kogashuko
Basic Member
Posts:169
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| 16 Dec 2012 08:41 PM |
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I am currently looking at doing a Geo install on an addition to my house. For about $200 more I can get a larger pump and replace my current second floor air source 14seer setup. My big hold back has been the loop. I have a buddy that has access to a backhoe that I was going to get to dig sever 100 foot trenches for slinky loops. Another person heard me talking and said that if I needed 100 foot trenches he could grab a trencher from the rental center and do a 6 foot by 100 foot trench in about 30 minutes. I explained that it needed to be about 3 feet wife for a slinky. It got me thinking though. The frost line here is at 18 inches. What if I dig a 6 foot trench, which is deeper than some of the 4 foot installs I have seen, and drop the slinky in sideways. The bottom of the slinky would be 6 feet deep and the top would be about 3.5 feet. Not ideal but I dont think it would be a big difference from a 4 foot trench. It would also be much faster to dig. Yes I would also need a lot of space between trenches.
Anyone seen this. |
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docjenser
Veteran Member
Posts:1400
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| 17 Dec 2012 02:35 AM |
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http://welserver.com/WEL0382/
Here are two vertical slinkies per trench, same concept, works great. Backfilling can be tricky with narrow trenches, you need to water the backfill in. The problem is that in general, you need about 50% more pipe at 4' compared to 6' down. That is why the vertical 3' slinkies in the example above are at 8', for an average of 6.5'. No need so much for a lot of space between trenches. What size pipe, how long, what is your load, how many circuits etc etc...? Where are you located? What is your deep ground temperature? |
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| www.buffalogeothermalheating.com |
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kogashuko
Basic Member
Posts:169
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| 17 Dec 2012 01:29 PM |
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Thanks for the link!
I am looking at 900 sqft on my second floor with 680 being added with the addition. I am looking at doing a 3 or 3.5 ton system (price isnt much difference) to replace the current 2 ton system in place on my second floor now servicing 900sft. This unit was installed before the addition of vinyl siding and house wrap and before the addition fixed a big leaky spot of missing insulation.
For the loop field I am considering 3 to 6 600foot sections of 3/4 inch poly. I am open to going bigger so that if I really like this system I can maybe replace the 2 ton system currently on my first floor. Before you ask, I spent a lot of time making the old system (had a 3 ton single system once upon a time) into two different pumps because the ductwork was so jacked up. The ductwork was not large enough to run between the first and second floors to effectively balance the two floors. Either way this house will have 2 units.
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johnny1720
New Member
Posts:21
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| 17 Dec 2012 08:13 PM |
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Posted By docjenser on 17 Dec 2012 02:35 AM
http://welserver.com/WEL0382/
Doc those loop temps are amazing, 52.9 Degrees EWT and 43.7 LWT. Can that be accurate? |
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jokin
Basic Member
Posts:105
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| 19 Dec 2012 06:42 AM |
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doc - love the pictures, schematics, and performance data. Thanks for the link. I'm just curious about the desuperheater piping. I thought the general consensus was it was best to pipe desuperheater "out" to the buffer tank drain. The schematic at the link above seems opposite ? Do you normally pipe the water from the buffer tank drain to the desuperheater "in" ? |
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docjenser
Veteran Member
Posts:1400
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| 19 Dec 2012 02:25 PM |
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Posted By johnny1720 on 17 Dec 2012 08:13 PM
Posted By docjenser on 17 Dec 2012 02:35 AM
http://welserver.com/WEL0382/
Doc those loop temps are amazing, 52.9 Degrees EWT and 43.7 LWT. Can that be accurate?
Yes it is accurate, but not the whole story. The home is owned by one of your installers. We are testing various applications, and the loop was setup to test if there is any performance loss in doing 2 vertical slinkies in 1 trench, versus 2 trenches with horizontal slinkies, and if yes, how much and how more pipe would we need to install to get us to a similar heat extraction. The answer was less than 4%. Now we moved on and ask the question how much we can slow down the flow loosing turbulent flow before we can see a significant loss in performance compared to a high turbulent loop. In other words flow in the vertical loop is very low, returning a higher EWT. We just want to see if the savings in pumping power equals out with a performance penalty of having not enough turbulence flow.
I should have explained this before me posting this specific system. My apologies. The point is that a vertical loop at an average depth slightly below (6.5' versus 6') to a horizontal loop performs similar, with an performance penalty of about 4%. Not worth worrying in real life. |
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| www.buffalogeothermalheating.com |
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docjenser
Veteran Member
Posts:1400
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| 19 Dec 2012 02:27 PM |
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Posted By jokin on 19 Dec 2012 06:42 AM
doc - love the pictures, schematics, and performance data. Thanks for the link. I'm just curious about the desuperheater piping. I thought the general consensus was it was best to pipe desuperheater "out" to the buffer tank drain. The schematic at the link above seems opposite ? Do you normally pipe the water from the buffer tank drain to the desuperheater "in" ?
No, we usually do it just a s you mentioned for the only reason not to get any debris from the bottom of the tank into the DSH or the DSH pump, but this was a new tank and we were trying to see if there is a thermodynamic impact. There was none.
"Our normal" way of DSH piping is as follows:
http://welserver.com/WEL0545/ |
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| www.buffalogeothermalheating.com |
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jokin
Basic Member
Posts:105
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| 20 Dec 2012 01:01 PM |
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Top Notch! An experiment under real life conditions. Thanks for the great info.
What did you determine with the flowrates in the ground loop? How slow can you go? What are the impacts on performance?
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docjenser
Veteran Member
Posts:1400
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| 22 Dec 2012 10:12 PM |
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We went down to a reynolds number <1000 and did not pick up any measurable difference in performance. So 2.0 gpm down to 1.5 gpm is very possible.
However, we also oversize our loops, so here are 1050 ft/ton, which might explain the lack of impact of the low Reynolds number.
The point is that I would rather reduce the flowrate and save circulation power when needed than installing an inefficient pump just to keep the flowrate up, just because a book tells me so. |
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| www.buffalogeothermalheating.com |
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ACES-Energy
New Member
Posts:67
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| 23 Dec 2012 07:44 AM |
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In addition to Doc, we have also been able to reduce flow rates, save energy and keep the heat pumps happy.
Also, our open loop systems we have been able to push the envelope on flow rates as low as possible to reduce water consumption and discharge and pumping power of a well pump. We have been monitoring source and refrigerate temps to help set our circuit setters/throttling valves. Just be sure to tell the customer to NOT touch the valves unless they want to see our service tech's pretty face, as it will cause a service call. Had two of them recently where the homeowners "dog" ran by and adjusted the valve causing the heat pump to trip off.....
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| www.ACES-Energy.com |
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jonr
Senior Member
Posts:5341
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| 23 Dec 2012 08:24 AM |
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Data such as here will show the effect of flow rate on COP (assuming the same EWT, which isn't quite accurate for closed loop).
With open loop, using a two pump system (well pump + booster) with the minimum pressure needed for geothermal saves more pumping energy than throttling. |
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kogashuko
Basic Member
Posts:169
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| 26 Dec 2012 04:56 PM |
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Ok so I did some research and the depest trencher I can get in my area is about a 5.5 foot trencher. Not ideal but hey it will be much easier, cheaper, than a small backhoe. Also, I am located in central Virginia and not Baffalo. I am spending a week in Rochester with the wife's family and have notice it is MUCH colder here and the frost line is lower. If need be I can make up for the depth with more pipe, make the slinky smaller, and only one slinky per trench.
Now here is my main delima. I just installed the current air source system for the second floor a year ago and the air source ground floor 2 years ago. For $200 more I can get a system that would not only heat and cool my addition but also the entire second floor. But, the 2 ton system for just the addition has a 28 err rating. The 3 and 3.5 ton systems are 22. This is much higher than my air source at 12 err. I like having different zones for different areas.
Is it possible to do one huge loop rated for like 6 tons and eventually have 3 seperate ground source heat pumps? Or is it better to screw the err value and go with 2 instead. Finally, is it worth it to jack up my house and ductwork to install just 1 5 ton unit with zoning and just one big loop? I am looking at about 2600-2700 sft when I am done.
I know these questions were beyond the scope of my original. Thanks for all the help. |
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kogashuko
Basic Member
Posts:169
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| 26 Dec 2012 05:07 PM |
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Ok after more research all of the Miami heat pumps I am looking at have a very close ERR value using a ground loop. So, now I am faced mainly with the efficency.
a) Eventually, 3 sepeate 2 ton heat pumps. So right now One ground source for the edition and two air sources for second floor and first floor.
b) Right now getting one ground source for the entire second floor and having an air source for the first floor.
c) Spend about $600 more than option one and getting one big unit for the whole house and fight with zone sensors.
I would think option A would be the most efficent to a point. Option B would be the most cost effective and that I could probably sell my old system for at least $1000 (the system has already paid for itself since I am now getting a max power bill of $200 in deep summer or winter with no gas logs and was getting well over $300 before WITH heavy use of gas logs.)
Option C might be better in the long run but for some reason everyone I know with one system for two floors has complained and had issues even with zoneing.
Is it even possible to economically attach multiple heat pumps to one big ground loop? Would I need like 3 flow centers?
Thanks.
EDIT
Actually I just did the math and the total square footage for the house is going to be 2900 sqft. Which doing a little research I dont think will be too unreasonable for the current 2 tons of heating and cooling currently in place with the 7 kw heat strips. I think that maybe I will be better off trying to add ductwork to the current system, plug leaks, add attic insulation, and better seal the crawl space. That way maybe in 5 years I can then go with a geothermal system. Worst case scenario I still have to put a geo system on the second floor. |
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joe.ami
Veteran Member
Posts:4377
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| 27 Dec 2012 08:08 AM |
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All else is supposition until you have a heat loss/gain. |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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docjenser
Veteran Member
Posts:1400
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| 27 Dec 2012 01:18 PM |
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Posted By kogashuko on 26 Dec 2012 04:56 PM
I am spending a week in Rochester with the wife's family and have notice it is MUCH colder here and the frost line is lower. If need be I can make up for the depth with more pipe, make the slinky smaller, and only one slinky per trench.
I hate to tell you, but this is not a very scientific approach. You need to now your weather data, deep ground temp, surface swing....and the list goes on and on. How much more pipe? What size? what length? Number of circuits? what pump to circulate the water? What soil do you have (conductivity)? You get one of those things wrong and your entire system's performance will be off.
With your approach the upper edge of a 3' slinky is only 2.5' deep in the ground. You will likely need at least 50% more pipe at 4' below surface than at 6'.
While we have multiple heatpumps on a common loopfield all the time, it actually works more economical, usually with one flowcenter. However, it requires more expertise to design and install.
But you are approaching this from the wrong end. You are counting sqf, which means not much, and you are guessing on the equipment needs.
Get you loads together first, than you can design your system. |
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| www.buffalogeothermalheating.com |
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kogashuko
Basic Member
Posts:169
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| 28 Dec 2012 12:59 AM |
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"I hate to tell you, but this is not a very scientific approach. You need to now your weather data, deep ground temp, surface swing....and the list goes on and on."
Despite all of that I was mostly worried about the depth. The frost line in Buffalo is between 35 and 48 inches, I could bury the whole thing at 5' in Virginia and still not have to worry about the cold issues that you have in Ny. Bottom line is that depth is my only issue in designing the system, I can easily calculate the rest of the stuff based on load after getting some deep soil info. I dont really care if I have to bury 1000ft or 3000ft of pipe because I can easily do it with 5.25 foot trench.
Either way it is going to be pointless to do a good manual J at this point or even consider putting in more units because I plan on adding quite a bit more insulation anyway. I would hate to size the system and add about r40 to the attic and bring the ductwork into the housing envelope only to find the system is way to large. So, in the meantime I am going to educate myself more on geothermal system building and when I am done with the insulation do a good load calc. I am even considering getting an energy audit for more accurate testing. I am really happy with how my system currently works and mainly consider geothermal as an option to keep bills down when this square footage is added. That approach is backwards when I should really be sealing everything up and insulating first.
Thanks for all the help. You guys definitly answered the questions banging around my head about multipumps and slinky design. |
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ACES-Energy
New Member
Posts:67
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| 28 Dec 2012 09:44 AM |
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Get an energy audit by someone not trying to sell you something. I use an inependant person who sometimes will tell a potential customer geothermal is not right for them, but its the truth |
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| www.ACES-Energy.com |
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docjenser
Veteran Member
Posts:1400
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| 29 Dec 2012 01:41 AM |
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Posted By kogashuko on 28 Dec 2012 12:59 AM
"I hate to tell you, but this is not a very scientific approach. You need to now your weather data, deep ground temp, surface swing....and the list goes on and on."
Despite all of that I was mostly worried about the depth. The frost line in Buffalo is between 35 and 48 inches, I could bury the whole thing at 5' in Virginia and still not have to worry about the cold issues that you have in Ny. Bottom line is that depth is my only issue in designing the system, I can easily calculate the rest of the stuff based on load after getting some deep soil info. I dont really care if I have to bury 1000ft or 3000ft of pipe because I can easily do it with 5.25 foot trench.
That is all I want to hear. Frost line in Buffalo is less than 24". As long as you can calculate a loopfield design based on 4' average depth and your load requirements, that is all what is needed. |
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| www.buffalogeothermalheating.com |
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kogashuko
Basic Member
Posts:169
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| 30 Dec 2012 12:39 AM |
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Thanks again!
Looks like I have to study up on some flow rates and stuff I havnt used for years.
Something else also occurred that I should also take the time, since I am waiting, to do some seasonal samples. I know already that certain times of the year there is a lot of water in the soil at very little depth and then other times of the year it is dry. I probably should plan for that. |
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engineer
Veteran Member
Posts:2749
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| 30 Dec 2012 11:11 PM |
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I was engaged by a remote client to assist with selecting amongst several geothermal alternatives. I wound up talking him completely out of geo owing to availability of natural gas. If NG is available, geo is harder to justify unless electricity is relatively cheap. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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