I am struggling with replacing our 21 year old WF heat pumps and would appreciate some advice. We are thinking of using two WF System7 036 units, one for upstairs and one for downstairs in our 3,300 sq. ft. home. A variable speed one-pump flow center is anticipated for each unit. Question 1. Is there an advantage to connect the two loops and run them as a unit – in parallel, even though their lengths are quite dissimilar (as described below)? Is there a problem with leaving them separate? Question 2. Do I have enough loop to operate the two 036 heat pumps (nominally 3 Ton each)? I hope that System7 is real smart and can de-rate itself gracefully when the need arises. I am worried about low EWT for the shorter loop. Background Info: We drilled two 6” diameter wells in 1985 of 265 ft. and 390 ft. in depth to service a 2-Ton heat pump for upstairs and a 3-Ton heat pump for downstairs. The wells are 8 feet apart. The heat pumps are WF ATV028 and ATV034. They were installed in 1993 replacing the original 1985 WF Command-Aire models which had serious compressor problems. The loop piping is 1.5” cts. Polybutylene. Both loops and units are currently separate, not connected in any way to each other.
Hello and Welcome. If both units do not run at identical run times time every day 24/7. I would look at merging the loop field. This is an older loop field. Maybe job one or ten. What is the piping again? Are you sure? My thinking is to join the wells. If there is no call from either unit the the ground and non-moving water make a heat transfer. Heat always goes to cold no matter how fast the water moves. That is law. Duck here comes the solar flair. I live under a CLE flight path so I watch that stuff. I do not know where this system is located. Will you tell us? In the land of clev the greater cooling load happens on the up stairs unit. So if you are in the south of CA area your units may have been zoned backwards. I look at heat transfer. Loop wells drilled to match units is not how I would do your home. Since we have 1 1/2" pipe, and we can maybe get fittings to join the wells, I would mate them and give the new machines the ability to extract what they need when they need it from the entire field. Piping will need to be designed. So up or down calls the whole field is available. MtrentW and I did this at his house. Mark
Mark, Thank you for your reply. I agree, it would be attractive to join the loops, but I am unsure how the preferential flow through the shorter loop, if connected in parallel, will affect things. As there are two pumps in two separate flow centers, would it be a good idea to combine the effluents in a mixing vessel so as to present to the heat pumps the same, blended EWT? However, I cannot quite picture how to pipe this and how it might work. Answer: The system is located in NJ, near Princeton. Answer: The proposal of November 4, 1984 calls for installation of polybutylene loop piping of 1.5" cts. I peeled back the pipe insulation and measured with a caliper. Outside dia is 1.6". Four blue pipes enter the basement. (The original installer is since deceased and the company has gone out of business). Our existing system is definitely heat limited as we are getting quite cold in winter and use resistive heat to supplement the GEO system. Air conditioning in the summer is a piece of cake, adequately handled by the upstairs unit alone. We are just using the fan to distribute cool air coming down from upstairs through foyer and other openings. We are in the process of conducting an energy audit with blower door measurements and manual J calculations to get a 'firm' handle on the building BTUh requirements. I am attaching the WF energy analysis of 1993 which was conducted as part of the installation of the current units. Thanks, again, for the help.
Since the loop field is 1 1/2" CTS you can move 240,000 BTUH at a 20* delta T. That would easily supply the 72,000 BTUH the new machines will use even at a lower delta T. If fittings can be found one could pipe in series with or without an indoor buffering tank. Piping to the two units can then be handled by two properly sized single pumps and swing check valves or a ECM drive pump looking at Delta P. They make them in RI. Either concept would greatly reduce your watts to water power needs. More savings. This set up would give each or both units access to all the pipe in the ground. Adding a buffering tank may require an additional pump. With an energy audit on deck I would not chose equipment with out seeing the audit report. I can help electronically but a rescue road trip to NJ from the home of the Browns and the King, pulling our Travel Trailer may not work until spring. We just got back from York PA last week. Mark lake-erie-indoor-air-services.net
Putting the two loops in series would mean about 1,300 ft. of pipe and even with a 1.5'' diameter pipe a head of about 50 to 60 ft., if not more. WF System7 model 036, the smallest of System7, have a minimum flow of 5 and max flow of 12 gal/min. Two 036s would be needed, so when both units are cranking hard, 20 gal/min will flow. At that kind of flow, one can look forward to 5-6 ft. of head per 100 ft. of pipe. I do not think there is a pump made ( I have looked at the GrundFos offerings) to overcome that kind of resistance and who would want to pump against that kind of a head? Unless one is willing to put several pumps in series, I do not see putting the loops in series as a viable option.
There are piping tricks that can be used to over come the head. I count 72.6 feet of head with machines if the loops are piped in series. Manifolding the loops with flow balancing valves would help. I was not really thinking about the head when I typed above. Sorry. The pipe is in the ground so I wanted to use it all. Mark
This is an interesting question. If you had the chance, in a new design you would make sure they are more balanced and the loop field larger, but you have to play with the cards you got. Yes, it seems you have enough loop, although I do not have your precise numbers in term of ground conductivity. Yes, I would definitely pipe them together inside. Again, not ideal, but making the best out of the current situation. A couple things: 1) The 7 series needs more loop than conventionally heat pumps, since they are more efficient, and use less compressor heat, thus at the same capacity they have to extract more heat from the ground. 2) Your annual load is still heating dominated, and yes, your shorter loop will see more flow. But keep in mind the flow is self limiting, because the pressure drop increases exponentially if that loop sees significantly more flow. So I sometimes butt head with Mark, and this time I disagree with him. No piping in series, you want to keep the pressure drop as low as possible, nor do you want balance valves on the loops, they only create significant flow restrictions and only increase your pressure drop, where you would need more pumping power to overcome. None of that is desirable. Don't worry about the lower EWT coming from the shorter loop, it will mix with the slightly warmer water in heating mode from the longer loop. Also the pumps will run in part load most of the time, which much lesser flow, so peak flow is not so much an issue. Do you have the individual length of the header pipes going from the inside to the wells? Then I can run some numbers. But looking at it quickly, the total pressure drop difference at 24 gpm ( (2) 7 series running at full speed) for the 2 loops in parallel is only 10ft/hd, resulting in about 11 gpm going down the longer borehole, and 13 gpm going down the shorter borehole. The project below is not done yet, but here is the concept. Two 7 series on common loop field. http://welserver.com/WEL0835/
I agree with Doc. Pipe the loops in parallel with no balancing. The loops will find their own balance point and average out. Pump with one properly sized variable speed pump and use modulating valves on each HP (controlled by internal AXB board respectively). During low load low flow conditions the shorter loop will predominantly contribute. During high load high flow conditions the longer loop will contribute at a much greater percentage relative to low flow conditions. Have your WF installer run your current loop through GeoLink to see if it is adequate to support your load with the Series7. Please keep in mind when calculating head, 1.5" PB CTS SDR13.5 is the functional equivelant to 1.25" PE IPS SDR11.
Alternatively you can have a single variable speed pump for each heatpump. It depends on your installer's skills, costs might be similar, but you would have redundancy built in.
