Switching over R407c 15 ton air cooled chiller to R134a

[Stefan Weiss]

I work for a small R&D company where we do some pretty crazy things. Right now we have a project where we are powering a cooling system from boiler exhaust. The concept was to create one loop to get heat from the boiler stack with oil and through our own plate to plate heat exchanger transfer that heat into an organic rankine cycle whereas the expander (or compressor running backward) will be mechanically or electrically linked to another compressor and power that system. We have tried using R245fa which is what some white papers have used int he past with ORC's but on the cooling side, the density when cold is insanely small so the volumetric flow has to be gigantic...

ANYWAY.... we have moved onto to trying R134a since we found a few papers that use that instead. This in turn, would be perfect for both sides of the cycle. In house we have a R407c 15 ton air cooled chiller we want to switch over to R134a.

@40F Saturation:
pressure: 49.7psia R134a
95psia R407c

@130F Saturation:
pressure: 213psia R134a
360psia R407c

Thats double the Delta P...

Evap density ratio is 76.2 lb/ft3 for R134a and 132.5 lb/ft3 for R407c
Evap enthalpy change is 84btu/lb for R134a and 89.5btu/lb for R407c

Condenser density ratio is 14.5 lb/ft3 for R134a and 459.48 lb/ft3 for R407c
Condenser enthalpy change is 63 btu/lb for R134a and 60 btu/lb for R407c

With such a huge density ratio, do we need to just switch out the compressor and TXV?

[Stefan Weiss]

Sorry.. error. Density ratio is actually is 1/.1337 = 8.2

So it seems it should be an easy changeover with no change???

[Stefan Weiss]

lol.. i meant 8.2 is the density ratio. Ignore the 1/.1337 (that was the specific volume i used earlier as the vapor density)

[Stefan Weiss]

The density going into the compressor is ~1.05 lb/ft3 for R134a and ~1.73 lb/ft3 for R407c. Since the compressor is by volume, not mass, would the capacity now be diminished by 60% (1.05/173)? So if we switch out the compressor and TXV we should be fine, right? Its also the same POE oil since R407c is a blend containing R134a... right?

[Stefan Weiss]

Anyone??? Does no one understand or know the answer to my dilemma? :(