Charge Compensator?

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Old 11-19-15, 07:48 PM
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Charge Compensator?

From my understanding, Rheem/Ruud uses something called a "Charge Compensator" in many of their heat pumps. Based on my understanding, parts takes some of the charge out when it heat mode so one wouldn't need to remove a bit of charge for the heating season then charge again during cooling season.

My question is, what isn't this thing used on all heat pumps? Is there any drawback to having a "Charge Compensator" and if a heat pump doesn't have one, would it make sense to add on to any heat pump?
 
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Old 11-20-15, 01:02 PM
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Think you need to find a new HVAC guy. Tell him thank you for your time now run along.
 
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Old 11-20-15, 05:04 PM
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Think you need to find a new HVAC guy. Tell him thank you for your time now run along.
Why would you say that? Plus this has nothing to do with a HVAC guy. This is something I want to know. Why wouldn't a Charge Compensator be good on all heat pumps? It makes sense to me for all heat pumps to have such a thing, especially these days with high seer and eer ratings being needed.

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Old 11-20-15, 07:54 PM
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From Emerson.... Charge Compensators

Charge compensators are devices that store excess refrigerant during the heating operation of a heat pump with a TXV refrigerant control. Unlike an orifice, a TXV will not allow excessive refrigerant to flood back to the compressor. This means that the excess system refrigerant will either have to back up in the indoor coil during heating, causing high head pressure, or be stored in a charge compensator until needed.

A charge compensator is normally a hollow vessel with only one opening that is attached to the vapor line. The shell is usually attached to the outdoor coil or has a line from the outdoor coil running through it for extra cooling during heating and to drive the refrigerant out during the cooling cycle. The size is dependent on how much refrigerant has to be removed from the system throughout the system operating map.

It sounds good in theory but one problem is dumping liquid refrigerant back in to the compressor on defrost. I couldn't find any details in how it's sized or where it becomes required. If it were required.... all heat pumps would have one.
 
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Old 11-21-15, 09:51 AM
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crabjoe: Thanks for the post ; I found it interesting and now also wonder how to know if such a device would really be effective. Presumably Emerson would have data.
As for why all heat pumps don't sport such a device ? Well this industry is hardly known for innovation - more for cost reduction than improvements.
 
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Old 11-21-15, 10:27 AM
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Googling has showing that it's not just Rheem that uses it.. From what I've found, Trane and Carrier use these things too.. They tend to do it on more of their higher seer models, which makes sense, since the compensator adjusts the charge for heat or cooling mode for optimum efficiency. Pete does bring up a good point about the defrost mode... But maybe they don't need to worry about defrost since defrost is just the compressor running in AC mode without the fan..

To me, if a heat pump doesn't have one, it might make sense to add one if efficiency is the concern.. I think the big trick, when adding it is getting it sized correctly.
 
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Old 11-21-15, 05:37 PM
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This "charge compensator" is not new, it's only this company renaming something that has existed for a very long time.
They are used on commercial refrigeration systems with thermostatic expansion valves and are called a "refrigerant receiver".
They store refrigerant to allow thermostatic expansion valves to be fed a solid column of liquid refrigerant when the system is under a high load and then store the excess refrigerant when under low load.
 
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Old 11-21-15, 08:58 PM
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Thanks, Greg. I was thinking it was just a receiver but since I have very little experience with heat pumps I didn't want to post in error.
 
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Old 11-22-15, 07:21 AM
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Ya, I too don't have much experience with residential heat pumps.
Refrigerant receivers are pretty much the norm in commercial refrigeration where there is a TXV.
They are needed when there is a thermostatic expansion valve on an evaporator.
On residential and a lot of packaged commercial units however, manufacturers design the condenser, liquid line and drier to hold a precise amount of refrigerant.
These systems need an exact amount of refrigerant to work at both high and low load.
Many will make adjustments to condenser and liquid line size and then use the size of the drier to fine tune the amount of refrigerant in the system.
Rheem does this but also adds value to the system by giving it the "compensator" name then saving a few bucks by installing an empty shell rather than a filter/drier!

Kinda like selling an air compressor based on "gallons" rather than cfm but that's a whole other story.
 
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Old 11-22-15, 05:23 PM
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Based on my understanding, parts takes some of the charge out when it heat mode so one wouldn't need to remove a bit of charge for the heating season then charge again during cooling season
Actually it's the other way around if I am not mistaken? You need to ADD refrigerant as the temperature goes down (pressure decreases as ambient temperature goes down). I had to add a bit to my HP as the temp approached 5 degrees (F). There was a bit of frost 'banding' happening at that temp which usually indicates low charge. As ambient temp went up during the day thee 'banding' stopped
 
 

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