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Member Post posted an update
Trane rtaf tab reports
Just had these 2 rtaf chillers tab’d last week. Install was 7-2025 and still not really fully commissioned due to so many issues with controls,programming, and some yet to be completed odds and ends. But my focus here is water flowrate. This is literally all we recieved for a tab report. The guy performing the tab work said he didnt have the proper tools to do it the way he’d prefer for starters, said he needed some ultrasonic instrument but didnt have it. Ive never heard of this. He did have a hydromanometer. Short ridge. Old school. But I think he fudged the whole job. He did not take any dp measurements at the pump, he did check dp across the tdv. Im going to look to see if I can find the flow charts for those valves. The evap and system dp he got off the symbio 800 control screen. Can someone explain to me what the design evap dp actually tells us besides thats the dp the bypass valve will try to maintain if it goes under? Like how can I use that design value to estimate my flow at varying conditions? I was not taught this. The 85ft tdh I have no idea where he got that from as that is not on any of the engineering submittals,this was a changeout not new chw system. And pump specs I see in the subs is 400gpm at 65ft with 30%glycol mix. He didnt even check pump head so… I checked myself next day under same conditions (full flow) and got 31psi (71.6ft) see where im going with this? Wouldn’t that mean theres less than the 400gpm if it 400 at 65? I need to look up the correct pump curve still, theres discrepancy on what we actually have for pumps,they were insulated over so I have to find the tag on pump to get impeller dia since nobody seems to know what pumps were ordered. Installed by trane at factory under chillers. But how can I at least use design data and and take proper measurements to at least estimate my flowrate? Im not a chiller pro,but working on it. Thank you guys
Member Post, Member Post and 2 others6 Comments-
This is variable Primary System (VPF) with a controlled bypass?
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@brian-medley correct. Two chillers in parallel each with there own pump packages installed at the factory rite beside the evap. Very tight fit under there. 2 pumps per chiller but set up for only one to run at a time. Supposed to be 400 gpm each chiller/pump. Although I cant tell you why the engineer chose 400gpm since our previous chillers were 650gpm Aaon air cooled chillers. My total load (all chw coils design flow) is about 1200gpm. I got this info from original Aaon install submittals from 2006 and those original tab reports they had 654gpm from each chiller. We did have some design days this year and one of these rtafs could not keep up with load. But I was not able to run the 2 new chillers together because trane just cant get the pumping controls worked out. Im having major issues with the pump ramping up and down aggressively for hours or even a full 9 hr day where the controls just cant find a spot to settle in in regards to pump speed and bypass position. They just fight themselves all day and sometimes even loss of evap flow alarms come in. I believe its something in their pid but the trane tech is afraid to adjust it any further because its taken so long to get it to where he has it he said last week. This all happens as a response to building dp change whether up or down,the chiller controls over or under shoot the target dp and sometimes never get there. But thats all a whole other issue. Which id love to get input on but I really wanted to learn how I can tell how much flow I have at any given time and how it relates to the design evap dp. But any help is much appreciated of course
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@brian-medley also yes the bypass is factory installed and controlled in each chiller rite downstream of evap outlet.
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The IOM has flow charts that correspond to evaporator DP. If you know your DP you can find your flow rate on the chart.
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@jgallant4353 correct, I started there before I posted on here but they dont give a flow chart for a 30%glycol mix and they dont give any correction factors. I contacted “an engineer” at trane that was part of this project and he provided me with a couple performance charts that he says is for these chillers with the particular system conditions but both of them contradict eachother and dont appear accurate to what im seeing while monitoring the system while running. But according to his chart,13.6 psi dp through evap is closer to 550gpm (dont have chart with me atm)and the tab reports are saying 438gpm or close to that. Big difference. I looked up the pump curve on taco system builder and pump is rated at 400gpm@86′ with 30%pg but at full flow im measuring as low as 74′ at the pump which puts the flow around 522 to 528gpm on the curve
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Ya when the TAB guy comes out and lets you know he doesn’t have the right tools it’s not a good sign lol. So I think your right to not trust his readings. The evaporator design flow of 400 gpm at 6.4 psi…is that design with glycol or without? If you can confirm the design and minimum PDs are accurate it sounds like you just need the controls figured out so the pump and bypass work properly to maintain flow. The pump should respond according to system load and the bypass only opens when your close to minimum flow. You also have to make sure the pumps minimum speed is not too low so as to maintain minimum flow during low load conditions. I haven’t worked on these chillers but I assume there are some setpoints to look at and adjust if required. As for the PI loop you may need Tracer TU. I’d be curious to see what the setpoint is for the bypass valve to open. As for the exact gpm number personally I’m not too concerned. So long as it’s always above minimum DP or close to design DP and delta T across the evaporator is at design that means the flow is good. Makes sense that your seeing high flow if the original system design is for 1200 gpm. The engineers are just making sure your paying attention
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