re best at, while farming out other tasks to people who specialize in those. When taxes are very high, there’s a big cost to hiring someone else to do something — you paid taxes on your income, and the people you hire pay taxes on what you pay them, and so on — which is why most of us try to do a lot of the work ourselves to save money. If I pay someone $1,000 to paint, I have to earn $1500-2000 more to make up for that expense. So I do the painting. And I get distracted, and do a worse job.

You can waste a lot of your life buying and selling houses, decorating and moving. I admire people who can stay in one spot for fifty years, happy with what they have — that’s not really me. We’ve moved one more time, and this time is the last! [He said, knowing it’s not true.]

Mansion Engineer

Welcome to Mansion Engineer, where we make bigger houses better.

Small houses are great for many people, but some of us want more space or have more family members than can fit into a smaller house. Mansion Engineer will report on ways to make big houses more efficient and easier to maintain. A big house doesn’t have to be wasteful, so if you own or are thinking of buying a big house, look here for projects to convert lighting to LEDs, add solar, and turn that white elephant into a green castle. You don’t have to live in a cramped house to be energy-thrifty.