ColdInNY
New Member
Posts:9
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| 18 Dec 2011 04:35 PM |
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What is the industry standard loop sizing for a horizontal closed loop system per Ton of heating?
We have a 5 ton forced air heat pump unit and a looped trench about 6' deep, 350 feet out with 2 out bound lines (straight not slinky) 3 feet apart and comes back in a seperate trech with about 15' separation from first trench and return lines 3ft apart. Soil is sandy loam for the first 150 feet closest to the house (about 300 total out and last segment back) and the furthest 400 feet is a wet clay high water table. Target Balance point is 0 f and house is 2300 sqft old 1900 farm house with poor insulation rating. We live in the Adirondacks and get 10-20 sub zero (f) nights on average in the winter.
Does anyone know of good reference documents for proper loop engineering?
System is brand new.....and not quite complete. Unit was made operational but last 30-50 feet is exposed/not covered to depth do to contractor issues getting through the foundation. With a jack hammer, we got through just fine and are awaiting the lines being moved before covering them up.
System is having water flow lockout issues when temps are below freezing...fortunately it had been above freezing most of the week so only having no heat conditions 4.5 out of the last 10 days (coldest night 15f).
Reading forums we are seeing guidlines of 300-500 nominal feet per Ton and recommendations of more in cold weather climates. We see happy people with 600'+/Ton. We realize that there is heat loss with the uncovered section but is that 60-100' out of 1400' loop that significant that we don't need to be concerned that we may been heating every winter night on the auxilary electric coil?
Want to know if we need more loop before we cover the system for good?
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Palace Geothermal
Veteran Member
Posts:1609
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| 18 Dec 2011 06:46 PM |
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So how many feet of pipe do you have in your loop now?
What is the Manual J load of your house?
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Dewayne Dean
<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system |
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jonr
Senior Member
Posts:5341
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| 18 Dec 2011 07:05 PM |
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For the loop design, you want to use software such as Ground Loop Design.
http://www.groundloopdesign.com/ |
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docjenser
Veteran Member
Posts:1400
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| 18 Dec 2011 08:59 PM |
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I do not like to judge the work of others and be critical of it through a forum like this, but the numbers do not match up.
While a 2300 sqf old leaky farmhouse might be OK with a 5 ton system, systems in our western NY climate requires 600 ft of straight pipe or 800 ft of slinky per ton to not drop below 30 F Entering Water Temperature (EWT) at the end of the winter heating season. Your loop seems to be less than half that length, and it will not support the heat extraction of a 5 ton heat pump. You will need at least twice at much, if not more due to your sandy loam. Your loop will become too cold too quick. You also need to find out if you have the correct antifreeze protection. It should not lockout that quick after running just a bit.
You can measure the EWT and the LWT (going out to the loopfield) and let us know here. |
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| www.buffalogeothermalheating.com |
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SkyHeating
Basic Member
Posts:203
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| 19 Dec 2011 01:50 AM |
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I also typically design for about 600 to 800' per ton depending on soil conditions and operating temps. What is your Reynolds number?
Also is there anyway to seal up your house better so you don't need to use all 5 tons of the system |
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Visit my Youtube channel for product reviews and customer testimonials http://www.youtube.com/user/skyheating1
http://www.welserver.com/WEL0626/
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ColdInNY
New Member
Posts:9
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| 19 Dec 2011 06:56 AM |
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Thanks for the replies.
I beleive that we have about 1400-1500 ft of pipe. I wish I educated myself more ahead of time so I have a report of the heating requirements that we need, but I don't think that is the manual J. That report indicates estimates that we need 77,000 BTU/hr to heat our house to 70 with a 69 degree difference in the outdoor air temps.
We had other heating contractors indicating that we needed 78,000 BTU systems for our house (not geothermal) so those numbers seem in line. However, now that I am concerned...., when I calculate the numbers for 78,000 BTUs of heat transfer with the ground..... I calculated atleast 3600 ft and that was making some ver.
We had the system off yesterday between 2:30am and 5:30pm. We coverd more of the pipe so we are down to about 20ft of exposed pipe and have wrapped that in R-13 fiberglass to see if we could get through the night as contractor is indicating that the exposed pipe and the lack of electric coil, settling time are the only issue. We checked the temps of the pipes with an infrared temperature guage and it was running about 30-31 degrees in and 24-25 out at about 9:30pm. Air temps at the register was 85.
It got down to 19 degrees outside overnight and by 12:00 am the system was not keeping up and thermostat was dropping but 70 degree air was still coming out of the registers, did not check the pipes. By 5 this morning the compress was in lockout state. Fan still running but just circulating 59 degree air at the registers 62 degrees in the house.
I have reviewed the contract....and unfortunately it just spells out that they will install 1000+ feet of geothermal pipe so this will be interesting....I am hoping that we can negotiate some kind of happy medium where we have heat all winter long that is not coming from an electric coil.....
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Palace Geothermal
Veteran Member
Posts:1609
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| 19 Dec 2011 10:46 AM |
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Posted By ColdInNY on 19 Dec 2011 06:56 AM
I have reviewed the contract....and unfortunately it just spells out that they will install 1000+ feet of geothermal pipe so this will be interesting...
How convenient for them  Hope you get some resolution. |
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Dewayne Dean
<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system |
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docjenser
Veteran Member
Posts:1400
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| 19 Dec 2011 12:34 PM |
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You are setting yourselves up for disaster. The 20ft (out of 1400ft) will not make a difference. The electric strip heat will only mask the problem. He delivered a nonfunctioning system, even with supplement heat your system will continue to lockout.
It does not matter what is in the contract (1000+ is good, that can mean 3600!), your contractor has to deliver a system which does not lockout. What do you think the situation will be at sub 0 nights?
You need to assure that your loopfield is increased to bring up the EWT, and that the flow requirements of the heatpump are met.
How experienced is your contractor?
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| www.buffalogeothermalheating.com |
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cnygeo
Basic Member
Posts:170
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| 19 Dec 2011 01:34 PM |
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I'm in the fingerlakes, so a bit milder climate, but as a semi-local datapoint, my system is somewhat similar in size and loop configuration (but not total loop length!) to yours. It is a 6-1/2 ton system supplying a load of about 45kbtu/hr at 70deg delta T (the oversizing is semi-deliberate taking future loads into account). I also have 2 parallel pipes per trench, spaced about 3 feet apart, and soil conditions sound similar as well (damp to very wet clay depending on the season). I have 6 loops (3 trenches) with about 3200 feet of pipe total including 40 feet of headers. My original design called for a full 3600ft, but we ran into some issues excavating so I settled for what I could get accepting that I might have to add another loop someday in the future.
As it turns out, I'd say my loop is just about perfectly sized for the current load. The EWT is currently about 45deg, but based on the past 3 years that will drop to about 32deg in late Dec/early Jan and stay there until March when it will start to warm up again. You can clearly see the EWT flatline in the coldest months as it absorbs latent heat from freezing the ground. Based on this, I think I have a bit of extra capacity that will hopefully support slightly more load when I bring the rest of the house online. The COP of the heat pump is also lower than advertised which reduces the load on the loop field a bit.
So anyway, I'm at about 550' of loop per ton going by heat pump capacity and about 7-800' per ton going by actual 24-hour peak load, and I definitely wouldn't go any smaller than that. Again, I'd prefer to have more pipe in the ground, but circumstances didn't allow that and I've been lucky that what I ended up with works pretty well. This all agrees pretty well with "rule of thumb" numbers I've heard here and elsewhere for horizontal systems in similar climates.
Also, my loops did a ton of settling - we waited to do the final grading until the following spring, and the soil over each trench sunk a good foot or so over the winter. Interestingly I didn't see any appreciable change in loop performance from the first year to the 2nd, but it's not a perfect comparsion because I made quite a few changes to the indoor parts of the system over the first year. |
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docjenser
Veteran Member
Posts:1400
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| 19 Dec 2011 07:25 PM |
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What kind of flowcenter (with what kind of pumps?) do you have? What kind of pipe do you have? 0.75", 1" or 1.25"? What brand and model of heatpump do you have?
A 5 ton HP would need nominal 3 gpm/ton, so this is 10 GPM in first and 15 gpm in second stage. If you have only 2 outbound lines, that is 7.5 gpm flow per line. OK with 1.25", very bad if your pipe size is 3/4". I am not talking about your header pipe here, but your actual loop. |
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| www.buffalogeothermalheating.com |
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Earth Fire Energy
New Member
Posts:4
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| 19 Dec 2011 08:59 PM |
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Unfortunately, there is seldom a nominal loop sizing that applies to all situations. It is not clear to me the exact layout of your system, but it does sound like you may need additional piping to support the 5 ton heat pump. If you can send me an email with a sketch of your piping in the ground I may be able to assist you.
Best Regards,
Bret Hutchinson
[email protected]
www.earthfire-energy.ca |
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ColdInNY
New Member
Posts:9
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| 20 Dec 2011 08:03 AM |
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I am meeting with the contractor today. Call some of the references and found out that this contractor installed in the area 1200ft loop for 2 ton heat pump for another one of his customers. Wondering why similiar sized loop for 5 ton. I have asked him to bring the heat transfer calcs that support 77,000BTU/hr as was in the cost savings worksheet.
We have a 5ton envision dual capacity (2/3) waterfurnace with a geolink flow center. All pipe is 1.25 hde.
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ColdInNY
New Member
Posts:9
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| 20 Dec 2011 10:28 AM |
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Here is the info that I received from the contractor:
He pluged the following into the software provided by waterfurnace.
Heating Operating Load of 87713 BTU per hour
Based on 2200 sq ft
Wall R-Valu 10.99
Floor R-Value 10.00
Ceiling R-Value 12.99
Window U-Value 1
Window SHGF 0.65
System Efficiency Loss 15%
System Efficiency Gain 15%
Cooling Infiltration Rate 0.6 ACH
Heating Infiltration Rate 0.8 ACH
Winter Ventilation 0 CFM
Summer Ventilation 0 CFM
Horizontal straight 2 pipe 1.25" HDPE 2' apart plugged into progam, actual 42" apart
racetrack config
He indicated that software indicated 480' loop required and acutal installed is 600'
Loop Min 20 degrees F Max 95 degrees F
0.9 Damp Sand
Deep Earth temp 50 deg F
Loop Conductivity 2.33
Min Freeze protection 0 degrees plug in to computer actual -20 degee 22% prop glycol
Aux Required as inidcated by program 13kw, full emergency 26kw, actual installed into our system 15kw
Heating
Geo 2.96 COP
94% Heat
aux Heat 6% Heat
Full system 8 hr purge has not happend yet...
The problem is the exposed pipe....
We need finish the system and close the pipe and we will not have a problem....
600 ft per ton would be based on .75" pipe not 1.25" pipe or slink configurations....It is all dependent on soil types and pipe sizing etc....you can't rely on information that you read online as you don't know the factors that go into those numbers.
He indicated that the other customer was mistaken and he only has 600ft single loop with 2 ton heat pump designed for airconditioning only since the customer already had Baseboard hot water with natural gas boiler.
I can't get a commital to what the balance point of the designed system because told to many variables. I'm told that the auxilary system is designed to supplement the system not just when it is sub-zero out.
The system is designed to an 87,000 BTU/hr heat load if after we get the system complete and we still have problems we should get an energy audit and tighten up the house. I just want to verify his calcs that this system will support an 87,000 BTU/hr heat exchange geothermal not electric.....
Since we are moving to pipe from above the foundation to coming in the foundation at depth....think we will move the header inside so it will be easier should we need to add to the loop.
I have checked some of the loop design software but the trial/demo versions say that the numbers may not be accurate in the trial versions. Based on the money it costs to purchase and since I am not up to speed on how to use....are there good reference materials out there for manually calculating the required loop lengths based on 1.25" pipe or are there professionals out there who are already licensed to run the expensive software that are willing run and supply an analysis at a fraction of buying to software for a one time use since I am not a contractor?
Thanks for the feedback.
Does anyone have recomendations on precautionary steps that I should be taking at this stage in the game to ensure that I am protecting my interests.... I got a whole lot of numbers and excuses but don't have and heat transfer calcs that I can review and feel confident in and I am very nervous......Hope that I am overly skeptical......
Thinking about investing in welserver software so I will have data incase I need it. What are others thoughts?
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docjenser
Veteran Member
Posts:1400
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| 20 Dec 2011 11:29 AM |
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Posted By ColdInNY on 20 Dec 2011 10:28 AM
Here is the info that I received from the contractor:
He pluged the following into the software provided by waterfurnace.
Heating Operating Load of 87713 BTU per hour
Based on 2200 sq ft
Wall R-Valu 10.99
Floor R-Value 10.00
Ceiling R-Value 12.99
Window U-Value 1
Window SHGF 0.65
System Efficiency Loss 15%
System Efficiency Gain 15%
Cooling Infiltration Rate 0.6 ACH
Heating Infiltration Rate 0.8 ACH
Winter Ventilation 0 CFM
Summer Ventilation 0 CFM
Horizontal straight 2 pipe 1.25" HDPE 2' apart plugged into progam, actual 42" apart
racetrack config
He indicated that software indicated 480' loop required and acutal installed is 600'
Loop Min 20 degrees F Max 95 degrees F
0.9 Damp Sand
Deep Earth temp 50 deg F
Loop Conductivity 2.33
Min Freeze protection 0 degrees plug in to computer actual -20 degee 22% prop glycol
Aux Required as inidcated by program 13kw, full emergency 26kw, actual installed into our system 15kw
Heating
Geo 2.96 COP
94% Heat
aux Heat 6% Heat
Full system 8 hr purge has not happend yet...
The problem is the exposed pipe....
We need finish the system and close the pipe and we will not have a problem....
600 ft per ton would be based on .75" pipe not 1.25" pipe or slink configurations....It is all dependent on soil types and pipe sizing etc....you can't rely on information that you read online as you don't know the factors that go into those numbers.
He indicated that the other customer was mistaken and he only has 600ft single loop with 2 ton heat pump designed for airconditioning only since the customer already had Baseboard hot water with natural gas boiler.
I can't get a commital to what the balance point of the designed system because told to many variables. I'm told that the auxilary system is designed to supplement the system not just when it is sub-zero out.
The system is designed to an 87,000 BTU/hr heat load if after we get the system complete and we still have problems we should get an energy audit and tighten up the house. I just want to verify his calcs that this system will support an 87,000 BTU/hr heat exchange geothermal not electric.....
Since we are moving to pipe from above the foundation to coming in the foundation at depth....think we will move the header inside so it will be easier should we need to add to the loop.
I have checked some of the loop design software but the trial/demo versions say that the numbers may not be accurate in the trial versions. Based on the money it costs to purchase and since I am not up to speed on how to use....are there good reference materials out there for manually calculating the required loop lengths based on 1.25" pipe or are there professionals out there who are already licensed to run the expensive software that are willing run and supply an analysis at a fraction of buying to software for a one time use since I am not a contractor?
Thanks for the feedback.
Does anyone have recomendations on precautionary steps that I should be taking at this stage in the game to ensure that I am protecting my interests.... I got a whole lot of numbers and excuses but don't have and heat transfer calcs that I can review and feel confident in and I am very nervous......Hope that I am overly skeptical......
Thinking about investing in welserver software so I will have data incase I need it. What are others thoughts?
Your contractor does not seem to have much experience with geo system design. The way it is designed it will fail.
If he plugged in 20F min loop temperature into the software, this explains everything. You should design for a min loop temperature, meaning EWT, of 30 degree F, which would make the loop about 3 times as long. 20 degrees is the absolute limit the heatpump would be able to operate. If you leave the software on autosize, it sets the EWT to a minimum of 30F. He must have manually over written it.
Then the antifreeze is off. 22% of glycol give you about 17F freeze protection. However, if your incoming water is 20F, and the heatpump takes 5-6 degrees out of it, the leaving water is 14-15F. And your heat exchange coil is even colder. Plus chances are that he does not have a glycol product that uses 100% glycol. Most of them from the local supply house only have 60% glycol in the product. In any way, your loop is too short, runs too cold, and does not have enough antifreeze in there. Thus your heat exchanges freezes shut, and your unit shuts off on high pressure. This will get worse down the road, and can very easily damage your heat exchanger. Here is the chart for the glycol freeze points.
http://www.prochiller.com/reGlycolChart.html
Yes, 1.25" pipe will get you more heat exchange than 0.75" pipe, but only about 9-10%. You are about at least 60% undersized.
This will get worse the more heat you pull out, so don't run the unit anymore. Contact Waterfurnace, they can help you with your contractor. Their unit will get damaged, and it is not in their interest. PM me, and I can hook you up with your local Waterfurnace rep.
Yes, 5 ton otherwise is a good size to support 87,000 BTU/H heatload. But that is insignificant right now. Your loop needs to be completely redesigned. |
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| www.buffalogeothermalheating.com |
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jonr
Senior Member
Posts:5341
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| 20 Dec 2011 12:09 PM |
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You should try the free demo software any way - it's mostly accurate, but verify the final result with someone who has a full version.
Why is damp sand being used when you have wet clay? |
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ColdInNY
New Member
Posts:9
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| 20 Dec 2011 12:53 PM |
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a portion of the loop is sandy soil |
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ColdInNY
New Member
Posts:9
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| 20 Dec 2011 08:24 PM |
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Does the free trial version of Ground Loop Design allow you to change the ground temp. It is set to 62 degrees and it won't allow me to click into the box to change.
Does raising the ewt 12 degrees to match the 12 degree difference of the actual ground temp provided an equivalent calc? |
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docjenser
Veteran Member
Posts:1400
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| 20 Dec 2011 11:16 PM |
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Please send me your email. I ran the numbers, and with 1.25" pipe in damp sand, you need 1155 ft of trench length (2310 ft of pipe) with 2 pipes in the ground at 6 ft depth to keep the loop above 30 F. Assuming 78 KBTU/H heatloss with Albany, NY weather data and a 5 ton Envison 2 stage heat pump. |
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| www.buffalogeothermalheating.com |
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jonr
Senior Member
Posts:5341
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| 21 Dec 2011 01:00 PM |
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True, that is the problem with free GLD so it is mostly useful for relative comparisons. With WF free software, I get 600' of trench @20F and 1355' @30F, both with a 60K load in Albany. |
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docjenser
Veteran Member
Posts:1400
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| 21 Dec 2011 01:21 PM |
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I got 550' trench length @20F and 1155' @ 30F, with Albany weather, and 78K load. Did you do 0.75" pipe or 1.25"? Six feet deep, damp sand? |
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| www.buffalogeothermalheating.com |
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