Hypothetically, suppose a chosen circulator pump is matched to a system and will acommodate any diameter pipe run from 3/4" to 2", will the circulator pump use less electricity to operate the system with a larger diameter pipe due to less head loss for the same length, as opposed to a run with a smaller diameter?
Realistically, why kind of circulator? Constant speed, centrifugal, variable speed, inverter driven, constant pressure...? The circulator does not know if the pipe is 3/4" or 2". The goal is to move a certain amount of GPM, at least most of the time.
Pump input power is directly proportional to flow and head. I'd generally expect a fixed speed pump to maintain its kwh and vary flow based on the head changes you suggest.
> are you trying to move a set GPM? or BTUH? My heat pump (3 ton unit) manual talks about maintaining a required GPM flow for it to work correctly ~ 7 GPM, provided the loop design is adequate. It has a table to match up the required GPM flow to the various diameter pipes to ensure sufficient turbulence needed for heat transfer in the pipe. It also has a worksheet on how to calculate head loss due to the different pipe diameters, for circulator pump selection. What it doesn't discuss are the advantages / disadvantages in selection of pipe diameter... obviously more diameter requires more water / antifreeze. Also, I'm assuming a larger diameter pipe is more expensive, of any grade of pipe. docjenser (replied on http://www.geoexchange.org/forum/threads/impact-of-changing-pipe-size-for-a-horizontal-loop.5733/ ) However....since the diameter of the pipe increases, the contact area to the ground increases as well. But also the thickness of the increases, hindering heat transfer. But overall you gain about 10% to go from 3/4" to 1.25". We measure that with our monitoring, but also every loop software will confirm that. More importantly, you need about 3x the volume for 1.25" versus 3/4", which will create a thermal inertia, similar to a buffer or thermal storage tank, meaning that the loop when heat gets rejected in cooling mode will heat up slower, and stay cooler. The opposite will occur in heating mode. The thermal inertia is something the loop software does not account for, but the performance gain is significant. I would always go with larger pipe if practical, but wrestling 1.25" pipe is another issue. You also need 3x the amount of antifreeze, so sometimes you don't save much upfront expenses. Make sure you calculate pressure drop, flow and make sure the reynolds numbers are not too much off. But overall I would account safely for a 10% performance gain ... which sounds to me that functionally using a larger diameter pipe is better, even if the material cost is more expensive. > I'd generally expect a fixed speed pump to maintain its kwh and vary flow based on the head changes you suggest. hmmm. I am glad I asked, I better reread the manual with circulator pump / gpm in mind.
> I better reread the manual with circulator pump / gpm in mind. With that in mind, I did a PDF search through the manual and found it, the manual does address it. It says that due to pressure loss they list the maximum recommended pipe length for each diameter pipe, and flow rate in GPM. Thanks everyone!
> It may not be that simple. > pressure drop through ... Agreed, the heat pump installation manual has a whole section on calculating "head loss" (at the moment I am assuming it is their way of saying 'pressure drop') through a system of any given design they cover. My question for this thread only pertained to the pipe diameter considerations; specifically between any two diameters what is upside of choosing the larger diameter. Which as I understand from the answers I was mistaken, choosing the diameter is more to do with the GPM required by the heat pump and loop design than any of the other aspects I was thinking about.
If I understand you correctly: It depends, some pumps draw more power with a lighter load. In general, one should shoot for the lowest pressure drop for the least pumping power. But then other things come into play with larger pipes. Assuming same flow. Pro: Higher volume, more surface area of the loop pipe, lesser pumping power required. Con: Less turbulent flow
Unlike 'normal' heat exchangers, ground loops have flow only on one side. Give that, and the long lengths of pipe, and generally slow thermal transfer rates, turbulence is not very relevant. You will want to target 9 GPM (3 GPM per ton) if possible. And some newer units such as WF 7 recommend even higher flow rates. The less pipe friction, the lower pumping cost can be. But another factor that is important is designing the field so that it can be flushed properly (removing sand/dirt and air from loops). For flushing, flow rates need to be fast (> 2'/sec ??) and the system needs to either allow that flow for flushing as a whole or to isolate parts so that each part can be properly purged. For example, if the whole field was build with several 2" loops in parallel, it would be hard to find equipment that could flush that properly - certainly without being able to flush each loop separately. Conceptually these systems are simple. But building them to be setup and then work well requires more knowledge.
When your loop field is generously sized, turbulent flow might not add much, but it is more relevant in shorter circuits, when your water has lesser "contact" time with the pipe wall. So on the colder days, you might be glad you have when you have turbulent flow. It might be a design choice when you opt for lesser pumping power and compensate for the loss of turbulent flow by increasing your loop field size, but in general turbulent flow enhances heat transfer an can be relevant.
Mark, kind of funny. Before this turns out to be a basic physics update again, could you be more specific which of the above statements I do not have prove for? It would make it easier to provide you with exactly that "prove".
If you google "benefit of turbulent flow for heat exchange pipe" you get about 962,000 links to websites indicating and explaining the benefit of turbulent for heat exchange, including a few thousand scientific articles. Here are a few from the first page. http://www.advantageengineering.com/fyi/156/advantageFYI156.php http://www.hrs-heatexchangers.com/en/resources/comparison-of-laminar-and-turbulent-flow.aspx http://web2.clarkson.edu/projects/subramanian/ch302/notes/Convective Heat Transfer 1.pdf http://www.ou.edu/class/che-design/design 1-2013/Heat Exchangers.pdf http://hydraulicspneumatics.com/200...s/Article/False/6451/TechZone-FluidPowerAcces
