Okay since my last post was way too much for some I will post several and then some can answer what they are comfortable with.

many thanks,

It is time to get rid of my 5 ton, seer 8 heat pump and replace it.
The house and the heat pump is almost 14 years old.  Installed in 1997 but the unit was most likely manufactured in 1996. 
I live in the Denton Texas area, (DFW).  It gets HOT in summer (heat index around 100 -110 from mid July to mid Sept).
I have a two story home with standard 8 foot ceiling, somewhere around 3500 sq ft. Around 1500 down and 2000 up. (All of the full bathrooms are upstairs (humidity concerns)).

I am more interested in heating than in cooling but we do have a few cold months respectivetly.  (20 degrees is cold when you live in 110 degree summers).


I have replaced all of my doors and have new weather stripping.  I have 3 whirly birds in my attic at 50 cfm (at most). 

In the summer we have to close most of the downstairs vents (keeping the upstairs ones wide open) to keep the upstairs cool in summer. We do the reverse in winter. Close the upstairs vents (leaving them slightly cracked) and open the downstairs fully to keep it warm.
I also added a small window unit upstairs (8000 btu, seer 10.8) and it has reduced my bill by $100 a month and made the upstairs so much more comfortable. It paid for itself in and then some in one summer.
I also added heat reflecting window tint that has also reduced temperatures in east and west facing rooms. Big help. 

The next step is to have a manual J calculation done.

The current configuration is one ton per 700 sq of home. 

Step 1. upgrade from a single 5 ton unit to two 3 ton units. 

I have the room for the extra air handler.

I am thinking two 3 tons for the following reasons.
The current 5 ton cannot keep up in winter. It runs day and night and we freeze eventhough we are bundled up.
However it does a good job the rest of the year (providing we have half of the vents in the house shut).
I currently have 700 sq ft per ton and it does not do the job. This is a 3500 sq ft house with standard 8 foot ceilings.
If I go with 600 sq per ton I will need (3500 / 600 = 5.8) or 6 tons. I have been told that I may have to go with 400 sq ft per ton.

Would 500 be overkill? I have to add that the downstairs stays cool in summer due to the cold air sinking and the upstairs stays warmer due to the heat rising. So I think I definitely need to stay with two 3 ton units. Although maybe a 4 ton up and 3 ton down. 
Extra cooling for upstairs in summer (mostly hot in Texas).
My question Any major or minor problems with step 1? any holes? Did I overlook something? 

of course I will have to post the manual J before anyone can comment. 

Step 2.

I know how to trench, so I can trench around the house and put in 1'' coil tubing. I am figuring on trenching 430 linear feet to a depth of 6 feet and about a foot wide.

Each curl will be spaced a few inches apart (or does it have to be spaced)?
There is roughly .785375 sq inch per 1 inch tubing (1" I.D.) or is that cubic inches?
100 feet or 1200 inches of one inch (I.D.) tubing has an area (I hope that I am saying this right) of 943 cubic inches.

A gallon of water has roughly 231 cubic inches.

So 1200 inches (or l00 feet) of 1'' tubing should hold around 4 gallons of water. Pi * (1/2)^2 = .785375

If I have 1900 linear feet of tubing or 22,800 inches it should be able to hold 76 gallons of fluid.
if my calculations are off (and they very well could be, I was not a math major), wrong, incorrect, way out in left field, not even close please let me know what they should be?

Questions
For a ground loop.
is it 150 linear feet per ton or 300 linear feet per ton? I have heard installers give several different lengths which is correct?

am I better off with one continuous loop?

or with two loops?

Will I need a buffer tank?
if so what size?

A long continuous loop has an advantage of normalizing temperature by the time it gets back but how much extra pump will I need?

What are the chances of the water reaching ground temperature in shorter loops?

Can someone help me calculate the difference between two 900 foot loops and one 1800 foot loop.
I do plan to grout using a TC Grout.
My soil is sandy loam.
I am still trying to find out the thermal conductivity of the soil.

Speculating about whether x or y hundred SF per ton is worthless. You need a proper Manuals J, D, and S - compliant load and design calculations for your home. Not an average home, not the home down the street or the last home a prospective bidder worked on...YOUR home.

Calculating the total volume of liquid in a loop is interesting, but only useful for figuring out how much antifreeze to order, other than that it doesn't figure into the design.

Loop feet per ton depends on soil type and moisture. Individual loop length is a tradeoff between maintaining turbulent flow and minimizing pump power - one very long loop is rarely the right answer

You need to engage trustworthy knowledgeable local contractor(s) - we here can help you evaluate the offers

Curt,

thanks for the kind reply. 

I have spoken to several contrators and none have ever even suggested any manual J, D, S or anything.  Only on this board and I am greatful.

The ones that I have spoken too or I have had come out, all used a rule of thumb. 
Since they all have different thumbs the all have different rule.

400, 500, 600 square feet per ton.

I like the fact that there are real guidelines instead of "well we always do it this way".

One contractor has quoted 165 feet of loop per ton while another has stated nothing less than 250 feet of loop per ton.
Another contractor told me (without even coming to my house) that he would need 65k to sink the wells.
total install around 100k.  On a single family home?  It does not make sense.  That would be a 50 year payback on equipment that wont last that long.  I may not even last that long. lol.


Since everything that the contractors have said has countradicted each other greatly.  I think that I would like
to understand the design process fully before getting a home loan and throwing a bunch of money down the toilet.

I really want to go with geo thermal but I have to make sure that it is done properly.

Help me conserve

Okay,

So I will go with 2 seperate loops.  Based on the size of my yard the max I can trench is around 500 feet of trench about 5 - 6 feet deep.

If I can use some spiral flex tube and space the spirals a few inches apart.  This should give me two lines of around 900 feet each. 

Then I plan to add TC grout just slightly better than my soil.  Gasil fine sandy loam. 

Where I live in Texas it shows the soil temperatures to be around 70 degrees.  I am not sure that is right but I got that info off of a government GIS site.  It actually said that is the ground water temp. 

maybe I am better off without geo thermal. 

I just don't want to shell out a bunch of money and have the same thing that I have.

I am really trying to be more helpful than critical, but you are setting yourself up for failure.

 Loop design is not the first thing you do. An accurate Manual J heat load is the first thing that you need.

Most loop designs call for one loop per ton of heat pump. You are talking two loops for 6 tons. Big mistake.

 A design of 200' of pipe in a vertical bore does not mean that you can coil 200' of pipe in a trench and expect success.

If your ground temp is 70°, you are going to need something like 2000' of pipe per ton if you go horizontal.



“maybe I am better off without geo thermal. “


you might be right.

As you have found,  there are plenty of hacks impersonating installers.

You should take charge here,  insist that the bidders do a manual J,  show you a computer generated loop design, and give you straight answers.

There are good installers out there,  I don't think you have found any yet.

You might want to check out this thread

If nothing else, for $50 you can buy a temporary 60 day license for HVAC-CALC. Key in all your rooms and zones and find out for yourself the Man J load. Dewayne's feet of horizontal loop per ton may seem fearsomely high, but 70 deg sandy dry soil is a major challenge to overcome.

I do Man J and D load calcs along with measuring airflows for $300+, locally - not offering online since I do a site visit for measurements.

Dewayne, is that 2k feet per ton Slinky or straight?

Posted By engineer on 29 Aug 2010 11:29 PM


Dewayne, is that 2k feet per ton Slinky or straight?

We do 1000' of slinky pipe per ton in Utah where the soil temp @ 5'  is 50° in the spring and fall and climbs to 70° by the end of summer.   If  the deep earth temp in Texas is 70°, then the soil temp @5' in the summer might be 85 or 90°.  If  so,  then 2000' of slinky pipe would be needed to keep EWT's below 100°.

I don't think that many do horizontal sytems in Texas for this reason.

That's what I expected. Same or similar conditions would apply here in FL, especially during the occasional summer drought, which has to be taken into account.

I think if Bill were reading this thread, he could make recommendations about installing companies. His location is near help-me-conserve's. I noticed the name of Bill's drilling company was Johnson Drilling on the rig in a picture, and part of phone number showing. I remember he was happy with their work!

Regards,

Masoud

I started with max trench and loop calculations then ground temps to see at best what my soil and area can support.

I may have put the cart before the horse but I need to know what is the max # of BTUs I can draw from the ground without overloading.  

Once I know and understand the limits of the soil and see if anything can be tweeked... 
then a system can be designed with the limitations in mind. 
 
if the soil in my yard can support a 2, 2.5 or 3 ton system or even a 4 ton system then I will go with one of those and an efficient heatpump for the other level.  I can run the geo unit most of the time and use the heatpump for backup.   Plus I plan to be able to pull the return air from either floor as needed in different seasons.
I sure it can be done. I can at max run a 1900 foot loop of spiral tubing, add TC grout, and maybe a drip line to help the heat dispurse by cooling off the grout.

with soil temps what they are I may want to run a single tube so that the fluid temp would normalize before returning to the system.  If 1'' would give me too much turbulence then maybe 1 1/4 or 1 1/2 plus this would give me more fluid in the system.

If I drill instead of trench...

I heard that the cross timbers aquifer is less than 200 feet deep. If I have loops that extend into well water I have to be better off than just ground temps? Right. Plus if the ground temps get to high or low I can always discharge well water into my lawn sprinkler system normalize the temp? Worst case maybe I can go with one geo thermal heat pump and one normal heat pump. I heard that a company makes a hybrid that pulls from either the loop or the air temp whatever is optimum temp.

just trying to weigh my options.

Ask your designer about using a standing column well with lawn sprinklers used to discharge the bleed water (a small percentage of the total flow).

Posted By help-me-conserve on 31 Aug 2010 10:34 AM




I may have put the cart before the horse but I need to know what is the max # of BTUs I can draw from the ground without overloading.  

In your case you are not drawing BTUs from the ground,  you are adding BTUs to the ground.  The ground can react differently in each case.

Good luck making a slinky with 1 1/2" pipe

Posted By geodean on 01 Sep 2010 09:44 AM

 

Good luck making a slinky with 1 1/2" pipe

Would it be just as easy to say, you might have a hard time trying to make a slinky with 1 1/2'' pipe?

please do not post sarcasm to my questions.  I find it very rude.

Lets keep it professional. 

Plus my dec, jan, feb bills are higher than my jun, july, aug
so I would be taking BTUs from the ground in those months.
or am I missing something here?

Summer, I would be putting BTUs into the ground
Winter, I would draw BTUs from the ground.

"Ask your designer about using a standing column well with lawn sprinklers used to discharge the bleed water (a small percentage of the total flow).



Great Advice.

Thank you.

Posted By help-me-conserve on 01 Sep 2010 03:41 PM

Posted By geodean on 01 Sep 2010 09:44 AM
Good luck making a slinky with 1 1/2" pipe

Would it be just as easy to say, you might have a hard time trying to make a slinky with 1 1/2'' pipe?

Since it is about 6 words shorter, Dewayne's way is easier.  Sorry, I couldn't resist. 

Seriously though, you have been given great advice from professionals here, including Dewayne.  It is unfortunate that the installers who have quoted you so far have not done the necessary calculations to insure appropriately sized equipment and a successful job.

People here want to help you, but can't without the needed information.  Loops can be speculated about forever, but without the manual J and other information that has been requested, it's just speculation.  I don't think you will find anyone here that will tell you for x sized system you need this loop configuration, for y sized system you need that loop configuration, etc.  Just my 2 cents.

Posted By jonr on 01 Sep 2010 09:27 AM
Ask your designer about using a standing column well with lawn sprinklers used to discharge the bleed water (a small percentage of the total flow).

What does one do during the winter? A sprinkler system does not work well below freezing.

Bergy

Posted By help-me-conserve on 01 Sep 2010 03:41 PM

Would it be just as easy to say, you might have a hard time trying to make a slinky with 1 1/2'' pipe?

please do not post sarcasm to my questions.  I find it very rude.

Lets keep it professional. 

What if I asked you whether I could get to Toledo from here with the gas in my truck? You might reply..........
....."I don't know, how far is it? How many gallons of gas do you have? How many miles to the gallon to you get?"

I reply: I don't know, but what if I add 2 gallons? 

Dewayne, I and others have repeatedly told you we can't answer your questions without back ground. In response you rephrase, re-post etc.
Do not mistake frustration, for poor manners, Dewayne is more the gentleman than most here. I stopped responding 'til now to avoid an acidic retort.
Is it good manners to disregard our questions and advice yet ask for more? If you would like to "keep it professional" and recieve professional advice, begin to gather the information required for us to "professionally" evaluate and answer your questions.....

RE: Heat in the ground, I recently studied a project in TX where the project was (to my suprise) heating dominated. So while you are correct that delta T can be higher in the winter than the summer requiring large contribution from heating system, this is all subject to heating degree days and things we might gleen from a heat loss/gain calculation yet to be provided.

We really are trying to help, but you must help us help you.

I really do wish you luck,
Joe