Suction line heat exchanger

jeff5may · 02-03-13, 10:55 AM

Mikesolar and/or AC_Hacker,

Yes, the two main places I look are the hvac talk forum and refrigeration engineers forum. The pros in the know all design the PTAC and RAC setups for 30 degrees superheat at the inlet line to the cxr at design conditions (85 deg F/30 deg C ambient). Asked about SLHX, they said it's just another part that could make these things fail. In walk-in freezer systems, though, they are commonly used since they save money. Their main focus is on reliability, then cost, efficiency comes in a distant third. Unless it's a big system that costs a lot to run.

I read in an article I can't find now that a designer noticed the "foam burp" effect. What the pros know is that it is a well known condition and design for it not to happen. This one briefly discusses it in section 4.2

http://docs.lib.purdue.edu/cgi/viewc...8&context=icec

The main idea is that at "high" evap temps (>-10 deg c) and below about 15 k of superheat, the propane boils so rapidly in the evap that the oil doesn't fully separate. The obvious solution is to keep superheat above 15 k. You can do this by either raising the superheat setting on the TXV or by adding SOMETHING in between the evap and cxr. This something will be the SLHX in my unit. With it, I will be able to set the TXV to a lower superheat setting (than 15K).

For an insight into the theoretical arguments surrounding this subject, just google 'R290 suction superheat'. The pros will argue this to death because it depends so much on specific situations. When narrowed to R22a (refrigeration engineer grade propane), the topic quickly devolves into scare tactics and warnings that propane is explosive. They are all against drop-in replacement of r12/r134/r22.

All my experimental systems have been made from old R22-based units. They are plentiful and dirt cheap. Mineral oil, 10 SEER type units.

02-03-13, 10:55 AM	#11
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Mikesolar and/or AC_Hacker, Yes, the two main places I look are the hvac talk forum and refrigeration engineers forum. The pros in the know all design the PTAC and RAC setups for 30 degrees superheat at the inlet line to the cxr at design conditions (85 deg F/30 deg C ambient). Asked about SLHX, they said it's just another part that could make these things fail. In walk-in freezer systems, though, they are commonly used since they save money. Their main focus is on reliability, then cost, efficiency comes in a distant third. Unless it's a big system that costs a lot to run. I read in an article I can't find now that a designer noticed the "foam burp" effect. What the pros know is that it is a well known condition and design for it not to happen. This one briefly discusses it in section 4.2 http://docs.lib.purdue.edu/cgi/viewc...8&context=icec The main idea is that at "high" evap temps (>-10 deg c) and below about 15 k of superheat, the propane boils so rapidly in the evap that the oil doesn't fully separate. The obvious solution is to keep superheat above 15 k. You can do this by either raising the superheat setting on the TXV or by adding SOMETHING in between the evap and cxr. This something will be the SLHX in my unit. With it, I will be able to set the TXV to a lower superheat setting (than 15K). For an insight into the theoretical arguments surrounding this subject, just google 'R290 suction superheat'. The pros will argue this to death because it depends so much on specific situations. When narrowed to R22a (refrigeration engineer grade propane), the topic quickly devolves into scare tactics and warnings that propane is explosive. They are all against drop-in replacement of r12/r134/r22. All my experimental systems have been made from old R22-based units. They are plentiful and dirt cheap. Mineral oil, 10 SEER type units. Last edited by jeff5may; 02-03-13 at 11:01 AM..