11-19-18-WS - Laserfiche WebLink

Home Browse Search

City Hall Chiller 1.The condensing unit we have now uses compressors in the outdoor unit to mechanically reject the heat from the refrigerant. The “cooled” refrigerant travels back through the lines to the AHU indoors, where it picks up heat from the building air, and moves it to the outdoor unit, creating the complete refrigeration cycle. The compressors on the current unit (or any refrigeration compressors for that matter) require oil to lubricate the components. Think of it much like a 2‐stroke engine where the oil is mixed directly with the gas, or refrigerant in this case. Oil is heavier than refrigerant, so it naturally wants to settle in the lowest point of the system. Because the condensing unit is located 1 story above the AHU, the lowest point is the coil in the AHU, not the condensing unit where the compressors are. There are double suction risers on the refrigerant lines to help with oil return in installations like this, but we’re naturally going to have issues regardless. 2.The current condensing unit is R‐22, which is being phased out by the government because of its global warming potential. The new condensing units use R‐410a. The two refrigerants don’t use the same pipe size, so to do the job right, we will need to replace all the piping in the refrigerant system, including the coil in the AHU itself (because a coil is just an extension of the piping in a compact cross sectional area). In summary, the current system will inherently have oil return issues back to the compressors because of the setup, shortening the lifespan of the unit by some amount. We have to replace the refrigerant piping anyway because of the refrigerant change, so why not install chilled water piping instead, install the chiller outside, and have a more robust system in the end. A typical chiller system, properly cared for will last 25‐30 years. A typical condensing unit system (without having oil return issues) will last 20‐25 years. 14