BX23 trenching speed

[ESM]

I am considering the installation of a Geothermal heating system in conjunction with some major renovation work on our house we have planned for this summer.

These systems are expensive but a large part of the cost involves installing the underground piping required. The piping can be installed several different ways but in my case it would utilize a horizontal trench system. I do not yet know how long the trench will need to be but probably somewhere between 300 and 600 feet.

I know I "could" do this with my BX23 but realize it's probably not practical. I haven't used my backhoe for too much other then digging out stumps so I have no concept how long it would take.

Local soil is a medium clay so stability on the walls of the trench shouldn't be a problem (although I would NOT personally get in without bracing) but the clay may tend to stick in the bucket.

So my question is, what is anyones' best guess on how long it would take to dig a trench 5 feet deep, 2 feet wide, and 10 feet long? I'd look to get a 12 inch or larger bucket if I do this project. Does 3 hours seems reasonable?

I arrived at 3 hours by dividing the trench volume (100 cubic feet) by a bucket volume of .3 cubic feet (off-the-wall guesstimate) for a total number of 333 scoops required. If I assume an average of 2 scoops per minute that would be 167 minutes or pretty close to 3 hours. Does this seem reasonable?

At that rate it would take at least 90 hours to dig the whole trench /forums/images/graemlins/frown.gif

 

[5030tinkerer]

I am in the same boat, but I have been told that here in Des Moines, Iowa at least (zone 5), I'd have to go 8' down. In fact, horizontal boring companies are indicating that they go down 15'! Everyone agrees that 8' should do it, though. I was contemplating using my 5030 with a BH90 backhoe, but am also concerned about the amount of time that this would take. I haven't yet looked into the rental cost of a trenching machine that could go 8', but plan to.

 

[Jimbrown]

I have dug a lot of trench with my BX 22. I usually only go about 24 inches or so. My ground is hard and it takes about 1 hour to dig 2ft deep by 50 or 60 ft long. I gurantee you you will not dig 5 ft deep with a BX very fast. At that depth you will have to move the BX in 2 or 3 ft increments maybe less, at that depth the hoe will be straight down. 5ft deep for 600 ft is going to take you a week. I suggest you try a test trench 5 ft deep by 5 ft long. I think you will decide very fast to hire it done or rent a real back hoe.

 

[escavader]

5 FT DEEP 2 FT WIDE 10 FT LONG?....about an hour would be my guess,for someone for someone use to the bx-23,as lot as there aint to many large boulders.
ALAN

 

[techman]

Interesting to see your post. I just installed a geo system last fall. I considered (for about 1 second) doing the loop trenching with my BX22, but decided for the better. I did dig the trench from the house to the loop with the BX, but that was about 10' long and I went about 3' deep. At the end of the trench I elbowed down to the loop piping. The trench I dug was not as deep, since I wanted the pipes to come out in the basement at a reasonable height on the wall, not at the floor.

For the loop I hired a local who used a big Ford FEL/BH. His 2' BH bucket held about the same as the BX FEL. I wanted to go down 7', but we hit blue shale at about 6.5', so that was the average depth. Being on a solid layer of rock is actually one of the best conditions for a geo loop, so I was happy with what we hit. Overall length of the trench was 500' It took him about 10 hours and cost me around $ 600. I did do all of the backfilling with the BX. Took me about a week (about 600 tons of dirt to move), and I also regraded the yard , etc with the Kubota.

If you are attempting the geo job yourself, you need to be trained and practiced on the thermal fusion of the geo pipe. Also make sure that the pipes are surrounded by at least 6" of gravel screenings (very fine) to provide the thermal coupling between the pipe and ground. DO NOT use sand.

Paul

 

[techman]

Another shot

paul

 

[ESM]

Wow, 15 feet! That would take some serious machinery to do that. I'm sure the winter climate is much colder in Iowa the it gets around here. Actually, half my piping will only need to be at 3 feet. The pipe would be installed on both sides at the bottom of the 5' trench, 2 feet of backfill and then the pipe would run back again on both sides at 3' of depth.

I will have to check further into renting a big backhoe or hiring out the job. I wouldn't hesitate to pay $600 like techman but I'm in the Baltimore - D.C. corridor and everything, especially labor is very expensive. Still, maybe I can save some money just doing the backfill and grading with my BX.

Thanks for the pics techman. Kinda gives me an idea of what to expect. What's your opinion of your system thus far? What brand did you install? Do have any advice to share for someone like me who is just starting to look into these systems? I assumed the pipe was glued together but now I understand it is actually welded. I don't think I will be trying to do the install myself, I'm just looking for some ways to shave some of the cost.

 

[techman]

The system has been running since November. I put in 2 systems (2 zones), 1st and 2nd floor. The 2nd floor is a split. After much research I went with ClimateMaster. I have a few new jobs line up for this year. My own system was sort of my learning job for geo systems.

Loop entering water started out at about 52 deg, and now near the end of the season it is 39 deg, having sucessfully chilled the ground. My electric bills are running 1000 to 1400 KWH/mo less this year as compared to the same months last year. Granted it has been warmer this year, but comparing to some friends my savings is much greater than from just the warmer climate this year. I also installed the domestic hot water generators in both units (desuperheater option) along with a second non-powered HW tank as a preheat tank for the main tank. I usually have 80-95 deg water feeding into my powered HW heater, another key energy saver.

As for the job, it took me about a week to do the piping, 3 full days and 3 half, plus several weekends and evenings to finish the backfill and cleanup. I did 99% myself, and would not do that again. You need at least 1 helper for the outdoor work; handling pipe, shoveling and raking out screenings took a lot of energy. I did the same scheme as you mentioned, 2 layers with backfill between. Next job I will use a 3' bucket for the trench to get a 3-4' wide trench and put all 4 pipes along the bottom. After talking to other installers, that is the way they are going. Much less work. The 2' backfill between layers was a lot of work to level out in the trench. I used the BH bucket lowered into the trench for some, but a lot of shoveling was needed. All on 1 level eliminates all of that. Also with the 2 layers I used 60 tons of screenings. 1 layer would cut that to nearly half.

As for the pipe, geo pipe should be used (heaver wall - stronger) and it is shipped sealed and pressurized. Thermal welding is a must for a solid high strength joint. Polyethelene does not glue well, and any mechanical joint has metal that can corrode and fail. You do not want to have to find and fix a problem in the trench in a few years. Pressure testing was done on the pipes before closing the trench.

Inside work was mostly adapting ductwork to fit the new units (ducting was existing from older heat pump system). I put in a new airhandler/coil in the attic for the 2nd floor zone. This was needed since the old one was 18+ years old and would not be suitable for the desired efficiency. 3 days of crawling and laying on my side was bad enough, but I planned it for November when it should have been cool up there, but we had an 85 deg warm spell that week, so it was not so nice. I had to disassemble old and new units to get them up/down and then reassemble. Hardest job was getting new freon line in the wall. A bigger line was needed by spec for the efficiency. I fished out the old and had a rope through, but getting the new line through 2 stories was a real fight despite the fact that it was a straight run through nice sized holes. Almost a full day for that. (I hate big jobs in small attics).

Finally filling/flushing/antifreeze fill was relatively easy but time consuming. Quite a few hours of circulating to get it as good as possible. Perhaps I was a bit overboard since it was my first system, but I will most likely do the same next time. I an the kind of guy who wants it right.

In the end it is a great system. Low cost to run, quiet, much warmer duct air temperatures and no defrost cycles. Greatest of all is that when it is 10 degrees howling cold out, the system performs the same as when it is 40 degrees out. The old air source units would run 24/7 in very cold snaps, and the geo runs 10-20 minute cycles. If you can spend the money it is a great option. I am pushing them now for some customers and have a couple on the hook for this year.

paul

 

[techman]

Units

 

[techman]

Piping