Liquid Injection Adding Load?

[man from trane]

I've got a Kysor-Warren rack (set up just like a Protocol), med/low temp 404A with ZF Copeland scrolls. The low side has (3) 3.5 hp scrolls with liquid injection solenoids. Only 2 low circuits, IC reach-in and FF tub. Both are on SORITs. I'm losing temp on both.

This is strange- with all 3 liquid injection valves closed it runs fine, about 13 psi. Setpoint is 16 psi so one comp occasionally cycles. When one or more injection valves open the pressure skyrockets to 22, 26, or even 30 psi! It's like there's too much liquid being fed into the compressors. I can watch the low side suction pressure on the rack jump 7 psi or more with each solenoid opening. Isn't this a fixed orifice valve or is there a way to control it? This rack is only 2 years old so it doesn't have the soup cans, just a small valve I'm not familiar with.

Head pressure runs 230-250 with 85 degree ambient. Suction temp at compressors is 30-34 degrees.

This rack has not had anyone who knew what they were doing touch it since it was installed. Who knows if it ever worked right?

[icemeister]

According to Copeland's bulletin AE-1299 if the side injection port is used, there should be no loss of capacity with liquid injection:

Liquid Injection
The low temperature scroll compressor is provided with
an injection port suitable for connection to a source of
liquid refrigerant. Internally, this port is connected to an
inner pocket of the scroll mechanism. Since this pocket
is separated from the suction inlet, no loss of capacity or
mass flow results from injecting at this point.

I haven't seen any effect on suction pressure due to LI on any LT scrolls.

[the mojo]

https://opi.emersonclimate.com/was.e...blication=1327

[icemeister]

https://opi.emersonclimate.com/was.e...blication=1327

(That link doesn't work unless you're logged in at the Emerson site so I've attached it as a pdf.)

AE-1327 deals with Vapor Injection (VI) which is not the same thing as Liquid Injection (LI). While they are both side ports which introduce refrigerant flow to some intermediate point in the compression process, VI is used to subcool the main liquid flow to attain system capacity and efficiency gain whereas LI is for controlling discharge gas temperature.

[man from trane]

According to Copeland's bulletin AE-1299 if the side injection port is used, there should be no loss of capacity with liquid injection:

Makes sense, so why is my suction pressure up and down with the injection? It's liquid injection, not vapor and there is no subcooling. The injection port is on the side.

[itsamine]

Do these compressors run non-stop? It looks like a quench vlv set up so the compressor doesn't overheat. Is this set up with a solenoid vlv attached to a stat with an expansion vlv? If so we have these at work all over the place and the chillrooms they are attached to run at a constant 5*c so the compressors run all the time.

[man from trane]

Do these compressors run non-stop? It looks like a quench vlv set up so the compressor doesn't overheat. Is this set up with a solenoid vlv attached to a stat with an expansion vlv? If so we have these at work all over the place and the chillrooms they are attached to run at a constant 5*c so the compressors run all the time.

No, the comps run non-stop only because they never satisfy the suction setpoint until one of the circuits goes into defrost. There's a Klixon on each compressor discharge that somehow energizes a solenoid valve that injects non-subcooled liquid into the side of the compressor.

When the solenoid is energized frost appears after it, at the entrance to the side of the compressor. Drop leg temp is about 95 Degrees so there must be some load required to drop the temp from 95 to <32.

This is on another island so I won't get to go back and investigate further until next weekend. Does anyone have any info on the solenoid valve and metering device this may use?

[icemeister]

...Does anyone have any info on the solenoid valve and metering device this may use?

Copeland AE-1299 See p.2

[man from trane]

^ Thanks for that wealth of info on the Copeland Scroll. According to the operating envelope for R-404A it looks like I don't even need liquid injection. My condensing temp is <115 with 34 Degree return temp, 20 Degree evap temp.

In any case, it seems that what I thought is happening is not. The solenoid must be energized any time the compressor runs. Maybe what I'm seeing is the compressor cycling off on high discharge temp instead. I'll update when I get a chance to look at it again.

[basser]

Makes sense, so why is my suction pressure up and down with the injection? It's liquid injection, not vapor and there is no subcooling. The injection port is on the side.

Trane, verify this statement if you can. If there is no subcooling, then you are injecting vapor instead of liquid. This still should not raise the suction pressure through the compressor. I'm wondering if you are loosing the liquid seal at the evaporator TXV and putting some amount hot vapor in to the evap to raise the pressure?

Possible checks would be verify subcooling at evap TXV and compressor DTC (injection) valve, also verify evap pressure and evap superheat with and without injection.

Look at Figure 4 of bulletin 4-1299, coming from the injection valve to the top of the compressor is a temperature sensing bulb. When this bulb senses 193° it allows the DTC valve to open, in an attempt to cool the compressor. When the compressor cools down, the bulb will allow the DTC valve to close. A solenoid valve, in the injection line, is not required, but will not hurt anything as long as it is open and unrestricted when the compressor is operating. If the compressor does not cool down with by the injection, the required discharge line thermostat will open the compressor control circuit. I think this is what you are calling the Klixon. This thermostat has no control of the injection, only high discharge temperature.

I hope this helps a little.

[man from trane]

^ Thanks for pointing that out; "no subcooling" is a bit misleading. What I meant is that there is no additional subcooling, such as a heat exchanger providing 45°F liquid. There is the usual 8-15° subcooling from the condenser to ensure a liquid column at the injection valve.

This rack does not have the DTC, rather just a Klixon (which I think functions as a high temp limit that shuts off the compressor) and a solenoid valve that is energized continuously when the comp is running. I think the Klixon is shutting down one or more compressors due to high temp and that's why I'm seeing the suction pressure surge. The scrolls are so quiet compared to everything else around them that it's hard to tell if they are running or not.

I will verify this weekend.

[basser]

Ok, I understand what you're saying about the subcooling. No addtional subcooling is required.

Another question, You say "liquid injection solenoid". If you don't have the DTC valve, is there a "cap tube canister" mounted to the side of the compressor? This would be about 1.75" in diameter and 2.5" long, probably mounted in the vertical position. If not, how is the solenoid connected to the compressor? What is between the solenoid and the compressor (1/4 or 3/8 line)? With a cap tube injection, the solenoid is typically open when the compressor is operating and closed when the compressor is off. The metering of the liquid is done through the cap tube. The solenoid is either open or closed and is not a fixed orifice.

Now the other question is did Kysor-Warren do something different then what Copeland recommends. If you can answer the above questions, I can contact the application engineer that handles the Kysor account if necessary.

[man from trane]

^ That is the question I intend to answer when I get back there. I don't recall seeing a cap tube canister but maybe I missed it. When I was looking at this injection system, the guy who is familiar with the store told me it was like the Discus Demand Cooling but after reading the bulletins it's quite different. Now I need to look at it and see what's really there. Serves me right for assuming.

[basser]

The DTC valve works off of the temperature for injection. The cap tube system injects all the time when the compressor is operating. Discus Demand cooling also injects off of the temperature.

If your system has no metering device (cap tube) then you are most likely overinjecting. But like you say verify this. However it still doesn't explain the suction pressure swings. I'm trying to gather some information on this.

[man from trane]

Well, this one was embarrassingly simple. It is a DTC valve, not a solenoid. Someone broke the cap tube at the power element but I did not see it right away because the spring was holding it together. The compressor is overheating and tripping the Klixon on the discharge line.

Anyone know where to get a new power element proto? United is having a hard time locating the part.

[MikeySq]

from my experience a line with a solenoid going to the upper side of the compressor is Vapor Injection. The Liquid injection compressors I have worked on have a valve with a liquid refrigerant supply and the valve is actuated with internal springs and pressures it has a temperature sensing bulb that fits in to the Well on the top of the Scroll compressor, (it's not electrically actuated)

Mike

[man from trane]

from my experience a line with a solenoid going to the upper side of the compressor is Vapor Injection. The Liquid injection compressors I have worked on have a valve with a liquid refrigerant supply and the valve is actuated with internal springs and pressures it has a temperature sensing bulb that fits in to the Well on the top of the Scroll compressor, (it's not electrically actuated)

Mike

Good to know. I was going off what someone else at the site was telling me and they were confused.

[icemeister]

Well, this one was embarrassingly simple. It is a DTC valve, not a solenoid. Someone broke the cap tube at the power element but I did not see it right away because the spring was holding it together. The compressor is overheating and tripping the Klixon on the discharge line.

Anyone know where to get a new power element proto? United is having a hard time locating the part.

See p.11 Fig. 4:
http://www.hvacrinfo.com/cope_ae_bulletins/TAE1299.PDF