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What would the implication be for the compressor on the following:
Compressor is a 4 HP Maneurope
Liquid line 3/8"
Gas Line 5/8"
Connected to an evaporator suitable for 8HP Compressor
ie: Liquid goes from 3/8" to 1/2"
Gas line goes from 11/8" to 5/8"
So its a mismatch of components but thats how it is.
Would the compressor take a hammering, fail prematurely or what?
Hi Abe, :)
The lineset size is determined by the system (condensing unit) capacity and the resulting refrigerant velocities and pressure drops.
The evaporator's line connections are sized for the most common application to ease installation.
If you check line size tables for that application, you may find the lineset to be appropriate.
The system has an evaporator twice as large as it needs, which would lead to high operating suction pressures. A concern would be overloading the compressor. One could compensate somewhat by reducing air flow across the coil.
Hi, Abe:)
you could fit a crankcase pressure regulator to ensure that the compressor is not overloaded or a mop TEV if the system is low temp. Trimming in the TEV a little to give a slightly higher than normal superheat would help also.
Regards. Andy.
Quote:
Originally posted by Prof Sporlan
The system has an evaporator twice as large as it needs, which would lead to high operating suction pressures. A concern would be overloading the compressor. One could compensate somewhat by reducing air flow across the coil.
What if the application calls for a (low) TD? Such as a floral box. By increasing coil surface area (large coil), suction pressure (temperature) is increased which results in increased compressor capacity (output). As long as the conditions are understood:
total condenser capacity (BTUh) @ S.S.T......... =....... TD
unit cooler capacity (BTUh) @ 1degF TD
To say that (any) evaporator is suitable for an 8hp condensing unit and NOT a 4hp condensing unit, I consider to be an untruth.
The coil manufacutrers mostly publish the capacity of a unit cooler @ a 10degF TD, which is the most common application. But if you look at the tables of evap. capacities it will specify the TD of the rating, "AT 10degF TD". That is indicated, because at a 5degF TD, the unit cooler capacity is half of that of the 10degF TD application.
Quote:
you could fit a crankcase pressure regulator to ensure that the compressor is not overloaded
That is assuming that the compressor is overloaded. If it is, it is likely that the TEV is a misapplication (oversized). One would have to be aware of the maximum evaporating temperature rating particular to the compressor or condensing unit. Of course such a scenario would manifest itself in a complaint about the operation of the system.
:)
Whoever connected that condensing unit to that twice capacity evaporator also left the expansion valve with orifice suited for 8hp condensing unit.
Poor 4hp maneurope must have suffered serious high back pressure and liquid floodback.
Its stopped working. Im going to see it this weekend.
...there ya' go.... :)..... I mean.... :(
the TEV should be matched to the CU capacity. The orifice size should probably be checked with the unit cooler manufacuter (or the valve manufacturer)in order to establish a proper total PD....though I'm sure standard ratings would do the job. One thing that you have to remember though, is that the humidity in that space is going to be 99.9% RH....
... Unless you, as the Prof. suggested, decrease the airflow. What is the application? for 90% RH, you would want a 10degF TD.... "knock" half of the fans out, or have your supplier provide fans with 1/2 the airflow rate of the existing ( I would also suggested changing the fan motors to prevent premature failure due to overheating of an unloaded motor). If its a floral cooler, or servicing some product that requires (or is unaffected) by a high humidity, you may not wish or want to adress de-rating the evaporator.... perhaps your customer is in the market for a new unit cooler.... but considering what they've got, I assume they don't want to put out the cash... :)
Check your CU capacity and verify the TEV application and perhaps even that the load will be satisfied by the CU, also. It sounds like your customer bought some thrown together used equipment, huh?
Remember... for a 35 to 38degF design room temp, your design SST will be 30 to 33degF with your existing configuration.....if you de-rate the evaporator (decrease airflow 50% for 10degF TD), the design SST will be 25 to 28 degF. this might be an important consideration in your valve selection and furthermore determining what your CU capacity will be..... Be comfortable with your load before you determine which avenue to take. with the higher SST, you do less "latent" work, and increase CU capacity...
Quote:
Whoever connected that condensing unit to that twice capacity evaporator also left the expansion valve with orifice suited for 8hp condensing unit.
... by the way, its not the Evap that is twice the capacity.... it's the TEV....:p
Hi, Herefishy and Abe:)
in theory their is no such thing as an over sized evap, the system balance point is found and the cooler just operates with a smaller td and as such the system is more effecient.
That's the theory, but in practice the latent load drops off and suction pressure rises to a point where the load is higher on the CU that we would realiy like.
I would fit a new valve based on the capacity at the system balance point by taking a look at what capacity the CU will handle comfortably at a higher evaportion, I would also cross referance this against what duty the cooler will do at that evaporation, checking the cooler TD so that we detemine that we actually have a td and as such are not evaporation at a temp that is above the room temp we desire.
Hope this helps.
Regards. Andy.
Hi Andy :)
We agree on the principle (theory). But my point is that there are assumptions being made about the capacity of the CU, the capacity of the unit cooler, and the application that is being serviced. All of this conversation is being based on Abe's statement :
Quote:
Compressor is a 4 HP Maneurope....Connected to an evaporator suitable for 8HP Compressor
... and that's all we've got.
All I'm saying is that the actual characteristics of the equipment and the application need to be investigated prior to any action to remedy any problem with the system.
:)
Hi, Herefishy:)
yep I agree, personally I would check the capacity of the unit against the cooler. The cooler may be fine with the unit if it's capacity is checked at a smaller td say 3-4 Degrees C instead of 6 Deg C (10 Deg F). We also have to find an evaporation to fix our CU capacity as it will rise and fall with evaporation, this evaporation will be subject to our cooler td. If our return air is at 0 Deg C (32 Deg F) our evaporation will be lower by the selected cooler td (minus say 2 Deg C pressure drop).
Anyway that is how I would figure out the various capacities, it may not be right but it is how I would do it.
Regards. Andy.
I'm surprised that there is so much concern over the evaporator size and not the line sizes. The liquid line size is irrelevant as long as it's not undersized, but, an oversized suction line can lead to failure of lubricant to return to the crankcase. This may have been the cause for the failure of your Maneurope compressor. See how much oil is remaining in the crankcase to determine if this was the cause. Also the TEV sizing is critical to prevent liquid floodback as others have mentioned. I wouldn't think that a reduction of a few degrees in the coil TD would cause overloading of the compressor.
Just to update you on this one. Ive replaced the compressor with a Le Unite model, changed the TEV with a smaller sized orifice. The line sizes are unchanged. So far everything is working fine.
Only thing worrying me is the comment about the oil return. Fortunately it is not a very long pipe run, I think about 6 metres max, but compressor is about 2 metres higher then evaporator.
We didnt bother too much about oil traps , perhaps I should have. Using R413b refrigerant, or Iceon 49. I think this gas carries oil fairly well.
If your rise is only 2 meters DO NOT employ any traps!!! I only apply traps for rises over 10ft (3 meters approx.) . Some manufacturers will void warranties in the instance of the application of oIl "traps"..... becuase sometimes that is exactly what they are..... oil "TRAPS!!!!!
:)
Abe,
I would be interested in your valve/orifice selction and perhaps CU/compressor application.
:)
Quote:
Originally posted by Marc O'Brien
...........The storage capability of the trap is unnecessary if the suction line is slightly sloped away from the compressor.[/B]
:confused:
hi Marc,
Would I be entirely inappropriate in suggesting that perhaps your previous statement should be, "the trap is unnecessary if the suction line is slightly sloped "toward" the compressor? .
:confused:
Too little information to diagnose a compressor failure. Seen lots of R-A/C systems operate at low load condition for years, without problems, if designed and set up to do so.
I have always been under the impression that if the valve matches the compressor, the coils don't mater much. There is a max suction pressure the compressor can take, but...
I would say that undersized lines could counteract on oversized coil by increasing the pressure drop in the suction line.
Best to do it right, but sometimes they will only pay for some stupid stuff.
I was going to relate a story but will put it into a new thread.