I'm now in to the 5th month of operation for my 4 Ton Tranquility 27 HP. Some people may remember from previous postings, I had a bit of a hiccup with glycol/water ratios in December that was causing freeze-ups near 30 degrees LWT, but that has passed. Since the, as long as my LWT stays above 25.5 degrees it's been clear sailing. My system is running perfectly , but for the fact that once the LWT gets below 25.5 degrees it locks up and goes to emergency heat. This isn't too big a deal, but in the ideal world I'd like to never have to rely on coil strip heaters. I'm thinking that if I can just eek out 1 more degree out of my slinky field, I may be able to go entirely geothermal. So, here's the question, does anyone have a suggestion for how to optimized loops to get better heat exchange? For those who want to see the data, visit the URL below for EWT, LWT, Supply and Return temps. http://carver.homedns.org/temps/data/day-gnu.png THanks -david

David, I wonder if you can get that extra degree (or more):

by insulating, air sealing, and/or duct sealing.

How much are you setting back at night? I wonder what would be the impact of 1 degree F less or more??? Of course, you don't want aux to engage during recovery.

It should be able to run with a LWT lower than 25.5. Do you know why it is locking up? Maybe one of the pros on here could help with that.

If your code allows, you can change to Methanol. That will reduce viscocity and improve flow rates some and thus raise the LWT some. Some better heat transfer with loop too. All this should help your loop temps some.

Looks like your return from night setback is calling for stage 2 and driving loop temps lower at that time. Maybe try to reduce that setback.

Your delta T could also be reduced with more flow by getting a more powerful pump or reducing loop fitting frictions. Does anything look very restrictive on the indoor connetions?

how to optimized loops to get better heat exchange

You could investigate a soaker hose to increase the thermal conduction of the soil.

You may get that degree for free after the loop field settles a bit more. .... if not, I would go the non glycol path.

What's your setup for tracking your data? I see you are running Apache/Ubuntu. What is your sensor setup?

Thanks

Thanks to everyone for the responses and suggestions.

I'm going to continue to improve insulation and air-sealing around the house. I'm confident that the work that I, and the electric company energy audit folks have done on the air sealing front has helped and tightened up the house considerably. I suspect there's some minor heat retention improvement I can make, but unless I do a deep retrofit of my wall insulation I'm not going to get too much saving here.

I'm leaning towards switching to Methanol, and adding another foot or so of topsoil to the area above my slinky field. From what I understand,the increased heat exchange and decreased viscosity I get with Methanol should help. On the top-soil front, I figure I have the leeway on adding more mass above the slinky's so it can't hurt.

I also was asked about my data logging configuration. The temperature sensors I use are 1-wire chips and I use a package called Digitemp to read and store the temperature data. The system I use to collect and process the data is a very low power Linux server. Up until very recently I dumped the collected data in to RRDTOOL based repository and graphed it using RRD-based tools , but I found the features available in that package too restrictive in terms of data recovery, archiving, and graphing functions. Now I take advantage of Digitemp's ability to dump data to MYSQL and then I use some simple BASH scripts to query the DB and graph data using GNUPLOT. Most of what I'm doing is pretty vanilla, but at the same time it's powerful to have detailed data logging and archives available.

Thanks again to everyone. This site and the people using it are tremendous resources.

David

Yep you need to get the antifreeze to better protect your loop.
j

Posted By davewick on 10 Mar 2011 09:16 AM
...the increased heat exchange and decreased viscosity I get with Methanol should help.

ON EDIT: OOPS! The denaturant comments (below) apply to ethanol, not methanol.

Be careful to use an ETHANOL product (such as WaterFurnace Environol™)
that's safe for geo systems. Various denaturants are added to ETHANOL
to make it non-drinkable (and thus, non-taxable) -- and some of them
are incompatible with common geo system materials (especially HDPE).

Looby

Good advice. I'm a DIY-er, and glycol was easy to deal with, but methanol is a different animal.

Any suggestions for a expert in Western Massachusetts who'd be willing to flush and fill my system?

Also, does anyone have a ballpark number on how much something like this should cost?

Thanks

Posted By davewick on 10 Mar 2011 12:50 PM
Good advice. I'm a DIY-er, and glycol was easy to deal with, but methanol is a different animal.

My comments on methanol were in error, denaturants are a potential problem
with ethanol -- not methanol.

I believe the only things you have to worry about with methanol is flammability
(before it's diluted to 20-25%), and possibly local water authority regulations.

The flammability hazard is best addressed by mixing the antifreeze outdoors.

Pure methanol is cheap and readily available with none of the denaturants used
in ethanol or "anticorrosion" additives commonly found in automotive p-glycol.

Dave, before you just ad topsoil and possibly affect your water run off, is to maybe add some hi density foam above the coils. This should reduce the ground freeze effect. I was looking into this but quickly figured I need wells and dropped the idea. Maybe others have experience with this. I am just west of you in NY so we went through similar weather this year and I ran all year without aux. I don't even have it wired yet.

Lets take a step back here. An LWT of 25 F at the peak of the winter is actually right on target, and the EWT I would suspect is around 30 F. This indicates w well designed and well performing loop. A loop should be protected down to at least 15F, and no loop should freeze or have freeze issues at 25F LWT. So this seems to be the only issue here.
The freeze issue you had never seemed to be fully resolved. Ensure that you have good freeze protection down to 15 F, with either methanol or glycol. Everything else is secondary.

Posted By joe.ami on 10 Mar 2011 10:08 AM
Yep you need to get the antifreeze to better protect your loop.
j

Yep