Liquid Refrigerant Pumping

[bersaga]

Has anyone actually used magnetically-coupled liquid pumps on the liquid line (after the receiver king valve) to increase the liquid line pressure ? This is supposed to ensure 100% liquid at the TXV inlet. There is also a liquid injection line (after this pump) to the compressor discharge line to desuperheat the discharge gas.

The intention is to increase refrigeration capacity ( for an inefficient system) and reduce compressor runtime ( energy saving)

Anyone with any experience in this?

[Calvin Becker]

Please check our site http://www.hysave.biz for more information.

HY-SAVE (UK) LTD
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[rudyreg]

As I understand it, the main saving is during low ambient conditions because you can have a low condensing temperature without fear of starving the TEV. The compressor is therefore giving more duty, running less hours and saving energy. In your case however, being in Malaysia, there may not be a particular benefit as I doubt ambient temperature ever drop far enough to justify the need for LPA ( Liquid Pressure Amplification ).

[Michael Bellstedt]

It will be much cheaper to install a liquid subcooler heat exchanger - this would have the same effect of preventing vapour formation in the liquid line ahead of the TX valve, and as long as your condensing pressure does not drop too low, you should be fine with a TX valve.

Michael

[Norty]

We use the liquid pumps once in a blue moon on racks that have an unusually high rises in the liquid line from the machine room. An example would be in a warehouse with the machine room in the basement and the coils mounted 20 ft above ground level.

We also use the pumps to cool oil on screw compressors in lieu of a jet kool system or an external oil cooler.

Norty

[Andy]

Hi, Norty
Pump used for oil cooling, thermosyphon oil cooling with a pump?
Regards. Andy.

[Norty]

Ya in a way. Basically you "push" high pressure liquid through a heat exchanger and the "suction" is the main discharge gas line.

We've got a patent on this and it has worked quite well.

Norty

[Andy]

Hi, Norty
I learned something today, thankyou.

Regards. Andy.

P.S anyother good ideas you care to share?

Regards. Andy

[Norty]

Well this one my dad taught me at a young age, and it doesn't relate to refrigeration:

Don't pee into the wind!

Norty

[Andy]

[Don't pee into the wind!]

or on electric stock fencing for livestock

Regards. Andy

[Dan]

Hey Norty, why didn't you like the jet Kool? Seems like a nice design from the few I have seen.

[Norty]

With the jet kool, you need to have the condenser at least 10 feet above the rack. If the racks are in a machine house on a store, this is usually not possible.

We have also had problems using jet kool with a split condenser system. The price between the two is about the same, so I like to go with the one with the less hassle.

The jet kool works nice if it is set up correctly, I'm not knocking it, I just like the liquid pump better for that application.

Norty

[bersaga]

Thanks for all the replys.

How do you change from a fixed head to a floating head system? This is supposed to be a benefit of the Liquid Refrigerant Pumping (LRP). This may be a basic question to most practical guys ( I do understand the theoretical benefits from the P-E diagram)

Furthermore , has anyone any practical experience with desuperheating the dischrge gas using a tap-off from an LRP - does this actually give you additional condensor capacity ( as per the P-E chart ) How does the P-E chart's compression line look like ? Ideally its isentropic and practically its something else, I think. But with desuperheating, does it still maintain the same compression line but a temperature drop horizontally at constant pressure ?

Again, I agree with those who proposed liquid subcooling - it's cheaper. I have designed and installed a system Bitzer 2-stage compound semi hermetic with a SWEP phe liquid subcooler and get about 5 deg C sub cooled liquid on a -31 deg C SST and 45 deg C SCT system.

Thanks guys

[Andy]

Hi, Bersaga
where would you be injecting the pumped refrigerant, between stages on a two stage system?
Who this would increase condenser capacity escapes me, the only benifit that becomes apparent is lower head will lower the discharge temperatures on the compessor, reducing injection.
Floating head is simply running the condenser fans when they would normally be cycled off to hold the head pressure within certain limits for proper system operation.
Regards. Andy.

[bersaga]

Dear Andy,

The pumped refrigerant is conveyed in this manner : 95% to the TXV ( single stage system) and 5% to the compressor discharge ( via aliquid injector and a check valve)

What I mean by increased condensor capacity is this : a condensor is normally selected based on the sum of the refrigeration capacity and the compressor power with the Tevap , Tcond and initial temperature pulldown playing deciding roles. Now , having the P-E chart in mind (God! I wish I could draw it here!), desuperheating is going to bring down the discharge temperature by a certain amount. Here I presume that I can draw a line towards the left horizontally from the end of the compression curve to the new and lower discharge temperature(with the pressure constant ?)

If you draw it, you can see that the condensation line is decreased and now the condensor is oversized for the system it was designed for originally ( because the desuperheating occurs before HP vapour into the condensor).This should also lead to the excess capacity of condensor tube space being used for sub-cooling and thereby increasing the COP.

As for the fixed to floating head control , maybe some from Hysave care to explain how it's done on the field without cutting in/out condensor fans.

Thanks

[Andy]

Hi, Bersaga
you are correct that be desuperheating in the discharge line you are increasing the condenser capacity (by about 33%) This system I have seen used on small screw compressor, but with a thing called ejector (which is basically a venturi) causing a the liquid to be drawn into the discharge.
The ejector is not very effective, but the pump should be efffective especially at low head pressures, say in the wintertime.
Sounds like a good idea especially on single stage low temp systems.
Regards Andy

[Dan]

I have seen ads for such arrangements. The savings claimed made it apparent that the market was for retrofitting deteriorating a/c and refrigeration condensers. I do not see how this intrinsically can make the system more efficient. All you are doing is reintroducing already condensed liquid into the condenser, expanding it and recondensing it again; and you consumed a certain amount of energy in the process. Maybe some benefit for out-of-parameter condensing situations, but: 33% Andy?

[Prof Sporlan]

Conservation of mass requires:

m_cond = m_comp + m_inj

where:
m_cond = refrigerant flow thru condenser
m_comp = refrigerant flow thru compressor
m_inj = refrigerant flow thru injector/pump

Also, conservation of energy requires:

m_condh_cond = m_comph_comp + m_injh_inj

where:
h_cond = enthalpy of refrigerant flow entering condenser (mix of hot gas and liquid)
h_comp = enthalpy of vapor refrigerant provided by compressor
h_inj = enthalpy of liquid refrigerant provided by injector/pump (assume it to be saturated)

For argument's sake, say we have an R-22 system operating at a -20°F evaporator, a 100°F condenser, and a 100,000 Btu/hr load. Let us also assume discharge gas temp of 200°F entering the condenser.

Refrigerant flow rate thru the system becomes: 100,000 Btu/hr / (h_g - h_f) = 100,000 / (169.05 - 106.03) = 1587 lb_m/hr = 26.4 lb_m/min.

Now we install a pump/injector for discharge gas desuperheating. Let's assume for the moment it has no effect on compressor performance. Therefore:

m_cond = 26.4 lb_m/min

If we divert 5 percent of this flow for desuperheating, we get:

m_inj = 26.4 * 0.05 = 1.3 lb_m/min

and

m_comp = 26.4 - 1.3 = 25.1 lb_m/min

We can look up h_comp and h_inj. Using the Prof's program:

h_comp = 199.37 Btu/lb_m
h_inj = 106.03 Btu/lb_m

Which allows us to solve for h_cond:

26.4 * h_cond = 25.1 * 199.37 + 1.3 * 106.03

h_cond = 194.77 Btu/lb_m

Which works out to about 177°F discharge gas temperature

So what does this tell us?

Condenser capacity can be calculated as follows:

(199.37 - 106.03) * 26.4 lb_m/min = 2464 Btu/min = 147,840 Btu/hr

Let's assume the condenser was sized at a 15°F TD, and that by desuperheating the gas ahead of the condenser, we obtain no change in the performance of the condenser. With desuperheating, the condenser load is reduced to:

(194.77 - 106.03) * 26.4 lb_m/min = 2343 Btu/min = 140,580 Btu/hr

Which not surprisingly, is 5 percent less than the original load. With the lower load, we can expect TD to be reduced to: 15 * 0.95 = 14.25°F.

This where the problem gets interesting. We are assuming no change in compressor and condenser preformance when liquid injection is employed. Reducing the TD on the condenser three quarters of a degree F should provide a small improvement in compressor capacity and efficiency, albeit at a reduced refrigerant flow to the evaporators. If the reduction in refrigerant flow rate to the evaporators causes lower suction pressures/starving, then any efficiency gains due to lower head pressures will be quickly lost.

[Andy]

Hi, Dan
look like you gut feeling was right

Which not surprisingly, is 5 percent less than the original load. With the lower load, 

I was not thinking correctly. Normally we fit desuperheaters on NH3 low temp plant, expecting 33% of the heat rejection to the condenser to be picked up or recovered, but we are not using refrigerant or rejecting heat back into the system, but removing it altogether, also I suspect we are partially condensing the refrigerant as well as desuperheating it to obtain 33% recovery.
Regards. Andy

[Andy]

Hi, Dan

I am going to try that post again, so here goes it!

Which not surprisingly, is 5 percent less than the original load. With the lower load,

The desuperheating I was considering was rejecting heat outside the system, with the the heat exchanger sized for 33% of the Total Heat Rejection to the condenser, based on low temperature plant operating on NH3.

Regards. Andy

[Dan]

Reducing the TD on the condenser three quarters of a degree F should provide a small improvement in compressor capacity and efficiency, albeit at a reduced refrigerant flow to the evaporators.

I wonder how the power consumed by the pump would compare to that small improvement.

[Calvin Becker]

Im selling distributor agreements- buy now or hang in with the rest. One time offer, reply to purchase@hysave.co.uk

[Calvin Becker]

Originally posted by Michael Bellstedt
It will be much cheaper to install a liquid subcooler heat exchanger - this would have the same effect of preventing vapour formation in the liquid line ahead of the TX valve, and as long as your condensing pressure does not drop too low, you should be fine with a TX valve.

Michael

[Norty]

Nope,

Not a dealer. We just use the product once in a while. Right now I have a situation where the thrust washer on the pump keeps breaking in two. I'll fill you in on the details on what we find.

Norty

[Calvin Becker]

Made of Ceramic for many reasons. How long has your LRP been in service? Do you use PumpPro Xp as a means of pump control?

[Calvin Becker]

Originally posted by Marc O'Brien
The heat exchangers aren't that cheap and while they might lower liquid enthalpy affecting increased net refrigeration effect they also add to liquid line pressure drop leaving you with no net gain other than increased system performance but even then only if the heat removed is by means external to the system.



Leave all the pre-required training to me at £300.00 per day

Marc, You mean £300 per Half day!

[Norty]

Calvin,

System was just started up this spring. We use the Rack controller to control the pump. Same logic as the PumpPro.

[Calvin Becker]

Did we meet at the last FMI show in Chicago?

[Calvin Becker]

I and a friend developed the PumpPro to work with LRPs to prevent and cater for any abnormal conditions to provide LRP fault free operation. In 11 years, I have sold and installed 100`s of LRPs to have sold only 1 O ring as a replacement part . A bust thrust washer needs investigation into system operation.

[Calvin Becker]

Originally posted by bersaga
Thanks for all the replys.

How do you change from a fixed head to a floating head system? This is supposed to be a benefit of the Liquid Refrigerant Pumping (LRP). This may be a basic question to most practical guys ( I do understand the theoretical benefits from the P-E diagram)

Furthermore , has anyone any practical experience with desuperheating the dischrge gas using a tap-off from an LRP - does this actually give you additional condensor capacity ( as per the P-E chart ) How does the P-E chart's compression line look like ? Ideally its isentropic and practically its something else, I think. But with desuperheating, does it still maintain the same compression line but a temperature drop horizontally at constant pressure ?

Again, I agree with those who proposed liquid subcooling - it's cheaper. I have designed and installed a system Bitzer 2-stage compound semi hermetic with a SWEP phe liquid subcooler and get about 5 deg C sub cooled liquid on a -31 deg C SST and 45 deg C SCT system.

Thanks guys

Check out the Ph chart and observe THR. The % shown between(desuperheat) (latent) enthalpy ratio could provide the answer-provided, liquid introduction at. sat conditions and increased mass flow, prove lower head operation.

[RogGoetsch]

Just noticed this thread. Liquid injection for desuperheating an advantage?

If we inject liquid refrigerant (subcooled to the ambient, say) between the compressor discharge and the condenser inlet, I can see that we would have the same BTU's to be rejected by the condenser, but with the disadvantage of lower temperature at the condenser inlet (first pass or two?)

Since we have the same airflow across the condenser, I wonder if the difference would be due to more rapid heat transfer to the condenser surface due to the "wetter" mixture (per someone above), yielding a greater rise in condenser air delta T at the same TD (for more subcooling). Does this happen?

Or does the additional mass of refrigerant, injected and partially vaporized, slightly raise the condensing pressure, hence condensing temp, creating a larger TD? (This assumes the mass flow thru the compressor is unchanged, i.e. evaporator not starved, but that additional receiver liquid is available for injection.)

In either case, we have to show an increase in condenser air delta T, it seems to me (same air, more BTU's, more subcooling) or where is the advantage?

Anybody build one?

[Calvin Becker]

Very Interesting!!!

Your thoughts are very similar to mine... Have seen some amazing things hapen when injecting into a water cooled condenser!

www.hysave.com

[Calvin Becker]

Very Interesting!!!

Your thoughts are very similar to mine... Have seen some amazing things hapen when injecting into a water cooled condenser!

www.hysave.com

[Calvin Becker]

For a limited time I can offer financed distribution agreements worldwide for hysave technology. Try me at cb@hysave.com

[RogGoetsch]

What "amazing things" have you seen? What measurements have you taken?

I was recently asked to evaluate potential savings from a device that slows down evaporator fans during the compressor "off" cycle. Finally got a brochure from the manufacturer in which it was claimed that in walk-in coolers, evaporator fan loads frequently account for 40% of the cooling load!

So pardon me if I am extreeeemly skeptical and wish to see actual test data. What have you got?