The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by hikerjohnson

...topsoil for 10-14 inches, followed by seeming bottomless sand, and a water table at no more than 10 feet of depth, sometimes 8 feet if you dig in a low spot...all sand for some tens of feet before he hits ledge.

OK, great!

Originally Posted by hikerjohnson

...I have friends with excavators, so what's the difference between three trenches and four? It's a marginal material cost, to be sure...

Well, the heck with boreholes then.

There was one guy on here named 'rhino' I think, who did trenches for cooling rather than heating (he lives in Florida). The reason I mention this is that he found out that his water table rises and falls. Therefore, the best time to dig your trenches is when the water table is at the lowest point, so you can achieve maximum depth and don't have problems with cave-ins.

Randen did a trench system, I believe he went with straight pipes. Make sure you looked over his work.

You'll also need to be aware of fluid friction and how it is affected by velocity, pipe diameter, pipe length, and viscosity (due to the possible presence and percentage of anti-freeze). Taco, the pump people have some good documentation on this. And of course, the IGSHPA Installation Guide has all this and much, much more.

Best,

-AC

[hikerjohnson]

Yes, I need to look over randen and rhino's work, and find out a little more about field sizing. I pretty much have walked away from the formula Bard provided, it just doesn't seem to make much sense to me.. I did "chase units" to make sure all the units dumped into the equation would yield the correct units on the other end of the equation, and they did, but still; something is wrong if I need half a mile of pipe per ton of cooling.

I ought to purchase the IGSHPA design manual, but the money ($165) just isn't going to be in the budget for a little while yet, I need to fix a shower and do a couple of other higher priority projects. I suppose I ought to plan on getting it. Do you find it is worth the cost, or can I learn well enough from all the other sources out there?

I'm hoping 4x600' 3/4" poly pipe slinky coils will provide enough capacity.

AC, have you found a reasonably reliable slinky field calculation anywhere online? It's probably not fair to ask you to give up whatever formula IGSHPA has evolved.

I did find this blog post with some (seemingly) professional recommendations regarding slinky fields:

5 Tips on Designing Vertical or Slinky Geothermal Loop Fields | HeatSpring Magazine

[AC_Hacker]

Originally Posted by hikerjohnson

...I ought to purchase the IGSHPA design manual, but the money ($165) just isn't going to be in the budget for a little while yet, I need to fix a shower and do a couple of other higher priority projects. I suppose I ought to plan on getting it. Do you find it is worth the cost, or can I learn well enough from all the other sources out there?

The book I mentioned is THE BOOK that professional GSHP firms rely on. It is not a hobby book... you don't need to be an engineer to read it, but it is not light reading.

If you were to hire out this entire project to an experienced professional firm, and it did not turn out as was expected, you would have legal recourse, if it didn't turn out right. You would also spend maybe $40,000 TO $60,000 to have someone else do the work.

So, for matters of comparison, since you are going to do a $60,000 job without the benefit of legal recourse, don't you think that spending $165 for the best professional information available is prudent?

Besides, if you look around a bit you can find a library with it or a used copy for considerably less. I did (find both) after 30 seconds of searching.

Originally Posted by hikerjohnson

I'm hoping 4x600' 3/4" poly pipe slinky coils will provide enough capacity.

I hope you are right.

Originally Posted by hikerjohnson

It's probably not fair to ask you to give up whatever formula IGSHPA has evolved.

The book doesn't have just a formula, it uses tables with various 'tweaking values' to apply.

Regarding 'fairness', the book is copyright material, and if I were to print out all the pages that would be relevant to your project, not only would I be very, very busy, but I would also be breaking the law.

I did a general search HERE, that may provide inspiration.

Some (but not all) of the factors you will need to consider:

• your heat load
• your ground temperature
• ground thermal characteristics
• presence of aquifer
• pipe diameter
• loop branch lengths
• loop fluid velocity
• loop fluid viscosity
• number of parallel branches
• total loop friction losses (AKA: 'head loss')
• pump power needed to achieve the circulation rate that will deliver the heat you require

The information on the Internet about this topic isn't really hidden, but it is diffuse. If you are relentless, you will prevail.

-AC

[randen]

I checked in with some local installers. The common response was 600 ft of 3/4 HDPE per ton. The suggestion of slinky was frowned upon as a lot of the tube passes closer than 16" from tube to tube as it coils.

The heat-pump system is worth a lot of time and money to install it properly. To not revel in the superior efficiency is a complete waste.

Randen

[hikerjohnson]

Thanks randen, AC.

I am pretty solidly cognizant of the design issues facing me; I spent a year maintaining the pumps of a paper mill in college, and so spent a lot of quality time doing head loss and pump curve analysis. Try pumping starch slurry. Now there's a challenge! Now, I do hydraulic system maintenance on subs, same idea, different working fluids. I just have a strong DIY tendency, and when the situation allows (or mandates, being a new homeowner [i.e. BROKE]), I do my best to work out the mathematical issues and technical problems before I dive in and start with the hands-on stuff. Also, refrigeration was for a long time a "spooky" kind of subject, where I bowed out and let a professional take care of it. People like you two have shown me that it is no more challenging than any other pressurized system.

I'm watching ebay like a hawk, and when I can, I am trying to snag the pertinent tools of the refrigerant trade. I have a vacuum pump, but it is only a single stage carbon vane, and won't pull as deep a vacuum as I thought. When I accumulate these things, I will start playing with tiny refrigeration systems and I will contribute my experiences here.

Anyway, back to the topic. I spent almost an hour today on the phone with the loop sizing engineer at a large geothermal firm here in New England. PM me for his name, I don't think it's kind to mention him here, since he was wicked helpful, but I sure didn't tell him I was going to write about it on the internet.

So he said, even with wet sand like I have, he recommended 125' of slinky trench per ton (about 800' total loop length), with a solid 10' edge-to-edge from slinky to slinky. Beyond that, he uses a 32F loop entry temperature and 20% glycol. Said he has seen too many shallow "permafrost" systems and that with power outages being what they are in New England, a day or two without power would be enough to solidify the loops if they were straight water, and then you'd be doomed until springtime.

In other news, I scored a brand-new in the box Modine unit heater! Found it at a yard sale for 50 bucks, it's just exactly the right size for my basement when de-rated fr 140F water feed. Another 50 got me almost 300 feet of red, blue and heating PEX. I think this is a sign that I must continue with the heat pump endeavours!

Something else of interest that the engineer mentioned: An EPA card to handle up to 5 pounds of refrigerant is only $25 and an on-line, open-book exam. Now, DIY or not, this is really pretty interesting info, since it opens up other refrigerants to the DIY-er besides R-290, which everyone can admit is great stuff, but has a couple of notable drawbacks. **I see wyrtwister has one now!**

[AC_Hacker]

Originally Posted by hikerjohnson

I'm watching ebay like a hawk, and when I can, I am trying to snag the pertinent tools of the refrigerant trade. I have a vacuum pump, but it is only a single stage carbon vane, and won't pull as deep a vacuum as I thought. When I accumulate these things, I will start playing with tiny refrigeration systems and I will contribute my experiences here.

This is good to hear! In my opinion, a reliable micron gauge is an essential piece of kit. If you're buying used equipment, a micron gauge will tell you what's happening at the extremely important low end of your vacuum. And don't underestimate the importance of using fresh vacuum pump oil when you really get down to business.

Originally Posted by hikerjohnson

...he recommended 125' of slinky trench per ton (about 800' total loop length), with a solid 10' edge-to-edge from slinky to slinky. Beyond that, he uses a 32F loop entry temperature and 20% glycol. Said he has seen too many shallow "permafrost" systems and that with power outages being what they are in New England, a day or two without power would be enough to solidify the loops if they were straight water, and then you'd be doomed until springtime.g with tiny refrigeration systems and I will contribute my experiences here.

This is really valuable information! Did he happen to mention pipe diameter too? ( BTW, you probably already came across THIS...)

Originally Posted by hikerjohnson

...Modine unit heater! Found it at a yard sale for 50 bucks, it's just exactly the right size for my basement when de-rated fr 140F water feed. Another 50 got me almost 300 feet of red, blue and heating PEX. I think this is a sign that I must continue with the heat pump endeavours!

I'll be very interested to see how your heat pump project progresses. It is good that you found the paper regarding the high temp heat pump, but my experience indicates that 120F degrees it pretty high for a heat pump to produce. I'm pretty sure that you've already read conversations regarding heat pump 'temperature lift' and efficiency. I think that it is prudent to plan your in house HXs (radiant floor, radiators, Modine heat unit, whatever...) for a water temperature that is lower than 120F, and if your heat pump exceeds that, you'll be well ahead of the game.

Right now, I'm embarking on the first chapter of a radiant floor project, which is coming on the heels of a radical insulation project, and I am targeting water temperatures in the 85F to 90F range... admittedly I won't encounter the same severe winter temperatures that you will.

Originally Posted by hikerjohnson

Something else of interest that the engineer mentioned: An EPA card to handle up to 5 pounds of refrigerant is only $25 and an on-line, open-book exam. Now, DIY or not, this is really pretty interesting info, since it opens up other refrigerants to the DIY-er besides R-290, which everyone can admit is great stuff, but has a couple of notable drawbacks. **I see wyrtwister has one now!**

This is very good to know.

Best,

-AC

[hikerjohnson]

The vacuum pump and the micron gauge are definitely the two biggest $$ purchases, and I am holding out for a little overtime and good ebay timing. There is no trusting bourdon tubes at the extremes of their scales.

I have not seen that manual in person, but i did find THIS!

The engineer said he generally used 3/4" for slinky loops, but at the 800 foot length, it can be a toss-up between 3/4" and 1". The deciding factor is head vs. flow (which must be fast enough to be turbulent) for the system pump. Basically, is it cheaper to purchase a higher-head, lower flow pump, or a lower-head, higher flow pump? Also, the heat exchanger plays into the decision, as it must not have too much head loss at the increased flow you would need for 1" lines. He uses packaged heat pumps, of course, so his exchanger choices are more limited than a DIY-er.

I'm on my way to the library this evening to get my shiny new library card and put in a request for the two IGSHPA manuals. Thank you for mentioning this possibility, in the internet age, I forget that the library exists as a resource most of the time.

I didn't realize it would be so difficult to get to 140, and I have been provisionally sizing equipment based on those numbers. I have just found a Mollier diagram for propane, and I am going to look at it over the next day or so to get an idea of mass flow and compressor requirements to design a theoretical 140F system. Who knows, it may be theoretically feasible but too technically difficult. Isn't digging into the unknown FUN?!

Good luck on your flooring project, I am watching it closely. I just refloored my upstairs, and the downstairs must follow in a couple of years, and I'd love to do radiant, but like you, I have found all the commercially available heatboards to be beyond absurd in price. Sam with insulation, the house is OK for now, but when it comes time to do siding, I plan to out-sulate with foam board beneath the new siding, and really button the house up tight. All in good time, no?

[AC_Hacker]

Originally Posted by hikerjohnson

...but i did find THIS!

This is a really good find, and from Oklahoma State, where IGSHPA is situated. My guess is that this document is earlier work that has been integrated into one of their manuals. It's realy appropriate for the curent stage of your project.

Originally Posted by hikerjohnson

The engineer said he generally used 3/4" for slinky loops, but at the 800 foot length, it can be a toss-up between 3/4" and 1". The deciding factor is head vs. flow (which must be fast enough to be turbulent) for the system pump. Basically, is it cheaper to purchase a higher-head, lower flow pump, or a lower-head, higher flow pump?

The turbulent zone of fluid flow is really interesting. Fluid in a laminar flow mode doesn't exchange heat as readily as turbulent flow. And it takes more energy to drive fluid into the turbulent flow mode. In a conversation I had with a fluid engineer, he told me that the fluid friction losses from turbulent flow were lower than for laminar flow. Hard for me to believe. I also came across some fluid flow formulas that encapsulated the idea that the power required to pump fluid through pipe varies proportionally with the square of velocity.

Curious stuff, fluid dynamics...

Originally Posted by hikerjohnson

Also, the heat exchanger plays into the decision, as it must not have too much head loss at the increased flow you would need for 1" lines.

This sounds like the kind of complex interdependency that a computer program, or a trade chart could handle for you.

Originally Posted by hikerjohnson

I'm on my way to the library this evening to get my shiny new library card and put in a request for the two IGSHPA manuals. Thank you for mentioning this possibility, in the internet age, I forget that the library exists as a resource most of the time.

I'll be really interested to see what your reaction is to actually getting your hands on these books. For me, it was like discovering the Holy Grail.

Originally Posted by hikerjohnson

I didn't realize it would be so difficult to get to 140, and I have been provisionally sizing equipment based on those numbers. I have just found a Mollier diagram for propane, and I am going to look at it over the next day or so to get an idea of mass flow and compressor requirements to design a theoretical 140F system. Who knows, it may be theoretically feasible but too technically difficult. Isn't digging into the unknown FUN?!

There is considerable industry interest in being able to hit 140F reliably with a heat pump, because currently, domestic hot water is often stored at that temperature. If it is stored at a lower temperature, the possibility of pathogens setting up shop becomes a concern. Also, much of the conventional thinking regarding radiant heating is based on fossil fuel, which can very easily hit 140F... so if you have a 140F capable heat pump, it can be plugged right into the existing construction methodologies, which has a definite marketing attraction.

But what really interests me is the low exergy quality of heat pumps and also solar, and other alternative heating approaches.

The sources of high exergy energy such as oil, gas, etc. are not finite, and already we are bumping up against our limits. I have set a Google News alert for terms like "gas shortage" and "fuel shortage", and I have been watching these bulletins come in for the last ten years or so. We currently live at the center of the empire, and so we are remote from and protected from the everyday realities of fuel shortages. But I read about them every week, as they play out on the fringes of the empire, in places like Africa and the Middle East... I sometimes feel like I am reading accounts of what our lives will be like in the years ahead. How many years is not easy to say... Maybe 10 maybe 30 years, but things will change.

So, the high exergy sources are on the decline, but the low exergy sources are in great abundance. Being able to derive the energy required from low exergy resources takes a different kind of thinking.

I don't know if you've come across the Carnot Efficiency Theorem, but it applies to this discussion. In our specific case, the Carnot idea is that the system efficiency will be lower, when you use a heat pump to try to raise the temperature of some fluid higher... the higher you raise it (AKA: higher "temperature lift"), the lower the overall efficiency. Conversely, the lower the temperature your need to create (lower temperature lift) to reach your objective, the higher the efficiency.

I used the Carnot Theorem and generated a series of temperatures and plotted them against efficiency, and much to my surprise, the plot is not linear, it is logarithmic, and looks a bit like this curve:

Temperature lift would be on the Y-axis, the energy to achieve that lift is on the Y-axis. This is not the chart I drew, but it is a similar shape. As you can see efficiency will drop off rapidly, as temperature lift increases.

So, to my way of thinking, it is most advantageous to view the whole system, wherein the house and the heat pump are all part of that system. A heat pump is a very efficient form of heating, precisely because it takes advantage of low exergy energy, such as that energy which can be found in cold ground and cold air. So if you are able to maximize the retention of energy in your house, then you can focus on a heat pump that will work on the lower end of temperature lift, where the greatest efficiency can be found. In short, it gives you a double-advantage.

Some things that will allow you to reach your objective with a lower temperature are:

• Reduce infiltration
• Increase insulation
• Maximize any solar advantage
• Maximize your radiant area
• Maximize the efficiency of your radiant area, and your radiant system overall

I know I may be repeating myself here, but it never hurts to repeat some of the basic ideas, and new viewers may be joining us at any time...

Originally Posted by hikerjohnson

Good luck on your flooring project, I am watching it closely. I just refloored my upstairs, and the downstairs must follow in a couple of years, and I'd love to do radiant, but like you, I have found all the commercially available heatboards to be beyond absurd in price. Sam with insulation, the house is OK for now, but when it comes time to do siding, I plan to out-sulate with foam board beneath the new siding, and really button the house up tight. All in good time, no?

Thanks... I got delayed, because I have a very small machine shop in my cellar, and it can be very mesmerizing, making things with a metal lathe and milling machine.

But my back room is almost completely empty and ready for the demolition bar.

Best,

-AC

[hikerjohnson]

Hi AC, time for an update on my progress;

I did get the books, and they were terrific reading! Tons of valuable information in them with respect to sizing fields and many other considerations. I took the time to scan them ( I have access to a high-speed scanner, so it wasn’t all that bad, and now I have a permanent copy.)

Now, due to a few unexpected (and expected) issues, I have had to back-burner a GSHP and go for an ASHP mini-split for the time being. I think I mentioned that my house was originally equipped with electric baseboard heat, so there is absolutely no existing infrastructure to use for heat distribution. I would be retro-fitting any system that I chose, at huge expense. Decisions would be different if I had existing hot air or water baseboard heat. That was the expected part, but wow, when I started pricing things out, well, WOW. Heating components, especially for low-temp water, are not cheap. Also, DIY-ing it takes time, which, you’ll see, is sparse at the present time.

The unexpected part was when I was told at work recently that I’d be away from home for the coldest 2 months of winter, leaving just my girlfriend to work full-time and feed a very hungry woodstove. That’s not acceptable, and neither is running the electric heaters to do full-house heating, as they can run significantly over $600 a month, which is about what a winter’s worth of firewood costs.

With that in mind, I did some more research, and found out that commercial GSHP’s (I had a long conversation with a WaterFurnace tech over the phone.) can only expect to get a COP of 3.5 to 4 in a typical installation, once you factor in pumping losses. I know this issue has been discussed here, but I thought, surely, that proper sizing would help improve that number. Nope.

The solution to the above issue, I hope, is a Mitsubishi HyperHeat 18KBtu mini split (Engineering Data HERE), which is on a truck headed toward my house right now. It’s cheap (Under 3K with all the refrigeration tools to do the job correctly) and easy to install. Furthermore, at 5F, it will still put out 10300 Btu/hr at a consumption of 0.87 kW, for a COP of 3.47. That’s pretty good! I’ll write up a thread to document my installation of that, and I have already in hand a refurbished electric meter to sub-meter the power that the mini-split will consume. I cannot easily measure the output of the heat pump, though. All I can report is on how comfortable it kept us, and what temperatures it can maintain. I know this machine will only support part of my heating demand, but it’s what we can afford right now; else I’d have bought the 9K model for the upstairs, too.

I am also actively sealing many little gaps in the house, and insulating the rim joist in the basement (4 inches of pink Dow, cut to size and foamed in with Great Stuff. It’s tedious, but neater than straight sprayed foam.

Anyway, I am veering off-topic. As far as GSHP goes for me, it is still interesting, but is deferred until spring. Then, I will be drilling (myself) a well to supply my garden irrigation needs, and when I do that, I will see how easy or hard it is to do. Based on that, I may put in either a pump and dump, or a small borehole field like yours to support, say, a ton of energy extraction, so that I can experiment, and also hopefully heat my basement, which I have not yet come up with a way to heat this winter besides running the coal stove.

[mejunkhound]

graphic COP vs. vent air temp and outside air temp (or ground temp minu 5-10F)