The Homemade Heat Pump Manifesto - Page 157

stevehull · 09-05-13, 02:59 PM

Quote:

Originally Posted by AC_Hacker

This website and this thread are rare pieces of Internet real estate where people with gumption and talent share their work and ideas that either apply to their work, or are tempered by their actual experiences.

Steve, this thread is for people who want to actually build Homemade Heat Pumps (not think about it, not hire it out) and for actually building loop fields and all the other related efforts.

This is NOT a talking shop.

Is this clear?

-AC

Oh my - think I just got spanked

!
But I will add in the motto of "measure twice, cut once" and have AC ruminate on that for a bit.

Steve

mejunkhound · 09-05-13, 06:06 PM

yeah, and $6K is about 10X what most of the folks here are willing to spend for a full system.

BTW: DIY cost do not include time - near infinite, classed as 'recreation' - nor does it include one's investment in tools and machinery - e. G a 'good' diy needs to have at least a lathe and mill, probably a backhoe and dozer, not to mention a few hundred 'sets' of hand tools and a few different types of welders, drill press, compressors, 200kW laser 3D printer, etc...... well, maybe the 200kW laser 3D printer is stretching things a bit.

randen · 09-05-13, 06:23 PM

mejunkhound

I disagree I think that most handy ambitious people could build a system for less than 6K if they are careful. I do have most of the tools you had mention but it was mostly hand tools to build my 2 heat-pumps. Any of the specialty fitting I spun up could have been made from valves and fittings.The best tool is the one between your ears. I think I had done my ground loop for (4ton) for less than 3K and the heat pump was mostly scrap pieces and ebay components purchased for a song.

I had recouped my investment the second heating season. Who would want to apply themselves for that kind of ROI.

Randen

mejunkhound · 09-06-13, 07:38 AM

Grin:
I think you misread, and actually agree.

re: $6K is about 10X what most of the folks here are willing to spend for a full system I was implying that most folks here think a system can be built for $600!!, not $6K, ACH would have a Taj McHeatpump for $6K <G>

jeff5may · 09-06-13, 06:13 PM

I believe I rigged up my air source window unit for under $50. If I had bought all new parts to do the mod, it still would have been under $100. The most expensive part of these projects is the skilled labor involved. I believe geothermal specialists charge even more than a Cadillac dealership for their time and effort. More in line with Ferrari service centers. The sweat equity invested is well worth your time (unless you're a Ferrari mechanic).

There are really no comparable units to what I built. The closest thing is a floorstanding portable unit, which at 15kbtu start at around $500. Next cheaper are the mini-splits...spend however much makes you happy. For a DIY project, I am extremely satisfied with the results.

With a ground source system, the ground loop/loops are arguably the most expensive portion. For a homeowner with some land to work with, a trencher and hdpe water pipe can be gotten from the same store. Just rent a ditch witch that will dig deep enough, then drive along and lay the loop like a water supply line. If feasible conditions exist, the price would be very small compared to drilling boreholes or excavating, both in time and money.

AC_Hacker · 09-06-13, 07:47 PM

Quote:

Originally Posted by jeff5may

With a ground source system, the ground loop/loops are arguably the most expensive portion. For a homeowner with some land to work with, a trencher and hdpe water pipe can be gotten from the same store. Just rent a ditch witch that will dig deep enough, then drive along and lay the loop like a water supply line. If feasible conditions exist, the price would be very small compared to drilling boreholes or excavating, both in time and money.

This is all true, but there are some factors to guide your approach...

There is the depth factor:

What this graph is meant to convey is that seasonal temperature swings are lower in amplitude, the deeper you go. At 25 feet and deeper, the swings can be considered to not matter, they are diminishingly small. The temperature at 25 feet for your area is actually the total sum of all temperatures (day and night) averaged over many years. How thoughtful of nature to do all that math!

Another factor is the average soil temperature at your location:

There in Kentucky, the average soil temperature should be pretty reasonable. When I look at that chart, the average soil temp looks to be 58-ish.

Yet another factor is how soil temperature changes with the rolling of the seasons, and how that plays out at different depths.

If you are physics or electronics minded, it is a phase delay... as you can see from this chart, the deeper you go, the greater the delay of the seasonal temperature swings.

So, ideally you'd like to have your pipe buried at such a depth that the time of your greatest heat need (January) coincides with the highest soil temp swing.

This chart is not complete, but I think that when you consider the factors, deeper and deeper gets to be better and better.

So, if you did want to use the method that you outlined above, you'd need to plant more pipe. But planting pipe at a shallow depth is very much easier.

Also to consider is that the temperature of your loop field drops over the heating season, as you extract heat. The amount of the drop will depend on your heating load, and also the size of your loop field.

Even if you are running some kind of antifreeze in your pipe, if you draw the temperature of your loop field below freezing, you will experience a reduction in output after ground freezing.

So all this points to:

Keep your heat load low (reduce infiltration, increase insulation, reduce the amount of house you heat, take advantage of solar whenever possible.
Make your loop field larger than you think you need.
Go deeper

The experiments that I have done with my little loopfield (16 holes, 17 feet deep) is that it does produce useful heat, but probably not so much as I would like, but it's there for me when I need it... so I am working on a ASHP (air-in-water-out) that can gather heat in the mild times and I will rely on my loop field during severe times. I have even learned that they have a name for it... "Hybrid Heat Pump". How grand!

Best,

-AC

berniebenz · 09-09-13, 09:34 AM

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AC_Hacker · 09-10-13, 12:38 PM

I have my loop field in... even tried it out and realized that I had too much fluid friction for my 3/4" pipe, and so I cut the loop field in half, so that I could have two liips in parallel. So far so good.

This is what I have:

So, I just have the loop pipes sticking out of the cellar wall...

I am now at the part where I need to connect the loop pipes that terminate in my basement in a useful way.

This will involve a loop pump, correctly size, and some valving that will allow me to stop flow to one branch or the other. It would also be good to have flow meters that will let me know how much flow is going to each loop so that I can get them balanced. I also need fittings that will let me attach a high-volume water source so that I can purge the loops, should the need arise. I also need to construct a manifold so that the loops flow into one pipe. Then there is the heat pump side of things, and I wuill need to connect to the HX of that. There is also the problem of the radiant floor that I am in the process of building, and how that connection will happen... more pumps, more valves. This is definitely less straight forward, compared to just building a heat pump. There are other considerations that may arise, but at this point I haven't envisioned them.

So what I need to build is what is known as a 'mechanical wall' where all the pipes and valves and pump(s) be fastened and made available.

I've had the good fortune of being able to borrow a HDPE fusing device for socket fusing...

Can you see the family resemblance?

So the difference is the addition of the teflon coated socket fusing fittings...

So, just for a test, I took my Mini-Hack apart...

and drilled the center hole out just a bit and fit the socket fusion fittings to my Mini-Hack...

The socket fusion fittings fit pretty well. The way they work is that one fitting is the male fitting (outie) and one fitting is female (innie). There are special HDPE couplings of various shapes and various diameters, and the coupling goes on the male fitting and the HDPE pipe goes on the female fitting. The heat from the resistance heating element causes the surface of the coupling and the pipe to melt, and then the two are removed from the fittings, pushed together, twisted just a bit in the process and held until they cool some. Then they are forever fused, and very strong.

My Mini-Hack was designed to be hand held, and fusion welding definitely require two free hands. So either this is a two-man job, or a holding device is needed for the fusion device.

Who can say no to a vice on a bench?

I tried a couple of test fusions...

...and discovered that there is a bit of a learning curve. In this photo, I held the pipe and the coupling too long on the heat and when I pushed them together, molten HDPE kind of spludged out, ever so messy.

On the next weld, I counted out about 25 seconds and the result was a perfect fusion weld.

Here's a video of some YouTube guy showing us how it is done...

http://www.youtube.com/watch?v=Jx2u7DQvpgM

NOTE: The temperature setting on my Mini-Hack for HDPE is about 400F, so you try different settings until you find the setting that works best for you.

* * *

So I'm still stuck with figuring out how my mechanical wall should go. Has anyone done one of these things, and would like to offer knowledgeable advice?

-AC

maciej_pl · 09-10-13, 07:47 PM

Quote:

Originally Posted by AC_Hacker

As you can see, once the level of turbulent flow is reached, there is a noticeable jump in heat transfer.

So steve, who is funding this research and why is the flow enhansing fluid proprietary? Do you have any diagrams or photos of the 'improved' tube?

And what role are you playing in this study?

Lastly, what have you learned form this experience that will enable DIY folks to improve their efforts?

-AC

Hello everyone

I am building my own heat pump home installation and reading this thread with pleasure for some time

As the soil in my parcel is sand and my parcel is not big, I oversized the ground loops by increasing length (smaller pitch of Slinky) and by increasing diameter of the ground tube. I did that on purpose to achieve slower, easier heat exchange with the ground and to have "better pipe coverage" of the ground area. In my humble opinion tubular flow is not necessary in the case of long pipes burried in ground.

I think the chart above does not refer to heat pump ground collectors. In my opinion the chart above refers either to:
- small size fluid-fluid, fluid-gas or gas-gas scenarios where fluids flow in opposite directions, or
- furnace heat exchangers of limited size, or
- pipes of less than 100 meters in length.

In such cases there is plenty of heat, but the exchange area is very limited. For this reason it is always preferable to achieve turbulent flow on such occasions, so the heat may be transferred rapidly and using limited space. A typical plate of a typical plate heat exchanger is e.g. 3" wide x 10"-20" long, and such plate has to exchange a lot of heat. On that area new 'subflows' come in contact with the plate and exchange heat.
With laminar flow, the whole fluid would not come in contact with the plates and would not 'catch' (exchange) the heat on this small typical distance of 10"-20". So turbulence greatly increases heat exchange rate in small (compact) plate or tube in tube exchangers. Therefore the inner heat exchangers in the heat pumps are always designed for turbulence.

The soil is a different matter. The turbulence is not necessary as the heat comes slowly to the pipe. The slowest process is getting the heat to the pipe in the soil. For this reason slow fluid speeds, long pipes, large pipe diameters and large quantities of fluid are advisable (in my opinion). The longer the pipe the better.

Why? For example - let's assume 4 coils of PE 40mm pipe 150meters each. This length is allowable for this diameter. That is situation A - big pipe with lots of glycol.

Situation B - smaller diameter, faster flow. PE 32mm, 4 coils of 120 meters each (longer is impossible due to high friction loss and pump head necessary to move fluid).

Heat pump 7kW, 3000 liters of flow per hour.

Land area is the same.

Let's have a fight.

Category 1 - Time spent in ground.

A. There are 600 liters in the slinky. Flow of 3000 liters per hour means the whole glycol comes back to the exchanger in the heat pump after 12 minutes. So it spends 12 minutes in the ground.

B. There are 300 liters in the slinky. The whole glycol flows back to the heat pump within 6 minutes and gets cooled again. The glycol has only 6 minutes to sprint to the end of the trench, acquire higher temperature and come back to the heat pump.

1:0 for bigger pipe

----------

Category 2 - Heat exchanger area

A. The wall area of PE40 pipe 600meters long is... 75 square meters. The coil occupies more space under ground as the bending diameter of larger pipe is bigger. The trenches must be 150cm wide to put the PE40 in. So in this exchanger the pipe is everywhere, even in the places PE32 can't reach. Hence, the heat exchange is better. The heat does not have to travel so long distance in the ground to come to the pipe.

B. The wall area of PE32 pipe 480meters long is... 48 square meters. Considerably less. The bending diameter is only 1 meter, so the trenches are usually also 1 meter wide. The pipe covers less ground. Not only the glycol has less time to raise temperature, but also the heat-exchange area is much smaller.

2:0 for bigger pipe

--------

Category 3: Pumping energy and heat exchange speed

A. Bigger pipe has no turbulent flow. Pumping energy is much lower. Heat is exchanged slowly with the ground. So it is exchanged consistently on the whole length of the trenches.

B. Smaller pipe has turbulent flow. Required pumping energy is biger. Heat is exchanged rapidly on the first meters of the pipe. Distant parts of the trench give no new energy to the fluid as the whole mass aquires temperature of the ground on a very small distance due to the small subflows in contact with the wall of the pipe. There is a danger of freezing first parts of trenches.

3:0 for the bigger pipe

And the winners are 2 rule: "The Bigger the Pipe the Better" and "Put More Glycol in the Ground"

What do you think?

AC_Hacker · 09-11-13, 01:39 AM

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