I would rather trouble shoot a 1500 ton centrifugal than a heat pump anyday.As for having to run a chilled pump for 5 minutes after the chiller shuts down, that is a recommendation but not a requirement.There is lots of jobs out there that start a chiller pump on outside air temp,chilled water flow switch makes, chiller starts the condensor pump and away it goes,OAT drops and chilled pump goes off and so does the chiller.This is bad practice but seems to be the poor mans guide to controls on chillers. The new screw machines they sell don't even require a flow switch anymore,I have started up a few RTAA's where they didn't put them in but I always try to demand flow switches and strainers.I had to rod out crushed aggregate from a brand new 700 ton chiller one time because they didn't think strainers were important.
[Edited by acjourneyman on 08-06-2004 at 10:42 AM]
the thing about chillers is that theres more to it than working on chillers usually you will have to work on the pumps,cooling towers,airhandlers,and the most important the thing that makes the whole ball of wax work like pnumatics and controls.
after a repair or compressor change out and your totally vac'd.if you go to liquid charge the unit from the vac make sure you have the chiller pumps running for the evap or empty the barrel...results not doing either you will bust the tubes in the evap with the liquid going thru the TXV with the stagnent water and the vac in the micron range.either the chiller being a package or large split filling the LL is cool off a VAC,but run that water as a heat load!
Basic performance testing on centrifugal chillers will tell you many things about what is going on inside. Get accurate water flow readings across both evap and condenser barrels. Next get accurate temperature deltas across both sides. Convert these values to tons and see how they compare to design capacity. With these things checked compare the tons against the Kw to determine efficiency. A comprehensive test will reveal evap tons, cond. tons, motor tons and % design efficiency. On larger chillers you will be able to determine if the tubes are fouled by less than design temp. deltas and higher than design Kw/ton. Flow rates above or below design will indicate improper water balance, worn pumps, or foriegn material wedged against the tube sheet.
I have operated large chilled water plants where performancee tests were taken weekly and tubes cleaned, flow adjusted, or the machine taken down for other maintenance based on the results of the test. This proceedure kept operating costs to a minimum and indicated required maintenance before disaster struck.
Good luck with the chillers, they are by far my favorite piece of equipment.