Automotive Air Conditioning Information Forum (Archives)

PicoHydro on Tue October 30, 2012 1:24 AM

Designing a heatpump using a Sanden TRSA12, I have a scenario where a Discharge Bypass Valve bleeds 2/3 of the hot gas to the suction side. This results in a suction Temperature of 120°F and a Discharge temperature of 180°F. Can the Sanden scroll take it?

ice-n-tropics on Tue October 30, 2012 4:43 PM

Yep. The TPS doesn't trip until 117C outer surface temp.
Idling in front of Cesar's, or in Buckeye, or at the 3 holer @Stove Pipe Wells, on the hot asphalt results in Ts of over 130F.
The TRs used on Bradleys operate OK at 130F ambient in Iraq/Afg. Hot soak to 170F @ initial start of cooldown. The driver has a suit w/ imbeded coolant tubes from a heatX for absorbing heat from the coolant return from driver to refrigerant loop, and a IV to avoid dehydration.
The Ford Visteon scroll built in Portugal will bypass partially compressed gas w/o all the wasted energy of bypassing fully compressed gas (like you plan). This reduces cycling 50% based on suction pressure. Mitsubishi hermetic mini splits also utilize mid cycle /mid pressure bypass.
hotternhell@TRBGradU.edu

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Tue October 30, 2012 at 4:44 PM by ice-n-tropics

PicoHydro on Thu November 01, 2012 11:29 PM

Thanks, ice!

I'm within a stones throw of finishing the design!

NickD on Fri November 02, 2012 6:40 AM

Is using a belt driver automotive compressor for a heat pump application a good choice? Incredible what those belt losses are and then leakage problems with that compressor seal.

But on the basis that an automotive engine is wasting over 85% of the energy in heat loss, assuming this is NOT an automotive application. Companies like Coleman made a good heat pump/AC mobile motorhome type of device using a direct driven motor driven completely sealed system. Would feel a compressor of that type would be a far better choice.

Designing an optimum system starts with using the latest state of the art technology and developing the components for that specific application. Not just buying stuff and slapping it together.

PicoHydro on Mon November 05, 2012 12:43 PM

Thanks Nick. A hermetic system certainly is preferable, but my power source is a turgo runner spun by a jet of water, so open drive is what I'm stuck with. The Sanden scrolls are about 73% efficient, and that's the best automotive scroll available as far as I know.

What would you estimate the power loss thru a 6 micro groove belt is?

Edited: Mon November 05, 2012 at 12:45 PM by PicoHydro

ice-n-tropics on Thu November 15, 2012 4:48 PM

Pico,
Serpentine belt loss/heat is less than 1%.
Your dual TR system is very complicated, and my suggestions will not help to simplify it:
1) My experience w/ oil separators is that a sight glass and metering valve are required in the oil return line to control/reduce hot gas bypass w/ the hot oil. In one high rpm scroll application, I added a oil cooler.
2) The oil separator is not 100% efficient and the bypass oil must return to the compressor.
3) The accumulator should have a oil pickup in the bottom of the "J" tube, but what oil return orifice size?
4) The challenge to return by pass oil to the operating compressor instead of the inactive compressor involves vertical suction oil return so that gravity is beneficial.
5) The scroll single discharge valve at each compressor outlet should prevent the inactive scroll compressor from back spinning it's orbiting scroll.
6) Interesting to consider the energy balance when the lower capacity/slower scroll is operating.
7) Avoid oil traps in the plumbing that reduce OCR.
8) TR energy input (or BTU output) will be different from manufacturers specs because they ignore oil circulation which reduce volumetric & isentropic efficiency.
hotternhell @TRBGradU.edu


-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Thu November 15, 2012 at 6:28 PM by ice-n-tropics

PicoHydro on Sat November 17, 2012 4:36 PM

Thanks for the detailed suggestions, ice!
1) My experience w/ oil separators is that a sight glass and metering valve are required in the oil return line to control/reduce hot gas bypass w/ the hot oil. In one high rpm scroll application, I added a oil cooler.

• Should I use a see-all type sight glass and a needle valve to adjust oil flow until there are minimal bubbles present in the line?

3) The accumulator should have a oil pickup in the bottom of the "J" tube, but what oil return orifice size?

• Accumulator sizing charts have a minimum and maximum ton capacity. Is this sufficient to account for the oil return orifice size?

4) The challenge to return by pass oil to the operating compressor instead of the inactive compressor involves vertical suction oil return so that gravity is beneficial.

• I thought I'd deliver the oil to a tee, from which the suction goes upward to the compressor, so it would not fill the inactive compressor with oil.

6) Interesting to consider the energy balance when the lower capacity/slower scroll is operating.

• Please explain further.

ice-n-tropics on Sat November 17, 2012 5:16 PM

Quote
Originally posted by: PicoHydro
Thanks for the detailed suggestions, ice!

1) My experience w/ oil separators is that a sight glass and metering valve are required in the oil return line to control/reduce hot gas bypass w/ the hot oil. In one high rpm scroll application, I added a oil cooler.



• Should I use a see-all type sight glass and a needle valve to adjust oil flow until there are minimal bubbles present in the line?

Yes

3) The accumulator should have a oil pickup in the bottom of the "J" tube, but what oil return orifice size?



• Accumulator sizing charts have a minimum and maximum ton capacity. Is this sufficient to account for the oil return orifice size?

Automotive size is 0.062"

4) The challenge to return by pass oil to the operating compressor instead of the inactive compressor involves vertical suction oil return so that gravity is beneficial.



• I thought I'd deliver the oil to a tee, from which the suction goes upward to the compressor, so it would not fill the inactive compressor with oil.

Your way has positive features. My device has patent potential.

6) Interesting to consider the energy balance when the lower capacity/slower scroll is operating.



• Please explain further.

Oil carrying may be less. Accumulator fill different. Suction pressure needs to be above 15 psig for durability. Freeze up considerations.
hotternhell@TRBGradU.edu

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

PicoHydro on Sat November 17, 2012 8:24 PM

1)

Would a standard needle valve leak? Do I actually need a packless valve for oil metering?

Catherin on Mon December 10, 2012 2:34 AM

Quote
Originally posted by: PicoHydro
Designing a heatpump using a Sanden TRSA12, I have a scenario where a Discharge Bypass Valve bleeds 2/3 of the hot gas to the suction side. This results in a suction Temperature of 120°F and a Discharge temperature of 180°F. Can the Sanden scroll take it?

The maximum suction gas temperature is usually about 70°F. 36.11 COMPRESSOR SPEEDS (RPM) Modern air-conditioning compressors used in the small temperature.