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I have just concluded a small project assigned to me. I was to increase the cooling capacity of a chiller. I did this by wiring the electric motor to an inverter and increasing frequency from 50Hz to 60Hz, to improve the flow rate by increasing speed. However, I am rather dubious, having the feeling something could go wrong later. The chiller is an old one. No one could locate the wiring diagrams. All the parameters used were obtained from the motor nameplate.
Increasing the cooling capacity of a chiller.
- Thread starter Jibola
- Start date
I agree with your feeling that you may be shortening the life of the compressor my increasing the operating frequency and speed.
With a constant load, or no load at all, the speed increase of 20% might not make much difference. Perhaps a motor has a lifetime of X rotations, and you'll get there 20% sooner at higher speed.
But increasing the speed of the compressor likely increases the operating pressures in your chiller. (I'm assuming this is a vapor recompression cooler). So now your motor is actually working harder as well as faster. This would be similar to adding more than the specified amount of refrigerant.
Higher refrigerant pressure introduces another problem: The temperature at the evaporator coil is set by the boiling point of the refrigerant at the pressure of the evaporator coil. That's the low-side pressure, as opposed to the high-side pressure after the compressor. Your higher speed compressor is causing a higher pressure and temperature to appear throughout the system and particularly at the evaporator coil. Depending on your operating conditions, this might actually reduce your cooling capacity.
You should measure the cooling capacity at both operating frequencies, to see if you've improved or degraded the capacity.
With a constant load, or no load at all, the speed increase of 20% might not make much difference. Perhaps a motor has a lifetime of X rotations, and you'll get there 20% sooner at higher speed.
But increasing the speed of the compressor likely increases the operating pressures in your chiller. (I'm assuming this is a vapor recompression cooler). So now your motor is actually working harder as well as faster. This would be similar to adding more than the specified amount of refrigerant.
Higher refrigerant pressure introduces another problem: The temperature at the evaporator coil is set by the boiling point of the refrigerant at the pressure of the evaporator coil. That's the low-side pressure, as opposed to the high-side pressure after the compressor. Your higher speed compressor is causing a higher pressure and temperature to appear throughout the system and particularly at the evaporator coil. Depending on your operating conditions, this might actually reduce your cooling capacity.
You should measure the cooling capacity at both operating frequencies, to see if you've improved or degraded the capacity.
There are lots of DIY "solutions" out there, and a favorite is using a swamp cooler to cool the air passing over the Condenser (hot, outdoor) coil. Basically you build a swamp cooler around the entire outdoor portion of the air conditioning system. It's less effective in humid environments but still contributes a lot as long as the Wet Build temp is below the dry bulb.
You can get even more effective cooling by wetting the condenser coil directly, but that would void any warranty and introduces all sorts of corrosion/fouling issues. Window unit A/Cs use this approach though, and use the nice, clean condensate off the evaporator coil to spritz onto the condenser coil.
You can get even more effective cooling by wetting the condenser coil directly, but that would void any warranty and introduces all sorts of corrosion/fouling issues. Window unit A/Cs use this approach though, and use the nice, clean condensate off the evaporator coil to spritz onto the condenser coil.
