A Penny for Your Therms
Energy costs driving you crazy? Take a closer look at your wash aisle

By Steven J. Tinker

Natural gas future prices have more than doubled through the last year, only to plunge 44% in the first few weeks of 2006. You may not see this type of variation in gas costs from your supplier, but everyone has seen that big increases are forcing us to look at more ways to control and conserve energy. One of the fastest ways to cut energy costs is by working with your chemical supplier. Modifications to your wash formula and changing your detergents and builders can be implemented quickly, and will not require a capital investment.

Focus on water use
Much of the energy utilized at a laundry operation is used to heat the water for the wash process. So, your first step in reviewing your company’s energy costs should be to thoroughly review your water consumption—wash formula by wash formula. A close look at the mechanics, accuracy and repeatability of water level controls is an important part of this review. Make sure the water levels you call for are consistently delivered every time to prevent waste or overuse. With the help of your chemical supplier, closely review the use of pre-flushes, rinses, water levels, and loading factors to make sure you are most efficiently utilizing water. The elimination of one hot water pre-flush or rinse in a high volume wash classification could save thousands of gallons of water a week.

Next, consider an increase in load sizes. If you can increase loads by 5% across the board, you may be able to save as much as 5% of water, and the energy associated with heating that water. But a change in loading may require slightly longer wash times and slightly higher chemical concentrations to offset the higher soil factors. Therefore, it is very important to ensure wash load poundage is consistent, meets your standards, and that you avoid under-loading as much as possible.

Low-energy wash chemistry
One important modification you should consider is to convert your washroom to low-energy technology. Working with your chemical supplier, consider converting your chemistry to a line that performs better at lower temperatures. A conversion to low-energy technology may not work for everyone, so make sure that the quality meets you standards and those of your customers.
If you decide to convert your chemistry, there are several principles to keep in mind. First, when you reduce the temperature by 10ºC (18ºF) the rate of a chemical reaction will decrease by about half. That means if all other factors are equal, it will take twice as long for the chemical reactions in the wash process to be completed with an 18ºF drop in wash temperature. This “law” of chemical reaction rates means that you must make significant modifications in the wash process. You may need to modify other factors that influence soil removal, such as wash time and mechanical action. Most important, you will probably have to increase the concentration of the wash chemistry to offset the slower reaction rates.

The second basic chemical principle concerns the performance of surfactants in the wash process. Surfactants are surface-active chemicals. They interact with the physical surfaces of a solution and a solid. We are interested in surfaces where the wash water comes in contact with a soil impregnated in a fabric. Surfactants will migrate to these dissimilar interfacial surfaces and react with the soils, the fabric and the water. The surfactant will break up the soil and pull it away from the fabric.

Surfactants tend to work best at a temperature within 10ºF of the cloud point of the surfactant. A cloud point is the temperature at which a solution of the surfactant in water becomes cloudy or hazy. It is a measurement of how soluble the surfactant is in water. As the surfactant “clouds,” it becomes less soluble in water and therefore seeks out other surfaces (oils, greases, fabric) to absorb or penetrate into.

Traditional detergents in the laundry industry have cloud points in the 140-160ºF range, which is the optimum temperature range in which they perform. With lower-temperature washing you must formulate with surfactants that have cloud points in a much lower range, such as the 110-130ºF. Most chemical suppliers have detergents designed for lower temperatures. Increased detergent levels, wash times, and mechanical action may be needed to regain the soil removal levels that you and your customers demand.

Calculate potential energy savings
Before you start making radical changes in detergents and wash formulas, it is important assess how much energy you can save. Determine how many gallons of water you use per month, and then estimate the average temperature decrease you wish to achieve. A gallon of water weighs 8.3 lbs. So if you use 500,000 gallons of water per month, you’ve got 4.15 million lbs. of water. A Btu (British thermal unit) is the amount of energy required to increase the temperature of a pound of water 1ºF. If you decrease your average temperature by 15ºF, you can save 62.25 million Btu per month. One cubic foot of natural gas is equivalent to 1,031 Btu and 1 therm is equal to 100,000 Btu. Check with your natural gas supplier to determine what they charge per ccf (100 cubic feet) or per therm to determine potential savings. Remember that your boiler or water heating system will not be 100% efficient; so adjust your savings accordingly. If your water heater is 80% efficient, then the savings will really be 77.8 million Btu per month.

Drying energy
Don’t ignore the effects of the wash aisle energy savings on the energy consumption in the rest of your operation. The greatest amount of energy used in a laundry can be in the drying operation. It is a fact of physics that the energy required to evaporate water is as much as 10 times more than the energy required to heat the water 100ºF, from 60º to 160ºF. Here’s the actual relationship: As we mentioned above, it takes 1 Btu to raise the temperature of 1 lb. of water 1º F. It takes 980 Btu to convert 1 lb. of liquid water at 212º F into steam at 212º F. In other words the energy used to evaporate water can be much greater in the dryer or ironer as compared to heating water in the wash aisle. For example, if you use three gallons of water to process 1 lb. of fabric, that is 25 lbs. of water. If you lower the water temperature by an average of 15ºF, the energy saved in water heating is about 375 Btu per lb. of fabric. If after extraction there is 0.5 lb. of water left in the fabric, you will require 490 Btu just to evaporate the water. This does not even take into consideration the fuel efficiency factors of your boiler or dryers.

There is a strong potential for higher energy costs if your extraction rates are not optimum. You should try to remove as much water from the fabric and textiles as possible during the extract process to reduce the energy required to dry the fabric. That is where the real energy savings can be found. Unfortunately, that’s where you will often observe unintended consequences of changing conditions in the wash aisle.

Extraction efficiency is key
Cotton fabrics can absorb 2-3 times their weight in water. The extraction process removes most of this absorbed water. Extractors work much more efficiently when the water is warmer. Warmer water has a lower surface tension and will not “cling” to fiber surfaces as much as cold water. Centrifugal extractors are most efficient with cotton when the water temperature is 140ºF. Polyester blends react similarly, but the extraction efficiency levels out at about 120ºF. So, the simple thing to remember is that the final rinse in your facility should always be over 100ºF and is best at 120ºF.

At 120ºF the extraction removes more water from the fabric, requiring significantly less drying energy. Any so-called “low temperature” wash formulas designed to save energy by reducing hot water usage must be adjusted to use warm-to-hot water in the final rinse to improve extraction. Otherwise the energy saved in the boiler will be dwarfed by increased energy requirements in the drying operation. Since drying energy can be the largest energy requirement in your facility, it pays to make sure that your dryers and conditioners are tuned to peak efficiency. Don’t forget to set your drying programs to avoid overdrying.

Review your options
It’s amazing how much energy savings you can reap by reassessing your water usage, energy consumptions, wash and drying temperatures. With today’s erratic energy prices, it pays to look closely at the basic processes in your operation. You may be surprised at the big savings a little attention can make. TR

Steven J. Tinker is director of research and development for Gurtler Industries Inc., South Holland, IL. Contact him at 800/638-7300 or e-mail sjtinker@gurtler.com.