I've learned this year a key principle with respect to how difficult it is for the earth to accept/provide heat from/to the closed water loop:  the earth needs time, both daily and monthly, to 'recover' when forcing the earth to accept high rejection/acceptance rates of heat.

For example, at the moment, I'm dumping, on average, about tw-thirds of a million BTUs into the earth each day (671 KBTU/day).  During a good portion of the day, my heat transfer rate is at 80 KBTU/hr.  This is a rate of heat transfer too much for the earth to absorb quickly.  So interestingly, my EWT rises almost 10° (F) during the course of each 24 hour day.  While I had an average EWT of 78° last month (June), the first chart below shows how dynamic EWT is on an hourly basis during each day (black and blue lines are EWT; red line is rate of heat transfer in KBTU/hr X 10).

It's not cost effective to put in a vertical closed loop that can handle the peak heat transfer demand.  Many, particularly Joe, have advocated this for some time here.  What I've learned, though, is there's a minimum size, such that there can be 'recovery' time each day for the EWT to return to a more steady state temperature.

It's clear - it takes the earth a good amount of time to move the heat - for my environment, it can't handle a 'steady diet' at 80KBTU/hr.  Thus, there has to be night recovery time to be ready for the next day.

This same phenomena occurs longer term.  The second chart shows the gradual EWT 'march' of increasing temperature for the past 16 weeks.  Looking at the last 6 weeks (again black and blue lines are EWT), you see 3 'dips' in daily average EWT temperature - each corresponding to when we had a couple of cloudy/rainy days.

I'm learning that these occasional moderate temperature days give the earth time to move a good amount more heat away from the vertical loop.  Giving EWT an opportunity to drop, on a daily average, a few degrees.  This becomes EWT capacity ready for the next batch of hot days.

I have found the dynamics of how the closed water loop interacts with the earth to be a fascinating subject.  The comments here are just FYI to pass along some learnings to those of you equally interested.

I don't think these comments are applicable for those with open loops.

Best regards,

Bill

I don't think I'm knowledgable enough to know what to store or how to effectively use storage tanks, for anything other than collecting rain water.

Best regards,

Bill

Are you serious?

It would be much more cost effective to simply drill another 300' deep well and add it to the existing borefield, versus purchasing very large tanks, that can be pressurized, and doing the excavation, installation, loop line air purging, and follow on maintenance, etc.

Best regards,

Bill

Thanks Dewayne.  I hope your charts on your customers' installations are proving educational to you.  I'm sure your customers are getting good performance from you as a contractor - what I'd be using the charts for would be to determine if you're putting in the right amount of pipe or too much pipe, etc., thereby giving you opportunity to affirm / adjust your internal cost expenditures.

My summer is similar to the harsh winter for many contributors here.  Right now, dumping up to three-fourths of a million BTUs per day into the ground, for a residential system, is no small feat.  I've clearly learned that it's not cost effective to build a loop that can keep up with transfering heat to the earth as much as is presented on design days.  But still, the loop has to be big enough to allow for 'recovery' time, both daily (night during summer, day during winter) and occasionally through the season period (i.e., an occasional rainy day right now for me).  The earth can't otherwise move heat fast enough to allow run times approaching 24 x 7.

It's easy to appreciate the (expensive) commercially available design s/w packages that allow contractors to get the loop designed right, horizontal or vertical, at optimum construction cost.  It's increasingly obvious this is not a DIY exercise.

And here in this Dallas heat, it's hard to see how a horizontal loop would work well without have have a loonnngggg amout of pipe in the ground.  Helps me appreciate how much depcreciation/insurance/operating cost there must be a with a deep hole drilling machine - otherwise everyone would simply put in a vertical loop down here.

Another area I'm looking at is long term heating / cooling of the earth.  For example, my guess is, looking at the chart below and imagining what it's going to look like when I have 1+ years of data on it, each year I'm going to reject to the earth more heat than I'm going to extract.  I'm going to be curioius if this affects my EWT long term.

Hope business has expanded a lot for you now, Dewayne, now that you've got capability to offer, in-house, vertical loops, with your fancy new machine.  I'd come ask if I could work for you if I lived in georgeous not-nearly-so-hot Utah!

Best regards,

Bill

http://welserver.com/WEL0043/

Curt, thanks.  In a few years I'll be able to present some fact, at least for my specific conditions (borefield of 8 holes, spaced 20' apart).

Best regards,

Bill