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MAINTENANCE


Service visit check sheets? Not anymore!


Mike Creamer, managing director of Business Edge takes a light-hearted look at using performance analysers instead of check sheets.


M


ary Lamb, the new facilities manager at the huge London building of Rob NM Blind Lawyers LLP, is sweeping away the old and bringing in the new, where caring for her water chillers is concerned. A sound engineering background and a basic knowledge of thermodynamics tells her there’s a lot of scope for improvement and so she calls in the air conditioning contractor for a chat


After conducting the chiller service work and completing the service record sheets, Bill and Ben meet with Ms Lamb. Mary: Morning Bill, thanks for coming in today. Who’s this with you?


Bill: This is Ben, our new junior engineer. He’s fresh out of college and thinks he knows better than us old-timers. So, I brought him along to teach him a thing or two.


Mary: Welcome Ben. Just what I want to hear. Some new ideas may be just what we need. Our running costs are off the scale, as is our carbon footprint. The CO2


we’re


releasing keeps me up at night. I’ve installed electrical metering on the main items of plant around the building and I’ve matched the results against our total energy bill. I’ve also looked at the bills over the last few years and our electricity cost, which comes straight off our bottom- line profit, are mind-boggling. A few simple calculations are telling me that something is seriously wrong.


Bill: What do you think is causing this? The chillers appear to be working well and nothing looks especially odd or wrong.


Mary: Well, the two large water chillers in the basement are consuming around 65% of the total building electrical energy. I checked the manufacturer’s performance data at various chilled water and ambient


20 June 2020


conditions and the power input readings from my metering equipment disagree considerably with the manufacturers stated power input.


Bill: That’s odd. Over the last few years we’ve conducted our usual quarterly health checks on the chillers, noting all the salient readings and completing the service record sheets, which you should have.


Mary: Yes, and I’m glad you brought that up. The service record sheets are not much use to me and I’m not sure how useful they are to you. For example, I note that you record volts and amps per phase for each machine, but you don’t show the kilowatt power input for the compressors. So, how many kilowatts power input is each compressor consuming?


Bill: Er…? Mary: And another thing. What about the cooling capacity? If you can’t tell me the kilowatt power input or the cooling capacity, how can you tell if the machine’s running at full efficiency?


Bill: Well... we look at the suction pressure and the discharge pressure from our gauges, which we connect at the service points and we make a note of the readings and the evaporating and the condensing temperatures, using a comparator. If the discharge pressure looks to be too high or the suction pressure looks to be too low, we make a note that the refrigerant charge might need adjusting. Or maybe that something else is wrong. Mary: Oh, and then what? Bill: Well, we then usually add a note to the service record sheet stating what we think might need doing next and the previous FM chappie would normally ask us for a


quotation to come in and play around with it until it runs better.


Mary: Right. It’s now February and the machines are having it easy with low power input. When you come back in July, the building load and ambient conditions will be very different from your previous visit, which means the chillers will be running in an entirely different way. So how can you check the efficiency, especially if you still don’t know the new cooling capacity and the power input?


Bill: Er... we can look at the COP. Mary: How? Without the cooling capacity and the power input you can’t calculate the COP. In any event, COP is no good to either of us. COP is up and down like a fiddler’s elbow across the day and the year. So how can we draw any meaningful conclusions? Ben: Sorry boss, but she’s right, you know. Bill: Really? Mary: Look Bill, I see you’ve done great work for us over the years and you always do your best. But without the right information, we just can’t make any sound decisions. If you can’t see it, you can’t fix it.


The water chillers are consuming far more energy than they should be and we must do something about it.


In my experience, an efficient machine is a far more reliable machine and the investment we’ve made in these chillers is such that we must look after them. And if we ever needed to replace them, how on earth would we ever get them out of the basement, anyway?


In a nutshell, COP, EER and so on are no good to us. We need a means of true performance analysis that is much better. Bill: Okay, well, I see your need to minimise


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