I have a question on a proposed install on a new home. Both contractors have proposed a 6-18 ton system to heat and cool the home. One contractor has proposed a one loop field with one inlet and one outlet running into the house while the other has proposed a three field system with 3 inlets and 3 outlets running into the home. I am at a loss to figure which is a better idea. The contractor proposing the 3 field system tells me that the pumps needed to control the three fields are more efficent to operate than a larger single pump and the 3 field wil allow the geo pumps to operate more efficently. The single field guy says not a problem, his system will perform just as well as a single field with two less pumps to run and maintain. Obviously I am an end user with no knowledge. Hope someone can help.

Hi,

I am confused what a 6-18 ton system means. If it is between 6 and 18 tons then something is wrong. That is too big of a spread.

As far as the loops go, good loop design practices always have one loop for all heat pumps to share. We have worked on numerous schools with 50+ heat pumps and they always share the same loop.

Are you looking at 3 separate heat pumps? They should all share the same loop. Each heat pump might have it's own loop pump, but they still should be on one common loop.

I made a mistake. It should be 16-18 ton. Each contractor will use 3 separate heat pumps. The contractor with three separate fields will manifold all three inside the house so all three geo pumps can use all parts of the field. I hope this clarifies the situation.

Well this raises more questions then. At 18 tons, you need 3*18=54 Gallons per minute flow when all heat pumps are running. It makes no sense to have one big loop pump which pumps 54 GPM running if only one heat pump is on. If the manifold is inside or outside really makes no difference in how the system performs. The best pumping scheme will be to have a separate loop pump for each heat pump.

If one of these guys is suggesting that you only have one loop pump for three heat pumps then he doesn't understand proper system design.

Let's make sure that you get a well designed system. Keep us informed.

Hi! Thanks for your reply. I will get additional details and report back.

Two questions pop to mind:

1) 16-18 tons is one heckuva load - does a properly executed ACCA Manual J calculation call for such tonnage?

2) In the case of several small systems each with its own pump, if just one system and its loop pump is running in a loop field sized for several units are water velocities sufficient to guarantee turbulent flow. Or, in this case is laminar flow not a concern when the loop field is way oversized for single pump operation?

Right laminar flow is not a concern for the reasons you stated.