Opinions (and facts) is wanted.

[urgross]

Opinions (and facts) is wanted.

I've been assigned to deciding how to replace or repair a geothermal (GSHP) for supporting a 30,000 SF warehouse. I've been discussing whether to install 17 additional wells (additional wells to supplement well design, all but 14 of the wells pooped out at 120') or something else. On a site with very much land to spare and utilize. However, the site is karst which is why 11 wells into a sinkhole.

Three alternatives are:

1. Add an air cooled chiller to provide supplemental cooling.
2. Install additional vertical wells to provide cooling, 250' depth. I'm concerned with this alternative having had 11 wells already failed at 120 feet.
3. Provide additional cooling by using a slinky. I like this alternative because of reduced risk or failure and project adjoins an empty field of about 35 acres.

I don't have experience with slinkies, so this is exploring a new area.

Your two cents is appreciated.

 

[EnergyProfessional]

If the added cooling load is only needed a few days or hours a year, the air-cooled chiller may be the most economical solution. You should do a load/energy simulation to find out how often the added load is actually there.

 

[itsmoked]

Perhaps an audit of the insulation system of the warehouse might be in order to make sure your load is as low as can be reasonably achieved.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BronYrAur]

Does the GSHP system provide heating as well? You only mention a chiller; what about heat?

 

[urgross]

The design and construction is to the ASHRAE 189.1 standard for envelop. Architect wants an award so it includes solar panels, light harvesting, passive air preheat for outside air, energy recovery, GSHP, etc. I provided three alternatives for the failed wells. Customer wants this done immediately, and then cost.

BronYrAur,

Heating is also provided by the GSHP, but needs to be supplemented. Boiler plant is close enough to supplement the HP. It was decided to size the steam pipes to take whole heating load, not just for load at 0*F. Last two winters (this project has been delayed for a long time) it has run off the boiler. I updated the costs it cost to run from the chiller plants to the boiler plant, and then from boiler plant to this project. Prohibitive costs and disruptions on two highways, so long time to get approvals.

I appreciate all the responses. Owner decided that no digging alternative will be allowed, risk after all the delays is not acceptable. That leaves only one alternative, air cooled chiller. I'm thinking the same as I did about 5 years ago, size it to take full load, not just partial, like with the chilled water piping. The architect can still say that an innovative hybrid GSHP has been installed.

 

[Atlantic Engineer]

Energy Professional is right, you should have done a complete annual energy analysis to find out the heat balance of you building and geo field. Take a look at HyGCHP software it is a free geothermal hybrid download that works really good if you understand the inputs. A hybrid approach should work for you here now that your stuck. If your GSHP machine is large enough you shouldn't need an air-cooled chiller just additional air-cooled heat rejection equipment such as a dry cooler, cooling tower or evaporative cooler, which one best would depend on your climate (dry or wet). It shouldn't need to be sized for full load just the offset of the wellfield capacity vs peak load day. You should or next time have sub-consulted with someone with experience with these geothermal designs. Next time do a full geotechnical analysis of the site including a test well to determine feasibility of drilling depth and thermal characteristics of the soil. Then you know how many wells, depth etc. before starting a trail and error process.

 

[urgross]

Atlantic,

As old people used to say, "...now for the rest of the story."

Design was performed by a consultant, who was told in his contract to perform TRACE and BLCC for LCCA before 30% design submittal for review. A-E was asked to consider slinky as an alternative. A-E performed vertical instead, having hired a well digger firm with Geotech PE on site investigation. Site included 25 wells at 250 ft depth, each. Only 14 of the wells has not fallen down the sinkhole. Sub-consultant has found an error in the drawing, having casing should only to be installed as far as needed. They interpreted differently than most. Having a sinkhole is definitely a part of the error process. Most recent proposal is to put in 18 wells at 120 ft.

Project began in 2014. Same situation was encountered in 2015. I was told to provide supplemental steam to allow partial occupancy and as supplement to the GSHP. Preheat temp of -3*F was told to design to. I designed to full load, supplementing the GSHP when it is not working. Was really needed the last two winters, and I was thanked (no bone-us) for forethought. Deja vu. This one is going to supplement the GSHP when the GSHP isn't running.

When geotech, TRACE, BLCC and hiring a geotech well digger through the lead consultant are used, the error trail can still be followed for years. I did not want to hire this consultant because of still cleaning up HVAC (my next task) on their last task. I think hiring better lawyers is needed, not better engineers. I think I'll tell them to use EnergyPlus, if there is a next time, it's free and takes three times as long.