water heater energy efficiency
Before you purchase a water heater for your home, it's important to know
how energy efficient it is. Usually the most energy-efficient water heater
models or systems are more expensive. However, if you purchase an energy-efficient
model, you may save more money in the long run on your water heating bills
than if you purchase a less efficient model.
of storage, demand, and heat pump water heaters
Use the energy factor to determine the energy efficiency of a storage,
demand, or heat
pump water heater.
The energy factor (EF) indicates a water heater's overall energy efficiency
based on the amount of hot water produced per unit of fuel consumed over
a typical day. This includes the following:
The higher the energy factor, the more efficient the water heater. However,
higher energy factor values don't always mean lower annual operating costs,
especially when you compare fuel sources.
- Recovery efficiency – how efficiently the heat from the energy
source is transferred to the water
- Standby losses – the percentage of heat loss per hour from
the stored water compared to the heat content of the water (water heaters
with storage tanks)
- Cycling losses – the loss of heat as the water circulates through
a water heater tank, and/or inlet and outlet pipes.
When choosing a storage, demand, or heat pump water heater model, you need
to factor in not only energy efficiency but alsio:
Solar water heater energy efficiency
For a solar water heating system, use the solar energy factor (SEF) and
solar fraction (SF) to determine its energy efficiency.
energy factor is defined as the energy delivered by the system divided
by the electrical or gas energy put into the system. The higher the number,
the more energy efficient. Solar energy factors range from 1.0 to 11.
Systems with solar energy factors of 2 or 3 are the most common.
Another solar water heater performance metric is the solar fraction. The
solar fraction is the portion of the total conventional hot water heating
load (delivered energy and tank standby losses). The higher the solar
fraction, the greater the solar contribution to water heating, which reduces
the energy required by the backup water heater. The solar fraction varies
from 0 to 1.0. Typical solar factors are 0.5–0.75.
Don't choose a solar water heating system based solely on its energy efficiency.
When selecting a solar water heater, it's also important to consider the