7/8 lineset on a 5 ton system

[jdere]

I have seen at least 2 AC 5 ton R-410 systems run with 7/8 lineset instead of 1 and 1/8".
I didn't take any readings, but the owners said they are running fine.
What do you guys think?

[mason]

I have seen at least 2 AC 5 ton R-410 systems run with 7/8 lineset instead of 1 and 1/8".
I didn't take any readings, but the owners said they are running fine.
What do you guys think?

They are most likely fine. Not every 5 ton calls for an 1 1/8 line set, sometimes it's actually better to keep up your velocity.

[ga-hvac-tech]

Tricky subject...
Length of lineset and location of coil and AC unit (over/under and how much)... Different manufacturers say different things... And if it is a 2 stage... most will go with 7/8.

Usually running a too small SL will reduce efficiency by 3-4-5%... not a huge amount if re-running the lineset was difficult.

[BaldLoonie]

Many are happy with that, especially 410.

[mark beiser]

Even with fairly long lines, 50-70', with a few fittings, AS/Trane's piping software will almost always spit out 7/8" as the recommended SL size for a 5 ton R-410 AC or heat pump system.
For shorter line set applications, it will even recommend, a 3/4" SL, or at least list it as an approved alternative.

For the ARI ratings manufacturers will run short, larger diameter, suction lines to maximize the efficiency ratings, but the size that yields the most reliable system is generally smaller.

[jdere]

Thanks for all the replies!

[54regcab]

I've seen FAR more problems with 5 tons systems being attached to less than 2,000 CFM worth of ductwork...

[Barrettservices]

I have seen multiple compressor failures from companies putting 1 1/8 on current systems. If you look in most install manuals on current 14 plus seer systems they specifically warn you about oversizing lines because it will starve the compressor of oil especially on long runs.

Also according to Rheem install manuals it is not efficiency you loose with oversized or undersized lines its capacity. for instance i put a 3 ton 15 seer on a home that had a 5/8 suction 3/8 liquid at 70 ft long and there was no way of changing it and the rheem manual stated that i would only loose 3% of capacity so instead of 36kbtu i would only get 35kbtu. Not worth tearing the home apart.

[mark beiser]

Also according to Rheem install manuals it is not efficiency you loose with oversized or undersized lines its capacity.

The small capacity loss directly causes a small loss of efficiency.
Lower btuh per watt = lower efficiency.

I'd rather have a more reliable system, that is 1-3% less efficient though.

Not worth tearing the home apart.

I absolutely agree.
In most cases, the potential increase in efficiency from changing to the ideal refrigerant line size won't cover the cost of replacing it within the life span of the system, or even the next system.

[54regcab]

If you really want to help lower power bills for the homeowner install a 2.5 ton instead of the 3 ton. If it can't keep up fix the leaks/solar gain in the house. Fudging the numbers on manual J calculations to get about 500sqft per ton that has been used since the 60's has got to stop. It's rare that a well designed house with a properly installed HVAC and duct system should need more than 750sft per ton.

[Barrettservices]

If you really want to help lower power bills for the homeowner install a 2.5 ton instead of the 3 ton. If it can't keep up fix the leaks/solar gain in the house. Fudging the numbers on manual J calculations to get about 500sqft per ton that has been used since the 60's has got to stop. It's rare that a well designed house with a properly installed HVAC and duct system should need more than 750sft per ton.

I agree however there are thousands of homes in our area that were built without dual pane windows, wall or floor insulation and very little insulation in the attic. The majority of homewners will not spend the money to fix those issues so we have to install slightly larger systems to compensate.

[54regcab]

I agree however there are thousands of homes in our area that were built without dual pane windows, wall or floor insulation and very little insulation in the attic. The majority of homewners will not spend the money to fix those issues so we have to install slightly larger systems to compensate.

Agree, older homes with single pane windows/leaks/poor insulation typically need more cooling per sqft. My gripe is newer homes being sized the same ton per sqft as older homes.

[craig1]

The small capacity loss directly causes a small loss of efficiency.
Lower btuh per watt = lower efficiency.

I'd rather have a more reliable system, that is 1-3% less efficient though.

Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.

[carmon]

Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.

under sized suction lines cause a capacity loss and hi velocity.....

[mark beiser]

Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.

I was just pointing out that you do in fact lose efficiency, not attempting to exactly quantify the efficiency loss.

Continuing the discussion though, when you are dealing with total system capacity losses due to pressure losses, and other issues within the system, the electrical consumption per btuh of net refrigeration usually doesn't go down, or even stay the same.
Typically it will go up.

Either way, in most instances the small efficiency loss, due to the small capacity loss incurred by having the smallest recommended vapor line for the application, isn't worth the cost of replacing the refrigerant lines.

[dijit]

under sized suction lines cause a capacity loss and hi velocity.....

I was just pointing out that you do in fact lose efficiency, not attempting to exactly quantify the efficiency loss.

Continuing the discussion though, when you are dealing with total system capacity losses due to pressure losses, and other issues within the system, the electrical consumption per btuh of net refrigeration usually doesn't go down, or even stay the same.
Typically it will go up.

Either way, in most instances the small efficiency loss, due to the small capacity loss incurred by having the smallest recommended vapor line for the application, isn't worth the cost of replacing the refrigerant lines.

Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.

Yes, it is more complicated than that. Remember pump laws and fan laws state that when you block flow, the amp draw is reduced. How much would be hard to determine and you may gain/lose efficiency or stay the same. Calculations for this stuff are just estimations, and you would really have to test it and get real numbers and plot an efficiency curve to find out. But with such a small difference, it doesn't really make sense to worry about. There are a lot of other things that can make a bigger difference, one being orientation and location of the condenser to minimize solar radiation effects which can raise the head pressure considerably and drop efficiency.

[beenthere]

Yes, it is more complicated than that. Remember pump laws and fan laws state that when you block flow, the amp draw is reduced. How much would be hard to determine and you may gain/lose efficiency or stay the same. Calculations for this stuff are just estimations, and you would really have to test it and get real numbers and plot an efficiency curve to find out. But with such a small difference, it doesn't really make sense to worry about. There are a lot of other things that can make a bigger difference, one being orientation and location of the condenser to minimize solar radiation effects which can raise the head pressure considerably and drop efficiency.

Solar radiation doesn't have much effect either. unless the condenser is on a roof, or other surface that is reflecting both radiant heat and convection heat.

[Premium Comfort]

If you really want to help lower power bills for the homeowner install a 2.5 ton instead of the 3 ton. If it can't keep up fix the leaks/solar gain in the house. Fudging the numbers on manual J calculations to get about 500sqft per ton that has been used since the 60's has got to stop. It's rare that a well designed house with a properly installed HVAC and duct system should need more than 750sft per ton.

Its finally nice to see someone else thinking on the same page. I've been using for rough estimates around 700sft/ ton on sizing. It would be great if the "old guys" in the industry would pick up their socks, open their eyes and realize it's approx 40 years after their way was relevant. The worst is, most of the young apprentice's listen to them because they have been doing it for years. I had a guy tell me the other day that he was told by one of the head engineers at ******* furnace manufacturer, that static pressure was irrelevent. not to worry about it, that his ducts were fine. PARDON????

[captaincompressor]

I have a 1.5 ton in an apartment with a 7/8 x 3/8 running 10 feet. The condenser is below grade of the coil. I hope my pressure drop is not severe.lol

[mrkelly]

So, How do 'you size an old house,built in '27 with NO 'upgrade's?
My 'socks are just 'fine and,Yes,I do account for the Future.