Does anybody know how to quantify the performance difference when using 60/40 egw instead of water in a chiller evaporator that uses R134a refrigerant?
Performance difference may exist or may not. As far as chiller is concerned, there is no difference. If you want to get the same capacity at secondary refrigerant side, keep the same heat capacity (i.e product of mass flowrate and specific heat).
Glycol is 5-10% less efficient than water in transferring heat. However, this is more than recouped by the elimination of scale, dirt, and corrosion that can reduce heat transfer!Also,
Glycol systems are usually slightly more expensive than water systems. There is a one-time initial cost to fill the system with 30-40% glycol.
Convenience - In cooling systems where components are frequently disconnected and reconnected, the glycol is typically captured and added back to the system
In adition to the above if you want to maintain the same cooling capacity as just water then at a 40% ethalene glycol solution you will have to increase the pumping capacity 14%
Add glycols only to prevent freezing/slushing, not for corrosion protection. You can buy corrosion inhibitor packages to add to pure water systems, at less cost than glycol, and still maintain the heat exchange performance of pure water. Glycols by themselves are not corrosion inhibiting (and in fact glycols can decompose/oxidize to form acids that will actually accelerate corrosion); commercial anti-freeze products have the inhibitors already added in.
