Loop for office building (25 total tons)

I plan to build a new office building for my business, location Evansville, IN, building about 28,000 sq ft, two story, about 120x120 ft footprint. My estimate is that I need about 25 tons of GSHP which will be provided by a number of 3 to 5 ton units for zoning purposes. I do admit I have not had a load calculation done yet, so this is just a starting point.

Open loop has been considered, but well water capacity in this area isn't sufficient and too risky. No pond loops are possible. A horizontal loop may be possible (~5 acres of land), but would require using land that may be required for future expansion. The horizontal loop is also somewhat lower performance due to seasonal ground temperature variations.

So the likely winner is a vertical loop system which brings me to these questions:

1. Anybody want to bid on installing the loops and/or the entire system?

2. Can the loops be located entirely under the building footprint? I see that as advantageous for short header runs, not taking land space, and not being exposed to seasonal ground temperature changes. My biggest concern is that the loops might get damaged during construction of the building foundation/slab, but I see no technical reason why the loops wouldn't work under the building. Another concern is that a loop fault would be nearly impossible to repair.

3. With multiple units, would you build the loop field such that each unit had its separate wells, or would you build one large loop field that each unit could tie into?

4. An idea is to run each well independently to the mechanical room, that is, don't put in a header underground. This idea allows choosing after the fact whether you have one large loop or isolated loops by how you plumb the well piping. This also allows isolation of a bad well from the system, somewhat protecting me from loop faults. Further, you can adjust the loops used by each unit by load if you find something out of balance.

Thoughts?

Mike C.
mikec@ciholas.com

 

At the 25 ton mark you better be sure that you are recieving qualified bids, if you are doing a design build project. I would suggest a test bore with conductivity testing to verify thermal conductivity at your site. Follow that with at least soft engineering that starts with data to ensure that your project is successfull.

Do you have the monies for this project? You could also call some engineering firms and get them to generate some soft engineering and then request budget numbers to deem feasability of your project.

A project that size would get a budget number of around 75k here.

hope this helps
Eric

 

Sounds like a good idea. The test well would become part of the loop system, so the money to drill it isn't wasted.

I suspect the test equipment to perform the test is not commonly found. It may be possible to build it since it seems fairly simple (water heater, pump, temperature logger). Is there guidance on how the test is performed so it yields usable numbers?

That is inline with my expectations, maybe even a bit on the low side given maybe 5000 ft of wells.

Any commentary on the under slab install? The common manifold versus isolated?

Mike C.
mikec@ciholas.com

 

Familiar

I work on such projects.

- you can install beneath footprint. I coordinate with structural to see their requirements and work within their limitations. You can install loops in pilings for example.
- get the architect, geo, and conventional mechanical guys in the same room at the start. Find out who is doing the hourly loads and go from there. If you don't, just wait to see how the conventional guys can stonewall your project over venting demands or such. They get confused by hourly loads primarily and generally default to 100% peak load requirements.
- a header vault may be your best option. See kwh pipe for an example.
- you would likely build off one large loop, but individual is an option.

 

I personally have never seen a commercial job done under foundation of building.
But I have seen a lot of commercial buildings put the loop field under the proposed parking lot during construction of the building.

 

Mike

This could be fun to do.

mark

 

We would layout the building on the ground and locate the perimeter foundation and the support column footings so the wells wouldn't be under those things. The wells would be drilled and piped to a central location, probably a sunken pit in the main floor. With the building being 120x120 ft, no well is more than about 60 ft from the pit, so line runs are short. I like the idea of having each well independently plumbed to the pit so I can isolate a leaky well and also monitor the performance of each loop.

One of my concerns is disturbing the soil under the building during well drilling and trench digging. We would need to get the soil properly compacted to support the concrete floor.

Doing it under a parking lot is possible, too, but with increased pipe length and will still have at least one trench into the center of the building for the header line.

I take it "hourly loads" are the expected heating and cooling loads at each hour of the day. I need to find someone who can run such numbers and do a real load calculation. We're dong a much better job of insulating the building than typical steel buildings with the idea this reduces the size of the system capacity quite a bit.

Interesting idea. I think a pit basically does the same thing.

That is what I was thinking. I presume each unit can have its own pump pack and a check valve and the system would work. We'd want isolation valves so any given unit can be removed from the loop for service without affecting the others. The advantage of the combined loop is that sometimes we have heat being called for (outside north wall zone) and cooling (interior conference room zone) and using a combined field means we trade the heat from one system to another as opposed to heating some wells and cooling others.

Mike C.
mikec@ciholas.com

 

Although the peices and parts to construct a conductivity testing machine appear to be simple to construct, it really is not. Even if you accumulate the data it still needs to be extrapolated into engineer speak for the design phase to move forward. I highly reccomend useing GRTI. They rent the machine with data logger attached. They ups it to you, you set up the test, you down load the data to them via phone line, you send the machine back to them. They generate a report that is in engineer speak for you to turn over to the owner. Game over.

Eric

 

I agree with Eric.

 

I agree with other 2 drillers who posted above me. Get the test bore and see the outcome of the test. Then have it size accordingly. This is not something you wanna go half assed into.

 

I agree with other 2 drillers who posted above me. Get the test bore and see the outcome of the test. Then have it size accordingly. This is not something you wanna go half assed into.

 

Similar on a residential project

This is very interesting. I did something very similar to this at my residence on Long Island. We have a small lot with a big house, so decided to put most of the vertical bores beneath the house. We did a 10-ton ground loop with (16) 125 ft bores. I paired them together underground to make 8 loops which I manifolded in the house. Shallow groundwater required the house to sit on piles, so this further complicated things. I let the structural engineer design the foundation / pile locations, then laid out my borings where I could. I drilled the vertical bores first, then put the helical piles in, then trenched all the loops to the garage location (and tested them) right before concrete guys poured. I wanted the manifold inside so I could monitor all loops and isolate any problems as underground reapirs would be near impossible. I put the circulator right next to the manifold in the garage and the heat pumps on a shelf above the manifold. 18 months running and so far, so good. Let me know if you have any questions. Good luck

 

We have also done alot of work in between piles prior to actual house construction. VERY nice looking work inside!
Eric

 

We have put verticals under slabs several times on beachfront houses - itty-bitty lots

 

A few things strike me as important.
1) Get an engineer who specializes in geo, or an experienced installer. Your system size is not too big where an experienced installer could not handle it.

2) You should have a common loopfield for efficiency and simplicity. You can have this going through a single flowcenter. It is very inefficient to run multiple flowcenters with high consuming constant speed pumps. For me, everything more than 2 heatpumps screams for a variable speed circulation pump. Phoenix Energy supply distributes custom B&D flowcenters with Wilo Stratos pumps up to 50 gpm. Phoenix Flow Centers

3) Most importantly, you can header up to 6 ton capacity together, everything above that you need to be able to control in form of a header with individual shot off valves. You can use an outside vault, or bring the pipe into the building individually. Other wise it will be very tough to get the air out. In your case 4 supply and 4 return lines coming into the building into a header would be very simple, saves you the outside vault.

 

That is what I was talking about. Custom flowcenter with a variable speed Wilo pump! Who supplied you with it?

 

Flow center with variable speed pump

Hey Doc- I got the flow center and pump from Phoenix Energy. They were great with helping us select the proper pump for my application. Although I am running only two seperate heat pumps on the system right, the original system called for a third heat pump to heat my garage. Unbelievably, I haven't needed to install garage unit yet. I have been able to maintain >53 degree temps in the garage in the winter. I assume I am getting some heat from the heat pumps, manifold and piping in the garage. I also insulated very well (closed cell foam).

 

Yes, the guys at Phoenix Energy Supply really know their stuff, and the custom flowcenters they have designed really work so well in combination with the Wilo Stratus pumps. I love it how you just dial in the needed head pressure for the required flow, and the pump revs up and down depending on how many heatpumps come online, keeping the flow steady to each heatpump.

Plus you measure the amps drawn, and everyone thinks it is unreal. Soon or later, every pump will be like this. For me, every 2 or more HP application has this setup.

 

Hopefully

Can't justify the cost of getting those pumps in to Canada, but I'm a fan of them.

 

If you have 2 or more heatpumps needing 4 or more constant speed circulation pumps, things start to make economical sense pretty quickly.