Multi Zone systems vs. two pipe VRF system

[gpier]

Good morning. I know a few commercial systems (e.g. Mitsubishi VRFs have a two pipe system from the outdoor unit that runs to each head), but do multi zone systems "share" the refrigerant in a similar way? Or is each zone partitioned off in the out door unit somehow?

For example, if you have multi zone system made up of 5 zones lets say, with a total of 5 separate line sets running to each indoor unit from the outdoor unit, if there is a refrigerant leak on ONE indoor unit, the entire system will eventually be depleted of refrigerant, correct?

[rider77]

Yes, mutizone units share a common refrigerant circuit.

[gpier]

Yes, mutizone units share a common refrigerant circuit.

Okay thanks. I noticed with one multizone system I installed less than 24 hours ago (2 indoor units), one head is blowing ice cold and the other blowing moderately cold air. My first thought always tends to go to worse case scenario, like "must be a refrigerant leak". More than likely it's another reason. Thanks again.

[pecmsg]

Okay thanks. I noticed with one multizone system I installed less than 24 hours ago (2 indoor units), one head is blowing ice cold and the other blowing moderately cold air. My first thought always tends to go to worse case scenario, like "must be a refrigerant leak". .

Safe assumption.

[ESokoloff]

Safe assumption.

Insufficient information to assume.

[pecmsg]

Insufficient information to assume.

I’d make a bet on it!

[gpier]

I’d make a bet on it!

I hope you’re wrong.

I’m going to put a leak detector on the only place there could be a leak this afternoon. I can’t get in the space until then. I’ll follow up with results.

Here’s my question (assuming a leak in fact) why would one indoor unit blow so much colder than the other? Thus my original question.

[ESokoloff]

I’d make a bet on it!

It’s a high probability of insufficient refrigerant to the coil that’s not cooling but there’s insufficient info to say the systems short on charge.

I’m not saying your wrong (low charge), rather saying I don’t (yet) agree based on given info.


To the OP, follow manufacturers charging procedure to determine if unit is low on charge before looking for leaks that may or may not exist.

Your issue sounds to be a shortage of refrigerant to the effected coil but that could also be a restriction (filter/strainer or metering device) rather then system under charge.

[ESokoloff]

I hope you’re wrong.

Here’s my question (assuming a leak in fact) why would one indoor unit blow so much colder than the other? Thus my original question.

I don’t have enough information to accurately answer that but I can surmise it possibly be similar to how hydronic (water) heat pump strainers will contaminate the lowest (elevation) one(s) in a building due to gravity.

The piping to your systems two heads MIGHT tend to direct liquid to one head & mixed phase (liquid/vapor) to the other this shorting it of sufficient liquid.

You need to check system charge/metering device operation before leak checking.

[gpier]

All good points. I will investigate further.

[gpier]

I donÂ’t have enough information to accurately answer that but I can surmise it possibly be similar to how hydronic (water) heat pump strainers will contaminate the lowest (elevation) one(s) in a building due to gravity.

The piping to your systems two heads MIGHT tend to direct liquid to one head & mixed phase (liquid/vapor) to the other this shorting it of sufficient liquid.

You need to check system charge/metering device operation before leak checking.

Well, happy to report I solved my problem. Not a refrigerant loss. I did waste about 2 hours today trying to figure it out. What I'm not happy to report is how stupid I am. Let me explain:

I had my teenage son helping me yesterday. Everything went well, although we worked late, on a Sat night, till about 7:00pm (never a good idea). We started it up, and it worked fine. This AM one unit (like I originally said) was blowing cold, the other not so much.

This afternoon I used the leak detector. Nothing. Pressure test went well yesterday, triple evacuation, and I held a vacuum at less than 500 for over 2 hours for each zone before I released the refrigerant. All my joints are good. I opened the outdoor unit and the accumulator was covered in heavy frost. One line set was iced over. The other wasn't. Now I'm racking my brain, thinking low on charge from the factory? My line set to each unit is only about 25 ft. (I didn't need to add refrigerant) Is the expansion valve stuck? Or bad? Is it another restriction of some sort? Not looking good. I don't want to spend half the day tomorrow to recover refrigerant and weigh it out to find out it's exactly what it should be. This is a Bosch system, and I've been pretty happy with them. This is the third Bosch I've installed, and the first two were solid and still running fine.

Note: I assigned my kid yesterday to wire up the communication cables. Wondering if he got the color/number sequence off, I opened up the indoor unit in question, and it was correct. "Red, Black, White, Ground". WHILE I'M LOOKING AT THIS, I hear the other unit in the other room (which is in the "off" position) making a popping noise. I go look at it, and the outside cover is dripping with condensate.

Now I think I know what it is. I go back to the outdoor unit to see if he got the wires backwards. And he did. He wired zone A to zone B. And zone B to zone A. So the indoor unit in question was calling for refrigerant, but the outdoor unit was sending it to the other unit even when it was off (thus the popping noise and the condensate). Last night, they were both working fine because they were both on full blast, and both calling for refrigerant, so the offices cooled very well over night.

All that to say, I was happy to find this mistake. Glad it was simple. Certainly can't blame my kid. I should have checked his work. That's my fault for not checking it.

Anyhow, thanks for reading this far and helping me today. Time for a beer.

[gpier]

I donÂ’t have enough information to accurately answer that but I can surmise it possibly be similar to how hydronic (water) heat pump strainers will contaminate the lowest (elevation) one(s) in a building due to gravity.

The piping to your systems two heads MIGHT tend to direct liquid to one head & mixed phase (liquid/vapor) to the other this shorting it of sufficient liquid.

You need to check system charge/metering device operation before leak checking.

Well, happy to report I solved my problem. Not a refrigerant loss. I did waste about 2 hours today trying to figure it out. What I'm not happy to report is how stupid I am. Let me explain:

I had my teenage son helping me yesterday. Everything went well, although we worked late, on a Sat night, till about 7:00pm (never a good idea). We started it up, and it worked fine. This AM one unit (like I originally said) was blowing cold, the other not so much.

This afternoon I used the leak detector. Nothing. Pressure test went well yesterday, triple evacuation, and I held a vacuum at less than 500 for over 2 hours for each zone before I released the refrigerant. All my joints are good. I opened the outdoor unit and the accumulator was covered in heavy frost. One line set was iced over. The other wasn't. Now I'm racking my brain, thinking low on charge from the factory? My line set to each unit is only about 25 ft. (I didn't need to add refrigerant) Is the expansion valve stuck? Or bad? Is it another restriction of some sort? Not looking good. I don't want to spend half the day tomorrow to recover refrigerant and weigh it out to find out it's exactly what it should be. This is a Bosch system, and I've been pretty happy with them. This is the third Bosch I've installed, and the first two were solid and still running fine.

Note: I assigned my kid yesterday to wire up the communication cables. Wondering if he got the color/number sequence off, I opened up the indoor unit in question, and it was correct. "Red, Black, White, Ground". WHILE I'M LOOKING AT THIS, I hear the other unit in the other room (which is in the "off" position) making a popping noise. I go look at it, and the outside cover is dripping with condensate.

Now I think I know what it is. I go back to the outdoor unit to see if he got the wires backwards. And he did. He wired zone A to zone B. And zone B to zone A. So the indoor unit in question was calling for refrigerant, but the outdoor unit was sending it to the other unit even when it was off (thus the popping noise and the condensate). Last night, they were both working fine because they were both on full blast, and both calling for refrigerant, so the offices cooled very well over night.

All that to say, I was happy to find this mistake. Glad it was simple. Certainly can't blame my kid. I should have checked his work. That's my fault for not checking it.

Anyhow, thanks for reading this far and helping me today. Time for a beer.

[pecmsg]

Been there
Got the t-shirt!