Hi Modellers,
In EnergyPlus, we are attempting to model the part load performance of an air cooled chiller by generating custom performance curves using the E+ HVAC curve fit tool. We are unsure exactly what performance data to request from the manufacturer to do so.
For the biquadratic CAP_FT and EIR_FT, we plan to request data at various Leaving CHW Temperature (say 44-54?F) and Outdoor Air Dry Bulb Temperatures (~55-105?F). However, to define the load on the chiller at these points, we need to specify more information.
? Should CHW flow rate be held constant at 2.4 GPM/ton (AHRI)?
? Should Entering CHW Temperature be held constant (~54?F)? I imagine not because there would be no Delta T when you reset leaving CHW Temperature up higher. So, should the CHW delta T be held constant instead?
For the quadratic EIR_FPLR, at 100% load, the ratings would be at AHRI conditions: 2.4 GPM/ton, 54/44?F Entering/Leaving Chilled Water Temperature, 95?F Outdoor Air Dry Bulb Temperature. For part load ratios:
? Should CHW flow rate be varied with a fixed Entering CHW Temperature? Or vice-versa?
We would appreciate insight from anyone who has run into this before!
Thanks,
Kyle
Dear Kyle,
I've got DX coil part load curves well figured out, but don't model
chillers very often, so they haven't got much attention from me. That said,
and assuming the chiller curves work consistently with the approach used
for DX coils, I think...
- Chilled water flow should be assumed at the AHRI test condition for
all curve derivations.
- The curves don't pay attention to the returning / entering water temp,
only the leaving / supply water temp.
- Capacity as f(T) looks at leaving CH water temp and entering
condenser water temp
- EIR as f(T) uses the same temps as above
- EIR as f(PLR) only looks at the ratio of current load vs rated
capacity
- You have no control over the entering / return CHW temp. "It is
what it is" based on load and leaving water temperature control.
- CHW flow rate (assuming a variable flow pump) normally varies with
load, not water temp.
I hope that is helpful.