Hawaii Building Engineers Association

Cooling Tower Maintenance

COOLING TOWERS: Regular Care Saves Time, Money, Energy

by Glenn A. Babcock 

A cooling tower is a marvelous device that enables building owners and operators to take advantage of operating cost savings inherent in water-cooled systems. By conserving both energy and water, a well maintained tower enables the cooling system to perform reliably and cost-effectively at optimum efficiency. Contractors who maintain existing cooling systems can provide their customers a great service by implementing a comprehensive, routine cooling tower maintenance program.

Unfortunately, for many years the cooling tower has been the forgotten component of the water cooling system when it comes to maintenance. A newly installed cooling tower reliably delivers the design fluid temperature and flow rate. However, since its heat transfer operation creates a “hurricane-like” environment and is a natural “air-washer”, the cooling tower needs routine inspection and maintenance to continue performing as designed.

This article takes a brief look at routine maintenance, and suggests ways to help you improve your customers' cooling tower performance.

How They Work
Let's start with a look at how a cooling tower works. In an open circuit cooling tower, warm water from the heat source is evenly distributed directly over a heat transfer surface called “fill” or “wet deck,” while air is simultaneously forced or drawn through the tower. This causes a small percentage of the water to evaporate. The evaporation process removes heat and cools the remaining water, which is collected in the tower cold water basin and is returned to the heat source (typically a water-cooled condenser or other heat exchanger). Similarly, in a closed circuit cooling tower or evaporative condenser, the heat is rejected indirectly from a fluid or vapor in the coil section by spraying re-circulated water over the coil section, evaporating a small percentage of the water.

The temperature at which the cooled fluid is returned to the system measures tower performance. This temperature can vary depending upon the actual cooling load, water flow, airflow, and ambient temperature conditions.

To perform properly, all tower components must be kept clean and free of obstructions. The following sections describe how this is accomplished through routine maintenance. Maintenance-frequency will depend largely upon the condition of the circulating water and the environment in which the tower is operating.

Keep Strainer Systems Clean
Strainers in the tower provide a means of keeping debris out of the condenser system water loop. Strainers in the cold water basin outlet prevent debris from reaching the pump. Some towers feature low-pressure drop pre-strainers upstream of the hot water basin to prevent clogging of distribution nozzles. Inspect and clean both strainers as necessary. Some tower designs allow external access to the strainers, which enables maintenance to take place without the need to turn off the unit.

Maintain Even Water Distribution
The water distribution system should evenly distribute water over the wet deck surface or coil section via either a gravity distribution system or a pressurized spray system, using a series of nozzles. If water distribution is found to be uneven, the nozzles need to be checked. Clean clogged nozzles in accordance with the manufacturer's recommendations.

In a gravity distribution system, the nozzles can be externally accessed, visually inspected, and cleaned by removing the hot water basin covers on the fan deck. Some innovative spray distribution systems have nozzles and branches held in place by snap-in rubber grommets, which allow easy removal to clean and flush debris.

A well-designed cold water basin is sloped toward the strainer to keep dirt (which can accelerate corrosion) from accumulating. Keep these basins clean by occasionally flushing the dirt out of the system. Another way to accomplish this is to install accessories such as a sump sweeper piping system in conjunction with water filtration or separator devices. Water filtration saves maintenance costs by reducing the dirt in the cooling water system, which in turn reduces the time required to clean the cold water basins. It also reduces water treatment cost.

Water Conservation

                                                    

Watergy by definition means “connecting water with energy.” In simple sense it takes a certain amount of electricity to deal with the water that we use. The connection can be seen when we turn on the faucet for hot water and the hot water tank must reproduce the hot water that was used. The water going down the drain must be purified and the cost to do so is billed back to us in the cost of the electricity and maintenance to perform that task. So what saves us more money turning off our lights or turning off our faucets? Given a scenario of five minutes of a faucet running would be equal to the cost of lighting a 60 watt light bulb, if not more. Water on Oahu needs to be conserved and we can do our part, by reducing our waste.  The Environmental Protection Agency (EPA) has come up with a program called Water Sense.  The U.S. General Accounting Office (GAO) has estimated that, even assuming non-drought conditions, at least 36 states will suffer some sort of water shortage by 2013. On Oahu the water shortage is expected to affect us by 2010. In an effort to promote water efficiency and help protect the future of our water supply, the EPA has launched the Water Sense Program that has been in effect since 2006. The program has found that the reduction in water is driven by the cost of building new wastewater plants and other projects to meet the demand for water. Taxpayers and users of water would be the revenue stream to provide new facilities and products to reduce consumption.  Demand side management is one means to reach their goal through the reduction of use and not utilize taxpayer’s money to increase the infrastructure. Regardless, the price of water is on the rise. With an estimated 7% - 12% increase annually.

Product Review

ICI Paints is pleased to offer a variety of complimentary services designed to make the painting process as efficient and painless as possible. ICI has a comprehensive program, specific to the maintenance industry and can be customized to meet individual needs. the services are as follows:

• Custom Specifications
• Bid Packages
• Job walks
• Contractor referrals
• Project Inspections
• Design and Color coordination
• Order Forms/ Color records

Variable Air Volume Manual

This book takes the reader from design to testing and balancing to troubleshooting, this practical book covers all the aspects of variable air volume systems for heating, cooling and ventilation systems. With a hands on approach with expertise in the trade, the reader is shown all the tricks of the trade for reducing the installation and operating costs while increasing occupant comfort. VAV applications are explained in detail for all the systems with drawings showing the different component and their function. Topics covered are temperature, pneumatics, direct digital control, and conversions from pneumatic to digital. Written by Herb Wendes, P.E. and distributed by AEE.

FIX MY PROBLEM

A building Engineer responds to a building that has had a hot complaint for years. The Engineer investigates the chill water system and finds the chill water set point is 43 degrees. The air handle is a constant velocity unit (10,000 CFM) with a three way valve. the air wet bulb temperature was 70 (34.09) entering and leaving was 67 degrees (31.62 Enthalpy), the chill water valve was a three way valve. The leaving air had an inline thermostat to control the valve and supply air temperature. What was the proper troubleshooting procedure? What should he look for? Calculate the System Total BTU delivery

4.5 x ________(CFM) x (Enthalpy change) = system total Btu

What is the equipment rated BTU ?

2006 AWARD

The 2006 Oahu ARM Committee Members and Advisors were recently recognized by the Hawaii Chapter of The Community Associations Institute (CAI) with CAI's highest honor - The Richard Murray Gourley Distinguished Service Award. Those honored with the prestigious award were ARMs Diane Romero, Chair; Rick Larson, Vice Chair; Committee Members Jennifer Gerard, Kawika Keala, Russ Kulinski, Anthony Sedillo, Bruce Thompson, Diane Wack; and Committee Advisors Don Higgins, Duane Komine, Ken Plummer and Ralph Shumway.

2006 Oahu ARM Committee was lauded "for providing outstanding education, leadership and brotherhood to the property management industry and for setting a new standard of excellence for resident managers." CAI Hawaii Chapter President Sue Savio presented the award at the Japanese Cultural Center in front of a packed room of nearly 100 guests.

CAI's Gourley Award honors outstanding service to the community association industry. Past honorees have been Former IREM National President Aaron M. Chaney CPM; Senator-Elect Mazie Hirono; Community Association Attorneys Bruce Dinman, John Morris, Jane Sugimura; CAI Hawaii Chapter Co-Founders Leonard Kacher PCAM and Milton Motooka; Insurance Professional Sue Savio and Registered Parliamentarian Steve Glanstein. This marks the first time the award has ever been given to a committee and is especially noteworthy since the committee is not affiliated with CAI.

Richard Murray Gourley, PCAM was President of both the Hawaii Chapter of CAI and Hawaiiana Management Company, Ltd. when he passed away in 1993. Mr. Gourley, a highly respected leader in Hawaii's residential property management industry, spent countless hours championing legislation benefiting Hawaii's community association industry. Richard Gourley's wife Polly and son Rip were among the guests in attendance for the award ceremony.

Diane Romero, A.R.M.

Resident Manager, Kalakaua Vista

Editor's Note

In 2006 the cost of energy exceeded our budgets dramatically as the average cost of a barrel of oil rose to $60 - $69 per barrel. In the United States producers continue to recover from the losses suffered from the hurricanes in the southern regions. Growth in 2007 non-OPEC (Orgainization of Petroleum Exporting Countries) likely will rise to more than 1.4 million barrels per day. The United States uses 70% of the natural resourses worldwide and is in heavy competition with China for Natural resources. After saying that, Relative to world crude production capacity most of which is located in Saudi Arabia, is only expected to rise slightly in 2007. Only limited surplus capacity could be tapped of the existing supplies because of potential supply problems in Nigeria, Iran, Iraq, and Venezulea. These factors as well of the fact another Hurricane season is just months away could continue to tighten the supply pricing patterns.

Good luck on your electrical budgeting for 2007. Any ideas on accurate forecasting can be sent to the HBEA for distribution to all our members. HBEA745@AOL.COM

Safety

Safety – Keys to Lockout/Tagout

The Occupational Safety and Health Administration currently lists the 10 most violated OSHA standards based on past citations, lockout/tagout was the fifth most cited standard.

Companies continue to ignore the importance of tagout and the fines and citations usually occur after something happens to the worker or the building. Companies should comply with lockout/tagout to prevent accidents and save lives.

During lockout/tagout, a person authorized by the company places locks and or tags on energy isolating devices before working on equipment, and only that person can remove those locks and tags. Isolation devices are mechanical appliances, such as circuit breakers, used to stop energy from being released to the equipment. Lockout is usually accomplished with a keyed lock holding an isolating device in an “off” position. Tagout, which is often used when lockout can not take place, uses tags to warn people that the equipment and isolating device may not be operated.

Lockout/tagout is required when servicing or performing maintenance on equipment. Effective lockout/tagout should occur in three phases 1) taking the equipment out of service 2) locking out the equipment by isolation and tags 3) performing the repair or service and returning the equipment back to service. Applying the lockout/tagout requires an authorized person trained in lockout/tagout and in writing as a qualified person. Only that person will be able to apply the lockout/tagout and will have the key and locks to tagout the equipment. He/she will tagout the equipment and log the time, location, equipment and the person tagging the equipment out of service in the lockout/tagout procedure manual. After the repair or service the tags will be removed after the equipment has been verified to be safe to operate. At that time the authorized person will tag the machinery in and clear all the logs associated with the tagout.

Today question is how often do you tagout a lighting system in a space to change a ballast? Most tenants will argue about turning the lights outs and then you are faced with a dilemma, what should you do? The right answer is to tell the tenant in order to replace the burnt out lamp the power must be turned off or it will have to be done after hours at their expense. Many times maintenance workers are put in places of great danger by tenants or managers that want to do it with the power on. Or as the workers say “doing it hot”. It is just a matter of time until someone gets hurt. Are you willing to take that change on a stupid 2 lamp lighting fixture?

Test your knowledge

AIR COMPRESSOR RUN TIME

Many building in Hawaii still have pneumatic controls systems or a hybrid system utilizing digital and air for controls. Many people do not know about compressor sizing and starts per hour. The compressor is normally sized to operate up to one half of the time to provide normal system air consumption. The air storage tank capacity is matched to the pump and is designed to give a reasonable number of cycles per hour. The storage tank provides sufficient storage capacity to carry peak air consumption loads. To determine the SCFM rating of compressors the load must be determined. The compressor should have a rated SCFM output of at least 33% or 50% of operation.

It may be necessary to determine the effects of sizing, pressure switch settings, and tank size on compressor starts per hour. Air compressors will specify maximum starts per hour. Some smaller sizes will specify no more than 12 while some larger models will enable 30 starts per hour. The minimum bleed off time should also be calculated. Then you can decide on other things like oil less, lubricated, single, or duplex compressors.

Run time testing should be accomplished because in many cases in some buildings the poor air compressors never shut off, due to leaks and improper air settings. A run test is an air compressor performance test that measures the percentage of time that a compressor runs to enable it to maintain a supply of compressed air to the control system. A run time test determines whether an air compressor is sized properly for the job. The run time test is performed under a normal compressed air load on the system. The length of time (in minutes and seconds) that the air compressor is on is measured with the length of time that the air compressor is off. The run time percentage is found by dividing the compressor on time by the compressor on time plus the compressor off time.  This number is multiplied by 100 to convert to a percentage. Use the following formula.

Air compressors

Air compressors Question

  I had been told that by replacing or changing all air compressor motors to variable speed drive (VSD), I will lower my electrical energy costs. I have three horsepower 100 rotary screw compressors and all three run all the time. Should I replace all these with variable speed drives?

This question can not be answered correctly without more data especially a load profile. Many times the conception of changing to a variable speed drive will save money and is very inaccurate. It is recommended that an assessment of your total system be done first before any equipment is changed. Variable speed compressors are great depending on how the overall system is in regards to the new drive, in some cases a drive may make it worse. Facts about variable speed drives include:

• A VSD is much more efficient, as a trim unit, than a similar size constant speed compressor version at loads of 25% to 75%.
• A variable speed is close equal to a constant speed compressor at 75% to 100% of load.
• A VSD, when applied at full load, will draw more power, for the same flow, than a similar size constant speed compressor. This can be 4 – 6% more in lubricated rotary screws and up to 13% more in oil free designs.