water heater efficiency...

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water heater efficiency...

Post  Guest on Thu Jun 23, 2011 9:24 am

a bit OT, as a result of a discussion that got me curious...

Step 1: Fuel Choice and Sizing

Fuel Options
More U.S. households use natural gas to heat water than any other fuel source, and about 40% use electricity. A small percentage use propane or heating oil. Typical water heaters in the U.S. are electric resistance or atmospheric natural gas tank water heaters. Electric water heaters typically have Energy Factors (efficiency ratings) of about 0.9, while gas ones will be rated about 0.6.
The energy factor is based on site energy use, which is the amount of energy your water heater uses. However, it takes about three times as much source energy (this includes the energy needed to generate and distribute a fuel) to deliver a unit of electricity to the site as gas, since only about 1/3 of the fuel energy that enters the power plant reaches the house. The rest is lost due to inefficiency at the power plant and the power lines. Therefore, an electric water heater that appears to be 50% “better” than a gas one (0.9 Energy Factor versus 0.6 Energy Factor) actually uses much more source energy than the average gas water heater.
There is a lot of good news, though. Manufacturers are bringing many kinds of advanced water heaters to the U.S. market, with much higher efficiency. The big news for electricity users is the Heat Pump Water Heater, which (like any other heat pump) takes energy from the air to heat water. At the same time, the heat pump water heater dehumidifies the air, saving the cost of buying and operating a separate dehumidifier. This is especially beneficial when the water heater is located in a basement and/or in a humid climate.
For natural gas, many customers are choosing tankless or instantaneous water heaters. These are very compact, and generally wall-hung. Their rated efficiency is higher than that of tank units, and some units are Energy Star rated. However, the delivered efficiency gains may be somewhat more modest in typical home use (see table below). And, they can be very expensive to install in retrofit applications, requiring special ductwork and upsizing the gas lines. Condensing gas water heaters are a very promising new entry to the residential market. A condensing gas water heater works like a normal tank-type water heater, except that before the combustion gases are vented outside, the heat in those gases is captured and used to help heat the water in the tank.
In general, most choices available for natural gas are also sold for propane.
Oil users have fewer choices. If you currently have an oil-fired boiler, your best options are to purchase in indirect tank that connects to your boiler (best if your boiler is relatively new), or an integrated unit that provides space heat and hot water in one.
Conventional electric water heaters (other than heat pump water heaters) are not recommended. If you don't have access to natural gas, you may want to consider a heat pump water heater.

Sizing a Water Heater
The capacity of a water heater is an important consideration. The water heater should provide enough hot water at the busiest time of the day. For a storage water heater, this capacity is indicated by its "first hour rating," which accounts for the effects of tank size and the speed by which cold water is heated. First hour rating is included in product literature and on the EnergyGuide label alongside efficiency rating.
For tankless, solar and indirect water heaters, sizing requires a few other calculations that your installation contractor can help you with.
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Step 2: Compare Life-Cycle Costs
Water Heater Type Efficiency (EF) Installed Cost 1 Yearly Energy Cost 2 Life (years) 3 Total Cost (Over 13 Years) 4
Conventional gas storage
0.60 $850 $350 13 $5,394
High-efficiency gas storage
0.65 $1,025 $323 13 $5,220
Condensing gas storage
0.86 $2,000 $244 13 $5,170
Conventional oil-fired storage
0.55 $1,400 $654 8 $11,299
Minimum Efficiency electric storage
0.90 $750 $463 13 $6,769
High-eff. electric storage
0.95 $820 $439 13 $6,528
Demand gas (no pilot) 5
0.82 $1,600 $256 13 $4,925
Electric heat pump water heater
2.20 $1,660 $190 13 $4,125
Solar with electric back-up
1.20 $4,800 $175 13 $7,072

1. Purchase costs include our best estimates of installation labor and do not include financial incentives.
2. Operating cost based on hot water needs for typical family of four and energy costs of 9.5¢/kWh for electricity, $1.40/therm for gas, $2.40/gallon for oil.
3. Life expectancy for water heaters is highly variable, largely dependent on water hardness, and on maintenance.
4. Future operating costs are neither discounted nor adjusted for inflation.
5. Currently, there is too little data to accurately estimate life expectancy for tankless water heaters, but preliminary data shows that tankless water heaters could last up to 20 years. For all water heaters, life expectancy will depend on local variables such as water chemistry and homeowner maintenance.

I also found out that the Gas Heaters from ferroli (city gas) as at least 0.78 - 0.9x efficient....

Very Happy


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