Chapter 9 Tactics

The measures outlined below can reduce the energy required to heat water and the quantity of waste heat released from tanks and pipes.

1. Efficient use adjustments and upgrades

• Set water heater temperature appropriately.
The factory temperature setting for water heaters is typically 140°F, but can usually be lowered to 1207F (or lower) without affecting performance. An energy efficiency consultant can determine the appropriate temperature setting for a specific application. By one estimate, a switch from 140°F to 120°F can save 18% of water heating energy and a 107 thermostat reduction can save 6% of water heating energy.1 Table 9.1 gives an estimate of temperatures required for a range of applications.

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Costs, rebates and payback period: Adjusting water heater temperature is a no cost efficiency measure.

• Install pipe and water tank insulation.
Pipe and tank insulation reduces standby heat loss from hot water, reducing energy required to maintain the correct water temperature. Energy saved with pipe and tank insulation varies widely depending on application, but can be estimated for a specific building by an efficiency engineer.

Costs, rebates and payback period: Consult with an energy efficiency engineer for an estimate of insulation installation costs and payback period. PG&E provides rebates for insulating previously bare liquid storage or transfer pipes connected to gas-fired water heaters, at $2.00-$4.00/linear foot.2

• For electric heaters: install timers and heat water at night using off-peak electricity.

Costs, rebates and payback period: Consult with an energy efficiency engineer for an estimate of timer installation costs and energy savings.

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When calculating payback, it is important to account for savings due to off-peak electricity purchase. Payback periods vary greatly depending on specifics of the time-of-day power pricing structure.

• Install low-flow fixtures and automatic sensor controls.
Lowering flow in hot water fixtures (faucets, showerheads, etc.) reduces the energy required to heat water by reducing the volume of hot water consumed. The Energy Policy Act of 1992 established maximum flow rate guidelines for faucets, showerheads, toilets and other fixtures. Average flow rates for faucet aerators and showerheads are now around 2.5 gallons per minute (GPM). Super-efficient faucet fixtures have flows of 0.5 GPM, and super-efficient showerheads have flows of 1.5 GPM.3

In addition to energy savings from avoided water heating, installation of low-flow fixtures and automatic sensor controls will result in savings from reduced water use. According to Greener Buildings, a resource center for environmentally responsible building: “In a typical 100,000-square-foot office building, low-flow fixtures coupled with sensors and automatic controls can save a minimum of one million gallons of water
per year, based on 650 building occupants each using an average of 20 gallons per day.”4

Costs, rebates and payback period: Consult with an energy efficiency engineer for an estimate of low-flow fixture installation costs and energy and water savings. When estimating payback, it is important to account for savings due to energy and water savings.


Additional information

For more information on low-flow fixtures and automatic sensor controls, see:
• James Piper, Maintenance Solutions. “Water Use: Slowing the Flow.” 2003. Accessible at http://www.facilitiesnet.com/ms/article.asp?id=1969&keywords


2. Equipment upgrades

Upgrading equipment will require substantial up-front capital investment and will therefore be easiest to justify financially when existing equipment is due or nearly due for replacement.

• Correctly size water heater for company needs.
The host company’s office may be operating with a larger-than-necessary water heater. An energy efficiency consultant can evaluate the heater size required to meet office hot water demand. The hot water needs of a typical office building are: 0.4 gal/person maximum hour,
2.0 gal/person maximum day and 1.0 gal/person average day.5

Costs, rebates and payback period: Consult with an energy efficiency engineer for an estimate of costs and payback period for a water heater replacement. PG&E will rebate $0.80/therm saved for customized water heating efficiency projects.6

• Purchase a water heater with higher thermal efficiency.
Efficiency of commercial water heaters is expressed as a thermal efficiency percentage (0–100%), which represents the percentage of energy from the fuel or electric heating element that is transferred to the water being heated (the higher the value, the more efficient the heater). Commercial heaters are also rated on standby loss, a measure of the percentage of heat lost per hour once water is heated. Standby loss is also expressed as a percentage, typically ranging from 0.5-2.0% (the lower the value, the more efficient the heater).7

Note: Residential water heater efficiency is expressed in a different unit: energy factor (EF), which ranges from 0.00 to 1.00 (higher values are more efficient). EF is a combined measurement of thermal efficiency and standby loss.

Typical oil and gas-fired heaters have thermal efficiencies of ~80%, but can range up to 95%. Gas-condensing water heaters are more efficient than traditional gas-fired heaters because they can increase thermal efficiency by up to 20%.8 Electric water heaters typically have a thermal efficiency of 98%.9 Whereas electric units themselves are very efficient, it is important to consider that the process of electricity generation and distribution is quite inefficient. The average thermal efficiency of American power plants is around 33% (33% of input fuel energy is output as electricity). Additional efficiency losses occur during electricity transmission and distribution (9.5% on average in 2001).10 These inefficiencies contribute to the high price of electricity in relation to gas and oil in most markets. As a result, in most areas, oil and gas-fired water heaters have better economics and reduced climate impacts compared to electric water heaters.

In many applications, a tankless water heater may be the most efficient option. Tankless heaters heat water on demand instead of storing preheated water, which eliminates standby loss. An energy engineer can estimate potential efficiency gains from a switch to a tankless heater at the host company. Tankless heaters are typically more expensive than comparable storage type heaters.

Costs, rebates and payback period: Consult with an energy efficiency engineer for an estimate of costs and payback period for a water heater replacement. PG&E will rebate $0.80/therm saved for customized water heating efficiency projects.11

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