Heat pump purging

Paul F · 01-07-13, 06:51 AM

I have just installed a heat pump, the outside unit came pre-charged with R410-A, the connecting pipework was pre-evacuated and sealed but the interior unit was filled with nitrogen (not pressurised).
The seals on the pipework are pierced during connection so that the pipework remains sealed until part of the circuit.
The exterior unit has valves which seal in the R410-A until the circuit is sealed.
When the interior unit is connected to the sealed pipework, it is still full of nitrogen, so when the valves on the exterior unit are opened, the R410-A will fill the evacuated pipework and the interior unit but there will still be some traces of nitrogen in the system remaining from the interior unit.
Will this affect the performance a bit/ not much / seriously ?

BradC · 01-07-13, 05:21 PM

Quote:

Originally Posted by Paul F

Will this affect the performance a bit/ not much / seriously ?

Seriously. Why would they do that? It makes no sense at all to supply parts of the system per-charged like that if another part of it is pumped up with nitrogen.

Paul F · 01-08-13, 04:35 AM

Hi BradC
I could just answer "they are french" but that would be a little racist.
I have had a long correspondence with the salesman (key word here is "salesman")
who tells me that they have been selling them like that for 5 years
however, telling me that you have been making the same mistake for a long time doesn't help,
I was hoping for a more scientific reply. My unit does seem to work OK but I'm wondering if it should work better, I was surprised by the residual nitrogen, not made clear in the "sales" blurb.

BradC · 01-08-13, 04:45 AM

As an Australian, any sleight on the French is humorous you silly Kniggit. Why do you think I have this outraaaaaegous accent ?

Let's look at it this way. Calculate the volume of the evaporator and the approximate pressure the Nitrogen may be under (all my Nitrogen gassed units here were under ~15PSI of Nitrogen). Now calculate the volume of that gas given the volume of the pipework in the evaporator and estimated pressure. We now have a quantifiable amount of N2.

Now, let's look at your Condenser and estimate the approximate condensation temperature you will see under "normal" conditions. Using Boyles law we can calculate the volume of that N2 at the condensation pressure and temperature.

Look at the condenser pipework and estimate how much of the condenser will be N2 under normal condensation pressures. That part of the condenser becomes ineffective. The N2 will sit at the top of the condenser taking up space and playing no part in the heat exchange process.

Now, 410A is a pretty high pressure refrigerant, so the real volume of N2 might be relatively small. None the less, you have paid for a condenser of size X and it would be nice to get that rather than X - N2 space. Lost space is lost efficiency, no matter how small.

Paul F · 01-09-13, 06:21 AM

Thanks Brad, very logical, I vaguely remember Boyles law from schooldays, I had to look up “Kniggit”, not used here, more likely to be called a “Rostbif”. Anyway, I like it here and I wouldn’t want to be accused of being a “whinging Pom”.

I didn’t know that the interior unit hadn’t been evacuated until I started to install it, then it was too late, not clear in the sales blurb. I am going to install a second unit but this time I’ll get an engineer to pressure test, evacuate it and fill it with refrigerant. That’s all tightly regulated here.

I tried researching the volumes of the pipework, molecular weights of nitrogen v R410A etc but Daikin doesn’t quote volumes and the formulas were getting more complicated. I found that R410A has a molecular weight 2 ½ times higher than nitrogen and that the outdoor compressor is “probably” pre-charged at about 120psi compared to indoor unit filled with nitrogen at atmospheric pressure (14psi) so I will “assume” (dangerous, I know) that the residual nitrogen gets compressed to a volume that will not affect the efficiency too much, I won’t know unless I get the system re-commissioned.

I will try to explain some of this to the salesman but I think I can guess what his response will be.

Anyway, thanks again, nice to get confirmation that I wasn’t on the wrong track.

learyyme · 01-24-13, 10:44 AM

I encourage you to check performance.

Mikesolar · 01-24-13, 05:46 PM

Paul, if I remember correctly Brads "Kniggit" comment comes from Monty Python, Holy Grail.

Your system really should have been vacced out before the valves were open. Nito does nothing for the system and lowers the performance.

01-07-13, 06:51 AM	#1
Paul F Lurking Renovator Join Date: Jan 2013 Location: France Posts: 3 Thanks: 1 Thanked 0 Times in 0 Posts	Heat pump purging I have just installed a heat pump, the outside unit came pre-charged with R410-A, the connecting pipework was pre-evacuated and sealed but the interior unit was filled with nitrogen (not pressurised). The seals on the pipework are pierced during connection so that the pipework remains sealed until part of the circuit. The exterior unit has valves which seal in the R410-A until the circuit is sealed. When the interior unit is connected to the sealed pipework, it is still full of nitrogen, so when the valves on the exterior unit are opened, the R410-A will fill the evacuated pipework and the interior unit but there will still be some traces of nitrogen in the system remaining from the interior unit. Will this affect the performance a bit/ not much / seriously ?

01-24-13, 10:44 AM	#6
learyyme Lurking Renovator Join Date: Jan 2013 Location: US Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	I encourage you to check performance. Last edited by learyyme; 01-27-13 at 10:23 PM..

01-08-13, 04:35 AM	#3
Paul F Lurking Renovator Join Date: Jan 2013 Location: France Posts: 3 Thanks: 1 Thanked 0 Times in 0 Posts	Hi BradC I could just answer "they are french" but that would be a little racist. I have had a long correspondence with the salesman (key word here is "salesman") who tells me that they have been selling them like that for 5 years however, telling me that you have been making the same mistake for a long time doesn't help, I was hoping for a more scientific reply. My unit does seem to work OK but I'm wondering if it should work better, I was surprised by the residual nitrogen, not made clear in the "sales" blurb.

01-08-13, 04:45 AM	#4
BradC Apprentice EcoRenovator Join Date: Dec 2010 Location: Western Australia Posts: 148 Thanks: 1 Thanked 48 Times in 34 Posts	As an Australian, any sleight on the French is humorous you silly Kniggit. Why do you think I have this outraaaaaegous accent ? Let's look at it this way. Calculate the volume of the evaporator and the approximate pressure the Nitrogen may be under (all my Nitrogen gassed units here were under ~15PSI of Nitrogen). Now calculate the volume of that gas given the volume of the pipework in the evaporator and estimated pressure. We now have a quantifiable amount of N2. Now, let's look at your Condenser and estimate the approximate condensation temperature you will see under "normal" conditions. Using Boyles law we can calculate the volume of that N2 at the condensation pressure and temperature. Look at the condenser pipework and estimate how much of the condenser will be N2 under normal condensation pressures. That part of the condenser becomes ineffective. The N2 will sit at the top of the condenser taking up space and playing no part in the heat exchange process. Now, 410A is a pretty high pressure refrigerant, so the real volume of N2 might be relatively small. None the less, you have paid for a condenser of size X and it would be nice to get that rather than X - N2 space. Lost space is lost efficiency, no matter how small.

01-09-13, 06:21 AM	#5
Paul F Lurking Renovator Join Date: Jan 2013 Location: France Posts: 3 Thanks: 1 Thanked 0 Times in 0 Posts	Thanks Brad, very logical, I vaguely remember Boyles law from schooldays, I had to look up “Kniggit”, not used here, more likely to be called a “Rostbif”. Anyway, I like it here and I wouldn’t want to be accused of being a “whinging Pom”. I didn’t know that the interior unit hadn’t been evacuated until I started to install it, then it was too late, not clear in the sales blurb. I am going to install a second unit but this time I’ll get an engineer to pressure test, evacuate it and fill it with refrigerant. That’s all tightly regulated here. I tried researching the volumes of the pipework, molecular weights of nitrogen v R410A etc but Daikin doesn’t quote volumes and the formulas were getting more complicated. I found that R410A has a molecular weight 2 ½ times higher than nitrogen and that the outdoor compressor is “probably” pre-charged at about 120psi compared to indoor unit filled with nitrogen at atmospheric pressure (14psi) so I will “assume” (dangerous, I know) that the residual nitrogen gets compressed to a volume that will not affect the efficiency too much, I won’t know unless I get the system re-commissioned. I will try to explain some of this to the salesman but I think I can guess what his response will be. Anyway, thanks again, nice to get confirmation that I wasn’t on the wrong track.

01-24-13, 05:46 PM	#7
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Paul, if I remember correctly Brads "Kniggit" comment comes from Monty Python, Holy Grail. Your system really should have been vacced out before the valves were open. Nito does nothing for the system and lowers the performance.