TXV sizing with a larger condensing unit

[kengineering]

A customer is having issues with the noise level of a recipricating condensing unit currently installed in a self contained, self select merchandiser. Remoting the unit is not an option and the unit runs with normal sound levels for this model. He has decided to have me replace the recip with a scroll when I prented the idea as a possible solution. The present components are; condensing unit is R-22 rated a 7,200 btu with a 1/2-C TXV. The smallest scroll available to me is rated at 10,500 btu with refrigerant 134A. The question: Would I stay with the same size TXV just changing the refrigerant type? Or must I up-size the TXV to more closly match the larger Condensing unit? The evaporator coil and fan set-up will remain unchanged. Thanks , Ken

[paul_h]

You'd have to change the txv going from r22 to r134a anyway.
but the txv size will remain the same, as they're rated by evap cooling capacity. You'll just have an oversized condenser, which may cause problems over condensing in cooler weather. I'd fit a fan controller on it to keep hp and lp up.

[US Iceman]

The bigger issue is the capaicity of the new scroll compressor. It's capacity on R-134a is already 30% greater than the smaller R-22 compressor. That will cause the system to operate with much lower suction pressures too.:(

[DEVITG]

You need to change the condenser coil too , as the scroll y bigger.
There is on matter on how big the condenser is , because the TXV will open or close as needed , and the flow will as much the TVX allow.
But you will need to match the condenser coil and fan with the new compressor.

[Dan]

Ken, the quietest compressors are the hermetic reciprocating compressors. Do you have a semi-hermetic? If so, just change it to a hermetic. A scroll will not be quieter than a hermetic.

[lana]

Hi there,

I would worry about the oil first.
R22 uses mineral oil but R134a uses synthetic one. Washing the old oil out is the major concern here. If your equipment is changed properly but the contaminated oil is there then the system would not work.
Be very careful.

Cheers

[monkey spanners]

As Lana points out you'd need to use an R12 drop in with the R134a compressor for oil compatability not to be a problem.

Jon

[TXiceman]

Another issue is the orifice and the distributor fro the R-134a vs the one on the coil fro R-22.

I don't feel you will get any appreciable reduction in noise on the condensing unit with a different compressor.

The noise you are getting...is it coming from the compressor itself, the mounting structure of the fan? Have you tried a better mount for the unit with vibration absorbers under the frame?

I have a small scroll on my home A/C as I did on the last house. It sounds like a trash can full of rocks when it starts and then quietens down after the initial rattling.

Ken

[kengineering]

Thanks to all for your suggestions and advice and it is now done! The entire condensing unit was changed to 134A and as suggested I used a 1/2 c TXV. As far as the oil goes there was no burnout so I blew the evap coil with dry nitrogen and there wasn't much oil in it. Changed the TXV and installed the cond unit. Set lpc to cycle for the 134a @ CI 34psi and CO @14psi and after adjusting the superheat the box temps are at about 36*f which is great! I wasn't really sure what the noise levels were going to be but this customer was willing to take the risk and boy did it pay off. It is nearrly silent!. The only complaint now is the evaporator and condenser fans being louder than the compressor. This was one project that came out better than I expected.

The noise you are getting...is it coming from the Compressor itself, the mounting structure of the fan? Have you tried a better mount for the unit with vibration absorbers under the frame? [/QUOTE]actualy it was the valve sound all recips make. There wasn't anything wrong all normal. This customer is just a bit picky and willing to pay for what he wants.

Thanks again, Ken

[ckone180]

Ken, the quietest compressors are the hermetic reciprocating compressors. Do you have a semi-hermetic? If so, just change it to a hermetic. A scroll will not be quieter than a hermetic.


Damn! I have read several posts before I got to this one. Good going Dan, right on target. Changing a recip to scroll has got to be going in the wrong direction. Stop the MADNESS! :eek:

[Dan]

Damn! I have read several posts before I got to this one. Good going Dan, right on target. Changing a recip to scroll has got to be going in the wrong direction. Stop the MADNESS!

Thanks, CK, but I guess Ken got it all better with a scroll, judging by his last post. But there is a lot to be said about a compressor welded housing with a compressor mounted on springs inside it to keep things quiet. I do not find scroll compressors all that quiet.

[kengineering]

Changing a recip to scroll has got to be going in the wrong direction. Stop the MADNESS!
I was not aware the scrolls would be considered more noisy than a hermetic recip. I haven't any experience with them but many of our customers are asking for them so I'd better learn fast. I beleive it's the sales people. Any buzz-word to stimulate sales. But I must say I had done eveything possible to the Hermetic before changing it out for the scroll and the results amazed me. I cannot hear the new compressor at all. Even after defrost when presures are up you can't hear it. The chat seems to be anti-scroll? Or am I just reading into it? Please tell me what you guys really think about them. As I said, there's a buzz about scrolls in Kengineering land. Thanks, Ken

[Dan]

I was not aware the scrolls would be considered more noisy than a hermetic recip. I haven't any experience with them but many of our customers are asking for them so I'd better learn fast. I beleive it's the sales people. Any buzz-word to stimulate sales. But I must say I had done eveything possible to the Hermetic before changing it out for the scroll and the results amazed me. I cannot hear the new compressor at all. Even after defrost when presures are up you can't hear it. The chat seems to be anti-scroll? Or am I just reading into it? Please tell me what you guys really think about them. As I said, there's a buzz about scrolls in Kengineering land. Thanks, Ken

Ken, I was wondering if you had a semi-hermetic reciprocating compressor and if so, suggested a hermetic. My experience with scrolls is that they are touted as the quietest compressors, but I have found them to be noisy often. If you are saying that you went from a hermetic reciprocating compressor to a scroll and it became much quieter, I stand corrected. My experience with scrolls are mostly the larger sizes.

[kengineering]

Quieter without a doubt but small yes it was a 12,500 btu copeland. The smallest they make I believe. Ken