Compressor Capacity Troubleshooting Help

[reds007]

Hi,

I'm designing new system with an LG Compressor...I finished charging it but the system capacity is about 20% below what it should be. The capacity on spec sheets at these temperatures should be 9400btuh.
However I get 8000btuh. The amperages I am getting are also much less than the ones on the spec sheets.

I'm thinking it might be a wrong compressor spec?

Can someone please help me troubleshoot it?

Here are the numbers I got:

Refrigerant = R410A
Evap Temp = 45degF
Compressor Temp = 105degF
TXV System
Superheat = 8degF
Subcooling = 15degF

Let me know if you need any more info.

Thanks,
Reds

[Brian_UK]

How are you measuring the loading on the system?

[mad fridgie]

Hi,

I'm designing new system with an LG Compressor...I finished charging it but the system capacity is about 20% below what it should be. The capacity on spec sheets at these temperatures should be 9400btuh.
However I get 8000btuh. The amperages I am getting are also much less than the ones on the spec sheets.

I'm thinking it might be a wrong compressor spec?

Can someone please help me troubleshoot it?

Here are the numbers I got:

Refrigerant = R410A
Evap Temp = 45degF
Compressor Temp = 105degF
TXV System
Superheat = 8degF
Subcooling = 15degF

Let me know if you need any more info.

Thanks,
Reds

Are the compressor specs at these conditions, if not you can not compare. you change any one of the above, then the performance will change.
As Brain says what is accuracy of your loading.

[reds007]

Thanks guys for the reply.

The rated conditions are for Evap = 45degF, Condenser = 105degF, Superheat = 50degF, Subcooling = 15degF

The capacity was obtained by measuring the water loop temperature difference.

Capacity = 500 * GPM * (Water In - Water out)

(Heat pump in heating mode)

I did the same measurement on our older R22 units and the capacities of those units are very close to rated.

Right now I'm thinking its the compressor. So after the weekend I will try to build another unit with a Tecumseh compressor.

Would there be another reason for loosing capacity? I'm pretty sure the piping sizing is correct.

I appreciate your help. Let me know if you need any other info.

Reds

[Gary]

Did you measure GPM?... or use an estimate?

[mad fridgie]

Thanks guys for the reply.

The rated conditions are for Evap = 45degF, Condenser = 105degF, Superheat = 50degF, Subcooling = 15degF

The capacity was obtained by measuring the water loop temperature difference.

Capacity = 500 * GPM * (Water In - Water out)

(Heat pump in heating mode)

I did the same measurement on our older R22 units and the capacities of those units are very close to rated.

Right now I'm thinking its the compressor. So after the weekend I will try to build another unit with a Tecumseh compressor.

Would there be another reason for loosing capacity? I'm pretty sure the piping sizing is correct.

I appreciate your help. Let me know if you need any other info.

Reds

With lower current, and lower performance, indicates as noted, ratings are not for that compressor, or the compressor has the wrong label. (incorrect displacement)

[Brian_UK]

Also, at moment we don't have any measured readings as yet from what I can see.

In one post you stated the evaporator and condenser temperatures as measured and in the second you state that they are design.

Have you got exactly the design operating conditions?

Your subcooling seems as per spec but the superheat is way off.

[reds007]

The measured evaporator and condenser temperatures were +/- 3%

Flow was measured with a turbine type flow meter.

The only measurement that was off was the superheat. I will try to adjust it higher before I try changing compressors but I don't think it will increase performance much.

Thanks.