There’s A Ghost in the Chilled Water System

 Ghost-in-chilled-water

Holmes: Did I ever tell you about finding a ghost in a chilled water system Watson?

Watson: Come on Holmes. I may be a young pup and not as smart as some humans, but I know there is no such thing as a ghost.

Holmes: Let me tell you what happened before you make up your mind.

We were working in a shopping mall that took up a few city blocks in the middle of the downtown in a Midwestern city. The mall had a complex central plant with two centrifugal chillers, a large steam boiler, pumps, dual duct air handling units, a cooling tower, etc.

Watson: I am assuming you installed a monitoring system and began to make changes to match the operation of the energy systems to the needs of the stores and common areas in the mall.

Holmes: Right. The mall was open 7 days a weeks from 9 AM to 10 PM so the first thing we did was to insure that the energy systems only ran as required to maintain each of the spaces at the required temperatures when they were occupied.

During much of the spring, early summer and fall, when the outdoor temperature and humidty were low, we used the fresh air intake dampers on the air handling units to bring in 100% outdoor air to cool the mall. This allowed the chillers to come on later, run at lower loads during the day and shut off earlier in the evening. The chilled water and tower water pumps were controlled to run when the chillers were on and be off when the chillers were off.

Watson: Make perfect scents. Equipment saves the most energy when it is off. So how did you find the ghost in the chilled water system?

Holmes: Actually, we didn’t find it. Claude, the custodian found it. As we have encountered in so many buildings with sophisticated energy systems, they were treated by the owner the same as a drinking fountain, toilet or light bulb. The energy systems were the responsibility of the custodians; the same people who swept the floors at night.

Claude was older and a hard worker; a good person for us to deal with but he was very limited in his knowledge of the energy systems.

Watson: Let me rephrase my question. How did Claude find the ghost in the chilled water system?

Holmes: I was in the mechanical room one day when Claude came in. He said he had been cleaning up after the mall had closed the previous evening and noticed that the chilled water pump was off. He knew the chiller shut down on cool evenings but thought that the pumps had to run continuously. He believed that turning pumps off and on would damage them and shorten their lives.

Watson: That’s a pretty common misconception isn’t it Holmes? I’ve heard it many times.

Holmes: Another one of those energy myths that have been around for many years. I agreed with Claude that turning a 75 Hp pump off and on many times during the day would be hard on it but turning it on once in the morning and off once at night would not hurt it. Running that pump an extra 12 hours a day could cost the owner $100.

Watson: Did Claude understand and agree? What did you do?

Holmes: With no training and little experience with mechanical systems, he was convinced that the pump had to run 24/7. It was just one of those things that everybody knew.

We always emphasized working with and supporting the employees in all of our projects so I agreed to leave the chilled water pump on that night.

Watson: When are you going to tell me about the ghost?

Holmes: That night was when the ghost appeared. When I went to the mall the next morning Claude said, “We’ve got a problem; there’s a heater on in the chilled water system. I asked him what he meant and he said when he came in the chilled water temperature was 95 degrees. He was used to seeing in around 65 or 70 before the chillers came on.

Okay Watson, now you tell me about the ghost, the phantom heater in the chilled water system.

Watson: I think I’m starting to see the problem. First of all, Heat In has to equal Heat Out. The way a chilled water system works is by circulating 42-45 degree water through coils in the building to pick up building and ventilation air heat. That water comes back to the chiller maybe 8-10 degrees warmer where the heat is transferred by the refrigerant in the chiller to the condenser water and then it is dumped outside through the cooling tower.

However, along with the building heat, heat from the electric motors in the chiller and the circulating pumps must be rejected through the cooling towers.

Holmes: You’ve got it. From my teaching days for Purdue I still remember seeing the faces of students when they first grasped the concept that all of the energy used by a motor eventually ends up as heat. In the case of the 75 Hp chilled water pump that ran all night, the amount electricity required to run the pump was approximately 75 KW. Of that energy, some of it was lost to the surroundings from the hot pump running in the mechanical room, some of it was lost in transferring the electrical energy supplied to the pump to the rotating pump shaft and the rest was transferred to overcome the friction required to move the water through the pipes, chiller and cooling coils.

Watson: So if the chilled water pump had an efficiency of 33%, then 25 KW essentially ends up as heat added to the chilled water. A 25 KW electric heater is enough to heat most houses. That’s a lot of heat.

Holmes: Correct. And with the chiller and air handling units shut off, where does that heat go? Nowhere. It acts as a heater for the water in the closed, insulated piping system.

Watson: That was Claude’s ghost.

Holmes: A tremendous amount of energy is wasted in this country by unqualified people running complex energy systems. Relying on myths and misinformation instead of science is not only costly for the ones paying the bills but it is wasting our natural resources and dumping tons of unnecessary emissions into the atmosphere.

Watson: More people need to understand that Heat In = Heat Out. We need more trained Energy Professionals operating energy systems.

Holmes: You’re right. A poorly trained operator can waste more of an owner’s money every year than what it would have cost to hire one with the required education, skills and experience.

Tell us about your experiences, both good and bad with energy professionals, what has worked and what hasn’t. Send us your comments, thoughts and suggestions on how to improve our profession so we can all continue to learn from each other. Thanks – Holmes & Watson.

 

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