Btu Buddy 50: Reciprocating Chiller With Fouled Condenser Tubes
Bob arrived at the motel and the manager showed him to the equipment room where the chiller was located. It was not running. Bob began to look around and opened the control panel on the chiller and noticed that the manual reset high-pressure control button was out, indicating that high-pressure control had shut the chiller down (Figure 1). Bob was reaching to reset the high-pressure control when Btu Buddy appeared and said, “Why don’t you check around a little bit before you reset the control. It would also be a good idea to fasten your gauges to the compressor so you could monitor the pressures when it starts up.”
Bob then said, “Well, that is just like me, just push a button without thinking. You are right. I should think more before I act.”
Bob installed gauges on the compressor on the high and low side gauge ports. Then Btu Buddy said, “It is a good idea to check the water tower before you reset the control to see how dirty it is and to see if there is a proper water flow over the tower.”
Bob went to the tower and noticed that there was plenty of water flowing over the tower, but the water was dirty and there was a lot of green algae scum in the tower basin. He then told Btu Buddy, “There is no need to try to start this chiller until the tower is cleaned up.”
Bob then reset the high-pressure control and the chiller started. After running for about 15 minutes, the head pressure began to rise. The water from the cooling tower was returning to the condenser at 83° and the water from the condenser back to the tower was 88° (Figure 2). Bob then scratched his head. Btu Buddy asked, “What is the matter? What do you see?”
Bob said, “I thought this chiller should add 10° to the water and it is only adding 5°. The chiller is operating at full load; the head pressure is 229 psig (R-22) and climbing. I am not sure what I see.”
Btu Buddy said, “Feel the liquid line going to the expansion valve and tell me what you feel.”
Bob held the line in his hand and said, “It is really hot, with 83° entering water. You would think it would be cool.”
Bob then said, “I get it. There is plenty of capacity to remove the heat, but it is not being removed. The condenser tubes must be dirty, like the tower basin was.”
“Correct,” said Btu Buddy. “The only thing to do is shut it down and clean the tubes.”
Bob shut the chiller down and removed the head from the condenser. The tubes were really dirty. He again called the office and they sent a helper with a tube cleaning machine that turns a nylon brush and injects water at the same time (Figure 3). They cleaned the tubes and flushed out the condenser shell with fresh water and replaced the head on the condenser. It was ready to start up again.
Bob started the chiller while watching the gauges. The entering water to the cooling tower quickly rose to 85° and the leaving water went to 95°. The chiller was operating really well as the outside temperature was now 95° (Figure 4).
Btu Buddy then said, “You went about this with a systematic approach and you were able to find the problem. Now it is time to recommend to the owner that they get a water treatment program going as well as a service contract to keep the machine operating at peak efficiency. This machine was costing them extra money operating at high head pressures for such a long time. They were paying extra for poor efficiency.”
Bob gave the motel management a proposal and they decided that it was a good idea. Bob had sold a service contract that was worth something to his company, and a good value to the customer.
As they were riding away, Btu Buddy said, “Well, Bob, your service call was a good value to the customer and you added business to your company volume. It is hard to beat that for a good day’s work. Everyone is pleased with that. Every technician should try for this kind of day.”
Bob said, “Thanks for the advice along the way.”
Publication date: 05/21/2007