This is my first post since registering with GeoExchange, so if I have chosen the wrong forum, or done anything else inappropriate, I apologize and would appreciate someone directing me to the correct place. When installing two GSHPs in a residence (each happens to be a zone) is there a standard or recommended method when it comes to the loop field? i.e. do you put a loop field in for each unit or would you do one loop field shared by the two units? Based on the load calc. and loop calculation software I am using there doesn't appear to be a strong argument for one over the other based on dollars. I know in commercial applications where you have lots of vertical bore holes and multiple units the shared field is used all the time. But I can't seem to find any conversation regarding residential installations. The 2nd part of my question is: If the two units are of different size and each has a Flow Center how does one go about doing this installation? It seems to me you will have a difficult time controlling the GPM on each unit if it is running alone or if the other unit is also running. I found one statement by a Dr. Harry Braud (he is/was a Professor at Louisiana State U. and supposedly help to get IGSHPA started in the early days) where he preached "Keep it Simple"....one unit, one field & one pump. Thank you
Hi and welcome, How you apply the the load to the HX is really installer prefrance. For the Mcmansions we do, we usually devide the fields among the units so that there can never be a catastrophic failure that shuts down the entire house. To run multiple units on one field you would construct what is known as a inside building loop, prolly with variable speed circ pump. A new hvac guy I just worked for did sensors on the units to measure delta T to control the flow center. Prettty nifty I thought. Eric
Both Steve, Both work. I think of it as individual loops can use "dumb" pumping: fixed speed. And shared loops require smart pumps: variable speed, staging. With a shared loop you generally have an oversized loop for most operating conditions and you get benefits from this. But if you put dumb pumping on a shared loop, you lose some of these benefits. For shared loops you could - use a multi loop flowcenter that has pumps on individual circuits - divide the flow with plumbing and check valves - build an inside loop
We completed a large system recently where we employed a ECM main circulator and then had 3 paralell sub-loops for 6 heat pumps that activate a slaved PSC cirulator if either of the 2 units served calls. Main circulator ramps up as it senses greater draw. There is not one right way so installer comfort and experience are important in the selected design.
It depends on the experience you have. While IGSPA has done a great job of standardizing installations by giving you rules and formulas which will always work if you follow them. That does not mean they are the most efficient way of doing it. For me, the common loop field will run so much more efficient, plus the variable speed pumps run so much more efficient as well. I used to do one loop per heat pump, but since the variable speed pumps like the Wilo Stratos are out, I cannot imagine ever going back. We have seen whole system efficiency increases between 15-30 % due to the common loop field and variable speed pump(s). That is for the life of the system! It has become a no brainer. if you have different pressure drops in different units with a single variable speed pump (not within 10 % of each other), you have to balance the flow a bit. Usually the shut off valve (ball valve) adjustment will do it.
Being New Doesn't Always Work Thank you to all the responded. All is excellent feedback and all fits in the realm of ways I had thought about, but did not fully understand. But mainly the reinforncement that I was not a complete idiot. I am sorry for not replying sooner, believe it or not I thought my post did not get posted because I could not find it until tonight. Regards Steve
