Water
Here are some energy- and resource-saving tips from the experts on the domestic water system:
Insulate cold water piping to reduce condensation. Insulate hot water piping to minimize heat loss.
Fix water leaks! A faucet leaking one drop each second wastes one thousand gallons of water a year. Even one drop a minute adds up:
Drips/minute
- 1 55 gallons/year
- 20 1000
- 50 2500
Water closets are notorious for slow leaks that can go on for years, unnoticed. If your toilet valve suddenly opens (for no reason) to fill up the tank, it’s leaking water. Change out the rubber “flapper valve” at the bottom of the tank.
High-efficiency water-saving toilets have a flush rate of 1.6 Gallons Per Flush (GPF) versus 3.5 GPF for commercial water closets. A bidet only requires 1/8th of a gallon.
Heat traps are one-way valves installed at the water inlet and outlet to the water heater. They prevent the convection of hot water out of the tank when no hot water is flowing into the house.
In dual-use systems, recycled gray water can be used to flush toilets, wash cars, and water the lawn or garden.
Indoor water management: low-flow faucets and showerheads, water-efficient dishwashers, and low-water clothes washers all save water but also hotwater energy.
Clean and adjust the combustion apparatus for a gas water heater. (Best done by a qualified technician on regular maintenance visits.)
Clean the burners and adjust the air-to-fuel ratio for maximum efficiency.
Clean off accumulated combustion residuals (soot, grime) from the fireside of the burners.
Lubricate the fan motor and clean the burner fan blades.
Clean and adjust the combustion air and flue dampers.
Water heat energy losses versus water temperature.
More heat is required relative to each unit volume of water delivered.
More water is consumed because users often have a higher flow rate for better temperature control (i.e., when the hot water is very hot).
Greater surface losses from all the piping the hot water passes through.
Higher standby losses from the storage tank.
Higher thermal losses from the stack and combustion vent for a gas water heater.
Faucet aerators (with a fine screen) add a stream of air into the water leaving a faucet, as a way to reduce the volume flow rate. They can save 20 to 40 percent net water and hot-water energy.
Thermostat settings on water heaters are not exact. Install a thermometer at the outlet of the water heater for a more accurate reading, or measure the outlet temperature at the closest faucet to the water heater.
Install a separate water heater for high-temperature applications (e.g., for the kitchen and laundry versus the bathroom and lavatories).
Install water heaters that use the least cost energy (natural gas is much less expensive than electric) and that are the most efficient available.
Water heaters work 24/7 for ten to fifteen years. This is where you spend a little extra to max out the efficiency of the unit.
An external flue damper on a fuel-fired water heater lowers standby losses. This only works for units that rely on convection to circulate gas out of the flue.
A larger water heater tank (even a second large tank in parallel) may permit “interruptible” service: heating water at the off-peak electric rates, with enough volume to satisfy all hot-water needs for the rest of the day. These “storage water heaters” have a very large volume and are extremely well insulated to minimize standby losses.
Two water heaters in series and controlled separately: one to satisfy small daytime needs and the larger tank when everybody is home in the evening and on weekends bathing, washing clothes, cooking, and washing dishes.
If a large water heater has many heating elements, stage them to match the demand profile.
“Indirect water heaters” have a storage tank and get all the heat from a gasfired furnace via a heat exchanger. You need a heat source for the summer, perhaps solar water panels.
Drain-water heat recovery systems extract heat from a hot-water shower and transfer that thermal energy to the cold-water supply going into the water heater.
Turn the water heater off if you’re away from the house for a long time. Throw the breaker for an electric unit, close the gas valve for a gas water heater. Be sure to re-light the pilot light when you turn it back on unless it has electronic ignition.
A dual-flush toilet has two flow volumes: low for liquids and high for solids.
Do pilot lights waste a lot of gas or what? The gas savings alone can justify a new electronic-ignition water heater (stove, clothes dryer).
Install a timer to turn an electric water heater off at night and during the day when nobody needs it. Experiment to see how much the water cools down. Right after the timer goes on in the A.M., you might still be able to take a shower—but with all hot water, no cold added to the stream.
If you put a couple of bricks (rocks, water bottles full of water) into the toilet tank of an older water closet, you save that much water with each flush. Careful not to block the flapper valve or the flushing lever-mechanism.
Low-flow faucets (with an aerator) give people the pressure they expect but with a lower total volume.
A two-valve faucet (one cold-water knob and one for hot water) is more efficient than a single-valve faucet. The latter almost always wastes hot water with each use because people tend to keep the lever in the middle, half-hot and half-cold.
A typical family of four uses two hundred to three hundred and fifty gallons of water each day for indoor use. Californians are now limited to fifty-five gallons per day. (You don’t suppose bidets are going to be the new fad there?)
Keep a spa or hot tub covered when not in use. Insulate the bottom and sides, too. Build a nice two-by-four frame around the spa tub, stuff the cavities with rigid foam insulation (impervious to water, like they use under foundations), and finish the outside with wood panels, all trimmed nicely.
Sharp angles in the pool, spa, or hot tub water-circulation piping make the pump work harder than swept elbows. Increasing the pipe size also decreases pressure-head power usage. Low-loss filtration can reduce energy use even more.
Water heating accounts for 70 to 90 percent of the energy used to wash clothes, so a low-water style washer is worth every penny.
Hot water gallons
- 25 clothes washer
- 20 shower/bath
- 8 dishwasher
- 4 hand-wash dishes
- 2 shave/wash hands
If you leave the water running for the two or more minutes you brush your teeth, you’re wasting almost five gallons of water—10 percent of the house’s entire budget if you live in California.
Natural gas water heating costs roughly the same as a heat-pump water heater. Straight electric and propane water heating cost twice as much.
The smaller the water heater tank, the higher the efficiency. Why? Because of “standby losses” of thermal energy from the outside shell of the tank.
The size of the water heater you need depends on the peak-hour hot water demand of the household. If everybody takes a shower in the morning plus cooking and laundering clothes, well, that requires a very large tank.
Wash clothes later in the day, stagger showers between evening and morning, and your family can get by with a small, high-efficiency water heater.
The peak load capacity or first-hour rating of the water heater is larger than the actual size of the tank because the unit keeps working while hot water flows out.
Since your clothes washer heats incoming hot water anyway, there’s no loss in efficiency if the incoming water temperature is lower (i.e., after all the “hot water” has been used for showers). As far as that goes, “Who’s in the penalty box this morning? Doh! You get to take the last shower. Chill!”
Water heaters last ten to fifteen years. Tremendous advances have happened in water heater efficiency. If your unit is a decade old, the return on installing a new, efficient system should be quite favorable.
What’s your water heater’s Energy Factor? A 1.0 is a 100 percent use of the energy input. Electric water heaters have an EF of 0.75 to 0.95. Gas water heaters, which always lose some heat up the flue, go from 0.5 to 0.7. The higher the EF, the better. This is where you spend extra for the highest efficiency unit: The more you use an appliance, the more important its efficiency rating.
Manufacturers recommend you drain and refill the water heater (at least a third of the volume) every year to remove sediment, which reduces the efficiency of the unit.
Water heaters have a sacrificial anode, a thick metal rod inside the water tank. It prevents the interior of the steel tank from rusting and corroding. The softer your water, the faster the anode is used up. The anode lasts three to five years, on the low end, for soft water (or if you use a water softener).
Most electric water heaters don’t have any insulation in the bottom of the tank (which invariably sits on a very cold floor). Next time you drain the tank to remove sediments, slide a two-inch sheet of extruded polystyrene insulation (what they use under foundation slabs) under the unit to save some energy.
Insulate the first six feet of hot- and cold-water pipe going to the water heater with R-6 foam sleeves. Tape the seams for a tight fit.
Hot water remains in the piping after you turn the faucet off. All the energy to heat the water is wasted!
Pick up a “water heater blanket” and wrap the one-inch insulation sheet around the unit for a quick way to save energy all year long.
Adjust the water heater setpoint temperature to 120°F. If you use “cold water” laundry detergent, take 105°F showers, and wash dishes by hand at the same temperature, well, you can lower the water heater setting a little more.
Water conservation is essential, mostly east of the Mississippi River, where rainfall is scarce to nil. California has new, stringent regulations that limit domestic consumption of water to the bare minimum. Other western states are soon to follow. “Water is the new oil.”
This book is always concerned with preserving natural resources because (1) it’s the right thing to do, and (2) doing so gives people a little extra motivation to conserve energy.
12.1 WATER IS THE NEW CRUDE OIL.
One drop of water per minute wastes fifty gallons a week. If it’s hot water, you’re wasting energy, too.
If that leaking water happens outside of the plumbing, you’ve got big trouble— damage to floors, framing in the walls, electrical problems, mold inside the walls!
So, if your water bill is ever outside its usual range and there’s no reason for it, investigate.
12.2 DO I HAVE TO STATE THE OBVIOUS?
I said it for lights (“turn it off”), and I’ll repeat it for hot water: You can’t save more energy than by just not using hot water.
And the corollary: “If you don’t need hot water, don’t get your water out of the hot-water spigot.”
During the summer months, the “cold” water out of the tap might even be warm enough for most hot-water uses, even in the kitchen and laundry (Hint: “cold water” detergents?).
12.3 SET THE WATER HEATER TEMPERATURE TO 120° F.
The government recommends a relatively low setpoint for your water heater: 120° F.
Dermatologists say bath water should be no warmer than 105° F. Anything higher (1) washes beneficial oils from your skin, and (2) erodes the biome of beneficial microbes that lives on your skin, keeps your skin healthy, and acts as the first line of defense against infection. Don’t kill your skin’s first responders to disease and injury.
The washing machine experts recommend the “warm” setting for white clothes (90 to 110° F) and cold for everything else.
Even washing dishes by hand needs only 110 to 115° F, which is the maximum tolerance for your hands.
So, the government is right: 120° F hot water will meet all your household needs.
12.4 PUT THE WATER HEATER ON A TIMER. OR NOT!
When I was a consulting engineer doing energy audits, a common project for schools was to put the water heater on a timer. A mechanical timer is very dependable and relatively inexpensive. Just think of all the energy you save!
Except. Schools don’t use water on weekends, and homes need hot water 24/7. What little you save by not heating water for a few hours in the wee hours of the night is used to heat the water back up before the household wakes up.
Great idea, but only in the proper circumstances. As an aside, notice that you can’t put a gas water heater on a timer unless the pilot light has electronic ignition.
12.5 THE IDEAL LOCATION FOR THE WATER HEATER.
Architects and builders are loath to use valuable floor space in the interior of a house for a water heater closet. Yet, the ideal location is closest to the highest hot water loads: the kitchen, laundry, and the main bathroom(s). In the house I grew up in, in Baton Rouge, the water heater was in a closet off the utility, which was right next to the kitchen and ten feet from the two main bathrooms. Perfect location for a water heater: right in the center of the house!
The proximity of the water heater to the points-of-use means (1) lower installation costs (shorter pipe runs), (2) less water wasted waiting for hot water to come out of the faucet, (3) almost immediate access to hot water, and (4) lower thermal losses from the system (a lower volume of hot water remaining in the pipes).
Instead, most houses have the water heater in the worse possible location: the garage. Plumbers will continue to install the water heater there (because they make more money on the job) until told otherwise. Tell them!
12.6 INTRODUCING THE BRITISH THERMAL UNIT (BTU).
There are many ways to heat water, using any number of different sources: electricity, natural gas, solar, heating oil, and propane. We need a new unit of energy, for heat, to contrast and compare these different thermal sources.
A British Thermal Unit (BTU) is the amount of energy it takes to raise 1 pound of water by 1° F.
We’ve seen BTUs before, if only indirectly. R-values are in units of BTU: 1 BTU of heat flows through 1 square foot of area per hour per 1° F of temperature difference.
The capacity of your home AC is in BTUs: one ton of cooling equals 12,000
BTU, which is the rate of heat transfer to freeze one ton of water in twenty-four hours.
One watt of electrical power is equal to 3.412 BTUs per hour.
12.7 AVAILABLE ENERGY IN VARIOUS HOT–WATER HEAT SOURCES.
Engineers do energy-use calculations in units of mmBTUs, shorthand for a million BTUs. We can now quantify the inefficiency of electric “strip heat” (pure resistance) versus a heat pump.
For one mmBTU of heat, it costs $36 for straight electric heat or propane, $20 using fuel oil, $14 from natural gas, and roughly $9 using an electric heat pump.
Electric heat pump efficiency varies inversely with the outside temperature, from a high of 5.0 at 80° F (five units of heat output for every unit of electricity input) to a low of 1.0 (equal to straight electric heat) below 0°F.
Fossil-fuel heat sources become more competitive versus a heat pump the colder you get (e.g., the northern states).
$ cost per mmBTU
- $36 – electric, propane
- $20 – fuel oil (diesel)
- $14 – natural gas
- $6 – heat pump
12.8 NOW, WE NEED TO QUANTIFY HEAT TRANSFER.
A simple equation governs the rate of heat transfer:
Q = U*A*(T1-T2)
Where Q = the heat transfer, U=U-value, A=area, and (T1-T2) is the temperature difference.
Heat always flows from the high-temperature T1 to the low-temperature T2.
That heat flow is directly proportional to the area and the temperature difference.
The U-value in the equation is the inverse of the R-value, U = 1/R. Hence, the higher the R-value, the smaller the fraction 1/R and the less heat that flows.
The units of Q are in BTUs/hour.
12.9 HEAT TRANSFER CALCULATIONS FOR HOT WATER.
Electric water heaters all have the same basic efficiency because they all use electric strip heat (metal bars that heat up just like in your oven). What makes one unit “more efficient” than another is the amount of insulation inside the metal shell.
A water heater with R-20 insulation is twice as “efficient” as an R-10 tank because it loses half as much heat from the outside.
Say what? Look at the heat equation: A is the surface area of the tank (top, bottom, sides), (T1-T2) is the temperature difference between the water inside T1 and the ambient temperature in the water heater closet T2, both of which are constant between any two water heaters with the same volume capacity.
The only thing that makes one electric water heater use less electricity than another is the amount of insulation inside the shell. (Gas water heaters differ in the efficiency of the combustion process and the amount of heat lost through the flue pipe.)
12.10 WATER HEATERS LOSE HEAT OUT OF THE SHELL 24/7.
Water heaters use energy to (1) heat cold water from the water mains and (2) maintain the setpoint temperature inside the tank. Standby losses (2) happen because of (T1-T2). Heat is always flowing out of the tank enclosure.
If your tank is warm to the touch, you need to add insulation.
Water heater blankets (a one-inch blanket of insulation that you wrap around the water heater) at your local hardware store are inexpensive, easy to install, and reduce the standby losses. The payback is almost always less than one year, after which time you’re saving energy – and money.
The water heater in my house is on the lower floor. In the winter, the standby losses are negligible because the heat rises up to the upper floor. Still, one of the first things I did when I moved into this house was to spend $20 for a water heater blanket and take five minutes installing it.
12.11 THE MATH OF SAVING ENERGY ON HEATING WATER.
The water-heater analysis is a straightforward example of the heat-transfer equation. If you lower the temperature setpoint, you (1) use less energy heating cold water from the mains, and (2) reduce standby losses through the shell.
If you add a water heater blanket, you lower the U-value and further reduce the energy for both (1) and (2).
If your house is unoccupied for a week or more, turn the water heater off, so heating energy isn’t wasted via standby losses. If there’s a danger of freezing, just turn the temperature way down. (Be sure the piping is well insulated, or drain the lines outright if you’re to be gone for a very long time, and turn the water heater off at the circuit breaker panel.)
12.12 FOSSIL–FUEL WATER HEATERS HAVE THE SAME ISSUES.
No matter what the energy source, water heater thermal losses are relatively consistent. The only possible difference is that propane and natural gas water heaters need a steady supply of combustion air. (Be sure not to block the free flow of air to the burner when you install the insulating blanket.)
This nominal airflow might lower the temperature in the heater enclosure in the winter, increasing standby losses. (Remember: the higher the temperature difference, the more heat flows.)
Otherwise, the cost of propane heating is roughly the same as electric (propane, where I live, is a fair bit more than electric). Still, natural gas heating of water costs about one-third of the cost of using electricity.
12.13 HEAT PUMP WATER HEATERS.
Just as heat pumps heat your house more efficiently than electric “resistance heat,” there are new water heaters that also use heat pump technology. They cost a fair bit more but are two to three times more efficient than straight-electric and therefore have an excellent payback (especially if your household uses a lot of hot water).
However, with all those savings, you do have a new device to maintain.
Electric water-heating elements are as dependable as they are simple. A small heat pump for a water heater potentially has all the same issues as an HVAC heat pump, probably more because small systems are invariably more problematic (think gasoline leaf blowers versus gasoline automobile engines).
As with any unfamiliar technology, be sure and do your research, buy reputable brands, and have the system installed by an experienced contractor.
12.14 TANKLESS WATER HEATERS FOR LOW–VOLUME HOUSE HOLDS.
Instantaneous water heaters don’t have a tank. They use electricity or natural gas to heat water on demand. With no tank, there are no standby losses, and the unit takes up a lot less room (they can be installed on an outside wall).
Tankless systems have a limited flow rate, so you won’t be able to wash dishes and take a shower simultaneously. Up-front installation costs can be three times as much. Also, since an electric tankless water heater draws a lot more watts (because the demand is instantaneous), you may need a new electric service (wiring and circuit breakers) to the unit location.
Again, it’s hard to beat the simplicity and dependability of an electric water heater. Two electric elements, no moving parts—who hasn’t had a water heater go ten or more years without an iota of trouble?
Saving energy is all great and good, but there’s much to be said for dependability and peace of mind, too.
Note: A significant issue when I was a consulting engineer, trying to talk facility managers into installing a new technology to save energy: “I like things the way they are.” Or, “I don’t have the time or experience to maintain all that fancy new tech.”
12.15 MINI, UNDER–SINK INSTANTANEOUS WATER HEATERS.
Going on forty years ago, my father had a small instantaneous water heater installed in a remote bathroom of the house. (“Don’t stand in the refrigerator door,” Pop also had one of the first heat-recovery fireplace units.)
This bathroom (1) opened off a guest bedroom that was rarely used, and (2) instant hot water made a cranky mother-in-law happy so that Pop could lay off the valium pills (instant relaxation) for his heart condition.
Modern instantaneous water heaters are quite sleek and “efficient” (as much as electric water heating can be).
12.16 REMOTE HOT WATER ENERGY–SAVING CALCULATION.
The instantaneous under-counter water heater, in a bathroom very far away from the water heater, does save energy. Whenever you turn on the hot water spigot, for a regular hot water system, you wait for two to four gallons of water to flow until you get hot water. When you turn the flow off, the piping remains filled with two to four gallons of piping hot water. Very soon, that water will return to ambient temperature, and all the energy used to heat it is lost. With an instantaneous water heater, no water is lost waiting for hot water at the point of use.
It’s unlikely you’ll save enough energy to achieve a reasonable payback on an instantaneous water heater, except under unusual circumstances. Can you think of any? What if you have to heat very cold water, circa 35° F? If you use that remote faucet many times each day (OMG: the mother-in-law sets up permanent residence)? If electricity costs three times the going rate (for example, in the Upper Peninsula of Michigan, very high electric rates plus very cold)?
12.17 IS IT WORTHWHILE TO INSULATE HOT WATER PIPING?
People assume that if there’s heat inside, insulating it will save energy. Energy engineers phrase it a little differently: “If you burn your hand when you touch it, you probably need to add some insulation.”
In a house, there are hot water mains from the water heater to the bathroom(s), kitchen, and laundry. Imagine all the heat lost! Of course, if the piping goes in a crawl space, you need to insulate it against freezing if you live in that kind of climate. But otherwise, to save energy?
How is hot water used in the average home? Usually in short bursts, spaced widely apart. Wrapping hot water lines with R-4 insulation won’t drastically reduce heat loss for that kind of usage pattern. Why not? Because the heated water will remain in that insulated pipe for hours anyway and still lose all its thermal energy!
Try this experiment: Run the tap water in the kitchen until you get hot water. Wait for half an hour. How hot is the water now? It’s stone cold! If you need hot water now, you run the water the same amount of time as before until you got hot water at the fixture. Add insulation to the piping, and you might, at best, get tepid, warm water half an hour later. You’d still run the water until you got hot water directly from the water heater: same net amount of water (and thermal energy) lost. If you don’t get hot water but every three hours: cold, cold, cold!
Hot water piping insulation: another good idea, but the economics don’t often justify the cost (except for freeze protection).
12.18 STAGING SEVERAL WATER HEATERS.
One possible application for a tankless water heater is as a second source for a high demand load. Say you have a large household and run many laundry loads each week. You keep the regular water heater temperature high, so you can wash whites at the highest setting (to kill germs for a member of the household with limited immunity or to launder heavily soiled work clothes—kids in sports).
Given the limited on-demand volume required (only one wash load at a time), having a second, tankless water heater (dedicated to the laundry room) allows you to turn the temperature setting of the main (tank) unit down to 120° F.
No more scalding-hot water in the shower or kitchen. Less energy to heat the water, and lower “standby” losses (e.g., lower temperature difference and less heat lost from the main tank) and zero standby losses for the tankless water heater.
12.19 WATER HEATER CLOSET
There are more ways to further “insulate” the water heater than a wrap-around thermal blanket. Many houses have the water heater near an outside wall. So, if the tank leaks, the water will drain outside (or at least out of harm’s way).
The absence of insulation on the outside wall of the water heater closet (for example, an exterior access door) means the temperature inside the closet closely tracks the ambient temperature outside. When it’s very cold out, it’s very cold in the water heater closet, and a lot of “standby heat” escapes from the water tank. (The water heater should be in the middle of the house.)
Insulating that outside wall (or door) is an inexpensive way to minimize those new thermal losses. Add batt insulation to all the other walls of the water heater enclosure while you’re at it, for even more energy savings. (Plus a water heater blanket, of course: can’t have too much insulation.)
12.20 GAS–FIRED WATER HEATERS HAVE SPECIAL NEEDS.
Burning propane or natural gas requires a steady supply of fresh air. This combustion air usually comes directly from, say, an opening in an outside wall. If the water heater is in the interior of the house, fresh air must be ducted to the unit (from the crawl space, attic, or an outside wall), or the burning gas draws oxygen from the household air.
Building codes have stringent guidelines on how to provide combustion air to appliances. If you get ambitious and insulate the water heater closet walls with batt insulation, be sure not to cover the combustion air intake for a gas heater or otherwise alter the ventilation setup.
If in doubt, ask a qualified contractor to review your completed work. (That large crack under the exterior water-heater-closet door is for combustion air.)
12.21 WATER HEATER DRAIN PAN
Building codes require a metal or plastic drain pan under the water heater to capture leaking water from the tank or fittings. (The inside HVAC unit should have a pan underneath as well for condensate draining from the cooling coils.) The pan is vital because a little bit of water can do an awful lot of damage – to floors, flooring, wood framing, and everything else the water contacts.
That leaking water adds excess humidity to an enclosed space. During the cooling season, this indoor humidity puts an extra latent load on the cooling coils, which must condense all that moisture out of the air before the air volume can be cooled down. (Refrigerators have similar drain pans underneath the unit; that condensation evaporates into the conditioned space.)
12.22 SOLAR HOT WATER.
The sun heats water directly in solar panels. Or photovoltaic solar panels create electricity, which, in turn, runs the water heater. There is no direct-unit conversion-comparison for solar versus natural gas and electricity.
Technically solar is free, but you still have to pay for the equipment. Solar costs involve a complicated “payback” calculation, which compares the cost of solar versus one of the other energy sources. You must also quantify the available sunlight: via location, inclination of the panels, and possible shading by trees.
The fewer sunlight hours per year, the longer the payback for a solar system. Northern states can be quite cloudy three to four months of the year. Not to be discouraging, solar can be competitive in cold and cloudy climates, but not so much when competing with dirt-cheat natural gas.
12.23 HYBRID SOLAR WATER–HEATING SYSTEM.
Just because your location doesn’t get steady sunshine for a few months a year doesn’t mean solar can’t more than pay for itself heating water. The solution is a “hybrid” system:
The existing water heater tank remains (with an electric or gas heat source). Every solar water heating system requires a storage tank anyway. You simply add an auxiliary loop to circulate water to panels on the roof. When the sun’s shining, and the water from the solar panels is hot enough, the panel water circulates into the storage tank, eliminating the need for thermal input from the electric element or the gas burner.
All you need is some piping to the roof, a small in-line circulating pump (very efficient, very dependable), and some simple on-off controls to tell the pump when to move water.
The payback calculation of this project is based on the energy saved versus the non-solar heat source. Notice that the higher cost of an electric heat source cuts the payback time in half versus a natural-gas-powered water heater. Northern latitudes may be cloudier in the winter, but they also have much longer days in the summer, during which time a well-designed hybrid solar panel system can meet the entire hot water load.
12.24 PHOTOVOLTAIC PANELS FOR HOT–WATER SERVICE.
Solar electric panels are expensive and, even in the best of applications, have a payback of ten years and more. Solar water heating systems, on the other hand, are much cheaper and have a shorter payback. Consequently, if you have the annual sun-hours for a photovoltaic system, start with a solar water heater (i.e., do not use solar-sourced electricity to run an electric water heater). Doing so, you can install a smaller photovoltaic solar array to meet your needs.
Photovoltaic systems are very complicated. You need an inverter, a tie-in to the power company, a new electric meter (that can turn backward when you’re sending excess electricity back into the utility grid), and extra wiring. All by a licensed electrician.
Solar water heating systems, on the other hand, are much more straightforward: a few pipes, a small circulating pump, a small controls panel, and a couple of temperature sensors.
It’s like comparing a bicycle to a motorcycle. Simple is better, especially if you’re new to the energy biz and want to try a good project to get started.
12.25 THE ELECTRICITY CALCULATIONS VERSUS NON–STANDARD UTILITY RATES.
California now requires all new houses to have solar electric panels. That adds about $15,000 to the cost of an average home, with a fifteen-plus year payback. Given the copious sunlight available in California, requiring solar water heaters, adding only $5,000 to the costs, with a two-year payback, would be more beneficial to homeowners.
Both solar systems operate at their most efficient during the utility’s peak hours, roughly 4-6 PM. All commercial rate structures, and a few residential rates, incentivize peak load reduction to the point of charging residential users up to 50 percent less during off-peak hours. This cuts the payback by half for all solar applications, down to a year for solar water heating and five or more years for photovoltaics.
Finally, given California’s new water-use policies, folks will be using much less water, necessitating a smaller solar array to meet their hot water needs.
12.26 THE RED–EYE EXPRESS.
You’ve seen those spring-activated electronic water taps in hospitals, grocery stores, and Big Box stores. They’re motion-activated to provide only a short stream of water to wash your hands (or flush the urinal or toilet). They save a minuscule amount of energy.
Then you go and dry your hands in a five-minute blast of hot air that costs a small fortune in electricity? That’s what they make shirttails for.
12.27 INSULATE HOT WATER PIPING IN UNCONDITIONED SPACES.
This is a DIY project for colder climates. If you do all the work yourself, however, the cost is low enough that you don’t have to worry about the payback, so you might as well do it in any climate.
Install specialized ½” foam or ¾” fiberglass pipe insulation over all hot water piping that passes through areas that are not heated or air-conditioned (attic, crawl space under the house). Tape the seams to ensure a uniform thermal barrier.
Future Tech!
12.28
Why don’t they insulate the hot water piping when they build houses? If the piping is in the slab, you’re out of luck.
12.29
In water-challenged places like California, can a peak demand water-rate structure help conserve water?
12.30
Building codes can’t require the electric panel and the water heater to be installed in the most economical, energy-efficient location of a new-house construction?
12.31
All water heaters should be constructed with integral heat traps.
12.32
Heat pump HVAC systems need a desuperheater option that allows the system to also satisfy a home’s hot water needs.
12.33
Just like the government requires in Israel, every new house built in an area with sufficient annual sun-hours should have a solar water heating system.
12.34
Adding a large, well-insulated water tank to a solar water heating system improves system efficiency by using all available solar energy. Controls can use this extra hot water during peak demand electricity times to lower the utility bill.