We had a very exciting evening at my house yesterday. At about 6:30 pm, my husband interrupted my post-run shower to tell me that the our hot water heater’s inlet pipe — the one that fills the water heater from the City’s supply lines — was hot.
“You actually put your hand on it?” I said, a bit incredulously.
“No, no, on the insulation,” he assured me. “The insulation is just warm, I’m sure the pipe is very hot.”
This was good news. It meant that as my shower depleted the hot water tank, it was being replenished with water that was already hot.
Not to be outdone, I waited until his post-exercise shower was finished, then went out to the garage and listened closely. No whooshing natural gas noise.
“Hey,” I shouted. “The water heater isn’t heating!”
I repeated this ritual no fewer than 3 more times over the course of the evening. I did it when my daughter took her shower. And when the dishwasher was running through its first cycle. And when it was running through some other cycle, just to be sure.
Throughout the evening, the water heater performed perfectly, delivering nice hot water without ever tripping the temperature sensor (usually tripped by cold water coming in from the city to replenish the warm water we use from the tank). As a result, the natural gas flame never ignited and we enjoyed fossil-fuel-free hot water.
The joys of a solar water heating in action!
As I noted in an earlier blog post, I pledged to install a solar water heating system as my New Year’s resolution. My utility enacted an incentive program enabled by a recent state law, and mine was the first project installed under that program by my contractor.
I learned a few things about solar water heaters. The concept is extremely simple: divert the incoming city water to your roof, let it get hot up there, then send it down “pre-heated” to your existing water heater. Indeed my neighbor has a jury-rigged system that does exactly and only that; they’ve piped the city water up top where a long, rugged, black hose snakes back and forth several times before returning to a joint which send the water down to the water heater. This arrangement probably cost a few hundred dollars (including labor) many years ago, and I assume it has served them well.
That system has several pitfalls, however. The water in the big black hose can freeze. The hose can degrade and leak. Squirrels can chew on it. I suspect it wouldn’t pass a building inspection, and perhaps most importantly, it doesn’t make the best use of the sun’s energy.
Among modern engineered systems, there are two broad categories: passive systems and active ones. Passive installations are similar to my neighbor’s in that the city’s water pressure is the only source of energy required to move water through the system. Turn on a hot water faucet and the water moves. No electricity needed, no moving parts. Active systems, on the other hand, use a pump which circulates either the water or a heat-transfer fluid (like antifreeze) up into the sun and down into the water tank. Since it uses a pump, active systems can include electronic controllers which optimize the system’s efficiency and minimize the need for the fossil-fuel system to kick in. Heat-transfer fluid systems are great in areas where the temperature routinely drops below freezing.
Since I live in temperate northern California, I chose a passive system (pdf). It’s less expensive and I like the fact that there’s virtually nothing to maintain. My water moves through a series of copper tubes treated with a selective surface coating, all contained within a collector panel. The collector panel is designed to minimize heat loss and positioned to maximize sun exposure.
We’re thrilled with our system. We’ll benefit from a federal solar tax credit (available for systems installed before December 31) as well as our utility rebate. All-in, my cost will be about $3,800 and will pay back in about 7 years.