Monday, August 4, 2008

Reducing Hot Water Heating Cost

The “Big Three” electric consumers in most households are hot water heating, heating/cooling and clothes drying. In this article we will discuss how to reduce hot water cost.

What can be done now!

1. Reduce hot water temperature

The quickest and easiest way to reduce this hot water cost is to reduce the temperature. First, hot water temperatures above 110 are generally uncomfortable and temperatures above 125 can be dangerous (hot tubs run at 105-108 degrees). Therefore, why set your hot water above this? Most newer hot water heaters come pre-set at 130 degrees. Some older units are even set from 140 to 180 degrees. Setting the temperature above what is comfortable to bathe in is wasteful.

Dishwashers monitor the temperature of the water and heat to the desired 135-140 degrees. The idea behind reducing hot water cost is to heat the water only as much as needed and, if possible, heat it only at the source of consumption. This is what the dishwasher does best. It heats the water to the desired temperature at the point of consumption. We don’t pay needlessly for heating and storing hot water.

For an average consumption of 50 gallons per day of hot water, at an average US residential rate of $.10/kwh, reducing the temperature of the hot water by just 10 degrees saves approximately $50 per year.

2. Reduce the amount of hot water needed.

Reduce the need for hot water by utilizing low flow shower heads and sink aerators. Use warm or hot sparingly for laundry; most modern energy efficient washing machines and detergents work fine with cold water. When it may be necessary to wash with warm or hot water, never rinse with anything but cold.

Maximize the load in your dishwasher. Surprisingly the dishwasher, if used correctly, is the most energy efficient way of washing dishes. A modern dishwasher will use less than 9 gallons of water per load. Even an older dishwasher uses around 12 gallons per load. To maximize the benefit of a dishwasher, pre-rinse all dishes in cold water before loading and run full loads in the dishwasher.

What can we plan for!

1. Tankless water heaters.

Storing hot water in a central tank is “so last year” and is so wasteful. Even though modern hot water heaters have improved insulation to minimize heat loss when not in use, we still loose heat and have to re-heat throughout the day. Temperature loss from the tank depends on several factors including tank size, temperature of the room where tank is located and temperature of the hot water,however, a loss of 1kwh/day or 365 kwh/year aren’t uncommon. At the $0.10/kwh average US electric rate, this add ups to $36.50/year just to overcome the heat lost in the tank. Not to mention the wasted water it takes to get the hot water to the sink or shower.

The most efficient way to heat water is to heat it on-demand, or only where needed and when needed. Many companies have tankless water heaters such as Rinnai, Bosch Aquastar, Rheem and Skye. Although these tankless systems can be pricey, the cost with competition is coming down.

2. Pre-heat water going into hot water heater.

The higher we can get the temperature of the water going into the hot water heater, the less work it has to do to heat it up. Going back to our previous example of lowering the hot water temperature, if we can pre-heat the water feeding the hot water heater by 10 degrees we can save $50 per year. There are several ways to pre-heat the water.

Run hot water piping through hot areas such as the attic or garage. In the summer attic temperatures can easily pre-heat water to the point that little work is done by the hot water heater. Other un-conditioned spaces such as a garage can pre-heat water. Care must be taken to prevent the piping from sweating or condensing and dripping onto the ceiling or other critical area. Also keep in mind that these same areas may get cold in the winter. Having the water system designed so that water can be routed through the hot areas in the summer and through a warmer area in the winter will be the most efficient. Your plumber can make specific recommendations about routing and installation.

Another way to pre-heat water is through solar panels. In the energy crisis of the 1970’s Israel passed a law that all new construction contain solar hot water heaters. There are many options for solar hot water heating including some plans on building them yourself.

For years companies have used a process of capturing heat from the high pressure side of the air conditioner to heat water for pools. This process uses a refrigerant to water heat exchanger. Packless Industries and Tranter Heat Exchangers make small heat exchangers for this purpose. This has two benefits: First it pre-heats water going into the hot water heater. Secondly it helps cool the hot refrigerant going outside to the condenser. You get free water heating and an improvement in air conditioning performance at the same time. You can go to one of the heat exchanger manufacturer's website for help in sizing the heat exchanger.

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