9 First Things First As a rule, conservation is the most cost-effective way to reduce water-heating bills. For example, a low-flow showerhead costing $9 saves nearly $17 for 275 kWh of electrical energy per year, for payback in less than 7 months. Other examples of hot- water-saving measures include faucet aerators; timed or optical-sensor faucets; water- saving clothes washers, dishwashers or other appliances; water heater insulation; lower-setting or timed water heaters; and swimming pool covers. If inexpensive con- ventional water heating is available, conservation measures alone may suffice and be the most cost-effective action.
If, however, conventional water heating is expensive, solar water heating is also worth considering in addition to or in conjunction with conservation. Energy efficiency measures such as those mentioned above are all compatible with solar water heating, and often reduce the size of the systems needed. Reducing hot-water use saves on water and sewage as well as energy. For more information, ask the FEMP Help Desk about the Water Conservation Program. (See Federal Program Contacts.) Next, check the conventional water-heating system. Is it the right size for the facility’s needs? Is the system using the most cost-effective fuel in the area? Is it efficient?
For larger systems, electric water heaters are now available with efficiency as high as 98%.* Large natural gas, propane, or fuel oil water heaters are available with 75% to 80% efficiency.* Switching boilers or water heaters alone may be the most effective action, but it can also be done as related work as part of a contract for parabolic- trough system installation. Then do a quick assessment of whether solar water heating is likely to be effective for the facility and whether parabolic-troughs or nonconcentrating flat-plate or evacu- ated-tube collectors are more likely to be appropriate.
(See Application Screening section and sidebar on page 14 for information on FRESA, computer software that can quickly give a preliminary assessment of whether solar water heating will be feasible.) *These numbers are for fuel conversion and do not include heat losses from the tank or delivery system. These losses can be significant—particularly for smaller water heaters—so a better insulated tank or additional insulation may also be very effective.