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heat production recording and consequential lower than actual COP recording. During affected months, energy delivered by the CO2 heat pumps was extrapolated using actual energy recorded of 10 MMBTU on February 28, 2017 with the flow transmitters cleaned and operating. The ASLC facilities staff have periodically removed and cleaned the paddle wheels. As a permanent solution a micro-screen bag filter to catch the material fouling the meters has been purchased for installation following the busy 2017 summer season. • On March 1, 2017, the Tracer SC and ES controls ceased logging the system operating data. This resulted in no data being transmitted to ACEP between March 1st and April 13th when the problem was corrected by Trane. The issue was that the SQL database on the Tracer server had gotten full and the trending stopped. It was not a physical hard drive issue or a report template/emailing issue. Trane came to Seward, installed an external hard drive, made a backup of the existing SQL and then purged the active one and trending re- started. Unfortunately Trane cannot recreate the lost data. • When the heat pumps are attempting to heat up the boiler loop after a cooling period, or at start up, they chill the source loop significantly. This caused the heat pumps to cycle on and off to prevent a freeze event inside the evaporator heat exchangers. This required increasing the source loop propylene glycol to a 20% concentration to permit lowering the freeze protection setting from 36F to 34F. Lessons Learned • Unit COP is most impacted by load entering temperature. The output is a constant 194 F load side leaving temperature, however the load side entering temperature can vary significantly depending on heat loads and loop design. The ideal range of load side entering temperature is 80F to 100F which allows the units to make the most of electricity consumed by compressor work. In order to provide a load side entering temperature that is 80F lower than the building loop at 160F, a smaller volume side loop must be routed thru a series of heat loads that sequentially cool this side loop down to 100F or less. • Unit COP is moderately impacted by source side entering temperature. Sea water from Resurrection Bay is used as the primary source of heat on the cold side of the heat pump units. The colder sea water temperatures of late spring and early summer can be as low as 38F which forces the compressors to do more work to lift on the hot side. A simple and effective method of adding heat to the source side of the CO2 heat pumps is to install branch loops off the main source loop that is routed to fan coils in over heating mechanical or electrical rooms. Waste heat from these rooms is then effectively recovered back into the heating system; the rooms are cooled with minimal energy input; and the unit COP is improved due to warmer source entering temperature. • Overall COP can be improved by turning off CO2 heat pump system sea water supply pumps, and utilizing waste heat loops instead. ASLC is planning to 7PDF Image | Trans-Critical CO2 Heat Pump System AEA Grant
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