The Homemade Heat Pump Manifesto - Page 147

AC_Hacker · 03-31-13, 08:50 AM

Quote:

Originally Posted by michael

...The next phase for me is to put in one 300' loop of a field of loops I hope to install, hook it up to the 1 ton heat pump, monitor soil temperatures near the pipe and water temperatures entering and leaving the heat pump and try to get a fix on how many ground loops will be required. I think I'll be able to base predictions on data I collect from a straightforward but simple installation. Meanwhile, I'll keep reading the Forum. Many thanks for your comments, mm

Sounds reasonable.

Questions:

How are you going to do this?
Straight?
Coils?
How deep?
Diameter of Pipe?
Material of pipe?
How are you going to monitor water temps?

-AC

michael · 03-31-13, 08:53 PM

Questions:
How are you going to do this? Hmmm...ok, here goes: The first trench I will dig with a backhoe because it’s what I have available, and I can do it myself at my own speed using a Kubota BX23 with a backhoe attachment that will dig 6’ deep with a 9” bucket.
Straight? Coils? How deep? Yes, straight. No coils. The return side of the loop in the bottom of the trench; the cold side of the loop about 1.5-2’ above it with the bottom of the trench at 5’ below grade. If the results are what I hope for, I'll install another dozen or so pipes at 18-24" intervals for a total of roughly 4000 LF of source pipe to heat a 2000 SF house with a 2.5 ton GSHP. I'd like to do those with a trencher or hire an excavator, so it won't go on forever.
Diameter of Pipe? Material of pipe? 3/4” HDPE is what I think I'm expected to use, but I want to use 3/4" PVC because it will be so much easier for me to manage, and PVC appears to retain up to 80% of its strength up to 140 degrees; 120 deg. is the highest temperature I expect to obtain from a heat recovery system that will be used to recharge the source field.
How are you going to monitor water temps? Using a Parallax BS2pe microcontroller and a number of one wire temperature sensors such as DS18B20 config. To-92 for data logging (not yet assembled). I will place sensors in the trench at the exit and entrance of the pipe as well at the bend in the distance. Additional sensors will be placed beside the pipes 1”, 2”, 6” and 12” separated from it to monitor temperature changes in the soil, and sensors at the four heat pump pipe attachments. Finally, there will be a sensor in the attic and a short program to operate the circulators and valves to switch between heat gathering and ground source recharging. I’ll run trials of the heat pump without the benefit of recharging the soil and additional trials including intervals of recharging.

In one of your posts you encourage the reader to visualize the heat source field as a cylinder around the source pipe. That captured perfectly my visualization of the operation of the source pipe. What follows is all hypothesis, but I share it here to give an idea of my thinking on this subject.

If most of the heat stored in the earth's crust is from solar radiation as opposed to geothermal heat migrating toward the surface from the earth's center, then the heat that is at any significant distance below the immediate surface has to be what I'll call "old heat." It's an idea akin to the idea of old water. A little digression: in this water starved part of California, we have no uniform aquifer except in a local geologic phenomenon called the Pygmy Forest. Most of our water is found in fractures and gravel layers, and it's pretty near the surface. Some folks drill deep wells into the rock in search of a better source, and often they find it, but I've heard that water called "old water." It's there in relative abundance, but it has taken millennia to get there, and as a resource, it's finite or at least slow to return. Those of us who extract water from shallow wells depend on the water cycle, snow pack and melt, and while the supply is limited, it's annually renewable...well, at least until we turn the planet into an oven. I tend to think of deep bore holes reaching for deep, stored BTUs in the earth as having the same limitation as deep wells. The resource is there, but it's finite. I have no idea how long it would take to exhaust it, but I believe that whatever is taken out will never be replaced in the lifetime of the user.

So, I am putting my money on what I think of as a flat plate type collector as far from the surface as is necessary to avoid serious losses during the winter but near enough to benefit quickly from the sun's warmth, and I'm enthusiastic (and I hear MikeSolar's cautionary statements in the back of my mind) and perhaps somewhat foolish in my hope that I can derive some benefit from recharging the soil with heat obtained from my attic or from a more efficient but smaller solar collector.

Mikesolar · 04-01-13, 05:26 AM

About the solar panel: as long as it is of low efficiency such as pex and aluminum plates (painted or otherwise), the stagnation temp won't be high enough to degrade glycol fast and you need to use energy to either dump or store the heat. I am all for more of a roof being used as a collector or adding lots of panels at a steeper angle. 5000 gallons is a lot of liquid so it either requires a lot of panel area or dumping into the tank all summer to get it high enough to use in the winter. In that case I would have 2 tanks, one 80 gal for immediate summer use and the big one for the winter.

I am quite concerned about the use of PVC as a pipe due to the number of joints in it (and the fact that it is not very environmentally appropriate). Remember that this is something you want to have in the ground for 50+ years so I would stick with PE or PEX (which is used in Europe a lot, Rehau sells a lot of it for this) and if you are going to do one loop at a time, it is pretty easy to have the manifold inside.

AC_Hacker · 04-01-13, 10:43 AM

Quote:

Originally Posted by michael

Kubota BX23 with a backhoe attachment that will dig 6’ deep with a 9” bucket.

Oh, this is great! It sure would have made my life different if I had one of those!

Quote:

Originally Posted by michael

Material of pipe? 3/4” HDPE is what I think I'm expected to use, but I want to use 3/4" PVC because it will be so much easier for me to manage, and PVC appears to retain up to 80% of its strength up to 140 degrees; 120 deg. is the highest temperature I expect to obtain from a heat recovery system that will be used to recharge the source field.

I was also very tempted to use PVC, because it is so available and cheap and easy to work with, But mostly because I had used PVC and CPVC and I knew how easy cutting & gluing was.

However, during the course of putting together the manifesto thread, I did a huge amount of research. Some of the most informative documents were contract specifications that were drawn up between various municipalities throughout the country, and the contractors who were doing the work. Again and again, I came across specifications that called for welded HDPE. Additional research along this line indicated that my idea of the nature of underground pipe was in error. I learned that the earth is NOT static, but moves and settles and can place considerable force on buried pipe (just imagine old houses and how, over time their foundations settle and walls and floors that were originally even and true, no longer are). PVC becomes more brittle as it ages and as a result of settling of the earth, it can break and the glued joints can fail. HDPE is very tough stuff, and a thermo-welded joint has all of the strength of the parent material. The GSHP industry says that the life of an HDPE loop field is at least 50 years. I have been to professional GSHP seminars, and they all know that the 50 year life span is a huge understatement. They know that if they told the truth and said that the lifespan of buried HDPE was actually in the hundreds of years (or longer), they could move the customer's attention off of closing the deal, and they might lose a contract.

So, I would only recommend using PVC to someone who was intent on doing one minor test hole, in order to convince themselves that GSHP could work.

Please, for the love of god, do not use PVC.

My little HDPE welding paddle worked great, and the pipe and joints were pretty much indestructible. However, it did produce little 'rolls' that were inside the tube that reduced flow somewhat. If I had done a layout similar to the one you propose, and had fewer butt welds (instead of the nearly 100 that I did make), everything would have been just fine. Socket welding is a better bet, because there are no rolls in side the tube. Vlad found a socket welder on ebay new for around $225, as I recall, and he was very pleased with the result. Also, in the manifesto, there is a link to a company that will sell Teflon coated socket welding fittings and you could build your own tool. But at $225, why bother?

When you build your loop field, even with construction machinery, you're gonna do a lot of work. Don't undermine it with marginal materials.

Quote:

Originally Posted by michael

Yes, straight. No coils. The return side of the loop in the bottom of the trench; the cold side of the loop about 1.5-2’ above it with the bottom of the trench at 5’ below grade. If the results are what I hope for, I'll install another dozen or so pipes at 18-24" intervals for a total of roughly 4000 LF of source pipe to heat a 2000 SF house with a 2.5 ton GSHP.

I think you're trench depth of 6 feet sounds ok, for your area. But your pipe intervals are way too close. You should be thinking in terms of 8' intervals bare minimum, 12' better and 16' best. Also making the turn you envision will require a welded return configuration because HDPE will not bend that tight.

Layout information is exactly the kind of thing that you will find in the IGSHPA literature. They have done the math, they have collected experiential information for the last 60 years, from all over the world. They know... buy the book, you will thank me.

Your idea to use 3/4" pipe sounds good... I wish I had done that.

You can get information on calculating fluid resistance from Taco (pump company). With that, you can determine the 'head loss' of your loop field configuration, and what alternatives (branches, etc.) will favor adequate flow and minimized pump power requirements. The IGSHPA manual has this info, too.

Best,

-AC

jdrimm · 04-06-13, 08:52 PM

I just finished reading this entire thread, took me a week with all the excursions it sent me on. I'm currently deployed overseas, so everything is theoretical right now, but I ultimately plan to use DIY solar hot water to heat my garage, and hopefully GSHP to cool it. Pending success there, I'll approach the wife about doing this for the house. Thanks to all who have posted, even the weird questions have been valuable!

AC_Hacker · 04-07-13, 09:37 AM

Quote:

Originally Posted by jdrimm

I just finished reading this entire thread, took me a week with all the excursions it sent me on. I'm currently deployed overseas, so everything is theoretical right now, but I ultimately plan to use DIY solar hot water to heat my garage, and hopefully GSHP to cool it. Pending success there, I'll approach the wife about doing this for the house. Thanks to all who have posted, even the weird questions have been valuable!

Thanks, jdrimm for your message.

I'm pretty sure that this response you have sent is from the most remote location so far... what a miracle is the Internet.

If you have any questions, don't fail to ask... that's why this thread was started.

I wish you the best and send my hopes that the mission you are involved in has the best outcome for everyone involved.

Stay true, stay well, and keep in touch.

Best,

-AC

jdrimm · 04-07-13, 01:07 PM

Quote:

Originally Posted by AC_Hacker

Thanks, jdrimm for your message.

I'm pretty sure that this response you have sent is from the most remote location so far... what a miracle is the Internet. The Army runs on the Internet these days, we can get online from the oddest places!

If you have any questions, don't fail to ask... that's why this thread was started.Thanks, I will.

I wish you the best and send my hopes that the mission you are involved in has the best outcome for everyone involved

The mission here is fascinating, and so far, no shooting. There has been some well-drilling, although I wasn't part of that.

AC_Hacker · 04-10-13, 08:38 AM

Quote:

Originally Posted by michael

...The first trench I will dig with a backhoe because it’s what I have available, and I can do it myself at my own speed using a Kubota BX23 with a backhoe attachment that will dig 6’ deep with a 9” bucket...

michael,

How's the project coming along?

-AC

michael · 04-11-13, 01:55 AM

Hmmm...Got three publications from IGSHPA: Spiral bound manual, soils pamphlet and slinky pamphlet. Everything is at a stand-still while I stare into those. Got the first trench location set. Completed some initial experiments with the E-Tech heat pump. Ordering a three way motorized valve and a digital flow meter. Trying to decide between PEX and HDPE; you successfully talked me out of PVC. Nothing substantial to report, but it's in the mental mill. Thanks for asking. I'll check in when there's something show. Thanks for the book recommendation. mm

michael · 04-11-13, 02:07 AM

On a related note, however, is my search for a 2-3 ton w2w heat pump. I just stumbled across the brand Roth which appears to be a German company. Their product stood out mainly because they offer specs that I can understand, and the heat pumps are geared toward use with radiant floors or water to forced air heating. Their heat pumps are designed to accept 85 deg return water from the floor and produce 100 to 110 deg water for the floor with one trip through the heat pump. They strongly recommend a buffer tank between the HP and the floor loop, but the size they recommend is 10 gal per ton, so in my case, a 20 gallon tank will suffice for a 2 ton HP. I was looking at the water to water engineering data and installation manual, and focusing on model O26A. http://www.roth-usa.com/PDF_Download...ies%20EDIM.pdf

Haven't inquired about prices yet...probably that will be a shocker.

03-31-13, 08:53 PM	#1462
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	Questions: How are you going to do this? Hmmm...ok, here goes: The first trench I will dig with a backhoe because it’s what I have available, and I can do it myself at my own speed using a Kubota BX23 with a backhoe attachment that will dig 6’ deep with a 9” bucket. Straight? Coils? How deep? Yes, straight. No coils. The return side of the loop in the bottom of the trench; the cold side of the loop about 1.5-2’ above it with the bottom of the trench at 5’ below grade. If the results are what I hope for, I'll install another dozen or so pipes at 18-24" intervals for a total of roughly 4000 LF of source pipe to heat a 2000 SF house with a 2.5 ton GSHP. I'd like to do those with a trencher or hire an excavator, so it won't go on forever. Diameter of Pipe? Material of pipe? 3/4” HDPE is what I think I'm expected to use, but I want to use 3/4" PVC because it will be so much easier for me to manage, and PVC appears to retain up to 80% of its strength up to 140 degrees; 120 deg. is the highest temperature I expect to obtain from a heat recovery system that will be used to recharge the source field. How are you going to monitor water temps? Using a Parallax BS2pe microcontroller and a number of one wire temperature sensors such as DS18B20 config. To-92 for data logging (not yet assembled). I will place sensors in the trench at the exit and entrance of the pipe as well at the bend in the distance. Additional sensors will be placed beside the pipes 1”, 2”, 6” and 12” separated from it to monitor temperature changes in the soil, and sensors at the four heat pump pipe attachments. Finally, there will be a sensor in the attic and a short program to operate the circulators and valves to switch between heat gathering and ground source recharging. I’ll run trials of the heat pump without the benefit of recharging the soil and additional trials including intervals of recharging. In one of your posts you encourage the reader to visualize the heat source field as a cylinder around the source pipe. That captured perfectly my visualization of the operation of the source pipe. What follows is all hypothesis, but I share it here to give an idea of my thinking on this subject. If most of the heat stored in the earth's crust is from solar radiation as opposed to geothermal heat migrating toward the surface from the earth's center, then the heat that is at any significant distance below the immediate surface has to be what I'll call "old heat." It's an idea akin to the idea of old water. A little digression: in this water starved part of California, we have no uniform aquifer except in a local geologic phenomenon called the Pygmy Forest. Most of our water is found in fractures and gravel layers, and it's pretty near the surface. Some folks drill deep wells into the rock in search of a better source, and often they find it, but I've heard that water called "old water." It's there in relative abundance, but it has taken millennia to get there, and as a resource, it's finite or at least slow to return. Those of us who extract water from shallow wells depend on the water cycle, snow pack and melt, and while the supply is limited, it's annually renewable...well, at least until we turn the planet into an oven. I tend to think of deep bore holes reaching for deep, stored BTUs in the earth as having the same limitation as deep wells. The resource is there, but it's finite. I have no idea how long it would take to exhaust it, but I believe that whatever is taken out will never be replaced in the lifetime of the user. So, I am putting my money on what I think of as a flat plate type collector as far from the surface as is necessary to avoid serious losses during the winter but near enough to benefit quickly from the sun's warmth, and I'm enthusiastic (and I hear MikeSolar's cautionary statements in the back of my mind) and perhaps somewhat foolish in my hope that I can derive some benefit from recharging the soil with heat obtained from my attic or from a more efficient but smaller solar collector.

04-01-13, 05:26 AM	#1463
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	About the solar panel: as long as it is of low efficiency such as pex and aluminum plates (painted or otherwise), the stagnation temp won't be high enough to degrade glycol fast and you need to use energy to either dump or store the heat. I am all for more of a roof being used as a collector or adding lots of panels at a steeper angle. 5000 gallons is a lot of liquid so it either requires a lot of panel area or dumping into the tank all summer to get it high enough to use in the winter. In that case I would have 2 tanks, one 80 gal for immediate summer use and the big one for the winter. I am quite concerned about the use of PVC as a pipe due to the number of joints in it (and the fact that it is not very environmentally appropriate). Remember that this is something you want to have in the ground for 50+ years so I would stick with PE or PEX (which is used in Europe a lot, Rehau sells a lot of it for this) and if you are going to do one loop at a time, it is pretty easy to have the manifold inside.

04-06-13, 08:52 PM	#1465
jdrimm Lurking Renovator Join Date: Apr 2013 Location: KY, USA (deployed to Djibouti, Africa) Posts: 8 Thanks: 3 Thanked 0 Times in 0 Posts	I just finished reading this entire thread, took me a week with all the excursions it sent me on. I'm currently deployed overseas, so everything is theoretical right now, but I ultimately plan to use DIY solar hot water to heat my garage, and hopefully GSHP to cool it. Pending success there, I'll approach the wife about doing this for the house. Thanks to all who have posted, even the weird questions have been valuable!

04-11-13, 01:55 AM	#1469
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	Hmmm...Got three publications from IGSHPA: Spiral bound manual, soils pamphlet and slinky pamphlet. Everything is at a stand-still while I stare into those. Got the first trench location set. Completed some initial experiments with the E-Tech heat pump. Ordering a three way motorized valve and a digital flow meter. Trying to decide between PEX and HDPE; you successfully talked me out of PVC. Nothing substantial to report, but it's in the mental mill. Thanks for asking. I'll check in when there's something show. Thanks for the book recommendation. mm

04-11-13, 02:07 AM	#1470
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	On a related note, however, is my search for a 2-3 ton w2w heat pump. I just stumbled across the brand Roth which appears to be a German company. Their product stood out mainly because they offer specs that I can understand, and the heat pumps are geared toward use with radiant floors or water to forced air heating. Their heat pumps are designed to accept 85 deg return water from the floor and produce 100 to 110 deg water for the floor with one trip through the heat pump. They strongly recommend a buffer tank between the HP and the floor loop, but the size they recommend is 10 gal per ton, so in my case, a 20 gallon tank will suffice for a 2 ton HP. I was looking at the water to water engineering data and installation manual, and focusing on model O26A. http://www.roth-usa.com/PDF_Download...ies%20EDIM.pdf Haven't inquired about prices yet...probably that will be a shocker.